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remove run-time check for now-required GTK 2.4
[wxWidgets.git] / src / png / libpng.3
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1.TH LIBPNG 3 "December 15, 2011"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.5.7
4.SH SYNOPSIS
5\fI\fB
6
7\fB#include <png.h>\fP
8
9\fI\fB
10
11\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
12
13\fI\fB
14
15\fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
16
17\fI\fB
18
19\fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
20
21\fI\fB
22
23\fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
24
25\fI\fB
26
27\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
28
29\fI\fB
30
31\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
32
33\fI\fB
34
35\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
36
37\fI\fB
38
39\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
40
41\fI\fB
42
43\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
44
45\fI\fB
46
47\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
48
49\fI\fB
50
51\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
52
53\fI\fB
54
55\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
56
57\fI\fB
58
59\fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
60
61\fI\fB
62
63\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
64
65\fI\fB
66
67\fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
68
69\fI\fB
70
71\fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
72
73\fI\fB
74
75\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
76
77\fI\fB
78
79\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
80
81\fI\fB
82
83\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
84
85\fI\fB
86
87\fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
88
89\fI\fB
90
91\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
92
93\fI\fB
94
95\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
96
97\fI\fB
98
99\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
100
101\fI\fB
102
103\fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
104
105\fI\fB
106
107\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
108
109\fI\fB
110
111\fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
112
113\fI\fB
114
115\fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
116
117\fI\fB
118
119\fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
120
121\fI\fB
122
123\fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
124
125\fI\fB
126
127\fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
128
129\fI\fB
130
131\fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fIpng_ptr,
132
133\fBpng_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fI*red_Z,
134
135\fBdouble \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fI*blue_X,
136
137\fBdouble \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
138
139\fI\fB
140
141\fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
142
143\fI\fB
144
145\fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
146
147\fI\fB
148
149\fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
150
151\fI\fB
152
153\fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
154
155\fI\fB
156
157\fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
158
159\fI\fB
160
161\fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
162
163\fI\fB
164
165\fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
166
167\fI\fB
168
169\fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
170
171\fI\fB
172
173\fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
174
175\fI\fB
176
177\fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
178
179\fI\fB
180
181\fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
182
183\fI\fB
184
185\fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
186
187\fI\fB
188
189\fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
190
191\fI\fB
192
193\fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
194
195\fI\fB
196
197\fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
198
199\fI\fB
200
201\fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
202
203\fI\fB
204
205\fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
206
207\fI\fB
208
209\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
210
211\fI\fB
212
213\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
214
215\fI\fB
216
217\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
218
219\fI\fB
220
221\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
222
223\fI\fB
224
225\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
226
227\fI\fB
228
229\fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
230
231\fI\fB
232
233\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
234
235\fI\fB
236
237\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
238
239\fI\fB
240
241\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
242
243\fI\fB
244
245\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
246
247\fI\fB
248
249\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
250
251\fI\fB
252
253\fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
254
255\fI\fB
256
257\fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
258
259\fI\fB
260
261\fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
262
263\fI\fB
264
265\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
266
267\fI\fB
268
269\fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
270
271\fI\fB
272
273\fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
274
275\fI\fB
276
277\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
278
279\fI\fB
280
281\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
282
283\fI\fB
284
285\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
286
287\fI\fB
288
289\fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
290
291\fI\fB
292
293\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
294
295\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
296
297\fI\fB
298
299\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
300
301\fI\fB
302
303\fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
304
305\fI\fB
306
307\fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
308
309\fI\fB
310
311\fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
312
313\fI\fB
314
315\fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
316
317\fI\fB
318
319\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
320
321\fI\fB
322
323\fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
324
325\fI\fB
326
327\fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
328
329\fI\fB
330
331\fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
332
333\fI\fB
334
335\fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
336
337\fI\fB
338
339\fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
340
341\fI\fB
342
343\fB/* This function is really an inline macro. \fI*/
344
345\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
346
347\fI\fB
348
349\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
350
351\fI\fB
352
353\fB/* This function is really an inline macro. \fI*/
354
355\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
356
357\fI\fB
358
359\fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
360
361\fI\fB
362
363\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
364
365\fI\fB
366
367\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
368
369\fI\fB
370
371\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
372
373\fI\fB
374
375\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
376
377\fI\fB
378
379\fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
380
381\fI\fB
382
383\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
384
385\fI\fB
386
387\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
388
389\fI\fB
390
391\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
392
393\fI\fB
394
395\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
396
397\fI\fB
398
399\fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
400
401\fI\fB
402
403\fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
404
405\fI\fB
406
407\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
408
409\fI\fB
410
411\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
412
413\fI\fB
414
415\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
416
417\fI\fB
418
419\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
420
421\fI\fB
422
423\fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
424
425\fI\fB
426
427\fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
428
429\fI\fB
430
431\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
432
433\fI\fB
434
435\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
436
437\fI\fB
438
439\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
440
441\fI\fB
442
443\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
444
445\fI\fB
446
447\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
448
449\fI\fB
450
451\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
452
453\fI\fB
454
455\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
456
457\fI\fB
458
459\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
460
461\fI\fB
462
463\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
464
465\fI\fB
466
467\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
468
469\fI\fB
470
471\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
472
473\fI\fB
474
475\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
476
477\fI\fB
478
479\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
480
481\fI\fB
482
483\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
484
485\fI\fB
486
487\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
488
489\fI\fB
490
491\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
492
493\fI\fB
494
495\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
496
497\fI\fB
498
499\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
500
501\fI\fB
502
503\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
504
505\fI\fB
506
507\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
508
509\fI\fB
510
511\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
512
513\fI\fB
514
515\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
516
517\fI\fB
518
519\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
520
521\fI\fB
522
523\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
524
525\fI\fB
526
527\fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
528
529\fI\fB
530
531\fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
532
533\fI\fB
534
535\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
536
537\fI\fB
538
539\fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
540
541\fI\fB
542
543\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
544
545\fI\fB
546
547\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
548
549\fI\fB
550
551\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
552
553\fI\fB
554
555\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
556
557\fI\fB
558
559\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
560
561\fI\fB
562
563\fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fIgreen_Y,
564
565\fBdouble \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
566
567\fI\fB
568
569\fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
570
571\fI\fB
572
573\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
574
575\fI\fB
576
577\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
578
579\fI\fB
580
581\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
582
583\fI\fB
584
585\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
586
587\fI\fB
588
589\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
590
591\fI\fB
592
593\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
594
595\fI\fB
596
597\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
598
599\fI\fB
600
601\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
602
603\fI\fB
604
605\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
606
607\fI\fB
608
609\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
610
611\fI\fB
612
613\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
614
615\fI\fB
616
617\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
618
619\fI\fB
620
621\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
622
623\fI\fB
624
625\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
626
627\fI\fB
628
629\fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
630
631\fI\fB
632
633\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
634
635\fI\fB
636
637\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
638
639\fI\fB
640
641\fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
642
643\fI\fB
644
645\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
646
647\fI\fB
648
649\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
650
651\fI\fB
652
653\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
654
655\fI\fB
656
657\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
658
659\fI\fB
660
661\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
662
663\fI\fB
664
665\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
666
667\fI\fB
668
669\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
670
671\fI\fB
672
673\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
674
675\fI\fB
676
677\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
678
679\fI\fB
680
681\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
682
683\fI\fB
684
685\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
686
687\fI\fB
688
689\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
690
691\fI\fB
692
693\fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
694
695\fI\fB
696
697\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
698
699\fI\fB
700
701\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
702
703\fI\fB
704
705\fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
706
707\fI\fB
708
709\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
710
711\fI\fB
712
713\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
714
715\fI\fB
716
717\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
718
719\fI\fB
720
721\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
722
723\fI\fB
724
725\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
726
727\fI\fB
728
729\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
730
731\fI\fB
732
733\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
734
735\fI\fB
736
737\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
738
739\fI\fB
740
741\fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
742
743\fI\fB
744
745\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
746
747\fI\fB
748
749\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
750
751\fI\fB
752
753\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
754
755\fI\fB
756
757\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
758
759\fI\fB
760
761\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
762
763\fI\fB
764
765\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
766
767\fI\fB
768
769\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
770
771\fI\fB
772
773\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
774
775\fI\fB
776
777\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
778
779\fI\fB
780
781\fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
782
783\fI\fB
784
785\fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
786
787\fI\fB
788
789\fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
790
791\fI\fB
792
793\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
794
795\fI\fB
796
797\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
798
799\fI\fB
800
801\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
802
803\fI\fB
804
805\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
806
807\fI\fB
808
809\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
810
811\fI\fB
812
813\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
814
815\fI\fB
816
817\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
818
819\fI\fB
820
821\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
822
823\fI\fB
824
825\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
826
827\fI\fB
828
829\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
830
831\fI\fB
832
833\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
834
835\fI\fB
836
837\fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
838
839\fI\fB
840
841\fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
842
843\fI\fB
844
845\fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
846
847\fI\fB
848
849\fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
850
851\fI\fB
852
853\fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
854
855\fI\fB
856
857\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
858
859\fI\fB
860
861\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
862
863\fI\fB
864
865\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
866
867\fI\fB
868
869\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
870
871\fI\fB
872
873\fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
874
875\fI\fB
876
877\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
878
879\fI\fB
880
881\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
882
883\fI\fB
884
885\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
886
887\fI\fB
888
889\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
890
891\fI\fB
892
893\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
894
895\fI\fB
896
897\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
898
899\fI\fB
900
901\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
902
903\fI\fB
904
905\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
906
907\fI\fB
908
909\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
910
911\fI\fB
912
913\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
914
915\fI\fB
916
917\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
918
919\fI\fB
920
921\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
922
923\fI\fB
924
925\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
926
927\fI\fB
928
929\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
930
931\fI\fB
932
933\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
934
935\fI\fB
936
937\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
938
939\fI\fB
940
941\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
942
943\fI\fB
944
945\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
946
947\fI\fB
948
949\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
950
951\fI\fB
952
953\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
954
955\fI\fB
956
957\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
958
959\fI\fB
960
961\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
962
963\fI\fB
964
965\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
966
967\fI\fB
968
969.SH DESCRIPTION
970The
971.I libpng
972library supports encoding, decoding, and various manipulations of
973the Portable Network Graphics (PNG) format image files. It uses the
974.IR zlib(3)
975compression library.
976Following is a copy of the libpng-manual.txt file that accompanies libpng.
977.SH LIBPNG.TXT
978libpng-manual.txt - A description on how to use and modify libpng
979
980 libpng version 1.5.7 - December 15, 2011
981 Updated and distributed by Glenn Randers-Pehrson
982 <glennrp at users.sourceforge.net>
983 Copyright (c) 1998-2011 Glenn Randers-Pehrson
984
985 This document is released under the libpng license.
986 For conditions of distribution and use, see the disclaimer
987 and license in png.h
988
989 Based on:
990
991 libpng versions 0.97, January 1998, through 1.5.7 - December 15, 2011
992 Updated and distributed by Glenn Randers-Pehrson
993 Copyright (c) 1998-2011 Glenn Randers-Pehrson
994
995 libpng 1.0 beta 6 version 0.96 May 28, 1997
996 Updated and distributed by Andreas Dilger
997 Copyright (c) 1996, 1997 Andreas Dilger
998
999 libpng 1.0 beta 2 - version 0.88 January 26, 1996
1000 For conditions of distribution and use, see copyright
1001 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
1002 Schalnat, Group 42, Inc.
1003
1004 Updated/rewritten per request in the libpng FAQ
1005 Copyright (c) 1995, 1996 Frank J. T. Wojcik
1006 December 18, 1995 & January 20, 1996
1007
1008.SH I. Introduction
1009
1010This file describes how to use and modify the PNG reference library
1011(known as libpng) for your own use. There are five sections to this
1012file: introduction, structures, reading, writing, and modification and
1013configuration notes for various special platforms. In addition to this
1014file, example.c is a good starting point for using the library, as
1015it is heavily commented and should include everything most people
1016will need. We assume that libpng is already installed; see the
1017INSTALL file for instructions on how to install libpng.
1018
1019For examples of libpng usage, see the files "example.c", "pngtest.c",
1020and the files in the "contrib" directory, all of which are included in
1021the libpng distribution.
1022
1023Libpng was written as a companion to the PNG specification, as a way
1024of reducing the amount of time and effort it takes to support the PNG
1025file format in application programs.
1026
1027The PNG specification (second edition), November 2003, is available as
1028a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
1029<http://www.w3.org/TR/2003/REC-PNG-20031110/
1030The W3C and ISO documents have identical technical content.
1031
1032The PNG-1.2 specification is available at
1033<http://www.libpng.org/pub/png/documents/>. It is technically equivalent
1034to the PNG specification (second edition) but has some additional material.
1035
1036The PNG-1.0 specification is available
1037as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
1038W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
1039
1040Some additional chunks are described in the special-purpose public chunks
1041documents at <http://www.libpng.org/pub/png/documents/>.
1042
1043Other information
1044about PNG, and the latest version of libpng, can be found at the PNG home
1045page, <http://www.libpng.org/pub/png/>.
1046
1047Most users will not have to modify the library significantly; advanced
1048users may want to modify it more. All attempts were made to make it as
1049complete as possible, while keeping the code easy to understand.
1050Currently, this library only supports C. Support for other languages
1051is being considered.
1052
1053Libpng has been designed to handle multiple sessions at one time,
1054to be easily modifiable, to be portable to the vast majority of
1055machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
1056to use. The ultimate goal of libpng is to promote the acceptance of
1057the PNG file format in whatever way possible. While there is still
1058work to be done (see the TODO file), libpng should cover the
1059majority of the needs of its users.
1060
1061Libpng uses zlib for its compression and decompression of PNG files.
1062Further information about zlib, and the latest version of zlib, can
1063be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
1064The zlib compression utility is a general purpose utility that is
1065useful for more than PNG files, and can be used without libpng.
1066See the documentation delivered with zlib for more details.
1067You can usually find the source files for the zlib utility wherever you
1068find the libpng source files.
1069
1070Libpng is thread safe, provided the threads are using different
1071instances of the structures. Each thread should have its own
1072png_struct and png_info instances, and thus its own image.
1073Libpng does not protect itself against two threads using the
1074same instance of a structure.
1075
1076.SH II. Structures
1077
1078There are two main structures that are important to libpng, png_struct
1079and png_info. Both are internal structures that are no longer exposed
1080in the libpng interface (as of libpng 1.5.0).
1081
1082The png_info structure is designed to provide information about the
1083PNG file. At one time, the fields of png_info were intended to be
1084directly accessible to the user. However, this tended to cause problems
1085with applications using dynamically loaded libraries, and as a result
1086a set of interface functions for png_info (the png_get_*() and png_set_*()
1087functions) was developed, and direct access to the png_info fields was
1088deprecated..
1089
1090The png_struct structure is the object used by the library to decode a
1091single image. As of 1.5.0 this structure is also not exposed.
1092
1093Almost all libpng APIs require a pointer to a png_struct as the first argument.
1094Many (in particular the png_set and png_get APIs) also require a pointer
1095to png_info as the second argument. Some application visible macros
1096defined in png.h designed for basic data access (reading and writing
1097integers in the PNG format) don't take a png_info pointer, but it's almost
1098always safe to assume that a (png_struct*) has to be passed to call an API
1099function.
1100
1101You can have more than one png_info structure associated with an image,
1102as illustrated in pngtest.c, one for information valid prior to the
1103IDAT chunks and another (called "end_info" below) for things after them.
1104
1105The png.h header file is an invaluable reference for programming with libpng.
1106And while I'm on the topic, make sure you include the libpng header file:
1107
1108#include <png.h>
1109
1110and also (as of libpng-1.5.0) the zlib header file, if you need it:
1111
1112#include <zlib.h>
1113
1114.SS Types
1115
1116The png.h header file defines a number of integral types used by the
1117APIs. Most of these are fairly obvious; for example types corresponding
1118to integers of particular sizes and types for passing color values.
1119
1120One exception is how non-integral numbers are handled. For application
1121convenience most APIs that take such numbers have C (double) arguments,
1122however internally PNG, and libpng, use 32 bit signed integers and encode
1123the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
1124macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
1125which is simply (png_int_32).
1126
1127All APIs that take (double) arguments also have a matching API that
1128takes the corresponding fixed point integer arguments. The fixed point
1129API has the same name as the floating point one with "_fixed" appended.
1130The actual range of values permitted in the APIs is frequently less than
1131the full range of (png_fixed_point) (-21474 to +21474). When APIs require
1132a non-negative argument the type is recorded as png_uint_32 above. Consult
1133the header file and the text below for more information.
1134
1135Special care must be take with sCAL chunk handling because the chunk itself
1136uses non-integral values encoded as strings containing decimal floating point
1137numbers. See the comments in the header file.
1138
1139.SS Configuration
1140
1141The main header file function declarations are frequently protected by C
1142preprocessing directives of the form:
1143
1144 #ifdef PNG_feature_SUPPORTED
1145 declare-function
1146 #endif
1147 ...
1148 #ifdef PNG_feature_SUPPORTED
1149 use-function
1150 #endif
1151
1152The library can be built without support for these APIs, although a
1153standard build will have all implemented APIs. Application programs
1154should check the feature macros before using an API for maximum
1155portability. From libpng 1.5.0 the feature macros set during the build
1156of libpng are recorded in the header file "pnglibconf.h" and this file
1157is always included by png.h.
1158
1159If you don't need to change the library configuration from the default, skip to
1160the next section ("Reading").
1161
1162Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
1163of the build project files in the 'projects' directory simply copy
1164scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
1165systems do not permit easy auto-configuration of the library - they only
1166support the default configuration.
1167
1168The easiest way to make minor changes to the libpng configuration when
1169auto-configuration is supported is to add definitions to the command line
1170using (typically) CPPFLAGS. For example:
1171
1172CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
1173
1174will change the internal libpng math implementation for gamma correction and
1175other arithmetic calculations to fixed point, avoiding the need for fast
1176floating point support. The result can be seen in the generated pnglibconf.h -
1177make sure it contains the changed feature macro setting.
1178
1179If you need to make more extensive configuration changes - more than one or two
1180feature macro settings - you can either add -DPNG_USER_CONFIG to the build
1181command line and put a list of feature macro settings in pngusr.h or you can set
1182DFA_XTRA (a makefile variable) to a file containing the same information in the
1183form of 'option' settings.
1184
1185A. Changing pnglibconf.h
1186
1187A variety of methods exist to build libpng. Not all of these support
1188reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
1189rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
1190
1191Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
1192pnglibconf.h and changing the lines defining the supported features, paying
1193very close attention to the 'option' information in scripts/pnglibconf.dfa
1194that describes those features and their requirements. This is easy to get
1195wrong.
1196
1197B. Configuration using DFA_XTRA
1198
1199Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
1200variant such as 'nawk' or 'gawk', is available. The configure build will
1201automatically find an appropriate awk and build pnglibconf.h.
1202The scripts/pnglibconf.mak file contains a set of make rules for doing the
1203same thing if configure is not used, and many of the makefiles in the scripts
1204directory use this approach.
1205
1206When rebuilding simply write a new file containing changed options and set
1207DFA_XTRA to the name of this file. This causes the build to append the new file
1208to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
1209of the following forms:
1210
1211everything = off
1212
1213This turns all optional features off. Include it at the start of pngusr.dfa to
1214make it easier to build a minimal configuration. You will need to turn at least
1215some features on afterward to enable either reading or writing code, or both.
1216
1217option feature on
1218option feature off
1219
1220Enable or disable a single feature. This will automatically enable other
1221features required by a feature that is turned on or disable other features that
1222require a feature which is turned off. Conflicting settings will cause an error
1223message to be emitted by awk.
1224
1225setting feature default value
1226
1227Changes the default value of setting 'feature' to 'value'. There are a small
1228number of settings listed at the top of pnglibconf.h, they are documented in the
1229source code. Most of these values have performance implications for the library
1230but most of them have no visible effect on the API. Some can also be overridden
1231from the API.
1232
1233This method of building a customized pnglibconf.h is illustrated in
1234contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
1235pngusr.dfa in these directories.
1236
1237C. Configuration using PNG_USR_CONFIG
1238
1239If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
1240pngusr.h will automatically be included before the options in
1241scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
1242macro definitions turning features on or off or setting settings.
1243
1244Apart from the global setting "everything = off" all the options listed above
1245can be set using macros in pngusr.h:
1246
1247#define PNG_feature_SUPPORTED
1248
1249is equivalent to:
1250
1251option feature on
1252
1253#define PNG_NO_feature
1254
1255is equivalent to:
1256
1257option feature off
1258
1259#define PNG_feature value
1260
1261is equivalent to:
1262
1263setting feature default value
1264
1265Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
1266pngusr file you supply override the contents of scripts/pnglibconf.dfa
1267
1268If confusing or incomprehensible behavior results it is possible to
1269examine the intermediate file pnglibconf.dfn to find the full set of
1270dependency information for each setting and option. Simply locate the
1271feature in the file and read the C comments that precede it.
1272
1273This method is also illustrated in the contrib/pngminim/* makefiles and
1274pngusr.h.
1275
1276.SH III. Reading
1277
1278We'll now walk you through the possible functions to call when reading
1279in a PNG file sequentially, briefly explaining the syntax and purpose
1280of each one. See example.c and png.h for more detail. While
1281progressive reading is covered in the next section, you will still
1282need some of the functions discussed in this section to read a PNG
1283file.
1284
1285.SS Setup
1286
1287You will want to do the I/O initialization(*) before you get into libpng,
1288so if it doesn't work, you don't have much to undo. Of course, you
1289will also want to insure that you are, in fact, dealing with a PNG
1290file. Libpng provides a simple check to see if a file is a PNG file.
1291To use it, pass in the first 1 to 8 bytes of the file to the function
1292png_sig_cmp(), and it will return 0 (false) if the bytes match the
1293corresponding bytes of the PNG signature, or nonzero (true) otherwise.
1294Of course, the more bytes you pass in, the greater the accuracy of the
1295prediction.
1296
1297If you are intending to keep the file pointer open for use in libpng,
1298you must ensure you don't read more than 8 bytes from the beginning
1299of the file, and you also have to make a call to png_set_sig_bytes_read()
1300with the number of bytes you read from the beginning. Libpng will
1301then only check the bytes (if any) that your program didn't read.
1302
1303(*): If you are not using the standard I/O functions, you will need
1304to replace them with custom functions. See the discussion under
1305Customizing libpng.
1306
1307
1308 FILE *fp = fopen(file_name, "rb");
1309 if (!fp)
1310 {
1311 return (ERROR);
1312 }
1313
1314 fread(header, 1, number, fp);
1315 is_png = !png_sig_cmp(header, 0, number);
1316
1317 if (!is_png)
1318 {
1319 return (NOT_PNG);
1320 }
1321
1322
1323Next, png_struct and png_info need to be allocated and initialized. In
1324order to ensure that the size of these structures is correct even with a
1325dynamically linked libpng, there are functions to initialize and
1326allocate the structures. We also pass the library version, optional
1327pointers to error handling functions, and a pointer to a data struct for
1328use by the error functions, if necessary (the pointer and functions can
1329be NULL if the default error handlers are to be used). See the section
1330on Changes to Libpng below regarding the old initialization functions.
1331The structure allocation functions quietly return NULL if they fail to
1332create the structure, so your application should check for that.
