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fixing focus, fixes #11911
[wxWidgets.git] / src / png / libpng.3
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1.TH LIBPNG 3 "December 18, 2008"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.2.34
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\fB#if \fI!defined(PNG_1_0_X)
180
181\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
182
183\fI\fB#endif
184
185\fI\fB
186
187\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
188
189\fI\fB
190
191\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
192
193\fI\fB
194
195\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
196
197\fI\fB
198
199\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
200
201\fI\fB
202
203\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
204
205\fI\fB
206
207\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
208
209\fI\fB
210
211\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
212
213\fI\fB
214
215\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
216
217\fI\fB
218
219\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
220
221\fI\fB
222
223\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
224
225\fI\fB
226
227\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
228
229\fI\fB
230
231\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
232
233\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
234
235\fI\fB
236
237\fBpng_bytepp png_get_rows (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_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
242
243\fI\fB
244
245\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
246
247\fI\fB
248
249\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
250
251\fI\fB
252
253\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
254
255\fI\fB
256
257\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
258
259\fI\fB
260
261\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
262
263\fI\fB
264
265\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
266
267\fI\fB
268
269\fB#if \fI!defined(PNG_1_0_X)
270
271\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
272
273\fI\fB
274
275\fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
276
277\fI\fB
278
279\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
280
281\fI\fB#endif
282
283\fI\fB
284
285\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
286
287\fI\fB
288
289\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
290
291\fI\fB
292
293\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
294
295\fI\fB
296
297\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
298
299\fI\fB
300
301\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
302
303\fI\fB
304
305\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
306
307\fI\fB
308
309\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
310
311\fI\fB
312
313\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
314
315\fI\fB
316
317\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
318
319\fI\fB
320
321\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
322
323\fI\fB
324
325\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
326
327\fI\fB
328
329\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
330
331\fI\fB
332
333\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
334
335\fI\fB
336
337\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
338
339\fI\fB
340
341\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
342
343\fI\fB
344
345\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
346
347\fI\fB
348
349\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
350
351\fI\fB
352
353\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
354
355\fI\fB
356
357\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
358
359\fI\fB
360
361\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
362
363\fI\fB
364
365\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
366
367\fI\fB
368
369\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
370
371\fI\fB
372
373\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
374
375\fI\fB
376
377\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
378
379\fI\fB
380
381\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
382
383\fI\fB
384
385\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
386
387\fI\fB
388
389\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
390
391\fI\fB
392
393\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
394
395\fI\fB
396
397\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
398
399\fI\fB
400
401\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
402
403\fI\fB
404
405\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
406
407\fI\fB
408
409\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
410
411\fI\fB
412
413\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
414
415\fI\fB
416
417\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
418
419\fI\fB
420
421\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
422
423\fI\fB
424
425\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
426
427\fI\fB
428
429\fB#if \fI!defined(PNG_1_0_X)
430
431\fBpng_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
432
433\fI\fB
434
435\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
436
437\fI\fB
438
439\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
440
441\fI\fB
442
443\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
444
445\fI\fB#endif
446
447\fI\fB
448
449\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
450
451\fI\fB
452
453\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
454
455\fI\fB
456
457\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
458
459\fI\fB
460
461\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
462
463\fI\fB
464
465\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
466
467\fI\fB
468
469\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
470
471\fI\fB
472
473\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
474
475\fI\fB
476
477\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
478
479\fI\fB
480
481\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
482
483\fI\fB
484
485\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
486
487\fI\fB
488
489\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
490
491\fI\fB
492
493\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
494
495\fI\fB
496
497\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
498
499\fI\fB
500
501\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
502
503\fI\fB
504
505\fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
506
507\fI\fB
508
509\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
510
511\fI\fB
512
513\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
514
515\fI\fB
516
517\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
518
519\fI\fB
520
521\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
522
523\fI\fB
524
525\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
526
527\fI\fB
528
529\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
530
531\fI\fB
532
533\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
534
535\fI\fB
536
537\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
538
539\fI\fB
540
541\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
542
543\fI\fB
544
545\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
546
547\fI\fB
548
549\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
550
551\fI\fB
552
553\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
554
555\fI\fB
556
557\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
558
559\fI\fB
560
561\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
562
563\fI\fB
564
565\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
566
567\fI\fB
568
569\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
570
571\fI\fB
572
573\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
574
575\fI\fB
576
577\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
578
579\fI\fB
580
581\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
582
583\fI\fB
584
585\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
586
587\fI\fB
588
589\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
590
591\fI\fB
592
593\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
594
595\fI\fB
596
597\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
598
599\fI\fB
600
601\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
602
603\fI\fB
604
605\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
606
607\fI\fB
608
609\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
610
611\fI\fB
612
613\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
614
615\fI\fB
616
617\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
618
619\fI\fB
620
621\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
622
623\fI\fB
624
625\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
626
627\fI\fB
628
629\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
630
631\fI\fB
632
633\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
634
635\fI\fB
636
637\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
638
639\fI\fB
640
641\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
642
643\fI\fB
644
645\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
646
647\fI\fB
648
649\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
650
651\fI\fB
652
653\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
654
655\fI\fB
656
657\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
658
659\fI\fB
660
661\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
662
663\fI\fB
664
665\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
666
667\fI\fB
668
669\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
670
671\fI\fB
672
673\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
674
675\fI\fB
676
677\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
678
679\fI\fB
680
681\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
682
683\fI\fB
684
685\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
686
687\fI\fB
688
689\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
690
691\fI\fB
692
693\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
694
695\fI\fB
696
697\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
698
699\fI\fB
700
701\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
702
703\fI\fB
704
705\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
706
707\fI\fB
708
709\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
710
711\fI\fB
712
713\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
714
715\fI\fB
716
717\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
718
719\fI\fB
720
721\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
722
723\fI\fB
724
725\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
726
727\fI\fB
728
729\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
730
731\fI\fB
732
733\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
734
735\fI\fB
736
737\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
738
739\fI\fB
740
741\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
742
743\fI\fB
744
745\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
746
747\fI\fB
748
749\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
750
751\fI\fB
752
753\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
754
755\fI\fB
756
757\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
758
759\fI\fB
760
761\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
762
763\fI\fB
764
765\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
766
767\fI\fB
768
769\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
770
771\fI\fB
772
773\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
774
775\fI\fB
776
777\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
778
779\fI\fB
780
781\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
782
783\fI\fB
784
785\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
786
787\fI\fB
788
789\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
790
791\fI\fB
792
793\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
794
795\fI\fB
796
797\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
798
799\fI\fB
800
801\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
802
803\fI\fB
804
805\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
806
807\fI\fB
808
809\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
810
811\fI\fB
812
813.SH DESCRIPTION
814The
815.I libpng
816library supports encoding, decoding, and various manipulations of
817the Portable Network Graphics (PNG) format image files. It uses the
818.IR zlib(3)
819compression library.
820Following is a copy of the libpng.txt file that accompanies libpng.
821.SH LIBPNG.TXT
822libpng.txt - A description on how to use and modify libpng
823
824 libpng version 1.2.34 - December 18, 2008
825 Updated and distributed by Glenn Randers-Pehrson
826 <glennrp at users.sourceforge.net>
827 Copyright (c) 1998-2008 Glenn Randers-Pehrson
828 For conditions of distribution and use, see copyright
829 notice in png.h.
830
831 Based on:
832
833 libpng versions 0.97, January 1998, through 1.2.34 - December 18, 2008
834 Updated and distributed by Glenn Randers-Pehrson
835 Copyright (c) 1998-2008 Glenn Randers-Pehrson
836
837 libpng 1.0 beta 6 version 0.96 May 28, 1997
838 Updated and distributed by Andreas Dilger
839 Copyright (c) 1996, 1997 Andreas Dilger
840
841 libpng 1.0 beta 2 - version 0.88 January 26, 1996
842 For conditions of distribution and use, see copyright
843 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
844 Schalnat, Group 42, Inc.
845
846 Updated/rewritten per request in the libpng FAQ
847 Copyright (c) 1995, 1996 Frank J. T. Wojcik
848 December 18, 1995 & January 20, 1996
849
850.SH I. Introduction
851
852This file describes how to use and modify the PNG reference library
853(known as libpng) for your own use. There are five sections to this
854file: introduction, structures, reading, writing, and modification and
855configuration notes for various special platforms. In addition to this
856file, example.c is a good starting point for using the library, as
857it is heavily commented and should include everything most people
858will need. We assume that libpng is already installed; see the
859INSTALL file for instructions on how to install libpng.
860
861For examples of libpng usage, see the files "example.c", "pngtest.c",
862and the files in the "contrib" directory, all of which are included in the
863libpng distribution.
864
865Libpng was written as a companion to the PNG specification, as a way
866of reducing the amount of time and effort it takes to support the PNG
867file format in application programs.
868
869The PNG specification (second edition), November 2003, is available as
870a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
871<http://www.w3.org/TR/2003/REC-PNG-20031110/
872The W3C and ISO documents have identical technical content.
873
874The PNG-1.2 specification is available at
875<http://www.libpng.org/pub/png/documents/>. It is technically equivalent
876to the PNG specification (second edition) but has some additional material.
877
878The PNG-1.0 specification is available
879as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
880W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
881
882Some additional chunks are described in the special-purpose public chunks
883documents at <http://www.libpng.org/pub/png/documents/>.
884
885Other information
886about PNG, and the latest version of libpng, can be found at the PNG home
887page, <http://www.libpng.org/pub/png/>.
888
889Most users will not have to modify the library significantly; advanced
890users may want to modify it more. All attempts were made to make it as
891complete as possible, while keeping the code easy to understand.
892Currently, this library only supports C. Support for other languages
893is being considered.
894
895Libpng has been designed to handle multiple sessions at one time,
896to be easily modifiable, to be portable to the vast majority of
897machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
898to use. The ultimate goal of libpng is to promote the acceptance of
899the PNG file format in whatever way possible. While there is still
900work to be done (see the TODO file), libpng should cover the
901majority of the needs of its users.
902
903Libpng uses zlib for its compression and decompression of PNG files.
904Further information about zlib, and the latest version of zlib, can
905be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
906The zlib compression utility is a general purpose utility that is
907useful for more than PNG files, and can be used without libpng.
908See the documentation delivered with zlib for more details.
909You can usually find the source files for the zlib utility wherever you
910find the libpng source files.
911
912Libpng is thread safe, provided the threads are using different
913instances of the structures. Each thread should have its own
914png_struct and png_info instances, and thus its own image.
915Libpng does not protect itself against two threads using the
916same instance of a structure.
917
918.SH II. Structures
919
920There are two main structures that are important to libpng, png_struct
921and png_info. The first, png_struct, is an internal structure that
922will not, for the most part, be used by a user except as the first
923variable passed to every libpng function call.
924
925The png_info structure is designed to provide information about the
926PNG file. At one time, the fields of png_info were intended to be
927directly accessible to the user. However, this tended to cause problems
928with applications using dynamically loaded libraries, and as a result
929a set of interface functions for png_info (the png_get_*() and png_set_*()
930functions) was developed. The fields of png_info are still available for
931older applications, but it is suggested that applications use the new
932interfaces if at all possible.
933
934Applications that do make direct access to the members of png_struct (except
935for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
936and applications that make direct access to the members of png_info must
937be recompiled if they were compiled or loaded with libpng version 1.0.6,
938in which the members were in a different order. In version 1.0.7, the
939members of the png_info structure reverted to the old order, as they were
940in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
941structures are going to be hidden, and the contents of the structures will
942only be accessible through the png_get/png_set functions.
943
944The png.h header file is an invaluable reference for programming with libpng.
945And while I'm on the topic, make sure you include the libpng header file:
946
947#include <png.h>
948
949.SH III. Reading
950
951We'll now walk you through the possible functions to call when reading
952in a PNG file sequentially, briefly explaining the syntax and purpose
953of each one. See example.c and png.h for more detail. While
954progressive reading is covered in the next section, you will still
955need some of the functions discussed in this section to read a PNG
956file.
957
958.SS Setup
959
960You will want to do the I/O initialization(*) before you get into libpng,
961so if it doesn't work, you don't have much to undo. Of course, you
962will also want to insure that you are, in fact, dealing with a PNG
963file. Libpng provides a simple check to see if a file is a PNG file.
964To use it, pass in the first 1 to 8 bytes of the file to the function
965png_sig_cmp(), and it will return 0 if the bytes match the corresponding
966bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
967you pass in, the greater the accuracy of the prediction.
968
969If you are intending to keep the file pointer open for use in libpng,
970you must ensure you don't read more than 8 bytes from the beginning
971of the file, and you also have to make a call to png_set_sig_bytes_read()
972with the number of bytes you read from the beginning. Libpng will
973then only check the bytes (if any) that your program didn't read.
974
975(*): If you are not using the standard I/O functions, you will need
976to replace them with custom functions. See the discussion under
977Customizing libpng.
978
979
980 FILE *fp = fopen(file_name, "rb");
981 if (!fp)
982 {
983 return (ERROR);
984 }
985 fread(header, 1, number, fp);
986 is_png = !png_sig_cmp(header, 0, number);
987 if (!is_png)
988 {
989 return (NOT_PNG);
990 }
991
992
993Next, png_struct and png_info need to be allocated and initialized. In
994order to ensure that the size of these structures is correct even with a
995dynamically linked libpng, there are functions to initialize and
996allocate the structures. We also pass the library version, optional
997pointers to error handling functions, and a pointer to a data struct for
998use by the error functions, if necessary (the pointer and functions can
999be NULL if the default error handlers are to be used). See the section
1000on Changes to Libpng below regarding the old initialization functions.
1001The structure allocation functions quietly return NULL if they fail to
1002create the structure, so your application should check for that.
1003
1004 png_structp png_ptr = png_create_read_struct
1005 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1006 user_error_fn, user_warning_fn);
1007 if (!png_ptr)
1008 return (ERROR);
1009
1010 png_infop info_ptr = png_create_info_struct(png_ptr);
1011 if (!info_ptr)
1012 {
1013 png_destroy_read_struct(&png_ptr,
1014 (png_infopp)NULL, (png_infopp)NULL);
1015 return (ERROR);
1016 }
1017
1018 png_infop end_info = png_create_info_struct(png_ptr);
1019 if (!end_info)
1020 {
1021 png_destroy_read_struct(&png_ptr, &info_ptr,
1022 (png_infopp)NULL);
1023 return (ERROR);
1024 }
1025
1026If you want to use your own memory allocation routines,
1027define PNG_USER_MEM_SUPPORTED and use
1028png_create_read_struct_2() instead of png_create_read_struct():
1029
1030 png_structp png_ptr = png_create_read_struct_2
1031 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1032 user_error_fn, user_warning_fn, (png_voidp)
1033 user_mem_ptr, user_malloc_fn, user_free_fn);
1034
1035The error handling routines passed to png_create_read_struct()
1036and the memory alloc/free routines passed to png_create_struct_2()
1037are only necessary if you are not using the libpng supplied error
1038handling and memory alloc/free functions.
1039
1040When libpng encounters an error, it expects to longjmp back
1041to your routine. Therefore, you will need to call setjmp and pass
1042your png_jmpbuf(png_ptr). If you read the file from different
1043routines, you will need to update the jmpbuf field every time you enter
1044a new routine that will call a png_*() function.
1045
1046See your documentation of setjmp/longjmp for your compiler for more
1047information on setjmp/longjmp. See the discussion on libpng error
1048handling in the Customizing Libpng section below for more information
1049on the libpng error handling. If an error occurs, and libpng longjmp's
1050back to your setjmp, you will want to call png_destroy_read_struct() to
1051free any memory.
1052
1053 if (setjmp(png_jmpbuf(png_ptr)))
1054 {
1055 png_destroy_read_struct(&png_ptr, &info_ptr,
1056 &end_info);
1057 fclose(fp);
1058 return (ERROR);
1059 }
1060
1061If you would rather avoid the complexity of setjmp/longjmp issues,
1062you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1063errors will result in a call to PNG_ABORT() which defaults to abort().
1064
1065Now you need to set up the input code. The default for libpng is to
1066use the C function fread(). If you use this, you will need to pass a
1067valid FILE * in the function png_init_io(). Be sure that the file is
1068opened in binary mode. If you wish to handle reading data in another
1069way, you need not call the png_init_io() function, but you must then
1070implement the libpng I/O methods discussed in the Customizing Libpng
1071section below.
1072
1073 png_init_io(png_ptr, fp);
1074
1075If you had previously opened the file and read any of the signature from
1076the beginning in order to see if this was a PNG file, you need to let
1077libpng know that there are some bytes missing from the start of the file.
