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fix another memory leak in SetCommand() (coverity checker CID 52)
[wxWidgets.git] / src / png / libpng.3
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1.TH LIBPNG 3 "September 12, 2004"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.2.7
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\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
16
17\fI\fB
18
19\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
20
21\fI\fB
22
23\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
24
25\fI\fB
26
27\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
28
29\fI\fB
30
31\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
32
33\fI\fB
34
35\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
36
37\fI\fB
38
39\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
40
41\fI\fB
42
43\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
44
45\fI\fB
46
47\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
48
49\fI\fB
50
51\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
52
53\fI\fB
54
55\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
56
57\fI\fB
58
59\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
60
61\fI\fB
62
63\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
64
65\fI\fB
66
67\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
68
69\fI\fB
70
71\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
72
73\fI\fB
74
75\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
76
77\fI\fB
78
79\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
80
81\fI\fB
82
83\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
84
85\fI\fB
86
87\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
88
89\fI\fB
90
91\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
92
93\fI\fB
94
95\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
96
97\fI\fB
98
99\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
100
101\fI\fB
102
103\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
104
105\fI\fB
106
107\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
108
109\fI\fB
110
111\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
112
113\fI\fB
114
115\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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
116
117\fI\fB
118
119\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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
120
121\fI\fB
122
123\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
124
125\fI\fB
126
127\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
128
129\fI\fB
130
131\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
132
133\fI\fB
134
135\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
136
137\fI\fB
138
139\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
140
141\fI\fB
142
143\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
144
145\fI\fB
146
147\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
148
149\fI\fB
150
151\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
152
153\fI\fB
154
155\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
156
157\fI\fB
158
159\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
160
161\fI\fB
162
163\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
164
165\fI\fB
166
167\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
168
169\fI\fB
170
171\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
172
173\fI\fB
174
175\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
176
177\fI\fB
178
179\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
180
181\fI\fB
182
183\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
184
185\fI\fB
186
187\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
188
189\fI\fB
190
191\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
192
193\fI\fB
194
195\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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
196
197\fI\fB
198
199\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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
200
201\fI\fB
202
203\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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
204
205\fI\fB
206
207\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
208
209\fI\fB
210
211\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
212
213\fI\fB
214
215\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
216
217\fI\fB
218
219\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
220
221\fI\fB
222
223\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
224
225\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
226
227\fI\fB
228
229\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
230
231\fI\fB
232
233\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
234
235\fI\fB
236
237\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
238
239\fI\fB
240
241\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
242
243\fI\fB
244
245\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
246
247\fI\fB
248
249\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
250
251\fI\fB
252
253\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
254
255\fI\fB
256
257\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
258
259\fI\fB
260
261\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
262
263\fI\fB
264
265\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
266
267\fI\fB
268
269\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
270
271\fI\fB
272
273\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
274
275\fI\fB
276
277\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
278
279\fI\fB
280
281\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
282
283\fI\fB
284
285\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
286
287\fI\fB
288
289\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
290
291\fI\fB
292
293\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
294
295\fI\fB
296
297\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
298
299\fI\fB
300
301\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
302
303\fI\fB
304
305\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
306
307\fI\fB
308
309\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
310
311\fI\fB
312
313\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
314
315\fI\fB
316
317\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
318
319\fI\fB
320
321\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
322
323\fI\fB
324
325\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
326
327\fI\fB
328
329\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
330
331\fI\fB
332
333\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
334
335\fI\fB
336
337\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
338
339\fI\fB
340
341\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
342
343\fI\fB
344
345\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
346
347\fI\fB
348
349\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
350
351\fI\fB
352
353\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
354
355\fI\fB
356
357\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
358
359\fI\fB
360
361\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
362
363\fI\fB
364
365\fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
366
367\fI\fB
368
369\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
370
371\fI\fB
372
373\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
374
375\fI\fB
376
377\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
378
379\fI\fB
380
381\fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
382
383\fI\fB
384
385\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
386
387\fI\fB
388
389\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
390
391\fI\fB
392
393\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
394
395\fI\fB
396
397\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
398
399\fI\fB
400
401\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
402
403\fI\fB
404
405\fB#if \fI!defined(PNG_1_0_X)
406
407\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
408
409\fI\fB#endif
410
411\fI\fB
412
413\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
414
415\fI\fB
416
417\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
418
419\fI\fB
420
421\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
422
423\fI\fB
424
425\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
426
427\fI\fB
428
429\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
430
431\fI\fB
432
433\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
434
435\fI\fB
436
437\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
438
439\fI\fB
440
441\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
442
443\fI\fB
444
445\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
446
447\fI\fB
448
449\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
450
451\fI\fB
452
453\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
454
455\fI\fB
456
457\fBvoid png_set_dither (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_dither\fP\fB);\fP
458
459\fI\fB
460
461\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
462
463\fI\fB
464
465\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
466
467\fI\fB
468
469\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
470
471\fI\fB
472
473\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
474
475\fI\fB
476
477\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
478
479\fI\fB
480
481\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
482
483\fI\fB
484
485\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
486
487\fI\fB
488
489\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
490
491\fI\fB
492
493\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
494
495\fI\fB
496
497\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
498
499\fI\fB
500
501\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
502
503\fI\fB
504
505\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
506
507\fI\fB
508
509\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
510
511\fI\fB
512
513\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
514
515\fI\fB
516
517\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
518
519\fI\fB
520
521\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
522
523\fI\fB
524
525\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
526
527\fI\fB
528
529\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
530
531\fI\fB
532
533\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
534
535\fI\fB
536
537\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
538
539\fI\fB
540
541\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
542
543\fI\fB
544
545\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
546
547\fI\fB
548
549\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
550
551\fI\fB
552
553\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
554
555\fI\fB
556
557\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
558
559\fI\fB
560
561\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
562
563\fI\fB
564
565\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
566
567\fI\fB
568
569\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
570
571\fI\fB
572
573\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
574
575\fI\fB
576
577\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
578
579\fI\fB
580
581\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
582
583\fI\fB
584
585\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
586
587\fI\fB
588
589\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
590
591\fI\fB
592
593\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
594
595\fI\fB
596
597\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
598
599\fI\fB
600
601\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
602
603\fI\fB
604
605\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
606
607\fI\fB
608
609\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
610
611\fI\fB
612
613\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
614
615\fI\fB
616
617\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
618
619\fI\fB
620
621\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
622
623\fI\fB
624
625\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
626
627\fI\fB
628
629\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
630
631\fI\fB
632
633\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
634
635\fI\fB
636
637\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
638
639\fI\fB
640
641\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
642
643\fI\fB
644
645\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
646
647\fI\fB
648
649\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
650
651\fI\fB
652
653\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
654
655\fI\fB
656
657\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
658
659\fI\fB
660
661\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
662
663\fI\fB
664
665\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
666
667\fI\fB
668
669\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
670
671\fI\fB
672
673\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
674
675\fI\fB
676
677\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
678
679\fI\fB
680
681\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
682
683\fI\fB
684
685\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
686
687\fI\fB
688
689\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
690
691\fI\fB
692
693\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
694
695\fI\fB
696
697\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
698
699\fI\fB
700
701\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
702
703\fI\fB
704
705\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
706
707\fI\fB
708
709\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
710
711\fI\fB
712
713\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
714
715\fI\fB
716
717\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
718
719\fI\fB
720
721\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
722
723\fI\fB
724
725\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
726
727\fI\fB
728
729\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
730
731\fI\fB
732
733\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
734
735\fI\fB
736
737\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
738
739\fI\fB
740
741\fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
742
743\fI\fB
744
745\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
746
747\fI\fB
748
749\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
750
751\fI\fB
752
753\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
754
755\fI\fB
756
757\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
758
759\fI\fB
760
761\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
762
763\fI\fB
764
765\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
766
767\fI\fB
768
769\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
770
771\fI\fB
772
773.SH DESCRIPTION
774The
775.I libpng
776library supports encoding, decoding, and various manipulations of
777the Portable Network Graphics (PNG) format image files. It uses the
778.IR zlib(3)
779compression library.
780Following is a copy of the libpng.txt file that accompanies libpng.
781.SH LIBPNG.TXT
782libpng.txt - A description on how to use and modify libpng
783
784 libpng version 1.2.7 - September 12, 2004
785 Updated and distributed by Glenn Randers-Pehrson
786 <glennrp@users.sourceforge.net>
787 Copyright (c) 1998-2004 Glenn Randers-Pehrson
788 For conditions of distribution and use, see copyright
789 notice in png.h.
790
791 based on:
792
793 libpng 1.0 beta 6 version 0.96 May 28, 1997
794 Updated and distributed by Andreas Dilger
795 Copyright (c) 1996, 1997 Andreas Dilger
796
797 libpng 1.0 beta 2 - version 0.88 January 26, 1996
798 For conditions of distribution and use, see copyright
799 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
800 Schalnat, Group 42, Inc.
801
802 Updated/rewritten per request in the libpng FAQ
803 Copyright (c) 1995, 1996 Frank J. T. Wojcik
804 December 18, 1995 & January 20, 1996
805
806.SH I. Introduction
807
808This file describes how to use and modify the PNG reference library
809(known as libpng) for your own use. There are five sections to this
810file: introduction, structures, reading, writing, and modification and
811configuration notes for various special platforms. In addition to this
812file, example.c is a good starting point for using the library, as
813it is heavily commented and should include everything most people
814will need. We assume that libpng is already installed; see the
815INSTALL file for instructions on how to install libpng.
816
817Libpng was written as a companion to the PNG specification, as a way
818of reducing the amount of time and effort it takes to support the PNG
819file format in application programs.
820
821The PNG specification (second edition), November 2003, is available as
822a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
823<http://www.w3.org/TR/2003/REC-PNG-20031110/
824The W3C and ISO documents have identical technical content.
825
826The PNG-1.2 specification is available at
827<http://www.libpng.org/pub/png/documents/>
828
829The PNG-1.0 specification is available
830as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
831W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
832additional chunks are described in the special-purpose public chunks
833documents at <http://www.libpng.org/pub/png/documents/>.
834
835Other information
836about PNG, and the latest version of libpng, can be found at the PNG home
837page, <http://www.libpng.org/pub/png/>.
838
839Most users will not have to modify the library significantly; advanced
840users may want to modify it more. All attempts were made to make it as
841complete as possible, while keeping the code easy to understand.
842Currently, this library only supports C. Support for other languages
843is being considered.
844
845Libpng has been designed to handle multiple sessions at one time,
846to be easily modifiable, to be portable to the vast majority of
847machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
848to use. The ultimate goal of libpng is to promote the acceptance of
849the PNG file format in whatever way possible. While there is still
850work to be done (see the TODO file), libpng should cover the
851majority of the needs of its users.
852
853Libpng uses zlib for its compression and decompression of PNG files.
854Further information about zlib, and the latest version of zlib, can
855be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
856The zlib compression utility is a general purpose utility that is
857useful for more than PNG files, and can be used without libpng.
858See the documentation delivered with zlib for more details.
859You can usually find the source files for the zlib utility wherever you
860find the libpng source files.
861
862Libpng is thread safe, provided the threads are using different
863instances of the structures. Each thread should have its own
864png_struct and png_info instances, and thus its own image.
865Libpng does not protect itself against two threads using the
866same instance of a structure. Note: thread safety may be defeated
867by use of some of the MMX assembler code in pnggccrd.c, which is only
868compiled when the user defines PNG_THREAD_UNSAFE_OK.
869
870.SH II. Structures
871
872There are two main structures that are important to libpng, png_struct
873and png_info. The first, png_struct, is an internal structure that
874will not, for the most part, be used by a user except as the first
875variable passed to every libpng function call.
876
877The png_info structure is designed to provide information about the
878PNG file. At one time, the fields of png_info were intended to be
879directly accessible to the user. However, this tended to cause problems
880with applications using dynamically loaded libraries, and as a result
881a set of interface functions for png_info (the png_get_*() and png_set_*()
882functions) was developed. The fields of png_info are still available for
883older applications, but it is suggested that applications use the new
884interfaces if at all possible.
885
886Applications that do make direct access to the members of png_struct (except
887for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
888and applications that make direct access to the members of png_info must
889be recompiled if they were compiled or loaded with libpng version 1.0.6,
890in which the members were in a different order. In version 1.0.7, the
891members of the png_info structure reverted to the old order, as they were
892in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
893structures are going to be hidden, and the contents of the structures will
894only be accessible through the png_get/png_set functions.
895
896The png.h header file is an invaluable reference for programming with libpng.
897And while I'm on the topic, make sure you include the libpng header file:
898
899#include <png.h>
900
901.SH III. Reading
902
903We'll now walk you through the possible functions to call when reading
904in a PNG file sequentially, briefly explaining the syntax and purpose
905of each one. See example.c and png.h for more detail. While
906progressive reading is covered in the next section, you will still
907need some of the functions discussed in this section to read a PNG
908file.
909
910.SS Setup
911
912You will want to do the I/O initialization(*) before you get into libpng,
913so if it doesn't work, you don't have much to undo. Of course, you
914will also want to insure that you are, in fact, dealing with a PNG
915file. Libpng provides a simple check to see if a file is a PNG file.
916To use it, pass in the first 1 to 8 bytes of the file to the function
917png_sig_cmp(), and it will return 0 if the bytes match the corresponding
918bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
919you pass in, the greater the accuracy of the prediction.
920
921If you are intending to keep the file pointer open for use in libpng,
922you must ensure you don't read more than 8 bytes from the beginning
923of the file, and you also have to make a call to png_set_sig_bytes_read()
924with the number of bytes you read from the beginning. Libpng will
925then only check the bytes (if any) that your program didn't read.
926
927(*): If you are not using the standard I/O functions, you will need
928to replace them with custom functions. See the discussion under
929Customizing libpng.
930
931
932 FILE *fp = fopen(file_name, "rb");
933 if (!fp)
934 {
935 return (ERROR);
936 }
937 fread(header, 1, number, fp);
938 is_png = !png_sig_cmp(header, 0, number);
939 if (!is_png)
940 {
941 return (NOT_PNG);
942 }
943
944
945Next, png_struct and png_info need to be allocated and initialized. In
946order to ensure that the size of these structures is correct even with a
947dynamically linked libpng, there are functions to initialize and
948allocate the structures. We also pass the library version, optional
949pointers to error handling functions, and a pointer to a data struct for
950use by the error functions, if necessary (the pointer and functions can
951be NULL if the default error handlers are to be used). See the section
952on Changes to Libpng below regarding the old initialization functions.
953The structure allocation functions quietly return NULL if they fail to
954create the structure, so your application should check for that.
955
956 png_structp png_ptr = png_create_read_struct
957 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
958 user_error_fn, user_warning_fn);
959 if (!png_ptr)
960 return (ERROR);
961
962 png_infop info_ptr = png_create_info_struct(png_ptr);
963 if (!info_ptr)
964 {
965 png_destroy_read_struct(&png_ptr,
966 (png_infopp)NULL, (png_infopp)NULL);
967 return (ERROR);
968 }
969
970 png_infop end_info = png_create_info_struct(png_ptr);
971 if (!end_info)
972 {
973 png_destroy_read_struct(&png_ptr, &info_ptr,
974 (png_infopp)NULL);
975 return (ERROR);
976 }
977
978If you want to use your own memory allocation routines,
979define PNG_USER_MEM_SUPPORTED and use
980png_create_read_struct_2() instead of png_create_read_struct():
981
982 png_structp png_ptr = png_create_read_struct_2
983 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
984 user_error_fn, user_warning_fn, (png_voidp)
985 user_mem_ptr, user_malloc_fn, user_free_fn);
986
987The error handling routines passed to png_create_read_struct()
988and the memory alloc/free routines passed to png_create_struct_2()
989are only necessary if you are not using the libpng supplied error
990handling and memory alloc/free functions.
991
992When libpng encounters an error, it expects to longjmp back
993to your routine. Therefore, you will need to call setjmp and pass
994your png_jmpbuf(png_ptr). If you read the file from different
995routines, you will need to update the jmpbuf field every time you enter
996a new routine that will call a png_*() function.