1333
1334 png_structp png_ptr = png_create_read_struct
1335 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1336 user_error_fn, user_warning_fn);
1337
1338 if (!png_ptr)
1339 return (ERROR);
1340
1341 png_infop info_ptr = png_create_info_struct(png_ptr);
1342
1343 if (!info_ptr)
1344 {
1345 png_destroy_read_struct(&png_ptr,
1346 (png_infopp)NULL, (png_infopp)NULL);
1347 return (ERROR);
1348 }
1349
1350If you want to use your own memory allocation routines,
1351use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
1352png_create_read_struct_2() instead of png_create_read_struct():
1353
1354 png_structp png_ptr = png_create_read_struct_2
1355 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1356 user_error_fn, user_warning_fn, (png_voidp)
1357 user_mem_ptr, user_malloc_fn, user_free_fn);
1358
1359The error handling routines passed to png_create_read_struct()
1360and the memory alloc/free routines passed to png_create_struct_2()
1361are only necessary if you are not using the libpng supplied error
1362handling and memory alloc/free functions.
1363
1364When libpng encounters an error, it expects to longjmp back
1365to your routine. Therefore, you will need to call setjmp and pass
1366your png_jmpbuf(png_ptr). If you read the file from different
1367routines, you will need to update the longjmp buffer every time you enter
1368a new routine that will call a png_*() function.
1369
1370See your documentation of setjmp/longjmp for your compiler for more
1371information on setjmp/longjmp. See the discussion on libpng error
1372handling in the Customizing Libpng section below for more information
1373on the libpng error handling. If an error occurs, and libpng longjmp's
1374back to your setjmp, you will want to call png_destroy_read_struct() to
1375free any memory.
1376
1377 if (setjmp(png_jmpbuf(png_ptr)))
1378 {
1379 png_destroy_read_struct(&png_ptr, &info_ptr,
1380 &end_info);
1381 fclose(fp);
1382 return (ERROR);
1383 }
1384
1385Pass (png_infopp)NULL instead of &end_info if you didn't create
1386an end_info structure.
1387
1388If you would rather avoid the complexity of setjmp/longjmp issues,
1389you can compile libpng with PNG_NO_SETJMP, in which case
1390errors will result in a call to PNG_ABORT() which defaults to abort().
1391
1392You can #define PNG_ABORT() to a function that does something
1393more useful than abort(), as long as your function does not
1394return.
1395
1396Now you need to set up the input code. The default for libpng is to
1397use the C function fread(). If you use this, you will need to pass a
1398valid FILE * in the function png_init_io(). Be sure that the file is
1399opened in binary mode. If you wish to handle reading data in another
1400way, you need not call the png_init_io() function, but you must then
1401implement the libpng I/O methods discussed in the Customizing Libpng
1402section below.
1403
1404 png_init_io(png_ptr, fp);
1405
1406If you had previously opened the file and read any of the signature from
1407the beginning in order to see if this was a PNG file, you need to let
1408libpng know that there are some bytes missing from the start of the file.
1409
1410 png_set_sig_bytes(png_ptr, number);
1411
1412You can change the zlib compression buffer size to be used while
1413reading compressed data with
1414
1415 png_set_compression_buffer_size(png_ptr, buffer_size);
1416
1417where the default size is 8192 bytes. Note that the buffer size
1418is changed immediately and the buffer is reallocated immediately,
1419instead of setting a flag to be acted upon later.
1420
1421If you want CRC errors to be handled in a different manner than
1422the default, use
1423
1424 png_set_crc_action(png_ptr, crit_action, ancil_action);
1425
1426The values for png_set_crc_action() say how libpng is to handle CRC errors in
1427ancillary and critical chunks, and whether to use the data contained
1428therein. Note that it is impossible to "discard" data in a critical
1429chunk.
1430
1431Choices for (int) crit_action are
1432 PNG_CRC_DEFAULT 0 error/quit
1433 PNG_CRC_ERROR_QUIT 1 error/quit
1434 PNG_CRC_WARN_USE 3 warn/use data
1435 PNG_CRC_QUIET_USE 4 quiet/use data
1436 PNG_CRC_NO_CHANGE 5 use the current value
1437
1438Choices for (int) ancil_action are
1439 PNG_CRC_DEFAULT 0 error/quit
1440 PNG_CRC_ERROR_QUIT 1 error/quit
1441 PNG_CRC_WARN_DISCARD 2 warn/discard data
1442 PNG_CRC_WARN_USE 3 warn/use data
1443 PNG_CRC_QUIET_USE 4 quiet/use data
1444 PNG_CRC_NO_CHANGE 5 use the current value
1445
1446.SS Setting up callback code
1447
1448You can set up a callback function to handle any unknown chunks in the
1449input stream. You must supply the function
1450
1451 read_chunk_callback(png_structp png_ptr,
1452 png_unknown_chunkp chunk);
1453 {
1454 /* The unknown chunk structure contains your
1455 chunk data, along with similar data for any other
1456 unknown chunks: */
1457
1458 png_byte name[5];
1459 png_byte *data;
1460 png_size_t size;
1461
1462 /* Note that libpng has already taken care of
1463 the CRC handling */
1464
1465 /* put your code here. Search for your chunk in the
1466 unknown chunk structure, process it, and return one
1467 of the following: */
1468
1469 return (-n); /* chunk had an error */
1470 return (0); /* did not recognize */
1471 return (n); /* success */
1472 }
1473
1474(You can give your function another name that you like instead of
1475"read_chunk_callback")
1476
1477To inform libpng about your function, use
1478
1479 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1480 read_chunk_callback);
1481
1482This names not only the callback function, but also a user pointer that
1483you can retrieve with
1484
1485 png_get_user_chunk_ptr(png_ptr);
1486
1487If you call the png_set_read_user_chunk_fn() function, then all unknown
1488chunks will be saved when read, in case your callback function will need
1489one or more of them. This behavior can be changed with the
1490png_set_keep_unknown_chunks() function, described below.
1491
1492At this point, you can set up a callback function that will be
1493called after each row has been read, which you can use to control
1494a progress meter or the like. It's demonstrated in pngtest.c.
1495You must supply a function
1496
1497 void read_row_callback(png_structp png_ptr,
1498 png_uint_32 row, int pass);
1499 {
1500 /* put your code here */
1501 }
1502
1503(You can give it another name that you like instead of "read_row_callback")
1504
1505To inform libpng about your function, use
1506
1507 png_set_read_status_fn(png_ptr, read_row_callback);
1508
1509When this function is called the row has already been completely processed and
1510the 'row' and 'pass' refer to the next row to be handled. For the
1511non-interlaced case the row that was just handled is simply one less than the
1512passed in row number, and pass will always be 0. For the interlaced case the
1513same applies unless the row value is 0, in which case the row just handled was
1514the last one from one of the preceding passes. Because interlacing may skip a
1515pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1516need to know what the last pass is record (row,pass) from the callback and use
1517the last recorded value each time.
1518
1519As with the user transform you can find the output row using the
1520PNG_ROW_FROM_PASS_ROW macro.
1521
1522.SS Unknown-chunk handling
1523
1524Now you get to set the way the library processes unknown chunks in the
1525input PNG stream. Both known and unknown chunks will be read. Normal
1526behavior is that known chunks will be parsed into information in
1527various info_ptr members while unknown chunks will be discarded. This
1528behavior can be wasteful if your application will never use some known
1529chunk types. To change this, you can call:
1530
1531 png_set_keep_unknown_chunks(png_ptr, keep,
1532 chunk_list, num_chunks);
1533 keep - 0: default unknown chunk handling
1534 1: ignore; do not keep
1535 2: keep only if safe-to-copy
1536 3: keep even if unsafe-to-copy
1537
1538 You can use these definitions:
1539 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1540 PNG_HANDLE_CHUNK_NEVER 1
1541 PNG_HANDLE_CHUNK_IF_SAFE 2
1542 PNG_HANDLE_CHUNK_ALWAYS 3
1543
1544 chunk_list - list of chunks affected (a byte string,
1545 five bytes per chunk, NULL or '\0' if
1546 num_chunks is 0)
1547
1548 num_chunks - number of chunks affected; if 0, all
1549 unknown chunks are affected. If nonzero,
1550 only the chunks in the list are affected
1551
1552Unknown chunks declared in this way will be saved as raw data onto a
1553list of png_unknown_chunk structures. If a chunk that is normally
1554known to libpng is named in the list, it will be handled as unknown,
1555according to the "keep" directive. If a chunk is named in successive
1556instances of png_set_keep_unknown_chunks(), the final instance will
1557take precedence. The IHDR and IEND chunks should not be named in
1558chunk_list; if they are, libpng will process them normally anyway.
1559If you know that your application will never make use of some particular
1560chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1561
1562Here is an example of the usage of png_set_keep_unknown_chunks(),
1563where the private "vpAg" chunk will later be processed by a user chunk
1564callback function:
1565
1566 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1567
1568 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1569 png_byte unused_chunks[]=
1570 {
1571 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1572 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1573 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1574 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1575 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1576 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1577 };
1578 #endif
1579
1580 ...
1581
1582 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1583 /* ignore all unknown chunks: */
1584 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1585
1586 /* except for vpAg: */
1587 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1588
1589 /* also ignore unused known chunks: */
1590 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1591 (int)sizeof(unused_chunks)/5);
1592 #endif
1593
1594.SS User limits
1595
1596The PNG specification allows the width and height of an image to be as
1597large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1598Since very few applications really need to process such large images,
1599we have imposed an arbitrary 1-million limit on rows and columns.
1600Larger images will be rejected immediately with a png_error() call. If
1601you wish to change this limit, you can use
1602
1603 png_set_user_limits(png_ptr, width_max, height_max);
1604
1605to set your own limits, or use width_max = height_max = 0x7fffffffL
1606to allow all valid dimensions (libpng may reject some very large images
1607anyway because of potential buffer overflow conditions).
1608
1609You should put this statement after you create the PNG structure and
1610before calling png_read_info(), png_read_png(), or png_process_data().
1611
1612When writing a PNG datastream, put this statement before calling
1613png_write_info() or png_write_png().
1614
1615If you need to retrieve the limits that are being applied, use
1616
1617 width_max = png_get_user_width_max(png_ptr);
1618 height_max = png_get_user_height_max(png_ptr);
1619
1620The PNG specification sets no limit on the number of ancillary chunks
1621allowed in a PNG datastream. You can impose a limit on the total number
1622of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1623
1624 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1625
1626where 0x7fffffffL means unlimited. You can retrieve this limit with
1627
1628 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1629
1630This limit also applies to the number of buffers that can be allocated
1631by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1632
1633You can also set a limit on the amount of memory that a compressed chunk
1634other than IDAT can occupy, with
1635
1636 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1637
1638and you can retrieve the limit with
1639
1640 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1641
1642Any chunks that would cause either of these limits to be exceeded will
1643be ignored.
1644
1645.SS Information about your system
1646
1647If you intend to display the PNG or to incorporate it in other image data you
1648need to tell libpng information about your display or drawing surface so that
1649libpng can convert the values in the image to match the display.
1650
1651From libpng-1.5.4 this information can be set before reading the PNG file
1652header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1653called before the PNG file header had been read and png_set_alpha_mode() did not
1654exist.
1655
1656If you need to support versions prior to libpng-1.5.4 test the version number
1657as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1658described in the appropriate manual page.
1659
1660You give libpng the encoding expected by your system expressed as a 'gamma'
1661value. You can also specify a default encoding for the PNG file in
1662case the required information is missing from the file. By default libpng
1663assumes that the PNG data matches your system, to keep this default call:
1664
1665 png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
1666
1667or you can use the fixed point equivalent:
1668
1669 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma);
1670
1671If you don't know the gamma for your system it is probably 2.2 - a good
1672approximation to the IEC standard for display systems (sRGB). If images are
1673too contrasty or washed out you got the value wrong - check your system
1674documentation!
1675
1676Many systems permit the system gamma to be changed via a lookup table in the
1677display driver, a few systems, including older Macs, change the response by
1678default. As of 1.5.4 three special values are available to handle common
1679situations:
1680
1681 PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1
1682 standard. This matches almost all systems.
1683 PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6)
1684 Apple Macintosh system with the default settings.
1685 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the
1686 system expects data with no gamma encoding.
1687
1688You would use the linear (unencoded) value if you need to process the pixel
1689values further because this avoids the need to decode and reencode each
1690component value whenever arithmetic is performed. A lot of graphics software
1691uses linear values for this reason, often with higher precision component values
1692to preserve overall accuracy.
1693
1694The second thing you may need to tell libpng about is how your system handles
1695alpha channel information. Some, but not all, PNG files contain an alpha
1696channel. To display these files correctly you need to compose the data onto a
1697suitable background, as described in the PNG specification.
1698
1699Libpng only supports composing onto a single color (using png_set_background;
1700see below). Otherwise you must do the composition yourself and, in this case,
1701you may need to call png_set_alpha_mode:
1702
1703#if PNG_LIBPNG_VER >= 10504
1704 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1705#else
1706 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1707#endif
1708
1709The screen_gamma value is the same as the argument to png_set_gamma; however,
1710how it affects the output depends on the mode. png_set_alpha_mode() sets the
1711file gamma default to 1/screen_gamma, so normally you don't need to call
1712png_set_gamma. If you need different defaults call png_set_gamma() before
1713png_set_alpha_mode() - if you call it after it will override the settings made
1714by png_set_alpha_mode().
1715
1716The mode is as follows:
1717
1718 PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
1719green and blue, or gray, components are gamma encoded color
1720values and are not premultiplied by the alpha value. The
1721alpha value is a linear measure of the contribution of the
1722pixel to the corresponding final output pixel.
1723
1724You should normally use this format if you intend to perform
1725color correction on the color values; most, maybe all, color
1726correction software has no handling for the alpha channel and,
1727anyway, the math to handle pre-multiplied component values is
1728unnecessarily complex.
1729
1730Before you do any arithmetic on the component values you need
1731to remove the gamma encoding and multiply out the alpha
1732channel. See the PNG specification for more detail. It is
1733important to note that when an image with an alpha channel is
1734scaled, linear encoded, pre-multiplied component values must
1735be used!
1736
1737The remaining modes assume you don't need to do any further color correction or
1738that if you do, your color correction software knows all about alpha (it
1739probably doesn't!)
1740
1741 PNG_ALPHA_STANDARD: The data libpng produces
1742is encoded in the standard way
1743assumed by most correctly written graphics software.
1744The gamma encoding will be removed by libpng and the
1745linear component values will be pre-multiplied by the
1746alpha channel.
1747
1748With this format the final image must be re-encoded to
1749match the display gamma before the image is displayed.
1750If your system doesn't do that, yet still seems to
1751perform arithmetic on the pixels without decoding them,
1752it is broken - check out the modes below.
1753
1754With PNG_ALPHA_STANDARD libpng always produces linear
1755component values, whatever screen_gamma you supply. The
1756screen_gamma value is, however, used as a default for
1757the file gamma if the PNG file has no gamma information.
1758
1759If you call png_set_gamma() after png_set_alpha_mode() you
1760will override the linear encoding. Instead the
1761pre-multiplied pixel values will be gamma encoded but
1762the alpha channel will still be linear. This may
1763actually match the requirements of some broken software,
1764but it is unlikely.
1765
1766While linear 8-bit data is often used it has
1767insufficient precision for any image with a reasonable
1768dynamic range. To avoid problems, and if your software
1769supports it, use png_set_expand_16() to force all
1770components to 16 bits.
1771
1772 PNG_ALPHA_OPTIMIZED: This mode is the same
1773as PNG_ALPHA_STANDARD except that
1774completely opaque pixels are gamma encoded according to
1775the screen_gamma value. Pixels with alpha less than 1.0
1776will still have linear components.
1777
1778Use this format if you have control over your
1779compositing software and do don't do other arithmetic
1780(such as scaling) on the data you get from libpng. Your
1781compositing software can simply copy opaque pixels to
1782the output but still has linear values for the
1783non-opaque pixels.
1784
1785In normal compositing, where the alpha channel encodes
1786partial pixel coverage (as opposed to broad area
1787translucency), the inaccuracies of the 8-bit
1788representation of non-opaque pixels are irrelevant.
1789
1790You can also try this format if your software is broken;
1791it might look better.
1792
1793 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
1794however, all component values,
1795including the alpha channel are gamma encoded. This is
1796an appropriate format to try if your software, or more
1797likely hardware, is totally broken, i.e., if it performs
1798linear arithmetic directly on gamma encoded values.
1799
1800In most cases of broken software or hardware the bug in the final display
1801manifests as a subtle halo around composited parts of the image. You may not
1802even perceive this as a halo; the composited part of the image may simply appear
1803separate from the background, as though it had been cut out of paper and pasted
1804on afterward.
1805
1806If you don't have to deal with bugs in software or hardware, or if you can fix
1807them, there are three recommended ways of using png_set_alpha_mode():
1808
1809 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1810 screen_gamma);
1811
1812You can do color correction on the result (libpng does not currently
1813support color correction internally). When you handle the alpha channel
1814you need to undo the gamma encoding and multiply out the alpha.
1815
1816 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1817 screen_gamma);
1818 png_set_expand_16(png_ptr);
1819
1820If you are using the high level interface, don't call png_set_expand_16();
1821instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1822
1823With this mode you can't do color correction, but you can do arithmetic,
1824including composition and scaling, on the data without further processing.
1825
1826 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1827 screen_gamma);
1828
1829You can avoid the expansion to 16-bit components with this mode, but you
1830lose the ability to scale the image or perform other linear arithmetic.
1831All you can do is compose the result onto a matching output. Since this
1832mode is libpng-specific you also need to write your own composition
1833software.
1834
1835If you don't need, or can't handle, the alpha channel you can call
1836png_set_background() to remove it by compositing against a fixed color. Don't
1837call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1838transparent parts of this image.
1839
1840 png_set_background(png_ptr, &background_color,
1841 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1842
1843The background_color is an RGB or grayscale value according to the data format
1844libpng will produce for you. Because you don't yet know the format of the PNG
1845file, if you call png_set_background at this point you must arrange for the
1846format produced by libpng to always have 8-bit or 16-bit components and then
1847store the color as an 8-bit or 16-bit color as appropriate. The color contains
1848separate gray and RGB component values, so you can let libpng produce gray or
1849RGB output according to the input format, but low bit depth grayscale images
1850must always be converted to at least 8-bit format. (Even though low bit depth
1851grayscale images can't have an alpha channel they can have a transparent
1852color!)
1853
1854You set the transforms you need later, either as flags to the high level
1855interface or libpng API calls for the low level interface. For reference the
1856settings and API calls required are:
1857
18588-bit values:
1859 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1860 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1861
1862 If you must get exactly the same inaccurate results
1863 produced by default in versions prior to libpng-1.5.4,
1864 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1865 instead.
1866
186716-bit values:
1868 PNG_TRANSFORM_EXPAND_16
1869 png_set_expand_16(png_ptr);
1870
1871In either case palette image data will be expanded to RGB. If you just want
1872color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1873to the list.
1874
1875Calling png_set_background before the PNG file header is read will not work
1876prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1877errors it is therefore much safer to call png_set_background after the head has
1878been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1879used with the high level interface.
1880
1881.SS The high-level read interface
1882
1883At this point there are two ways to proceed; through the high-level
1884read interface, or through a sequence of low-level read operations.
1885You can use the high-level interface if (a) you are willing to read
1886the entire image into memory, and (b) the input transformations
1887you want to do are limited to the following set:
1888
1889 PNG_TRANSFORM_IDENTITY No transformation
1890 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1891 8-bit accurately
1892 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1893 8-bit less accurately
1894 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1895 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1896 samples to bytes
1897 PNG_TRANSFORM_PACKSWAP Change order of packed
1898 pixels to LSB first
1899 PNG_TRANSFORM_EXPAND Perform set_expand()
1900 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1901 PNG_TRANSFORM_SHIFT Normalize pixels to the
1902 sBIT depth
1903 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1904 to BGRA
1905 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1906 to AG
1907 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1908 to transparency
1909 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1910 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1911 to RGB (or GA to RGBA)
1912 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1913
1914(This excludes setting a background color, doing gamma transformation,
1915quantizing, and setting filler.) If this is the case, simply do this:
1916
1917 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1918
1919where png_transforms is an integer containing the bitwise OR of some
1920set of transformation flags. This call is equivalent to png_read_info(),
1921followed the set of transformations indicated by the transform mask,
1922then png_read_image(), and finally png_read_end().
1923
1924(The final parameter of this call is not yet used. Someday it might point
1925to transformation parameters required by some future input transform.)
1926
1927You must use png_transforms and not call any png_set_transform() functions
1928when you use png_read_png().
1929
1930After you have called png_read_png(), you can retrieve the image data
1931with
1932
1933 row_pointers = png_get_rows(png_ptr, info_ptr);
1934
1935where row_pointers is an array of pointers to the pixel data for each row:
1936
1937 png_bytep row_pointers[height];
1938
1939If you know your image size and pixel size ahead of time, you can allocate
1940row_pointers prior to calling png_read_png() with
1941
1942 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1943 png_error (png_ptr,
1944 "Image is too tall to process in memory");
1945
1946 if (width > PNG_UINT_32_MAX/pixel_size)
1947 png_error (png_ptr,
1948 "Image is too wide to process in memory");
1949
1950 row_pointers = png_malloc(png_ptr,
1951 height*png_sizeof(png_bytep));
1952
1953 for (int i=0; i<height, i++)
1954 row_pointers[i]=NULL; /* security precaution */
1955
1956 for (int i=0; i<height, i++)
1957 row_pointers[i]=png_malloc(png_ptr,
1958 width*pixel_size);
1959
1960 png_set_rows(png_ptr, info_ptr, &row_pointers);
1961
1962Alternatively you could allocate your image in one big block and define
1963row_pointers[i] to point into the proper places in your block.
1964
1965If you use png_set_rows(), the application is responsible for freeing
1966row_pointers (and row_pointers[i], if they were separately allocated).
1967
1968If you don't allocate row_pointers ahead of time, png_read_png() will
1969do it, and it'll be free'ed by libpng when you call png_destroy_*().
1970
1971.SS The low-level read interface
1972
1973If you are going the low-level route, you are now ready to read all
1974the file information up to the actual image data. You do this with a
1975call to png_read_info().
1976
1977 png_read_info(png_ptr, info_ptr);
1978
1979This will process all chunks up to but not including the image data.
1980
1981This also copies some of the data from the PNG file into the decode structure
1982for use in later transformations. Important information copied in is:
1983
19841) The PNG file gamma from the gAMA chunk. This overwrites the default value
1985provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1986
19872) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1988damages the information provided by an earlier call to png_set_background
1989resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1990
19913) The number of significant bits in each component value. Libpng uses this to
1992optimize gamma handling by reducing the internal lookup table sizes.
1993
19944) The transparent color information from a tRNS chunk. This can be modified by
1995a later call to png_set_tRNS.
1996
1997.SS Querying the info structure
1998
1999Functions are used to get the information from the info_ptr once it
2000has been read. Note that these fields may not be completely filled
2001in until png_read_end() has read the chunk data following the image.
2002
2003 png_get_IHDR(png_ptr, info_ptr, &width, &height,
2004 &bit_depth, &color_type, &interlace_type,
2005 &compression_type, &filter_method);
2006
2007 width - holds the width of the image
2008 in pixels (up to 2^31).
2009
2010 height - holds the height of the image
2011 in pixels (up to 2^31).