1078
1079 png_set_sig_bytes(png_ptr, number);
1080
1081.SS Setting up callback code
1082
1083You can set up a callback function to handle any unknown chunks in the
1084input stream. You must supply the function
1085
1086 read_chunk_callback(png_ptr ptr,
1087 png_unknown_chunkp chunk);
1088 {
1089 /* The unknown chunk structure contains your
1090 chunk data, along with similar data for any other
1091 unknown chunks: */
1092
1093 png_byte name[5];
1094 png_byte *data;
1095 png_size_t size;
1096
1097 /* Note that libpng has already taken care of
1098 the CRC handling */
1099
1100 /* put your code here. Search for your chunk in the
1101 unknown chunk structure, process it, and return one
1102 of the following: */
1103
1104 return (-n); /* chunk had an error */
1105 return (0); /* did not recognize */
1106 return (n); /* success */
1107 }
1108
1109(You can give your function another name that you like instead of
1110"read_chunk_callback")
1111
1112To inform libpng about your function, use
1113
1114 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1115 read_chunk_callback);
1116
1117This names not only the callback function, but also a user pointer that
1118you can retrieve with
1119
1120 png_get_user_chunk_ptr(png_ptr);
1121
1122If you call the png_set_read_user_chunk_fn() function, then all unknown
1123chunks will be saved when read, in case your callback function will need
1124one or more of them. This behavior can be changed with the
1125png_set_keep_unknown_chunks() function, described below.
1126
1127At this point, you can set up a callback function that will be
1128called after each row has been read, which you can use to control
1129a progress meter or the like. It's demonstrated in pngtest.c.
1130You must supply a function
1131
1132 void read_row_callback(png_ptr ptr, png_uint_32 row,
1133 int pass);
1134 {
1135 /* put your code here */
1136 }
1137
1138(You can give it another name that you like instead of "read_row_callback")
1139
1140To inform libpng about your function, use
1141
1142 png_set_read_status_fn(png_ptr, read_row_callback);
1143
1144.SS Width and height limits
1145
1146The PNG specification allows the width and height of an image to be as
1147large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1148Since very few applications really need to process such large images,
1149we have imposed an arbitrary 1-million limit on rows and columns.
1150Larger images will be rejected immediately with a png_error() call. If
1151you wish to override this limit, you can use
1152
1153 png_set_user_limits(png_ptr, width_max, height_max);
1154
1155to set your own limits, or use width_max = height_max = 0x7fffffffL
1156to allow all valid dimensions (libpng may reject some very large images
1157anyway because of potential buffer overflow conditions).
1158
1159You should put this statement after you create the PNG structure and
1160before calling png_read_info(), png_read_png(), or png_process_data().
1161If you need to retrieve the limits that are being applied, use
1162
1163 width_max = png_get_user_width_max(png_ptr);
1164 height_max = png_get_user_height_max(png_ptr);
1165
1166.SS Unknown-chunk handling
1167
1168Now you get to set the way the library processes unknown chunks in the
1169input PNG stream. Both known and unknown chunks will be read. Normal
1170behavior is that known chunks will be parsed into information in
1171various info_ptr members while unknown chunks will be discarded. This
1172behavior can be wasteful if your application will never use some known
1173chunk types. To change this, you can call:
1174
1175 png_set_keep_unknown_chunks(png_ptr, keep,
1176 chunk_list, num_chunks);
1177 keep - 0: default unknown chunk handling
1178 1: ignore; do not keep
1179 2: keep only if safe-to-copy
1180 3: keep even if unsafe-to-copy
1181 You can use these definitions:
1182 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1183 PNG_HANDLE_CHUNK_NEVER 1
1184 PNG_HANDLE_CHUNK_IF_SAFE 2
1185 PNG_HANDLE_CHUNK_ALWAYS 3
1186 chunk_list - list of chunks affected (a byte string,
1187 five bytes per chunk, NULL or '\0' if
1188 num_chunks is 0)
1189 num_chunks - number of chunks affected; if 0, all
1190 unknown chunks are affected. If nonzero,
1191 only the chunks in the list are affected
1192
1193Unknown chunks declared in this way will be saved as raw data onto a
1194list of png_unknown_chunk structures. If a chunk that is normally
1195known to libpng is named in the list, it will be handled as unknown,
1196according to the "keep" directive. If a chunk is named in successive
1197instances of png_set_keep_unknown_chunks(), the final instance will
1198take precedence. The IHDR and IEND chunks should not be named in
1199chunk_list; if they are, libpng will process them normally anyway.
1200
1201Here is an example of the usage of png_set_keep_unknown_chunks(),
1202where the private "vpAg" chunk will later be processed by a user chunk
1203callback function:
1204
1205 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1206
1207 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1208 png_byte unused_chunks[]=
1209 {
1210 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1211 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1212 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1213 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1214 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1215 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1216 };
1217 #endif
1218
1219 ...
1220
1221 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1222 /* ignore all unknown chunks: */
1223 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1224 /* except for vpAg: */
1225 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1226 /* also ignore unused known chunks: */
1227 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1228 (int)sizeof(unused_chunks)/5);
1229 #endif
1230
1231
1232.SS The high-level read interface
1233
1234At this point there are two ways to proceed; through the high-level
1235read interface, or through a sequence of low-level read operations.
1236You can use the high-level interface if (a) you are willing to read
1237the entire image into memory, and (b) the input transformations
1238you want to do are limited to the following set:
1239
1240 PNG_TRANSFORM_IDENTITY No transformation
1241 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1242 8 bits
1243 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1244 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1245 samples to bytes
1246 PNG_TRANSFORM_PACKSWAP Change order of packed
1247 pixels to LSB first
1248 PNG_TRANSFORM_EXPAND Perform set_expand()
1249 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1250 PNG_TRANSFORM_SHIFT Normalize pixels to the
1251 sBIT depth
1252 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1253 to BGRA
1254 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1255 to AG
1256 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1257 to transparency
1258 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1259
1260(This excludes setting a background color, doing gamma transformation,
1261dithering, and setting filler.) If this is the case, simply do this:
1262
1263 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1264
1265where png_transforms is an integer containing the bitwise OR of
1266some set of transformation flags. This call is equivalent to png_read_info(),
1267followed the set of transformations indicated by the transform mask,
1268then png_read_image(), and finally png_read_end().
1269
1270(The final parameter of this call is not yet used. Someday it might point
1271to transformation parameters required by some future input transform.)
1272
1273You must use png_transforms and not call any png_set_transform() functions
1274when you use png_read_png().
1275
1276After you have called png_read_png(), you can retrieve the image data
1277with
1278
1279 row_pointers = png_get_rows(png_ptr, info_ptr);
1280
1281where row_pointers is an array of pointers to the pixel data for each row:
1282
1283 png_bytep row_pointers[height];
1284
1285If you know your image size and pixel size ahead of time, you can allocate
1286row_pointers prior to calling png_read_png() with
1287
1288 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1289 png_error (png_ptr,
1290 "Image is too tall to process in memory");
1291 if (width > PNG_UINT_32_MAX/pixel_size)
1292 png_error (png_ptr,
1293 "Image is too wide to process in memory");
1294 row_pointers = png_malloc(png_ptr,
1295 height*png_sizeof(png_bytep));
1296 for (int i=0; i<height, i++)
1297 row_pointers[i]=png_malloc(png_ptr,
1298 width*pixel_size);
1299 png_set_rows(png_ptr, info_ptr, &row_pointers);
1300
1301Alternatively you could allocate your image in one big block and define
1302row_pointers[i] to point into the proper places in your block.
1303
1304If you use png_set_rows(), the application is responsible for freeing
1305row_pointers (and row_pointers[i], if they were separately allocated).
1306
1307If you don't allocate row_pointers ahead of time, png_read_png() will
1308do it, and it'll be free'ed when you call png_destroy_*().
1309
1310.SS The low-level read interface
1311
1312If you are going the low-level route, you are now ready to read all
1313the file information up to the actual image data. You do this with a
1314call to png_read_info().
1315
1316 png_read_info(png_ptr, info_ptr);
1317
1318This will process all chunks up to but not including the image data.
1319
1320.SS Querying the info structure
1321
1322Functions are used to get the information from the info_ptr once it
1323has been read. Note that these fields may not be completely filled
1324in until png_read_end() has read the chunk data following the image.
1325
1326 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1327 &bit_depth, &color_type, &interlace_type,
1328 &compression_type, &filter_method);
1329
1330 width - holds the width of the image
1331 in pixels (up to 2^31).
1332 height - holds the height of the image
1333 in pixels (up to 2^31).
1334 bit_depth - holds the bit depth of one of the
1335 image channels. (valid values are
1336 1, 2, 4, 8, 16 and depend also on
1337 the color_type. See also
1338 significant bits (sBIT) below).
1339 color_type - describes which color/alpha channels
1340 are present.
1341 PNG_COLOR_TYPE_GRAY
1342 (bit depths 1, 2, 4, 8, 16)
1343 PNG_COLOR_TYPE_GRAY_ALPHA
1344 (bit depths 8, 16)
1345 PNG_COLOR_TYPE_PALETTE
1346 (bit depths 1, 2, 4, 8)
1347 PNG_COLOR_TYPE_RGB
1348 (bit_depths 8, 16)
1349 PNG_COLOR_TYPE_RGB_ALPHA
1350 (bit_depths 8, 16)
1351
1352 PNG_COLOR_MASK_PALETTE
1353 PNG_COLOR_MASK_COLOR
1354 PNG_COLOR_MASK_ALPHA
1355
1356 filter_method - (must be PNG_FILTER_TYPE_BASE
1357 for PNG 1.0, and can also be
1358 PNG_INTRAPIXEL_DIFFERENCING if
1359 the PNG datastream is embedded in
1360 a MNG-1.0 datastream)
1361 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1362 for PNG 1.0)
1363 interlace_type - (PNG_INTERLACE_NONE or
1364 PNG_INTERLACE_ADAM7)
1365 Any or all of interlace_type, compression_type, of
1366 filter_method can be NULL if you are
1367 not interested in their values.
1368
1369 channels = png_get_channels(png_ptr, info_ptr);
1370 channels - number of channels of info for the
1371 color type (valid values are 1 (GRAY,
1372 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1373 4 (RGB_ALPHA or RGB + filler byte))
1374 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1375 rowbytes - number of bytes needed to hold a row
1376
1377 signature = png_get_signature(png_ptr, info_ptr);
1378 signature - holds the signature read from the
1379 file (if any). The data is kept in
1380 the same offset it would be if the
1381 whole signature were read (i.e. if an
1382 application had already read in 4
1383 bytes of signature before starting
1384 libpng, the remaining 4 bytes would
1385 be in signature[4] through signature[7]
1386 (see png_set_sig_bytes())).
1387
1388
1389 width = png_get_image_width(png_ptr,
1390 info_ptr);
1391 height = png_get_image_height(png_ptr,
1392 info_ptr);
1393 bit_depth = png_get_bit_depth(png_ptr,
1394 info_ptr);
1395 color_type = png_get_color_type(png_ptr,
1396 info_ptr);
1397 filter_method = png_get_filter_type(png_ptr,
1398 info_ptr);
1399 compression_type = png_get_compression_type(png_ptr,
1400 info_ptr);
1401 interlace_type = png_get_interlace_type(png_ptr,
1402 info_ptr);
1403
1404
1405These are also important, but their validity depends on whether the chunk
1406has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1407png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1408data has been read, or zero if it is missing. The parameters to the
1409png_get_<chunk> are set directly if they are simple data types, or a pointer
1410into the info_ptr is returned for any complex types.
1411
1412 png_get_PLTE(png_ptr, info_ptr, &palette,
1413 &num_palette);
1414 palette - the palette for the file
1415 (array of png_color)
1416 num_palette - number of entries in the palette
1417
1418 png_get_gAMA(png_ptr, info_ptr, &gamma);
1419 gamma - the gamma the file is written
1420 at (PNG_INFO_gAMA)
1421
1422 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1423 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1424 The presence of the sRGB chunk
1425 means that the pixel data is in the
1426 sRGB color space. This chunk also
1427 implies specific values of gAMA and
1428 cHRM.
1429
1430 png_get_iCCP(png_ptr, info_ptr, &name,
1431 &compression_type, &profile, &proflen);
1432 name - The profile name.
1433 compression - The compression type; always
1434 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1435 You may give NULL to this argument to
1436 ignore it.
1437 profile - International Color Consortium color
1438 profile data. May contain NULs.
1439 proflen - length of profile data in bytes.
1440
1441 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1442 sig_bit - the number of significant bits for
1443 (PNG_INFO_sBIT) each of the gray,
1444 red, green, and blue channels,
1445 whichever are appropriate for the
1446 given color type (png_color_16)
1447
1448 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1449 &trans_values);
1450 trans - array of transparent entries for
1451 palette (PNG_INFO_tRNS)
1452 trans_values - graylevel or color sample values of
1453 the single transparent color for
1454 non-paletted images (PNG_INFO_tRNS)
1455 num_trans - number of transparent entries
1456 (PNG_INFO_tRNS)
1457
1458 png_get_hIST(png_ptr, info_ptr, &hist);
1459 (PNG_INFO_hIST)
1460 hist - histogram of palette (array of
1461 png_uint_16)
1462
1463 png_get_tIME(png_ptr, info_ptr, &mod_time);
1464 mod_time - time image was last modified
1465 (PNG_VALID_tIME)
1466
1467 png_get_bKGD(png_ptr, info_ptr, &background);
1468 background - background color (PNG_VALID_bKGD)
1469 valid 16-bit red, green and blue
1470 values, regardless of color_type
1471
1472 num_comments = png_get_text(png_ptr, info_ptr,
1473 &text_ptr, &num_text);
1474 num_comments - number of comments
1475 text_ptr - array of png_text holding image
1476 comments
1477 text_ptr[i].compression - type of compression used
1478 on "text" PNG_TEXT_COMPRESSION_NONE
1479 PNG_TEXT_COMPRESSION_zTXt
1480 PNG_ITXT_COMPRESSION_NONE
1481 PNG_ITXT_COMPRESSION_zTXt
1482 text_ptr[i].key - keyword for comment. Must contain
1483 1-79 characters.
1484 text_ptr[i].text - text comments for current
1485 keyword. Can be empty.
1486 text_ptr[i].text_length - length of text string,
1487 after decompression, 0 for iTXt
1488 text_ptr[i].itxt_length - length of itxt string,
1489 after decompression, 0 for tEXt/zTXt
1490 text_ptr[i].lang - language of comment (empty
1491 string for unknown).
1492 text_ptr[i].lang_key - keyword in UTF-8
1493 (empty string for unknown).
1494 num_text - number of comments (same as
1495 num_comments; you can put NULL here
1496 to avoid the duplication)
1497 Note while png_set_text() will accept text, language,
1498 and translated keywords that can be NULL pointers, the
1499 structure returned by png_get_text will always contain
1500 regular zero-terminated C strings. They might be
1501 empty strings but they will never be NULL pointers.
1502
1503 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1504 &palette_ptr);
1505 palette_ptr - array of palette structures holding
1506 contents of one or more sPLT chunks
1507 read.
1508 num_spalettes - number of sPLT chunks read.
1509
1510 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1511 &unit_type);
1512 offset_x - positive offset from the left edge
1513 of the screen
1514 offset_y - positive offset from the top edge
1515 of the screen
1516 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1517
1518 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1519 &unit_type);
1520 res_x - pixels/unit physical resolution in
1521 x direction
1522 res_y - pixels/unit physical resolution in
1523 x direction
1524 unit_type - PNG_RESOLUTION_UNKNOWN,
1525 PNG_RESOLUTION_METER
1526
1527 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1528 &height)
1529 unit - physical scale units (an integer)
1530 width - width of a pixel in physical scale units
1531 height - height of a pixel in physical scale units
1532 (width and height are doubles)
1533
1534 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1535 &height)
1536 unit - physical scale units (an integer)
1537 width - width of a pixel in physical scale units
1538 height - height of a pixel in physical scale units
1539 (width and height are strings like "2.54")
1540
1541 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1542 info_ptr, &unknowns)
1543 unknowns - array of png_unknown_chunk
1544 structures holding unknown chunks
1545 unknowns[i].name - name of unknown chunk
1546 unknowns[i].data - data of unknown chunk
1547 unknowns[i].size - size of unknown chunk's data
1548 unknowns[i].location - position of chunk in file
1549
1550 The value of "i" corresponds to the order in which the
1551 chunks were read from the PNG file or inserted with the
1552 png_set_unknown_chunks() function.
