]> git.saurik.com Git - wxWidgets.git/blame - src/png/libpng.3
projects / wxWidgets.git / blame
? search:
summary | shortlog | log | commit | commitdiff | tree
blob | blame (incremental) | history | HEAD
Source cleaning: whitespaces, tabs, TRUE/true, FALSE/false.
[wxWidgets.git] / src / png / libpng.3
CommitLineData
5b02c8a1 1.TH LIBPNG 3 "August 15, 2004"
75b6e0a0 2.SH NAME
5b02c8a1 3libpng \- Portable Network Graphics (PNG) Reference Library 1.2.6
75b6e0a0 4.SH SYNOPSIS
4946a942 5\fI\fB
75b6e0a0 6
4946a942
GD		 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
4946a942
GD		 103\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
104
105\fI\fB
106
107\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
108
109\fI\fB
110
111\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
112
113\fI\fB
114
115\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
116
117\fI\fB
118
119\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
120
121\fI\fB
122
123\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
124
125\fI\fB
126
127\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
128
129\fI\fB
130
131\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
132
133\fI\fB
134
135\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
136
137\fI\fB
138
139\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
140
141\fI\fB
142
143\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
144
145\fI\fB
146
147\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
148
149\fI\fB
150
151\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
152
153\fI\fB
154
155\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
156
157\fI\fB
158
159\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
160
161\fI\fB
162
163\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
164
165\fI\fB
166
167\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
168
169\fI\fB
170
171\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
172
173\fI\fB
174
175\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
176
177\fI\fB
178
179\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
180
181\fI\fB
182
183\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
184
185\fI\fB
186
187\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
188
189\fI\fB
190
191\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
192
193\fI\fB
194
4946a942
GD		 195\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
196
197\fI\fB
198
199\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
200
201\fI\fB
202
203\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
204
205\fI\fB
206
207\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
208
209\fI\fB
210
211\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
212
213\fI\fB
214
215\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
216
217\fI\fB
218
219\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
220
221\fI\fB
222
223\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
224
225\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
226
227\fI\fB
228
229\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
230
231\fI\fB
232
233\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
234
235\fI\fB
236
237\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
238
239\fI\fB
240
241\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
242
243\fI\fB
244
245\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
246
247\fI\fB
248
249\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
250
251\fI\fB
252
253\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
254
255\fI\fB
256
257\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
258
259\fI\fB
260
261\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
262
263\fI\fB
264
265\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
266
267\fI\fB
268
5b02c8a1
VS		 269\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
270
271\fI\fB
272
4946a942
GD		 273\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
274
275\fI\fB
276
5b02c8a1
VS		 277\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
278
279\fI\fB
280
4946a942
GD		 281\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
282
283\fI\fB
284
285\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
286
287\fI\fB
288
289\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
290
291\fI\fB
292
293\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
294
295\fI\fB
296
297\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
298
299\fI\fB
300
301\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
302
303\fI\fB
304
305\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
306
307\fI\fB
308
309\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
310
311\fI\fB
312
313\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
314
315\fI\fB
316
317\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
318
319\fI\fB
320
321\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
322
323\fI\fB
324
325\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
326
327\fI\fB
328
329\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
330
331\fI\fB
332
333\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
334
335\fI\fB
336
4946a942
GD		 337\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
338
339\fI\fB
340
341\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
342
343\fI\fB
344
345\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
346
347\fI\fB
348
349\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
350
351\fI\fB
352
4946a942
GD		 353\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
354
355\fI\fB
356
357\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
358
359\fI\fB
360
361\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
362
363\fI\fB
364
365\fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
366
367\fI\fB
368
369\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
370
371\fI\fB
372
373\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
374
375\fI\fB
376
377\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
378
379\fI\fB
380
381\fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
382
383\fI\fB
384
385\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
386
387\fI\fB
388
389\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
390
391\fI\fB
392
393\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
394
395\fI\fB
396
397\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
398
399\fI\fB
400
401\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
402
403\fI\fB
404
4946a942
GD		 405\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
406
407\fI\fB
408
409\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
410
411\fI\fB
75b6e0a0 412
4946a942 413\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
75b6e0a0 414
4946a942 415\fI\fB
75b6e0a0 416
4946a942 417\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
75b6e0a0 418
4946a942 419\fI\fB
75b6e0a0 420
4946a942 421\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
75b6e0a0 422
4946a942 423\fI\fB
75b6e0a0 424
4946a942 425\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
75b6e0a0 426
4946a942 427\fI\fB
75b6e0a0 428
4946a942 429\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
75b6e0a0 430
4946a942 431\fI\fB
75b6e0a0 432
4946a942 433\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
75b6e0a0 434
4946a942 435\fI\fB
75b6e0a0 436
4946a942 437\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
75b6e0a0 438
4946a942 439\fI\fB
75b6e0a0 440
4946a942 441\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
75b6e0a0 442
4946a942 443\fI\fB
75b6e0a0 444
4946a942 445\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
75b6e0a0 446
4946a942 447\fI\fB
75b6e0a0 448
4946a942 449\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
75b6e0a0 450
4946a942 451\fI\fB
75b6e0a0 452
4946a942 453\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
75b6e0a0 454
4946a942 455\fI\fB
75b6e0a0 456
4946a942 457\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 458
4946a942 459\fI\fB
75b6e0a0 460
4946a942 461\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
75b6e0a0 462
4946a942 463\fI\fB
75b6e0a0 464
4946a942 465\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
75b6e0a0 466
4946a942 467\fI\fB
75b6e0a0 468
4946a942 469\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
75b6e0a0 470
4946a942 471\fI\fB
75b6e0a0 472
4946a942 473\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
75b6e0a0 474
4946a942 475\fI\fB
75b6e0a0 476
4946a942 477\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
75b6e0a0 478
4946a942 479\fI\fB
75b6e0a0 480
4946a942 481\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
75b6e0a0 482
4946a942 483\fI\fB
75b6e0a0 484
4946a942 485\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
75b6e0a0 486
4946a942 487\fI\fB
75b6e0a0 488
4946a942 489\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 490
4946a942 491\fI\fB
75b6e0a0 492
4946a942 493\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 494
4946a942 495\fI\fB
75b6e0a0 496
4946a942 497\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
75b6e0a0 498
4946a942 499\fI\fB
75b6e0a0 500
4946a942 501\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
75b6e0a0 502
4946a942 503\fI\fB
75b6e0a0 504
4946a942 505\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 506
4946a942 507\fI\fB
75b6e0a0 508
4946a942 509\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
75b6e0a0 510
4946a942 511\fI\fB
75b6e0a0 512
4946a942 513\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 514
4946a942 515\fI\fB
75b6e0a0 516
4946a942 517\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 518
4946a942 519\fI\fB
75b6e0a0 520
4946a942 521\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
75b6e0a0 522
4946a942 523\fI\fB
75b6e0a0 524
4946a942 525\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
75b6e0a0 526
4946a942 527\fI\fB
75b6e0a0 528
4946a942 529\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
75b6e0a0 530
4946a942 531\fI\fB
75b6e0a0 532
4946a942 533\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
75b6e0a0 534
4946a942 535\fI\fB
75b6e0a0 536
4946a942 537\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 538
4946a942 539\fI\fB
75b6e0a0 540
4946a942 541\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 542
4946a942 543\fI\fB
75b6e0a0 544
4946a942 545\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 546
4946a942 547\fI\fB
75b6e0a0 548
4946a942 549\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
75b6e0a0 550
4946a942 551\fI\fB
75b6e0a0 552
4946a942 553\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
75b6e0a0 554
4946a942 555\fI\fB
75b6e0a0 556
4946a942 557\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
75b6e0a0 558
4946a942 559\fI\fB
75b6e0a0 560
4946a942 561\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
75b6e0a0 562
4946a942 563\fI\fB
75b6e0a0 564
4946a942 565\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
75b6e0a0 566
4946a942 567\fI\fB
75b6e0a0 568
4946a942 569\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
75b6e0a0 570
4946a942 571\fI\fB
75b6e0a0 572
4946a942 573\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
75b6e0a0 574
4946a942 575\fI\fB
75b6e0a0 576
4946a942 577\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
75b6e0a0 578
4946a942 579\fI\fB
75b6e0a0 580
4946a942 581\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
75b6e0a0 582