2012
2013 bit_depth - holds the bit depth of one of the
2014 image channels. (valid values are
2015 1, 2, 4, 8, 16 and depend also on
2016 the color_type. See also
2017 significant bits (sBIT) below).
2018
2019 color_type - describes which color/alpha channels
2020 are present.
2021 PNG_COLOR_TYPE_GRAY
2022 (bit depths 1, 2, 4, 8, 16)
2023 PNG_COLOR_TYPE_GRAY_ALPHA
2024 (bit depths 8, 16)
2025 PNG_COLOR_TYPE_PALETTE
2026 (bit depths 1, 2, 4, 8)
2027 PNG_COLOR_TYPE_RGB
2028 (bit_depths 8, 16)
2029 PNG_COLOR_TYPE_RGB_ALPHA
2030 (bit_depths 8, 16)
2031
2032 PNG_COLOR_MASK_PALETTE
2033 PNG_COLOR_MASK_COLOR
2034 PNG_COLOR_MASK_ALPHA
2035
2036 interlace_type - (PNG_INTERLACE_NONE or
2037 PNG_INTERLACE_ADAM7)
2038
2039 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
2040 for PNG 1.0)
2041
2042 filter_method - (must be PNG_FILTER_TYPE_BASE
2043 for PNG 1.0, and can also be
2044 PNG_INTRAPIXEL_DIFFERENCING if
2045 the PNG datastream is embedded in
2046 a MNG-1.0 datastream)
2047
2048 Any or all of interlace_type, compression_type, or
2049 filter_method can be NULL if you are
2050 not interested in their values.
2051
2052 Note that png_get_IHDR() returns 32-bit data into
2053 the application's width and height variables.
2054 This is an unsafe situation if these are 16-bit
2055 variables. In such situations, the
2056 png_get_image_width() and png_get_image_height()
2057 functions described below are safer.
2058
2059 width = png_get_image_width(png_ptr,
2060 info_ptr);
2061
2062 height = png_get_image_height(png_ptr,
2063 info_ptr);
2064
2065 bit_depth = png_get_bit_depth(png_ptr,
2066 info_ptr);
2067
2068 color_type = png_get_color_type(png_ptr,
2069 info_ptr);
2070
2071 interlace_type = png_get_interlace_type(png_ptr,
2072 info_ptr);
2073
2074 compression_type = png_get_compression_type(png_ptr,
2075 info_ptr);
2076
2077 filter_method = png_get_filter_type(png_ptr,
2078 info_ptr);
2079
2080 channels = png_get_channels(png_ptr, info_ptr);
2081
2082 channels - number of channels of info for the
2083 color type (valid values are 1 (GRAY,
2084 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
2085 4 (RGB_ALPHA or RGB + filler byte))
2086
2087 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
2088
2089 rowbytes - number of bytes needed to hold a row
2090
2091 signature = png_get_signature(png_ptr, info_ptr);
2092
2093 signature - holds the signature read from the
2094 file (if any). The data is kept in
2095 the same offset it would be if the
2096 whole signature were read (i.e. if an
2097 application had already read in 4
2098 bytes of signature before starting
2099 libpng, the remaining 4 bytes would
2100 be in signature[4] through signature[7]
2101 (see png_set_sig_bytes())).
2102
2103These are also important, but their validity depends on whether the chunk
2104has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
2105png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
2106data has been read, or zero if it is missing. The parameters to the
2107png_get_<chunk> are set directly if they are simple data types, or a
2108pointer into the info_ptr is returned for any complex types.
2109
2110 png_get_PLTE(png_ptr, info_ptr, &palette,
2111 &num_palette);
2112
2113 palette - the palette for the file
2114 (array of png_color)
2115
2116 num_palette - number of entries in the palette
2117
2118 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
2119 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
2120
2121 file_gamma - the gamma at which the file is
2122 written (PNG_INFO_gAMA)
2123
2124 int_file_gamma - 100,000 times the gamma at which the
2125 file is written
2126
2127 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y,
2128 &green_x, &green_y, &blue_x, &blue_y)
2129 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X,
2130 &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z)
2131 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y,
2132 &int_red_x, &int_red_y, &int_green_x, &int_green_y,
2133 &int_blue_x, &int_blue_y)
2134 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
2135 &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z,
2136 &int_blue_X, &int_blue_Y, &int_blue_Z)
2137
2138 {white,red,green,blue}_{x,y}
2139 A color space encoding specified using the chromaticities
2140 of the end points and the white point. (PNG_INFO_cHRM)
2141
2142 {red,green,blue}_{X,Y,Z}
2143 A color space encoding specified using the encoding end
2144 points - the CIE tristimulus specification of the intended
2145 color of the red, green and blue channels in the PNG RGB
2146 data. The white point is simply the sum of the three end
2147 points. (PNG_INFO_cHRM)
2148
2149 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
2150
2151 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
2152 The presence of the sRGB chunk
2153 means that the pixel data is in the
2154 sRGB color space. This chunk also
2155 implies specific values of gAMA and
2156 cHRM.
2157
2158 png_get_iCCP(png_ptr, info_ptr, &name,
2159 &compression_type, &profile, &proflen);
2160
2161 name - The profile name.
2162
2163 compression_type - The compression type; always
2164 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2165 You may give NULL to this argument to
2166 ignore it.
2167
2168 profile - International Color Consortium color
2169 profile data. May contain NULs.
2170
2171 proflen - length of profile data in bytes.
2172
2173 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
2174
2175 sig_bit - the number of significant bits for
2176 (PNG_INFO_sBIT) each of the gray,
2177 red, green, and blue channels,
2178 whichever are appropriate for the
2179 given color type (png_color_16)
2180
2181 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
2182 &num_trans, &trans_color);
2183
2184 trans_alpha - array of alpha (transparency)
2185 entries for palette (PNG_INFO_tRNS)
2186
2187 num_trans - number of transparent entries
2188 (PNG_INFO_tRNS)
2189
2190 trans_color - graylevel or color sample values of
2191 the single transparent color for
2192 non-paletted images (PNG_INFO_tRNS)
2193
2194 png_get_hIST(png_ptr, info_ptr, &hist);
2195 (PNG_INFO_hIST)
2196
2197 hist - histogram of palette (array of
2198 png_uint_16)
2199
2200 png_get_tIME(png_ptr, info_ptr, &mod_time);
2201
2202 mod_time - time image was last modified
2203 (PNG_VALID_tIME)
2204
2205 png_get_bKGD(png_ptr, info_ptr, &background);
2206
2207 background - background color (of type
2208 png_color_16p) (PNG_VALID_bKGD)
2209 valid 16-bit red, green and blue
2210 values, regardless of color_type
2211
2212 num_comments = png_get_text(png_ptr, info_ptr,
2213 &text_ptr, &num_text);
2214
2215 num_comments - number of comments
2216
2217 text_ptr - array of png_text holding image
2218 comments
2219
2220 text_ptr[i].compression - type of compression used
2221 on "text" PNG_TEXT_COMPRESSION_NONE
2222 PNG_TEXT_COMPRESSION_zTXt
2223 PNG_ITXT_COMPRESSION_NONE
2224 PNG_ITXT_COMPRESSION_zTXt
2225
2226 text_ptr[i].key - keyword for comment. Must contain
2227 1-79 characters.
2228
2229 text_ptr[i].text - text comments for current
2230 keyword. Can be empty.
2231
2232 text_ptr[i].text_length - length of text string,
2233 after decompression, 0 for iTXt
2234
2235 text_ptr[i].itxt_length - length of itxt string,
2236 after decompression, 0 for tEXt/zTXt
2237
2238 text_ptr[i].lang - language of comment (empty
2239 string for unknown).
2240
2241 text_ptr[i].lang_key - keyword in UTF-8
2242 (empty string for unknown).
2243
2244 Note that the itxt_length, lang, and lang_key
2245 members of the text_ptr structure only exist when the
2246 library is built with iTXt chunk support. Prior to
2247 libpng-1.4.0 the library was built by default without
2248 iTXt support. Also note that when iTXt is supported,
2249 they contain NULL pointers when the "compression"
2250 field contains PNG_TEXT_COMPRESSION_NONE or
2251 PNG_TEXT_COMPRESSION_zTXt.
2252
2253 num_text - number of comments (same as
2254 num_comments; you can put NULL here
2255 to avoid the duplication)
2256
2257 Note while png_set_text() will accept text, language,
2258 and translated keywords that can be NULL pointers, the
2259 structure returned by png_get_text will always contain
2260 regular zero-terminated C strings. They might be
2261 empty strings but they will never be NULL pointers.
2262
2263 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2264 &palette_ptr);
2265
2266 num_spalettes - number of sPLT chunks read.
2267
2268 palette_ptr - array of palette structures holding
2269 contents of one or more sPLT chunks
2270 read.
2271
2272 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2273 &unit_type);
2274
2275 offset_x - positive offset from the left edge
2276 of the screen (can be negative)
2277
2278 offset_y - positive offset from the top edge
2279 of the screen (can be negative)
2280
2281 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2282
2283 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2284 &unit_type);
2285
2286 res_x - pixels/unit physical resolution in
2287 x direction
2288
2289 res_y - pixels/unit physical resolution in
2290 x direction
2291
2292 unit_type - PNG_RESOLUTION_UNKNOWN,
2293 PNG_RESOLUTION_METER
2294
2295 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2296 &height)
2297
2298 unit - physical scale units (an integer)
2299
2300 width - width of a pixel in physical scale units
2301
2302 height - height of a pixel in physical scale units
2303 (width and height are doubles)
2304
2305 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2306 &height)
2307
2308 unit - physical scale units (an integer)
2309
2310 width - width of a pixel in physical scale units
2311 (expressed as a string)
2312
2313 height - height of a pixel in physical scale units
2314 (width and height are strings like "2.54")
2315
2316 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2317 info_ptr, &unknowns)
2318
2319 unknowns - array of png_unknown_chunk
2320 structures holding unknown chunks
2321
2322 unknowns[i].name - name of unknown chunk
2323
2324 unknowns[i].data - data of unknown chunk
2325
2326 unknowns[i].size - size of unknown chunk's data
2327
2328 unknowns[i].location - position of chunk in file
2329
2330 The value of "i" corresponds to the order in which the
2331 chunks were read from the PNG file or inserted with the
2332 png_set_unknown_chunks() function.
2333
2334 The value of "location" is a bitwise "or" of
2335
2336 PNG_HAVE_IHDR (0x01)
2337 PNG_HAVE_PLTE (0x02)
2338 PNG_AFTER_IDAT (0x08)
2339
2340The data from the pHYs chunk can be retrieved in several convenient
2341forms:
2342
2343 res_x = png_get_x_pixels_per_meter(png_ptr,
2344 info_ptr)
2345
2346 res_y = png_get_y_pixels_per_meter(png_ptr,
2347 info_ptr)
2348
2349 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2350 info_ptr)
2351
2352 res_x = png_get_x_pixels_per_inch(png_ptr,
2353 info_ptr)
2354
2355 res_y = png_get_y_pixels_per_inch(png_ptr,
2356 info_ptr)
2357
2358 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2359 info_ptr)
2360
2361 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2362 info_ptr)
2363
2364 Each of these returns 0 [signifying "unknown"] if
2365 the data is not present or if res_x is 0;
2366 res_x_and_y is 0 if res_x != res_y
2367
2368 Note that because of the way the resolutions are
2369 stored internally, the inch conversions won't
2370 come out to exactly even number. For example,
2371 72 dpi is stored as 0.28346 pixels/meter, and
2372 when this is retrieved it is 71.9988 dpi, so
2373 be sure to round the returned value appropriately
2374 if you want to display a reasonable-looking result.
2375
2376The data from the oFFs chunk can be retrieved in several convenient
2377forms:
2378
2379 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2380
2381 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2382
2383 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2384
2385 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2386
2387 Each of these returns 0 [signifying "unknown" if both
2388 x and y are 0] if the data is not present or if the
2389 chunk is present but the unit is the pixel. The
2390 remark about inexact inch conversions applies here
2391 as well, because a value in inches can't always be
2392 converted to microns and back without some loss
2393 of precision.
2394
2395For more information, see the
2396PNG specification for chunk contents. Be careful with trusting
2397rowbytes, as some of the transformations could increase the space
2398needed to hold a row (expand, filler, gray_to_rgb, etc.).
2399See png_read_update_info(), below.
2400
2401A quick word about text_ptr and num_text. PNG stores comments in
2402keyword/text pairs, one pair per chunk, with no limit on the number
2403of text chunks, and a 2^31 byte limit on their size. While there are
2404suggested keywords, there is no requirement to restrict the use to these
2405strings. It is strongly suggested that keywords and text be sensible
2406to humans (that's the point), so don't use abbreviations. Non-printing
2407symbols are not allowed. See the PNG specification for more details.
2408There is also no requirement to have text after the keyword.
2409
2410Keywords should be limited to 79 Latin-1 characters without leading or
2411trailing spaces, but non-consecutive spaces are allowed within the
2412keyword. It is possible to have the same keyword any number of times.
2413The text_ptr is an array of png_text structures, each holding a
2414pointer to a language string, a pointer to a keyword and a pointer to
2415a text string. The text string, language code, and translated
2416keyword may be empty or NULL pointers. The keyword/text
2417pairs are put into the array in the order that they are received.
2418However, some or all of the text chunks may be after the image, so, to
2419make sure you have read all the text chunks, don't mess with these
2420until after you read the stuff after the image. This will be
2421mentioned again below in the discussion that goes with png_read_end().
2422
2423.SS Input transformations
2424
2425After you've read the header information, you can set up the library
2426to handle any special transformations of the image data. The various
2427ways to transform the data will be described in the order that they
2428should occur. This is important, as some of these change the color
2429type and/or bit depth of the data, and some others only work on
2430certain color types and bit depths.
2431
2432Transformations you request are ignored if they don't have any meaning for a
2433particular input data format. However some transformations can have an effect
2434as a result of a previous transformation. If you specify a contradictory set of
2435transformations, for example both adding and removing the alpha channel, you
2436cannot predict the final result.
2437
2438The color used for the transparency values should be supplied in the same
2439format/depth as the current image data. It is stored in the same format/depth
2440as the image data in a tRNS chunk, so this is what libpng expects for this data.
2441
2442The color used for the background value depends on the need_expand argument as
2443described below.
2444
2445Data will be decoded into the supplied row buffers packed into bytes
2446unless the library has been told to transform it into another format.
2447For example, 4 bit/pixel paletted or grayscale data will be returned
24482 pixels/byte with the leftmost pixel in the high-order bits of the
2449byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2450in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2451is called to insert filler bytes, either before or after each RGB triplet.
245216-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2453byte of the color value first, unless png_set_scale_16() is called to
2454transform it to regular RGB RGB triplets, or png_set_filler() or
2455png_set_add alpha() is called to insert filler bytes, either before or
2456after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2457be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2458or png_set_scale_16().
2459
2460The following code transforms grayscale images of less than 8 to 8 bits,
2461changes paletted images to RGB, and adds a full alpha channel if there is
2462transparency information in a tRNS chunk. This is most useful on
2463grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2464viewing application that wishes to treat all images in the same way.
2465
2466 if (color_type == PNG_COLOR_TYPE_PALETTE)
2467 png_set_palette_to_rgb(png_ptr);
2468
2469 if (png_get_valid(png_ptr, info_ptr,
2470 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2471
2472 if (color_type == PNG_COLOR_TYPE_GRAY &&
2473 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2474
2475The first two functions are actually aliases for png_set_expand(), added
2476in libpng version 1.0.4, with the function names expanded to improve code
2477readability. In some future version they may actually do different
2478things.
2479
2480As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2481added. It expands the sample depth without changing tRNS to alpha.
2482
2483As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2484png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2485Use this when the output color or gray channels are made linear to avoid fairly
2486severe accuracy loss.
2487
2488 if (bit_depth < 16)
2489 png_set_expand_16(png_ptr);
2490
2491PNG can have files with 16 bits per channel. If you only can handle
24928 bits per channel, this will strip the pixels down to 8-bit.
2493
2494 if (bit_depth == 16)
2495#if PNG_LIBPNG_VER >= 10504
2496 png_set_scale_16(png_ptr);
2497#else
2498 png_set_strip_16(png_ptr);
2499#endif
2500
2501(The more accurate "png_set_scale_16()" API became available in libpng version
25021.5.4).
2503
2504If you need to process the alpha channel on the image separately from the image
2505data (for example if you convert it to a bitmap mask) it is possible to have
2506libpng strip the channel leaving just RGB or gray data:
2507
2508 if (color_type & PNG_COLOR_MASK_ALPHA)
2509 png_set_strip_alpha(png_ptr);
2510
2511If you strip the alpha channel you need to find some other way of dealing with
2512the information. If, instead, you want to convert the image to an opaque
2513version with no alpha channel use png_set_background; see below.
2514
2515As of libpng version 1.5.2, almost all useful expansions are supported, the
2516major ommissions are conversion of grayscale to indexed images (which can be
2517done trivially in the application) and conversion of indexed to grayscale (which
2518can be done by a trivial manipulation of the palette.)
2519
2520In the following table, the 01 means grayscale with depth<8, 31 means
2521indexed with depth<8, other numerals represent the color type, "T" means
2522the tRNS chunk is present, A means an alpha channel is present, and O
2523means tRNS or alpha is present but all pixels in the image are opaque.
2524
2525 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2526 TO
2527 01 - [G] - - - - - - - - - - - - -
2528 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2529 0 1 G + . . G G G G G G B B GB GB
2530 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2531 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2532 2 C P C C C + . . C - - CB CB B B
2533 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2534 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2535 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2536 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2537 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2538 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2539 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2540 6A CA PA CA C C A T tT PA P P C CBA + BA
2541 6O CA PBA CA C C A tT T PA P P CBA C BA +
2542
2543Within the matrix,
2544 "+" identifies entries where 'from' and 'to' are the same.
2545 "-" means the transformation is not supported.
2546 "." means nothing is necessary (a tRNS chunk can just be ignored).
2547 "t" means the transformation is obtained by png_set_tRNS.
2548 "A" means the transformation is obtained by png_set_add_alpha().
2549 "X" means the transformation is obtained by png_set_expand().
2550 "1" means the transformation is obtained by
2551 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there
2552 is no transparency in the original or the final format).
2553 "C" means the transformation is obtained by png_set_gray_to_rgb().
2554 "G" means the transformation is obtained by png_set_rgb_to_gray().
2555 "P" means the transformation is obtained by
2556 png_set_expand_palette_to_rgb().
2557 "p" means the transformation is obtained by png_set_packing().
2558 "Q" means the transformation is obtained by png_set_quantize().
2559 "T" means the transformation is obtained by png_set_tRNS_to_alpha().
2560 "B" means the transformation is obtained by png_set_background(), or
2561 png_strip_alpha().
2562
2563When an entry has multiple transforms listed all are required to cause the
2564right overall transformation. When two transforms are separated by a comma
2565either will do the job. When transforms are enclosed in [] the transform should
2566do the job but this is currently unimplemented - a different format will result
2567if the suggested transformations are used.
2568
2569In PNG files, the alpha channel in an image
2570is the level of opacity. If you need the alpha channel in an image to
2571be the level of transparency instead of opacity, you can invert the
2572alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2573fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2574images) is fully transparent, with
2575
2576 png_set_invert_alpha(png_ptr);
2577
2578PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2579they can, resulting in, for example, 8 pixels per byte for 1 bit
2580files. This code expands to 1 pixel per byte without changing the
2581values of the pixels:
2582
2583 if (bit_depth < 8)
2584 png_set_packing(png_ptr);
2585
2586PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2587stored in a PNG image have been "scaled" or "shifted" up to the next
2588higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2589to 8 bits/sample in the range [0, 255]). However, it is also possible
2590to convert the PNG pixel data back to the original bit depth of the
2591image. This call reduces the pixels back down to the original bit depth:
2592
2593 png_color_8p sig_bit;
2594
2595 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2596 png_set_shift(png_ptr, sig_bit);
2597
2598PNG files store 3-color pixels in red, green, blue order. This code
2599changes the storage of the pixels to blue, green, red:
2600
2601 if (color_type == PNG_COLOR_TYPE_RGB ||
2602 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2603 png_set_bgr(png_ptr);
2604
2605PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2606into 4 or 8 bytes for windowing systems that need them in this format:
2607
2608 if (color_type == PNG_COLOR_TYPE_RGB)
2609 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2610
2611where "filler" is the 8 or 16-bit number to fill with, and the location is
2612either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2613you want the filler before the RGB or after. This transformation
2614does not affect images that already have full alpha channels. To add an
2615opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2616will generate RGBA pixels.
2617
2618Note that png_set_filler() does not change the color type. If you want
2619to do that, you can add a true alpha channel with
2620
2621 if (color_type == PNG_COLOR_TYPE_RGB ||
2622 color_type == PNG_COLOR_TYPE_GRAY)
2623 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2624
2625where "filler" contains the alpha value to assign to each pixel.
2626This function was added in libpng-1.2.7.
2627
2628If you are reading an image with an alpha channel, and you need the
2629data as ARGB instead of the normal PNG format RGBA:
2630
2631 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2632 png_set_swap_alpha(png_ptr);
2633
2634For some uses, you may want a grayscale image to be represented as
2635RGB. This code will do that conversion:
2636
2637 if (color_type == PNG_COLOR_TYPE_GRAY ||
2638 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2639 png_set_gray_to_rgb(png_ptr);
2640
2641Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2642with alpha.
2643
2644 if (color_type == PNG_COLOR_TYPE_RGB ||
2645 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2646 png_set_rgb_to_gray(png_ptr, error_action, double red_weight,
2647 double green_weight);
2648
2649 error_action = 1: silently do the conversion
2650
2651 error_action = 2: issue a warning if the original
2652 image has any pixel where
2653 red != green or red != blue
2654
2655 error_action = 3: issue an error and abort the
2656 conversion if the original
2657 image has any pixel where
2658 red != green or red != blue
2659
2660 red_weight: weight of red component
2661
2662 green_weight: weight of green component
2663 If either weight is negative, default
2664 weights are used.
2665
2666In the corresponding fixed point API the red_weight and green_weight values are
2667simply scaled by 100,000:
2668
2669 png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight,
2670 png_fixed_point green_weight);
2671
2672If you have set error_action = 1 or 2, you can
2673later check whether the image really was gray, after processing
2674the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2675It will return a png_byte that is zero if the image was gray or
26761 if there were any non-gray pixels. Background and sBIT data
2677will be silently converted to grayscale, using the green channel
2678data for sBIT, regardless of the error_action setting.
2679
2680The default values come from the PNG file cHRM chunk if present; otherwise, the
2681defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2682space, as recommended in the Charles Poynton's Colour FAQ,
2683<http://www.poynton.com/>, in section 9:
2684
2685 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2686
2687 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2688
2689Previous versions of this document, 1998 through 2002, recommended a slightly
2690different formula:
2691
2692 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2693
2694Libpng uses an integer approximation:
2695
2696 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2697
2698The calculation is done in a linear colorspace, if the image gamma
2699can be determined.
2700
2701The png_set_background() function has been described already; it tells libpng to
2702composite images with alpha or simple transparency against the supplied
2703background color. For compatibility with versions of libpng earlier than
2704libpng-1.5.4 it is recommended that you call the function after reading the file
2705header, even if you don't want to use the color in a bKGD chunk, if one exists.