1553
1554The data from the pHYs chunk can be retrieved in several convenient
1555forms:
1556
1557 res_x = png_get_x_pixels_per_meter(png_ptr,
1558 info_ptr)
1559 res_y = png_get_y_pixels_per_meter(png_ptr,
1560 info_ptr)
1561 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1562 info_ptr)
1563 res_x = png_get_x_pixels_per_inch(png_ptr,
1564 info_ptr)
1565 res_y = png_get_y_pixels_per_inch(png_ptr,
1566 info_ptr)
1567 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1568 info_ptr)
1569 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1570 info_ptr)
1571
1572 (Each of these returns 0 [signifying "unknown"] if
1573 the data is not present or if res_x is 0;
1574 res_x_and_y is 0 if res_x != res_y)
1575
1576The data from the oFFs chunk can be retrieved in several convenient
1577forms:
1578
1579 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1580 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1581 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1582 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1583
1584 (Each of these returns 0 [signifying "unknown" if both
1585 x and y are 0] if the data is not present or if the
1586 chunk is present but the unit is the pixel)
1587
1588For more information, see the png_info definition in png.h and the
1589PNG specification for chunk contents. Be careful with trusting
1590rowbytes, as some of the transformations could increase the space
1591needed to hold a row (expand, filler, gray_to_rgb, etc.).
1592See png_read_update_info(), below.
1593
1594A quick word about text_ptr and num_text. PNG stores comments in
1595keyword/text pairs, one pair per chunk, with no limit on the number
1596of text chunks, and a 2^31 byte limit on their size. While there are
1597suggested keywords, there is no requirement to restrict the use to these
1598strings. It is strongly suggested that keywords and text be sensible
1599to humans (that's the point), so don't use abbreviations. Non-printing
1600symbols are not allowed. See the PNG specification for more details.
1601There is also no requirement to have text after the keyword.
1602
1603Keywords should be limited to 79 Latin-1 characters without leading or
1604trailing spaces, but non-consecutive spaces are allowed within the
1605keyword. It is possible to have the same keyword any number of times.
1606The text_ptr is an array of png_text structures, each holding a
1607pointer to a language string, a pointer to a keyword and a pointer to
1608a text string. The text string, language code, and translated
1609keyword may be empty or NULL pointers. The keyword/text
1610pairs are put into the array in the order that they are received.
1611However, some or all of the text chunks may be after the image, so, to
1612make sure you have read all the text chunks, don't mess with these
1613until after you read the stuff after the image. This will be
1614mentioned again below in the discussion that goes with png_read_end().
1615
1616.SS Input transformations
1617
1618After you've read the header information, you can set up the library
1619to handle any special transformations of the image data. The various
1620ways to transform the data will be described in the order that they
1621should occur. This is important, as some of these change the color
1622type and/or bit depth of the data, and some others only work on
1623certain color types and bit depths. Even though each transformation
1624checks to see if it has data that it can do something with, you should
1625make sure to only enable a transformation if it will be valid for the
1626data. For example, don't swap red and blue on grayscale data.
1627
1628The colors used for the background and transparency values should be
1629supplied in the same format/depth as the current image data. They
1630are stored in the same format/depth as the image data in a bKGD or tRNS
1631chunk, so this is what libpng expects for this data. The colors are
1632transformed to keep in sync with the image data when an application
1633calls the png_read_update_info() routine (see below).
1634
1635Data will be decoded into the supplied row buffers packed into bytes
1636unless the library has been told to transform it into another format.
1637For example, 4 bit/pixel paletted or grayscale data will be returned
16382 pixels/byte with the leftmost pixel in the high-order bits of the
1639byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1640in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1641is called to insert filler bytes, either before or after each RGB triplet.
164216-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1643byte of the color value first, unless png_set_strip_16() is called to
1644transform it to regular RGB RGB triplets, or png_set_filler() or
1645png_set_add alpha() is called to insert filler bytes, either before or
1646after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1647be modified with
1648png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1649
1650The following code transforms grayscale images of less than 8 to 8 bits,
1651changes paletted images to RGB, and adds a full alpha channel if there is
1652transparency information in a tRNS chunk. This is most useful on
1653grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1654viewing application that wishes to treat all images in the same way.
1655
1656 if (color_type == PNG_COLOR_TYPE_PALETTE)
1657 png_set_palette_to_rgb(png_ptr);
1658
1659 if (color_type == PNG_COLOR_TYPE_GRAY &&
1660 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1661
1662 if (png_get_valid(png_ptr, info_ptr,
1663 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1664
1665These three functions are actually aliases for png_set_expand(), added
1666in libpng version 1.0.4, with the function names expanded to improve code
1667readability. In some future version they may actually do different
1668things.
1669
1670As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1671added. It expands the sample depth without changing tRNS to alpha.
1672At the same time, png_set_gray_1_2_4_to_8() was deprecated, and it
1673will be removed from a future version.
1674
1675
1676PNG can have files with 16 bits per channel. If you only can handle
16778 bits per channel, this will strip the pixels down to 8 bit.
1678
1679 if (bit_depth == 16)
1680 png_set_strip_16(png_ptr);
1681
1682If, for some reason, you don't need the alpha channel on an image,
1683and you want to remove it rather than combining it with the background
1684(but the image author certainly had in mind that you *would* combine
1685it with the background, so that's what you should probably do):
1686
1687 if (color_type & PNG_COLOR_MASK_ALPHA)
1688 png_set_strip_alpha(png_ptr);
1689
1690In PNG files, the alpha channel in an image
1691is the level of opacity. If you need the alpha channel in an image to
1692be the level of transparency instead of opacity, you can invert the
1693alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1694fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1695images) is fully transparent, with
1696
1697 png_set_invert_alpha(png_ptr);
1698
1699PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1700they can, resulting in, for example, 8 pixels per byte for 1 bit
1701files. This code expands to 1 pixel per byte without changing the
1702values of the pixels:
1703
1704 if (bit_depth < 8)
1705 png_set_packing(png_ptr);
1706
1707PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1708stored in a PNG image have been "scaled" or "shifted" up to the next
1709higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
17108 bits/sample in the range [0, 255]). However, it is also possible to
1711convert the PNG pixel data back to the original bit depth of the image.
1712This call reduces the pixels back down to the original bit depth:
1713
1714 png_color_8p sig_bit;
1715
1716 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1717 png_set_shift(png_ptr, sig_bit);
1718
1719PNG files store 3-color pixels in red, green, blue order. This code
1720changes the storage of the pixels to blue, green, red:
1721
1722 if (color_type == PNG_COLOR_TYPE_RGB ||
1723 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1724 png_set_bgr(png_ptr);
1725
1726PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1727into 4 or 8 bytes for windowing systems that need them in this format:
1728
1729 if (color_type == PNG_COLOR_TYPE_RGB)
1730 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1731
1732where "filler" is the 8 or 16-bit number to fill with, and the location is
1733either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1734you want the filler before the RGB or after. This transformation
1735does not affect images that already have full alpha channels. To add an
1736opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1737will generate RGBA pixels.
1738
1739Note that png_set_filler() does not change the color type. If you want
1740to do that, you can add a true alpha channel with
1741
1742 if (color_type == PNG_COLOR_TYPE_RGB ||
1743 color_type == PNG_COLOR_TYPE_GRAY)
1744 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1745
1746where "filler" contains the alpha value to assign to each pixel.
1747This function was added in libpng-1.2.7.
1748
1749If you are reading an image with an alpha channel, and you need the
1750data as ARGB instead of the normal PNG format RGBA:
1751
1752 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1753 png_set_swap_alpha(png_ptr);
1754
1755For some uses, you may want a grayscale image to be represented as
1756RGB. This code will do that conversion:
1757
1758 if (color_type == PNG_COLOR_TYPE_GRAY ||
1759 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1760 png_set_gray_to_rgb(png_ptr);
1761
1762Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1763with alpha.
1764
1765 if (color_type == PNG_COLOR_TYPE_RGB ||
1766 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1767 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1768 int red_weight, int green_weight);
1769
1770 error_action = 1: silently do the conversion
1771 error_action = 2: issue a warning if the original
1772 image has any pixel where
1773 red != green or red != blue
1774 error_action = 3: issue an error and abort the
1775 conversion if the original
1776 image has any pixel where
1777 red != green or red != blue
1778
1779 red_weight: weight of red component times 100000
1780 green_weight: weight of green component times 100000
1781 If either weight is negative, default
1782 weights (21268, 71514) are used.
1783
1784If you have set error_action = 1 or 2, you can
1785later check whether the image really was gray, after processing
1786the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1787It will return a png_byte that is zero if the image was gray or
17881 if there were any non-gray pixels. bKGD and sBIT data
1789will be silently converted to grayscale, using the green channel
1790data, regardless of the error_action setting.
1791
1792With red_weight+green_weight<=100000,
1793the normalized graylevel is computed:
1794
1795 int rw = red_weight * 65536;
1796 int gw = green_weight * 65536;
1797 int bw = 65536 - (rw + gw);
1798 gray = (rw*red + gw*green + bw*blue)/65536;
1799
1800The default values approximate those recommended in the Charles
1801Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1802Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1803
1804 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1805
1806Libpng approximates this with
1807
1808 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1809
1810which can be expressed with integers as
1811
1812 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1813
1814The calculation is done in a linear colorspace, if the image gamma
1815is known.
1816
1817If you have a grayscale and you are using png_set_expand_depth(),
1818png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1819a higher bit-depth, you must either supply the background color as a gray
1820value at the original file bit-depth (need_expand = 1) or else supply the
1821background color as an RGB triplet at the final, expanded bit depth
1822(need_expand = 0). Similarly, if you are reading a paletted image, you
1823must either supply the background color as a palette index (need_expand = 1)
1824or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1825
1826 png_color_16 my_background;
1827 png_color_16p image_background;
1828
1829 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1830 png_set_background(png_ptr, image_background,
1831 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1832 else
1833 png_set_background(png_ptr, &my_background,
1834 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1835
1836The png_set_background() function tells libpng to composite images
1837with alpha or simple transparency against the supplied background
1838color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1839you may use this color, or supply another color more suitable for
1840the current display (e.g., the background color from a web page). You
1841need to tell libpng whether the color is in the gamma space of the
1842display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1843(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1844that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1845know why anyone would use this, but it's here).
1846
1847To properly display PNG images on any kind of system, the application needs
1848to know what the display gamma is. Ideally, the user will know this, and
1849the application will allow them to set it. One method of allowing the user
1850to set the display gamma separately for each system is to check for a
1851SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1852correctly set.
1853
1854Note that display_gamma is the overall gamma correction required to produce
1855pleasing results, which depends on the lighting conditions in the surrounding
1856environment. In a dim or brightly lit room, no compensation other than
1857the physical gamma exponent of the monitor is needed, while in a dark room
1858a slightly smaller exponent is better.
1859
1860 double gamma, screen_gamma;
1861
1862 if (/* We have a user-defined screen
1863 gamma value */)
1864 {
1865 screen_gamma = user_defined_screen_gamma;
1866 }
1867 /* One way that applications can share the same
1868 screen gamma value */
1869 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1870 != NULL)
1871 {
1872 screen_gamma = (double)atof(gamma_str);
1873 }
1874 /* If we don't have another value */
1875 else
1876 {
1877 screen_gamma = 2.2; /* A good guess for a
1878 PC monitor in a bright office or a dim room */
1879 screen_gamma = 2.0; /* A good guess for a
1880 PC monitor in a dark room */
1881 screen_gamma = 1.7 or 1.0; /* A good
1882 guess for Mac systems */
1883 }
1884
1885The png_set_gamma() function handles gamma transformations of the data.
1886Pass both the file gamma and the current screen_gamma. If the file does
1887not have a gamma value, you can pass one anyway if you have an idea what
1888it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1889that file gammas are inverted from screen gammas. See the discussions
1890on gamma in the PNG specification for an excellent description of what
1891gamma is, and why all applications should support it. It is strongly
1892recommended that PNG viewers support gamma correction.
1893
1894 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1895 png_set_gamma(png_ptr, screen_gamma, gamma);
1896 else
1897 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1898
1899If you need to reduce an RGB file to a paletted file, or if a paletted
1900file has more entries then will fit on your screen, png_set_dither()
1901will do that. Note that this is a simple match dither that merely
1902finds the closest color available. This should work fairly well with
1903optimized palettes, and fairly badly with linear color cubes. If you
1904pass a palette that is larger then maximum_colors, the file will
1905reduce the number of colors in the palette so it will fit into
1906maximum_colors. If there is a histogram, it will use it to make
1907more intelligent choices when reducing the palette. If there is no
1908histogram, it may not do as good a job.
1909
1910 if (color_type & PNG_COLOR_MASK_COLOR)
1911 {
1912 if (png_get_valid(png_ptr, info_ptr,
1913 PNG_INFO_PLTE))
1914 {
1915 png_uint_16p histogram = NULL;
1916
1917 png_get_hIST(png_ptr, info_ptr,
1918 &histogram);
1919 png_set_dither(png_ptr, palette, num_palette,
1920 max_screen_colors, histogram, 1);
1921 }
1922 else
1923 {
1924 png_color std_color_cube[MAX_SCREEN_COLORS] =
1925 { ... colors ... };
1926
1927 png_set_dither(png_ptr, std_color_cube,
1928 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1929 NULL,0);
1930 }
1931 }
1932
1933PNG files describe monochrome as black being zero and white being one.
1934The following code will reverse this (make black be one and white be
1935zero):
1936
1937 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1938 png_set_invert_mono(png_ptr);
1939
1940This function can also be used to invert grayscale and gray-alpha images:
1941
1942 if (color_type == PNG_COLOR_TYPE_GRAY ||
1943 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1944 png_set_invert_mono(png_ptr);
1945
1946PNG files store 16 bit pixels in network byte order (big-endian,
1947ie. most significant bits first). This code changes the storage to the
1948other way (little-endian, i.e. least significant bits first, the
1949way PCs store them):
1950
1951 if (bit_depth == 16)
1952 png_set_swap(png_ptr);
1953
1954If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1955need to change the order the pixels are packed into bytes, you can use:
1956
1957 if (bit_depth < 8)
1958 png_set_packswap(png_ptr);
1959
1960Finally, you can write your own transformation function if none of
1961the existing ones meets your needs. This is done by setting a callback
1962with
1963
1964 png_set_read_user_transform_fn(png_ptr,
1965 read_transform_fn);
1966
1967You must supply the function
1968
1969 void read_transform_fn(png_ptr ptr, row_info_ptr
1970 row_info, png_bytep data)
1971
1972See pngtest.c for a working example. Your function will be called
1973after all of the other transformations have been processed.
1974
1975You can also set up a pointer to a user structure for use by your
1976callback function, and you can inform libpng that your transform
1977function will change the number of channels or bit depth with the
1978function
1979
1980 png_set_user_transform_info(png_ptr, user_ptr,
1981 user_depth, user_channels);
1982
1983The user's application, not libpng, is responsible for allocating and
1984freeing any memory required for the user structure.
1985
1986You can retrieve the pointer via the function
1987png_get_user_transform_ptr(). For example:
1988
1989 voidp read_user_transform_ptr =
1990 png_get_user_transform_ptr(png_ptr);
1991
1992The last thing to handle is interlacing; this is covered in detail below,
1993but you must call the function here if you want libpng to handle expansion
1994of the interlaced image.
1995
1996 number_of_passes = png_set_interlace_handling(png_ptr);
1997
1998After setting the transformations, libpng can update your png_info
1999structure to reflect any transformations you've requested with this
2000call. This is most useful to update the info structure's rowbytes
2001field so you can use it to allocate your image memory. This function
2002will also update your palette with the correct screen_gamma and
2003background if these have been given with the calls above.
2004
2005 png_read_update_info(png_ptr, info_ptr);
2006
2007After you call png_read_update_info(), you can allocate any
2008memory you need to hold the image. The row data is simply
2009raw byte data for all forms of images. As the actual allocation
2010varies among applications, no example will be given. If you
2011are allocating one large chunk, you will need to build an
2012array of pointers to each row, as it will be needed for some
2013of the functions below.
2014
2015.SS Reading image data
2016
2017After you've allocated memory, you can read the image data.
2018The simplest way to do this is in one function call. If you are
2019allocating enough memory to hold the whole image, you can just
2020call png_read_image() and libpng will read in all the image data
2021and put it in the memory area supplied. You will need to pass in
2022an array of pointers to each row.
2023
2024This function automatically handles interlacing, so you don't need
2025to call png_set_interlace_handling() or call this function multiple
2026times, or any of that other stuff necessary with png_read_rows().