997
998See your documentation of setjmp/longjmp for your compiler for more
999information on setjmp/longjmp. See the discussion on libpng error
1000handling in the Customizing Libpng section below for more information
1001on the libpng error handling. If an error occurs, and libpng longjmp's
1002back to your setjmp, you will want to call png_destroy_read_struct() to
1003free any memory.
1004
1005 if (setjmp(png_jmpbuf(png_ptr)))
1006 {
1007 png_destroy_read_struct(&png_ptr, &info_ptr,
1008 &end_info);
1009 fclose(fp);
1010 return (ERROR);
1011 }
1012
1013If you would rather avoid the complexity of setjmp/longjmp issues,
1014you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1015errors will result in a call to PNG_ABORT() which defaults to abort().
1016
1017Now you need to set up the input code. The default for libpng is to
1018use the C function fread(). If you use this, you will need to pass a
1019valid FILE * in the function png_init_io(). Be sure that the file is
1020opened in binary mode. If you wish to handle reading data in another
1021way, you need not call the png_init_io() function, but you must then
1022implement the libpng I/O methods discussed in the Customizing Libpng
1023section below.
1024
1025 png_init_io(png_ptr, fp);
1026
1027If you had previously opened the file and read any of the signature from
1028the beginning in order to see if this was a PNG file, you need to let
1029libpng know that there are some bytes missing from the start of the file.
1030
1031 png_set_sig_bytes(png_ptr, number);
1032
1033.SS Setting up callback code
1034
1035You can set up a callback function to handle any unknown chunks in the
1036input stream. You must supply the function
1037
1038 read_chunk_callback(png_ptr ptr,
1039 png_unknown_chunkp chunk);
1040 {
1041 /* The unknown chunk structure contains your
1042 chunk data: */
1043 png_byte name[5];
1044 png_byte *data;
1045 png_size_t size;
1046 /* Note that libpng has already taken care of
1047 the CRC handling */
1048
1049 /* put your code here. Return one of the
1050 following: */
1051
1052 return (-n); /* chunk had an error */
1053 return (0); /* did not recognize */
1054 return (n); /* success */
1055 }
1056
1057(You can give your function another name that you like instead of
1058"read_chunk_callback")
1059
1060To inform libpng about your function, use
1061
1062 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1063 read_chunk_callback);
1064
1065This names not only the callback function, but also a user pointer that
1066you can retrieve with
1067
1068 png_get_user_chunk_ptr(png_ptr);
1069
1070At this point, you can set up a callback function that will be
1071called after each row has been read, which you can use to control
1072a progress meter or the like. It's demonstrated in pngtest.c.
1073You must supply a function
1074
1075 void read_row_callback(png_ptr ptr, png_uint_32 row,
1076 int pass);
1077 {
1078 /* put your code here */
1079 }
1080
1081(You can give it another name that you like instead of "read_row_callback")
1082
1083To inform libpng about your function, use
1084
1085 png_set_read_status_fn(png_ptr, read_row_callback);
1086
1087.SS Width and height limits
1088
1089The PNG specification allows the width and height of an image to be as
1090large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1091Since very few applications really need to process such large images,
1092we have imposed an arbitrary 1-million limit on rows and columns.
1093Larger images will be rejected immediately with a png_error() call. If
1094you wish to override this limit, you can use
1095
1096 png_set_user_limits(png_ptr, width_max, height_max);
1097
1098to set your own limits, or use width_max = height_max = 0x7fffffffL
1099to allow all valid dimensions (libpng may reject some very large images
1100anyway because of potential buffer overflow conditions).
1101
1102You should put this statement after you create the PNG structure and
1103before calling png_read_info(), png_read_png(), or png_process_data().
1104If you need to retrieve the limits that are being applied, use
1105
1106 width_max = png_get_user_width_max(png_ptr);
1107 height_max = png_get_user_height_max(png_ptr);
1108
1109.SS Unknown-chunk handling
1110
1111Now you get to set the way the library processes unknown chunks in the
1112input PNG stream. Both known and unknown chunks will be read. Normal
1113behavior is that known chunks will be parsed into information in
1114various info_ptr members; unknown chunks will be discarded. To change
1115this, you can call:
1116
1117 png_set_keep_unknown_chunks(png_ptr, keep,
1118 chunk_list, num_chunks);
1119 keep - 0: do not handle as unknown
1120 1: do not keep
1121 2: keep only if safe-to-copy
1122 3: keep even if unsafe-to-copy
1123 You can use these definitions:
1124 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1125 PNG_HANDLE_CHUNK_NEVER 1
1126 PNG_HANDLE_CHUNK_IF_SAFE 2
1127 PNG_HANDLE_CHUNK_ALWAYS 3
1128 chunk_list - list of chunks affected (a byte string,
1129 five bytes per chunk, NULL or '\0' if
1130 num_chunks is 0)
1131 num_chunks - number of chunks affected; if 0, all
1132 unknown chunks are affected. If nonzero,
1133 only the chunks in the list are affected
1134
1135Unknown chunks declared in this way will be saved as raw data onto a
1136list of png_unknown_chunk structures. If a chunk that is normally
1137known to libpng is named in the list, it will be handled as unknown,
1138according to the "keep" directive. If a chunk is named in successive
1139instances of png_set_keep_unknown_chunks(), the final instance will
1140take precedence. The IHDR and IEND chunks should not be named in
1141chunk_list; if they are, libpng will process them normally anyway.
1142
1143.SS The high-level read interface
1144
1145At this point there are two ways to proceed; through the high-level
1146read interface, or through a sequence of low-level read operations.
1147You can use the high-level interface if (a) you are willing to read
1148the entire image into memory, and (b) the input transformations
1149you want to do are limited to the following set:
1150
1151 PNG_TRANSFORM_IDENTITY No transformation
1152 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1153 8 bits
1154 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1155 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1156 samples to bytes
1157 PNG_TRANSFORM_PACKSWAP Change order of packed
1158 pixels to LSB first
1159 PNG_TRANSFORM_EXPAND Perform set_expand()
1160 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1161 PNG_TRANSFORM_SHIFT Normalize pixels to the
1162 sBIT depth
1163 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1164 to BGRA
1165 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1166 to AG
1167 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1168 to transparency
1169 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1170
1171(This excludes setting a background color, doing gamma transformation,
1172dithering, and setting filler.) If this is the case, simply do this:
1173
1174 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1175
1176where png_transforms is an integer containing the logical OR of
1177some set of transformation flags. This call is equivalent to png_read_info(),
1178followed the set of transformations indicated by the transform mask,
1179then png_read_image(), and finally png_read_end().
1180
1181(The final parameter of this call is not yet used. Someday it might point
1182to transformation parameters required by some future input transform.)
1183
1184You must use png_transforms and not call any png_set_transform() functions
1185when you use png_read_png().
1186
1187After you have called png_read_png(), you can retrieve the image data
1188with
1189
1190 row_pointers = png_get_rows(png_ptr, info_ptr);
1191
1192where row_pointers is an array of pointers to the pixel data for each row:
1193
1194 png_bytep row_pointers[height];
1195
1196If you know your image size and pixel size ahead of time, you can allocate
1197row_pointers prior to calling png_read_png() with
1198
1199 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1200 png_error (png_ptr,
1201 "Image is too tall to process in memory");
1202 if (width > PNG_UINT_32_MAX/pixel_size)
1203 png_error (png_ptr,
1204 "Image is too wide to process in memory");
1205 row_pointers = png_malloc(png_ptr,
1206 height*png_sizeof(png_bytep));
1207 for (int i=0; i<height, i++)
1208 row_pointers[i]=png_malloc(png_ptr,
1209 width*pixel_size);
1210 png_set_rows(png_ptr, info_ptr, &row_pointers);
1211
1212Alternatively you could allocate your image in one big block and define
1213row_pointers[i] to point into the proper places in your block.
1214
1215If you use png_set_rows(), the application is responsible for freeing
1216row_pointers (and row_pointers[i], if they were separately allocated).
1217
1218If you don't allocate row_pointers ahead of time, png_read_png() will
1219do it, and it'll be free'ed when you call png_destroy_*().
1220
1221.SS The low-level read interface
1222
1223If you are going the low-level route, you are now ready to read all
1224the file information up to the actual image data. You do this with a
1225call to png_read_info().
1226
1227 png_read_info(png_ptr, info_ptr);
1228
1229This will process all chunks up to but not including the image data.
1230
1231.SS Querying the info structure
1232
1233Functions are used to get the information from the info_ptr once it
1234has been read. Note that these fields may not be completely filled
1235in until png_read_end() has read the chunk data following the image.
1236
1237 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1238 &bit_depth, &color_type, &interlace_type,
1239 &compression_type, &filter_method);
1240
1241 width - holds the width of the image
1242 in pixels (up to 2^31).
1243 height - holds the height of the image
1244 in pixels (up to 2^31).
1245 bit_depth - holds the bit depth of one of the
1246 image channels. (valid values are
1247 1, 2, 4, 8, 16 and depend also on
1248 the color_type. See also
1249 significant bits (sBIT) below).
1250 color_type - describes which color/alpha channels
1251 are present.
1252 PNG_COLOR_TYPE_GRAY
1253 (bit depths 1, 2, 4, 8, 16)
1254 PNG_COLOR_TYPE_GRAY_ALPHA
1255 (bit depths 8, 16)
1256 PNG_COLOR_TYPE_PALETTE
1257 (bit depths 1, 2, 4, 8)
1258 PNG_COLOR_TYPE_RGB
1259 (bit_depths 8, 16)
1260 PNG_COLOR_TYPE_RGB_ALPHA
1261 (bit_depths 8, 16)
1262
1263 PNG_COLOR_MASK_PALETTE
1264 PNG_COLOR_MASK_COLOR
1265 PNG_COLOR_MASK_ALPHA
1266
1267 filter_method - (must be PNG_FILTER_TYPE_BASE
1268 for PNG 1.0, and can also be
1269 PNG_INTRAPIXEL_DIFFERENCING if
1270 the PNG datastream is embedded in
1271 a MNG-1.0 datastream)
1272 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1273 for PNG 1.0)
1274 interlace_type - (PNG_INTERLACE_NONE or
1275 PNG_INTERLACE_ADAM7)
1276 Any or all of interlace_type, compression_type, of
1277 filter_method can be NULL if you are
1278 not interested in their values.
1279
1280 channels = png_get_channels(png_ptr, info_ptr);
1281 channels - number of channels of info for the
1282 color type (valid values are 1 (GRAY,
1283 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1284 4 (RGB_ALPHA or RGB + filler byte))
1285 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1286 rowbytes - number of bytes needed to hold a row
1287
1288 signature = png_get_signature(png_ptr, info_ptr);
1289 signature - holds the signature read from the
1290 file (if any). The data is kept in
1291 the same offset it would be if the
1292 whole signature were read (i.e. if an
1293 application had already read in 4
1294 bytes of signature before starting
1295 libpng, the remaining 4 bytes would
1296 be in signature[4] through signature[7]
1297 (see png_set_sig_bytes())).
1298
1299
1300 width = png_get_image_width(png_ptr,
1301 info_ptr);
1302 height = png_get_image_height(png_ptr,
1303 info_ptr);
1304 bit_depth = png_get_bit_depth(png_ptr,
1305 info_ptr);
1306 color_type = png_get_color_type(png_ptr,
1307 info_ptr);
1308 filter_method = png_get_filter_type(png_ptr,
1309 info_ptr);
1310 compression_type = png_get_compression_type(png_ptr,
1311 info_ptr);
1312 interlace_type = png_get_interlace_type(png_ptr,
1313 info_ptr);
1314
1315
1316These are also important, but their validity depends on whether the chunk
1317has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1318png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1319data has been read, or zero if it is missing. The parameters to the
1320png_get_<chunk> are set directly if they are simple data types, or a pointer
1321into the info_ptr is returned for any complex types.
1322
1323 png_get_PLTE(png_ptr, info_ptr, &palette,
1324 &num_palette);
1325 palette - the palette for the file
1326 (array of png_color)
1327 num_palette - number of entries in the palette
1328
1329 png_get_gAMA(png_ptr, info_ptr, &gamma);
1330 gamma - the gamma the file is written
1331 at (PNG_INFO_gAMA)
1332
1333 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1334 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1335 The presence of the sRGB chunk
1336 means that the pixel data is in the
1337 sRGB color space. This chunk also
1338 implies specific values of gAMA and
1339 cHRM.
1340
1341 png_get_iCCP(png_ptr, info_ptr, &name,
1342 &compression_type, &profile, &proflen);
1343 name - The profile name.
1344 compression - The compression type; always
1345 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1346 You may give NULL to this argument to
1347 ignore it.
1348 profile - International Color Consortium color
1349 profile data. May contain NULs.
1350 proflen - length of profile data in bytes.
1351
1352 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1353 sig_bit - the number of significant bits for
1354 (PNG_INFO_sBIT) each of the gray,
1355 red, green, and blue channels,
1356 whichever are appropriate for the
1357 given color type (png_color_16)
1358
1359 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1360 &trans_values);
1361 trans - array of transparent entries for
1362 palette (PNG_INFO_tRNS)
1363 trans_values - graylevel or color sample values of
1364 the single transparent color for
1365 non-paletted images (PNG_INFO_tRNS)
1366 num_trans - number of transparent entries
1367 (PNG_INFO_tRNS)
1368
1369 png_get_hIST(png_ptr, info_ptr, &hist);
1370 (PNG_INFO_hIST)
1371 hist - histogram of palette (array of
1372 png_uint_16)
1373
1374 png_get_tIME(png_ptr, info_ptr, &mod_time);
1375 mod_time - time image was last modified
1376 (PNG_VALID_tIME)
1377
1378 png_get_bKGD(png_ptr, info_ptr, &background);
1379 background - background color (PNG_VALID_bKGD)
1380 valid 16-bit red, green and blue
1381 values, regardless of color_type
1382
1383 num_comments = png_get_text(png_ptr, info_ptr,
1384 &text_ptr, &num_text);
1385 num_comments - number of comments
1386 text_ptr - array of png_text holding image
1387 comments
1388 text_ptr[i].compression - type of compression used
1389 on "text" PNG_TEXT_COMPRESSION_NONE
1390 PNG_TEXT_COMPRESSION_zTXt
1391 PNG_ITXT_COMPRESSION_NONE
1392 PNG_ITXT_COMPRESSION_zTXt
1393 text_ptr[i].key - keyword for comment. Must contain
1394 1-79 characters.
1395 text_ptr[i].text - text comments for current
1396 keyword. Can be empty.
1397 text_ptr[i].text_length - length of text string,
1398 after decompression, 0 for iTXt
1399 text_ptr[i].itxt_length - length of itxt string,
1400 after decompression, 0 for tEXt/zTXt
1401 text_ptr[i].lang - language of comment (empty
1402 string for unknown).
1403 text_ptr[i].lang_key - keyword in UTF-8
1404 (empty string for unknown).
1405 num_text - number of comments (same as
1406 num_comments; you can put NULL here
1407 to avoid the duplication)
1408 Note while png_set_text() will accept text, language,
1409 and translated keywords that can be NULL pointers, the
1410 structure returned by png_get_text will always contain
1411 regular zero-terminated C strings. They might be
1412 empty strings but they will never be NULL pointers.
1413
1414 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1415 &palette_ptr);
1416 palette_ptr - array of palette structures holding
1417 contents of one or more sPLT chunks
1418 read.
1419 num_spalettes - number of sPLT chunks read.