2706
2707If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2708you may use this color, or supply another color more suitable for
2709the current display (e.g., the background color from a web page). You
2710need to tell libpng how the color is represented, both the format of the
2711component values in the color (the number of bits) and the gamma encoding of the
2712color. The function takes two arguments, background_gamma_mode and need_expand
2713to convey this information, however only two combinations are likely to be
2714useful:
2715
2716 png_color_16 my_background;
2717 png_color_16p image_background;
2718
2719 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2720 png_set_background(png_ptr, image_background,
2721 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2722 else
2723 png_set_background(png_ptr, &my_background,
2724 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2725
2726The second call was described above - my_background is in the format of the
2727final, display, output produced by libpng. Because you now know the format of
2728the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2729output and to retain palette images (the palette colors will be modified
2730appropriately and the tRNS chunk removed.) However, if you are doing this,
2731take great care not to ask for transformations without checking first that
2732they apply!
2733
2734In the first call the background color has the original bit depth and color type
2735of the PNG file. So, for palette images the color is supplied as a palette
2736index and for low bit greyscale images the color is a reduced bit value in
2737image_background->gray.
2738
2739If you didn't call png_set_gamma() before reading the file header, for example
2740if you need your code to remain compatible with older versions of libpng prior
2741to libpng-1.5.4, this is the place to call it.
2742
2743Do not call it if you called png_set_alpha_mode(); doing so will damage the
2744settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2745supported then you can certainly do png_set_gamma() before reading the PNG
2746header.)
2747
2748This API unconditionally sets the screen and file gamma values, so it will
2749override the value in the PNG file unless it is called before the PNG file
2750reading starts. For this reason you must always call it with the PNG file
2751value when you call it in this position:
2752
2753 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2754 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2755
2756 else
2757 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2758
2759If you need to reduce an RGB file to a paletted file, or if a paletted
2760file has more entries then will fit on your screen, png_set_quantize()
2761will do that. Note that this is a simple match quantization that merely
2762finds the closest color available. This should work fairly well with
2763optimized palettes, but fairly badly with linear color cubes. If you
2764pass a palette that is larger than maximum_colors, the file will
2765reduce the number of colors in the palette so it will fit into
2766maximum_colors. If there is a histogram, libpng will use it to make
2767more intelligent choices when reducing the palette. If there is no
2768histogram, it may not do as good a job.
2769
2770 if (color_type & PNG_COLOR_MASK_COLOR)
2771 {
2772 if (png_get_valid(png_ptr, info_ptr,
2773 PNG_INFO_PLTE))
2774 {
2775 png_uint_16p histogram = NULL;
2776
2777 png_get_hIST(png_ptr, info_ptr,
2778 &histogram);
2779 png_set_quantize(png_ptr, palette, num_palette,
2780 max_screen_colors, histogram, 1);
2781 }
2782
2783 else
2784 {
2785 png_color std_color_cube[MAX_SCREEN_COLORS] =
2786 { ... colors ... };
2787
2788 png_set_quantize(png_ptr, std_color_cube,
2789 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2790 NULL,0);
2791 }
2792 }
2793
2794PNG files describe monochrome as black being zero and white being one.
2795The following code will reverse this (make black be one and white be
2796zero):
2797
2798 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2799 png_set_invert_mono(png_ptr);
2800
2801This function can also be used to invert grayscale and gray-alpha images:
2802
2803 if (color_type == PNG_COLOR_TYPE_GRAY ||
2804 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2805 png_set_invert_mono(png_ptr);
2806
2807PNG files store 16-bit pixels in network byte order (big-endian,
2808ie. most significant bits first). This code changes the storage to the
2809other way (little-endian, i.e. least significant bits first, the
2810way PCs store them):
2811
2812 if (bit_depth == 16)
2813 png_set_swap(png_ptr);
2814
2815If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2816need to change the order the pixels are packed into bytes, you can use:
2817
2818 if (bit_depth < 8)
2819 png_set_packswap(png_ptr);
2820
2821Finally, you can write your own transformation function if none of
2822the existing ones meets your needs. This is done by setting a callback
2823with
2824
2825 png_set_read_user_transform_fn(png_ptr,
2826 read_transform_fn);
2827
2828You must supply the function
2829
2830 void read_transform_fn(png_structp png_ptr, png_row_infop
2831 row_info, png_bytep data)
2832
2833See pngtest.c for a working example. Your function will be called
2834after all of the other transformations have been processed. Take care with
2835interlaced images if you do the interlace yourself - the width of the row is the
2836width in 'row_info', not the overall image width.
2837
2838If supported, libpng provides two information routines that you can use to find
2839where you are in processing the image:
2840
2841 png_get_current_pass_number(png_structp png_ptr);
2842 png_get_current_row_number(png_structp png_ptr);
2843
2844Don't try using these outside a transform callback - firstly they are only
2845supported if user transforms are supported, secondly they may well return
2846unexpected results unless the row is actually being processed at the moment they
2847are called.
2848
2849With interlaced
2850images the value returned is the row in the input sub-image image. Use
2851PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2852find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2853
2854The discussion of interlace handling above contains more information on how to
2855use these values.
2856
2857You can also set up a pointer to a user structure for use by your
2858callback function, and you can inform libpng that your transform
2859function will change the number of channels or bit depth with the
2860function
2861
2862 png_set_user_transform_info(png_ptr, user_ptr,
2863 user_depth, user_channels);
2864
2865The user's application, not libpng, is responsible for allocating and
2866freeing any memory required for the user structure.
2867
2868You can retrieve the pointer via the function
2869png_get_user_transform_ptr(). For example:
2870
2871 voidp read_user_transform_ptr =
2872 png_get_user_transform_ptr(png_ptr);
2873
2874The last thing to handle is interlacing; this is covered in detail below,
2875but you must call the function here if you want libpng to handle expansion
2876of the interlaced image.
2877
2878 number_of_passes = png_set_interlace_handling(png_ptr);
2879
2880After setting the transformations, libpng can update your png_info
2881structure to reflect any transformations you've requested with this
2882call.
2883
2884 png_read_update_info(png_ptr, info_ptr);
2885
2886This is most useful to update the info structure's rowbytes
2887field so you can use it to allocate your image memory. This function
2888will also update your palette with the correct screen_gamma and
2889background if these have been given with the calls above. You may
2890only call png_read_update_info() once with a particular info_ptr.
2891
2892After you call png_read_update_info(), you can allocate any
2893memory you need to hold the image. The row data is simply
2894raw byte data for all forms of images. As the actual allocation
2895varies among applications, no example will be given. If you
2896are allocating one large chunk, you will need to build an
2897array of pointers to each row, as it will be needed for some
2898of the functions below.
2899
2900Remember: Before you call png_read_update_info(), the png_get_*()
2901functions return the values corresponding to the original PNG image.
2902After you call png_read_update_info the values refer to the image
2903that libpng will output. Consequently you must call all the png_set_
2904functions before you call png_read_update_info(). This is particularly
2905important for png_set_interlace_handling() - if you are going to call
2906png_read_update_info() you must call png_set_interlace_handling() before
2907it unless you want to receive interlaced output.
2908
2909.SS Reading image data
2910
2911After you've allocated memory, you can read the image data.
2912The simplest way to do this is in one function call. If you are
2913allocating enough memory to hold the whole image, you can just
2914call png_read_image() and libpng will read in all the image data
2915and put it in the memory area supplied. You will need to pass in
2916an array of pointers to each row.
2917
2918This function automatically handles interlacing, so you don't
2919need to call png_set_interlace_handling() (unless you call
2920png_read_update_info()) or call this function multiple times, or any
2921of that other stuff necessary with png_read_rows().
2922
2923 png_read_image(png_ptr, row_pointers);
2924
2925where row_pointers is:
2926
2927 png_bytep row_pointers[height];
2928
2929You can point to void or char or whatever you use for pixels.
2930
2931If you don't want to read in the whole image at once, you can
2932use png_read_rows() instead. If there is no interlacing (check
2933interlace_type == PNG_INTERLACE_NONE), this is simple:
2934
2935 png_read_rows(png_ptr, row_pointers, NULL,
2936 number_of_rows);
2937
2938where row_pointers is the same as in the png_read_image() call.
2939
2940If you are doing this just one row at a time, you can do this with
2941a single row_pointer instead of an array of row_pointers:
2942
2943 png_bytep row_pointer = row;
2944 png_read_row(png_ptr, row_pointer, NULL);
2945
2946If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2947get somewhat harder. The only current (PNG Specification version 1.2)
2948interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2949a somewhat complicated 2D interlace scheme, known as Adam7, that
2950breaks down an image into seven smaller images of varying size, based
2951on an 8x8 grid. This number is defined (from libpng 1.5) as
2952PNG_INTERLACE_ADAM7_PASSES in png.h
2953
2954libpng can fill out those images or it can give them to you "as is".
2955It is almost always better to have libpng handle the interlacing for you.
2956If you want the images filled out, there are two ways to do that. The one
2957mentioned in the PNG specification is to expand each pixel to cover
2958those pixels that have not been read yet (the "rectangle" method).
2959This results in a blocky image for the first pass, which gradually
2960smooths out as more pixels are read. The other method is the "sparkle"
2961method, where pixels are drawn only in their final locations, with the
2962rest of the image remaining whatever colors they were initialized to
2963before the start of the read. The first method usually looks better,
2964but tends to be slower, as there are more pixels to put in the rows.
2965
2966If, as is likely, you want libpng to expand the images, call this before
2967calling png_start_read_image() or png_read_update_info():
2968
2969 if (interlace_type == PNG_INTERLACE_ADAM7)
2970 number_of_passes
2971 = png_set_interlace_handling(png_ptr);
2972
2973This will return the number of passes needed. Currently, this is seven,
2974but may change if another interlace type is added. This function can be
2975called even if the file is not interlaced, where it will return one pass.
2976You then need to read the whole image 'number_of_passes' times. Each time
2977will distribute the pixels from the current pass to the correct place in
2978the output image, so you need to supply the same rows to png_read_rows in
2979each pass.
2980
2981If you are not going to display the image after each pass, but are
2982going to wait until the entire image is read in, use the sparkle
2983effect. This effect is faster and the end result of either method
2984is exactly the same. If you are planning on displaying the image
2985after each pass, the "rectangle" effect is generally considered the
2986better looking one.
2987
2988If you only want the "sparkle" effect, just call png_read_rows() as
2989normal, with the third parameter NULL. Make sure you make pass over
2990the image number_of_passes times, and you don't change the data in the
2991rows between calls. You can change the locations of the data, just
2992not the data. Each pass only writes the pixels appropriate for that
2993pass, and assumes the data from previous passes is still valid.
2994
2995 png_read_rows(png_ptr, row_pointers, NULL,
2996 number_of_rows);
2997
2998If you only want the first effect (the rectangles), do the same as
2999before except pass the row buffer in the third parameter, and leave
3000the second parameter NULL.
3001
3002 png_read_rows(png_ptr, NULL, row_pointers,
3003 number_of_rows);
3004
3005If you don't want libpng to handle the interlacing details, just call
3006png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
3007Each of the images is a valid image by itself, however you will almost
3008certainly need to distribute the pixels from each sub-image to the
3009correct place. This is where everything gets very tricky.
3010
3011If you want to retrieve the separate images you must pass the correct
3012number of rows to each successive call of png_read_rows(). The calculation
3013gets pretty complicated for small images, where some sub-images may
3014not even exist because either their width or height ends up zero.
3015libpng provides two macros to help you in 1.5 and later versions:
3016
3017 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
3018 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
3019
3020Respectively these tell you the width and height of the sub-image
3021corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
3022this can be confusing because the specification refers to the same passes
3023as 1 to 7! Be careful, you must check both the width and height before
3024calling png_read_rows() and not call it for that pass if either is zero.
3025
3026You can, of course, read each sub-image row by row. If you want to
3027produce optimal code to make a pixel-by-pixel transformation of an
3028interlaced image this is the best approach; read each row of each pass,
3029transform it, and write it out to a new interlaced image.
3030
3031If you want to de-interlace the image yourself libpng provides further
3032macros to help that tell you where to place the pixels in the output image.
3033Because the interlacing scheme is rectangular - sub-image pixels are always
3034arranged on a rectangular grid - all you need to know for each pass is the
3035starting column and row in the output image of the first pixel plus the
3036spacing between each pixel. As of libpng 1.5 there are four macros to
3037retrieve this information:
3038
3039 png_uint_32 x = PNG_PASS_START_COL(pass);
3040 png_uint_32 y = PNG_PASS_START_ROW(pass);
3041 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
3042 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
3043
3044These allow you to write the obvious loop:
3045
3046 png_uint_32 input_y = 0;
3047 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
3048
3049 while (output_y < output_image_height)
3050 {
3051 png_uint_32 input_x = 0;
3052 png_uint_32 output_x = PNG_PASS_START_COL(pass);
3053
3054 while (output_x < output_image_width)
3055 {
3056 image[output_y][output_x] =
3057 subimage[pass][input_y][input_x++];
3058
3059 output_x += xStep;
3060 }
3061
3062 ++input_y;
3063 output_y += yStep;
3064 }
3065
3066Notice that the steps between successive output rows and columns are
3067returned as shifts. This is possible because the pixels in the subimages
3068are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
3069image. In practice you may need to directly calculate the output coordinate
3070given an input coordinate. libpng provides two further macros for this
3071purpose:
3072
3073 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
3074 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
3075
3076Finally a pair of macros are provided to tell you if a particular image
3077row or column appears in a given pass:
3078
3079 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
3080 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
3081
3082Bear in mind that you will probably also need to check the width and height
3083of the pass in addition to the above to be sure the pass even exists!
3084
3085With any luck you are convinced by now that you don't want to do your own
3086interlace handling. In reality normally the only good reason for doing this
3087is if you are processing PNG files on a pixel-by-pixel basis and don't want
3088to load the whole file into memory when it is interlaced.
3089
3090libpng includes a test program, pngvalid, that illustrates reading and
3091writing of interlaced images. If you can't get interlacing to work in your
3092code and don't want to leave it to libpng (the recommended approach), see
3093how pngvalid.c does it.
3094
3095.SS Finishing a sequential read
3096
3097After you are finished reading the image through the
3098low-level interface, you can finish reading the file. If you are
3099interested in comments or time, which may be stored either before or
3100after the image data, you should pass the separate png_info struct if
3101you want to keep the comments from before and after the image
3102separate.
3103
3104 png_infop end_info = png_create_info_struct(png_ptr);
3105
3106 if (!end_info)
3107 {
3108 png_destroy_read_struct(&png_ptr, &info_ptr,
3109 (png_infopp)NULL);
3110 return (ERROR);
3111 }
3112
3113 png_read_end(png_ptr, end_info);
3114
3115If you are not interested, you should still call png_read_end()
3116but you can pass NULL, avoiding the need to create an end_info structure.
3117
3118 png_read_end(png_ptr, (png_infop)NULL);
3119
3120If you don't call png_read_end(), then your file pointer will be
3121left pointing to the first chunk after the last IDAT, which is probably
3122not what you want if you expect to read something beyond the end of
3123the PNG datastream.
3124
3125When you are done, you can free all memory allocated by libpng like this:
3126
3127 png_destroy_read_struct(&png_ptr, &info_ptr,
3128 &end_info);
3129
3130or, if you didn't create an end_info structure,
3131
3132 png_destroy_read_struct(&png_ptr, &info_ptr,
3133 (png_infopp)NULL);
3134
3135It is also possible to individually free the info_ptr members that
3136point to libpng-allocated storage with the following function:
3137
3138 png_free_data(png_ptr, info_ptr, mask, seq)
3139
3140 mask - identifies data to be freed, a mask
3141 containing the bitwise OR of one or
3142 more of
3143 PNG_FREE_PLTE, PNG_FREE_TRNS,
3144 PNG_FREE_HIST, PNG_FREE_ICCP,
3145 PNG_FREE_PCAL, PNG_FREE_ROWS,
3146 PNG_FREE_SCAL, PNG_FREE_SPLT,
3147 PNG_FREE_TEXT, PNG_FREE_UNKN,
3148 or simply PNG_FREE_ALL
3149
3150 seq - sequence number of item to be freed
3151 (-1 for all items)
3152
3153This function may be safely called when the relevant storage has
3154already been freed, or has not yet been allocated, or was allocated
3155by the user and not by libpng, and will in those cases do nothing.
3156The "seq" parameter is ignored if only one item of the selected data
3157type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3158are allowed for the data type identified in the mask, such as text or
3159sPLT, only the n'th item in the structure is freed, where n is "seq".
3160
3161The default behavior is only to free data that was allocated internally
3162by libpng. This can be changed, so that libpng will not free the data,
3163or so that it will free data that was allocated by the user with png_malloc()
3164or png_zalloc() and passed in via a png_set_*() function, with
3165
3166 png_data_freer(png_ptr, info_ptr, freer, mask)
3167
3168 freer - one of
3169 PNG_DESTROY_WILL_FREE_DATA
3170 PNG_SET_WILL_FREE_DATA
3171 PNG_USER_WILL_FREE_DATA
3172
3173 mask - which data elements are affected
3174 same choices as in png_free_data()
3175
3176This function only affects data that has already been allocated.
3177You can call this function after reading the PNG data but before calling
3178any png_set_*() functions, to control whether the user or the png_set_*()
3179function is responsible for freeing any existing data that might be present,
3180and again after the png_set_*() functions to control whether the user
3181or png_destroy_*() is supposed to free the data. When the user assumes
3182responsibility for libpng-allocated data, the application must use
3183png_free() to free it, and when the user transfers responsibility to libpng
3184for data that the user has allocated, the user must have used png_malloc()
3185or png_zalloc() to allocate it.
3186
3187If you allocated your row_pointers in a single block, as suggested above in
3188the description of the high level read interface, you must not transfer
3189responsibility for freeing it to the png_set_rows or png_read_destroy function,
3190because they would also try to free the individual row_pointers[i].
3191
3192If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3193separately, do not transfer responsibility for freeing text_ptr to libpng,
3194because when libpng fills a png_text structure it combines these members with
3195the key member, and png_free_data() will free only text_ptr.key. Similarly,
3196if you transfer responsibility for free'ing text_ptr from libpng to your
3197application, your application must not separately free those members.
3198
3199The png_free_data() function will turn off the "valid" flag for anything
3200it frees. If you need to turn the flag off for a chunk that was freed by
3201your application instead of by libpng, you can use
3202
3203 png_set_invalid(png_ptr, info_ptr, mask);
3204
3205 mask - identifies the chunks to be made invalid,
3206 containing the bitwise OR of one or
3207 more of
3208 PNG_INFO_gAMA, PNG_INFO_sBIT,
3209 PNG_INFO_cHRM, PNG_INFO_PLTE,
3210 PNG_INFO_tRNS, PNG_INFO_bKGD,
3211 PNG_INFO_hIST, PNG_INFO_pHYs,
3212 PNG_INFO_oFFs, PNG_INFO_tIME,
3213 PNG_INFO_pCAL, PNG_INFO_sRGB,
3214 PNG_INFO_iCCP, PNG_INFO_sPLT,
3215 PNG_INFO_sCAL, PNG_INFO_IDAT
3216
3217For a more compact example of reading a PNG image, see the file example.c.
3218
3219.SS Reading PNG files progressively
3220
3221The progressive reader is slightly different then the non-progressive
3222reader. Instead of calling png_read_info(), png_read_rows(), and
3223png_read_end(), you make one call to png_process_data(), which calls
3224callbacks when it has the info, a row, or the end of the image. You
3225set up these callbacks with png_set_progressive_read_fn(). You don't
3226have to worry about the input/output functions of libpng, as you are
3227giving the library the data directly in png_process_data(). I will
3228assume that you have read the section on reading PNG files above,
3229so I will only highlight the differences (although I will show
3230all of the code).
3231
3232png_structp png_ptr;
3233png_infop info_ptr;
3234
3235 /* An example code fragment of how you would
3236 initialize the progressive reader in your
3237 application. */
3238 int
3239 initialize_png_reader()
3240 {
3241 png_ptr = png_create_read_struct
3242 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3243 user_error_fn, user_warning_fn);
3244
3245 if (!png_ptr)
3246 return (ERROR);
3247
3248 info_ptr = png_create_info_struct(png_ptr);
3249
3250 if (!info_ptr)
3251 {
3252 png_destroy_read_struct(&png_ptr,
3253 (png_infopp)NULL, (png_infopp)NULL);
3254 return (ERROR);
3255 }
3256
3257 if (setjmp(png_jmpbuf(png_ptr)))
3258 {
3259 png_destroy_read_struct(&png_ptr, &info_ptr,
3260 (png_infopp)NULL);
3261 return (ERROR);
3262 }
3263
3264 /* This one's new. You can provide functions
3265 to be called when the header info is valid,
3266 when each row is completed, and when the image
3267 is finished. If you aren't using all functions,
3268 you can specify NULL parameters. Even when all
3269 three functions are NULL, you need to call
3270 png_set_progressive_read_fn(). You can use
3271 any struct as the user_ptr (cast to a void pointer
3272 for the function call), and retrieve the pointer
3273 from inside the callbacks using the function
3274
3275 png_get_progressive_ptr(png_ptr);
3276
3277 which will return a void pointer, which you have
3278 to cast appropriately.
3279 */
3280 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3281 info_callback, row_callback, end_callback);
3282
3283 return 0;
3284 }
3285
3286 /* A code fragment that you call as you receive blocks
3287 of data */
3288 int
3289 process_data(png_bytep buffer, png_uint_32 length)
3290 {
3291 if (setjmp(png_jmpbuf(png_ptr)))
3292 {
3293 png_destroy_read_struct(&png_ptr, &info_ptr,
3294 (png_infopp)NULL);
3295 return (ERROR);
3296 }
3297
3298 /* This one's new also. Simply give it a chunk
3299 of data from the file stream (in order, of
3300 course). On machines with segmented memory
3301 models machines, don't give it any more than
3302 64K. The library seems to run fine with sizes
3303 of 4K. Although you can give it much less if
3304 necessary (I assume you can give it chunks of
3305 1 byte, I haven't tried less then 256 bytes
3306 yet). When this function returns, you may
3307 want to display any rows that were generated
3308 in the row callback if you don't already do
3309 so there.
3310 */
3311 png_process_data(png_ptr, info_ptr, buffer, length);
3312
3313 /* At this point you can call png_process_data_skip if
3314 you want to handle data the library will skip yourself;
3315 it simply returns the number of bytes to skip (and stops
3316 libpng skipping that number of bytes on the next
3317 png_process_data call).
3318 return 0;
3319 }
3320
3321 /* This function is called (as set by
3322 png_set_progressive_read_fn() above) when enough data
3323 has been supplied so all of the header has been
3324 read.
3325 */
3326 void
3327 info_callback(png_structp png_ptr, png_infop info)
3328 {
3329 /* Do any setup here, including setting any of
3330 the transformations mentioned in the Reading
3331 PNG files section. For now, you _must_ call
3332 either png_start_read_image() or
3333 png_read_update_info() after all the
3334 transformations are set (even if you don't set
3335 any). You may start getting rows before
3336 png_process_data() returns, so this is your
3337 last chance to prepare for that.
3338
3339 This is where you turn on interlace handling,
3340 assuming you don't want to do it yourself.