2027
2028 png_read_image(png_ptr, row_pointers);
2029
2030where row_pointers is:
2031
2032 png_bytep row_pointers[height];
2033
2034You can point to void or char or whatever you use for pixels.
2035
2036If you don't want to read in the whole image at once, you can
2037use png_read_rows() instead. If there is no interlacing (check
2038interlace_type == PNG_INTERLACE_NONE), this is simple:
2039
2040 png_read_rows(png_ptr, row_pointers, NULL,
2041 number_of_rows);
2042
2043where row_pointers is the same as in the png_read_image() call.
2044
2045If you are doing this just one row at a time, you can do this with
2046a single row_pointer instead of an array of row_pointers:
2047
2048 png_bytep row_pointer = row;
2049 png_read_row(png_ptr, row_pointer, NULL);
2050
2051If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2052get somewhat harder. The only current (PNG Specification version 1.2)
2053interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
2054is a somewhat complicated 2D interlace scheme, known as Adam7, that
2055breaks down an image into seven smaller images of varying size, based
2056on an 8x8 grid.
2057
2058libpng can fill out those images or it can give them to you "as is".
2059If you want them filled out, there are two ways to do that. The one
2060mentioned in the PNG specification is to expand each pixel to cover
2061those pixels that have not been read yet (the "rectangle" method).
2062This results in a blocky image for the first pass, which gradually
2063smooths out as more pixels are read. The other method is the "sparkle"
2064method, where pixels are drawn only in their final locations, with the
2065rest of the image remaining whatever colors they were initialized to
2066before the start of the read. The first method usually looks better,
2067but tends to be slower, as there are more pixels to put in the rows.
2068
2069If you don't want libpng to handle the interlacing details, just call
2070png_read_rows() seven times to read in all seven images. Each of the
2071images is a valid image by itself, or they can all be combined on an
20728x8 grid to form a single image (although if you intend to combine them
2073you would be far better off using the libpng interlace handling).
2074
2075The first pass will return an image 1/8 as wide as the entire image
2076(every 8th column starting in column 0) and 1/8 as high as the original
2077(every 8th row starting in row 0), the second will be 1/8 as wide
2078(starting in column 4) and 1/8 as high (also starting in row 0). The
2079third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
20801/8 as high (every 8th row starting in row 4), and the fourth pass will
2081be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
2082and every 4th row starting in row 0). The fifth pass will return an
2083image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
2084while the sixth pass will be 1/2 as wide and 1/2 as high as the original
2085(starting in column 1 and row 0). The seventh and final pass will be as
2086wide as the original, and 1/2 as high, containing all of the odd
2087numbered scanlines. Phew!
2088
2089If you want libpng to expand the images, call this before calling
2090png_start_read_image() or png_read_update_info():
2091
2092 if (interlace_type == PNG_INTERLACE_ADAM7)
2093 number_of_passes
2094 = png_set_interlace_handling(png_ptr);
2095
2096This will return the number of passes needed. Currently, this
2097is seven, but may change if another interlace type is added.
2098This function can be called even if the file is not interlaced,
2099where it will return one pass.
2100
2101If you are not going to display the image after each pass, but are
2102going to wait until the entire image is read in, use the sparkle
2103effect. This effect is faster and the end result of either method
2104is exactly the same. If you are planning on displaying the image
2105after each pass, the "rectangle" effect is generally considered the
2106better looking one.
2107
2108If you only want the "sparkle" effect, just call png_read_rows() as
2109normal, with the third parameter NULL. Make sure you make pass over
2110the image number_of_passes times, and you don't change the data in the
2111rows between calls. You can change the locations of the data, just
2112not the data. Each pass only writes the pixels appropriate for that
2113pass, and assumes the data from previous passes is still valid.
2114
2115 png_read_rows(png_ptr, row_pointers, NULL,
2116 number_of_rows);
2117
2118If you only want the first effect (the rectangles), do the same as
2119before except pass the row buffer in the third parameter, and leave
2120the second parameter NULL.
2121
2122 png_read_rows(png_ptr, NULL, row_pointers,
2123 number_of_rows);
2124
2125.SS Finishing a sequential read
2126
2127After you are finished reading the image through the
2128low-level interface, you can finish reading the file. If you are
2129interested in comments or time, which may be stored either before or
2130after the image data, you should pass the separate png_info struct if
2131you want to keep the comments from before and after the image
2132separate. If you are not interested, you can pass NULL.
2133
2134 png_read_end(png_ptr, end_info);
2135
2136When you are done, you can free all memory allocated by libpng like this:
2137
2138 png_destroy_read_struct(&png_ptr, &info_ptr,
2139 &end_info);
2140
2141It is also possible to individually free the info_ptr members that
2142point to libpng-allocated storage with the following function:
2143
2144 png_free_data(png_ptr, info_ptr, mask, seq)
2145 mask - identifies data to be freed, a mask
2146 containing the bitwise OR of one or
2147 more of
2148 PNG_FREE_PLTE, PNG_FREE_TRNS,
2149 PNG_FREE_HIST, PNG_FREE_ICCP,
2150 PNG_FREE_PCAL, PNG_FREE_ROWS,
2151 PNG_FREE_SCAL, PNG_FREE_SPLT,
2152 PNG_FREE_TEXT, PNG_FREE_UNKN,
2153 or simply PNG_FREE_ALL
2154 seq - sequence number of item to be freed
2155 (-1 for all items)
2156
2157This function may be safely called when the relevant storage has
2158already been freed, or has not yet been allocated, or was allocated
2159by the user and not by libpng, and will in those
2160cases do nothing. The "seq" parameter is ignored if only one item
2161of the selected data type, such as PLTE, is allowed. If "seq" is not
2162-1, and multiple items are allowed for the data type identified in
2163the mask, such as text or sPLT, only the n'th item in the structure
2164is freed, where n is "seq".
2165
2166The default behavior is only to free data that was allocated internally
2167by libpng. This can be changed, so that libpng will not free the data,
2168or so that it will free data that was allocated by the user with png_malloc()
2169or png_zalloc() and passed in via a png_set_*() function, with
2170
2171 png_data_freer(png_ptr, info_ptr, freer, mask)
2172 mask - which data elements are affected
2173 same choices as in png_free_data()
2174 freer - one of
2175 PNG_DESTROY_WILL_FREE_DATA
2176 PNG_SET_WILL_FREE_DATA
2177 PNG_USER_WILL_FREE_DATA
2178
2179This function only affects data that has already been allocated.
2180You can call this function after reading the PNG data but before calling
2181any png_set_*() functions, to control whether the user or the png_set_*()
2182function is responsible for freeing any existing data that might be present,
2183and again after the png_set_*() functions to control whether the user
2184or png_destroy_*() is supposed to free the data. When the user assumes
2185responsibility for libpng-allocated data, the application must use
2186png_free() to free it, and when the user transfers responsibility to libpng
2187for data that the user has allocated, the user must have used png_malloc()
2188or png_zalloc() to allocate it.
2189
2190If you allocated your row_pointers in a single block, as suggested above in
2191the description of the high level read interface, you must not transfer
2192responsibility for freeing it to the png_set_rows or png_read_destroy function,
2193because they would also try to free the individual row_pointers[i].
2194
2195If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2196separately, do not transfer responsibility for freeing text_ptr to libpng,
2197because when libpng fills a png_text structure it combines these members with
2198the key member, and png_free_data() will free only text_ptr.key. Similarly,
2199if you transfer responsibility for free'ing text_ptr from libpng to your
2200application, your application must not separately free those members.
2201
2202The png_free_data() function will turn off the "valid" flag for anything
2203it frees. If you need to turn the flag off for a chunk that was freed by your
2204application instead of by libpng, you can use
2205
2206 png_set_invalid(png_ptr, info_ptr, mask);
2207 mask - identifies the chunks to be made invalid,
2208 containing the bitwise OR of one or
2209 more of
2210 PNG_INFO_gAMA, PNG_INFO_sBIT,
2211 PNG_INFO_cHRM, PNG_INFO_PLTE,
2212 PNG_INFO_tRNS, PNG_INFO_bKGD,
2213 PNG_INFO_hIST, PNG_INFO_pHYs,
2214 PNG_INFO_oFFs, PNG_INFO_tIME,
2215 PNG_INFO_pCAL, PNG_INFO_sRGB,
2216 PNG_INFO_iCCP, PNG_INFO_sPLT,
2217 PNG_INFO_sCAL, PNG_INFO_IDAT
2218
2219For a more compact example of reading a PNG image, see the file example.c.
2220
2221.SS Reading PNG files progressively
2222
2223The progressive reader is slightly different then the non-progressive
2224reader. Instead of calling png_read_info(), png_read_rows(), and
2225png_read_end(), you make one call to png_process_data(), which calls
2226callbacks when it has the info, a row, or the end of the image. You
2227set up these callbacks with png_set_progressive_read_fn(). You don't
2228have to worry about the input/output functions of libpng, as you are
2229giving the library the data directly in png_process_data(). I will
2230assume that you have read the section on reading PNG files above,
2231so I will only highlight the differences (although I will show
2232all of the code).
2233
2234png_structp png_ptr;
2235png_infop info_ptr;
2236
2237 /* An example code fragment of how you would
2238 initialize the progressive reader in your
2239 application. */
2240 int
2241 initialize_png_reader()
2242 {
2243 png_ptr = png_create_read_struct
2244 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2245 user_error_fn, user_warning_fn);
2246 if (!png_ptr)
2247 return (ERROR);
2248 info_ptr = png_create_info_struct(png_ptr);
2249 if (!info_ptr)
2250 {
2251 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2252 (png_infopp)NULL);
2253 return (ERROR);
2254 }
2255
2256 if (setjmp(png_jmpbuf(png_ptr)))
2257 {
2258 png_destroy_read_struct(&png_ptr, &info_ptr,
2259 (png_infopp)NULL);
2260 return (ERROR);
2261 }
2262
2263 /* This one's new. You can provide functions
2264 to be called when the header info is valid,
2265 when each row is completed, and when the image
2266 is finished. If you aren't using all functions,
2267 you can specify NULL parameters. Even when all
2268 three functions are NULL, you need to call
2269 png_set_progressive_read_fn(). You can use
2270 any struct as the user_ptr (cast to a void pointer
2271 for the function call), and retrieve the pointer
2272 from inside the callbacks using the function
2273
2274 png_get_progressive_ptr(png_ptr);
2275
2276 which will return a void pointer, which you have
2277 to cast appropriately.
2278 */
2279 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2280 info_callback, row_callback, end_callback);
2281
2282 return 0;
2283 }
2284
2285 /* A code fragment that you call as you receive blocks
2286 of data */
2287 int
2288 process_data(png_bytep buffer, png_uint_32 length)
2289 {
2290 if (setjmp(png_jmpbuf(png_ptr)))
2291 {
2292 png_destroy_read_struct(&png_ptr, &info_ptr,
2293 (png_infopp)NULL);
2294 return (ERROR);
2295 }
2296
2297 /* This one's new also. Simply give it a chunk
2298 of data from the file stream (in order, of
2299 course). On machines with segmented memory
2300 models machines, don't give it any more than
2301 64K. The library seems to run fine with sizes
2302 of 4K. Although you can give it much less if
2303 necessary (I assume you can give it chunks of
2304 1 byte, I haven't tried less then 256 bytes
2305 yet). When this function returns, you may
2306 want to display any rows that were generated
2307 in the row callback if you don't already do
2308 so there.
2309 */
2310 png_process_data(png_ptr, info_ptr, buffer, length);
2311 return 0;
2312 }
2313
2314 /* This function is called (as set by
2315 png_set_progressive_read_fn() above) when enough data
2316 has been supplied so all of the header has been
2317 read.
2318 */
2319 void
2320 info_callback(png_structp png_ptr, png_infop info)
2321 {
2322 /* Do any setup here, including setting any of
2323 the transformations mentioned in the Reading
2324 PNG files section. For now, you _must_ call
2325 either png_start_read_image() or
2326 png_read_update_info() after all the
2327 transformations are set (even if you don't set
2328 any). You may start getting rows before
2329 png_process_data() returns, so this is your
2330 last chance to prepare for that.
2331 */
2332 }
2333
2334 /* This function is called when each row of image
2335 data is complete */
2336 void
2337 row_callback(png_structp png_ptr, png_bytep new_row,
2338 png_uint_32 row_num, int pass)
2339 {
2340 /* If the image is interlaced, and you turned
2341 on the interlace handler, this function will
2342 be called for every row in every pass. Some
2343 of these rows will not be changed from the
2344 previous pass. When the row is not changed,
2345 the new_row variable will be NULL. The rows
2346 and passes are called in order, so you don't
2347 really need the row_num and pass, but I'm
2348 supplying them because it may make your life
2349 easier.
2350
2351 For the non-NULL rows of interlaced images,
2352 you must call png_progressive_combine_row()
2353 passing in the row and the old row. You can
2354 call this function for NULL rows (it will just
2355 return) and for non-interlaced images (it just
2356 does the memcpy for you) if it will make the
2357 code easier. Thus, you can just do this for
2358 all cases:
2359 */
2360
2361 png_progressive_combine_row(png_ptr, old_row,
2362 new_row);
2363
2364 /* where old_row is what was displayed for
2365 previously for the row. Note that the first
2366 pass (pass == 0, really) will completely cover
2367 the old row, so the rows do not have to be
2368 initialized. After the first pass (and only
2369 for interlaced images), you will have to pass
2370 the current row, and the function will combine
2371 the old row and the new row.
2372 */
2373 }
2374
2375 void
2376 end_callback(png_structp png_ptr, png_infop info)
2377 {
2378 /* This function is called after the whole image
2379 has been read, including any chunks after the
2380 image (up to and including the IEND). You
2381 will usually have the same info chunk as you
2382 had in the header, although some data may have
2383 been added to the comments and time fields.
2384
2385 Most people won't do much here, perhaps setting
2386 a flag that marks the image as finished.
2387 */
2388 }
2389
2390
2391
2392.SH IV. Writing
2393
2394Much of this is very similar to reading. However, everything of
2395importance is repeated here, so you won't have to constantly look
2396back up in the reading section to understand writing.
2397
2398.SS Setup
2399
2400You will want to do the I/O initialization before you get into libpng,
2401so if it doesn't work, you don't have anything to undo. If you are not
2402using the standard I/O functions, you will need to replace them with
2403custom writing functions. See the discussion under Customizing libpng.
2404
2405 FILE *fp = fopen(file_name, "wb");
2406 if (!fp)
2407 {
2408 return (ERROR);
2409 }
2410
2411Next, png_struct and png_info need to be allocated and initialized.
2412As these can be both relatively large, you may not want to store these
2413on the stack, unless you have stack space to spare. Of course, you
2414will want to check if they return NULL. If you are also reading,
2415you won't want to name your read structure and your write structure
2416both "png_ptr"; you can call them anything you like, such as
2417"read_ptr" and "write_ptr". Look at pngtest.c, for example.
2418
2419 png_structp png_ptr = png_create_write_struct
2420 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2421 user_error_fn, user_warning_fn);
2422 if (!png_ptr)
2423 return (ERROR);
2424
2425 png_infop info_ptr = png_create_info_struct(png_ptr);
2426 if (!info_ptr)
2427 {
2428 png_destroy_write_struct(&png_ptr,
2429 (png_infopp)NULL);
2430 return (ERROR);
2431 }
2432
2433If you want to use your own memory allocation routines,
2434define PNG_USER_MEM_SUPPORTED and use
2435png_create_write_struct_2() instead of png_create_write_struct():
2436
2437 png_structp png_ptr = png_create_write_struct_2
2438 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2439 user_error_fn, user_warning_fn, (png_voidp)
2440 user_mem_ptr, user_malloc_fn, user_free_fn);
2441
2442After you have these structures, you will need to set up the
2443error handling. When libpng encounters an error, it expects to
2444longjmp() back to your routine. Therefore, you will need to call
2445setjmp() and pass the png_jmpbuf(png_ptr). If you
2446write the file from different routines, you will need to update
2447the png_jmpbuf(png_ptr) every time you enter a new routine that will
2448call a png_*() function. See your documentation of setjmp/longjmp
2449for your compiler for more information on setjmp/longjmp. See
2450the discussion on libpng error handling in the Customizing Libpng
2451section below for more information on the libpng error handling.
2452
2453 if (setjmp(png_jmpbuf(png_ptr)))
2454 {
2455 png_destroy_write_struct(&png_ptr, &info_ptr);
2456 fclose(fp);
2457 return (ERROR);
2458 }
2459 ...
2460 return;
2461
2462If you would rather avoid the complexity of setjmp/longjmp issues,
2463you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2464errors will result in a call to PNG_ABORT() which defaults to abort().