4946a942 583\fI\fB
75b6e0a0 584
4946a942 585\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
75b6e0a0 586
4946a942 587\fI\fB
75b6e0a0 588
4946a942 589\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
75b6e0a0 590
4946a942 591\fI\fB
75b6e0a0 592
4946a942 593\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
75b6e0a0 594
4946a942 595\fI\fB
75b6e0a0 596
4946a942 597\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
75b6e0a0 598
4946a942 599\fI\fB
75b6e0a0 600
4946a942 601\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
75b6e0a0 602
4946a942 603\fI\fB
75b6e0a0 604
4946a942 605\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
75b6e0a0 606
4946a942 607\fI\fB
75b6e0a0 608
4946a942 609\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
75b6e0a0 610
4946a942 611\fI\fB
75b6e0a0 612
4946a942 613\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
75b6e0a0 614
4946a942 615\fI\fB
75b6e0a0 616
4946a942 617\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 618
4946a942 619\fI\fB
75b6e0a0 620
4946a942 621\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 622
4946a942 623\fI\fB
75b6e0a0 624
4946a942 625\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 626
4946a942 627\fI\fB
75b6e0a0 628
4946a942 629\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 630
4946a942 631\fI\fB
75b6e0a0 632
4946a942 633\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
75b6e0a0 634
4946a942 635\fI\fB
75b6e0a0 636
4946a942 637\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
75b6e0a0 638
4946a942 639\fI\fB
75b6e0a0 640
4946a942 641\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
75b6e0a0 642
4946a942 643\fI\fB
75b6e0a0 644
4946a942 645\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 646
4946a942 647\fI\fB
75b6e0a0 648
4946a942 649\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
75b6e0a0 650
4946a942 651\fI\fB
75b6e0a0 652
4946a942 653\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
75b6e0a0 654
4946a942 655\fI\fB
75b6e0a0 656
4946a942 657\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
75b6e0a0 658
4946a942 659\fI\fB
75b6e0a0 660
5b02c8a1
VS		 661\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
662
663\fI\fB
664
4946a942 665\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
75b6e0a0 666
4946a942 667\fI\fB
75b6e0a0 668
4946a942 669\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
75b6e0a0 670
4946a942 671\fI\fB
75b6e0a0 672
4946a942 673\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
75b6e0a0 674
4946a942 675\fI\fB
75b6e0a0 676
4946a942 677\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
75b6e0a0 678
4946a942 679\fI\fB
75b6e0a0 680
4946a942 681\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
75b6e0a0 682
4946a942 683\fI\fB
75b6e0a0 684
4946a942 685\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
75b6e0a0 686
4946a942 687\fI\fB
75b6e0a0 688
4946a942 689\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
75b6e0a0 690
4946a942 691\fI\fB
75b6e0a0 692
4946a942
GD		 693\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
694
695\fI\fB
696
697\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
698
699\fI\fB
700
701\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
702
703\fI\fB
704
705\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
706
707\fI\fB
708
709\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
710
711\fI\fB
712
713\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
714
715\fI\fB
716
717\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
718
719\fI\fB
720
721\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
722
723\fI\fB
724
725\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
726
727\fI\fB
728
729\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
730
731\fI\fB
732
733\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
734
735\fI\fB
736
737\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
738
739\fI\fB
740
741\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
742
743\fI\fB
744
745\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
746
747\fI\fB
748
749\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
750
751\fI\fB
752
753\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
754
755\fI\fB
75b6e0a0 756
5b02c8a1
VS		 757\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
758
759\fI\fB
760
761\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
762
763\fI\fB
764
75b6e0a0
GD		 765.SH DESCRIPTION
766The
767.I libpng
768library supports encoding, decoding, and various manipulations of
769the Portable Network Graphics (PNG) format image files. It uses the
770.IR zlib(3)
771compression library.
772Following is a copy of the libpng.txt file that accompanies libpng.
773.SH LIBPNG.TXT
774libpng.txt - A description on how to use and modify libpng
775
5b02c8a1 776 libpng version 1.2.6 - August 15, 2004
75b6e0a0 777 Updated and distributed by Glenn Randers-Pehrson
5b02c8a1
VS		 778 <glennrp@users.sourceforge.net>
779 Copyright (c) 1998-2004 Glenn Randers-Pehrson
75b6e0a0
GD		 780 For conditions of distribution and use, see copyright
781 notice in png.h.
782
783 based on:
784
785 libpng 1.0 beta 6 version 0.96 May 28, 1997
786 Updated and distributed by Andreas Dilger
787 Copyright (c) 1996, 1997 Andreas Dilger
788
789 libpng 1.0 beta 2 - version 0.88 January 26, 1996
790 For conditions of distribution and use, see copyright
791 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
792 Schalnat, Group 42, Inc.
793
794 Updated/rewritten per request in the libpng FAQ
4946a942
GD		 795 Copyright (c) 1995, 1996 Frank J. T. Wojcik
796 December 18, 1995 & January 20, 1996
75b6e0a0
GD		 797
798.SH I. Introduction
799
800This file describes how to use and modify the PNG reference library
801(known as libpng) for your own use. There are five sections to this
802file: introduction, structures, reading, writing, and modification and
803configuration notes for various special platforms. In addition to this
804file, example.c is a good starting point for using the library, as
805it is heavily commented and should include everything most people
806will need. We assume that libpng is already installed; see the
807INSTALL file for instructions on how to install libpng.
808
809Libpng was written as a companion to the PNG specification, as a way
810of reducing the amount of time and effort it takes to support the PNG
4946a942
GD		 811file format in application programs.
812
813The PNG-1.2 specification is available at <http://www.libpng.org/pub/png>
814and at <ftp://ftp.uu.net/graphics/png/documents/>.
815
816The PNG-1.0 specification is available
75b6e0a0
GD		 817as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
818W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
819additional chunks are described in the special-purpose public chunks
4946a942
GD		 820documents at <ftp://ftp.uu.net/graphics/png/documents/>.
821
822Other information
75b6e0a0 823about PNG, and the latest version of libpng, can be found at the PNG home
4946a942
GD		 824page, <http://www.libpng.org/pub/png/>
825and at <ftp://ftp.uu.net/graphics/png/>.
75b6e0a0
GD		 826
827Most users will not have to modify the library significantly; advanced
828users may want to modify it more. All attempts were made to make it as
829complete as possible, while keeping the code easy to understand.
830Currently, this library only supports C. Support for other languages
831is being considered.
832
833Libpng has been designed to handle multiple sessions at one time,
834to be easily modifiable, to be portable to the vast majority of
835machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
836to use. The ultimate goal of libpng is to promote the acceptance of
837the PNG file format in whatever way possible. While there is still
838work to be done (see the TODO file), libpng should cover the
839majority of the needs of its users.
840
841Libpng uses zlib for its compression and decompression of PNG files.
842Further information about zlib, and the latest version of zlib, can
4946a942 843be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
75b6e0a0
GD		 844The zlib compression utility is a general purpose utility that is
845useful for more than PNG files, and can be used without libpng.
846See the documentation delivered with zlib for more details.
847You can usually find the source files for the zlib utility wherever you
848find the libpng source files.
849
850Libpng is thread safe, provided the threads are using different
851instances of the structures. Each thread should have its own
852png_struct and png_info instances, and thus its own image.
853Libpng does not protect itself against two threads using the
4946a942
GD		 854same instance of a structure. Note: thread safety may be defeated
855by use of some of the MMX assembler code in pnggccrd.c, which is only
856compiled when the user defines PNG_THREAD_UNSAFE_OK.
75b6e0a0
GD		 857
858
859.SH II. Structures
860
861There are two main structures that are important to libpng, png_struct
862and png_info. The first, png_struct, is an internal structure that
863will not, for the most part, be used by a user except as the first
864variable passed to every libpng function call.
865
866The png_info structure is designed to provide information about the
867PNG file. At one time, the fields of png_info were intended to be
868directly accessible to the user. However, this tended to cause problems
869with applications using dynamically loaded libraries, and as a result
4946a942
GD		 870a set of interface functions for png_info (the png_get_*() and png_set_*()
871functions) was developed. The fields of png_info are still available for
872older applications, but it is suggested that applications use the new
873interfaces if at all possible.
874
875Applications that do make direct access to the members of png_struct (except
876for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
877and applications that make direct access to the members of png_info must
878be recompiled if they were compiled or loaded with libpng version 1.0.6,
879in which the members were in a different order. In version 1.0.7, the
880members of the png_info structure reverted to the old order, as they were
881in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
882structures are going to be hidden, and the contents of the structures will
883only be accessible through the png_get/png_set functions.
75b6e0a0
GD		 884
885The png.h header file is an invaluable reference for programming with libpng.
886And while I'm on the topic, make sure you include the libpng header file:
887
888#include <png.h>
889
890.SH III. Reading
891
75b6e0a0 892We'll now walk you through the possible functions to call when reading
4946a942
GD		 893in a PNG file sequentially, briefly explaining the syntax and purpose
894of each one. See example.c and png.h for more detail. While
895progressive reading is covered in the next section, you will still
896need some of the functions discussed in this section to read a PNG
897file.
898
899.SS Setup
75b6e0a0
GD		 900
901You will want to do the I/O initialization(*) before you get into libpng,
902so if it doesn't work, you don't have much to undo. Of course, you
903will also want to insure that you are, in fact, dealing with a PNG
904file. Libpng provides a simple check to see if a file is a PNG file.