3341
3342 If you need to you can stop the processing of
3343 your original input data at this point by calling
3344 png_process_data_pause. This returns the number
3345 of unprocessed bytes from the last png_process_data
3346 call - it is up to you to ensure that the next call
3347 sees these bytes again. If you don't want to bother
3348 with this you can get libpng to cache the unread
3349 bytes by setting the 'save' parameter (see png.h) but
3350 then libpng will have to copy the data internally.
3351 */
3352 }
3353
3354 /* This function is called when each row of image
3355 data is complete */
3356 void
3357 row_callback(png_structp png_ptr, png_bytep new_row,
3358 png_uint_32 row_num, int pass)
3359 {
3360 /* If the image is interlaced, and you turned
3361 on the interlace handler, this function will
3362 be called for every row in every pass. Some
3363 of these rows will not be changed from the
3364 previous pass. When the row is not changed,
3365 the new_row variable will be NULL. The rows
3366 and passes are called in order, so you don't
3367 really need the row_num and pass, but I'm
3368 supplying them because it may make your life
3369 easier.
3370
3371 If you did not turn on interlace handling then
3372 the callback is called for each row of each
3373 sub-image when the image is interlaced. In this
3374 case 'row_num' is the row in the sub-image, not
3375 the row in the output image as it is in all other
3376 cases.
3377
3378 For the non-NULL rows of interlaced images when
3379 you have switched on libpng interlace handling,
3380 you must call png_progressive_combine_row()
3381 passing in the row and the old row. You can
3382 call this function for NULL rows (it will just
3383 return) and for non-interlaced images (it just
3384 does the memcpy for you) if it will make the
3385 code easier. Thus, you can just do this for
3386 all cases if you switch on interlace handling;
3387 */
3388
3389 png_progressive_combine_row(png_ptr, old_row,
3390 new_row);
3391
3392 /* where old_row is what was displayed for
3393 previously for the row. Note that the first
3394 pass (pass == 0, really) will completely cover
3395 the old row, so the rows do not have to be
3396 initialized. After the first pass (and only
3397 for interlaced images), you will have to pass
3398 the current row, and the function will combine
3399 the old row and the new row.
3400
3401 You can also call png_process_data_pause in this
3402 callback - see above.
3403 */
3404 }
3405
3406 void
3407 end_callback(png_structp png_ptr, png_infop info)
3408 {
3409 /* This function is called after the whole image
3410 has been read, including any chunks after the
3411 image (up to and including the IEND). You
3412 will usually have the same info chunk as you
3413 had in the header, although some data may have
3414 been added to the comments and time fields.
3415
3416 Most people won't do much here, perhaps setting
3417 a flag that marks the image as finished.
3418 */
3419 }
3420
3421
3422
3423.SH IV. Writing
3424
3425Much of this is very similar to reading. However, everything of
3426importance is repeated here, so you won't have to constantly look
3427back up in the reading section to understand writing.
3428
3429.SS Setup
3430
3431You will want to do the I/O initialization before you get into libpng,
3432so if it doesn't work, you don't have anything to undo. If you are not
3433using the standard I/O functions, you will need to replace them with
3434custom writing functions. See the discussion under Customizing libpng.
3435
3436 FILE *fp = fopen(file_name, "wb");
3437
3438 if (!fp)
3439 return (ERROR);
3440
3441Next, png_struct and png_info need to be allocated and initialized.
3442As these can be both relatively large, you may not want to store these
3443on the stack, unless you have stack space to spare. Of course, you
3444will want to check if they return NULL. If you are also reading,
3445you won't want to name your read structure and your write structure
3446both "png_ptr"; you can call them anything you like, such as
3447"read_ptr" and "write_ptr". Look at pngtest.c, for example.
3448
3449 png_structp png_ptr = png_create_write_struct
3450 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3451 user_error_fn, user_warning_fn);
3452
3453 if (!png_ptr)
3454 return (ERROR);
3455
3456 png_infop info_ptr = png_create_info_struct(png_ptr);
3457 if (!info_ptr)
3458 {
3459 png_destroy_write_struct(&png_ptr,
3460 (png_infopp)NULL);
3461 return (ERROR);
3462 }
3463
3464If you want to use your own memory allocation routines,
3465define PNG_USER_MEM_SUPPORTED and use
3466png_create_write_struct_2() instead of png_create_write_struct():
3467
3468 png_structp png_ptr = png_create_write_struct_2
3469 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3470 user_error_fn, user_warning_fn, (png_voidp)
3471 user_mem_ptr, user_malloc_fn, user_free_fn);
3472
3473After you have these structures, you will need to set up the
3474error handling. When libpng encounters an error, it expects to
3475longjmp() back to your routine. Therefore, you will need to call
3476setjmp() and pass the png_jmpbuf(png_ptr). If you
3477write the file from different routines, you will need to update
3478the png_jmpbuf(png_ptr) every time you enter a new routine that will
3479call a png_*() function. See your documentation of setjmp/longjmp
3480for your compiler for more information on setjmp/longjmp. See
3481the discussion on libpng error handling in the Customizing Libpng
3482section below for more information on the libpng error handling.
3483
3484 if (setjmp(png_jmpbuf(png_ptr)))
3485 {
3486 png_destroy_write_struct(&png_ptr, &info_ptr);
3487 fclose(fp);
3488 return (ERROR);
3489 }
3490 ...
3491 return;
3492
3493If you would rather avoid the complexity of setjmp/longjmp issues,
3494you can compile libpng with PNG_NO_SETJMP, in which case
3495errors will result in a call to PNG_ABORT() which defaults to abort().
3496
3497You can #define PNG_ABORT() to a function that does something
3498more useful than abort(), as long as your function does not
3499return.
3500
3501Now you need to set up the output code. The default for libpng is to
3502use the C function fwrite(). If you use this, you will need to pass a
3503valid FILE * in the function png_init_io(). Be sure that the file is
3504opened in binary mode. Again, if you wish to handle writing data in
3505another way, see the discussion on libpng I/O handling in the Customizing
3506Libpng section below.
3507
3508 png_init_io(png_ptr, fp);
3509
3510If you are embedding your PNG into a datastream such as MNG, and don't
3511want libpng to write the 8-byte signature, or if you have already
3512written the signature in your application, use
3513
3514 png_set_sig_bytes(png_ptr, 8);
3515
3516to inform libpng that it should not write a signature.
3517
3518.SS Write callbacks
3519
3520At this point, you can set up a callback function that will be
3521called after each row has been written, which you can use to control
3522a progress meter or the like. It's demonstrated in pngtest.c.
3523You must supply a function
3524
3525 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3526 int pass);
3527 {
3528 /* put your code here */
3529 }
3530
3531(You can give it another name that you like instead of "write_row_callback")
3532
3533To inform libpng about your function, use
3534
3535 png_set_write_status_fn(png_ptr, write_row_callback);
3536
3537When this function is called the row has already been completely processed and
3538it has also been written out. The 'row' and 'pass' refer to the next row to be
3539handled. For the
3540non-interlaced case the row that was just handled is simply one less than the
3541passed in row number, and pass will always be 0. For the interlaced case the
3542same applies unless the row value is 0, in which case the row just handled was
3543the last one from one of the preceding passes. Because interlacing may skip a
3544pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3545need to know what the last pass is record (row,pass) from the callback and use
3546the last recorded value each time.
3547
3548As with the user transform you can find the output row using the
3549PNG_ROW_FROM_PASS_ROW macro.
3550
3551You now have the option of modifying how the compression library will
3552run. The following functions are mainly for testing, but may be useful
3553in some cases, like if you need to write PNG files extremely fast and
3554are willing to give up some compression, or if you want to get the
3555maximum possible compression at the expense of slower writing. If you
3556have no special needs in this area, let the library do what it wants by
3557not calling this function at all, as it has been tuned to deliver a good
3558speed/compression ratio. The second parameter to png_set_filter() is
3559the filter method, for which the only valid values are 0 (as of the
3560July 1999 PNG specification, version 1.2) or 64 (if you are writing
3561a PNG datastream that is to be embedded in a MNG datastream). The third
3562parameter is a flag that indicates which filter type(s) are to be tested
3563for each scanline. See the PNG specification for details on the specific
3564filter types.
3565
3566
3567 /* turn on or off filtering, and/or choose
3568 specific filters. You can use either a single
3569 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3570 or more PNG_FILTER_NAME masks.
3571 */
3572 png_set_filter(png_ptr, 0,
3573 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3574 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3575 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3576 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3577 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3578 PNG_ALL_FILTERS);
3579
3580If an application wants to start and stop using particular filters during
3581compression, it should start out with all of the filters (to ensure that
3582the previous row of pixels will be stored in case it's needed later),
3583and then add and remove them after the start of compression.
3584
3585If you are writing a PNG datastream that is to be embedded in a MNG
3586datastream, the second parameter can be either 0 or 64.
3587
3588The png_set_compression_*() functions interface to the zlib compression
3589library, and should mostly be ignored unless you really know what you are
3590doing. The only generally useful call is png_set_compression_level()
3591which changes how much time zlib spends on trying to compress the image
3592data. See the Compression Library (zlib.h and algorithm.txt, distributed
3593with zlib) for details on the compression levels.
3594
3595 #include zlib.h
3596
3597 /* Set the zlib compression level */
3598 png_set_compression_level(png_ptr,
3599 Z_BEST_COMPRESSION);
3600
3601 /* Set other zlib parameters for compressing IDAT */
3602 png_set_compression_mem_level(png_ptr, 8);
3603 png_set_compression_strategy(png_ptr,
3604 Z_DEFAULT_STRATEGY);
3605 png_set_compression_window_bits(png_ptr, 15);
3606 png_set_compression_method(png_ptr, 8);
3607 png_set_compression_buffer_size(png_ptr, 8192)
3608
3609 /* Set zlib parameters for text compression
3610 * If you don't call these, the parameters
3611 * fall back on those defined for IDAT chunks
3612 */
3613 png_set_text_compression_mem_level(png_ptr, 8);
3614 png_set_text_compression_strategy(png_ptr,
3615 Z_DEFAULT_STRATEGY);
3616 png_set_text_compression_window_bits(png_ptr, 15);
3617 png_set_text_compression_method(png_ptr, 8);
3618
3619.SS Setting the contents of info for output
3620
3621You now need to fill in the png_info structure with all the data you
3622wish to write before the actual image. Note that the only thing you
3623are allowed to write after the image is the text chunks and the time
3624chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3625the latest PNG specification for more information on that. If you
3626wish to write them before the image, fill them in now, and flag that
3627data as being valid. If you want to wait until after the data, don't
3628fill them until png_write_end(). For all the fields in png_info and
3629their data types, see png.h. For explanations of what the fields
3630contain, see the PNG specification.
3631
3632Some of the more important parts of the png_info are:
3633
3634 png_set_IHDR(png_ptr, info_ptr, width, height,
3635 bit_depth, color_type, interlace_type,
3636 compression_type, filter_method)
3637
3638 width - holds the width of the image
3639 in pixels (up to 2^31).
3640
3641 height - holds the height of the image
3642 in pixels (up to 2^31).
3643
3644 bit_depth - holds the bit depth of one of the
3645 image channels.
3646 (valid values are 1, 2, 4, 8, 16
3647 and depend also on the
3648 color_type. See also significant
3649 bits (sBIT) below).
3650
3651 color_type - describes which color/alpha
3652 channels are present.
3653 PNG_COLOR_TYPE_GRAY
3654 (bit depths 1, 2, 4, 8, 16)
3655 PNG_COLOR_TYPE_GRAY_ALPHA
3656 (bit depths 8, 16)
3657 PNG_COLOR_TYPE_PALETTE
3658 (bit depths 1, 2, 4, 8)
3659 PNG_COLOR_TYPE_RGB
3660 (bit_depths 8, 16)
3661 PNG_COLOR_TYPE_RGB_ALPHA
3662 (bit_depths 8, 16)
3663
3664 PNG_COLOR_MASK_PALETTE
3665 PNG_COLOR_MASK_COLOR
3666 PNG_COLOR_MASK_ALPHA
3667
3668 interlace_type - PNG_INTERLACE_NONE or
3669 PNG_INTERLACE_ADAM7
3670
3671 compression_type - (must be
3672 PNG_COMPRESSION_TYPE_DEFAULT)
3673
3674 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3675 or, if you are writing a PNG to
3676 be embedded in a MNG datastream,
3677 can also be
3678 PNG_INTRAPIXEL_DIFFERENCING)
3679
3680If you call png_set_IHDR(), the call must appear before any of the
3681other png_set_*() functions, because they might require access to some of
3682the IHDR settings. The remaining png_set_*() functions can be called
3683in any order.
3684
3685If you wish, you can reset the compression_type, interlace_type, or
3686filter_method later by calling png_set_IHDR() again; if you do this, the
3687width, height, bit_depth, and color_type must be the same in each call.
3688
3689 png_set_PLTE(png_ptr, info_ptr, palette,
3690 num_palette);
3691
3692 palette - the palette for the file
3693 (array of png_color)
3694 num_palette - number of entries in the palette
3695
3696 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3697 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3698
3699 file_gamma - the gamma at which the image was
3700 created (PNG_INFO_gAMA)
3701
3702 int_file_gamma - 100,000 times the gamma at which
3703 the image was created
3704
3705 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3706 green_x, green_y, blue_x, blue_y)
3707 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3708 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3709 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3710 int_red_x, int_red_y, int_green_x, int_green_y,
3711 int_blue_x, int_blue_y)
3712 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3713 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3714 int_blue_X, int_blue_Y, int_blue_Z)
3715
3716 {white,red,green,blue}_{x,y}
3717 A color space encoding specified using the chromaticities
3718 of the end points and the white point.
3719
3720 {red,green,blue}_{X,Y,Z}
3721 A color space encoding specified using the encoding end
3722 points - the CIE tristimulus specification of the intended
3723 color of the red, green and blue channels in the PNG RGB
3724 data. The white point is simply the sum of the three end
3725 points.
3726
3727 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3728
3729 srgb_intent - the rendering intent
3730 (PNG_INFO_sRGB) The presence of
3731 the sRGB chunk means that the pixel
3732 data is in the sRGB color space.
3733 This chunk also implies specific
3734 values of gAMA and cHRM. Rendering
3735 intent is the CSS-1 property that
3736 has been defined by the International
3737 Color Consortium
3738 (http://www.color.org).
3739 It can be one of
3740 PNG_sRGB_INTENT_SATURATION,
3741 PNG_sRGB_INTENT_PERCEPTUAL,
3742 PNG_sRGB_INTENT_ABSOLUTE, or
3743 PNG_sRGB_INTENT_RELATIVE.
3744
3745
3746 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3747 srgb_intent);
3748
3749 srgb_intent - the rendering intent
3750 (PNG_INFO_sRGB) The presence of the
3751 sRGB chunk means that the pixel
3752 data is in the sRGB color space.
3753 This function also causes gAMA and
3754 cHRM chunks with the specific values
3755 that are consistent with sRGB to be
3756 written.
3757
3758 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3759 profile, proflen);
3760
3761 name - The profile name.
3762
3763 compression_type - The compression type; always
3764 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3765 You may give NULL to this argument to
3766 ignore it.
3767
3768 profile - International Color Consortium color
3769 profile data. May contain NULs.
3770
3771 proflen - length of profile data in bytes.
3772
3773 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3774
3775 sig_bit - the number of significant bits for
3776 (PNG_INFO_sBIT) each of the gray, red,
3777 green, and blue channels, whichever are
3778 appropriate for the given color type
3779 (png_color_16)
3780
3781 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3782 num_trans, trans_color);
3783
3784 trans_alpha - array of alpha (transparency)
3785 entries for palette (PNG_INFO_tRNS)
3786
3787 num_trans - number of transparent entries
3788 (PNG_INFO_tRNS)
3789
3790 trans_color - graylevel or color sample values
3791 (in order red, green, blue) of the
3792 single transparent color for
3793 non-paletted images (PNG_INFO_tRNS)
3794
3795 png_set_hIST(png_ptr, info_ptr, hist);
3796
3797 hist - histogram of palette (array of
3798 png_uint_16) (PNG_INFO_hIST)
3799
3800 png_set_tIME(png_ptr, info_ptr, mod_time);
3801
3802 mod_time - time image was last modified
3803 (PNG_VALID_tIME)
3804
3805 png_set_bKGD(png_ptr, info_ptr, background);
3806
3807 background - background color (of type
3808 png_color_16p) (PNG_VALID_bKGD)
3809
3810 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3811
3812 text_ptr - array of png_text holding image
3813 comments
3814
3815 text_ptr[i].compression - type of compression used
3816 on "text" PNG_TEXT_COMPRESSION_NONE
3817 PNG_TEXT_COMPRESSION_zTXt
3818 PNG_ITXT_COMPRESSION_NONE
3819 PNG_ITXT_COMPRESSION_zTXt
3820 text_ptr[i].key - keyword for comment. Must contain
3821 1-79 characters.
3822 text_ptr[i].text - text comments for current
3823 keyword. Can be NULL or empty.
3824 text_ptr[i].text_length - length of text string,
3825 after decompression, 0 for iTXt
3826 text_ptr[i].itxt_length - length of itxt string,
3827 after decompression, 0 for tEXt/zTXt
3828 text_ptr[i].lang - language of comment (NULL or
3829 empty for unknown).
3830 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3831 or empty for unknown).
3832
3833 Note that the itxt_length, lang, and lang_key
3834 members of the text_ptr structure only exist when the
3835 library is built with iTXt chunk support. Prior to
3836 libpng-1.4.0 the library was built by default without
3837 iTXt support. Also note that when iTXt is supported,
3838 they contain NULL pointers when the "compression"
3839 field contains PNG_TEXT_COMPRESSION_NONE or
3840 PNG_TEXT_COMPRESSION_zTXt.
3841
3842 num_text - number of comments
3843
3844 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3845 num_spalettes);
3846
3847 palette_ptr - array of png_sPLT_struct structures
3848 to be added to the list of palettes
3849 in the info structure.
3850 num_spalettes - number of palette structures to be
3851 added.
3852
3853 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3854 unit_type);
3855
3856 offset_x - positive offset from the left
3857 edge of the screen
3858
3859 offset_y - positive offset from the top
3860 edge of the screen
3861
3862 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3863
3864 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3865 unit_type);
3866
3867 res_x - pixels/unit physical resolution
3868 in x direction
3869
3870 res_y - pixels/unit physical resolution
3871 in y direction
3872
3873 unit_type - PNG_RESOLUTION_UNKNOWN,
3874 PNG_RESOLUTION_METER
3875
3876 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3877
3878 unit - physical scale units (an integer)
3879
3880 width - width of a pixel in physical scale units
3881
3882 height - height of a pixel in physical scale units
3883 (width and height are doubles)
3884
3885 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3886
3887 unit - physical scale units (an integer)
3888
3889 width - width of a pixel in physical scale units
3890 expressed as a string
3891
3892 height - height of a pixel in physical scale units
3893 (width and height are strings like "2.54")
3894
3895 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3896 num_unknowns)
3897
3898 unknowns - array of png_unknown_chunk
3899 structures holding unknown chunks
3900 unknowns[i].name - name of unknown chunk
3901 unknowns[i].data - data of unknown chunk
3902 unknowns[i].size - size of unknown chunk's data
3903 unknowns[i].location - position to write chunk in file
3904 0: do not write chunk
3905 PNG_HAVE_IHDR: before PLTE
3906 PNG_HAVE_PLTE: before IDAT
3907 PNG_AFTER_IDAT: after IDAT
3908
3909The "location" member is set automatically according to
3910what part of the output file has already been written.
3911You can change its value after calling png_set_unknown_chunks()
3912as demonstrated in pngtest.c. Within each of the "locations",
3913the chunks are sequenced according to their position in the
3914structure (that is, the value of "i", which is the order in which
3915the chunk was either read from the input file or defined with
3916png_set_unknown_chunks).
3917
3918A quick word about text and num_text. text is an array of png_text
3919structures. num_text is the number of valid structures in the array.
3920Each png_text structure holds a language code, a keyword, a text value,
3921and a compression type.
3922
3923The compression types have the same valid numbers as the compression
3924types of the image data. Currently, the only valid number is zero.
3925However, you can store text either compressed or uncompressed, unlike
3926images, which always have to be compressed. So if you don't want the
3927text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3928Because tEXt and zTXt chunks don't have a language field, if you
3929specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3930any language code or translated keyword will not be written out.
3931
3932Until text gets around a few hundred bytes, it is not worth compressing it.
3933After the text has been written out to the file, the compression type
3934is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3935so that it isn't written out again at the end (in case you are calling
3936png_write_end() with the same struct).
3937
3938The keywords that are given in the PNG Specification are:
3939
3940 Title Short (one line) title or
3941 caption for image
3942
3943 Author Name of image's creator
3944
3945 Description Description of image (possibly long)
3946
3947 Copyright Copyright notice
3948
3949 Creation Time Time of original image creation
3950 (usually RFC 1123 format, see below)
3951
3952 Software Software used to create the image
3953
3954 Disclaimer Legal disclaimer
3955
3956 Warning Warning of nature of content
3957
3958 Source Device used to create the image
3959
3960 Comment Miscellaneous comment; conversion
3961 from other image format
3962
3963The keyword-text pairs work like this. Keywords should be short
3964simple descriptions of what the comment is about. Some typical
3965keywords are found in the PNG specification, as is some recommendations
3966on keywords. You can repeat keywords in a file. You can even write
3967some text before the image and some after. For example, you may want
3968to put a description of the image before the image, but leave the
3969disclaimer until after, so viewers working over modem connections
3970don't have to wait for the disclaimer to go over the modem before
3971they start seeing the image. Finally, keywords should be full
3972words, not abbreviations. Keywords and text are in the ISO 8859-1
3973(Latin-1) character set (a superset of regular ASCII) and can not
3974contain NUL characters, and should not contain control or other
3975unprintable characters. To make the comments widely readable, stick
3976with basic ASCII, and avoid machine specific character set extensions
3977like the IBM-PC character set. The keyword must be present, but
3978you can leave off the text string on non-compressed pairs.
3979Compressed pairs must have a text string, as only the text string
3980is compressed anyway, so the compression would be meaningless.
3981
3982PNG supports modification time via the png_time structure. Two
3983conversion routines are provided, png_convert_from_time_t() for
3984time_t and png_convert_from_struct_tm() for struct tm. The
3985time_t routine uses gmtime(). You don't have to use either of
3986these, but if you wish to fill in the png_time structure directly,
3987you should provide the time in universal time (GMT) if possible
3988instead of your local time. Note that the year number is the full
3989year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3990that months start with 1.
3991
3992If you want to store the time of the original image creation, you should
3993use a plain tEXt chunk with the "Creation Time" keyword. This is
3994necessary because the "creation time" of a PNG image is somewhat vague,
3995depending on whether you mean the PNG file, the time the image was
3996created in a non-PNG format, a still photo from which the image was
3997scanned, or possibly the subject matter itself. In order to facilitate
3998machine-readable dates, it is recommended that the "Creation Time"
3999tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
4000although this isn't a requirement. Unlike the tIME chunk, the
4001"Creation Time" tEXt chunk is not expected to be automatically changed
4002by the software. To facilitate the use of RFC 1123 dates, a function
4003png_convert_to_rfc1123(png_timep) is provided to convert from PNG
4004time to an RFC 1123 format string.
4005
4006.SS Writing unknown chunks
4007
4008You can use the png_set_unknown_chunks function to queue up chunks
4009for writing. You give it a chunk name, raw data, and a size; that's
4010all there is to it. The chunks will be written by the next following
4011png_write_info_before_PLTE, png_write_info, or png_write_end function.