2465
2466Now you need to set up the output code. The default for libpng is to
2467use the C function fwrite(). If you use this, you will need to pass a
2468valid FILE * in the function png_init_io(). Be sure that the file is
2469opened in binary mode. Again, if you wish to handle writing data in
2470another way, see the discussion on libpng I/O handling in the Customizing
2471Libpng section below.
2472
2473 png_init_io(png_ptr, fp);
2474
2475If you are embedding your PNG into a datastream such as MNG, and don't
2476want libpng to write the 8-byte signature, or if you have already
2477written the signature in your application, use
2478
2479 png_set_sig_bytes(png_ptr, 8);
2480
2481to inform libpng that it should not write a signature.
2482
2483.SS Write callbacks
2484
2485At this point, you can set up a callback function that will be
2486called after each row has been written, which you can use to control
2487a progress meter or the like. It's demonstrated in pngtest.c.
2488You must supply a function
2489
2490 void write_row_callback(png_ptr, png_uint_32 row,
2491 int pass);
2492 {
2493 /* put your code here */
2494 }
2495
2496(You can give it another name that you like instead of "write_row_callback")
2497
2498To inform libpng about your function, use
2499
2500 png_set_write_status_fn(png_ptr, write_row_callback);
2501
2502You now have the option of modifying how the compression library will
2503run. The following functions are mainly for testing, but may be useful
2504in some cases, like if you need to write PNG files extremely fast and
2505are willing to give up some compression, or if you want to get the
2506maximum possible compression at the expense of slower writing. If you
2507have no special needs in this area, let the library do what it wants by
2508not calling this function at all, as it has been tuned to deliver a good
2509speed/compression ratio. The second parameter to png_set_filter() is
2510the filter method, for which the only valid values are 0 (as of the
2511July 1999 PNG specification, version 1.2) or 64 (if you are writing
2512a PNG datastream that is to be embedded in a MNG datastream). The third
2513parameter is a flag that indicates which filter type(s) are to be tested
2514for each scanline. See the PNG specification for details on the specific filter
2515types.
2516
2517
2518 /* turn on or off filtering, and/or choose
2519 specific filters. You can use either a single
2520 PNG_FILTER_VALUE_NAME or the bitwise OR of one
2521 or more PNG_FILTER_NAME masks. */
2522 png_set_filter(png_ptr, 0,
2523 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2524 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2525 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2526 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2527 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2528 PNG_ALL_FILTERS);
2529
2530If an application
2531wants to start and stop using particular filters during compression,
2532it should start out with all of the filters (to ensure that the previous
2533row of pixels will be stored in case it's needed later), and then add
2534and remove them after the start of compression.
2535
2536If you are writing a PNG datastream that is to be embedded in a MNG
2537datastream, the second parameter can be either 0 or 64.
2538
2539The png_set_compression_*() functions interface to the zlib compression
2540library, and should mostly be ignored unless you really know what you are
2541doing. The only generally useful call is png_set_compression_level()
2542which changes how much time zlib spends on trying to compress the image
2543data. See the Compression Library (zlib.h and algorithm.txt, distributed
2544with zlib) for details on the compression levels.
2545
2546 /* set the zlib compression level */
2547 png_set_compression_level(png_ptr,
2548 Z_BEST_COMPRESSION);
2549
2550 /* set other zlib parameters */
2551 png_set_compression_mem_level(png_ptr, 8);
2552 png_set_compression_strategy(png_ptr,
2553 Z_DEFAULT_STRATEGY);
2554 png_set_compression_window_bits(png_ptr, 15);
2555 png_set_compression_method(png_ptr, 8);
2556 png_set_compression_buffer_size(png_ptr, 8192)
2557
2558extern PNG_EXPORT(void,png_set_zbuf_size)
2559
2560.SS Setting the contents of info for output
2561
2562You now need to fill in the png_info structure with all the data you
2563wish to write before the actual image. Note that the only thing you
2564are allowed to write after the image is the text chunks and the time
2565chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2566the latest PNG specification for more information on that. If you
2567wish to write them before the image, fill them in now, and flag that
2568data as being valid. If you want to wait until after the data, don't
2569fill them until png_write_end(). For all the fields in png_info and
2570their data types, see png.h. For explanations of what the fields
2571contain, see the PNG specification.
2572
2573Some of the more important parts of the png_info are:
2574
2575 png_set_IHDR(png_ptr, info_ptr, width, height,
2576 bit_depth, color_type, interlace_type,
2577 compression_type, filter_method)
2578 width - holds the width of the image
2579 in pixels (up to 2^31).
2580 height - holds the height of the image
2581 in pixels (up to 2^31).
2582 bit_depth - holds the bit depth of one of the
2583 image channels.
2584 (valid values are 1, 2, 4, 8, 16
2585 and depend also on the
2586 color_type. See also significant
2587 bits (sBIT) below).
2588 color_type - describes which color/alpha
2589 channels are present.
2590 PNG_COLOR_TYPE_GRAY
2591 (bit depths 1, 2, 4, 8, 16)
2592 PNG_COLOR_TYPE_GRAY_ALPHA
2593 (bit depths 8, 16)
2594 PNG_COLOR_TYPE_PALETTE
2595 (bit depths 1, 2, 4, 8)
2596 PNG_COLOR_TYPE_RGB
2597 (bit_depths 8, 16)
2598 PNG_COLOR_TYPE_RGB_ALPHA
2599 (bit_depths 8, 16)
2600
2601 PNG_COLOR_MASK_PALETTE
2602 PNG_COLOR_MASK_COLOR
2603 PNG_COLOR_MASK_ALPHA
2604
2605 interlace_type - PNG_INTERLACE_NONE or
2606 PNG_INTERLACE_ADAM7
2607 compression_type - (must be
2608 PNG_COMPRESSION_TYPE_DEFAULT)
2609 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2610 or, if you are writing a PNG to
2611 be embedded in a MNG datastream,
2612 can also be
2613 PNG_INTRAPIXEL_DIFFERENCING)
2614
2615If you call png_set_IHDR(), the call must appear before any of the
2616other png_set_*() functions, which might require access to some of
2617the IHDR settings. The remaining png_set_*() functions can be called
2618in any order.
2619
2620 png_set_PLTE(png_ptr, info_ptr, palette,
2621 num_palette);
2622 palette - the palette for the file
2623 (array of png_color)
2624 num_palette - number of entries in the palette
2625
2626 png_set_gAMA(png_ptr, info_ptr, gamma);
2627 gamma - the gamma the image was created
2628 at (PNG_INFO_gAMA)
2629
2630 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2631 srgb_intent - the rendering intent
2632 (PNG_INFO_sRGB) The presence of
2633 the sRGB chunk means that the pixel
2634 data is in the sRGB color space.
2635 This chunk also implies specific
2636 values of gAMA and cHRM. Rendering
2637 intent is the CSS-1 property that
2638 has been defined by the International
2639 Color Consortium
2640 (http://www.color.org).
2641 It can be one of
2642 PNG_sRGB_INTENT_SATURATION,
2643 PNG_sRGB_INTENT_PERCEPTUAL,
2644 PNG_sRGB_INTENT_ABSOLUTE, or
2645 PNG_sRGB_INTENT_RELATIVE.
2646
2647
2648 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2649 srgb_intent);
2650 srgb_intent - the rendering intent
2651 (PNG_INFO_sRGB) The presence of the
2652 sRGB chunk means that the pixel
2653 data is in the sRGB color space.
2654 This function also causes gAMA and
2655 cHRM chunks with the specific values
2656 that are consistent with sRGB to be
2657 written.
2658
2659 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2660 profile, proflen);
2661 name - The profile name.
2662 compression - The compression type; always
2663 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2664 You may give NULL to this argument to
2665 ignore it.
2666 profile - International Color Consortium color
2667 profile data. May contain NULs.
2668 proflen - length of profile data in bytes.
2669
2670 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2671 sig_bit - the number of significant bits for
2672 (PNG_INFO_sBIT) each of the gray, red,
2673 green, and blue channels, whichever are
2674 appropriate for the given color type
2675 (png_color_16)
2676
2677 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2678 trans_values);
2679 trans - array of transparent entries for
2680 palette (PNG_INFO_tRNS)
2681 trans_values - graylevel or color sample values of
2682 the single transparent color for
2683 non-paletted images (PNG_INFO_tRNS)
2684 num_trans - number of transparent entries
2685 (PNG_INFO_tRNS)
2686
2687 png_set_hIST(png_ptr, info_ptr, hist);
2688 (PNG_INFO_hIST)
2689 hist - histogram of palette (array of
2690 png_uint_16)
2691
2692 png_set_tIME(png_ptr, info_ptr, mod_time);
2693 mod_time - time image was last modified
2694 (PNG_VALID_tIME)
2695
2696 png_set_bKGD(png_ptr, info_ptr, background);
2697 background - background color (PNG_VALID_bKGD)
2698
2699 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2700 text_ptr - array of png_text holding image
2701 comments
2702 text_ptr[i].compression - type of compression used
2703 on "text" PNG_TEXT_COMPRESSION_NONE
2704 PNG_TEXT_COMPRESSION_zTXt
2705 PNG_ITXT_COMPRESSION_NONE
2706 PNG_ITXT_COMPRESSION_zTXt
2707 text_ptr[i].key - keyword for comment. Must contain
2708 1-79 characters.
2709 text_ptr[i].text - text comments for current
2710 keyword. Can be NULL or empty.
2711 text_ptr[i].text_length - length of text string,
2712 after decompression, 0 for iTXt
2713 text_ptr[i].itxt_length - length of itxt string,
2714 after decompression, 0 for tEXt/zTXt
2715 text_ptr[i].lang - language of comment (NULL or
2716 empty for unknown).
2717 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2718 or empty for unknown).
2719 num_text - number of comments
2720
2721 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2722 num_spalettes);
2723 palette_ptr - array of png_sPLT_struct structures
2724 to be added to the list of palettes
2725 in the info structure.
2726 num_spalettes - number of palette structures to be
2727 added.
2728
2729 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2730 unit_type);
2731 offset_x - positive offset from the left
2732 edge of the screen
2733 offset_y - positive offset from the top
2734 edge of the screen
2735 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2736
2737 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2738 unit_type);
2739 res_x - pixels/unit physical resolution
2740 in x direction
2741 res_y - pixels/unit physical resolution
2742 in y direction
2743 unit_type - PNG_RESOLUTION_UNKNOWN,
2744 PNG_RESOLUTION_METER
2745
2746 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2747 unit - physical scale units (an integer)
2748 width - width of a pixel in physical scale units
2749 height - height of a pixel in physical scale units
2750 (width and height are doubles)
2751
2752 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2753 unit - physical scale units (an integer)
2754 width - width of a pixel in physical scale units
2755 height - height of a pixel in physical scale units
2756 (width and height are strings like "2.54")
2757
2758 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2759 num_unknowns)
2760 unknowns - array of png_unknown_chunk
2761 structures holding unknown chunks
2762 unknowns[i].name - name of unknown chunk
2763 unknowns[i].data - data of unknown chunk
2764 unknowns[i].size - size of unknown chunk's data
2765 unknowns[i].location - position to write chunk in file
2766 0: do not write chunk
2767 PNG_HAVE_IHDR: before PLTE
2768 PNG_HAVE_PLTE: before IDAT
2769 PNG_AFTER_IDAT: after IDAT
2770
2771The "location" member is set automatically according to
2772what part of the output file has already been written.
2773You can change its value after calling png_set_unknown_chunks()
2774as demonstrated in pngtest.c. Within each of the "locations",
2775the chunks are sequenced according to their position in the
2776structure (that is, the value of "i", which is the order in which
2777the chunk was either read from the input file or defined with
2778png_set_unknown_chunks).
2779
2780A quick word about text and num_text. text is an array of png_text
2781structures. num_text is the number of valid structures in the array.
2782Each png_text structure holds a language code, a keyword, a text value,
2783and a compression type.
2784
2785The compression types have the same valid numbers as the compression
2786types of the image data. Currently, the only valid number is zero.
2787However, you can store text either compressed or uncompressed, unlike
2788images, which always have to be compressed. So if you don't want the
2789text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2790Because tEXt and zTXt chunks don't have a language field, if you
2791specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2792any language code or translated keyword will not be written out.
2793
2794Until text gets around 1000 bytes, it is not worth compressing it.
2795After the text has been written out to the file, the compression type
2796is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2797so that it isn't written out again at the end (in case you are calling
2798png_write_end() with the same struct.
2799
2800The keywords that are given in the PNG Specification are:
2801
2802 Title Short (one line) title or
2803 caption for image
2804 Author Name of image's creator
2805 Description Description of image (possibly long)
2806 Copyright Copyright notice
2807 Creation Time Time of original image creation
2808 (usually RFC 1123 format, see below)
2809 Software Software used to create the image
2810 Disclaimer Legal disclaimer
2811 Warning Warning of nature of content
2812 Source Device used to create the image
2813 Comment Miscellaneous comment; conversion
2814 from other image format
2815
2816The keyword-text pairs work like this. Keywords should be short
2817simple descriptions of what the comment is about. Some typical
2818keywords are found in the PNG specification, as is some recommendations
2819on keywords. You can repeat keywords in a file. You can even write
2820some text before the image and some after. For example, you may want
2821to put a description of the image before the image, but leave the
2822disclaimer until after, so viewers working over modem connections
2823don't have to wait for the disclaimer to go over the modem before
2824they start seeing the image. Finally, keywords should be full
2825words, not abbreviations. Keywords and text are in the ISO 8859-1
2826(Latin-1) character set (a superset of regular ASCII) and can not
2827contain NUL characters, and should not contain control or other
2828unprintable characters. To make the comments widely readable, stick
2829with basic ASCII, and avoid machine specific character set extensions
2830like the IBM-PC character set. The keyword must be present, but
2831you can leave off the text string on non-compressed pairs.
2832Compressed pairs must have a text string, as only the text string
2833is compressed anyway, so the compression would be meaningless.
2834
2835PNG supports modification time via the png_time structure. Two
2836conversion routines are provided, png_convert_from_time_t() for
2837time_t and png_convert_from_struct_tm() for struct tm. The
2838time_t routine uses gmtime(). You don't have to use either of
2839these, but if you wish to fill in the png_time structure directly,
2840you should provide the time in universal time (GMT) if possible
2841instead of your local time. Note that the year number is the full
2842year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2843that months start with 1.
2844
2845If you want to store the time of the original image creation, you should
2846use a plain tEXt chunk with the "Creation Time" keyword. This is
2847necessary because the "creation time" of a PNG image is somewhat vague,
2848depending on whether you mean the PNG file, the time the image was
2849created in a non-PNG format, a still photo from which the image was
2850scanned, or possibly the subject matter itself. In order to facilitate
2851machine-readable dates, it is recommended that the "Creation Time"
2852tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2853although this isn't a requirement. Unlike the tIME chunk, the
2854"Creation Time" tEXt chunk is not expected to be automatically changed
2855by the software. To facilitate the use of RFC 1123 dates, a function
2856png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2857time to an RFC 1123 format string.
2858
2859.SS Writing unknown chunks
2860
2861You can use the png_set_unknown_chunks function to queue up chunks
2862for writing. You give it a chunk name, raw data, and a size; that's
2863all there is to it. The chunks will be written by the next following
2864png_write_info_before_PLTE, png_write_info, or png_write_end function.
2865Any chunks previously read into the info structure's unknown-chunk
2866list will also be written out in a sequence that satisfies the PNG
2867specification's ordering rules.
2868
2869.SS The high-level write interface
2870
2871At this point there are two ways to proceed; through the high-level
2872write interface, or through a sequence of low-level write operations.
2873You can use the high-level interface if your image data is present
2874in the info structure. All defined output
2875transformations are permitted, enabled by the following masks.
2876
2877 PNG_TRANSFORM_IDENTITY No transformation
2878 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2879 PNG_TRANSFORM_PACKSWAP Change order of packed
2880 pixels to LSB first
2881 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2882 PNG_TRANSFORM_SHIFT Normalize pixels to the
2883 sBIT depth
2884 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2885 to BGRA
2886 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2887 to AG
2888 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2889 to transparency
2890 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2891 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2892
2893If you have valid image data in the info structure (you can use
2894png_set_rows() to put image data in the info structure), simply do this:
2895
2896 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2897
2898where png_transforms is an integer containing the bitwise OR of some set of
2899transformation flags. This call is equivalent to png_write_info(),
2900followed the set of transformations indicated by the transform mask,
2901then png_write_image(), and finally png_write_end().