4946a942
GD		 905To use it, pass in the first 1 to 8 bytes of the file to the function
906png_sig_cmp(), and it will return 0 if the bytes match the corresponding
907bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
908you pass in, the greater the accuracy of the prediction.
75b6e0a0
GD		 909
910If you are intending to keep the file pointer open for use in libpng,
911you must ensure you don't read more than 8 bytes from the beginning
912of the file, and you also have to make a call to png_set_sig_bytes_read()
913with the number of bytes you read from the beginning. Libpng will
914then only check the bytes (if any) that your program didn't read.
915
916(*): If you are not using the standard I/O functions, you will need
917to replace them with custom functions. See the discussion under
918Customizing libpng.
919
920
921 FILE *fp = fopen(file_name, "rb");
922 if (!fp)
923 {
4946a942 924 return (ERROR);
75b6e0a0
GD		 925 }
926 fread(header, 1, number, fp);
927 is_png = !png_sig_cmp(header, 0, number);
928 if (!is_png)
929 {
4946a942 930 return (NOT_PNG);
75b6e0a0
GD		 931 }
932
933
934Next, png_struct and png_info need to be allocated and initialized. In
935order to ensure that the size of these structures is correct even with a
936dynamically linked libpng, there are functions to initialize and
937allocate the structures. We also pass the library version, optional
938pointers to error handling functions, and a pointer to a data struct for
939use by the error functions, if necessary (the pointer and functions can
940be NULL if the default error handlers are to be used). See the section
941on Changes to Libpng below regarding the old initialization functions.
4946a942
GD		 942The structure allocation functions quietly return NULL if they fail to
943create the structure, so your application should check for that.
75b6e0a0
GD		 944
945 png_structp png_ptr = png_create_read_struct
946 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
947 user_error_fn, user_warning_fn);
948 if (!png_ptr)
4946a942 949 return (ERROR);
75b6e0a0
GD		 950
951 png_infop info_ptr = png_create_info_struct(png_ptr);
952 if (!info_ptr)
953 {
954 png_destroy_read_struct(&png_ptr,
955 (png_infopp)NULL, (png_infopp)NULL);
4946a942 956 return (ERROR);
75b6e0a0
GD		 957 }
958
959 png_infop end_info = png_create_info_struct(png_ptr);
960 if (!end_info)
961 {
962 png_destroy_read_struct(&png_ptr, &info_ptr,
963 (png_infopp)NULL);
4946a942 964 return (ERROR);
75b6e0a0
GD		 965 }
966
967If you want to use your own memory allocation routines,
968define PNG_USER_MEM_SUPPORTED and use
969png_create_read_struct_2() instead of png_create_read_struct():
970
971 png_structp png_ptr = png_create_read_struct_2
972 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
973 user_error_fn, user_warning_fn, (png_voidp)
974 user_mem_ptr, user_malloc_fn, user_free_fn);
975
976The error handling routines passed to png_create_read_struct()
977and the memory alloc/free routines passed to png_create_struct_2()
978are only necessary if you are not using the libpng supplied error
979handling and memory alloc/free functions.
980
981When libpng encounters an error, it expects to longjmp back
982to your routine. Therefore, you will need to call setjmp and pass
4946a942 983your png_jmpbuf(png_ptr). If you read the file from different
75b6e0a0 984routines, you will need to update the jmpbuf field every time you enter
4946a942 985a new routine that will call a png_*() function.
75b6e0a0
GD		 986
987See your documentation of setjmp/longjmp for your compiler for more
4946a942
GD		 988information on setjmp/longjmp. See the discussion on libpng error
989handling in the Customizing Libpng section below for more information
990on the libpng error handling. If an error occurs, and libpng longjmp's
75b6e0a0
GD		 991back to your setjmp, you will want to call png_destroy_read_struct() to
992free any memory.
993
4946a942 994 if (setjmp(png_jmpbuf(png_ptr)))
75b6e0a0
GD		 995 {
996 png_destroy_read_struct(&png_ptr, &info_ptr,
997 &end_info);
998 fclose(fp);
4946a942 999 return (ERROR);
75b6e0a0
GD		 1000 }
1001
4946a942
GD		 1002If you would rather avoid the complexity of setjmp/longjmp issues,
1003you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1004errors will result in a call to PNG_ABORT() which defaults to abort().
1005
75b6e0a0
GD		 1006Now you need to set up the input code. The default for libpng is to
1007use the C function fread(). If you use this, you will need to pass a
1008valid FILE * in the function png_init_io(). Be sure that the file is
1009opened in binary mode. If you wish to handle reading data in another
1010way, you need not call the png_init_io() function, but you must then
1011implement the libpng I/O methods discussed in the Customizing Libpng
1012section below.
1013
1014 png_init_io(png_ptr, fp);
1015
1016If you had previously opened the file and read any of the signature from
1017the beginning in order to see if this was a PNG file, you need to let
1018libpng know that there are some bytes missing from the start of the file.
1019
1020 png_set_sig_bytes(png_ptr, number);
1021
4946a942
GD		 1022.SS Setting up callback code
1023
1024You can set up a callback function to handle any unknown chunks in the
1025input stream. You must supply the function
1026
1027 read_chunk_callback(png_ptr ptr,
1028 png_unknown_chunkp chunk);
1029 {
1030 /* The unknown chunk structure contains your
1031 chunk data: */
1032 png_byte name[5];
1033 png_byte *data;
1034 png_size_t size;
1035 /* Note that libpng has already taken care of
1036 the CRC handling */
1037
1038 /* put your code here. Return one of the
1039 following: */
1040
1041 return (-n); /* chunk had an error */
1042 return (0); /* did not recognize */
1043 return (n); /* success */
1044 }
1045
1046(You can give your function another name that you like instead of
1047"read_chunk_callback")
1048
1049To inform libpng about your function, use
1050
1051 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1052 read_chunk_callback);
1053
1054This names not only the callback function, but also a user pointer that
1055you can retrieve with
1056
1057 png_get_user_chunk_ptr(png_ptr);
1058
75b6e0a0
GD		 1059At this point, you can set up a callback function that will be
1060called after each row has been read, which you can use to control
1061a progress meter or the like. It's demonstrated in pngtest.c.
1062You must supply a function
1063
4946a942
GD		 1064 void read_row_callback(png_ptr ptr, png_uint_32 row,
1065 int pass);
75b6e0a0
GD		 1066 {
1067 /* put your code here */
1068 }
1069
1070(You can give it another name that you like instead of "read_row_callback")
1071
1072To inform libpng about your function, use
1073
1074 png_set_read_status_fn(png_ptr, read_row_callback);
1075
5b02c8a1
VS		 1076%-%.SS Width and height limits
1077%-%
1078%-%The PNG specification allows the width and height of an image to be as
1079%-%large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1080%-%Since very few applications really need to process such large images,
1081%-%we have imposed an arbitrary 1-million limit on rows and columns.
1082%-%Larger images will be rejected immediately with a png_error() call. If
1083%-%you wish to override this limit, you can use
1084%-%
1085%-% png_set_user_limits(png_ptr, width_max, height_max);
1086%-%
1087%-%to set your own limits, or use width_max = height_max = 0x7fffffffL
1088%-%to allow all valid dimensions (libpng may reject some very large images
1089%-%anyway because of potential buffer overflow conditions).
1090%-%
1091%-%You should put this statement after you create the PNG structure and
1092%-%before calling png_read_info(), png_read_png(), or png_process_data().
1093%-%If you need to retrieve the limits that are being applied, use
1094%-%
1095%-% width_max = png_get_user_width_max(png_ptr);
1096%-% height_max = png_get_user_height_max(png_ptr);
1097%-%
4946a942
GD		 1098.SS Unknown-chunk handling
1099
1100Now you get to set the way the library processes unknown chunks in the
1101input PNG stream. Both known and unknown chunks will be read. Normal
1102behavior is that known chunks will be parsed into information in
1103various info_ptr members; unknown chunks will be discarded. To change
1104this, you can call:
1105
5b02c8a1 1106 png_set_keep_unknown_chunks(png_ptr, keep,
4946a942 1107 chunk_list, num_chunks);
5b02c8a1
VS		 1108 keep - 0: do not handle as unknown
1109 1: do not keep
1110 2: keep only if safe-to-copy
1111 3: keep even if unsafe-to-copy
1112 You can use these definitions:
1113 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1114 PNG_HANDLE_CHUNK_NEVER 1
1115 PNG_HANDLE_CHUNK_IF_SAFE 2
1116 PNG_HANDLE_CHUNK_ALWAYS 3
4946a942
GD		 1117 chunk_list - list of chunks affected (a byte string,
1118 five bytes per chunk, NULL or '\0' if
1119 num_chunks is 0)
1120 num_chunks - number of chunks affected; if 0, all
5b02c8a1
VS		 1121 unknown chunks are affected. If nonzero,
1122 only the chunks in the list are affected
4946a942
GD		 1123
1124Unknown chunks declared in this way will be saved as raw data onto a
1125list of png_unknown_chunk structures. If a chunk that is normally
1126known to libpng is named in the list, it will be handled as unknown,
1127according to the "keep" directive. If a chunk is named in successive
1128instances of png_set_keep_unknown_chunks(), the final instance will
5b02c8a1
VS		 1129take precedence. The IHDR and IEND chunks should not be named in
1130chunk_list; if they are, libpng will process them normally anyway.