4012Any chunks previously read into the info structure's unknown-chunk
4013list will also be written out in a sequence that satisfies the PNG
4014specification's ordering rules.
4015
4016.SS The high-level write interface
4017
4018At this point there are two ways to proceed; through the high-level
4019write interface, or through a sequence of low-level write operations.
4020You can use the high-level interface if your image data is present
4021in the info structure. All defined output
4022transformations are permitted, enabled by the following masks.
4023
4024 PNG_TRANSFORM_IDENTITY No transformation
4025 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
4026 PNG_TRANSFORM_PACKSWAP Change order of packed
4027 pixels to LSB first
4028 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
4029 PNG_TRANSFORM_SHIFT Normalize pixels to the
4030 sBIT depth
4031 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
4032 to BGRA
4033 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
4034 to AG
4035 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
4036 to transparency
4037 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
4038 PNG_TRANSFORM_STRIP_FILLER Strip out filler
4039 bytes (deprecated).
4040 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
4041 filler bytes
4042 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
4043 filler bytes
4044
4045If you have valid image data in the info structure (you can use
4046png_set_rows() to put image data in the info structure), simply do this:
4047
4048 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
4049
4050where png_transforms is an integer containing the bitwise OR of some set of
4051transformation flags. This call is equivalent to png_write_info(),
4052followed the set of transformations indicated by the transform mask,
4053then png_write_image(), and finally png_write_end().
4054
4055(The final parameter of this call is not yet used. Someday it might point
4056to transformation parameters required by some future output transform.)
4057
4058You must use png_transforms and not call any png_set_transform() functions
4059when you use png_write_png().
4060
4061.SS The low-level write interface
4062
4063If you are going the low-level route instead, you are now ready to
4064write all the file information up to the actual image data. You do
4065this with a call to png_write_info().
4066
4067 png_write_info(png_ptr, info_ptr);
4068
4069Note that there is one transformation you may need to do before
4070png_write_info(). In PNG files, the alpha channel in an image is the
4071level of opacity. If your data is supplied as a level of transparency,
4072you can invert the alpha channel before you write it, so that 0 is
4073fully transparent and 255 (in 8-bit or paletted images) or 65535
4074(in 16-bit images) is fully opaque, with
4075
4076 png_set_invert_alpha(png_ptr);
4077
4078This must appear before png_write_info() instead of later with the
4079other transformations because in the case of paletted images the tRNS
4080chunk data has to be inverted before the tRNS chunk is written. If
4081your image is not a paletted image, the tRNS data (which in such cases
4082represents a single color to be rendered as transparent) won't need to
4083be changed, and you can safely do this transformation after your
4084png_write_info() call.
4085
4086If you need to write a private chunk that you want to appear before
4087the PLTE chunk when PLTE is present, you can write the PNG info in
4088two steps, and insert code to write your own chunk between them:
4089
4090 png_write_info_before_PLTE(png_ptr, info_ptr);
4091 png_set_unknown_chunks(png_ptr, info_ptr, ...);
4092 png_write_info(png_ptr, info_ptr);
4093
4094After you've written the file information, you can set up the library
4095to handle any special transformations of the image data. The various
4096ways to transform the data will be described in the order that they
4097should occur. This is important, as some of these change the color
4098type and/or bit depth of the data, and some others only work on
4099certain color types and bit depths. Even though each transformation
4100checks to see if it has data that it can do something with, you should
4101make sure to only enable a transformation if it will be valid for the
4102data. For example, don't swap red and blue on grayscale data.
4103
4104PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
4105the library to strip input data that has 4 or 8 bytes per pixel down
4106to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
4107bytes per pixel).
4108
4109 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
4110
4111where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
4112PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
4113is stored XRGB or RGBX.
4114
4115PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
4116they can, resulting in, for example, 8 pixels per byte for 1 bit files.
4117If the data is supplied at 1 pixel per byte, use this code, which will
4118correctly pack the pixels into a single byte:
4119
4120 png_set_packing(png_ptr);
4121
4122PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
4123data is of another bit depth, you can write an sBIT chunk into the
4124file so that decoders can recover the original data if desired.
4125
4126 /* Set the true bit depth of the image data */
4127 if (color_type & PNG_COLOR_MASK_COLOR)
4128 {
4129 sig_bit.red = true_bit_depth;
4130 sig_bit.green = true_bit_depth;
4131 sig_bit.blue = true_bit_depth;
4132 }
4133
4134 else
4135 {
4136 sig_bit.gray = true_bit_depth;
4137 }
4138
4139 if (color_type & PNG_COLOR_MASK_ALPHA)
4140 {
4141 sig_bit.alpha = true_bit_depth;
4142 }
4143
4144 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
4145
4146If the data is stored in the row buffer in a bit depth other than
4147one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
4148this will scale the values to appear to be the correct bit depth as
4149is required by PNG.
4150
4151 png_set_shift(png_ptr, &sig_bit);
4152
4153PNG files store 16-bit pixels in network byte order (big-endian,
4154ie. most significant bits first). This code would be used if they are
4155supplied the other way (little-endian, i.e. least significant bits
4156first, the way PCs store them):
4157
4158 if (bit_depth > 8)
4159 png_set_swap(png_ptr);
4160
4161If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
4162need to change the order the pixels are packed into bytes, you can use:
4163
4164 if (bit_depth < 8)
4165 png_set_packswap(png_ptr);
4166
4167PNG files store 3 color pixels in red, green, blue order. This code
4168would be used if they are supplied as blue, green, red:
4169
4170 png_set_bgr(png_ptr);
4171
4172PNG files describe monochrome as black being zero and white being
4173one. This code would be used if the pixels are supplied with this reversed
4174(black being one and white being zero):
4175
4176 png_set_invert_mono(png_ptr);
4177
4178Finally, you can write your own transformation function if none of
4179the existing ones meets your needs. This is done by setting a callback
4180with
4181
4182 png_set_write_user_transform_fn(png_ptr,
4183 write_transform_fn);
4184
4185You must supply the function
4186
4187 void write_transform_fn(png_structp png_ptr, png_row_infop
4188 row_info, png_bytep data)
4189
4190See pngtest.c for a working example. Your function will be called
4191before any of the other transformations are processed. If supported
4192libpng also supplies an information routine that may be called from
4193your callback:
4194
4195 png_get_current_row_number(png_ptr);
4196 png_get_current_pass_number(png_ptr);
4197
4198This returns the current row passed to the transform. With interlaced
4199images the value returned is the row in the input sub-image image. Use
4200PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
4201find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4202
4203The discussion of interlace handling above contains more information on how to
4204use these values.
4205
4206You can also set up a pointer to a user structure for use by your
4207callback function.
4208
4209 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4210
4211The user_channels and user_depth parameters of this function are ignored
4212when writing; you can set them to zero as shown.
4213
4214You can retrieve the pointer via the function png_get_user_transform_ptr().
4215For example:
4216
4217 voidp write_user_transform_ptr =
4218 png_get_user_transform_ptr(png_ptr);
4219
4220It is possible to have libpng flush any pending output, either manually,
4221or automatically after a certain number of lines have been written. To
4222flush the output stream a single time call:
4223
4224 png_write_flush(png_ptr);
4225
4226and to have libpng flush the output stream periodically after a certain
4227number of scanlines have been written, call:
4228
4229 png_set_flush(png_ptr, nrows);
4230
4231Note that the distance between rows is from the last time png_write_flush()
4232was called, or the first row of the image if it has never been called.
4233So if you write 50 lines, and then png_set_flush 25, it will flush the
4234output on the next scanline, and every 25 lines thereafter, unless
4235png_write_flush() is called before 25 more lines have been written.
4236If nrows is too small (less than about 10 lines for a 640 pixel wide
4237RGB image) the image compression may decrease noticeably (although this
4238may be acceptable for real-time applications). Infrequent flushing will
4239only degrade the compression performance by a few percent over images
4240that do not use flushing.
4241
4242.SS Writing the image data
4243
4244That's it for the transformations. Now you can write the image data.
4245The simplest way to do this is in one function call. If you have the
4246whole image in memory, you can just call png_write_image() and libpng
4247will write the image. You will need to pass in an array of pointers to
4248each row. This function automatically handles interlacing, so you don't
4249need to call png_set_interlace_handling() or call this function multiple
4250times, or any of that other stuff necessary with png_write_rows().
4251
4252 png_write_image(png_ptr, row_pointers);
4253
4254where row_pointers is:
4255
4256 png_byte *row_pointers[height];
4257
4258You can point to void or char or whatever you use for pixels.
4259
4260If you don't want to write the whole image at once, you can
4261use png_write_rows() instead. If the file is not interlaced,
4262this is simple:
4263
4264 png_write_rows(png_ptr, row_pointers,
4265 number_of_rows);
4266
4267row_pointers is the same as in the png_write_image() call.
4268
4269If you are just writing one row at a time, you can do this with
4270a single row_pointer instead of an array of row_pointers:
4271
4272 png_bytep row_pointer = row;
4273
4274 png_write_row(png_ptr, row_pointer);
4275
4276When the file is interlaced, things can get a good deal more complicated.
4277The only currently (as of the PNG Specification version 1.2, dated July
42781999) defined interlacing scheme for PNG files is the "Adam7" interlace
4279scheme, that breaks down an image into seven smaller images of varying
4280size. libpng will build these images for you, or you can do them
4281yourself. If you want to build them yourself, see the PNG specification
4282for details of which pixels to write when.
4283
4284If you don't want libpng to handle the interlacing details, just
4285use png_set_interlace_handling() and call png_write_rows() the
4286correct number of times to write all the sub-images
4287(png_set_interlace_handling() returns the number of sub-images.)
4288
4289If you want libpng to build the sub-images, call this before you start
4290writing any rows:
4291
4292 number_of_passes = png_set_interlace_handling(png_ptr);
4293
4294This will return the number of passes needed. Currently, this is seven,
4295but may change if another interlace type is added.
4296
4297Then write the complete image number_of_passes times.
4298
4299 png_write_rows(png_ptr, row_pointers, number_of_rows);
4300
4301Think carefully before you write an interlaced image. Typically code that
4302reads such images reads all the image data into memory, uncompressed, before
4303doing any processing. Only code that can display an image on the fly can
4304take advantage of the interlacing and even then the image has to be exactly
4305the correct size for the output device, because scaling an image requires
4306adjacent pixels and these are not available until all the passes have been
4307read.
4308
4309If you do write an interlaced image you will hardly ever need to handle
4310the interlacing yourself. Call png_set_interlace_handling() and use the
4311approach described above.
4312
4313The only time it is conceivable that you will really need to write an
4314interlaced image pass-by-pass is when you have read one pass by pass and
4315made some pixel-by-pixel transformation to it, as described in the read
4316code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4317to determine the size of each sub-image in turn and simply write the rows
4318you obtained from the read code.
4319
4320.SS Finishing a sequential write
4321
4322After you are finished writing the image, you should finish writing
4323the file. If you are interested in writing comments or time, you should
4324pass an appropriately filled png_info pointer. If you are not interested,
4325you can pass NULL.
4326
4327 png_write_end(png_ptr, info_ptr);
4328
4329When you are done, you can free all memory used by libpng like this:
4330
4331 png_destroy_write_struct(&png_ptr, &info_ptr);
4332
4333It is also possible to individually free the info_ptr members that
4334point to libpng-allocated storage with the following function:
4335
4336 png_free_data(png_ptr, info_ptr, mask, seq)
4337
4338 mask - identifies data to be freed, a mask
4339 containing the bitwise OR of one or
4340 more of
4341 PNG_FREE_PLTE, PNG_FREE_TRNS,
4342 PNG_FREE_HIST, PNG_FREE_ICCP,
4343 PNG_FREE_PCAL, PNG_FREE_ROWS,
4344 PNG_FREE_SCAL, PNG_FREE_SPLT,
4345 PNG_FREE_TEXT, PNG_FREE_UNKN,
4346 or simply PNG_FREE_ALL
4347
4348 seq - sequence number of item to be freed
4349 (-1 for all items)
4350
4351This function may be safely called when the relevant storage has
4352already been freed, or has not yet been allocated, or was allocated
4353by the user and not by libpng, and will in those cases do nothing.
4354The "seq" parameter is ignored if only one item of the selected data
4355type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
4356are allowed for the data type identified in the mask, such as text or
4357sPLT, only the n'th item in the structure is freed, where n is "seq".
4358
4359If you allocated data such as a palette that you passed in to libpng
4360with png_set_*, you must not free it until just before the call to
4361png_destroy_write_struct().
4362
4363The default behavior is only to free data that was allocated internally
4364by libpng. This can be changed, so that libpng will not free the data,
4365or so that it will free data that was allocated by the user with png_malloc()
4366or png_zalloc() and passed in via a png_set_*() function, with
4367
4368 png_data_freer(png_ptr, info_ptr, freer, mask)
4369
4370 freer - one of
4371 PNG_DESTROY_WILL_FREE_DATA
4372 PNG_SET_WILL_FREE_DATA
4373 PNG_USER_WILL_FREE_DATA
4374
4375 mask - which data elements are affected
4376 same choices as in png_free_data()
4377
4378For example, to transfer responsibility for some data from a read structure
4379to a write structure, you could use
4380
4381 png_data_freer(read_ptr, read_info_ptr,
4382 PNG_USER_WILL_FREE_DATA,
4383 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4384
4385 png_data_freer(write_ptr, write_info_ptr,
4386 PNG_DESTROY_WILL_FREE_DATA,
4387 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4388
4389thereby briefly reassigning responsibility for freeing to the user but
4390immediately afterwards reassigning it once more to the write_destroy
4391function. Having done this, it would then be safe to destroy the read
4392structure and continue to use the PLTE, tRNS, and hIST data in the write
4393structure.
4394
4395This function only affects data that has already been allocated.
4396You can call this function before calling after the png_set_*() functions
4397to control whether the user or png_destroy_*() is supposed to free the data.
4398When the user assumes responsibility for libpng-allocated data, the
4399application must use
4400png_free() to free it, and when the user transfers responsibility to libpng
4401for data that the user has allocated, the user must have used png_malloc()
4402or png_zalloc() to allocate it.
4403
4404If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4405separately, do not transfer responsibility for freeing text_ptr to libpng,
4406because when libpng fills a png_text structure it combines these members with
4407the key member, and png_free_data() will free only text_ptr.key. Similarly,
4408if you transfer responsibility for free'ing text_ptr from libpng to your
4409application, your application must not separately free those members.
4410For a more compact example of writing a PNG image, see the file example.c.
4411
4412.SH V. Modifying/Customizing libpng:
4413
4414There are two issues here. The first is changing how libpng does
4415standard things like memory allocation, input/output, and error handling.
4416The second deals with more complicated things like adding new chunks,
4417adding new transformations, and generally changing how libpng works.
4418Both of those are compile-time issues; that is, they are generally
4419determined at the time the code is written, and there is rarely a need
4420to provide the user with a means of changing them.
4421
4422Memory allocation, input/output, and error handling
4423
4424All of the memory allocation, input/output, and error handling in libpng
4425goes through callbacks that are user-settable. The default routines are
4426in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4427these functions, call the appropriate png_set_*_fn() function.
4428
4429Memory allocation is done through the functions png_malloc(), png_calloc(),
4430and png_free(). These currently just call the standard C functions.
4431png_calloc() calls png_malloc() and then clears the newly
4432allocated memory to zero. There is limited support for certain systems
4433with segmented memory architectures and the types of pointers declared by
4434png.h match this; you will have to use appropriate pointers in your
4435application. Since it is
4436unlikely that the method of handling memory allocation on a platform
4437will change between applications, these functions must be modified in
4438the library at compile time. If you prefer to use a different method
4439of allocating and freeing data, you can use png_create_read_struct_2() or
4440png_create_write_struct_2() to register your own functions as described
4441above. These functions also provide a void pointer that can be retrieved
4442via
4443
4444 mem_ptr=png_get_mem_ptr(png_ptr);
4445
4446Your replacement memory functions must have prototypes as follows:
4447
4448 png_voidp malloc_fn(png_structp png_ptr,
4449 png_alloc_size_t size);
4450
4451 void free_fn(png_structp png_ptr, png_voidp ptr);
4452
4453Your malloc_fn() must return NULL in case of failure. The png_malloc()
4454function will normally call png_error() if it receives a NULL from the
4455system memory allocator or from your replacement malloc_fn().
4456
4457Your free_fn() will never be called with a NULL ptr, since libpng's
4458png_free() checks for NULL before calling free_fn().
4459
4460Input/Output in libpng is done through png_read() and png_write(),
4461which currently just call fread() and fwrite(). The FILE * is stored in
4462png_struct and is initialized via png_init_io(). If you wish to change
4463the method of I/O, the library supplies callbacks that you can set
4464through the function png_set_read_fn() and png_set_write_fn() at run
4465time, instead of calling the png_init_io() function. These functions
4466also provide a void pointer that can be retrieved via the function
4467png_get_io_ptr(). For example:
4468
4469 png_set_read_fn(png_structp read_ptr,
4470 voidp read_io_ptr, png_rw_ptr read_data_fn)
4471
4472 png_set_write_fn(png_structp write_ptr,
4473 voidp write_io_ptr, png_rw_ptr write_data_fn,
4474 png_flush_ptr output_flush_fn);
4475
4476 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4477 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4478
4479The replacement I/O functions must have prototypes as follows:
4480
4481 void user_read_data(png_structp png_ptr,
4482 png_bytep data, png_size_t length);
4483
4484 void user_write_data(png_structp png_ptr,
4485 png_bytep data, png_size_t length);
4486
4487 void user_flush_data(png_structp png_ptr);
4488
4489The user_read_data() function is responsible for detecting and
4490handling end-of-data errors.
4491
4492Supplying NULL for the read, write, or flush functions sets them back
4493to using the default C stream functions, which expect the io_ptr to
4494point to a standard *FILE structure. It is probably a mistake
4495to use NULL for one of write_data_fn and output_flush_fn but not both
4496of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4497It is an error to read from a write stream, and vice versa.
4498
4499Error handling in libpng is done through png_error() and png_warning().
4500Errors handled through png_error() are fatal, meaning that png_error()
4501should never return to its caller. Currently, this is handled via
4502setjmp() and longjmp() (unless you have compiled libpng with
4503PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4504but you could change this to do things like exit() if you should wish,
4505as long as your function does not return.
4506
4507On non-fatal errors, png_warning() is called
4508to print a warning message, and then control returns to the calling code.
4509By default png_error() and png_warning() print a message on stderr via
4510fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4511(because you don't want the messages) or PNG_NO_STDIO defined (because
4512fprintf() isn't available). If you wish to change the behavior of the error
4513functions, you will need to set up your own message callbacks. These
4514functions are normally supplied at the time that the png_struct is created.
4515It is also possible to redirect errors and warnings to your own replacement
4516functions after png_create_*_struct() has been called by calling:
4517
4518 png_set_error_fn(png_structp png_ptr,
4519 png_voidp error_ptr, png_error_ptr error_fn,
4520 png_error_ptr warning_fn);
4521
4522 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4523
4524If NULL is supplied for either error_fn or warning_fn, then the libpng
4525default function will be used, calling fprintf() and/or longjmp() if a
4526problem is encountered. The replacement error functions should have
4527parameters as follows:
4528
4529 void user_error_fn(png_structp png_ptr,
4530 png_const_charp error_msg);
4531
4532 void user_warning_fn(png_structp png_ptr,
4533 png_const_charp warning_msg);
4534
4535The motivation behind using setjmp() and longjmp() is the C++ throw and
4536catch exception handling methods. This makes the code much easier to write,
4537as there is no need to check every return code of every function call.
4538However, there are some uncertainties about the status of local variables
4539after a longjmp, so the user may want to be careful about doing anything
4540after setjmp returns non-zero besides returning itself. Consult your
4541compiler documentation for more details. For an alternative approach, you
4542may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4543which is illustrated in pngvalid.c and in contrib/visupng.
4544
4545.SS Custom chunks
4546
4547If you need to read or write custom chunks, you may need to get deeper
4548into the libpng code. The library now has mechanisms for storing
4549and writing chunks of unknown type; you can even declare callbacks
4550for custom chunks. However, this may not be good enough if the
4551library code itself needs to know about interactions between your
4552chunk and existing `intrinsic' chunks.
4553
4554If you need to write a new intrinsic chunk, first read the PNG
4555specification. Acquire a first level of understanding of how it works.
4556Pay particular attention to the sections that describe chunk names,
4557and look at how other chunks were designed, so you can do things
4558similarly. Second, check out the sections of libpng that read and
4559write chunks. Try to find a chunk that is similar to yours and use
4560it as a template. More details can be found in the comments inside
4561the code. It is best to handle private or unknown chunks in a generic method,
4562via callback functions, instead of by modifying libpng functions. This
4563is illustrated in pngtest.c, which uses a callback function to handle a
4564private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4565libpng.
4566
4567If you wish to write your own transformation for the data, look through
4568the part of the code that does the transformations, and check out some of
4569the simpler ones to get an idea of how they work. Try to find a similar
4570transformation to the one you want to add and copy off of it. More details
4571can be found in the comments inside the code itself.
4572
4573.SS Configuring for 16-bit platforms
4574
4575You will want to look into zconf.h to tell zlib (and thus libpng) that
4576it cannot allocate more then 64K at a time. Even if you can, the memory
4577won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4578
4579.SS Configuring for DOS
4580
4581For DOS users who only have access to the lower 640K, you will
4582have to limit zlib's memory usage via a png_set_compression_mem_level()
4583call. See zlib.h or zconf.h in the zlib library for more information.
4584
4585.SS Configuring for Medium Model
4586
4587Libpng's support for medium model has been tested on most of the popular
4588compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4589defined, and FAR gets defined to far in pngconf.h, and you should be
4590all set. Everything in the library (except for zlib's structure) is
4591expecting far data. You must use the typedefs with the p or pp on
4592the end for pointers (or at least look at them and be careful). Make
4593note that the rows of data are defined as png_bytepp, which is
4594an "unsigned char far * far *".
4595
4596.SS Configuring for gui/windowing platforms:
4597
4598You will need to write new error and warning functions that use the GUI
4599interface, as described previously, and set them to be the error and
4600warning functions at the time that png_create_*_struct() is called,
4601in order to have them available during the structure initialization.
4602They can be changed later via png_set_error_fn(). On some compilers,
4603you may also have to change the memory allocators (png_malloc, etc.).
4604
4605.SS Configuring for compiler xxx:
4606
4607All includes for libpng are in pngconf.h. If you need to add, change
4608or delete an include, this is the place to do it.
4609The includes that are not needed outside libpng are placed in pngpriv.h,
4610which is only used by the routines inside libpng itself.
4611The files in libpng proper only include pngpriv.h and png.h, which
4612%14%in turn includes pngconf.h.
4613in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4614As of libpng-1.5.0, pngpriv.h also includes three other private header
4615files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4616that previously appeared in the public headers.
4617
4618.SS Configuring zlib:
4619
4620There are special functions to configure the compression. Perhaps the
4621most useful one changes the compression level, which currently uses
4622input compression values in the range 0 - 9. The library normally
4623uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4624have shown that for a large majority of images, compression values in
4625the range 3-6 compress nearly as well as higher levels, and do so much
4626faster. For online applications it may be desirable to have maximum speed
4627(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4628specify no compression (Z_NO_COMPRESSION = 0), but this would create
4629files larger than just storing the raw bitmap. You can specify the
4630compression level by calling:
4631
4632 #include zlib.h
4633 png_set_compression_level(png_ptr, level);
4634
4635Another useful one is to reduce the memory level used by the library.