1420
1421 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1422 &unit_type);
1423 offset_x - positive offset from the left edge
1424 of the screen
1425 offset_y - positive offset from the top edge
1426 of the screen
1427 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1428
1429 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1430 &unit_type);
1431 res_x - pixels/unit physical resolution in
1432 x direction
1433 res_y - pixels/unit physical resolution in
1434 x direction
1435 unit_type - PNG_RESOLUTION_UNKNOWN,
1436 PNG_RESOLUTION_METER
1437
1438 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1439 &height)
1440 unit - physical scale units (an integer)
1441 width - width of a pixel in physical scale units
1442 height - height of a pixel in physical scale units
1443 (width and height are doubles)
1444
1445 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1446 &height)
1447 unit - physical scale units (an integer)
1448 width - width of a pixel in physical scale units
1449 height - height of a pixel in physical scale units
1450 (width and height are strings like "2.54")
1451
1452 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1453 info_ptr, &unknowns)
1454 unknowns - array of png_unknown_chunk
1455 structures holding unknown chunks
1456 unknowns[i].name - name of unknown chunk
1457 unknowns[i].data - data of unknown chunk
1458 unknowns[i].size - size of unknown chunk's data
1459 unknowns[i].location - position of chunk in file
1460
1461 The value of "i" corresponds to the order in which the
1462 chunks were read from the PNG file or inserted with the
1463 png_set_unknown_chunks() function.
1464
1465The data from the pHYs chunk can be retrieved in several convenient
1466forms:
1467
1468 res_x = png_get_x_pixels_per_meter(png_ptr,
1469 info_ptr)
1470 res_y = png_get_y_pixels_per_meter(png_ptr,
1471 info_ptr)
1472 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1473 info_ptr)
1474 res_x = png_get_x_pixels_per_inch(png_ptr,
1475 info_ptr)
1476 res_y = png_get_y_pixels_per_inch(png_ptr,
1477 info_ptr)
1478 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1479 info_ptr)
1480 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1481 info_ptr)
1482
1483 (Each of these returns 0 [signifying "unknown"] if
1484 the data is not present or if res_x is 0;
1485 res_x_and_y is 0 if res_x != res_y)
1486
1487The data from the oFFs chunk can be retrieved in several convenient
1488forms:
1489
1490 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1491 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1492 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1493 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1494
1495 (Each of these returns 0 [signifying "unknown" if both
1496 x and y are 0] if the data is not present or if the
1497 chunk is present but the unit is the pixel)
1498
1499For more information, see the png_info definition in png.h and the
1500PNG specification for chunk contents. Be careful with trusting
1501rowbytes, as some of the transformations could increase the space
1502needed to hold a row (expand, filler, gray_to_rgb, etc.).
1503See png_read_update_info(), below.
1504
1505A quick word about text_ptr and num_text. PNG stores comments in
1506keyword/text pairs, one pair per chunk, with no limit on the number
1507of text chunks, and a 2^31 byte limit on their size. While there are
1508suggested keywords, there is no requirement to restrict the use to these
1509strings. It is strongly suggested that keywords and text be sensible
1510to humans (that's the point), so don't use abbreviations. Non-printing
1511symbols are not allowed. See the PNG specification for more details.
1512There is also no requirement to have text after the keyword.
1513
1514Keywords should be limited to 79 Latin-1 characters without leading or
1515trailing spaces, but non-consecutive spaces are allowed within the
1516keyword. It is possible to have the same keyword any number of times.
1517The text_ptr is an array of png_text structures, each holding a
1518pointer to a language string, a pointer to a keyword and a pointer to
1519a text string. The text string, language code, and translated
1520keyword may be empty or NULL pointers. The keyword/text
1521pairs are put into the array in the order that they are received.
1522However, some or all of the text chunks may be after the image, so, to
1523make sure you have read all the text chunks, don't mess with these
1524until after you read the stuff after the image. This will be
1525mentioned again below in the discussion that goes with png_read_end().
1526
1527.SS Input transformations
1528
1529After you've read the header information, you can set up the library
1530to handle any special transformations of the image data. The various
1531ways to transform the data will be described in the order that they
1532should occur. This is important, as some of these change the color
1533type and/or bit depth of the data, and some others only work on
1534certain color types and bit depths. Even though each transformation
1535checks to see if it has data that it can do something with, you should
1536make sure to only enable a transformation if it will be valid for the
1537data. For example, don't swap red and blue on grayscale data.
1538
1539The colors used for the background and transparency values should be
1540supplied in the same format/depth as the current image data. They
1541are stored in the same format/depth as the image data in a bKGD or tRNS
1542chunk, so this is what libpng expects for this data. The colors are
1543transformed to keep in sync with the image data when an application
1544calls the png_read_update_info() routine (see below).
1545
1546Data will be decoded into the supplied row buffers packed into bytes
1547unless the library has been told to transform it into another format.
1548For example, 4 bit/pixel paletted or grayscale data will be returned
15492 pixels/byte with the leftmost pixel in the high-order bits of the
1550byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1551in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1552is called to insert filler bytes, either before or after each RGB triplet.
155316-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1554byte of the color value first, unless png_set_strip_16() is called to
1555transform it to regular RGB RGB triplets, or png_set_filler|add alpha()
1556is called to insert filler bytes, either before or after each RRGGBB
1557triplet. Similarly, 8-bit or 16-bit grayscale data can be modified with
1558png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1559
1560The following code transforms grayscale images of less than 8 to 8 bits,
1561changes paletted images to RGB, and adds a full alpha channel if there is
1562transparency information in a tRNS chunk. This is most useful on
1563grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1564viewing application that wishes to treat all images in the same way.
1565
1566 if (color_type == PNG_COLOR_TYPE_PALETTE)
1567 png_set_palette_to_rgb(png_ptr);
1568
1569 if (color_type == PNG_COLOR_TYPE_GRAY &&
1570 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1571
1572 if (png_get_valid(png_ptr, info_ptr,
1573 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1574
1575These three functions are actually aliases for png_set_expand(), added
1576in libpng version 1.0.4, with the function names expanded to improve code
1577readability. In some future version they may actually do different
1578things.
1579
1580PNG can have files with 16 bits per channel. If you only can handle
15818 bits per channel, this will strip the pixels down to 8 bit.
1582
1583 if (bit_depth == 16)
1584 png_set_strip_16(png_ptr);
1585
1586If, for some reason, you don't need the alpha channel on an image,
1587and you want to remove it rather than combining it with the background
1588(but the image author certainly had in mind that you *would* combine
1589it with the background, so that's what you should probably do):
1590
1591 if (color_type & PNG_COLOR_MASK_ALPHA)
1592 png_set_strip_alpha(png_ptr);
1593
1594In PNG files, the alpha channel in an image
1595is the level of opacity. If you need the alpha channel in an image to
1596be the level of transparency instead of opacity, you can invert the
1597alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1598fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1599images) is fully transparent, with
1600
1601 png_set_invert_alpha(png_ptr);
1602
1603PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1604they can, resulting in, for example, 8 pixels per byte for 1 bit
1605files. This code expands to 1 pixel per byte without changing the
1606values of the pixels:
1607
1608 if (bit_depth < 8)
1609 png_set_packing(png_ptr);
1610
1611PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1612stored in a PNG image have been "scaled" or "shifted" up to the next
1613higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
16148 bits/sample in the range [0, 255]). However, it is also possible to
1615convert the PNG pixel data back to the original bit depth of the image.
1616This call reduces the pixels back down to the original bit depth:
1617
1618 png_color_8p sig_bit;
1619
1620 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1621 png_set_shift(png_ptr, sig_bit);
1622
1623PNG files store 3-color pixels in red, green, blue order. This code
1624changes the storage of the pixels to blue, green, red:
1625
1626 if (color_type == PNG_COLOR_TYPE_RGB ||
1627 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1628 png_set_bgr(png_ptr);
1629
1630PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1631into 4 or 8 bytes for windowing systems that need them in this format:
1632
1633 if (color_type == PNG_COLOR_TYPE_RGB)
1634 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1635
1636where "filler" is the 8 or 16-bit number to fill with, and the location is
1637either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1638you want the filler before the RGB or after. This transformation
1639does not affect images that already have full alpha channels. To add an
1640opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1641will generate RGBA pixels.
1642
1643Note that png_set_filler() does not change the color type. If you want
1644to do that, you can add a true alpha channel with
1645
1646 if (color_type == PNG_COLOR_TYPE_RGB ||
1647 color_type == PNG_COLOR_TYPE_GRAY)
1648 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1649
1650where "filler" contains the alpha value to assign to each pixel.
1651This function became available in libpng-1.2.7.
1652
1653If you are reading an image with an alpha channel, and you need the
1654data as ARGB instead of the normal PNG format RGBA:
1655
1656 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1657 png_set_swap_alpha(png_ptr);
1658
1659For some uses, you may want a grayscale image to be represented as
1660RGB. This code will do that conversion:
1661
1662 if (color_type == PNG_COLOR_TYPE_GRAY ||
1663 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1664 png_set_gray_to_rgb(png_ptr);
1665
1666Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1667with alpha.
1668
1669 if (color_type == PNG_COLOR_TYPE_RGB ||
1670 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1671 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1672 int red_weight, int green_weight);
1673
1674 error_action = 1: silently do the conversion
1675 error_action = 2: issue a warning if the original
1676 image has any pixel where
1677 red != green or red != blue
1678 error_action = 3: issue an error and abort the
1679 conversion if the original
1680 image has any pixel where
1681 red != green or red != blue
1682
1683 red_weight: weight of red component times 100000
1684 green_weight: weight of green component times 100000
1685 If either weight is negative, default
1686 weights (21268, 71514) are used.
1687
1688If you have set error_action = 1 or 2, you can
1689later check whether the image really was gray, after processing
1690the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1691It will return a png_byte that is zero if the image was gray or
16921 if there were any non-gray pixels. bKGD and sBIT data
1693will be silently converted to grayscale, using the green channel
1694data, regardless of the error_action setting.
1695
1696With red_weight+green_weight<=100000,
1697the normalized graylevel is computed:
1698
1699 int rw = red_weight * 65536;
1700 int gw = green_weight * 65536;
1701 int bw = 65536 - (rw + gw);
1702 gray = (rw*red + gw*green + bw*blue)/65536;
1703
1704The default values approximate those recommended in the Charles
1705Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1706Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1707
1708 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1709
1710Libpng approximates this with
1711
1712 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1713
1714which can be expressed with integers as
1715
1716 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1717
1718The calculation is done in a linear colorspace, if the image gamma
1719is known.
1720
1721If you have a grayscale and you are using png_set_expand_depth(),
1722png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1723a higher bit-depth, you must either supply the background color as a gray
1724value at the original file bit-depth (need_expand = 1) or else supply the
1725background color as an RGB triplet at the final, expanded bit depth
1726(need_expand = 0). Similarly, if you are reading a paletted image, you
1727must either supply the background color as a palette index (need_expand = 1)
1728or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1729
1730 png_color_16 my_background;
1731 png_color_16p image_background;
1732
1733 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1734 png_set_background(png_ptr, image_background,
1735 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1736 else
1737 png_set_background(png_ptr, &my_background,
1738 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1739
1740The png_set_background() function tells libpng to composite images
1741with alpha or simple transparency against the supplied background
1742color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1743you may use this color, or supply another color more suitable for
1744the current display (e.g., the background color from a web page). You
1745need to tell libpng whether the color is in the gamma space of the
1746display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1747(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1748that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1749know why anyone would use this, but it's here).
1750
1751To properly display PNG images on any kind of system, the application needs
1752to know what the display gamma is. Ideally, the user will know this, and
1753the application will allow them to set it. One method of allowing the user
1754to set the display gamma separately for each system is to check for a
1755SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1756correctly set.
1757
1758Note that display_gamma is the overall gamma correction required to produce
1759pleasing results, which depends on the lighting conditions in the surrounding
1760environment. In a dim or brightly lit room, no compensation other than
1761the physical gamma exponent of the monitor is needed, while in a dark room
1762a slightly smaller exponent is better.
1763
1764 double gamma, screen_gamma;
1765
1766 if (/* We have a user-defined screen
1767 gamma value */)
1768 {
1769 screen_gamma = user_defined_screen_gamma;
1770 }
1771 /* One way that applications can share the same
1772 screen gamma value */
1773 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1774 != NULL)
1775 {
1776 screen_gamma = (double)atof(gamma_str);
1777 }
1778 /* If we don't have another value */
1779 else
1780 {
1781 screen_gamma = 2.2; /* A good guess for a
1782 PC monitor in a bright office or a dim room */
1783 screen_gamma = 2.0; /* A good guess for a
1784 PC monitor in a dark room */
1785 screen_gamma = 1.7 or 1.0; /* A good
1786 guess for Mac systems */
1787 }
1788
1789The png_set_gamma() function handles gamma transformations of the data.
1790Pass both the file gamma and the current screen_gamma. If the file does
1791not have a gamma value, you can pass one anyway if you have an idea what
1792it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1793that file gammas are inverted from screen gammas. See the discussions
1794on gamma in the PNG specification for an excellent description of what
1795gamma is, and why all applications should support it. It is strongly
1796recommended that PNG viewers support gamma correction.
1797
1798 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1799 png_set_gamma(png_ptr, screen_gamma, gamma);
1800 else
1801 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1802
1803If you need to reduce an RGB file to a paletted file, or if a paletted
1804file has more entries then will fit on your screen, png_set_dither()
1805will do that. Note that this is a simple match dither that merely
1806finds the closest color available. This should work fairly well with
1807optimized palettes, and fairly badly with linear color cubes. If you
1808pass a palette that is larger then maximum_colors, the file will
1809reduce the number of colors in the palette so it will fit into
1810maximum_colors. If there is a histogram, it will use it to make
1811more intelligent choices when reducing the palette. If there is no
1812histogram, it may not do as good a job.
1813
1814 if (color_type & PNG_COLOR_MASK_COLOR)
1815 {
1816 if (png_get_valid(png_ptr, info_ptr,
1817 PNG_INFO_PLTE))
1818 {
1819 png_uint_16p histogram = NULL;
1820
1821 png_get_hIST(png_ptr, info_ptr,
1822 &histogram);
1823 png_set_dither(png_ptr, palette, num_palette,
1824 max_screen_colors, histogram, 1);
1825 }
1826 else
1827 {
1828 png_color std_color_cube[MAX_SCREEN_COLORS] =
1829 { ... colors ... };
1830
1831 png_set_dither(png_ptr, std_color_cube,
1832 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1833 NULL,0);
1834 }
1835 }
1836
1837PNG files describe monochrome as black being zero and white being one.
1838The following code will reverse this (make black be one and white be
1839zero):
1840
1841 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1842 png_set_invert_mono(png_ptr);
1843
1844This function can also be used to invert grayscale and gray-alpha images:
1845
1846 if (color_type == PNG_COLOR_TYPE_GRAY ||
1847 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1848 png_set_invert_mono(png_ptr);
1849
1850PNG files store 16 bit pixels in network byte order (big-endian,
1851ie. most significant bits first). This code changes the storage to the
1852other way (little-endian, i.e. least significant bits first, the
1853way PCs store them):
1854
1855 if (bit_depth == 16)
1856 png_set_swap(png_ptr);
1857
1858If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1859need to change the order the pixels are packed into bytes, you can use:
1860
1861 if (bit_depth < 8)
1862 png_set_packswap(png_ptr);
1863
1864Finally, you can write your own transformation function if none of
1865the existing ones meets your needs. This is done by setting a callback
1866with
1867
1868 png_set_read_user_transform_fn(png_ptr,
1869 read_transform_fn);
1870
1871You must supply the function
1872
1873 void read_transform_fn(png_ptr ptr, row_info_ptr
1874 row_info, png_bytep data)
1875
1876See pngtest.c for a working example. Your function will be called
1877after all of the other transformations have been processed.
1878
1879You can also set up a pointer to a user structure for use by your
1880callback function, and you can inform libpng that your transform
1881function will change the number of channels or bit depth with the
1882function
1883
1884 png_set_user_transform_info(png_ptr, user_ptr,
1885 user_depth, user_channels);
1886
1887The user's application, not libpng, is responsible for allocating and
1888freeing any memory required for the user structure.
1889
1890You can retrieve the pointer via the function
1891png_get_user_transform_ptr(). For example:
1892
1893 voidp read_user_transform_ptr =
1894 png_get_user_transform_ptr(png_ptr);
1895
1896The last thing to handle is interlacing; this is covered in detail below,
1897but you must call the function here if you want libpng to handle expansion
1898of the interlaced image.