4946a942
GD		 1131
1132.SS The high-level read interface
1133
1134At this point there are two ways to proceed; through the high-level
1135read interface, or through a sequence of low-level read operations.
1136You can use the high-level interface if (a) you are willing to read
1137the entire image into memory, and (b) the input transformations
1138you want to do are limited to the following set:
1139
1140 PNG_TRANSFORM_IDENTITY No transformation
1141 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1142 8 bits
1143 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1144 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1145 samples to bytes
1146 PNG_TRANSFORM_PACKSWAP Change order of packed
1147 pixels to LSB first
1148 PNG_TRANSFORM_EXPAND Perform set_expand()
1149 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1150 PNG_TRANSFORM_SHIFT Normalize pixels to the
1151 sBIT depth
1152 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1153 to BGRA
1154 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1155 to AG
1156 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1157 to transparency
1158 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1159
1160(This excludes setting a background color, doing gamma transformation,
1161dithering, and setting filler.) If this is the case, simply do this:
1162
1163 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1164
1165where png_transforms is an integer containing the logical OR of
1166some set of transformation flags. This call is equivalent to png_read_info(),
1167followed the set of transformations indicated by the transform mask,
1168then png_read_image(), and finally png_read_end().
1169
1170(The final parameter of this call is not yet used. Someday it might point
1171to transformation parameters required by some future input transform.)
1172
1173After you have called png_read_png(), you can retrieve the image data
1174with
75b6e0a0 1175
4946a942 1176 row_pointers = png_get_rows(png_ptr, info_ptr);
75b6e0a0 1177
4946a942 1178where row_pointers is an array of pointers to the pixel data for each row:
75b6e0a0 1179
4946a942 1180 png_bytep row_pointers[height];
75b6e0a0 1181
4946a942
GD		 1182If you know your image size and pixel size ahead of time, you can allocate
1183row_pointers prior to calling png_read_png() with
75b6e0a0 1184
5b02c8a1
VS		 1185 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1186 png_error (png_ptr,
1187 "Image is too tall to process in memory");
1188 if (width > PNG_UINT_32_MAX/pixel_size)
1189 png_error (png_ptr,
1190 "Image is too wide to process in memory");
4946a942 1191 row_pointers = png_malloc(png_ptr,
5b02c8a1 1192 height*png_sizeof(png_bytep));
4946a942
GD		 1193 for (int i=0; i<height, i++)
1194 row_pointers[i]=png_malloc(png_ptr,
1195 width*pixel_size);
1196 png_set_rows(png_ptr, info_ptr, &row_pointers);
75b6e0a0 1197
4946a942
GD		 1198Alternatively you could allocate your image in one big block and define
1199row_pointers[i] to point into the proper places in your block.
75b6e0a0 1200
4946a942
GD		 1201If you use png_set_rows(), the application is responsible for freeing
1202row_pointers (and row_pointers[i], if they were separately allocated).
1203
1204If you don't allocate row_pointers ahead of time, png_read_png() will
1205do it, and it'll be free'ed when you call png_destroy_*().
75b6e0a0 1206
4946a942
GD		 1207.SS The low-level read interface
1208
1209If you are going the low-level route, you are now ready to read all
1210the file information up to the actual image data. You do this with a
1211call to png_read_info().
75b6e0a0
GD		 1212
1213 png_read_info(png_ptr, info_ptr);
1214
4946a942
GD		 1215This will process all chunks up to but not including the image data.
1216
1217.SS Querying the info structure
1218
1219Functions are used to get the information from the info_ptr once it
1220has been read. Note that these fields may not be completely filled
1221in until png_read_end() has read the chunk data following the image.
75b6e0a0
GD		 1222
1223 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1224 &bit_depth, &color_type, &interlace_type,
4946a942 1225 &compression_type, &filter_method);
75b6e0a0
GD		 1226
1227 width - holds the width of the image
1228 in pixels (up to 2^31).
1229 height - holds the height of the image
1230 in pixels (up to 2^31).
1231 bit_depth - holds the bit depth of one of the
1232 image channels. (valid values are
1233 1, 2, 4, 8, 16 and depend also on
1234 the color_type. See also
1235 significant bits (sBIT) below).
1236 color_type - describes which color/alpha channels
1237 are present.
1238 PNG_COLOR_TYPE_GRAY
1239 (bit depths 1, 2, 4, 8, 16)
1240 PNG_COLOR_TYPE_GRAY_ALPHA
1241 (bit depths 8, 16)
1242 PNG_COLOR_TYPE_PALETTE
1243 (bit depths 1, 2, 4, 8)
1244 PNG_COLOR_TYPE_RGB
1245 (bit_depths 8, 16)
1246 PNG_COLOR_TYPE_RGB_ALPHA
1247 (bit_depths 8, 16)
1248
1249 PNG_COLOR_MASK_PALETTE
1250 PNG_COLOR_MASK_COLOR
1251 PNG_COLOR_MASK_ALPHA
1252
4946a942
GD		 1253 filter_method - (must be PNG_FILTER_TYPE_BASE
1254 for PNG 1.0, and can also be
1255 PNG_INTRAPIXEL_DIFFERENCING if
1256 the PNG datastream is embedded in
1257 a MNG-1.0 datastream)
75b6e0a0
GD		 1258 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1259 for PNG 1.0)
1260 interlace_type - (PNG_INTERLACE_NONE or
1261 PNG_INTERLACE_ADAM7)
1262 Any or all of interlace_type, compression_type, of
4946a942
GD		 1263 filter_method can be NULL if you are
1264 not interested in their values.
75b6e0a0
GD		 1265
1266 channels = png_get_channels(png_ptr, info_ptr);
1267 channels - number of channels of info for the
1268 color type (valid values are 1 (GRAY,
1269 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1270 4 (RGB_ALPHA or RGB + filler byte))
1271 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1272 rowbytes - number of bytes needed to hold a row
1273
1274 signature = png_get_signature(png_ptr, info_ptr);
1275 signature - holds the signature read from the
1276 file (if any). The data is kept in
1277 the same offset it would be if the
1278 whole signature were read (i.e. if an
1279 application had already read in 4
1280 bytes of signature before starting
1281 libpng, the remaining 4 bytes would
1282 be in signature[4] through signature[7]
1283 (see png_set_sig_bytes())).
1284
1285
1286 width = png_get_image_width(png_ptr,
1287 info_ptr);
1288 height = png_get_image_height(png_ptr,
1289 info_ptr);
1290 bit_depth = png_get_bit_depth(png_ptr,
1291 info_ptr);
1292 color_type = png_get_color_type(png_ptr,
1293 info_ptr);
4946a942 1294 filter_method = png_get_filter_type(png_ptr,
75b6e0a0
GD		 1295 info_ptr);
1296 compression_type = png_get_compression_type(png_ptr,
1297 info_ptr);
1298 interlace_type = png_get_interlace_type(png_ptr,
1299 info_ptr);
1300
1301
1302These are also important, but their validity depends on whether the chunk
1303has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1304png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1305data has been read, or zero if it is missing. The parameters to the
1306png_get_<chunk> are set directly if they are simple data types, or a pointer
1307into the info_ptr is returned for any complex types.
1308
1309 png_get_PLTE(png_ptr, info_ptr, &palette,
1310 &num_palette);
1311 palette - the palette for the file
1312 (array of png_color)
1313 num_palette - number of entries in the palette
1314
1315 png_get_gAMA(png_ptr, info_ptr, &gamma);
1316 gamma - the gamma the file is written
1317 at (PNG_INFO_gAMA)
1318
1319 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1320 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1321 The presence of the sRGB chunk
1322 means that the pixel data is in the
1323 sRGB color space. This chunk also
1324 implies specific values of gAMA and
1325 cHRM.
1326
4946a942
GD		 1327 png_get_iCCP(png_ptr, info_ptr, &name,
1328 &compression_type, &profile, &proflen);
1329 name - The profile name.
1330 compression - The compression type; always
1331 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1332 You may give NULL to this argument to
1333 ignore it.
1334 profile - International Color Consortium color
1335 profile data. May contain NULs.
1336 proflen - length of profile data in bytes.