4636The memory level defaults to 8, but it can be lowered if you are
4637short on memory (running DOS, for example, where you only have 640K).
4638Note that the memory level does have an effect on compression; among
4639other things, lower levels will result in sections of incompressible
4640data being emitted in smaller stored blocks, with a correspondingly
4641larger relative overhead of up to 15% in the worst case.
4642
4643 #include zlib.h
4644 png_set_compression_mem_level(png_ptr, level);
4645
4646The other functions are for configuring zlib. They are not recommended
4647for normal use and may result in writing an invalid PNG file. See
4648zlib.h for more information on what these mean.
4649
4650 #include zlib.h
4651 png_set_compression_strategy(png_ptr,
4652 strategy);
4653
4654 png_set_compression_window_bits(png_ptr,
4655 window_bits);
4656
4657 png_set_compression_method(png_ptr, method);
4658
4659 png_set_compression_buffer_size(png_ptr, size);
4660
4661As of libpng version 1.5.4, additional APIs became
4662available to set these separately for non-IDAT
4663compressed chunks such as zTXt, iTXt, and iCCP:
4664
4665 #include zlib.h
4666 #if PNG_LIBPNG_VER <= 10504
4667 png_set_text_compression_level(png_ptr, level);
4668
4669 png_set_text_compression_mem_level(png_ptr, level);
4670
4671 png_set_text_compression_strategy(png_ptr,
4672 strategy);
4673
4674 png_set_text_compression_window_bits(png_ptr,
4675 window_bits);
4676
4677 png_set_text_compression_method(png_ptr, method);
4678 #endif
4679
4680.SS Controlling row filtering
4681
4682If you want to control whether libpng uses filtering or not, which
4683filters are used, and how it goes about picking row filters, you
4684can call one of these functions. The selection and configuration
4685of row filters can have a significant impact on the size and
4686encoding speed and a somewhat lesser impact on the decoding speed
4687of an image. Filtering is enabled by default for RGB and grayscale
4688images (with and without alpha), but not for paletted images nor
4689for any images with bit depths less than 8 bits/pixel.
4690
4691The 'method' parameter sets the main filtering method, which is
4692currently only '0' in the PNG 1.2 specification. The 'filters'
4693parameter sets which filter(s), if any, should be used for each
4694scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4695to turn filtering on and off, respectively.
4696
4697Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4698PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4699ORed together with '|' to specify one or more filters to use.
4700These filters are described in more detail in the PNG specification.
4701If you intend to change the filter type during the course of writing
4702the image, you should start with flags set for all of the filters
4703you intend to use so that libpng can initialize its internal
4704structures appropriately for all of the filter types. (Note that this
4705means the first row must always be adaptively filtered, because libpng
4706currently does not allocate the filter buffers until png_write_row()
4707is called for the first time.)
4708
4709 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4710 PNG_FILTER_UP | PNG_FILTER_AVG |
4711 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4712
4713 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4714 filters);
4715 The second parameter can also be
4716 PNG_INTRAPIXEL_DIFFERENCING if you are
4717 writing a PNG to be embedded in a MNG
4718 datastream. This parameter must be the
4719 same as the value of filter_method used
4720 in png_set_IHDR().
4721
4722It is also possible to influence how libpng chooses from among the
4723available filters. This is done in one or both of two ways - by
4724telling it how important it is to keep the same filter for successive
4725rows, and by telling it the relative computational costs of the filters.
4726
4727 double weights[3] = {1.5, 1.3, 1.1},
4728 costs[PNG_FILTER_VALUE_LAST] =
4729 {1.0, 1.3, 1.3, 1.5, 1.7};
4730
4731 png_set_filter_heuristics(png_ptr,
4732 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4733 weights, costs);
4734
4735The weights are multiplying factors that indicate to libpng that the
4736row filter should be the same for successive rows unless another row filter
4737is that many times better than the previous filter. In the above example,
4738if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4739"sum of absolute differences" 1.5 x 1.3 times higher than other filters
4740and still be chosen, while the NONE filter could have a sum 1.1 times
4741higher than other filters and still be chosen. Unspecified weights are
4742taken to be 1.0, and the specified weights should probably be declining
4743like those above in order to emphasize recent filters over older filters.
4744
4745The filter costs specify for each filter type a relative decoding cost
4746to be considered when selecting row filters. This means that filters
4747with higher costs are less likely to be chosen over filters with lower
4748costs, unless their "sum of absolute differences" is that much smaller.
4749The costs do not necessarily reflect the exact computational speeds of
4750the various filters, since this would unduly influence the final image
4751size.
4752
4753Note that the numbers above were invented purely for this example and
4754are given only to help explain the function usage. Little testing has
4755been done to find optimum values for either the costs or the weights.
4756
4757.SS Removing unwanted object code
4758
4759There are a bunch of #define's in pngconf.h that control what parts of
4760libpng are compiled. All the defines end in _SUPPORTED. If you are
4761never going to use a capability, you can change the #define to #undef
4762before recompiling libpng and save yourself code and data space, or
4763you can turn off individual capabilities with defines that begin with
4764PNG_NO_.
4765
4766In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4767
4768You can also turn all of the transforms and ancillary chunk capabilities
4769off en masse with compiler directives that define
4770PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4771or all four,
4772along with directives to turn on any of the capabilities that you do
4773want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4774transformations but still leave the library fully capable of reading
4775and writing PNG files with all known public chunks. Use of the
4776PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4777that is incapable of reading or writing ancillary chunks. If you are
4778not using the progressive reading capability, you can turn that off
4779with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4780capability, which you'll still have).
4781
4782All the reading and writing specific code are in separate files, so the
4783linker should only grab the files it needs. However, if you want to
4784make sure, or if you are building a stand alone library, all the
4785reading files start with "pngr" and all the writing files start with "pngw".
4786The files that don't match either (like png.c, pngtrans.c, etc.)
4787are used for both reading and writing, and always need to be included.
4788The progressive reader is in pngpread.c
4789
4790If you are creating or distributing a dynamically linked library (a .so
4791or DLL file), you should not remove or disable any parts of the library,
4792as this will cause applications linked with different versions of the
4793library to fail if they call functions not available in your library.
4794The size of the library itself should not be an issue, because only
4795those sections that are actually used will be loaded into memory.
4796
4797.SS Requesting debug printout
4798
4799The macro definition PNG_DEBUG can be used to request debugging
4800printout. Set it to an integer value in the range 0 to 3. Higher
4801numbers result in increasing amounts of debugging information. The
4802information is printed to the "stderr" file, unless another file
4803name is specified in the PNG_DEBUG_FILE macro definition.
4804
4805When PNG_DEBUG > 0, the following functions (macros) become available:
4806
4807 png_debug(level, message)
4808 png_debug1(level, message, p1)
4809 png_debug2(level, message, p1, p2)
4810
4811in which "level" is compared to PNG_DEBUG to decide whether to print
4812the message, "message" is the formatted string to be printed,
4813and p1 and p2 are parameters that are to be embedded in the string
4814according to printf-style formatting directives. For example,
4815
4816 png_debug1(2, "foo=%d\n", foo);
4817
4818is expanded to
4819
4820 if (PNG_DEBUG > 2)
4821 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4822
4823When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4824can still use PNG_DEBUG to control your own debugging:
4825
4826 #ifdef PNG_DEBUG
4827 fprintf(stderr, ...
4828 #endif
4829
4830When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4831having level = 0 will be printed. There aren't any such statements in
4832this version of libpng, but if you insert some they will be printed.
4833
4834.SH VI. MNG support
4835
4836The MNG specification (available at http://www.libpng.org/pub/mng) allows
4837certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4838Libpng can support some of these extensions. To enable them, use the
4839png_permit_mng_features() function:
4840
4841 feature_set = png_permit_mng_features(png_ptr, mask)
4842
4843 mask is a png_uint_32 containing the bitwise OR of the
4844 features you want to enable. These include
4845 PNG_FLAG_MNG_EMPTY_PLTE
4846 PNG_FLAG_MNG_FILTER_64
4847 PNG_ALL_MNG_FEATURES
4848
4849 feature_set is a png_uint_32 that is the bitwise AND of
4850 your mask with the set of MNG features that is
4851 supported by the version of libpng that you are using.
4852
4853It is an error to use this function when reading or writing a standalone
4854PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4855in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4856and the MHDR and MEND chunks. Libpng does not provide support for these
4857or any other MNG chunks; your application must provide its own support for
4858them. You may wish to consider using libmng (available at
4859http://www.libmng.com) instead.
4860
4861.SH VII. Changes to Libpng from version 0.88
4862
4863It should be noted that versions of libpng later than 0.96 are not
4864distributed by the original libpng author, Guy Schalnat, nor by
4865Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4866distributed versions 0.89 through 0.96, but rather by another member
4867of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4868still alive and well, but they have moved on to other things.
4869
4870The old libpng functions png_read_init(), png_write_init(),
4871png_info_init(), png_read_destroy(), and png_write_destroy() have been
4872moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4873functions will be removed from libpng version 1.4.0.
4874
4875The preferred method of creating and initializing the libpng structures is
4876via the png_create_read_struct(), png_create_write_struct(), and
4877png_create_info_struct() because they isolate the size of the structures
4878from the application, allow version error checking, and also allow the
4879use of custom error handling routines during the initialization, which
4880the old functions do not. The functions png_read_destroy() and
4881png_write_destroy() do not actually free the memory that libpng
4882allocated for these structs, but just reset the data structures, so they
4883can be used instead of png_destroy_read_struct() and
4884png_destroy_write_struct() if you feel there is too much system overhead
4885allocating and freeing the png_struct for each image read.
4886
4887Setting the error callbacks via png_set_message_fn() before
4888png_read_init() as was suggested in libpng-0.88 is no longer supported
4889because this caused applications that do not use custom error functions
4890to fail if the png_ptr was not initialized to zero. It is still possible
4891to set the error callbacks AFTER png_read_init(), or to change them with
4892png_set_error_fn(), which is essentially the same function, but with a new
4893name to force compilation errors with applications that try to use the old
4894method.
4895
4896Starting with version 1.0.7, you can find out which version of the library
4897you are using at run-time:
4898
4899 png_uint_32 libpng_vn = png_access_version_number();
4900
4901The number libpng_vn is constructed from the major version, minor
4902version with leading zero, and release number with leading zero,
4903(e.g., libpng_vn for version 1.0.7 is 10007).
4904
4905Note that this function does not take a png_ptr, so you can call it
4906before you've created one.
4907
4908You can also check which version of png.h you used when compiling your
4909application:
4910
4911 png_uint_32 application_vn = PNG_LIBPNG_VER;
4912
4913.SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
4914
4915Support for user memory management was enabled by default. To
4916accomplish this, the functions png_create_read_struct_2(),
4917png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4918png_malloc_default(), and png_free_default() were added.
4919
4920Support for the iTXt chunk has been enabled by default as of
4921version 1.2.41.
4922
4923Support for certain MNG features was enabled.
4924
4925Support for numbered error messages was added. However, we never got
4926around to actually numbering the error messages. The function
4927png_set_strip_error_numbers() was added (Note: the prototype for this
4928function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4929builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4930
4931The png_malloc_warn() function was added at libpng-1.2.3. This issues
4932a png_warning and returns NULL instead of aborting when it fails to
4933acquire the requested memory allocation.
4934
4935Support for setting user limits on image width and height was enabled
4936by default. The functions png_set_user_limits(), png_get_user_width_max(),
4937and png_get_user_height_max() were added at libpng-1.2.6.
4938
4939The png_set_add_alpha() function was added at libpng-1.2.7.
4940
4941The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4942Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4943tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4944deprecated.
4945
4946A number of macro definitions in support of runtime selection of
4947assembler code features (especially Intel MMX code support) were
4948added at libpng-1.2.0:
4949
4950 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4951 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4952 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4953 PNG_ASM_FLAG_MMX_READ_INTERLACE
4954 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4955 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4956 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4957 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4958 PNG_ASM_FLAGS_INITIALIZED
4959 PNG_MMX_READ_FLAGS
4960 PNG_MMX_FLAGS
4961 PNG_MMX_WRITE_FLAGS
4962 PNG_MMX_FLAGS
4963
4964We added the following functions in support of runtime
4965selection of assembler code features:
4966
4967 png_get_mmx_flagmask()
4968 png_set_mmx_thresholds()
4969 png_get_asm_flags()
4970 png_get_mmx_bitdepth_threshold()
4971 png_get_mmx_rowbytes_threshold()
4972 png_set_asm_flags()
4973
4974We replaced all of these functions with simple stubs in libpng-1.2.20,
4975when the Intel assembler code was removed due to a licensing issue.
4976
4977These macros are deprecated:
4978
4979 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4980 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4981 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4982 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4983 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4984 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4985
4986They have been replaced, respectively, by:
4987
4988 PNG_NO_READ_TRANSFORMS
4989 PNG_NO_PROGRESSIVE_READ
4990 PNG_NO_SEQUENTIAL_READ
4991 PNG_NO_WRITE_TRANSFORMS
4992 PNG_NO_READ_ANCILLARY_CHUNKS
4993 PNG_NO_WRITE_ANCILLARY_CHUNKS
4994
4995PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4996deprecated since libpng-1.0.16 and libpng-1.2.6.
4997
4998The function
4999 png_check_sig(sig, num)
5000was replaced with
5001 !png_sig_cmp(sig, 0, num)
5002It has been deprecated since libpng-0.90.
5003
5004The function
5005 png_set_gray_1_2_4_to_8()
5006which also expands tRNS to alpha was replaced with
5007 png_set_expand_gray_1_2_4_to_8()
5008which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5009
5010.SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
5011
5012Private libpng prototypes and macro definitions were moved from
5013png.h and pngconf.h into a new pngpriv.h header file.
5014
5015Functions png_set_benign_errors(), png_benign_error(), and
5016png_chunk_benign_error() were added.
5017
5018Support for setting the maximum amount of memory that the application
5019will allocate for reading chunks was added, as a security measure.
5020The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5021were added to the library.
5022
5023We implemented support for I/O states by adding png_ptr member io_state
5024and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5025
5026We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5027input transforms.
5028
5029Checking for and reporting of errors in the IHDR chunk is more thorough.
5030
5031Support for global arrays was removed, to improve thread safety.
5032
5033Some obsolete/deprecated macros and functions have been removed.
5034
5035Typecasted NULL definitions such as
5036 #define png_voidp_NULL (png_voidp)NULL
5037were eliminated. If you used these in your application, just use
5038NULL instead.
5039
5040The png_struct and info_struct members "trans" and "trans_values" were
5041changed to "trans_alpha" and "trans_color", respectively.
5042
5043The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5044were removed.
5045
5046The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5047
5048The PNG_LEGACY_SUPPORTED macro was eliminated.
5049
5050Many WIN32_WCE #ifdefs were removed.
5051
5052The functions png_read_init(info_ptr), png_write_init(info_ptr),
5053png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5054have been removed. They have been deprecated since libpng-0.95.
5055
5056The png_permit_empty_plte() was removed. It has been deprecated
5057since libpng-1.0.9. Use png_permit_mng_features() instead.
5058
5059We removed the obsolete stub functions png_get_mmx_flagmask(),
5060png_set_mmx_thresholds(), png_get_asm_flags(),
5061png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5062png_set_asm_flags(), and png_mmx_supported()
5063
5064We removed the obsolete png_check_sig(), png_memcpy_check(), and
5065png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5066and memset(), respectively.
5067
5068The function png_set_gray_1_2_4_to_8() was removed. It has been
5069deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5070png_set_expand_gray_1_2_4_to_8() because the former function also
5071expanded any tRNS chunk to an alpha channel.
5072
5073Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5074were added and are used by default instead of the corresponding
5075functions. Unfortunately,
5076from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5077function) incorrectly returned a value of type png_uint_32.
5078
5079We changed the prototype for png_malloc() from
5080 png_malloc(png_structp png_ptr, png_uint_32 size)
5081to
5082 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5083
5084This also applies to the prototype for the user replacement malloc_fn().
5085
5086The png_calloc() function was added and is used in place of
5087of "png_malloc(); memset();" except in the case in png_read_png()
5088where the array consists of pointers; in this case a "for" loop is used
5089after the png_malloc() to set the pointers to NULL, to give robust.
5090behavior in case the application runs out of memory part-way through
5091the process.
5092
5093We changed the prototypes of png_get_compression_buffer_size() and
5094png_set_compression_buffer_size() to work with png_size_t instead of
5095png_uint_32.
5096
5097Support for numbered error messages was removed by default, since we
5098never got around to actually numbering the error messages. The function
5099png_set_strip_error_numbers() was removed from the library by default.
5100
5101The png_zalloc() and png_zfree() functions are no longer exported.
5102The png_zalloc() function no longer zeroes out the memory that it
5103allocates.
5104
5105Support for dithering was disabled by default in libpng-1.4.0, because
5106it has not been well tested and doesn't actually "dither".
5107The code was not
5108removed, however, and could be enabled by building libpng with
5109PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5110was reenabled, but the function was renamed png_set_quantize() to
5111reflect more accurately what it actually does. At the same time,
5112the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5113PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5114was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5115
5116We removed the trailing '.' from the warning and error messages.
5117
5118.SH X. Changes to Libpng from version 1.4.x to 1.5.x
5119
5120From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5121function) incorrectly returned a value of type png_uint_32.
5122
5123A. Changes that affect users of libpng
5124
5125There are no substantial API changes between the non-deprecated parts of
5126the 1.4.5 API and the 1.5.0 API, however the ability to directly access
5127the main libpng control structures, png_struct and png_info, deprecated
5128in earlier versions of libpng, has been completely removed from
5129libpng 1.5.
5130
5131We no longer include zlib.h in png.h. Applications that need access
5132to information in zlib.h will need to add the '#include "zlib.h"'
5133directive. It does not matter whether it is placed prior to or after
5134the '"#include png.h"' directive.
5135
5136We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),
5137png_memcmp(), png_sprintf, and png_memcpy() macros into a private
5138header file (pngpriv.h) that is not accessible to applications.
5139
5140In png_get_iCCP, the type of "profile" was changed from png_charpp
5141to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5142
5143There are changes of form in png.h, including new and changed macros to
5144declare parts of the API. Some API functions with arguments that are
5145pointers to data not modified within the function have been corrected to
5146declare these arguments with PNG_CONST.
5147
5148Much of the internal use of C macros to control the library build has also
5149changed and some of this is visible in the exported header files, in
5150particular the use of macros to control data and API elements visible
5151during application compilation may require significant revision to
5152application code. (It is extremely rare for an application to do this.)
5153
5154Any program that compiled against libpng 1.4 and did not use deprecated
5155features or access internal library structures should compile and work
5156against libpng 1.5, except for the change in the prototype for
5157png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5158
5159libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5160interlaced images. The macros return the number of rows and columns in
5161each pass and information that can be used to de-interlace and (if
5162absolutely necessary) interlace an image.
5163
5164libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5165the application-provided png_longjmp_ptr on the internal, but application
5166initialized, longjmp buffer. It is provided as a convenience to avoid
5167the need to use the png_jmpbuf macro, which had the unnecessary side
5168effect of resetting the internal png_longjmp_ptr value.
5169
5170libpng 1.5.0 includes a complete fixed point API. By default this is
5171present along with the corresponding floating point API. In general the
5172fixed point API is faster and smaller than the floating point one because
5173the PNG file format used fixed point, not floating point. This applies
5174even if the library uses floating point in internal calculations. A new
5175macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5176uses floating point arithmetic (the default) or fixed point arithmetic
5177internally for performance critical calculations such as gamma correction.
5178In some cases, the gamma calculations may produce slightly different
5179results. This has changed the results in png_rgb_to_gray and in alpha
5180composition (png_set_background for example). This applies even if the
5181original image was already linear (gamma == 1.0) and, therefore, it is
5182not necessary to linearize the image. This is because libpng has *not*
5183been changed to optimize that case correctly, yet.
5184
5185Fixed point support for the sCAL chunk comes with an important caveat;
5186the sCAL specification uses a decimal encoding of floating point values
5187and the accuracy of PNG fixed point values is insufficient for
5188representation of these values. Consequently a "string" API
5189(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5190arbitrary sCAL chunks in the absence of either the floating point API or
5191internal floating point calculations.
5192
5193Applications no longer need to include the optional distribution header
5194file pngusr.h or define the corresponding macros during application
5195build in order to see the correct variant of the libpng API. From 1.5.0
5196application code can check for the corresponding _SUPPORTED macro:
5197
5198#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5199 /* code that uses the inch conversion APIs. */
5200#endif
5201
5202This macro will only be defined if the inch conversion functions have been
5203compiled into libpng. The full set of macros, and whether or not support
5204has been compiled in, are available in the header file pnglibconf.h.
5205This header file is specific to the libpng build. Notice that prior to
52061.5.0 the _SUPPORTED macros would always have the default definition unless
5207reset by pngusr.h or by explicit settings on the compiler command line.
5208These settings may produce compiler warnings or errors in 1.5.0 because
5209of macro redefinition.
5210
5211From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5212function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
5213is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
5214did not exist.)
5215
5216Applications can now choose whether to use these macros or to call the
5217corresponding function by defining PNG_USE_READ_MACROS or
5218PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5219only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5220will lead to a link failure.
5221
5222Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5223when compressing the IDAT data and textual data such as zTXt and iCCP.
5224In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5225We added five png_set_text_*() functions for setting the parameters to
5226use with textual data.
5227
5228Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5229option was off by default, and slightly inaccurate scaling occurred.
5230This option can no longer be turned off, and the choice of accurate
5231or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5232API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5233chopping.
5234
5235Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5236used to reduce the width and height limits from the value of
5237PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5238that it could be used to override them. Now this function will reduce or
5239increase the limits.
5240
5241B. Changes to the build and configuration of libpng
5242
5243Details of internal changes to the library code can be found in the CHANGES
5244file and in the GIT repository logs. These will be of no concern to the vast
5245majority of library users or builders, however the few who configure libpng
5246to a non-default feature set may need to change how this is done.
5247
5248There should be no need for library builders to alter build scripts if
5249these use the distributed build support - configure or the makefiles -
5250however users of the makefiles may care to update their build scripts
5251to build pnglibconf.h where the corresponding makefile does not do so.
5252
5253Building libpng with a non-default configuration has changed completely.
5254The old method using pngusr.h should still work correctly even though the
5255way pngusr.h is used in the build has been changed; however, library
5256builders will probably want to examine the changes to take advantage of
5257new capabilities and to simplify their build system.
5258
5259B.1 Specific changes to library configuration capabilities
5260
5261The library now supports a complete fixed point implementation and can
5262thus be used on systems that have no floating point support or very
5263limited or slow support. Previously gamma correction, an essential part
5264of complete PNG support, required reasonably fast floating point.
5265
5266As part of this the choice of internal implementation has been made
5267independent of the choice of fixed versus floating point APIs and all the
5268missing fixed point APIs have been implemented.