1899
1900 number_of_passes = png_set_interlace_handling(png_ptr);
1901
1902After setting the transformations, libpng can update your png_info
1903structure to reflect any transformations you've requested with this
1904call. This is most useful to update the info structure's rowbytes
1905field so you can use it to allocate your image memory. This function
1906will also update your palette with the correct screen_gamma and
1907background if these have been given with the calls above.
1908
1909 png_read_update_info(png_ptr, info_ptr);
1910
1911After you call png_read_update_info(), you can allocate any
1912memory you need to hold the image. The row data is simply
1913raw byte data for all forms of images. As the actual allocation
1914varies among applications, no example will be given. If you
1915are allocating one large chunk, you will need to build an
1916array of pointers to each row, as it will be needed for some
1917of the functions below.
1918
1919.SS Reading image data
1920
1921After you've allocated memory, you can read the image data.
1922The simplest way to do this is in one function call. If you are
1923allocating enough memory to hold the whole image, you can just
1924call png_read_image() and libpng will read in all the image data
1925and put it in the memory area supplied. You will need to pass in
1926an array of pointers to each row.
1927
1928This function automatically handles interlacing, so you don't need
1929to call png_set_interlace_handling() or call this function multiple
1930times, or any of that other stuff necessary with png_read_rows().
1931
1932 png_read_image(png_ptr, row_pointers);
1933
1934where row_pointers is:
1935
1936 png_bytep row_pointers[height];
1937
1938You can point to void or char or whatever you use for pixels.
1939
1940If you don't want to read in the whole image at once, you can
1941use png_read_rows() instead. If there is no interlacing (check
1942interlace_type == PNG_INTERLACE_NONE), this is simple:
1943
1944 png_read_rows(png_ptr, row_pointers, NULL,
1945 number_of_rows);
1946
1947where row_pointers is the same as in the png_read_image() call.
1948
1949If you are doing this just one row at a time, you can do this with
1950a single row_pointer instead of an array of row_pointers:
1951
1952 png_bytep row_pointer = row;
1953 png_read_row(png_ptr, row_pointer, NULL);
1954
1955If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1956get somewhat harder. The only current (PNG Specification version 1.2)
1957interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1958is a somewhat complicated 2D interlace scheme, known as Adam7, that
1959breaks down an image into seven smaller images of varying size, based
1960on an 8x8 grid.
1961
1962libpng can fill out those images or it can give them to you "as is".
1963If you want them filled out, there are two ways to do that. The one
1964mentioned in the PNG specification is to expand each pixel to cover
1965those pixels that have not been read yet (the "rectangle" method).
1966This results in a blocky image for the first pass, which gradually
1967smooths out as more pixels are read. The other method is the "sparkle"
1968method, where pixels are drawn only in their final locations, with the
1969rest of the image remaining whatever colors they were initialized to
1970before the start of the read. The first method usually looks better,
1971but tends to be slower, as there are more pixels to put in the rows.
1972
1973If you don't want libpng to handle the interlacing details, just call
1974png_read_rows() seven times to read in all seven images. Each of the
1975images is a valid image by itself, or they can all be combined on an
19768x8 grid to form a single image (although if you intend to combine them
1977you would be far better off using the libpng interlace handling).
1978
1979The first pass will return an image 1/8 as wide as the entire image
1980(every 8th column starting in column 0) and 1/8 as high as the original
1981(every 8th row starting in row 0), the second will be 1/8 as wide
1982(starting in column 4) and 1/8 as high (also starting in row 0). The
1983third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
19841/8 as high (every 8th row starting in row 4), and the fourth pass will
1985be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1986and every 4th row starting in row 0). The fifth pass will return an
1987image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1988while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1989(starting in column 1 and row 0). The seventh and final pass will be as
1990wide as the original, and 1/2 as high, containing all of the odd
1991numbered scanlines. Phew!
1992
1993If you want libpng to expand the images, call this before calling
1994png_start_read_image() or png_read_update_info():
1995
1996 if (interlace_type == PNG_INTERLACE_ADAM7)
1997 number_of_passes
1998 = png_set_interlace_handling(png_ptr);
1999
2000This will return the number of passes needed. Currently, this
2001is seven, but may change if another interlace type is added.
2002This function can be called even if the file is not interlaced,
2003where it will return one pass.
2004
2005If you are not going to display the image after each pass, but are
2006going to wait until the entire image is read in, use the sparkle
2007effect. This effect is faster and the end result of either method
2008is exactly the same. If you are planning on displaying the image
2009after each pass, the "rectangle" effect is generally considered the
2010better looking one.
2011
2012If you only want the "sparkle" effect, just call png_read_rows() as
2013normal, with the third parameter NULL. Make sure you make pass over
2014the image number_of_passes times, and you don't change the data in the
2015rows between calls. You can change the locations of the data, just
2016not the data. Each pass only writes the pixels appropriate for that
2017pass, and assumes the data from previous passes is still valid.
2018
2019 png_read_rows(png_ptr, row_pointers, NULL,
2020 number_of_rows);
2021
2022If you only want the first effect (the rectangles), do the same as
2023before except pass the row buffer in the third parameter, and leave
2024the second parameter NULL.
2025
2026 png_read_rows(png_ptr, NULL, row_pointers,
2027 number_of_rows);
2028
2029.SS Finishing a sequential read
2030
2031After you are finished reading the image through either the high- or
2032low-level interfaces, you can finish reading the file. If you are
2033interested in comments or time, which may be stored either before or
2034after the image data, you should pass the separate png_info struct if
2035you want to keep the comments from before and after the image
2036separate. If you are not interested, you can pass NULL.
2037
2038 png_read_end(png_ptr, end_info);
2039
2040When you are done, you can free all memory allocated by libpng like this:
2041
2042 png_destroy_read_struct(&png_ptr, &info_ptr,
2043 &end_info);
2044
2045It is also possible to individually free the info_ptr members that
2046point to libpng-allocated storage with the following function:
2047
2048 png_free_data(png_ptr, info_ptr, mask, seq)
2049 mask - identifies data to be freed, a mask
2050 containing the logical OR of one or
2051 more of
2052 PNG_FREE_PLTE, PNG_FREE_TRNS,
2053 PNG_FREE_HIST, PNG_FREE_ICCP,
2054 PNG_FREE_PCAL, PNG_FREE_ROWS,
2055 PNG_FREE_SCAL, PNG_FREE_SPLT,
2056 PNG_FREE_TEXT, PNG_FREE_UNKN,
2057 or simply PNG_FREE_ALL
2058 seq - sequence number of item to be freed
2059 (-1 for all items)
2060
2061This function may be safely called when the relevant storage has
2062already been freed, or has not yet been allocated, or was allocated
2063by the user and not by libpng, and will in those
2064cases do nothing. The "seq" parameter is ignored if only one item
2065of the selected data type, such as PLTE, is allowed. If "seq" is not
2066-1, and multiple items are allowed for the data type identified in
2067the mask, such as text or sPLT, only the n'th item in the structure
2068is freed, where n is "seq".
2069
2070The default behavior is only to free data that was allocated internally
2071by libpng. This can be changed, so that libpng will not free the data,
2072or so that it will free data that was allocated by the user with png_malloc()
2073or png_zalloc() and passed in via a png_set_*() function, with
2074
2075 png_data_freer(png_ptr, info_ptr, freer, mask)
2076 mask - which data elements are affected
2077 same choices as in png_free_data()
2078 freer - one of
2079 PNG_DESTROY_WILL_FREE_DATA
2080 PNG_SET_WILL_FREE_DATA
2081 PNG_USER_WILL_FREE_DATA
2082
2083This function only affects data that has already been allocated.
2084You can call this function after reading the PNG data but before calling
2085any png_set_*() functions, to control whether the user or the png_set_*()
2086function is responsible for freeing any existing data that might be present,
2087and again after the png_set_*() functions to control whether the user
2088or png_destroy_*() is supposed to free the data. When the user assumes
2089responsibility for libpng-allocated data, the application must use
2090png_free() to free it, and when the user transfers responsibility to libpng
2091for data that the user has allocated, the user must have used png_malloc()
2092or png_zalloc() to allocate it.
2093
2094If you allocated your row_pointers in a single block, as suggested above in
2095the description of the high level read interface, you must not transfer
2096responsibility for freeing it to the png_set_rows or png_read_destroy function,
2097because they would also try to free the individual row_pointers[i].
2098
2099If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2100separately, do not transfer responsibility for freeing text_ptr to libpng,
2101because when libpng fills a png_text structure it combines these members with
2102the key member, and png_free_data() will free only text_ptr.key. Similarly,
2103if you transfer responsibility for free'ing text_ptr from libpng to your
2104application, your application must not separately free those members.
2105
2106The png_free_data() function will turn off the "valid" flag for anything
2107it frees. If you need to turn the flag off for a chunk that was freed by your
2108application instead of by libpng, you can use
2109
2110 png_set_invalid(png_ptr, info_ptr, mask);
2111 mask - identifies the chunks to be made invalid,
2112 containing the logical OR of one or
2113 more of
2114 PNG_INFO_gAMA, PNG_INFO_sBIT,
2115 PNG_INFO_cHRM, PNG_INFO_PLTE,
2116 PNG_INFO_tRNS, PNG_INFO_bKGD,
2117 PNG_INFO_hIST, PNG_INFO_pHYs,
2118 PNG_INFO_oFFs, PNG_INFO_tIME,
2119 PNG_INFO_pCAL, PNG_INFO_sRGB,
2120 PNG_INFO_iCCP, PNG_INFO_sPLT,
2121 PNG_INFO_sCAL, PNG_INFO_IDAT
2122
2123For a more compact example of reading a PNG image, see the file example.c.
2124
2125.SS Reading PNG files progressively
2126
2127The progressive reader is slightly different then the non-progressive
2128reader. Instead of calling png_read_info(), png_read_rows(), and
2129png_read_end(), you make one call to png_process_data(), which calls
2130callbacks when it has the info, a row, or the end of the image. You
2131set up these callbacks with png_set_progressive_read_fn(). You don't
2132have to worry about the input/output functions of libpng, as you are
2133giving the library the data directly in png_process_data(). I will
2134assume that you have read the section on reading PNG files above,
2135so I will only highlight the differences (although I will show
2136all of the code).
2137
2138png_structp png_ptr;
2139png_infop info_ptr;
2140
2141 /* An example code fragment of how you would
2142 initialize the progressive reader in your
2143 application. */
2144 int
2145 initialize_png_reader()
2146 {
2147 png_ptr = png_create_read_struct
2148 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2149 user_error_fn, user_warning_fn);
2150 if (!png_ptr)
2151 return (ERROR);
2152 info_ptr = png_create_info_struct(png_ptr);
2153 if (!info_ptr)
2154 {
2155 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2156 (png_infopp)NULL);
2157 return (ERROR);
2158 }
2159
2160 if (setjmp(png_jmpbuf(png_ptr)))
2161 {
2162 png_destroy_read_struct(&png_ptr, &info_ptr,
2163 (png_infopp)NULL);
2164 return (ERROR);
2165 }
2166
2167 /* This one's new. You can provide functions
2168 to be called when the header info is valid,
2169 when each row is completed, and when the image
2170 is finished. If you aren't using all functions,
2171 you can specify NULL parameters. Even when all
2172 three functions are NULL, you need to call
2173 png_set_progressive_read_fn(). You can use
2174 any struct as the user_ptr (cast to a void pointer
2175 for the function call), and retrieve the pointer
2176 from inside the callbacks using the function
2177
2178 png_get_progressive_ptr(png_ptr);
2179
2180 which will return a void pointer, which you have
2181 to cast appropriately.
2182 */
2183 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2184 info_callback, row_callback, end_callback);
2185
2186 return 0;
2187 }
2188
2189 /* A code fragment that you call as you receive blocks
2190 of data */
2191 int
2192 process_data(png_bytep buffer, png_uint_32 length)
2193 {
2194 if (setjmp(png_jmpbuf(png_ptr)))
2195 {
2196 png_destroy_read_struct(&png_ptr, &info_ptr,
2197 (png_infopp)NULL);
2198 return (ERROR);
2199 }
2200
2201 /* This one's new also. Simply give it a chunk
2202 of data from the file stream (in order, of
2203 course). On machines with segmented memory
2204 models machines, don't give it any more than
2205 64K. The library seems to run fine with sizes
2206 of 4K. Although you can give it much less if
2207 necessary (I assume you can give it chunks of
2208 1 byte, I haven't tried less then 256 bytes
2209 yet). When this function returns, you may
2210 want to display any rows that were generated
2211 in the row callback if you don't already do
2212 so there.
2213 */
2214 png_process_data(png_ptr, info_ptr, buffer, length);
2215 return 0;
2216 }
2217
2218 /* This function is called (as set by
2219 png_set_progressive_read_fn() above) when enough data
2220 has been supplied so all of the header has been
2221 read.
2222 */
2223 void
2224 info_callback(png_structp png_ptr, png_infop info)
2225 {
2226 /* Do any setup here, including setting any of
2227 the transformations mentioned in the Reading
2228 PNG files section. For now, you _must_ call
2229 either png_start_read_image() or
2230 png_read_update_info() after all the
2231 transformations are set (even if you don't set
2232 any). You may start getting rows before
2233 png_process_data() returns, so this is your
2234 last chance to prepare for that.
2235 */
2236 }
2237
2238 /* This function is called when each row of image
2239 data is complete */
2240 void
2241 row_callback(png_structp png_ptr, png_bytep new_row,
2242 png_uint_32 row_num, int pass)
2243 {
2244 /* If the image is interlaced, and you turned
2245 on the interlace handler, this function will
2246 be called for every row in every pass. Some
2247 of these rows will not be changed from the
2248 previous pass. When the row is not changed,
2249 the new_row variable will be NULL. The rows
2250 and passes are called in order, so you don't
2251 really need the row_num and pass, but I'm
2252 supplying them because it may make your life
2253 easier.
2254
2255 For the non-NULL rows of interlaced images,
2256 you must call png_progressive_combine_row()
2257 passing in the row and the old row. You can
2258 call this function for NULL rows (it will just
2259 return) and for non-interlaced images (it just
2260 does the memcpy for you) if it will make the
2261 code easier. Thus, you can just do this for
2262 all cases:
2263 */
2264
2265 png_progressive_combine_row(png_ptr, old_row,
2266 new_row);
2267
2268 /* where old_row is what was displayed for
2269 previously for the row. Note that the first
2270 pass (pass == 0, really) will completely cover
2271 the old row, so the rows do not have to be
2272 initialized. After the first pass (and only
2273 for interlaced images), you will have to pass
2274 the current row, and the function will combine
2275 the old row and the new row.
2276 */
2277 }
2278
2279 void
2280 end_callback(png_structp png_ptr, png_infop info)
2281 {
2282 /* This function is called after the whole image
2283 has been read, including any chunks after the
2284 image (up to and including the IEND). You
2285 will usually have the same info chunk as you
2286 had in the header, although some data may have
2287 been added to the comments and time fields.
2288
2289 Most people won't do much here, perhaps setting
2290 a flag that marks the image as finished.
2291 */
2292 }
2293
2294
2295
2296.SH IV. Writing
2297
2298Much of this is very similar to reading. However, everything of
2299importance is repeated here, so you won't have to constantly look
2300back up in the reading section to understand writing.
2301
2302.SS Setup
2303
2304You will want to do the I/O initialization before you get into libpng,
2305so if it doesn't work, you don't have anything to undo. If you are not
2306using the standard I/O functions, you will need to replace them with
2307custom writing functions. See the discussion under Customizing libpng.
2308
2309 FILE *fp = fopen(file_name, "wb");
2310 if (!fp)
2311 {
2312 return (ERROR);
2313 }
2314
2315Next, png_struct and png_info need to be allocated and initialized.
2316As these can be both relatively large, you may not want to store these
2317on the stack, unless you have stack space to spare. Of course, you
2318will want to check if they return NULL. If you are also reading,
2319you won't want to name your read structure and your write structure
2320both "png_ptr"; you can call them anything you like, such as
2321"read_ptr" and "write_ptr". Look at pngtest.c, for example.