1337
75b6e0a0
GD		 1338 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1339 sig_bit - the number of significant bits for
1340 (PNG_INFO_sBIT) each of the gray,
1341 red, green, and blue channels,
1342 whichever are appropriate for the
1343 given color type (png_color_16)
1344
1345 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1346 &trans_values);
1347 trans - array of transparent entries for
1348 palette (PNG_INFO_tRNS)
4946a942
GD		 1349 trans_values - graylevel or color sample values of
1350 the single transparent color for
1351 non-paletted images (PNG_INFO_tRNS)
75b6e0a0
GD		 1352 num_trans - number of transparent entries
1353 (PNG_INFO_tRNS)
1354
1355 png_get_hIST(png_ptr, info_ptr, &hist);
1356 (PNG_INFO_hIST)
1357 hist - histogram of palette (array of
4946a942 1358 png_uint_16)
75b6e0a0
GD		 1359
1360 png_get_tIME(png_ptr, info_ptr, &mod_time);
1361 mod_time - time image was last modified
1362 (PNG_VALID_tIME)
1363
1364 png_get_bKGD(png_ptr, info_ptr, &background);
1365 background - background color (PNG_VALID_bKGD)
4946a942
GD		 1366 valid 16-bit red, green and blue
1367 values, regardless of color_type
75b6e0a0 1368
4946a942
GD		 1369 num_comments = png_get_text(png_ptr, info_ptr,
1370 &text_ptr, &num_text);
1371 num_comments - number of comments
75b6e0a0
GD		 1372 text_ptr - array of png_text holding image
1373 comments
4946a942
GD		 1374 text_ptr[i].compression - type of compression used
1375 on "text" PNG_TEXT_COMPRESSION_NONE
1376 PNG_TEXT_COMPRESSION_zTXt
1377 PNG_ITXT_COMPRESSION_NONE
1378 PNG_ITXT_COMPRESSION_zTXt
1379 text_ptr[i].key - keyword for comment. Must contain
1380 1-79 characters.
1381 text_ptr[i].text - text comments for current
1382 keyword. Can be empty.
1383 text_ptr[i].text_length - length of text string,
1384 after decompression, 0 for iTXt
1385 text_ptr[i].itxt_length - length of itxt string,
1386 after decompression, 0 for tEXt/zTXt
1387 text_ptr[i].lang - language of comment (empty
1388 string for unknown).
1389 text_ptr[i].lang_key - keyword in UTF-8
1390 (empty string for unknown).
1391 num_text - number of comments (same as
1392 num_comments; you can put NULL here
1393 to avoid the duplication)
1394 Note while png_set_text() will accept text, language,
1395 and translated keywords that can be NULL pointers, the
1396 structure returned by png_get_text will always contain
1397 regular zero-terminated C strings. They might be
1398 empty strings but they will never be NULL pointers.
1399
1400 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1401 &palette_ptr);
1402 palette_ptr - array of palette structures holding
1403 contents of one or more sPLT chunks
1404 read.
1405 num_spalettes - number of sPLT chunks read.
75b6e0a0
GD		 1406
1407 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
4946a942 1408 &unit_type);
75b6e0a0
GD		 1409 offset_x - positive offset from the left edge
1410 of the screen
1411 offset_y - positive offset from the top edge
1412 of the screen
1413 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1414
1415 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
4946a942 1416 &unit_type);
75b6e0a0
GD		 1417 res_x - pixels/unit physical resolution in
1418 x direction
1419 res_y - pixels/unit physical resolution in
1420 x direction
1421 unit_type - PNG_RESOLUTION_UNKNOWN,
1422 PNG_RESOLUTION_METER
1423
4946a942
GD		 1424 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1425 &height)
1426 unit - physical scale units (an integer)
1427 width - width of a pixel in physical scale units
1428 height - height of a pixel in physical scale units
1429 (width and height are doubles)
1430
1431 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1432 &height)
1433 unit - physical scale units (an integer)
1434 width - width of a pixel in physical scale units
1435 height - height of a pixel in physical scale units
1436 (width and height are strings like "2.54")
1437
1438 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1439 info_ptr, &unknowns)
1440 unknowns - array of png_unknown_chunk
1441 structures holding unknown chunks
1442 unknowns[i].name - name of unknown chunk
1443 unknowns[i].data - data of unknown chunk
1444 unknowns[i].size - size of unknown chunk's data
1445 unknowns[i].location - position of chunk in file
1446
1447 The value of "i" corresponds to the order in which the
1448 chunks were read from the PNG file or inserted with the
1449 png_set_unknown_chunks() function.
1450
75b6e0a0
GD		 1451The data from the pHYs chunk can be retrieved in several convenient
1452forms:
1453
1454 res_x = png_get_x_pixels_per_meter(png_ptr,
4946a942 1455 info_ptr)
75b6e0a0 1456 res_y = png_get_y_pixels_per_meter(png_ptr,
4946a942 1457 info_ptr)
75b6e0a0 1458 res_x_and_y = png_get_pixels_per_meter(png_ptr,
4946a942
GD		 1459 info_ptr)
1460 res_x = png_get_x_pixels_per_inch(png_ptr,
1461 info_ptr)
1462 res_y = png_get_y_pixels_per_inch(png_ptr,
1463 info_ptr)
1464 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1465 info_ptr)
75b6e0a0 1466 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
4946a942 1467 info_ptr)
75b6e0a0
GD		 1468
1469 (Each of these returns 0 [signifying "unknown"] if
1470 the data is not present or if res_x is 0;
1471 res_x_and_y is 0 if res_x != res_y)
1472
4946a942
GD		 1473The data from the oFFs chunk can be retrieved in several convenient
1474forms:
1475
1476 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1477 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1478 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1479 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1480
1481 (Each of these returns 0 [signifying "unknown" if both
1482 x and y are 0] if the data is not present or if the
1483 chunk is present but the unit is the pixel)
1484
75b6e0a0
GD		 1485For more information, see the png_info definition in png.h and the
1486PNG specification for chunk contents. Be careful with trusting
1487rowbytes, as some of the transformations could increase the space
1488needed to hold a row (expand, filler, gray_to_rgb, etc.).
1489See png_read_update_info(), below.
1490
1491A quick word about text_ptr and num_text. PNG stores comments in
1492keyword/text pairs, one pair per chunk, with no limit on the number
1493of text chunks, and a 2^31 byte limit on their size. While there are
1494suggested keywords, there is no requirement to restrict the use to these
1495strings. It is strongly suggested that keywords and text be sensible
1496to humans (that's the point), so don't use abbreviations. Non-printing
1497symbols are not allowed. See the PNG specification for more details.
1498There is also no requirement to have text after the keyword.
1499
1500Keywords should be limited to 79 Latin-1 characters without leading or
1501trailing spaces, but non-consecutive spaces are allowed within the
1502keyword. It is possible to have the same keyword any number of times.
4946a942
GD		 1503The text_ptr is an array of png_text structures, each holding a
1504pointer to a language string, a pointer to a keyword and a pointer to
1505a text string. The text string, language code, and translated
1506keyword may be empty or NULL pointers. The keyword/text
1507pairs are put into the array in the order that they are received.
1508However, some or all of the text chunks may be after the image, so, to
1509make sure you have read all the text chunks, don't mess with these
1510until after you read the stuff after the image. This will be
1511mentioned again below in the discussion that goes with png_read_end().
1512
1513.SS Input transformations
75b6e0a0
GD		 1514
1515After you've read the header information, you can set up the library
1516to handle any special transformations of the image data. The various
1517ways to transform the data will be described in the order that they
1518should occur. This is important, as some of these change the color
1519type and/or bit depth of the data, and some others only work on
1520certain color types and bit depths. Even though each transformation
1521checks to see if it has data that it can do something with, you should
1522make sure to only enable a transformation if it will be valid for the
1523data. For example, don't swap red and blue on grayscale data.
1524
1525The colors used for the background and transparency values should be
1526supplied in the same format/depth as the current image data. They
1527are stored in the same format/depth as the image data in a bKGD or tRNS
1528chunk, so this is what libpng expects for this data. The colors are
1529transformed to keep in sync with the image data when an application
1530calls the png_read_update_info() routine (see below).
1531
1532Data will be decoded into the supplied row buffers packed into bytes
1533unless the library has been told to transform it into another format.
1534For example, 4 bit/pixel paletted or grayscale data will be returned
15352 pixels/byte with the leftmost pixel in the high-order bits of the
1536byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1537in RGB RGB RGB format unless png_set_filler() is called to insert filler
1538bytes, either before or after each RGB triplet. 16-bit RGB data will
1539be returned RRGGBB RRGGBB, with the most significant byte of the color
1540value first, unless png_set_strip_16() is called to transform it to
1541regular RGB RGB triplets, or png_set_filler() is called to insert
1542filler bytes, either before or after each RRGGBB triplet. Similarly,
15438-bit or 16-bit grayscale data can be modified with png_set_filler()
1544or png_set_strip_16().