5269
5270The exact mechanism used to control attributes of API functions has
5271changed. A single set of operating system independent macro definitions
5272is used and operating system specific directives are defined in
5273pnglibconf.h
5274
5275As part of this the mechanism used to choose procedure call standards on
5276those systems that allow a choice has been changed. At present this only
5277affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
5278running on Intel processors. As before, PNGAPI is defined where required
5279to control the exported API functions; however, two new macros, PNGCBAPI
5280and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
5281(PNGCAPI) for functions that must match a C library prototype (currently
5282only png_longjmp_ptr, which must match the C longjmp function.) The new
5283approach is documented in pngconf.h
5284
5285Despite these changes, libpng 1.5.0 only supports the native C function
5286calling standard on those platforms tested so far (__cdecl on Microsoft
5287Windows). This is because the support requirements for alternative
5288calling conventions seem to no longer exist. Developers who find it
5289necessary to set PNG_API_RULE to 1 should advise the mailing list
5290(png-mng-implement) of this and library builders who use Openwatcom and
5291therefore set PNG_API_RULE to 2 should also contact the mailing list.
5292
5293A new test program, pngvalid, is provided in addition to pngtest.
5294pngvalid validates the arithmetic accuracy of the gamma correction
5295calculations and includes a number of validations of the file format.
5296A subset of the full range of tests is run when "make check" is done
5297(in the 'configure' build.) pngvalid also allows total allocated memory
5298usage to be evaluated and performs additional memory overwrite validation.
5299
5300Many changes to individual feature macros have been made. The following
5301are the changes most likely to be noticed by library builders who
5302configure libpng:
5303
53041) All feature macros now have consistent naming:
5305
5306#define PNG_NO_feature turns the feature off
5307#define PNG_feature_SUPPORTED turns the feature on
5308
5309pnglibconf.h contains one line for each feature macro which is either:
5310
5311#define PNG_feature_SUPPORTED
5312
5313if the feature is supported or:
5314
5315/*#undef PNG_feature_SUPPORTED*/
5316
5317if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5318It does not, and libpng applications should not, check for the 'NO' macro
5319which will not normally be defined even if the feature is not supported.
5320The 'NO' macros are only used internally for setting or not setting the
5321corresponding 'SUPPORTED' macros.
5322
5323Compatibility with the old names is provided as follows:
5324
5325PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5326
5327And the following definitions disable the corresponding feature:
5328
5329PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5330PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5331PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5332PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5333PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5334PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5335
5336Library builders should remove use of the above, inconsistent, names.
5337
53382) Warning and error message formatting was previously conditional on
5339the STDIO feature. The library has been changed to use the
5340CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5341the library no longer uses the printf(3) functions, even though the
5342default read/write implementations use (FILE) style stdio.h functions.
5343
53443) Three feature macros now control the fixed/floating point decisions:
5345
5346PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5347
5348PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5349practice these are normally required internally anyway (because the PNG
5350file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5351merely stops the function from being exported.
5352
5353PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5354point implementation or the fixed point one. Typically the fixed point
5355implementation is larger and slower than the floating point implementation
5356on a system that supports floating point, however it may be faster on a
5357system which lacks floating point hardware and therefore uses a software
5358emulation.
5359
53604) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5361functions to read and write ints to be disabled independently of
5362PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5363even though the default is to use the macros - this allows applications
5364to choose at app buildtime whether or not to use macros (previously
5365impossible because the functions weren't in the default build.)
5366
5367B.2 Changes to the configuration mechanism
5368
5369Prior to libpng-1.5.0 library builders who needed to configure libpng
5370had either to modify the exported pngconf.h header file to add system
5371specific configuration or had to write feature selection macros into
5372pngusr.h and cause this to be included into pngconf.h by defining
5373PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
5374application built without PNG_USER_CONFIG defined would see the
5375unmodified, default, libpng API and thus would probably fail to link.
5376
5377These mechanisms still work in the configure build and in any makefile
5378build that builds pnglibconf.h, although the feature selection macros
5379have changed somewhat as described above. In 1.5.0, however, pngusr.h is
5380processed only once, when the exported header file pnglibconf.h is built.
5381pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
5382build of pnglibconf.h and it is never included in an application build.
5383
5384The rarely used alternative of adding a list of feature macros to the
5385CFLAGS setting in the build also still works, however the macros will be
5386copied to pnglibconf.h and this may produce macro redefinition warnings
5387when the individual C files are compiled.
5388
5389All configuration now only works if pnglibconf.h is built from
5390scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
5391(the original author of awk) maintains C source code of that awk and this
5392and all known later implementations (often called by subtly different
5393names - nawk and gawk for example) are adequate to build pnglibconf.h.
5394The Sun Microsystems (now Oracle) program 'awk' is an earlier version
5395and does not work; this may also apply to other systems that have a
5396functioning awk called 'nawk'.
5397
5398Configuration options are now documented in scripts/pnglibconf.dfa. This
5399file also includes dependency information that ensures a configuration is
5400consistent; that is, if a feature is switched off dependent features are
5401also removed. As a recommended alternative to using feature macros in
5402pngusr.h a system builder may also define equivalent options in pngusr.dfa
5403(or, indeed, any file) and add that to the configuration by setting
5404DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
5405how to do this, and a case where pngusr.h is still required.
5406
5407.SH XI. Detecting libpng
5408
5409The png_get_io_ptr() function has been present since libpng-0.88, has never
5410changed, and is unaffected by conditional compilation macros. It is the
5411best choice for use in configure scripts for detecting the presence of any
5412libpng version since 0.88. In an autoconf "configure.in" you could use
5413
5414 AC_CHECK_LIB(png, png_get_io_ptr, ...
5415
5416.SH XII. Source code repository
5417
5418Since about February 2009, version 1.2.34, libpng has been under "git" source
5419control. The git repository was built from old libpng-x.y.z.tar.gz files
5420going back to version 0.70. You can access the git repository (read only)
5421at
5422
5423 git://libpng.git.sourceforge.net/gitroot/libpng
5424
5425or you can browse it via "gitweb" at
5426
5427 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
5428
5429Patches can be sent to glennrp at users.sourceforge.net or to
5430png-mng-implement at lists.sourceforge.net or you can upload them to
5431the libpng bug tracker at
5432
5433 http://libpng.sourceforge.net
5434
5435We also accept patches built from the tar or zip distributions, and
5436simple verbal discriptions of bug fixes, reported either to the
5437SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5438mailing list, or directly to glennrp.
5439
5440.SH XIII. Coding style
5441
5442Our coding style is similar to the "Allman" style, with curly
5443braces on separate lines:
5444
5445 if (condition)
5446 {
5447 action;
5448 }
5449
5450 else if (another condition)
5451 {
5452 another action;
5453 }
5454
5455The braces can be omitted from simple one-line actions:
5456
5457 if (condition)
5458 return (0);
5459
5460We use 3-space indentation, except for continued statements which
5461are usually indented the same as the first line of the statement
5462plus four more spaces.
5463
5464For macro definitions we use 2-space indentation, always leaving the "#"
5465in the first column.
5466
5467 #ifndef PNG_NO_FEATURE
5468 # ifndef PNG_FEATURE_SUPPORTED
5469 # define PNG_FEATURE_SUPPORTED
5470 # endif
5471 #endif
5472
5473Comments appear with the leading "/*" at the same indentation as
5474the statement that follows the comment:
5475
5476 /* Single-line comment */
5477 statement;
5478
5479 /* This is a multiple-line
5480 * comment.
5481 */
5482 statement;
5483
5484Very short comments can be placed after the end of the statement
5485to which they pertain:
5486
5487 statement; /* comment */
5488
5489We don't use C++ style ("//") comments. We have, however,
5490used them in the past in some now-abandoned MMX assembler
5491code.
5492
5493Functions and their curly braces are not indented, and
5494exported functions are marked with PNGAPI:
5495
5496 /* This is a public function that is visible to
5497 * application programmers. It does thus-and-so.
5498 */
5499 void PNGAPI
5500 png_exported_function(png_ptr, png_info, foo)
5501 {
5502 body;
5503 }
5504
5505The prototypes for all exported functions appear in png.h,
5506above the comment that says
5507
5508 /* Maintainer: Put new public prototypes here ... */
5509
5510We mark all non-exported functions with "/* PRIVATE */"":
5511
5512 void /* PRIVATE */
5513 png_non_exported_function(png_ptr, png_info, foo)
5514 {
5515 body;
5516 }
5517
5518The prototypes for non-exported functions (except for those in
5519pngtest) appear in
5520pngpriv.h
5521above the comment that says
5522
5523 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
5524
5525To avoid polluting the global namespace, the names of all exported
5526functions and variables begin with "png_", and all publicly visible C
5527preprocessor macros begin with "PNG_". We request that applications that
5528use libpng *not* begin any of their own symbols with either of these strings.
5529
5530We put a space after each comma and after each semicolon
5531in "for" statements, and we put spaces before and after each
5532C binary operator and after "for" or "while", and before
5533"?". We don't put a space between a typecast and the expression
5534being cast, nor do we put one between a function name and the
5535left parenthesis that follows it:
5536
5537 for (i = 2; i > 0; --i)
5538 y[i] = a(x) + (int)b;
5539
5540We prefer #ifdef and #ifndef to #if defined() and if !defined()
5541when there is only one macro being tested.
5542
5543We prefer to express integers that are used as bit masks in hex format,
5544with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5545
5546We do not use the TAB character for indentation in the C sources.
5547
5548Lines do not exceed 80 characters.
5549
5550Other rules can be inferred by inspecting the libpng source.
5551
5552.SH XIV. Y2K Compliance in libpng
5553
5554December 15, 2011
5555
5556Since the PNG Development group is an ad-hoc body, we can't make
5557an official declaration.
5558
5559This is your unofficial assurance that libpng from version 0.71 and
5560upward through 1.5.7 are Y2K compliant. It is my belief that earlier
5561versions were also Y2K compliant.
5562
5563Libpng only has three year fields. One is a 2-byte unsigned integer that
5564will hold years up to 65535. The other two hold the date in text
5565format, and will hold years up to 9999.
5566
5567The integer is
5568 "png_uint_16 year" in png_time_struct.
5569
5570The strings are
5571 "png_charp time_buffer" in png_struct and
5572 "near_time_buffer", which is a local character string in png.c.
5573
5574There are seven time-related functions:
5575
5576 png_convert_to_rfc_1123() in png.c
5577 (formerly png_convert_to_rfc_1152() in error)
5578 png_convert_from_struct_tm() in pngwrite.c, called
5579 in pngwrite.c
5580 png_convert_from_time_t() in pngwrite.c
5581 png_get_tIME() in pngget.c
5582 png_handle_tIME() in pngrutil.c, called in pngread.c
5583 png_set_tIME() in pngset.c
5584 png_write_tIME() in pngwutil.c, called in pngwrite.c
5585
5586All appear to handle dates properly in a Y2K environment. The
5587png_convert_from_time_t() function calls gmtime() to convert from system
5588clock time, which returns (year - 1900), which we properly convert to
5589the full 4-digit year. There is a possibility that applications using
5590libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5591function, or that they are incorrectly passing only a 2-digit year
5592instead of "year - 1900" into the png_convert_from_struct_tm() function,
5593but this is not under our control. The libpng documentation has always
5594stated that it works with 4-digit years, and the APIs have been
5595documented as such.
5596
5597The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5598integer to hold the year, and can hold years as large as 65535.
5599
5600zlib, upon which libpng depends, is also Y2K compliant. It contains
5601no date-related code.
5602
5603
5604 Glenn Randers-Pehrson
5605 libpng maintainer
5606 PNG Development Group
5607
5608.SH NOTE
5609
5610Note about libpng version numbers:
5611
5612Due to various miscommunications, unforeseen code incompatibilities
5613and occasional factors outside the authors' control, version numbering
5614on the library has not always been consistent and straightforward.
5615The following table summarizes matters since version 0.89c, which was
5616the first widely used release:
5617
5618 source png.h png.h shared-lib
5619 version string int version
5620 ------- ------ ----- ----------
5621 0.89c ("beta 3") 0.89 89 1.0.89
5622 0.90 ("beta 4") 0.90 90 0.90
5623 0.95 ("beta 5") 0.95 95 0.95
5624 0.96 ("beta 6") 0.96 96 0.96
5625 0.97b ("beta 7") 1.00.97 97 1.0.1
5626 0.97c 0.97 97 2.0.97
5627 0.98 0.98 98 2.0.98
5628 0.99 0.99 98 2.0.99
5629 0.99a-m 0.99 99 2.0.99
5630 1.00 1.00 100 2.1.0
5631 1.0.0 1.0.0 100 2.1.0
5632 1.0.0 (from here on, the 100 2.1.0
5633 1.0.1 png.h string is 10001 2.1.0
5634 1.0.1a-e identical to the 10002 from here on, the
5635 1.0.2 source version) 10002 shared library is 2.V
5636 1.0.2a-b 10003 where V is the source
5637 1.0.1 10001 code version except as
5638 1.0.1a-e 10002 2.1.0.1a-e noted.
5639 1.0.2 10002 2.1.0.2
5640 1.0.2a-b 10003 2.1.0.2a-b
5641 1.0.3 10003 2.1.0.3
5642 1.0.3a-d 10004 2.1.0.3a-d
5643 1.0.4 10004 2.1.0.4
5644 1.0.4a-f 10005 2.1.0.4a-f
5645 1.0.5 (+ 2 patches) 10005 2.1.0.5
5646 1.0.5a-d 10006 2.1.0.5a-d
5647 1.0.5e-r 10100 2.1.0.5e-r
5648 1.0.5s-v 10006 2.1.0.5s-v
5649 1.0.6 (+ 3 patches) 10006 2.1.0.6
5650 1.0.6d-g 10007 2.1.0.6d-g
5651 1.0.6h 10007 10.6h
5652 1.0.6i 10007 10.6i
5653 1.0.6j 10007 2.1.0.6j
5654 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5655 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5656 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5657 1.0.7 1 10007 2.1.0.7
5658 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5659 1.0.8rc1 1 10008 2.1.0.8rc1
5660 1.0.8 1 10008 2.1.0.8
5661 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5662 1.0.9rc1 1 10009 2.1.0.9rc1
5663 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5664 1.0.9rc2 1 10009 2.1.0.9rc2
5665 1.0.9 1 10009 2.1.0.9
5666 1.0.10beta1 1 10010 2.1.0.10beta1
5667 1.0.10rc1 1 10010 2.1.0.10rc1
5668 1.0.10 1 10010 2.1.0.10
5669 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5670 1.0.11rc1 1 10011 2.1.0.11rc1
5671 1.0.11 1 10011 2.1.0.11
5672 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5673 1.0.12rc1 2 10012 2.1.0.12rc1
5674 1.0.12 2 10012 2.1.0.12
5675 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5676 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5677 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5678 1.2.0rc1 3 10200 3.1.2.0rc1
5679 1.2.0 3 10200 3.1.2.0
5680 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5681 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5682 1.2.1 3 10201 3.1.2.1
5683 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5684 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5685 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5686 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5687 1.0.13 10 10013 10.so.0.1.0.13
5688 1.2.2 12 10202 12.so.0.1.2.2
5689 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5690 1.2.3 12 10203 12.so.0.1.2.3
5691 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5692 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5693 1.0.14 10 10014 10.so.0.1.0.14
5694 1.2.4 13 10204 12.so.0.1.2.4
5695 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5696 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5697 1.0.15 10 10015 10.so.0.1.0.15
5698 1.2.5 13 10205 12.so.0.1.2.5
5699 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5700 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5701 1.0.16 10 10016 10.so.0.1.0.16
5702 1.2.6 13 10206 12.so.0.1.2.6
5703 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5704 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5705 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5706 1.0.17 10 10017 12.so.0.1.0.17
5707 1.2.7 13 10207 12.so.0.1.2.7
5708 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5709 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5710 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5711 1.0.18 10 10018 12.so.0.1.0.18
5712 1.2.8 13 10208 12.so.0.1.2.8
5713 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5714 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5715 1.2.9rc1 13 10209 12.so.0.9[.0]
5716 1.2.9 13 10209 12.so.0.9[.0]
5717 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5718 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5719 1.2.10 13 10210 12.so.0.10[.0]
5720 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5721 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5722 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5723 1.2.11 13 10211 12.so.0.11[.0]
5724 1.2.12 13 10212 12.so.0.12[.0]
5725 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5726 1.2.13 13 10213 12.so.0.13[.0]
5727 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5728 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5729 1.4.0rc01 14 10400 14.so.14.0[.0]
5730 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5731 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5732 1.4.0 14 10400 14.so.14.0[.0]
5733 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5734 1.4.1rc01 14 10401 14.so.14.1[.0]
5735 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5736 1.4.1 14 10401 14.so.14.1[.0]
5737 1.4.2 14 10402 14.so.14.2[.0]
5738 1.4.3 14 10403 14.so.14.3[.0]
5739 1.4.4 14 10404 14.so.14.4[.0]
5740 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5741 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5742 1.5.0 15 10500 15.so.15.0[.0]
5743 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5744 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5745 1.5.1 15 10501 15.so.15.1[.0]
5746 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5747 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5748 1.5.2 15 10502 15.so.15.2[.0]
5749 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5750 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5751 1.5.3beta11 15 10503 15.so.15.3[.0]
5752 1.5.3 [omitted]
5753 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5754 1.5.4rc01 15 10504 15.so.15.4[.0]
5755 1.5.4 15 10504 15.so.15.4[.0]
5756 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5757 1.5.5rc01 15 10505 15.so.15.5[.0]
5758 1.5.5 15 10505 15.so.15.5[.0]
5759 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5760 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5761 1.5.6 15 10506 15.so.15.6[.0]
5762 1.5.7beta01-05 15 10507 15.so.15.7[.0]
5763 1.5.7rc01-03 15 10507 15.so.15.7[.0]
5764 1.5.7 15 10507 15.so.15.7[.0]
5765
5766Henceforth the source version will match the shared-library minor
5767and patch numbers; the shared-library major version number will be
5768used for changes in backward compatibility, as it is intended. The
5769PNG_PNGLIB_VER macro, which is not used within libpng but is available
5770for applications, is an unsigned integer of the form xyyzz corresponding
5771to the source version x.y.z (leading zeros in y and z). Beta versions
5772were given the previous public release number plus a letter, until
5773version 1.0.6j; from then on they were given the upcoming public
5774release number plus "betaNN" or "rcN".
5775
5776.SH "SEE ALSO"
5777.BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5778
5779.LP
5780.IR libpng :
5781.IP
5782http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5783http://www.libpng.org/pub/png
5784
5785.LP
5786.IR zlib :
5787.IP
5788(generally) at the same location as
5789.I libpng
5790or at
5791.br
5792ftp://ftp.info-zip.org/pub/infozip/zlib
5793
5794.LP
5795.IR PNG specification: RFC 2083
5796.IP
5797(generally) at the same location as
5798.I libpng
5799or at
5800.br
5801ftp://ds.internic.net/rfc/rfc2083.txt
5802.br
5803or (as a W3C Recommendation) at
5804.br
5805http://www.w3.org/TR/REC-png.html
5806
5807.LP
5808In the case of any inconsistency between the PNG specification
5809and this library, the specification takes precedence.
5810
5811.SH AUTHORS
5812This man page: Glenn Randers-Pehrson
5813<glennrp at users.sourceforge.net>
5814
5815The contributing authors would like to thank all those who helped
5816with testing, bug fixes, and patience. This wouldn't have been
5817possible without all of you.
5818
5819Thanks to Frank J. T. Wojcik for helping with the documentation.
5820
5821Libpng version 1.5.7 - December 15, 2011:
5822Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5823Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5824
5825Supported by the PNG development group
5826.br
5827png-mng-implement at lists.sf.net
5828(subscription required; visit
5829png-mng-implement at lists.sourceforge.net (subscription required; visit
5830https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5831to subscribe).
5832
5833.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5834
5835(This copy of the libpng notices is provided for your convenience. In case of
5836any discrepancy between this copy and the notices in the file png.h that is
5837included in the libpng distribution, the latter shall prevail.)
5838
5839If you modify libpng you may insert additional notices immediately following
5840this sentence.
5841
5842This code is released under the libpng license.
5843
5844libpng versions 1.2.6, August 15, 2004, through 1.5.7, December 15, 2011, are
5845Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5846distributed according to the same disclaimer and license as libpng-1.2.5
5847with the following individual added to the list of Contributing Authors
5848
5849 Cosmin Truta
5850
5851libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5852Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5853distributed according to the same disclaimer and license as libpng-1.0.6
5854with the following individuals added to the list of Contributing Authors
5855
5856 Simon-Pierre Cadieux
5857 Eric S. Raymond
5858 Gilles Vollant
5859
5860and with the following additions to the disclaimer:
5861
5862 There is no warranty against interference with your
5863 enjoyment of the library or against infringement.
5864 There is no warranty that our efforts or the library
5865 will fulfill any of your particular purposes or needs.
5866 This library is provided with all faults, and the entire
5867 risk of satisfactory quality, performance, accuracy, and
5868 effort is with the user.
5869
5870libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5871Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5872Distributed according to the same disclaimer and license as libpng-0.96,
5873with the following individuals added to the list of Contributing Authors:
5874
5875 Tom Lane
5876 Glenn Randers-Pehrson
5877 Willem van Schaik
5878
5879libpng versions 0.89, June 1996, through 0.96, May 1997, are
5880Copyright (c) 1996, 1997 Andreas Dilger
5881Distributed according to the same disclaimer and license as libpng-0.88,
5882with the following individuals added to the list of Contributing Authors:
5883
5884 John Bowler
5885 Kevin Bracey
5886 Sam Bushell
5887 Magnus Holmgren
5888 Greg Roelofs
5889 Tom Tanner
5890
5891libpng versions 0.5, May 1995, through 0.88, January 1996, are
5892Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
5893
5894For the purposes of this copyright and license, "Contributing Authors"
5895is defined as the following set of individuals:
5896
5897 Andreas Dilger
5898 Dave Martindale
5899 Guy Eric Schalnat
5900 Paul Schmidt
5901 Tim Wegner
5902
5903The PNG Reference Library is supplied "AS IS". The Contributing Authors
5904and Group 42, Inc. disclaim all warranties, expressed or implied,
5905including, without limitation, the warranties of merchantability and of
5906fitness for any purpose. The Contributing Authors and Group 42, Inc.
5907assume no liability for direct, indirect, incidental, special, exemplary,
5908or consequential damages, which may result from the use of the PNG
5909Reference Library, even if advised of the possibility of such damage.
5910
5911Permission is hereby granted to use, copy, modify, and distribute this
5912source code, or portions hereof, for any purpose, without fee, subject
5913to the following restrictions:
5914
59151. The origin of this source code must not be misrepresented.
5916
59172. Altered versions must be plainly marked as such and
5918 must not be misrepresented as being the original source.
5919
59203. This Copyright notice may not be removed or altered from
5921 any source or altered source distribution.
5922
5923The Contributing Authors and Group 42, Inc. specifically permit, without
5924fee, and encourage the use of this source code as a component to
5925supporting the PNG file format in commercial products. If you use this
5926source code in a product, acknowledgment is not required but would be
5927appreciated.
5928
5929
5930A "png_get_copyright" function is available, for convenient use in "about"
5931boxes and the like:
5932
5933 printf("%s",png_get_copyright(NULL));
5934
5935Also, the PNG logo (in PNG format, of course) is supplied in the
5936files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
5937
5938Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
5939certification mark of the Open Source Initiative.
5940
5941Glenn Randers-Pehrson
5942glennrp at users.sourceforge.net
5943December 15, 2011
5944
5945.\" end of man page
5946
wxWidgets (Impactor)