2322
2323 png_structp png_ptr = png_create_write_struct
2324 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2325 user_error_fn, user_warning_fn);
2326 if (!png_ptr)
2327 return (ERROR);
2328
2329 png_infop info_ptr = png_create_info_struct(png_ptr);
2330 if (!info_ptr)
2331 {
2332 png_destroy_write_struct(&png_ptr,
2333 (png_infopp)NULL);
2334 return (ERROR);
2335 }
2336
2337If you want to use your own memory allocation routines,
2338define PNG_USER_MEM_SUPPORTED and use
2339png_create_write_struct_2() instead of png_create_write_struct():
2340
2341 png_structp png_ptr = png_create_write_struct_2
2342 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2343 user_error_fn, user_warning_fn, (png_voidp)
2344 user_mem_ptr, user_malloc_fn, user_free_fn);
2345
2346After you have these structures, you will need to set up the
2347error handling. When libpng encounters an error, it expects to
2348longjmp() back to your routine. Therefore, you will need to call
2349setjmp() and pass the png_jmpbuf(png_ptr). If you
2350write the file from different routines, you will need to update
2351the png_jmpbuf(png_ptr) every time you enter a new routine that will
2352call a png_*() function. See your documentation of setjmp/longjmp
2353for your compiler for more information on setjmp/longjmp. See
2354the discussion on libpng error handling in the Customizing Libpng
2355section below for more information on the libpng error handling.
2356
2357 if (setjmp(png_jmpbuf(png_ptr)))
2358 {
2359 png_destroy_write_struct(&png_ptr, &info_ptr);
2360 fclose(fp);
2361 return (ERROR);
2362 }
2363 ...
2364 return;
2365
2366If you would rather avoid the complexity of setjmp/longjmp issues,
2367you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2368errors will result in a call to PNG_ABORT() which defaults to abort().
2369
2370Now you need to set up the output code. The default for libpng is to
2371use the C function fwrite(). If you use this, you will need to pass a
2372valid FILE * in the function png_init_io(). Be sure that the file is
2373opened in binary mode. Again, if you wish to handle writing data in
2374another way, see the discussion on libpng I/O handling in the Customizing
2375Libpng section below.
2376
2377 png_init_io(png_ptr, fp);
2378
2379.SS Write callbacks
2380
2381At this point, you can set up a callback function that will be
2382called after each row has been written, which you can use to control
2383a progress meter or the like. It's demonstrated in pngtest.c.
2384You must supply a function
2385
2386 void write_row_callback(png_ptr, png_uint_32 row,
2387 int pass);
2388 {
2389 /* put your code here */
2390 }
2391
2392(You can give it another name that you like instead of "write_row_callback")
2393
2394To inform libpng about your function, use
2395
2396 png_set_write_status_fn(png_ptr, write_row_callback);
2397
2398You now have the option of modifying how the compression library will
2399run. The following functions are mainly for testing, but may be useful
2400in some cases, like if you need to write PNG files extremely fast and
2401are willing to give up some compression, or if you want to get the
2402maximum possible compression at the expense of slower writing. If you
2403have no special needs in this area, let the library do what it wants by
2404not calling this function at all, as it has been tuned to deliver a good
2405speed/compression ratio. The second parameter to png_set_filter() is
2406the filter method, for which the only valid values are 0 (as of the
2407July 1999 PNG specification, version 1.2) or 64 (if you are writing
2408a PNG datastream that is to be embedded in a MNG datastream). The third
2409parameter is a flag that indicates which filter type(s) are to be tested
2410for each scanline. See the PNG specification for details on the specific filter
2411types.
2412
2413
2414 /* turn on or off filtering, and/or choose
2415 specific filters. You can use either a single
2416 PNG_FILTER_VALUE_NAME or the logical OR of one
2417 or more PNG_FILTER_NAME masks. */
2418 png_set_filter(png_ptr, 0,
2419 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2420 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2421 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2422 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2423 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2424 PNG_ALL_FILTERS);
2425
2426If an application
2427wants to start and stop using particular filters during compression,
2428it should start out with all of the filters (to ensure that the previous
2429row of pixels will be stored in case it's needed later), and then add
2430and remove them after the start of compression.
2431
2432If you are writing a PNG datastream that is to be embedded in a MNG
2433datastream, the second parameter can be either 0 or 64.
2434
2435The png_set_compression_*() functions interface to the zlib compression
2436library, and should mostly be ignored unless you really know what you are
2437doing. The only generally useful call is png_set_compression_level()
2438which changes how much time zlib spends on trying to compress the image
2439data. See the Compression Library (zlib.h and algorithm.txt, distributed
2440with zlib) for details on the compression levels.
2441
2442 /* set the zlib compression level */
2443 png_set_compression_level(png_ptr,
2444 Z_BEST_COMPRESSION);
2445
2446 /* set other zlib parameters */
2447 png_set_compression_mem_level(png_ptr, 8);
2448 png_set_compression_strategy(png_ptr,
2449 Z_DEFAULT_STRATEGY);
2450 png_set_compression_window_bits(png_ptr, 15);
2451 png_set_compression_method(png_ptr, 8);
2452 png_set_compression_buffer_size(png_ptr, 8192)
2453
2454extern PNG_EXPORT(void,png_set_zbuf_size)
2455
2456.SS Setting the contents of info for output
2457
2458You now need to fill in the png_info structure with all the data you
2459wish to write before the actual image. Note that the only thing you
2460are allowed to write after the image is the text chunks and the time
2461chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2462the latest PNG specification for more information on that. If you
2463wish to write them before the image, fill them in now, and flag that
2464data as being valid. If you want to wait until after the data, don't
2465fill them until png_write_end(). For all the fields in png_info and
2466their data types, see png.h. For explanations of what the fields
2467contain, see the PNG specification.
2468
2469Some of the more important parts of the png_info are:
2470
2471 png_set_IHDR(png_ptr, info_ptr, width, height,
2472 bit_depth, color_type, interlace_type,
2473 compression_type, filter_method)
2474 width - holds the width of the image
2475 in pixels (up to 2^31).
2476 height - holds the height of the image
2477 in pixels (up to 2^31).
2478 bit_depth - holds the bit depth of one of the
2479 image channels.
2480 (valid values are 1, 2, 4, 8, 16
2481 and depend also on the
2482 color_type. See also significant
2483 bits (sBIT) below).
2484 color_type - describes which color/alpha
2485 channels are present.
2486 PNG_COLOR_TYPE_GRAY
2487 (bit depths 1, 2, 4, 8, 16)
2488 PNG_COLOR_TYPE_GRAY_ALPHA
2489 (bit depths 8, 16)
2490 PNG_COLOR_TYPE_PALETTE
2491 (bit depths 1, 2, 4, 8)
2492 PNG_COLOR_TYPE_RGB
2493 (bit_depths 8, 16)
2494 PNG_COLOR_TYPE_RGB_ALPHA
2495 (bit_depths 8, 16)
2496
2497 PNG_COLOR_MASK_PALETTE
2498 PNG_COLOR_MASK_COLOR
2499 PNG_COLOR_MASK_ALPHA
2500
2501 interlace_type - PNG_INTERLACE_NONE or
2502 PNG_INTERLACE_ADAM7
2503 compression_type - (must be
2504 PNG_COMPRESSION_TYPE_DEFAULT)
2505 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2506 or, if you are writing a PNG to
2507 be embedded in a MNG datastream,
2508 can also be
2509 PNG_INTRAPIXEL_DIFFERENCING)
2510
2511 png_set_PLTE(png_ptr, info_ptr, palette,
2512 num_palette);
2513 palette - the palette for the file
2514 (array of png_color)
2515 num_palette - number of entries in the palette
2516
2517 png_set_gAMA(png_ptr, info_ptr, gamma);
2518 gamma - the gamma the image was created
2519 at (PNG_INFO_gAMA)
2520
2521 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2522 srgb_intent - the rendering intent
2523 (PNG_INFO_sRGB) The presence of
2524 the sRGB chunk means that the pixel
2525 data is in the sRGB color space.
2526 This chunk also implies specific
2527 values of gAMA and cHRM. Rendering
2528 intent is the CSS-1 property that
2529 has been defined by the International
2530 Color Consortium
2531 (http://www.color.org).
2532 It can be one of
2533 PNG_sRGB_INTENT_SATURATION,
2534 PNG_sRGB_INTENT_PERCEPTUAL,
2535 PNG_sRGB_INTENT_ABSOLUTE, or
2536 PNG_sRGB_INTENT_RELATIVE.
2537
2538
2539 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2540 srgb_intent);
2541 srgb_intent - the rendering intent
2542 (PNG_INFO_sRGB) The presence of the
2543 sRGB chunk means that the pixel
2544 data is in the sRGB color space.
2545 This function also causes gAMA and
2546 cHRM chunks with the specific values
2547 that are consistent with sRGB to be
2548 written.
2549
2550 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2551 profile, proflen);
2552 name - The profile name.
2553 compression - The compression type; always
2554 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2555 You may give NULL to this argument to
2556 ignore it.
2557 profile - International Color Consortium color
2558 profile data. May contain NULs.
2559 proflen - length of profile data in bytes.
2560
2561 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2562 sig_bit - the number of significant bits for
2563 (PNG_INFO_sBIT) each of the gray, red,
2564 green, and blue channels, whichever are
2565 appropriate for the given color type
2566 (png_color_16)
2567
2568 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2569 trans_values);
2570 trans - array of transparent entries for
2571 palette (PNG_INFO_tRNS)
2572 trans_values - graylevel or color sample values of
2573 the single transparent color for
2574 non-paletted images (PNG_INFO_tRNS)
2575 num_trans - number of transparent entries
2576 (PNG_INFO_tRNS)
2577
2578 png_set_hIST(png_ptr, info_ptr, hist);
2579 (PNG_INFO_hIST)
2580 hist - histogram of palette (array of
2581 png_uint_16)
2582
2583 png_set_tIME(png_ptr, info_ptr, mod_time);
2584 mod_time - time image was last modified
2585 (PNG_VALID_tIME)
2586
2587 png_set_bKGD(png_ptr, info_ptr, background);
2588 background - background color (PNG_VALID_bKGD)
2589
2590 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2591 text_ptr - array of png_text holding image
2592 comments
2593 text_ptr[i].compression - type of compression used
2594 on "text" PNG_TEXT_COMPRESSION_NONE
2595 PNG_TEXT_COMPRESSION_zTXt
2596 PNG_ITXT_COMPRESSION_NONE
2597 PNG_ITXT_COMPRESSION_zTXt
2598 text_ptr[i].key - keyword for comment. Must contain
2599 1-79 characters.
2600 text_ptr[i].text - text comments for current
2601 keyword. Can be NULL or empty.
2602 text_ptr[i].text_length - length of text string,
2603 after decompression, 0 for iTXt
2604 text_ptr[i].itxt_length - length of itxt string,
2605 after decompression, 0 for tEXt/zTXt
2606 text_ptr[i].lang - language of comment (NULL or
2607 empty for unknown).
2608 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2609 or empty for unknown).
2610 num_text - number of comments
2611
2612 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2613 num_spalettes);
2614 palette_ptr - array of png_sPLT_struct structures
2615 to be added to the list of palettes
2616 in the info structure.
2617 num_spalettes - number of palette structures to be
2618 added.
2619
2620 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2621 unit_type);
2622 offset_x - positive offset from the left
2623 edge of the screen
2624 offset_y - positive offset from the top
2625 edge of the screen
2626 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2627
2628 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2629 unit_type);
2630 res_x - pixels/unit physical resolution
2631 in x direction
2632 res_y - pixels/unit physical resolution
2633 in y direction
2634 unit_type - PNG_RESOLUTION_UNKNOWN,
2635 PNG_RESOLUTION_METER
2636
2637 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2638 unit - physical scale units (an integer)
2639 width - width of a pixel in physical scale units
2640 height - height of a pixel in physical scale units
2641 (width and height are doubles)
2642
2643 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2644 unit - physical scale units (an integer)
2645 width - width of a pixel in physical scale units
2646 height - height of a pixel in physical scale units
2647 (width and height are strings like "2.54")
2648
2649 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2650 num_unknowns)
2651 unknowns - array of png_unknown_chunk
2652 structures holding unknown chunks
2653 unknowns[i].name - name of unknown chunk
2654 unknowns[i].data - data of unknown chunk
2655 unknowns[i].size - size of unknown chunk's data
2656 unknowns[i].location - position to write chunk in file
2657 0: do not write chunk
2658 PNG_HAVE_IHDR: before PLTE
2659 PNG_HAVE_PLTE: before IDAT
2660 PNG_AFTER_IDAT: after IDAT
2661
2662The "location" member is set automatically according to
2663what part of the output file has already been written.
2664You can change its value after calling png_set_unknown_chunks()
2665as demonstrated in pngtest.c. Within each of the "locations",
2666the chunks are sequenced according to their position in the
2667structure (that is, the value of "i", which is the order in which
2668the chunk was either read from the input file or defined with
2669png_set_unknown_chunks).
2670
2671A quick word about text and num_text. text is an array of png_text
2672structures. num_text is the number of valid structures in the array.
2673Each png_text structure holds a language code, a keyword, a text value,
2674and a compression type.
2675
2676The compression types have the same valid numbers as the compression
2677types of the image data. Currently, the only valid number is zero.
2678However, you can store text either compressed or uncompressed, unlike
2679images, which always have to be compressed. So if you don't want the
2680text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2681Because tEXt and zTXt chunks don't have a language field, if you
2682specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2683any language code or translated keyword will not be written out.
2684
2685Until text gets around 1000 bytes, it is not worth compressing it.
2686After the text has been written out to the file, the compression type
2687is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2688so that it isn't written out again at the end (in case you are calling
2689png_write_end() with the same struct.
2690
2691The keywords that are given in the PNG Specification are:
2692
2693 Title Short (one line) title or
2694 caption for image
2695 Author Name of image's creator
2696 Description Description of image (possibly long)
2697 Copyright Copyright notice
2698 Creation Time Time of original image creation
2699 (usually RFC 1123 format, see below)
2700 Software Software used to create the image
2701 Disclaimer Legal disclaimer
2702 Warning Warning of nature of content
2703 Source Device used to create the image
2704 Comment Miscellaneous comment; conversion
2705 from other image format
2706
2707The keyword-text pairs work like this. Keywords should be short
2708simple descriptions of what the comment is about. Some typical
2709keywords are found in the PNG specification, as is some recommendations
2710on keywords. You can repeat keywords in a file. You can even write
2711some text before the image and some after. For example, you may want
2712to put a description of the image before the image, but leave the
2713disclaimer until after, so viewers working over modem connections
2714don't have to wait for the disclaimer to go over the modem before
2715they start seeing the image. Finally, keywords should be full
2716words, not abbreviations. Keywords and text are in the ISO 8859-1
2717(Latin-1) character set (a superset of regular ASCII) and can not
2718contain NUL characters, and should not contain control or other
2719unprintable characters. To make the comments widely readable, stick
2720with basic ASCII, and avoid machine specific character set extensions
2721like the IBM-PC character set. The keyword must be present, but
2722you can leave off the text string on non-compressed pairs.
2723Compressed pairs must have a text string, as only the text string
2724is compressed anyway, so the compression would be meaningless.
2725
2726PNG supports modification time via the png_time structure. Two
2727conversion routines are provided, png_convert_from_time_t() for
2728time_t and png_convert_from_struct_tm() for struct tm. The
2729time_t routine uses gmtime(). You don't have to use either of
2730these, but if you wish to fill in the png_time structure directly,
2731you should provide the time in universal time (GMT) if possible
2732instead of your local time. Note that the year number is the full
2733year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2734that months start with 1.