1545
1546The following code transforms grayscale images of less than 8 to 8 bits,
1547changes paletted images to RGB, and adds a full alpha channel if there is
1548transparency information in a tRNS chunk. This is most useful on
1549grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1550viewing application that wishes to treat all images in the same way.
1551
4946a942
GD		 1552 if (color_type == PNG_COLOR_TYPE_PALETTE)
1553 png_set_palette_to_rgb(png_ptr);
75b6e0a0
GD		 1554
1555 if (color_type == PNG_COLOR_TYPE_GRAY &&
4946a942 1556 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
75b6e0a0
GD		 1557
1558 if (png_get_valid(png_ptr, info_ptr,
4946a942
GD		 1559 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1560
1561These three functions are actually aliases for png_set_expand(), added
1562in libpng version 1.0.4, with the function names expanded to improve code
1563readability. In some future version they may actually do different
1564things.
75b6e0a0
GD		 1565
1566PNG can have files with 16 bits per channel. If you only can handle
15678 bits per channel, this will strip the pixels down to 8 bit.
1568
1569 if (bit_depth == 16)
1570 png_set_strip_16(png_ptr);
1571
75b6e0a0
GD		 1572If, for some reason, you don't need the alpha channel on an image,
1573and you want to remove it rather than combining it with the background
1574(but the image author certainly had in mind that you *would* combine
1575it with the background, so that's what you should probably do):
1576
1577 if (color_type & PNG_COLOR_MASK_ALPHA)
1578 png_set_strip_alpha(png_ptr);
1579
4946a942
GD		 1580In PNG files, the alpha channel in an image
1581is the level of opacity. If you need the alpha channel in an image to
1582be the level of transparency instead of opacity, you can invert the
1583alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1584fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1585images) is fully transparent, with
1586
1587 png_set_invert_alpha(png_ptr);
1588
75b6e0a0
GD		 1589PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1590they can, resulting in, for example, 8 pixels per byte for 1 bit
1591files. This code expands to 1 pixel per byte without changing the
1592values of the pixels:
1593
1594 if (bit_depth < 8)
1595 png_set_packing(png_ptr);
1596
1597PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1598stored in a PNG image have been "scaled" or "shifted" up to the next
1599higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
16008 bits/sample in the range [0, 255]). However, it is also possible to
1601convert the PNG pixel data back to the original bit depth of the image.
1602This call reduces the pixels back down to the original bit depth:
1603
4946a942 1604 png_color_8p sig_bit;
75b6e0a0
GD		 1605
1606 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1607 png_set_shift(png_ptr, sig_bit);
1608
1609PNG files store 3-color pixels in red, green, blue order. This code
1610changes the storage of the pixels to blue, green, red:
1611
1612 if (color_type == PNG_COLOR_TYPE_RGB ||
1613 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1614 png_set_bgr(png_ptr);
1615
4946a942
GD		 1616PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1617into 4 or 8 bytes for windowing systems that need them in this format:
75b6e0a0 1618
4946a942
GD		 1619 if (color_type == PNG_COLOR_TYPE_RGB)
1620 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
75b6e0a0
GD		 1621
1622where "filler" is the 8 or 16-bit number to fill with, and the location is
1623either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1624you want the filler before the RGB or after. This transformation
4946a942
GD		 1625does not affect images that already have full alpha channels. To add an
1626opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1627will generate RGBA pixels.
75b6e0a0
GD		 1628
1629If you are reading an image with an alpha channel, and you need the
1630data as ARGB instead of the normal PNG format RGBA:
1631
1632 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1633 png_set_swap_alpha(png_ptr);
1634
1635For some uses, you may want a grayscale image to be represented as
1636RGB. This code will do that conversion:
1637
1638 if (color_type == PNG_COLOR_TYPE_GRAY ||
1639 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1640 png_set_gray_to_rgb(png_ptr);
1641
1642Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
4946a942 1643with alpha.
75b6e0a0
GD		 1644
1645 if (color_type == PNG_COLOR_TYPE_RGB ||
1646 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
4946a942
GD		 1647 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1648 int red_weight, int green_weight);
75b6e0a0
GD		 1649
1650 error_action = 1: silently do the conversion
1651 error_action = 2: issue a warning if the original
1652 image has any pixel where
1653 red != green or red != blue
1654 error_action = 3: issue an error and abort the
1655 conversion if the original
1656 image has any pixel where
1657 red != green or red != blue
1658
4946a942
GD		 1659 red_weight: weight of red component times 100000
1660 green_weight: weight of green component times 100000
1661 If either weight is negative, default
1662 weights (21268, 71514) are used.
75b6e0a0
GD		 1663
1664If you have set error_action = 1 or 2, you can
1665later check whether the image really was gray, after processing
1666the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1667It will return a png_byte that is zero if the image was gray or
16681 if there were any non-gray pixels. bKGD and sBIT data
1669will be silently converted to grayscale, using the green channel
1670data, regardless of the error_action setting.
1671
4946a942 1672With red_weight+green_weight<=100000,
75b6e0a0
GD		 1673the normalized graylevel is computed:
1674
4946a942
GD		 1675 int rw = red_weight * 65536;
1676 int gw = green_weight * 65536;
1677 int bw = 65536 - (rw + gw);
1678 gray = (rw*red + gw*green + bw*blue)/65536;
75b6e0a0
GD		 1679
1680The default values approximate those recommended in the Charles
1681Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1682Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1683
1684 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1685
1686Libpng approximates this with
1687
4946a942 1688 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
75b6e0a0
GD		 1689
1690which can be expressed with integers as
1691
4946a942 1692 Y = (6969 * R + 23434 * G + 2365 * B)/32768
75b6e0a0
GD		 1693
1694The calculation is done in a linear colorspace, if the image gamma
1695is known.
1696
4946a942
GD		 1697If you have a grayscale and you are using png_set_expand_depth(),
1698png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
75b6e0a0
GD		 1699a higher bit-depth, you must either supply the background color as a gray
1700value at the original file bit-depth (need_expand = 1) or else supply the
1701background color as an RGB triplet at the final, expanded bit depth
1702(need_expand = 0). Similarly, if you are reading a paletted image, you
1703must either supply the background color as a palette index (need_expand = 1)
1704or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1705
1706 png_color_16 my_background;
1707 png_color_16p image_background;
1708
1709 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1710 png_set_background(png_ptr, image_background,
1711 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1712 else
1713 png_set_background(png_ptr, &my_background,
1714 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1715
4946a942
GD		 1716The png_set_background() function tells libpng to composite images
1717with alpha or simple transparency against the supplied background
1718color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1719you may use this color, or supply another color more suitable for
1720the current display (e.g., the background color from a web page). You
1721need to tell libpng whether the color is in the gamma space of the
1722display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1723(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1724that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1725know why anyone would use this, but it's here).
1726
75b6e0a0
GD		 1727To properly display PNG images on any kind of system, the application needs
1728to know what the display gamma is. Ideally, the user will know this, and
1729the application will allow them to set it. One method of allowing the user
4946a942
GD		 1730to set the display gamma separately for each system is to check for a
1731SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1732correctly set.
1733
1734Note that display_gamma is the overall gamma correction required to produce
1735pleasing results, which depends on the lighting conditions in the surrounding
1736environment. In a dim or brightly lit room, no compensation other than
1737the physical gamma exponent of the monitor is needed, while in a dark room
1738a slightly smaller exponent is better.
1739
1740 double gamma, screen_gamma;
75b6e0a0
GD		 1741
1742 if (/* We have a user-defined screen
1743 gamma value */)
1744 {
1745 screen_gamma = user_defined_screen_gamma;
1746 }
1747 /* One way that applications can share the same
1748 screen gamma value */
1749 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1750 != NULL)
1751 {
4946a942 1752 screen_gamma = (double)atof(gamma_str);
75b6e0a0
GD		 1753 }
1754 /* If we don't have another value */
1755 else
1756 {
1757 screen_gamma = 2.2; /* A good guess for a
1758 PC monitor in a bright office or a dim room */
1759 screen_gamma = 2.0; /* A good guess for a
1760 PC monitor in a dark room */
1761 screen_gamma = 1.7 or 1.0; /* A good
1762 guess for Mac systems */
1763 }
1764
1765The png_set_gamma() function handles gamma transformations of the data.
1766Pass both the file gamma and the current screen_gamma. If the file does
1767not have a gamma value, you can pass one anyway if you have an idea what
1768it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1769that file gammas are inverted from screen gammas. See the discussions
1770on gamma in the PNG specification for an excellent description of what
1771gamma is, and why all applications should support it. It is strongly
1772recommended that PNG viewers support gamma correction.