2902
2903(The final parameter of this call is not yet used. Someday it might point
2904to transformation parameters required by some future output transform.)
2905
2906You must use png_transforms and not call any png_set_transform() functions
2907when you use png_write_png().
2908
2909.SS The low-level write interface
2910
2911If you are going the low-level route instead, you are now ready to
2912write all the file information up to the actual image data. You do
2913this with a call to png_write_info().
2914
2915 png_write_info(png_ptr, info_ptr);
2916
2917Note that there is one transformation you may need to do before
2918png_write_info(). In PNG files, the alpha channel in an image is the
2919level of opacity. If your data is supplied as a level of
2920transparency, you can invert the alpha channel before you write it, so
2921that 0 is fully transparent and 255 (in 8-bit or paletted images) or
292265535 (in 16-bit images) is fully opaque, with
2923
2924 png_set_invert_alpha(png_ptr);
2925
2926This must appear before png_write_info() instead of later with the
2927other transformations because in the case of paletted images the tRNS
2928chunk data has to be inverted before the tRNS chunk is written. If
2929your image is not a paletted image, the tRNS data (which in such cases
2930represents a single color to be rendered as transparent) won't need to
2931be changed, and you can safely do this transformation after your
2932png_write_info() call.
2933
2934If you need to write a private chunk that you want to appear before
2935the PLTE chunk when PLTE is present, you can write the PNG info in
2936two steps, and insert code to write your own chunk between them:
2937
2938 png_write_info_before_PLTE(png_ptr, info_ptr);
2939 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2940 png_write_info(png_ptr, info_ptr);
2941
2942After you've written the file information, you can set up the library
2943to handle any special transformations of the image data. The various
2944ways to transform the data will be described in the order that they
2945should occur. This is important, as some of these change the color
2946type and/or bit depth of the data, and some others only work on
2947certain color types and bit depths. Even though each transformation
2948checks to see if it has data that it can do something with, you should
2949make sure to only enable a transformation if it will be valid for the
2950data. For example, don't swap red and blue on grayscale data.
2951
2952PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2953the library to strip input data that has 4 or 8 bytes per pixel down
2954to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2955bytes per pixel).
2956
2957 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2958
2959where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2960PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2961is stored XRGB or RGBX.
2962
2963PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2964they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2965If the data is supplied at 1 pixel per byte, use this code, which will
2966correctly pack the pixels into a single byte:
2967
2968 png_set_packing(png_ptr);
2969
2970PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2971data is of another bit depth, you can write an sBIT chunk into the
2972file so that decoders can recover the original data if desired.
2973
2974 /* Set the true bit depth of the image data */
2975 if (color_type & PNG_COLOR_MASK_COLOR)
2976 {
2977 sig_bit.red = true_bit_depth;
2978 sig_bit.green = true_bit_depth;
2979 sig_bit.blue = true_bit_depth;
2980 }
2981 else
2982 {
2983 sig_bit.gray = true_bit_depth;
2984 }
2985 if (color_type & PNG_COLOR_MASK_ALPHA)
2986 {
2987 sig_bit.alpha = true_bit_depth;
2988 }
2989
2990 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2991
2992If the data is stored in the row buffer in a bit depth other than
2993one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2994this will scale the values to appear to be the correct bit depth as
2995is required by PNG.
2996
2997 png_set_shift(png_ptr, &sig_bit);
2998
2999PNG files store 16 bit pixels in network byte order (big-endian,
3000ie. most significant bits first). This code would be used if they are
3001supplied the other way (little-endian, i.e. least significant bits
3002first, the way PCs store them):
3003
3004 if (bit_depth > 8)
3005 png_set_swap(png_ptr);
3006
3007If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3008need to change the order the pixels are packed into bytes, you can use:
3009
3010 if (bit_depth < 8)
3011 png_set_packswap(png_ptr);
3012
3013PNG files store 3 color pixels in red, green, blue order. This code
3014would be used if they are supplied as blue, green, red:
3015
3016 png_set_bgr(png_ptr);
3017
3018PNG files describe monochrome as black being zero and white being
3019one. This code would be used if the pixels are supplied with this reversed
3020(black being one and white being zero):
3021
3022 png_set_invert_mono(png_ptr);
3023
3024Finally, you can write your own transformation function if none of
3025the existing ones meets your needs. This is done by setting a callback
3026with
3027
3028 png_set_write_user_transform_fn(png_ptr,
3029 write_transform_fn);
3030
3031You must supply the function
3032
3033 void write_transform_fn(png_ptr ptr, row_info_ptr
3034 row_info, png_bytep data)
3035
3036See pngtest.c for a working example. Your function will be called
3037before any of the other transformations are processed.
3038
3039You can also set up a pointer to a user structure for use by your
3040callback function.
3041
3042 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3043
3044The user_channels and user_depth parameters of this function are ignored
3045when writing; you can set them to zero as shown.
3046
3047You can retrieve the pointer via the function png_get_user_transform_ptr().
3048For example:
3049
3050 voidp write_user_transform_ptr =
3051 png_get_user_transform_ptr(png_ptr);
3052
3053It is possible to have libpng flush any pending output, either manually,
3054or automatically after a certain number of lines have been written. To
3055flush the output stream a single time call:
3056
3057 png_write_flush(png_ptr);
3058
3059and to have libpng flush the output stream periodically after a certain
3060number of scanlines have been written, call:
3061
3062 png_set_flush(png_ptr, nrows);
3063
3064Note that the distance between rows is from the last time png_write_flush()
3065was called, or the first row of the image if it has never been called.
3066So if you write 50 lines, and then png_set_flush 25, it will flush the
3067output on the next scanline, and every 25 lines thereafter, unless
3068png_write_flush() is called before 25 more lines have been written.
3069If nrows is too small (less than about 10 lines for a 640 pixel wide
3070RGB image) the image compression may decrease noticeably (although this
3071may be acceptable for real-time applications). Infrequent flushing will
3072only degrade the compression performance by a few percent over images
3073that do not use flushing.
3074
3075.SS Writing the image data
3076
3077That's it for the transformations. Now you can write the image data.
3078The simplest way to do this is in one function call. If you have the
3079whole image in memory, you can just call png_write_image() and libpng
3080will write the image. You will need to pass in an array of pointers to
3081each row. This function automatically handles interlacing, so you don't
3082need to call png_set_interlace_handling() or call this function multiple
3083times, or any of that other stuff necessary with png_write_rows().
3084
3085 png_write_image(png_ptr, row_pointers);
3086
3087where row_pointers is:
3088
3089 png_byte *row_pointers[height];
3090
3091You can point to void or char or whatever you use for pixels.
3092
3093If you don't want to write the whole image at once, you can
3094use png_write_rows() instead. If the file is not interlaced,
3095this is simple:
3096
3097 png_write_rows(png_ptr, row_pointers,
3098 number_of_rows);
3099
3100row_pointers is the same as in the png_write_image() call.
3101
3102If you are just writing one row at a time, you can do this with
3103a single row_pointer instead of an array of row_pointers:
3104
3105 png_bytep row_pointer = row;
3106
3107 png_write_row(png_ptr, row_pointer);
3108
3109When the file is interlaced, things can get a good deal more
3110complicated. The only currently (as of the PNG Specification
3111version 1.2, dated July 1999) defined interlacing scheme for PNG files
3112is the "Adam7" interlace scheme, that breaks down an
3113image into seven smaller images of varying size. libpng will build
3114these images for you, or you can do them yourself. If you want to
3115build them yourself, see the PNG specification for details of which
3116pixels to write when.
3117
3118If you don't want libpng to handle the interlacing details, just
3119use png_set_interlace_handling() and call png_write_rows() the
3120correct number of times to write all seven sub-images.
3121
3122If you want libpng to build the sub-images, call this before you start
3123writing any rows:
3124
3125 number_of_passes =
3126 png_set_interlace_handling(png_ptr);
3127
3128This will return the number of passes needed. Currently, this
3129is seven, but may change if another interlace type is added.
3130
3131Then write the complete image number_of_passes times.
3132
3133 png_write_rows(png_ptr, row_pointers,
3134 number_of_rows);
3135
3136As some of these rows are not used, and thus return immediately,
3137you may want to read about interlacing in the PNG specification,
3138and only update the rows that are actually used.
3139
3140.SS Finishing a sequential write
3141
3142After you are finished writing the image, you should finish writing
3143the file. If you are interested in writing comments or time, you should
3144pass an appropriately filled png_info pointer. If you are not interested,
3145you can pass NULL.
3146
3147 png_write_end(png_ptr, info_ptr);
3148
3149When you are done, you can free all memory used by libpng like this:
3150
3151 png_destroy_write_struct(&png_ptr, &info_ptr);
3152
3153It is also possible to individually free the info_ptr members that
3154point to libpng-allocated storage with the following function:
3155
3156 png_free_data(png_ptr, info_ptr, mask, seq)
3157 mask - identifies data to be freed, a mask
3158 containing the bitwise OR of one or
3159 more of
3160 PNG_FREE_PLTE, PNG_FREE_TRNS,
3161 PNG_FREE_HIST, PNG_FREE_ICCP,
3162 PNG_FREE_PCAL, PNG_FREE_ROWS,
3163 PNG_FREE_SCAL, PNG_FREE_SPLT,
3164 PNG_FREE_TEXT, PNG_FREE_UNKN,
3165 or simply PNG_FREE_ALL
3166 seq - sequence number of item to be freed
3167 (-1 for all items)
3168
3169This function may be safely called when the relevant storage has
3170already been freed, or has not yet been allocated, or was allocated
3171by the user and not by libpng, and will in those
3172cases do nothing. The "seq" parameter is ignored if only one item
3173of the selected data type, such as PLTE, is allowed. If "seq" is not
3174-1, and multiple items are allowed for the data type identified in
3175the mask, such as text or sPLT, only the n'th item in the structure
3176is freed, where n is "seq".
3177
3178If you allocated data such as a palette that you passed
3179in to libpng with png_set_*, you must not free it until just before the call to
3180png_destroy_write_struct().
3181
3182The default behavior is only to free data that was allocated internally
3183by libpng. This can be changed, so that libpng will not free the data,
3184or so that it will free data that was allocated by the user with png_malloc()
3185or png_zalloc() and passed in via a png_set_*() function, with
3186
3187 png_data_freer(png_ptr, info_ptr, freer, mask)
3188 mask - which data elements are affected
3189 same choices as in png_free_data()
3190 freer - one of
3191 PNG_DESTROY_WILL_FREE_DATA
3192 PNG_SET_WILL_FREE_DATA
3193 PNG_USER_WILL_FREE_DATA
3194
3195For example, to transfer responsibility for some data from a read structure
3196to a write structure, you could use
3197
3198 png_data_freer(read_ptr, read_info_ptr,
3199 PNG_USER_WILL_FREE_DATA,
3200 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3201 png_data_freer(write_ptr, write_info_ptr,
3202 PNG_DESTROY_WILL_FREE_DATA,
3203 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3204
3205thereby briefly reassigning responsibility for freeing to the user but
3206immediately afterwards reassigning it once more to the write_destroy
3207function. Having done this, it would then be safe to destroy the read
3208structure and continue to use the PLTE, tRNS, and hIST data in the write
3209structure.
3210
3211This function only affects data that has already been allocated.
3212You can call this function before calling after the png_set_*() functions
3213to control whether the user or png_destroy_*() is supposed to free the data.
3214When the user assumes responsibility for libpng-allocated data, the
3215application must use
3216png_free() to free it, and when the user transfers responsibility to libpng
3217for data that the user has allocated, the user must have used png_malloc()
3218or png_zalloc() to allocate it.
3219
3220If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3221separately, do not transfer responsibility for freeing text_ptr to libpng,
3222because when libpng fills a png_text structure it combines these members with
3223the key member, and png_free_data() will free only text_ptr.key. Similarly,
3224if you transfer responsibility for free'ing text_ptr from libpng to your
3225application, your application must not separately free those members.
3226For a more compact example of writing a PNG image, see the file example.c.
3227
3228.SH V. Modifying/Customizing libpng:
3229
3230There are two issues here. The first is changing how libpng does
3231standard things like memory allocation, input/output, and error handling.
3232The second deals with more complicated things like adding new chunks,
3233adding new transformations, and generally changing how libpng works.
3234Both of those are compile-time issues; that is, they are generally
3235determined at the time the code is written, and there is rarely a need
3236to provide the user with a means of changing them.
3237
3238Memory allocation, input/output, and error handling
3239
3240All of the memory allocation, input/output, and error handling in libpng
3241goes through callbacks that are user-settable. The default routines are
3242in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3243these functions, call the appropriate png_set_*_fn() function.
3244
3245Memory allocation is done through the functions png_malloc()
3246and png_free(). These currently just call the standard C functions. If
3247your pointers can't access more then 64K at a time, you will want to set
3248MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3249memory allocation on a platform will change between applications, these
3250functions must be modified in the library at compile time. If you prefer
3251to use a different method of allocating and freeing data, you can use
3252png_create_read_struct_2() or png_create_write_struct_2() to register
3253your own functions as described above.
3254These functions also provide a void pointer that can be retrieved via
3255
3256 mem_ptr=png_get_mem_ptr(png_ptr);
3257
3258Your replacement memory functions must have prototypes as follows:
3259
3260 png_voidp malloc_fn(png_structp png_ptr,
3261 png_size_t size);
3262 void free_fn(png_structp png_ptr, png_voidp ptr);
3263
3264Your malloc_fn() must return NULL in case of failure. The png_malloc()
3265function will normally call png_error() if it receives a NULL from the
3266system memory allocator or from your replacement malloc_fn().
3267
3268Your free_fn() will never be called with a NULL ptr, since libpng's
3269png_free() checks for NULL before calling free_fn().
3270
3271Input/Output in libpng is done through png_read() and png_write(),
3272which currently just call fread() and fwrite(). The FILE * is stored in
3273png_struct and is initialized via png_init_io(). If you wish to change
3274the method of I/O, the library supplies callbacks that you can set
3275through the function png_set_read_fn() and png_set_write_fn() at run
3276time, instead of calling the png_init_io() function. These functions
3277also provide a void pointer that can be retrieved via the function
3278png_get_io_ptr(). For example:
3279
3280 png_set_read_fn(png_structp read_ptr,
3281 voidp read_io_ptr, png_rw_ptr read_data_fn)
3282
3283 png_set_write_fn(png_structp write_ptr,
3284 voidp write_io_ptr, png_rw_ptr write_data_fn,
3285 png_flush_ptr output_flush_fn);
3286
3287 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3288 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3289
3290The replacement I/O functions must have prototypes as follows:
3291
3292 void user_read_data(png_structp png_ptr,
3293 png_bytep data, png_size_t length);
3294 void user_write_data(png_structp png_ptr,
3295 png_bytep data, png_size_t length);
3296 void user_flush_data(png_structp png_ptr);
3297
3298Supplying NULL for the read, write, or flush functions sets them back
3299to using the default C stream functions. It is an error to read from
3300a write stream, and vice versa.
3301
3302Error handling in libpng is done through png_error() and png_warning().
3303Errors handled through png_error() are fatal, meaning that png_error()
3304should never return to its caller. Currently, this is handled via
3305setjmp() and longjmp() (unless you have compiled libpng with
3306PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3307but you could change this to do things like exit() if you should wish.
3308
3309On non-fatal errors, png_warning() is called
3310to print a warning message, and then control returns to the calling code.
3311By default png_error() and png_warning() print a message on stderr via
3312fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3313(because you don't want the messages) or PNG_NO_STDIO defined (because
3314fprintf() isn't available). If you wish to change the behavior of the error
3315functions, you will need to set up your own message callbacks. These
3316functions are normally supplied at the time that the png_struct is created.
3317It is also possible to redirect errors and warnings to your own replacement
3318functions after png_create_*_struct() has been called by calling:
3319
3320 png_set_error_fn(png_structp png_ptr,
3321 png_voidp error_ptr, png_error_ptr error_fn,
3322 png_error_ptr warning_fn);
3323
3324 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3325
3326If NULL is supplied for either error_fn or warning_fn, then the libpng
3327default function will be used, calling fprintf() and/or longjmp() if a
3328problem is encountered. The replacement error functions should have
3329parameters as follows:
3330
3331 void user_error_fn(png_structp png_ptr,
3332 png_const_charp error_msg);
3333 void user_warning_fn(png_structp png_ptr,
3334 png_const_charp warning_msg);
3335
3336The motivation behind using setjmp() and longjmp() is the C++ throw and
3337catch exception handling methods. This makes the code much easier to write,
3338as there is no need to check every return code of every function call.