2735
2736If you want to store the time of the original image creation, you should
2737use a plain tEXt chunk with the "Creation Time" keyword. This is
2738necessary because the "creation time" of a PNG image is somewhat vague,
2739depending on whether you mean the PNG file, the time the image was
2740created in a non-PNG format, a still photo from which the image was
2741scanned, or possibly the subject matter itself. In order to facilitate
2742machine-readable dates, it is recommended that the "Creation Time"
2743tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2744although this isn't a requirement. Unlike the tIME chunk, the
2745"Creation Time" tEXt chunk is not expected to be automatically changed
2746by the software. To facilitate the use of RFC 1123 dates, a function
2747png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2748time to an RFC 1123 format string.
2749
2750.SS Writing unknown chunks
2751
2752You can use the png_set_unknown_chunks function to queue up chunks
2753for writing. You give it a chunk name, raw data, and a size; that's
2754all there is to it. The chunks will be written by the next following
2755png_write_info_before_PLTE, png_write_info, or png_write_end function.
2756Any chunks previously read into the info structure's unknown-chunk
2757list will also be written out in a sequence that satisfies the PNG
2758specification's ordering rules.
2759
2760.SS The high-level write interface
2761
2762At this point there are two ways to proceed; through the high-level
2763write interface, or through a sequence of low-level write operations.
2764You can use the high-level interface if your image data is present
2765in the info structure. All defined output
2766transformations are permitted, enabled by the following masks.
2767
2768 PNG_TRANSFORM_IDENTITY No transformation
2769 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2770 PNG_TRANSFORM_PACKSWAP Change order of packed
2771 pixels to LSB first
2772 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2773 PNG_TRANSFORM_SHIFT Normalize pixels to the
2774 sBIT depth
2775 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2776 to BGRA
2777 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2778 to AG
2779 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2780 to transparency
2781 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2782 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2783
2784If you have valid image data in the info structure (you can use
2785png_set_rows() to put image data in the info structure), simply do this:
2786
2787 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2788
2789where png_transforms is an integer containing the logical OR of some set of
2790transformation flags. This call is equivalent to png_write_info(),
2791followed the set of transformations indicated by the transform mask,
2792then png_write_image(), and finally png_write_end().
2793
2794(The final parameter of this call is not yet used. Someday it might point
2795to transformation parameters required by some future output transform.)
2796
2797You must use png_transforms and not call any png_set_transform() functions
2798when you use png_write_png().
2799
2800.SS The low-level write interface
2801
2802If you are going the low-level route instead, you are now ready to
2803write all the file information up to the actual image data. You do
2804this with a call to png_write_info().
2805
2806 png_write_info(png_ptr, info_ptr);
2807
2808Note that there is one transformation you may need to do before
2809png_write_info(). In PNG files, the alpha channel in an image is the
2810level of opacity. If your data is supplied as a level of
2811transparency, you can invert the alpha channel before you write it, so
2812that 0 is fully transparent and 255 (in 8-bit or paletted images) or
281365535 (in 16-bit images) is fully opaque, with
2814
2815 png_set_invert_alpha(png_ptr);
2816
2817This must appear before png_write_info() instead of later with the
2818other transformations because in the case of paletted images the tRNS
2819chunk data has to be inverted before the tRNS chunk is written. If
2820your image is not a paletted image, the tRNS data (which in such cases
2821represents a single color to be rendered as transparent) won't need to
2822be changed, and you can safely do this transformation after your
2823png_write_info() call.
2824
2825If you need to write a private chunk that you want to appear before
2826the PLTE chunk when PLTE is present, you can write the PNG info in
2827two steps, and insert code to write your own chunk between them:
2828
2829 png_write_info_before_PLTE(png_ptr, info_ptr);
2830 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2831 png_write_info(png_ptr, info_ptr);
2832
2833After you've written the file information, you can set up the library
2834to handle any special transformations of the image data. The various
2835ways to transform the data will be described in the order that they
2836should occur. This is important, as some of these change the color
2837type and/or bit depth of the data, and some others only work on
2838certain color types and bit depths. Even though each transformation
2839checks to see if it has data that it can do something with, you should
2840make sure to only enable a transformation if it will be valid for the
2841data. For example, don't swap red and blue on grayscale data.
2842
2843PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2844the library to strip input data that has 4 or 8 bytes per pixel down
2845to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2846bytes per pixel).
2847
2848 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2849
2850where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2851PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2852is stored XRGB or RGBX.
2853
2854PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2855they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2856If the data is supplied at 1 pixel per byte, use this code, which will
2857correctly pack the pixels into a single byte:
2858
2859 png_set_packing(png_ptr);
2860
2861PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2862data is of another bit depth, you can write an sBIT chunk into the
2863file so that decoders can recover the original data if desired.
2864
2865 /* Set the true bit depth of the image data */
2866 if (color_type & PNG_COLOR_MASK_COLOR)
2867 {
2868 sig_bit.red = true_bit_depth;
2869 sig_bit.green = true_bit_depth;
2870 sig_bit.blue = true_bit_depth;
2871 }
2872 else
2873 {
2874 sig_bit.gray = true_bit_depth;
2875 }
2876 if (color_type & PNG_COLOR_MASK_ALPHA)
2877 {
2878 sig_bit.alpha = true_bit_depth;
2879 }
2880
2881 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2882
2883If the data is stored in the row buffer in a bit depth other than
2884one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2885this will scale the values to appear to be the correct bit depth as
2886is required by PNG.
2887
2888 png_set_shift(png_ptr, &sig_bit);
2889
2890PNG files store 16 bit pixels in network byte order (big-endian,
2891ie. most significant bits first). This code would be used if they are
2892supplied the other way (little-endian, i.e. least significant bits
2893first, the way PCs store them):
2894
2895 if (bit_depth > 8)
2896 png_set_swap(png_ptr);
2897
2898If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2899need to change the order the pixels are packed into bytes, you can use:
2900
2901 if (bit_depth < 8)
2902 png_set_packswap(png_ptr);
2903
2904PNG files store 3 color pixels in red, green, blue order. This code
2905would be used if they are supplied as blue, green, red:
2906
2907 png_set_bgr(png_ptr);
2908
2909PNG files describe monochrome as black being zero and white being
2910one. This code would be used if the pixels are supplied with this reversed
2911(black being one and white being zero):
2912
2913 png_set_invert_mono(png_ptr);
2914
2915Finally, you can write your own transformation function if none of
2916the existing ones meets your needs. This is done by setting a callback
2917with
2918
2919 png_set_write_user_transform_fn(png_ptr,
2920 write_transform_fn);
2921
2922You must supply the function
2923
2924 void write_transform_fn(png_ptr ptr, row_info_ptr
2925 row_info, png_bytep data)
2926
2927See pngtest.c for a working example. Your function will be called
2928before any of the other transformations are processed.
2929
2930You can also set up a pointer to a user structure for use by your
2931callback function.
2932
2933 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2934
2935The user_channels and user_depth parameters of this function are ignored
2936when writing; you can set them to zero as shown.
2937
2938You can retrieve the pointer via the function png_get_user_transform_ptr().
2939For example:
2940
2941 voidp write_user_transform_ptr =
2942 png_get_user_transform_ptr(png_ptr);
2943
2944It is possible to have libpng flush any pending output, either manually,
2945or automatically after a certain number of lines have been written. To
2946flush the output stream a single time call:
2947
2948 png_write_flush(png_ptr);
2949
2950and to have libpng flush the output stream periodically after a certain
2951number of scanlines have been written, call:
2952
2953 png_set_flush(png_ptr, nrows);
2954
2955Note that the distance between rows is from the last time png_write_flush()
2956was called, or the first row of the image if it has never been called.
2957So if you write 50 lines, and then png_set_flush 25, it will flush the
2958output on the next scanline, and every 25 lines thereafter, unless
2959png_write_flush() is called before 25 more lines have been written.
2960If nrows is too small (less than about 10 lines for a 640 pixel wide
2961RGB image) the image compression may decrease noticeably (although this
2962may be acceptable for real-time applications). Infrequent flushing will
2963only degrade the compression performance by a few percent over images
2964that do not use flushing.
2965
2966.SS Writing the image data
2967
2968That's it for the transformations. Now you can write the image data.
2969The simplest way to do this is in one function call. If you have the
2970whole image in memory, you can just call png_write_image() and libpng
2971will write the image. You will need to pass in an array of pointers to
2972each row. This function automatically handles interlacing, so you don't
2973need to call png_set_interlace_handling() or call this function multiple
2974times, or any of that other stuff necessary with png_write_rows().
2975
2976 png_write_image(png_ptr, row_pointers);
2977
2978where row_pointers is:
2979
2980 png_byte *row_pointers[height];
2981
2982You can point to void or char or whatever you use for pixels.
2983
2984If you don't want to write the whole image at once, you can
2985use png_write_rows() instead. If the file is not interlaced,
2986this is simple:
2987
2988 png_write_rows(png_ptr, row_pointers,
2989 number_of_rows);
2990
2991row_pointers is the same as in the png_write_image() call.
2992
2993If you are just writing one row at a time, you can do this with
2994a single row_pointer instead of an array of row_pointers:
2995
2996 png_bytep row_pointer = row;
2997
2998 png_write_row(png_ptr, row_pointer);
2999
3000When the file is interlaced, things can get a good deal more
3001complicated. The only currently (as of the PNG Specification
3002version 1.2, dated July 1999) defined interlacing scheme for PNG files
3003is the "Adam7" interlace scheme, that breaks down an
3004image into seven smaller images of varying size. libpng will build
3005these images for you, or you can do them yourself. If you want to
3006build them yourself, see the PNG specification for details of which
3007pixels to write when.
3008
3009If you don't want libpng to handle the interlacing details, just
3010use png_set_interlace_handling() and call png_write_rows() the
3011correct number of times to write all seven sub-images.
3012
3013If you want libpng to build the sub-images, call this before you start
3014writing any rows:
3015
3016 number_of_passes =
3017 png_set_interlace_handling(png_ptr);
3018
3019This will return the number of passes needed. Currently, this
3020is seven, but may change if another interlace type is added.
3021
3022Then write the complete image number_of_passes times.
3023
3024 png_write_rows(png_ptr, row_pointers,
3025 number_of_rows);
3026
3027As some of these rows are not used, and thus return immediately,
3028you may want to read about interlacing in the PNG specification,
3029and only update the rows that are actually used.
3030
3031.SS Finishing a sequential write
3032
3033After you are finished writing the image, you should finish writing
3034the file. If you are interested in writing comments or time, you should
3035pass an appropriately filled png_info pointer. If you are not interested,
3036you can pass NULL.
3037
3038 png_write_end(png_ptr, info_ptr);
3039
3040When you are done, you can free all memory used by libpng like this:
3041
3042 png_destroy_write_struct(&png_ptr, &info_ptr);
3043
3044It is also possible to individually free the info_ptr members that
3045point to libpng-allocated storage with the following function:
3046
3047 png_free_data(png_ptr, info_ptr, mask, seq)
3048 mask - identifies data to be freed, a mask
3049 containing the logical OR of one or
3050 more of
3051 PNG_FREE_PLTE, PNG_FREE_TRNS,
3052 PNG_FREE_HIST, PNG_FREE_ICCP,
3053 PNG_FREE_PCAL, PNG_FREE_ROWS,
3054 PNG_FREE_SCAL, PNG_FREE_SPLT,
3055 PNG_FREE_TEXT, PNG_FREE_UNKN,
3056 or simply PNG_FREE_ALL
3057 seq - sequence number of item to be freed
3058 (-1 for all items)
3059
3060This function may be safely called when the relevant storage has
3061already been freed, or has not yet been allocated, or was allocated
3062by the user and not by libpng, and will in those
3063cases do nothing. The "seq" parameter is ignored if only one item
3064of the selected data type, such as PLTE, is allowed. If "seq" is not
3065-1, and multiple items are allowed for the data type identified in
3066the mask, such as text or sPLT, only the n'th item in the structure
3067is freed, where n is "seq".
3068
3069If you allocated data such as a palette that you passed
3070in to libpng with png_set_*, you must not free it until just before the call to
3071png_destroy_write_struct().
3072
3073The default behavior is only to free data that was allocated internally
3074by libpng. This can be changed, so that libpng will not free the data,
3075or so that it will free data that was allocated by the user with png_malloc()
3076or png_zalloc() and passed in via a png_set_*() function, with
3077
3078 png_data_freer(png_ptr, info_ptr, freer, mask)
3079 mask - which data elements are affected
3080 same choices as in png_free_data()
3081 freer - one of
3082 PNG_DESTROY_WILL_FREE_DATA
3083 PNG_SET_WILL_FREE_DATA
3084 PNG_USER_WILL_FREE_DATA
3085
3086For example, to transfer responsibility for some data from a read structure
3087to a write structure, you could use
3088
3089 png_data_freer(read_ptr, read_info_ptr,
3090 PNG_USER_WILL_FREE_DATA,
3091 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3092 png_data_freer(write_ptr, write_info_ptr,
3093 PNG_DESTROY_WILL_FREE_DATA,
3094 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3095
3096thereby briefly reassigning responsibility for freeing to the user but
3097immediately afterwards reassigning it once more to the write_destroy
3098function. Having done this, it would then be safe to destroy the read
3099structure and continue to use the PLTE, tRNS, and hIST data in the write
3100structure.
3101
3102This function only affects data that has already been allocated.
3103You can call this function before calling after the png_set_*() functions
3104to control whether the user or png_destroy_*() is supposed to free the data.
3105When the user assumes responsibility for libpng-allocated data, the
3106application must use
3107png_free() to free it, and when the user transfers responsibility to libpng
3108for data that the user has allocated, the user must have used png_malloc()
3109or png_zalloc() to allocate it.
3110
3111If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3112separately, do not transfer responsibility for freeing text_ptr to libpng,
3113because when libpng fills a png_text structure it combines these members with
3114the key member, and png_free_data() will free only text_ptr.key. Similarly,
3115if you transfer responsibility for free'ing text_ptr from libpng to your
3116application, your application must not separately free those members.
3117For a more compact example of writing a PNG image, see the file example.c.
3118
3119.SH V. Modifying/Customizing libpng:
3120
3121There are three issues here. The first is changing how libpng does
3122standard things like memory allocation, input/output, and error handling.
3123The second deals with more complicated things like adding new chunks,
3124adding new transformations, and generally changing how libpng works.
3125Both of those are compile-time issues; that is, they are generally
3126determined at the time the code is written, and there is rarely a need
3127to provide the user with a means of changing them. The third is a
3128run-time issue: choosing between and/or tuning one or more alternate
3129versions of computationally intensive routines; specifically, optimized
3130assembly-language (and therefore compiler- and platform-dependent)
3131versions.
3132
3133Memory allocation, input/output, and error handling
3134
3135All of the memory allocation, input/output, and error handling in libpng
3136goes through callbacks that are user-settable. The default routines are
3137in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3138these functions, call the appropriate png_set_*_fn() function.
3139
3140Memory allocation is done through the functions png_malloc()
3141and png_free(). These currently just call the standard C functions. If
3142your pointers can't access more then 64K at a time, you will want to set
3143MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3144memory allocation on a platform will change between applications, these
3145functions must be modified in the library at compile time. If you prefer
3146to use a different method of allocating and freeing data, you can use
3147png_create_read_struct_2() or png_create_write_struct_2() to register
3148your own functions as described above.
3149These functions also provide a void pointer that can be retrieved via
3150
3151 mem_ptr=png_get_mem_ptr(png_ptr);
3152
3153Your replacement memory functions must have prototypes as follows:
3154
3155 png_voidp malloc_fn(png_structp png_ptr,
3156 png_size_t size);
3157 void free_fn(png_structp png_ptr, png_voidp ptr);
3158
3159Your malloc_fn() must return NULL in case of failure. The png_malloc()
3160function will normally call png_error() if it receives a NULL from the
3161system memory allocator or from your replacement malloc_fn().