1773
1774 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1775 png_set_gamma(png_ptr, screen_gamma, gamma);
1776 else
1777 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1778
1779If you need to reduce an RGB file to a paletted file, or if a paletted
1780file has more entries then will fit on your screen, png_set_dither()
1781will do that. Note that this is a simple match dither that merely
1782finds the closest color available. This should work fairly well with
1783optimized palettes, and fairly badly with linear color cubes. If you
1784pass a palette that is larger then maximum_colors, the file will
1785reduce the number of colors in the palette so it will fit into
1786maximum_colors. If there is a histogram, it will use it to make
1787more intelligent choices when reducing the palette. If there is no
1788histogram, it may not do as good a job.
1789
1790 if (color_type & PNG_COLOR_MASK_COLOR)
1791 {
1792 if (png_get_valid(png_ptr, info_ptr,
1793 PNG_INFO_PLTE))
1794 {
2b5f62a0 1795 png_uint_16p histogram = NULL;
75b6e0a0
GD		 1796
1797 png_get_hIST(png_ptr, info_ptr,
1798 &histogram);
1799 png_set_dither(png_ptr, palette, num_palette,
1800 max_screen_colors, histogram, 1);
1801 }
1802 else
1803 {
1804 png_color std_color_cube[MAX_SCREEN_COLORS] =
1805 { ... colors ... };
1806
1807 png_set_dither(png_ptr, std_color_cube,
1808 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1809 NULL,0);
1810 }
1811 }
1812
1813PNG files describe monochrome as black being zero and white being one.
1814The following code will reverse this (make black be one and white be
1815zero):
1816
4946a942
GD		 1817 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1818 png_set_invert_mono(png_ptr);
1819
1820This function can also be used to invert grayscale and gray-alpha images:
1821
1822 if (color_type == PNG_COLOR_TYPE_GRAY ||
1823 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
75b6e0a0
GD		 1824 png_set_invert_mono(png_ptr);
1825
1826PNG files store 16 bit pixels in network byte order (big-endian,
1827ie. most significant bits first). This code changes the storage to the
1828other way (little-endian, i.e. least significant bits first, the
1829way PCs store them):
1830
1831 if (bit_depth == 16)
1832 png_set_swap(png_ptr);
1833
1834If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1835need to change the order the pixels are packed into bytes, you can use:
1836
1837 if (bit_depth < 8)
1838 png_set_packswap(png_ptr);
1839
4946a942
GD		 1840Finally, you can write your own transformation function if none of
1841the existing ones meets your needs. This is done by setting a callback
1842with
1843
1844 png_set_read_user_transform_fn(png_ptr,
1845 read_transform_fn);
1846
1847You must supply the function
1848
1849 void read_transform_fn(png_ptr ptr, row_info_ptr
1850 row_info, png_bytep data)
1851
1852See pngtest.c for a working example. Your function will be called
1853after all of the other transformations have been processed.
1854
1855You can also set up a pointer to a user structure for use by your
1856callback function, and you can inform libpng that your transform
1857function will change the number of channels or bit depth with the
1858function
1859
1860 png_set_user_transform_info(png_ptr, user_ptr,
1861 user_depth, user_channels);
1862
1863The user's application, not libpng, is responsible for allocating and
1864freeing any memory required for the user structure.
1865
1866You can retrieve the pointer via the function
1867png_get_user_transform_ptr(). For example:
1868
1869 voidp read_user_transform_ptr =
1870 png_get_user_transform_ptr(png_ptr);
1871
75b6e0a0
GD		 1872The last thing to handle is interlacing; this is covered in detail below,
1873but you must call the function here if you want libpng to handle expansion
1874of the interlaced image.
1875
1876 number_of_passes = png_set_interlace_handling(png_ptr);
1877
1878After setting the transformations, libpng can update your png_info
1879structure to reflect any transformations you've requested with this
1880call. This is most useful to update the info structure's rowbytes
1881field so you can use it to allocate your image memory. This function
1882will also update your palette with the correct screen_gamma and
1883background if these have been given with the calls above.
1884
1885 png_read_update_info(png_ptr, info_ptr);
1886
1887After you call png_read_update_info(), you can allocate any
1888memory you need to hold the image. The row data is simply
1889raw byte data for all forms of images. As the actual allocation
1890varies among applications, no example will be given. If you
1891are allocating one large chunk, you will need to build an
1892array of pointers to each row, as it will be needed for some
1893of the functions below.
1894
4946a942
GD		 1895.SS Reading image data
1896
75b6e0a0
GD		 1897After you've allocated memory, you can read the image data.
1898The simplest way to do this is in one function call. If you are
1899allocating enough memory to hold the whole image, you can just
1900call png_read_image() and libpng will read in all the image data
1901and put it in the memory area supplied. You will need to pass in
1902an array of pointers to each row.
1903
1904This function automatically handles interlacing, so you don't need
1905to call png_set_interlace_handling() or call this function multiple
1906times, or any of that other stuff necessary with png_read_rows().
1907
1908 png_read_image(png_ptr, row_pointers);
1909
1910where row_pointers is:
1911
1912 png_bytep row_pointers[height];
1913
1914You can point to void or char or whatever you use for pixels.
1915
1916If you don't want to read in the whole image at once, you can
1917use png_read_rows() instead. If there is no interlacing (check
1918interlace_type == PNG_INTERLACE_NONE), this is simple:
1919
1920 png_read_rows(png_ptr, row_pointers, NULL,
1921 number_of_rows);
1922
1923where row_pointers is the same as in the png_read_image() call.
1924
1925If you are doing this just one row at a time, you can do this with
4946a942 1926a single row_pointer instead of an array of row_pointers:
75b6e0a0 1927
4946a942
GD		 1928 png_bytep row_pointer = row;
1929 png_read_row(png_ptr, row_pointer, NULL);
75b6e0a0 1930
4946a942
GD		 1931If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1932get somewhat harder. The only current (PNG Specification version 1.2)
75b6e0a0
GD		 1933interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1934is a somewhat complicated 2D interlace scheme, known as Adam7, that
1935breaks down an image into seven smaller images of varying size, based
1936on an 8x8 grid.
1937
1938libpng can fill out those images or it can give them to you "as is".
1939If you want them filled out, there are two ways to do that. The one
1940mentioned in the PNG specification is to expand each pixel to cover
1941those pixels that have not been read yet (the "rectangle" method).
1942This results in a blocky image for the first pass, which gradually
1943smooths out as more pixels are read. The other method is the "sparkle"
1944method, where pixels are drawn only in their final locations, with the
1945rest of the image remaining whatever colors they were initialized to
1946before the start of the read. The first method usually looks better,
1947but tends to be slower, as there are more pixels to put in the rows.
1948
1949If you don't want libpng to handle the interlacing details, just call
1950png_read_rows() seven times to read in all seven images. Each of the
1951images is a valid image by itself, or they can all be combined on an
19528x8 grid to form a single image (although if you intend to combine them
1953you would be far better off using the libpng interlace handling).
1954
1955The first pass will return an image 1/8 as wide as the entire image
1956(every 8th column starting in column 0) and 1/8 as high as the original
1957(every 8th row starting in row 0), the second will be 1/8 as wide
1958(starting in column 4) and 1/8 as high (also starting in row 0). The
1959third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
19601/8 as high (every 8th row starting in row 4), and the fourth pass will
1961be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1962and every 4th row starting in row 0). The fifth pass will return an
1963image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1964while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1965(starting in column 1 and row 0). The seventh and final pass will be as
1966wide as the original, and 1/2 as high, containing all of the odd
1967numbered scanlines. Phew!
1968
1969If you want libpng to expand the images, call this before calling
1970png_start_read_image() or png_read_update_info():
1971
1972 if (interlace_type == PNG_INTERLACE_ADAM7)
1973 number_of_passes
1974 = png_set_interlace_handling(png_ptr);
1975
1976This will return the number of passes needed. Currently, this
1977is seven, but may change if another interlace type is added.
1978This function can be called even if the file is not interlaced,
1979where it will return one pass.
1980
1981If you are not going to display the image after each pass, but are
1982going to wait until the entire image is read in, use the sparkle
1983effect. This effect is faster and the end result of either method
1984is exactly the same. If you are planning on displaying the image
1985after each pass, the "rectangle" effect is generally considered the
1986better looking one.
1987
1988If you only want the "sparkle" effect, just call png_read_rows() as
1989normal, with the third parameter NULL. Make sure you make pass over
1990the image number_of_passes times, and you don't change the data in the
1991rows between calls. You can change the locations of the data, just
1992not the data. Each pass only writes the pixels appropriate for that
1993pass, and assumes the data from previous passes is still valid.
1994
1995 png_read_rows(png_ptr, row_pointers, NULL,
1996 number_of_rows);
1997
1998If you only want the first effect (the rectangles), do the same as
1999before except pass the row buffer in the third parameter, and leave
2000the second parameter NULL.