3339However, there are some uncertainties about the status of local variables
3340after a longjmp, so the user may want to be careful about doing anything after
3341setjmp returns non-zero besides returning itself. Consult your compiler
3342documentation for more details. For an alternative approach, you may wish
3343to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3344
3345.SS Custom chunks
3346
3347If you need to read or write custom chunks, you may need to get deeper
3348into the libpng code. The library now has mechanisms for storing
3349and writing chunks of unknown type; you can even declare callbacks
3350for custom chunks. However, this may not be good enough if the
3351library code itself needs to know about interactions between your
3352chunk and existing `intrinsic' chunks.
3353
3354If you need to write a new intrinsic chunk, first read the PNG
3355specification. Acquire a first level of
3356understanding of how it works. Pay particular attention to the
3357sections that describe chunk names, and look at how other chunks were
3358designed, so you can do things similarly. Second, check out the
3359sections of libpng that read and write chunks. Try to find a chunk
3360that is similar to yours and use it as a template. More details can
3361be found in the comments inside the code. It is best to handle unknown
3362chunks in a generic method, via callback functions, instead of by
3363modifying libpng functions.
3364
3365If you wish to write your own transformation for the data, look through
3366the part of the code that does the transformations, and check out some of
3367the simpler ones to get an idea of how they work. Try to find a similar
3368transformation to the one you want to add and copy off of it. More details
3369can be found in the comments inside the code itself.
3370
3371.SS Configuring for 16 bit platforms
3372
3373You will want to look into zconf.h to tell zlib (and thus libpng) that
3374it cannot allocate more then 64K at a time. Even if you can, the memory
3375won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3376
3377.SS Configuring for DOS
3378
3379For DOS users who only have access to the lower 640K, you will
3380have to limit zlib's memory usage via a png_set_compression_mem_level()
3381call. See zlib.h or zconf.h in the zlib library for more information.
3382
3383.SS Configuring for Medium Model
3384
3385Libpng's support for medium model has been tested on most of the popular
3386compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3387defined, and FAR gets defined to far in pngconf.h, and you should be
3388all set. Everything in the library (except for zlib's structure) is
3389expecting far data. You must use the typedefs with the p or pp on
3390the end for pointers (or at least look at them and be careful). Make
3391note that the rows of data are defined as png_bytepp, which is an
3392unsigned char far * far *.
3393
3394.SS Configuring for gui/windowing platforms:
3395
3396You will need to write new error and warning functions that use the GUI
3397interface, as described previously, and set them to be the error and
3398warning functions at the time that png_create_*_struct() is called,
3399in order to have them available during the structure initialization.
3400They can be changed later via png_set_error_fn(). On some compilers,
3401you may also have to change the memory allocators (png_malloc, etc.).
3402
3403.SS Configuring for compiler xxx:
3404
3405All includes for libpng are in pngconf.h. If you need to add/change/delete
3406an include, this is the place to do it. The includes that are not
3407needed outside libpng are protected by the PNG_INTERNAL definition,
3408which is only defined for those routines inside libpng itself. The
3409files in libpng proper only include png.h, which includes pngconf.h.
3410
3411.SS Configuring zlib:
3412
3413There are special functions to configure the compression. Perhaps the
3414most useful one changes the compression level, which currently uses
3415input compression values in the range 0 - 9. The library normally
3416uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3417have shown that for a large majority of images, compression values in
3418the range 3-6 compress nearly as well as higher levels, and do so much
3419faster. For online applications it may be desirable to have maximum speed
3420(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3421specify no compression (Z_NO_COMPRESSION = 0), but this would create
3422files larger than just storing the raw bitmap. You can specify the
3423compression level by calling:
3424
3425 png_set_compression_level(png_ptr, level);
3426
3427Another useful one is to reduce the memory level used by the library.
3428The memory level defaults to 8, but it can be lowered if you are
3429short on memory (running DOS, for example, where you only have 640K).
3430Note that the memory level does have an effect on compression; among
3431other things, lower levels will result in sections of incompressible
3432data being emitted in smaller stored blocks, with a correspondingly
3433larger relative overhead of up to 15% in the worst case.
3434
3435 png_set_compression_mem_level(png_ptr, level);
3436
3437The other functions are for configuring zlib. They are not recommended
3438for normal use and may result in writing an invalid PNG file. See
3439zlib.h for more information on what these mean.
3440
3441 png_set_compression_strategy(png_ptr,
3442 strategy);
3443 png_set_compression_window_bits(png_ptr,
3444 window_bits);
3445 png_set_compression_method(png_ptr, method);
3446 png_set_compression_buffer_size(png_ptr, size);
3447
3448.SS Controlling row filtering
3449
3450If you want to control whether libpng uses filtering or not, which
3451filters are used, and how it goes about picking row filters, you
3452can call one of these functions. The selection and configuration
3453of row filters can have a significant impact on the size and
3454encoding speed and a somewhat lesser impact on the decoding speed
3455of an image. Filtering is enabled by default for RGB and grayscale
3456images (with and without alpha), but not for paletted images nor
3457for any images with bit depths less than 8 bits/pixel.
3458
3459The 'method' parameter sets the main filtering method, which is
3460currently only '0' in the PNG 1.2 specification. The 'filters'
3461parameter sets which filter(s), if any, should be used for each
3462scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3463to turn filtering on and off, respectively.
3464
3465Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3466PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3467ORed together with '|' to specify one or more filters to use.
3468These filters are described in more detail in the PNG specification.
3469If you intend to change the filter type during the course of writing
3470the image, you should start with flags set for all of the filters
3471you intend to use so that libpng can initialize its internal
3472structures appropriately for all of the filter types. (Note that this
3473means the first row must always be adaptively filtered, because libpng
3474currently does not allocate the filter buffers until png_write_row()
3475is called for the first time.)
3476
3477 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3478 PNG_FILTER_UP | PNG_FILTER_AVE |
3479 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3480
3481 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3482 filters);
3483 The second parameter can also be
3484 PNG_INTRAPIXEL_DIFFERENCING if you are
3485 writing a PNG to be embedded in a MNG
3486 datastream. This parameter must be the
3487 same as the value of filter_method used
3488 in png_set_IHDR().
3489
3490It is also possible to influence how libpng chooses from among the
3491available filters. This is done in one or both of two ways - by
3492telling it how important it is to keep the same filter for successive
3493rows, and by telling it the relative computational costs of the filters.
3494
3495 double weights[3] = {1.5, 1.3, 1.1},
3496 costs[PNG_FILTER_VALUE_LAST] =
3497 {1.0, 1.3, 1.3, 1.5, 1.7};
3498
3499 png_set_filter_heuristics(png_ptr,
3500 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3501 weights, costs);
3502
3503The weights are multiplying factors that indicate to libpng that the
3504row filter should be the same for successive rows unless another row filter
3505is that many times better than the previous filter. In the above example,
3506if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3507"sum of absolute differences" 1.5 x 1.3 times higher than other filters
3508and still be chosen, while the NONE filter could have a sum 1.1 times
3509higher than other filters and still be chosen. Unspecified weights are
3510taken to be 1.0, and the specified weights should probably be declining
3511like those above in order to emphasize recent filters over older filters.
3512
3513The filter costs specify for each filter type a relative decoding cost
3514to be considered when selecting row filters. This means that filters
3515with higher costs are less likely to be chosen over filters with lower
3516costs, unless their "sum of absolute differences" is that much smaller.
3517The costs do not necessarily reflect the exact computational speeds of
3518the various filters, since this would unduly influence the final image
3519size.
3520
3521Note that the numbers above were invented purely for this example and
3522are given only to help explain the function usage. Little testing has
3523been done to find optimum values for either the costs or the weights.
3524
3525.SS Removing unwanted object code
3526
3527There are a bunch of #define's in pngconf.h that control what parts of
3528libpng are compiled. All the defines end in _SUPPORTED. If you are
3529never going to use a capability, you can change the #define to #undef
3530before recompiling libpng and save yourself code and data space, or
3531you can turn off individual capabilities with defines that begin with
3532PNG_NO_.
3533
3534You can also turn all of the transforms and ancillary chunk capabilities
3535off en masse with compiler directives that define
3536PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3537or all four,
3538along with directives to turn on any of the capabilities that you do
3539want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3540the extra transformations but still leave the library fully capable of reading
3541and writing PNG files with all known public chunks
3542Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3543produces a library that is incapable of reading or writing ancillary chunks.
3544If you are not using the progressive reading capability, you can
3545turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3546this with the INTERLACING capability, which you'll still have).
3547
3548All the reading and writing specific code are in separate files, so the
3549linker should only grab the files it needs. However, if you want to
3550make sure, or if you are building a stand alone library, all the
3551reading files start with pngr and all the writing files start with
3552pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3553are used for both reading and writing, and always need to be included.
3554The progressive reader is in pngpread.c
3555
3556If you are creating or distributing a dynamically linked library (a .so
3557or DLL file), you should not remove or disable any parts of the library,
3558as this will cause applications linked with different versions of the
3559library to fail if they call functions not available in your library.
3560The size of the library itself should not be an issue, because only
3561those sections that are actually used will be loaded into memory.
3562
3563.SS Requesting debug printout
3564
3565The macro definition PNG_DEBUG can be used to request debugging
3566printout. Set it to an integer value in the range 0 to 3. Higher
3567numbers result in increasing amounts of debugging information. The
3568information is printed to the "stderr" file, unless another file
3569name is specified in the PNG_DEBUG_FILE macro definition.
3570
3571When PNG_DEBUG > 0, the following functions (macros) become available:
3572
3573 png_debug(level, message)
3574 png_debug1(level, message, p1)
3575 png_debug2(level, message, p1, p2)
3576
3577in which "level" is compared to PNG_DEBUG to decide whether to print
3578the message, "message" is the formatted string to be printed,
3579and p1 and p2 are parameters that are to be embedded in the string
3580according to printf-style formatting directives. For example,
3581
3582 png_debug1(2, "foo=%d\n", foo);
3583
3584is expanded to
3585
3586 if(PNG_DEBUG > 2)
3587 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3588
3589When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3590can still use PNG_DEBUG to control your own debugging:
3591
3592 #ifdef PNG_DEBUG
3593 fprintf(stderr, ...
3594 #endif
3595
3596When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3597having level = 0 will be printed. There aren't any such statements in
3598this version of libpng, but if you insert some they will be printed.
3599
3600.SH VII. MNG support
3601
3602The MNG specification (available at http://www.libpng.org/pub/mng) allows
3603certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3604Libpng can support some of these extensions. To enable them, use the
3605png_permit_mng_features() function:
3606
3607 feature_set = png_permit_mng_features(png_ptr, mask)
3608 mask is a png_uint_32 containing the bitwise OR of the
3609 features you want to enable. These include
3610 PNG_FLAG_MNG_EMPTY_PLTE
3611 PNG_FLAG_MNG_FILTER_64
3612 PNG_ALL_MNG_FEATURES
3613 feature_set is a png_uint_32 that is the bitwise AND of
3614 your mask with the set of MNG features that is
3615 supported by the version of libpng that you are using.
3616
3617It is an error to use this function when reading or writing a standalone
3618PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3619in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3620and the MHDR and MEND chunks. Libpng does not provide support for these
3621or any other MNG chunks; your application must provide its own support for
3622them. You may wish to consider using libmng (available at
3623http://www.libmng.com) instead.
3624
3625.SH VIII. Changes to Libpng from version 0.88
3626
3627It should be noted that versions of libpng later than 0.96 are not
3628distributed by the original libpng author, Guy Schalnat, nor by
3629Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3630distributed versions 0.89 through 0.96, but rather by another member
3631of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3632still alive and well, but they have moved on to other things.
3633
3634The old libpng functions png_read_init(), png_write_init(),
3635png_info_init(), png_read_destroy(), and png_write_destroy() have been
3636moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3637functions will be removed from libpng version 2.0.0.
3638
3639The preferred method of creating and initializing the libpng structures is
3640via the png_create_read_struct(), png_create_write_struct(), and
3641png_create_info_struct() because they isolate the size of the structures
3642from the application, allow version error checking, and also allow the
3643use of custom error handling routines during the initialization, which
3644the old functions do not. The functions png_read_destroy() and
3645png_write_destroy() do not actually free the memory that libpng
3646allocated for these structs, but just reset the data structures, so they
3647can be used instead of png_destroy_read_struct() and
3648png_destroy_write_struct() if you feel there is too much system overhead
3649allocating and freeing the png_struct for each image read.
3650
3651Setting the error callbacks via png_set_message_fn() before
3652png_read_init() as was suggested in libpng-0.88 is no longer supported
3653because this caused applications that do not use custom error functions
3654to fail if the png_ptr was not initialized to zero. It is still possible
3655to set the error callbacks AFTER png_read_init(), or to change them with
3656png_set_error_fn(), which is essentially the same function, but with a new
3657name to force compilation errors with applications that try to use the old
3658method.
3659
3660Starting with version 1.0.7, you can find out which version of the library
3661you are using at run-time:
3662
3663 png_uint_32 libpng_vn = png_access_version_number();
3664
3665The number libpng_vn is constructed from the major version, minor
3666version with leading zero, and release number with leading zero,
3667(e.g., libpng_vn for version 1.0.7 is 10007).
3668
3669You can also check which version of png.h you used when compiling your
3670application:
3671
3672 png_uint_32 application_vn = PNG_LIBPNG_VER;
3673
3674.SH IX. Y2K Compliance in libpng
3675
3676December 18, 2008
3677
3678Since the PNG Development group is an ad-hoc body, we can't make
3679an official declaration.
3680
3681This is your unofficial assurance that libpng from version 0.71 and
3682upward through 1.2.34 are Y2K compliant. It is my belief that earlier
3683versions were also Y2K compliant.
3684
3685Libpng only has three year fields. One is a 2-byte unsigned integer that
3686will hold years up to 65535. The other two hold the date in text
3687format, and will hold years up to 9999.
3688
3689The integer is
3690 "png_uint_16 year" in png_time_struct.
3691
3692The strings are
3693 "png_charp time_buffer" in png_struct and
3694 "near_time_buffer", which is a local character string in png.c.
3695
3696There are seven time-related functions:
3697
3698 png_convert_to_rfc_1123() in png.c
3699 (formerly png_convert_to_rfc_1152() in error)
3700 png_convert_from_struct_tm() in pngwrite.c, called
3701 in pngwrite.c
3702 png_convert_from_time_t() in pngwrite.c
3703 png_get_tIME() in pngget.c
3704 png_handle_tIME() in pngrutil.c, called in pngread.c
3705 png_set_tIME() in pngset.c
3706 png_write_tIME() in pngwutil.c, called in pngwrite.c
3707
3708All appear to handle dates properly in a Y2K environment. The
3709png_convert_from_time_t() function calls gmtime() to convert from system
3710clock time, which returns (year - 1900), which we properly convert to
3711the full 4-digit year. There is a possibility that applications using
3712libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3713function, or that they are incorrectly passing only a 2-digit year
3714instead of "year - 1900" into the png_convert_from_struct_tm() function,
3715but this is not under our control. The libpng documentation has always
3716stated that it works with 4-digit years, and the APIs have been
3717documented as such.
3718
3719The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3720integer to hold the year, and can hold years as large as 65535.
3721
3722zlib, upon which libpng depends, is also Y2K compliant. It contains
3723no date-related code.
3724
3725
3726 Glenn Randers-Pehrson
3727 libpng maintainer
3728 PNG Development Group
3729
3730.SH NOTE
3731
3732Note about libpng version numbers:
3733
3734Due to various miscommunications, unforeseen code incompatibilities
3735and occasional factors outside the authors' control, version numbering
3736on the library has not always been consistent and straightforward.
3737The following table summarizes matters since version 0.89c, which was
3738the first widely used release:
3739
3740 source png.h png.h shared-lib
3741 version string int version
3742 ------- ------ ----- ----------
3743 0.89c ("beta 3") 0.89 89 1.0.89
3744 0.90 ("beta 4") 0.90 90 0.90
3745 0.95 ("beta 5") 0.95 95 0.95
3746 0.96 ("beta 6") 0.96 96 0.96
3747 0.97b ("beta 7") 1.00.97 97 1.0.1
3748 0.97c 0.97 97 2.0.97
3749 0.98 0.98 98 2.0.98
3750 0.99 0.99 98 2.0.99
3751 0.99a-m 0.99 99 2.0.99
3752 1.00 1.00 100 2.1.0
3753 1.0.0 1.0.0 100 2.1.0
3754 1.0.0 (from here on, the 100 2.1.0
3755 1.0.1 png.h string is 10001 2.1.0
3756 1.0.1a-e identical to the 10002 from here on, the
3757 1.0.2 source version) 10002 shared library is 2.V
3758 1.0.2a-b 10003 where V is the source
3759 1.0.1 10001 code version except as
3760 1.0.1a-e 10002 2.1.0.1a-e noted.