3162
3163Input/Output in libpng is done through png_read() and png_write(),
3164which currently just call fread() and fwrite(). The FILE * is stored in
3165png_struct and is initialized via png_init_io(). If you wish to change
3166the method of I/O, the library supplies callbacks that you can set
3167through the function png_set_read_fn() and png_set_write_fn() at run
3168time, instead of calling the png_init_io() function. These functions
3169also provide a void pointer that can be retrieved via the function
3170png_get_io_ptr(). For example:
3171
3172 png_set_read_fn(png_structp read_ptr,
3173 voidp read_io_ptr, png_rw_ptr read_data_fn)
3174
3175 png_set_write_fn(png_structp write_ptr,
3176 voidp write_io_ptr, png_rw_ptr write_data_fn,
3177 png_flush_ptr output_flush_fn);
3178
3179 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3180 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3181
3182The replacement I/O functions must have prototypes as follows:
3183
3184 void user_read_data(png_structp png_ptr,
3185 png_bytep data, png_size_t length);
3186 void user_write_data(png_structp png_ptr,
3187 png_bytep data, png_size_t length);
3188 void user_flush_data(png_structp png_ptr);
3189
3190Supplying NULL for the read, write, or flush functions sets them back
3191to using the default C stream functions. It is an error to read from
3192a write stream, and vice versa.
3193
3194Error handling in libpng is done through png_error() and png_warning().
3195Errors handled through png_error() are fatal, meaning that png_error()
3196should never return to its caller. Currently, this is handled via
3197setjmp() and longjmp() (unless you have compiled libpng with
3198PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3199but you could change this to do things like exit() if you should wish.
3200
3201On non-fatal errors, png_warning() is called
3202to print a warning message, and then control returns to the calling code.
3203By default png_error() and png_warning() print a message on stderr via
3204fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3205(because you don't want the messages) or PNG_NO_STDIO defined (because
3206fprintf() isn't available). If you wish to change the behavior of the error
3207functions, you will need to set up your own message callbacks. These
3208functions are normally supplied at the time that the png_struct is created.
3209It is also possible to redirect errors and warnings to your own replacement
3210functions after png_create_*_struct() has been called by calling:
3211
3212 png_set_error_fn(png_structp png_ptr,
3213 png_voidp error_ptr, png_error_ptr error_fn,
3214 png_error_ptr warning_fn);
3215
3216 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3217
3218If NULL is supplied for either error_fn or warning_fn, then the libpng
3219default function will be used, calling fprintf() and/or longjmp() if a
3220problem is encountered. The replacement error functions should have
3221parameters as follows:
3222
3223 void user_error_fn(png_structp png_ptr,
3224 png_const_charp error_msg);
3225 void user_warning_fn(png_structp png_ptr,
3226 png_const_charp warning_msg);
3227
3228The motivation behind using setjmp() and longjmp() is the C++ throw and
3229catch exception handling methods. This makes the code much easier to write,
3230as there is no need to check every return code of every function call.
3231However, there are some uncertainties about the status of local variables
3232after a longjmp, so the user may want to be careful about doing anything after
3233setjmp returns non-zero besides returning itself. Consult your compiler
3234documentation for more details. For an alternative approach, you may wish
3235to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3236
3237.SS Custom chunks
3238
3239If you need to read or write custom chunks, you may need to get deeper
3240into the libpng code. The library now has mechanisms for storing
3241and writing chunks of unknown type; you can even declare callbacks
3242for custom chunks. Hoewver, this may not be good enough if the
3243library code itself needs to know about interactions between your
3244chunk and existing `intrinsic' chunks.
3245
3246If you need to write a new intrinsic chunk, first read the PNG
3247specification. Acquire a first level of
3248understanding of how it works. Pay particular attention to the
3249sections that describe chunk names, and look at how other chunks were
3250designed, so you can do things similarly. Second, check out the
3251sections of libpng that read and write chunks. Try to find a chunk
3252that is similar to yours and use it as a template. More details can
3253be found in the comments inside the code. It is best to handle unknown
3254chunks in a generic method, via callback functions, instead of by
3255modifying libpng functions.
3256
3257If you wish to write your own transformation for the data, look through
3258the part of the code that does the transformations, and check out some of
3259the simpler ones to get an idea of how they work. Try to find a similar
3260transformation to the one you want to add and copy off of it. More details
3261can be found in the comments inside the code itself.
3262
3263.SS Configuring for 16 bit platforms
3264
3265You will want to look into zconf.h to tell zlib (and thus libpng) that
3266it cannot allocate more then 64K at a time. Even if you can, the memory
3267won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3268
3269.SS Configuring for DOS
3270
3271For DOS users who only have access to the lower 640K, you will
3272have to limit zlib's memory usage via a png_set_compression_mem_level()
3273call. See zlib.h or zconf.h in the zlib library for more information.
3274
3275.SS Configuring for Medium Model
3276
3277Libpng's support for medium model has been tested on most of the popular
3278compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3279defined, and FAR gets defined to far in pngconf.h, and you should be
3280all set. Everything in the library (except for zlib's structure) is
3281expecting far data. You must use the typedefs with the p or pp on
3282the end for pointers (or at least look at them and be careful). Make
3283note that the rows of data are defined as png_bytepp, which is an
3284unsigned char far * far *.
3285
3286.SS Configuring for gui/windowing platforms:
3287
3288You will need to write new error and warning functions that use the GUI
3289interface, as described previously, and set them to be the error and
3290warning functions at the time that png_create_*_struct() is called,
3291in order to have them available during the structure initialization.
3292They can be changed later via png_set_error_fn(). On some compilers,
3293you may also have to change the memory allocators (png_malloc, etc.).
3294
3295.SS Configuring for compiler xxx:
3296
3297All includes for libpng are in pngconf.h. If you need to add/change/delete
3298an include, this is the place to do it. The includes that are not
3299needed outside libpng are protected by the PNG_INTERNAL definition,
3300which is only defined for those routines inside libpng itself. The
3301files in libpng proper only include png.h, which includes pngconf.h.
3302
3303.SS Configuring zlib:
3304
3305There are special functions to configure the compression. Perhaps the
3306most useful one changes the compression level, which currently uses
3307input compression values in the range 0 - 9. The library normally
3308uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3309have shown that for a large majority of images, compression values in
3310the range 3-6 compress nearly as well as higher levels, and do so much
3311faster. For online applications it may be desirable to have maximum speed
3312(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3313specify no compression (Z_NO_COMPRESSION = 0), but this would create
3314files larger than just storing the raw bitmap. You can specify the
3315compression level by calling:
3316
3317 png_set_compression_level(png_ptr, level);
3318
3319Another useful one is to reduce the memory level used by the library.
3320The memory level defaults to 8, but it can be lowered if you are
3321short on memory (running DOS, for example, where you only have 640K).
3322Note that the memory level does have an effect on compression; among
3323other things, lower levels will result in sections of incompressible
3324data being emitted in smaller stored blocks, with a correspondingly
3325larger relative overhead of up to 15% in the worst case.
3326
3327 png_set_compression_mem_level(png_ptr, level);
3328
3329The other functions are for configuring zlib. They are not recommended
3330for normal use and may result in writing an invalid PNG file. See
3331zlib.h for more information on what these mean.
3332
3333 png_set_compression_strategy(png_ptr,
3334 strategy);
3335 png_set_compression_window_bits(png_ptr,
3336 window_bits);
3337 png_set_compression_method(png_ptr, method);
3338 png_set_compression_buffer_size(png_ptr, size);
3339
3340.SS Controlling row filtering
3341
3342If you want to control whether libpng uses filtering or not, which
3343filters are used, and how it goes about picking row filters, you
3344can call one of these functions. The selection and configuration
3345of row filters can have a significant impact on the size and
3346encoding speed and a somewhat lesser impact on the decoding speed
3347of an image. Filtering is enabled by default for RGB and grayscale
3348images (with and without alpha), but not for paletted images nor
3349for any images with bit depths less than 8 bits/pixel.
3350
3351The 'method' parameter sets the main filtering method, which is
3352currently only '0' in the PNG 1.2 specification. The 'filters'
3353parameter sets which filter(s), if any, should be used for each
3354scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3355to turn filtering on and off, respectively.
3356
3357Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3358PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3359ORed together with '|' to specify one or more filters to use.
3360These filters are described in more detail in the PNG specification.
3361If you intend to change the filter type during the course of writing
3362the image, you should start with flags set for all of the filters
3363you intend to use so that libpng can initialize its internal
3364structures appropriately for all of the filter types. (Note that this
3365means the first row must always be adaptively filtered, because libpng
3366currently does not allocate the filter buffers until png_write_row()
3367is called for the first time.)
3368
3369 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3370 PNG_FILTER_UP | PNG_FILTER_AVE |
3371 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3372
3373 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3374 filters);
3375 The second parameter can also be
3376 PNG_INTRAPIXEL_DIFFERENCING if you are
3377 writing a PNG to be embedded in a MNG
3378 datastream. This parameter must be the
3379 same as the value of filter_method used
3380 in png_set_IHDR().
3381
3382It is also possible to influence how libpng chooses from among the
3383available filters. This is done in one or both of two ways - by
3384telling it how important it is to keep the same filter for successive
3385rows, and by telling it the relative computational costs of the filters.
3386
3387 double weights[3] = {1.5, 1.3, 1.1},
3388 costs[PNG_FILTER_VALUE_LAST] =
3389 {1.0, 1.3, 1.3, 1.5, 1.7};
3390
3391 png_set_filter_heuristics(png_ptr,
3392 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3393 weights, costs);
3394
3395The weights are multiplying factors that indicate to libpng that the
3396row filter should be the same for successive rows unless another row filter
3397is that many times better than the previous filter. In the above example,
3398if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3399"sum of absolute differences" 1.5 x 1.3 times higher than other filters
3400and still be chosen, while the NONE filter could have a sum 1.1 times
3401higher than other filters and still be chosen. Unspecified weights are
3402taken to be 1.0, and the specified weights should probably be declining
3403like those above in order to emphasize recent filters over older filters.
3404
3405The filter costs specify for each filter type a relative decoding cost
3406to be considered when selecting row filters. This means that filters
3407with higher costs are less likely to be chosen over filters with lower
3408costs, unless their "sum of absolute differences" is that much smaller.
3409The costs do not necessarily reflect the exact computational speeds of
3410the various filters, since this would unduly influence the final image
3411size.
3412
3413Note that the numbers above were invented purely for this example and
3414are given only to help explain the function usage. Little testing has
3415been done to find optimum values for either the costs or the weights.
3416
3417.SS Removing unwanted object code
3418
3419There are a bunch of #define's in pngconf.h that control what parts of
3420libpng are compiled. All the defines end in _SUPPORTED. If you are
3421never going to use a capability, you can change the #define to #undef
3422before recompiling libpng and save yourself code and data space, or
3423you can turn off individual capabilities with defines that begin with
3424PNG_NO_.
3425
3426You can also turn all of the transforms and ancillary chunk capabilities
3427off en masse with compiler directives that define
3428PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3429or all four,
3430along with directives to turn on any of the capabilities that you do
3431want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3432the extra transformations but still leave the library fully capable of reading
3433and writing PNG files with all known public chunks
3434Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3435produces a library that is incapable of reading or writing ancillary chunks.
3436If you are not using the progressive reading capability, you can
3437turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3438this with the INTERLACING capability, which you'll still have).
3439
3440All the reading and writing specific code are in separate files, so the
3441linker should only grab the files it needs. However, if you want to
3442make sure, or if you are building a stand alone library, all the
3443reading files start with pngr and all the writing files start with
3444pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3445are used for both reading and writing, and always need to be included.
3446The progressive reader is in pngpread.c
3447
3448If you are creating or distributing a dynamically linked library (a .so
3449or DLL file), you should not remove or disable any parts of the library,
3450as this will cause applications linked with different versions of the
3451library to fail if they call functions not available in your library.
3452The size of the library itself should not be an issue, because only
3453those sections that are actually used will be loaded into memory.
3454
3455.SS Requesting debug printout
3456
3457The macro definition PNG_DEBUG can be used to request debugging
3458printout. Set it to an integer value in the range 0 to 3. Higher
3459numbers result in increasing amounts of debugging information. The
3460information is printed to the "stderr" file, unless another file
3461name is specified in the PNG_DEBUG_FILE macro definition.
3462
3463When PNG_DEBUG > 0, the following functions (macros) become available:
3464
3465 png_debug(level, message)
3466 png_debug1(level, message, p1)
3467 png_debug2(level, message, p1, p2)
3468
3469in which "level" is compared to PNG_DEBUG to decide whether to print
3470the message, "message" is the formatted string to be printed,
3471and p1 and p2 are parameters that are to be embedded in the string
3472according to printf-style formatting directives. For example,
3473
3474 png_debug1(2, "foo=%d\n", foo);
3475
3476is expanded to
3477
3478 if(PNG_DEBUG > 2)
3479 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3480
3481When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3482can still use PNG_DEBUG to control your own debugging:
3483
3484 #ifdef PNG_DEBUG
3485 fprintf(stderr, ...
3486 #endif
3487
3488When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3489having level = 0 will be printed. There aren't any such statements in
3490this version of libpng, but if you insert some they will be printed.
3491
3492.SH VI. Runtime optimization
3493
3494A new feature in libpng 1.2.0 is the ability to dynamically switch between
3495standard and optimized versions of some routines. Currently these are
3496limited to three computationally intensive tasks when reading PNG files:
3497decoding row filters, expanding interlacing, and combining interlaced or
3498transparent row data with previous row data. Currently the optimized
3499versions are available only for x86 (Intel, AMD, etc.) platforms with
3500MMX support, though this may change in future versions. (For example,
3501the non-MMX assembler optimizations for zlib might become similarly
3502runtime-selectable in future releases, in which case libpng could be
3503extended to support them. Alternatively, the compile-time choice of
3504floating-point versus integer routines for gamma correction might become
3505runtime-selectable.)
3506
3507Because such optimizations tend to be very platform- and compiler-dependent,
3508both in how they are written and in how they perform, the new runtime code
3509in libpng has been written to allow programs to query, enable, and disable
3510either specific optimizations or all such optimizations. For example, to
3511enable all possible optimizations (bearing in mind that some "optimizations"
3512may actually run more slowly in rare cases):
3513
3514 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3515 png_uint_32 mask, flags;
3516
3517 flags = png_get_asm_flags(png_ptr);
3518 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3519 png_set_asm_flags(png_ptr, flags | mask);
3520 #endif
3521
3522To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3523by itself when calling png_get_asm_flagmask(); similarly for optimizing
3524only writing. To disable all optimizations:
3525
3526 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3527 flags = png_get_asm_flags(png_ptr);
3528 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3529 png_set_asm_flags(png_ptr, flags & ~mask);
3530 #endif
3531
3532To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3533in place of png_get_asm_flagmask(). The mmx version takes one additional
3534parameter:
3535
3536 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3537 int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3538 int compilerID;
3539
3540 mask = png_get_mmx_flagmask(selection, &compilerID);
3541 #endif
3542
3543On return, compilerID will indicate which version of the MMX assembler
3544optimizations was compiled. Currently two flavors exist: Microsoft
3545Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3546On non-x86 platforms or on systems compiled without MMX optimizations, a
3547value of -1 is used.
3548
3549Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3550all valid, settable optimization bits for the version of the library that's
3551currently in use. In the case of shared (dynamically linked) libraries,
3552this may include optimizations that did not exist at the time the code was
3553written and compiled. It is also possible, of course, to enable only known,
3554specific optimizations; for example:
3555
3556 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3557 flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3558 | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3559 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3560 | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3561 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3562 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3563 png_set_asm_flags(png_ptr, flags);
3564 #endif
3565
3566This method would enable only the MMX read-optimizations available at the
3567time of libpng 1.2.0's release, regardless of whether a later version of
3568the DLL were actually being used. (Also note that these functions did not
3569exist in versions older than 1.2.0, so any attempt to run a dynamically
3570linked app on such an older version would fail.)
3571
3572To determine whether the processor supports MMX instructions at all, use
3573the png_mmx_support() function:
3574
3575 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3576 mmxsupport = png_mmx_support();
3577 #endif
3578
3579It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3580is compiled but MMX is not supported by the processor, or 1 if MMX support
3581is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3582and png_get_asm_flagmask() all may be called without allocating and ini-
3583tializing any PNG structures (for example, as part of a usage screen or
3584"about" box).
3585
3586The following code can be used to prevent an application from using the
3587thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3588defined:
3589
3590#if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3591 && defined(PNG_THREAD_UNSAFE_OK)
3592 /* Disable thread-unsafe features of pnggccrd */
3593 if (png_access_version() >= 10200)
3594 {
3595 png_uint_32 mmx_disable_mask = 0;
3596 png_uint_32 asm_flags;
3597
3598 mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3599 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3600 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3601 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3602 asm_flags = png_get_asm_flags(png_ptr);
3603 png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3604 }
3605#endif
3606
3607For more extensive examples of runtime querying, enabling and disabling
3608of optimized features, see contrib/gregbook/readpng2.c in the libpng
3609source-code distribution.
3610
3611.SH VII. MNG support
3612
3613The MNG specification (available at http://www.libpng.org/pub/mng) allows
3614certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3615Libpng can support some of these extensions. To enable them, use the
3616png_permit_mng_features() function:
3617
3618 feature_set = png_permit_mng_features(png_ptr, mask)
3619 mask is a png_uint_32 containing the logical OR of the
3620 features you want to enable. These include
3621 PNG_FLAG_MNG_EMPTY_PLTE
3622 PNG_FLAG_MNG_FILTER_64
3623 PNG_ALL_MNG_FEATURES
3624 feature_set is a png_uint_32 that is the logical AND of
3625 your mask with the set of MNG features that is
3626 supported by the version of libpng that you are using.
3627
3628It is an error to use this function when reading or writing a standalone
3629PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3630in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3631and the MHDR and MEND chunks. Libpng does not provide support for these
3632or any other MNG chunks; your application must provide its own support for
3633them. You may wish to consider using libmng (available at
3634http://www.libmng.com) instead.
3635
3636.SH VIII. Changes to Libpng from version 0.88
3637
3638It should be noted that versions of libpng later than 0.96 are not
3639distributed by the original libpng author, Guy Schalnat, nor by
3640Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3641distributed versions 0.89 through 0.96, but rather by another member
3642of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3643still alive and well, but they have moved on to other things.
3644
3645The old libpng functions png_read_init(), png_write_init(),
3646png_info_init(), png_read_destroy(), and png_write_destroy() have been
3647moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3648functions will be removed from libpng version 2.0.0.
3649
3650The preferred method of creating and initializing the libpng structures is
3651via the png_create_read_struct(), png_create_write_struct(), and
3652png_create_info_struct() because they isolate the size of the structures
3653from the application, allow version error checking, and also allow the
3654use of custom error handling routines during the initialization, which
3655the old functions do not. The functions png_read_destroy() and
3656png_write_destroy() do not actually free the memory that libpng
3657allocated for these structs, but just reset the data structures, so they
3658can be used instead of png_destroy_read_struct() and
3659png_destroy_write_struct() if you feel there is too much system overhead
3660allocating and freeing the png_struct for each image read.
3661
3662Setting the error callbacks via png_set_message_fn() before
3663png_read_init() as was suggested in libpng-0.88 is no longer supported
3664because this caused applications that do not use custom error functions
3665to fail if the png_ptr was not initialized to zero. It is still possible
3666to set the error callbacks AFTER png_read_init(), or to change them with
3667png_set_error_fn(), which is essentially the same function, but with a new
3668name to force compilation errors with applications that try to use the old
3669method.
3670
3671Starting with version 1.0.7, you can find out which version of the library
3672you are using at run-time:
3673
3674 png_uint_32 libpng_vn = png_access_version_number();
3675
3676The number libpng_vn is constructed from the major version, minor
3677version with leading zero, and release number with leading zero,
3678(e.g., libpng_vn for version 1.0.7 is 10007).
3679
3680You can also check which version of png.h you used when compiling your
3681application:
3682
3683 png_uint_32 application_vn = PNG_LIBPNG_VER;
3684
3685.SH IX. Y2K Compliance in libpng
3686
3687September 12, 2004
3688
3689Since the PNG Development group is an ad-hoc body, we can't make
3690an official declaration.
3691
3692This is your unofficial assurance that libpng from version 0.71 and
3693upward through 1.2.7 are Y2K compliant. It is my belief that earlier
3694versions were also Y2K compliant.
3695
3696Libpng only has three year fields. One is a 2-byte unsigned integer that
3697will hold years up to 65535. The other two hold the date in text
3698format, and will hold years up to 9999.
3699
3700The integer is
3701 "png_uint_16 year" in png_time_struct.
3702
3703The strings are
3704 "png_charp time_buffer" in png_struct and
3705 "near_time_buffer", which is a local character string in png.c.
3706
3707There are seven time-related functions:
3708
3709 png_convert_to_rfc_1123() in png.c
3710 (formerly png_convert_to_rfc_1152() in error)
3711 png_convert_from_struct_tm() in pngwrite.c, called
3712 in pngwrite.c
3713 png_convert_from_time_t() in pngwrite.c
3714 png_get_tIME() in pngget.c
3715 png_handle_tIME() in pngrutil.c, called in pngread.c
3716 png_set_tIME() in pngset.c
3717 png_write_tIME() in pngwutil.c, called in pngwrite.c
3718
3719All appear to handle dates properly in a Y2K environment. The
3720png_convert_from_time_t() function calls gmtime() to convert from system
3721clock time, which returns (year - 1900), which we properly convert to
3722the full 4-digit year. There is a possibility that applications using
3723libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3724function, or that they are incorrectly passing only a 2-digit year
3725instead of "year - 1900" into the png_convert_from_struct_tm() function,
3726but this is not under our control. The libpng documentation has always
3727stated that it works with 4-digit years, and the APIs have been
3728documented as such.
3729
3730The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3731integer to hold the year, and can hold years as large as 65535.
3732
3733zlib, upon which libpng depends, is also Y2K compliant. It contains
3734no date-related code.
3735
3736
3737 Glenn Randers-Pehrson
3738 libpng maintainer
3739 PNG Development Group
3740
3741.SH NOTE
3742
3743Note about libpng version numbers:
3744
3745Due to various miscommunications, unforeseen code incompatibilities
3746and occasional factors outside the authors' control, version numbering
3747on the library has not always been consistent and straightforward.
3748The following table summarizes matters since version 0.89c, which was
3749the first widely used release:
3750
3751 source png.h png.h shared-lib
3752 version string int version
3753 ------- ------ ----- ----------
3754 0.89c ("beta 3") 0.89 89 1.0.89
3755 0.90 ("beta 4") 0.90 90 0.90
3756 0.95 ("beta 5") 0.95 95 0.95
3757 0.96 ("beta 6") 0.96 96 0.96
3758 0.97b ("beta 7") 1.00.97 97 1.0.1
3759 0.97c 0.97 97 2.0.97
3760 0.98 0.98 98 2.0.98
3761 0.99 0.99 98 2.0.99
3762 0.99a-m 0.99 99 2.0.99
3763 1.00 1.00 100 2.1.0
3764 1.0.0 1.0.0 100 2.1.0
3765 1.0.0 (from here on, the 100 2.1.0
3766 1.0.1 png.h string is 10001 2.1.0
3767 1.0.1a-e identical to the 10002 from here on, the
3768 1.0.2 source version) 10002 shared library is 2.V
3769 1.0.2a-b 10003 where V is the source
3770 1.0.1 10001 code version except as
3771 1.0.1a-e 10002 2.1.0.1a-e noted.
3772 1.0.2 10002 2.1.0.2
3773 1.0.2a-b 10003 2.1.0.2a-b
3774 1.0.3 10003 2.1.0.3
3775 1.0.3a-d 10004 2.1.0.3a-d
3776 1.0.4 10004 2.1.0.4
3777 1.0.4a-f 10005 2.1.0.4a-f
3778 1.0.5 (+ 2 patches) 10005 2.1.0.5
3779 1.0.5a-d 10006 2.1.0.5a-d
3780 1.0.5e-r 10100 2.1.0.5e-r
3781 1.0.5s-v 10006 2.1.0.5s-v
3782 1.0.6 (+ 3 patches) 10006 2.1.0.6
3783 1.0.6d-g 10007 2.1.0.6d-g
3784 1.0.6h 10007 10.6h
3785 1.0.6i 10007 10.6i
3786 1.0.6j 10007 2.1.0.6j
3787 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3788 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3789 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3790 1.0.7 1 10007 2.1.0.7
3791 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3792 1.0.8rc1 1 10008 2.1.0.8rc1
3793 1.0.8 1 10008 2.1.0.8
3794 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3795 1.0.9rc1 1 10009 2.1.0.9rc1
3796 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3797 1.0.9rc2 1 10009 2.1.0.9rc2
3798 1.0.9 1 10009 2.1.0.9
3799 1.0.10beta1 1 10010 2.1.0.10beta1
3800 1.0.10rc1 1 10010 2.1.0.10rc1
3801 1.0.10 1 10010 2.1.0.10
3802 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3803 1.0.11rc1 1 10011 2.1.0.11rc1
3804 1.0.11 1 10011 2.1.0.11
3805 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3806 1.0.12rc1 2 10012 2.1.0.12rc1
3807 1.0.12 2 10012 2.1.0.12
3808 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3809 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3810 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3811 1.2.0rc1 3 10200 3.1.2.0rc1
3812 1.2.0 3 10200 3.1.2.0
3813 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3814 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3815 1.2.1 3 10201 3.1.2.1
3816 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3817 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3818 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3819 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3820 1.0.13 10 10013 10.so.0.1.0.13
3821 1.2.2 12 10202 12.so.0.1.2.2
3822 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3823 1.2.3 12 10203 12.so.0.1.2.3
3824 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3825 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3826 1.0.14 10 10014 10.so.0.1.0.14
3827 1.2.4 13 10204 12.so.0.1.2.4
3828 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3829 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3830 1.0.15 10 10015 10.so.0.1.0.15
3831 1.2.5 13 10205 12.so.0.1.2.5
3832 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3833 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3834 1.0.16 10 10016 10.so.0.1.0.16
3835 1.2.6 13 10206 12.so.0.1.2.6
3836 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3837 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
3838 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3839 1.0.17 10 10017 12.so.0.1.0.17
3840 1.2.7 13 10207 12.so.0.1.2.7
3841
3842Henceforth the source version will match the shared-library minor
3843and patch numbers; the shared-library major version number will be
3844used for changes in backward compatibility, as it is intended. The
3845PNG_PNGLIB_VER macro, which is not used within libpng but is available
3846for applications, is an unsigned integer of the form xyyzz corresponding
3847to the source version x.y.z (leading zeros in y and z). Beta versions
3848were given the previous public release number plus a letter, until
3849version 1.0.6j; from then on they were given the upcoming public
3850release number plus "betaNN" or "rcN".
3851
3852.SH "SEE ALSO"
3853libpngpf(3), png(5)
3854.LP
3855.IR libpng :
3856.IP
3857http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3858http://www.libpng.org/pub/png
3859
3860.LP
3861.IR zlib :
3862.IP
3863(generally) at the same location as
3864.I libpng
3865or at
3866.br
3867ftp://ftp.info-zip.org/pub/infozip/zlib
3868
3869.LP
3870.IR PNG specification: RFC 2083
3871.IP
3872(generally) at the same location as
3873.I libpng
3874or at
3875.br
3876ftp://ds.internic.net/rfc/rfc2083.txt
3877.br
3878or (as a W3C Recommendation) at
3879.br
3880http://www.w3.org/TR/REC-png.html
3881
3882.LP
3883In the case of any inconsistency between the PNG specification
3884and this library, the specification takes precedence.
3885
3886.SH AUTHORS
3887This man page: Glenn Randers-Pehrson
3888<glennrp@users.sourceforge.net>
3889
3890The contributing authors would like to thank all those who helped
3891with testing, bug fixes, and patience. This wouldn't have been
3892possible without all of you.
3893
3894Thanks to Frank J. T. Wojcik for helping with the documentation.
3895
3896Libpng version 1.2.7 - September 12, 2004:
3897Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3898Currently maintained by Glenn Randers-Pehrson (glennrp@users.sourceforge.net).
3899
3900Supported by the PNG development group
3901.br
3902png-implement@ccrc.wustl.edu (subscription required; write to
3903majordomo@ccrc.wustl.edu with "subscribe png-implement" in the message).
3904
3905.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3906
3907(This copy of the libpng notices is provided for your convenience. In case of
3908any discrepancy between this copy and the notices in the file png.h that is
3909included in the libpng distribution, the latter shall prevail.)
3910
3911If you modify libpng you may insert additional notices immediately following
3912this sentence.
3913
3914libpng version 1.2.6, September 12, 2004, is
3915Copyright (c) 2004 Glenn Randers-Pehrson, and is
3916distributed according to the same disclaimer and license as libpng-1.2.5
3917with the following individual added to the list of Contributing Authors
3918
3919 Cosmin Truta
3920
3921libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
3922Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3923distributed according to the same disclaimer and license as libpng-1.0.6
3924with the following individuals added to the list of Contributing Authors
3925
3926 Simon-Pierre Cadieux
3927 Eric S. Raymond
3928 Gilles Vollant
3929
3930and with the following additions to the disclaimer:
3931
3932 There is no warranty against interference with your
3933 enjoyment of the library or against infringement.
3934 There is no warranty that our efforts or the library
3935 will fulfill any of your particular purposes or needs.
3936 This library is provided with all faults, and the entire
3937 risk of satisfactory quality, performance, accuracy, and
3938 effort is with the user.
3939
3940libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3941Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3942Distributed according to the same disclaimer and license as libpng-0.96,
3943with the following individuals added to the list of Contributing Authors:
3944
3945 Tom Lane
3946 Glenn Randers-Pehrson
3947 Willem van Schaik
3948
3949libpng versions 0.89, June 1996, through 0.96, May 1997, are
3950Copyright (c) 1996, 1997 Andreas Dilger
3951Distributed according to the same disclaimer and license as libpng-0.88,
3952with the following individuals added to the list of Contributing Authors:
3953
3954 John Bowler
3955 Kevin Bracey
3956 Sam Bushell
3957 Magnus Holmgren
3958 Greg Roelofs
3959 Tom Tanner
3960
3961libpng versions 0.5, May 1995, through 0.88, January 1996, are
3962Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3963
3964For the purposes of this copyright and license, "Contributing Authors"
3965is defined as the following set of individuals:
3966
3967 Andreas Dilger
3968 Dave Martindale
3969 Guy Eric Schalnat
3970 Paul Schmidt
3971 Tim Wegner
3972
3973The PNG Reference Library is supplied "AS IS". The Contributing Authors
3974and Group 42, Inc. disclaim all warranties, expressed or implied,
3975including, without limitation, the warranties of merchantability and of
3976fitness for any purpose. The Contributing Authors and Group 42, Inc.
3977assume no liability for direct, indirect, incidental, special, exemplary,
3978or consequential damages, which may result from the use of the PNG
3979Reference Library, even if advised of the possibility of such damage.
3980
3981Permission is hereby granted to use, copy, modify, and distribute this
3982source code, or portions hereof, for any purpose, without fee, subject
3983to the following restrictions:
3984
39851. The origin of this source code must not be misrepresented.
3986
39872. Altered versions must be plainly marked as such and
3988 must not be misrepresented as being the original source.
3989
39903. This Copyright notice may not be removed or altered from
3991 any source or altered source distribution.
3992
3993The Contributing Authors and Group 42, Inc. specifically permit, without
3994fee, and encourage the use of this source code as a component to
3995supporting the PNG file format in commercial products. If you use this
3996source code in a product, acknowledgment is not required but would be
3997appreciated.
3998
3999
4000A "png_get_copyright" function is available, for convenient use in "about"
4001boxes and the like:
4002
4003 printf("%s",png_get_copyright(NULL));
4004
4005Also, the PNG logo (in PNG format, of course) is supplied in the
4006files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4007
4008Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4009certification mark of the Open Source Initiative.
4010
4011Glenn Randers-Pehrson
4012glennrp@users.sourceforge.net
4013September 12, 2004
4014
4015.\" end of man page
4016
wxWidgets (Impactor)