3761 1.0.2 10002 2.1.0.2
3762 1.0.2a-b 10003 2.1.0.2a-b
3763 1.0.3 10003 2.1.0.3
3764 1.0.3a-d 10004 2.1.0.3a-d
3765 1.0.4 10004 2.1.0.4
3766 1.0.4a-f 10005 2.1.0.4a-f
3767 1.0.5 (+ 2 patches) 10005 2.1.0.5
3768 1.0.5a-d 10006 2.1.0.5a-d
3769 1.0.5e-r 10100 2.1.0.5e-r
3770 1.0.5s-v 10006 2.1.0.5s-v
3771 1.0.6 (+ 3 patches) 10006 2.1.0.6
3772 1.0.6d-g 10007 2.1.0.6d-g
3773 1.0.6h 10007 10.6h
3774 1.0.6i 10007 10.6i
3775 1.0.6j 10007 2.1.0.6j
3776 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3777 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3778 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3779 1.0.7 1 10007 2.1.0.7
3780 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3781 1.0.8rc1 1 10008 2.1.0.8rc1
3782 1.0.8 1 10008 2.1.0.8
3783 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3784 1.0.9rc1 1 10009 2.1.0.9rc1
3785 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3786 1.0.9rc2 1 10009 2.1.0.9rc2
3787 1.0.9 1 10009 2.1.0.9
3788 1.0.10beta1 1 10010 2.1.0.10beta1
3789 1.0.10rc1 1 10010 2.1.0.10rc1
3790 1.0.10 1 10010 2.1.0.10
3791 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3792 1.0.11rc1 1 10011 2.1.0.11rc1
3793 1.0.11 1 10011 2.1.0.11
3794 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3795 1.0.12rc1 2 10012 2.1.0.12rc1
3796 1.0.12 2 10012 2.1.0.12
3797 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3798 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3799 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3800 1.2.0rc1 3 10200 3.1.2.0rc1
3801 1.2.0 3 10200 3.1.2.0
3802 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3803 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3804 1.2.1 3 10201 3.1.2.1
3805 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3806 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3807 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3808 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3809 1.0.13 10 10013 10.so.0.1.0.13
3810 1.2.2 12 10202 12.so.0.1.2.2
3811 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3812 1.2.3 12 10203 12.so.0.1.2.3
3813 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3814 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3815 1.0.14 10 10014 10.so.0.1.0.14
3816 1.2.4 13 10204 12.so.0.1.2.4
3817 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3818 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3819 1.0.15 10 10015 10.so.0.1.0.15
3820 1.2.5 13 10205 12.so.0.1.2.5
3821 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3822 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3823 1.0.16 10 10016 10.so.0.1.0.16
3824 1.2.6 13 10206 12.so.0.1.2.6
3825 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3826 1.0.17rc1 10 10017 10.so.0.1.0.17rc1
3827 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3828 1.0.17 10 10017 10.so.0.1.0.17
3829 1.2.7 13 10207 12.so.0.1.2.7
3830 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
3831 1.0.18rc1-5 10 10018 10.so.0.1.0.18rc1-5
3832 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
3833 1.0.18 10 10018 10.so.0.1.0.18
3834 1.2.8 13 10208 12.so.0.1.2.8
3835 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
3836 1.2.9beta4-11 13 10209 12.so.0.9[.0]
3837 1.2.9rc1 13 10209 12.so.0.9[.0]
3838 1.2.9 13 10209 12.so.0.9[.0]
3839 1.2.10beta1-8 13 10210 12.so.0.10[.0]
3840 1.2.10rc1-3 13 10210 12.so.0.10[.0]
3841 1.2.10 13 10210 12.so.0.10[.0]
3842 1.2.11beta1-4 13 10211 12.so.0.11[.0]
3843 1.0.19rc1-5 10 10019 10.so.0.19[.0]
3844 1.2.11rc1-5 13 10211 12.so.0.11[.0]
3845 1.0.19 10 10019 10.so.0.19[.0]
3846 1.2.11 13 10211 12.so.0.11[.0]
3847 1.0.20 10 10020 10.so.0.20[.0]
3848 1.2.12 13 10212 12.so.0.12[.0]
3849 1.2.13beta1 13 10213 12.so.0.13[.0]
3850 1.0.21 10 10021 10.so.0.21[.0]
3851 1.2.13 13 10213 12.so.0.13[.0]
3852 1.2.14beta1-2 13 10214 12.so.0.14[.0]
3853 1.0.22rc1 10 10022 10.so.0.22[.0]
3854 1.2.14rc1 13 10214 12.so.0.14[.0]
3855 1.2.15beta1-6 13 10215 12.so.0.15[.0]
3856 1.0.23rc1-5 10 10023 10.so.0.23[.0]
3857 1.2.15rc1-5 13 10215 12.so.0.15[.0]
3858 1.0.23 10 10023 10.so.0.23[.0]
3859 1.2.15 13 10215 12.so.0.15[.0]
3860 1.2.16beta1-2 13 10216 12.so.0.16[.0]
3861 1.2.16rc1 13 10216 12.so.0.16[.0]
3862 1.0.24 10 10024 10.so.0.24[.0]
3863 1.2.16 13 10216 12.so.0.16[.0]
3864 1.2.17beta1-2 13 10217 12.so.0.17[.0]
3865 1.0.25rc1 10 10025 10.so.0.25[.0]
3866 1.2.17rc1-3 13 10217 12.so.0.17[.0]
3867 1.0.25 10 10025 10.so.0.25[.0]
3868 1.2.17 13 10217 12.so.0.17[.0]
3869 1.0.26 10 10026 10.so.0.26[.0]
3870 1.2.18 13 10218 12.so.0.18[.0]
3871 1.2.19beta1-31 13 10219 12.so.0.19[.0]
3872 1.0.27rc1-6 10 10027 10.so.0.27[.0]
3873 1.2.19rc1-6 13 10219 12.so.0.19[.0]
3874 1.0.27 10 10027 10.so.0.27[.0]
3875 1.2.19 13 10219 12.so.0.19[.0]
3876 1.2.20beta01-04 13 10220 12.so.0.20[.0]
3877 1.0.28rc1-6 10 10028 10.so.0.28[.0]
3878 1.2.20rc1-6 13 10220 12.so.0.20[.0]
3879 1.0.28 10 10028 10.so.0.28[.0]
3880 1.2.20 13 10220 12.so.0.20[.0]
3881 1.2.21beta1-2 13 10221 12.so.0.21[.0]
3882 1.2.21rc1-3 13 10221 12.so.0.21[.0]
3883 1.0.29 10 10029 10.so.0.29[.0]
3884 1.2.21 13 10221 12.so.0.21[.0]
3885 1.2.22beta1-4 13 10222 12.so.0.22[.0]
3886 1.0.30rc1 13 10030 10.so.0.30[.0]
3887 1.2.22rc1 13 10222 12.so.0.22[.0]
3888 1.0.30 10 10030 10.so.0.30[.0]
3889 1.2.22 13 10222 12.so.0.22[.0]
3890 1.2.23beta01-05 13 10223 12.so.0.23[.0]
3891 1.2.23rc01 13 10223 12.so.0.23[.0]
3892 1.2.23 13 10223 12.so.0.23[.0]
3893 1.2.24beta01-02 13 10224 12.so.0.24[.0]
3894 1.2.24rc01 13 10224 12.so.0.24[.0]
3895 1.2.24 13 10224 12.so.0.24[.0]
3896 1.2.25beta01-06 13 10225 12.so.0.25[.0]
3897 1.2.25rc01-02 13 10225 12.so.0.25[.0]
3898 1.0.31 10 10031 10.so.0.31[.0]
3899 1.2.25 13 10225 12.so.0.25[.0]
3900 1.2.26beta01-06 13 10226 12.so.0.26[.0]
3901 1.2.26rc01 13 10226 12.so.0.26[.0]
3902 1.2.26 13 10226 12.so.0.26[.0]
3903 1.0.32 10 10032 10.so.0.32[.0]
3904 1.2.27beta01-06 13 10227 12.so.0.27[.0]
3905 1.2.27rc01 13 10227 12.so.0.27[.0]
3906 1.0.33 10 10033 10.so.0.33[.0]
3907 1.2.27 13 10227 12.so.0.27[.0]
3908 1.0.34 10 10034 10.so.0.34[.0]
3909 1.2.28 13 10228 12.so.0.28[.0]
3910 1.2.29beta01-03 13 10229 12.so.0.29[.0]
3911 1.2.29rc01 13 10229 12.so.0.29[.0]
3912 1.0.35 10 10035 10.so.0.35[.0]
3913 1.2.29 13 10229 12.so.0.29[.0]
3914 1.0.37 10 10037 10.so.0.37[.0]
3915 1.2.30beta01-04 13 10230 12.so.0.30[.0]
3916 1.0.38rc01-08 10 10038 10.so.0.38[.0]
3917 1.2.30rc01-08 13 10230 12.so.0.30[.0]
3918 1.0.38 10 10038 10.so.0.38[.0]
3919 1.2.30 13 10230 12.so.0.30[.0]
3920 1.0.39rc01-03 10 10039 10.so.0.39[.0]
3921 1.2.31rc01-03 13 10231 12.so.0.31[.0]
3922 1.0.39 10 10039 10.so.0.39[.0]
3923 1.2.31 13 10231 12.so.0.31[.0]
3924 1.2.32beta01-02 13 10232 12.so.0.32[.0]
3925 1.0.40rc01 10 10040 10.so.0.40[.0]
3926 1.2.32rc01 13 10232 12.so.0.32[.0]
3927 1.0.40 10 10040 10.so.0.40[.0]
3928 1.2.32 13 10232 12.so.0.32[.0]
3929 1.2.33beta01-02 13 10233 12.so.0.33[.0]
3930 1.2.33rc01-02 13 10233 12.so.0.33[.0]
3931 1.0.41rc01 10 10041 10.so.0.41[.0]
3932 1.2.33 13 10233 12.so.0.33[.0]
3933 1.0.41 10 10041 10.so.0.41[.0]
3934 1.2.34beta01-07 13 10234 12.so.0.34[.0]
3935 1.0.42rc01 10 10042 10.so.0.42[.0]
3936 1.2.34rc01 13 10234 12.so.0.34[.0]
3937 1.0.42 10 10042 10.so.0.42[.0]
3938 1.2.34 13 10234 12.so.0.34[.0]
3939
3940Henceforth the source version will match the shared-library minor
3941and patch numbers; the shared-library major version number will be
3942used for changes in backward compatibility, as it is intended. The
3943PNG_PNGLIB_VER macro, which is not used within libpng but is available
3944for applications, is an unsigned integer of the form xyyzz corresponding
3945to the source version x.y.z (leading zeros in y and z). Beta versions
3946were given the previous public release number plus a letter, until
3947version 1.0.6j; from then on they were given the upcoming public
3948release number plus "betaNN" or "rcN".
3949
3950.SH "SEE ALSO"
3951.IR libpngpf(3) ", " png(5)
3952.LP
3953.IR libpng :
3954.IP
3955http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3956http://www.libpng.org/pub/png
3957
3958.LP
3959.IR zlib :
3960.IP
3961(generally) at the same location as
3962.I libpng
3963or at
3964.br
3965ftp://ftp.info-zip.org/pub/infozip/zlib
3966
3967.LP
3968.IR PNG specification: RFC 2083
3969.IP
3970(generally) at the same location as
3971.I libpng
3972or at
3973.br
3974ftp://ftp.rfc-editor.org:/in-notes/rfc2083.txt
3975.br
3976or (as a W3C Recommendation) at
3977.br
3978http://www.w3.org/TR/REC-png.html
3979
3980.LP
3981In the case of any inconsistency between the PNG specification
3982and this library, the specification takes precedence.
3983
3984.SH AUTHORS
3985This man page: Glenn Randers-Pehrson
3986<glennrp at users.sourceforge.net>
3987
3988The contributing authors would like to thank all those who helped
3989with testing, bug fixes, and patience. This wouldn't have been
3990possible without all of you.
3991
3992Thanks to Frank J. T. Wojcik for helping with the documentation.
3993
3994Libpng version 1.2.34 - December 18, 2008:
3995Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3996Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
3997
3998Supported by the PNG development group
3999.br
4000png-mng-implement at lists.sf.net
4001(subscription required; visit
4002png-mng-implement at lists.sourceforge.net (subscription required; visit
4003https://lists.sourceforge.net/lists/listinfo/png-mng-implement
4004to subscribe).
4005
4006.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
4007
4008(This copy of the libpng notices is provided for your convenience. In case of
4009any discrepancy between this copy and the notices in the file png.h that is
4010included in the libpng distribution, the latter shall prevail.)
4011
4012If you modify libpng you may insert additional notices immediately following
4013this sentence.
4014
4015libpng versions 1.2.6, August 15, 2004, through 1.2.34, December 18, 2008, are
4016Copyright (c) 2004,2006-2008 Glenn Randers-Pehrson, and are
4017distributed according to the same disclaimer and license as libpng-1.2.5
4018with the following individual added to the list of Contributing Authors
4019
4020 Cosmin Truta
4021
4022libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
4023Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
4024distributed according to the same disclaimer and license as libpng-1.0.6
4025with the following individuals added to the list of Contributing Authors
4026
4027 Simon-Pierre Cadieux
4028 Eric S. Raymond
4029 Gilles Vollant
4030
4031and with the following additions to the disclaimer:
4032
4033 There is no warranty against interference with your
4034 enjoyment of the library or against infringement.
4035 There is no warranty that our efforts or the library
4036 will fulfill any of your particular purposes or needs.
4037 This library is provided with all faults, and the entire
4038 risk of satisfactory quality, performance, accuracy, and
4039 effort is with the user.
4040
4041libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
4042Copyright (c) 1998, 1999 Glenn Randers-Pehrson
4043Distributed according to the same disclaimer and license as libpng-0.96,
4044with the following individuals added to the list of Contributing Authors:
4045
4046 Tom Lane
4047 Glenn Randers-Pehrson
4048 Willem van Schaik
4049
4050libpng versions 0.89, June 1996, through 0.96, May 1997, are
4051Copyright (c) 1996, 1997 Andreas Dilger
4052Distributed according to the same disclaimer and license as libpng-0.88,
4053with the following individuals added to the list of Contributing Authors:
4054
4055 John Bowler
4056 Kevin Bracey
4057 Sam Bushell
4058 Magnus Holmgren
4059 Greg Roelofs
4060 Tom Tanner
4061
4062libpng versions 0.5, May 1995, through 0.88, January 1996, are
4063Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
4064
4065For the purposes of this copyright and license, "Contributing Authors"
4066is defined as the following set of individuals:
4067
4068 Andreas Dilger
4069 Dave Martindale
4070 Guy Eric Schalnat
4071 Paul Schmidt
4072 Tim Wegner
4073
4074The PNG Reference Library is supplied "AS IS". The Contributing Authors
4075and Group 42, Inc. disclaim all warranties, expressed or implied,
4076including, without limitation, the warranties of merchantability and of
4077fitness for any purpose. The Contributing Authors and Group 42, Inc.
4078assume no liability for direct, indirect, incidental, special, exemplary,
4079or consequential damages, which may result from the use of the PNG
4080Reference Library, even if advised of the possibility of such damage.
4081
4082Permission is hereby granted to use, copy, modify, and distribute this
4083source code, or portions hereof, for any purpose, without fee, subject
4084to the following restrictions:
4085
40861. The origin of this source code must not be misrepresented.
4087
40882. Altered versions must be plainly marked as such and
4089 must not be misrepresented as being the original source.
4090
40913. This Copyright notice may not be removed or altered from
4092 any source or altered source distribution.
4093
4094The Contributing Authors and Group 42, Inc. specifically permit, without
4095fee, and encourage the use of this source code as a component to
4096supporting the PNG file format in commercial products. If you use this
4097source code in a product, acknowledgment is not required but would be
4098appreciated.
4099
4100
4101A "png_get_copyright" function is available, for convenient use in "about"
4102boxes and the like:
4103
4104 printf("%s",png_get_copyright(NULL));
4105
4106Also, the PNG logo (in PNG format, of course) is supplied in the
4107files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4108
4109Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4110certification mark of the Open Source Initiative.
4111
4112Glenn Randers-Pehrson
4113glennrp at users.sourceforge.net
4114December 18, 2008
4115
4116.\" end of man page
4117
wxWidgets (Impactor)