2001
2002 png_read_rows(png_ptr, NULL, row_pointers,
2003 number_of_rows);
2004
4946a942
GD		 2005.SS Finishing a sequential read
2006
2007After you are finished reading the image through either the high- or
2008low-level interfaces, you can finish reading the file. If you are
2009interested in comments or time, which may be stored either before or
2010after the image data, you should pass the separate png_info struct if
2011you want to keep the comments from before and after the image
2012separate. If you are not interested, you can pass NULL.
75b6e0a0
GD		 2013
2014 png_read_end(png_ptr, end_info);
2015
2016When you are done, you can free all memory allocated by libpng like this:
2017
2018 png_destroy_read_struct(&png_ptr, &info_ptr,
2019 &end_info);
2020
4946a942
GD		 2021It is also possible to individually free the info_ptr members that
2022point to libpng-allocated storage with the following function:
2023
2024 png_free_data(png_ptr, info_ptr, mask, seq)
2025 mask - identifies data to be freed, a mask
2026 containing the logical OR of one or
2027 more of
2028 PNG_FREE_PLTE, PNG_FREE_TRNS,
2029 PNG_FREE_HIST, PNG_FREE_ICCP,
2030 PNG_FREE_PCAL, PNG_FREE_ROWS,
2031 PNG_FREE_SCAL, PNG_FREE_SPLT,
2032 PNG_FREE_TEXT, PNG_FREE_UNKN,
2033 or simply PNG_FREE_ALL
2034 seq - sequence number of item to be freed
2035 (-1 for all items)
2036
2037This function may be safely called when the relevant storage has
2038already been freed, or has not yet been allocated, or was allocated
2039by the user and not by libpng, and will in those
2040cases do nothing. The "seq" parameter is ignored if only one item
2041of the selected data type, such as PLTE, is allowed. If "seq" is not
2042-1, and multiple items are allowed for the data type identified in
2043the mask, such as text or sPLT, only the n'th item in the structure
2044is freed, where n is "seq".
2045
2046The default behavior is only to free data that was allocated internally
2047by libpng. This can be changed, so that libpng will not free the data,
2048or so that it will free data that was allocated by the user with png_malloc()
2049or png_zalloc() and passed in via a png_set_*() function, with
2050
2051 png_data_freer(png_ptr, info_ptr, freer, mask)
2052 mask - which data elements are affected
2053 same choices as in png_free_data()
2054 freer - one of
2055 PNG_DESTROY_WILL_FREE_DATA
2056 PNG_SET_WILL_FREE_DATA
2057 PNG_USER_WILL_FREE_DATA
2058
2059This function only affects data that has already been allocated.
2060You can call this function after reading the PNG data but before calling
2061any png_set_*() functions, to control whether the user or the png_set_*()
2062function is responsible for freeing any existing data that might be present,
2063and again after the png_set_*() functions to control whether the user
2064or png_destroy_*() is supposed to free the data. When the user assumes
2065responsibility for libpng-allocated data, the application must use
2066png_free() to free it, and when the user transfers responsibility to libpng
2067for data that the user has allocated, the user must have used png_malloc()
2068or png_zalloc() to allocate it.
2069
2070If you allocated your row_pointers in a single block, as suggested above in
2071the description of the high level read interface, you must not transfer
2072responsibility for freeing it to the png_set_rows or png_read_destroy function,
2073because they would also try to free the individual row_pointers[i].
2074
2075If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2076separately, do not transfer responsibility for freeing text_ptr to libpng,
2077because when libpng fills a png_text structure it combines these members with
2078the key member, and png_free_data() will free only text_ptr.key. Similarly,
2079if you transfer responsibility for free'ing text_ptr from libpng to your
2080application, your application must not separately free those members.
2081
2082The png_free_data() function will turn off the "valid" flag for anything
2083it frees. If you need to turn the flag off for a chunk that was freed by your
2084application instead of by libpng, you can use
2085
2086 png_set_invalid(png_ptr, info_ptr, mask);
2087 mask - identifies the chunks to be made invalid,
2088 containing the logical OR of one or
2089 more of
2090 PNG_INFO_gAMA, PNG_INFO_sBIT,
2091 PNG_INFO_cHRM, PNG_INFO_PLTE,
2092 PNG_INFO_tRNS, PNG_INFO_bKGD,
2093 PNG_INFO_hIST, PNG_INFO_pHYs,
2094 PNG_INFO_oFFs, PNG_INFO_tIME,
2095 PNG_INFO_pCAL, PNG_INFO_sRGB,
2096 PNG_INFO_iCCP, PNG_INFO_sPLT,
2097 PNG_INFO_sCAL, PNG_INFO_IDAT
75b6e0a0 2098
4946a942 2099For a more compact example of reading a PNG image, see the file example.c.
75b6e0a0 2100
4946a942 2101.SS Reading PNG files progressively
75b6e0a0
GD		 2102
2103The progressive reader is slightly different then the non-progressive
2104reader. Instead of calling png_read_info(), png_read_rows(), and
2105png_read_end(), you make one call to png_process_data(), which calls
2106callbacks when it has the info, a row, or the end of the image. You
2107set up these callbacks with png_set_progressive_read_fn(). You don't
2108have to worry about the input/output functions of libpng, as you are
2109giving the library the data directly in png_process_data(). I will
2110assume that you have read the section on reading PNG files above,
2111so I will only highlight the differences (although I will show
2112all of the code).
2113
2114png_structp png_ptr;
2115png_infop info_ptr;
2116
2117 /* An example code fragment of how you would
2118 initialize the progressive reader in your
2119 application. */
2120 int
2121 initialize_png_reader()
2122 {
2123 png_ptr = png_create_read_struct
2124 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2125 user_error_fn, user_warning_fn);
2126 if (!png_ptr)
4946a942 2127 return (ERROR);
75b6e0a0
GD		 2128 info_ptr = png_create_info_struct(png_ptr);
2129 if (!info_ptr)
2130 {
2131 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2132 (png_infopp)NULL);
4946a942 2133 return (ERROR);
75b6e0a0
GD		 2134 }
2135
4946a942 2136 if (setjmp(png_jmpbuf(png_ptr)))
75b6e0a0
GD		 2137 {
2138 png_destroy_read_struct(&png_ptr, &info_ptr,
2139 (png_infopp)NULL);
4946a942 2140 return (ERROR);
75b6e0a0
GD		 2141 }
2142
2143 /* This one's new. You can provide functions
2144 to be called when the header info is valid,
2145 when each row is completed, and when the image
2146 is finished. If you aren't using all functions,
2147 you can specify NULL parameters. Even when all
2148 three functions are NULL, you need to call
2149 png_set_progressive_read_fn(). You can use
2150 any struct as the user_ptr (cast to a void pointer
2151 for the function call), and retrieve the pointer
2152 from inside the callbacks using the function
2153
2154 png_get_progressive_ptr(png_ptr);
2155
2156 which will return a void pointer, which you have
2157 to cast appropriately.
2158 */
2159 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2160 info_callback, row_callback, end_callback);
2161
2162 return 0;
2163 }
2164
2165 /* A code fragment that you call as you receive blocks
2166 of data */
2167 int
2168 process_data(png_bytep buffer, png_uint_32 length)
2169 {
4946a942 2170 if (setjmp(png_jmpbuf(png_ptr)))
75b6e0a0
GD		 2171 {
2172 png_destroy_read_struct(&png_ptr, &info_ptr,
2173 (png_infopp)NULL);
4946a942 2174 return (ERROR);
75b6e0a0
GD		 2175 }
2176
2177 /* This one's new also. Simply give it a chunk
2178 of data from the file stream (in order, of
2179 course). On machines with segmented memory
2180 models machines, don't give it any more than
2181 64K. The library seems to run fine with sizes
2182 of 4K. Although you can give it much less if
2183 necessary (I assume you can give it chunks of
2184 1 byte, I haven't tried less then 256 bytes
2185 yet). When this function returns, you may
2186 want to display any rows that were generated
2187 in the row callback if you don't already do
2188 so there.
2189 */
2190 png_process_data(png_ptr, info_ptr, buffer, length);
2191 return 0;
2192 }
2193
2194 /* This function is called (as set by
2195 png_set_progressive_read_fn() above) when enough data
2196 has been supplied so all of the header has been
2197 read.
2198 */
2199 void
2200 info_callback(png_structp png_ptr, png_infop info)
2201 {
2202 /* Do any setup here, including setting any of
2203 the transformations mentioned in the Reading
2204 PNG files section. For now, you _must_ call
2205 either png_start_read_image() or
2206 png_read_update_info() after all the
2207 transformations are set (even if you don't set
2208 any). You may start getting rows before
2209 png_process_data() returns, so this is your
2210 last chance to prepare for that.
2211 */
2212 }
2213
2214 /* This function is called when each row of image
2215 data is complete */
2216 void
2217 row_callback(png_structp png_ptr, png_bytep new_row,
2218 png_uint_32 row_num, int pass)
2219 {
2220 /* If the image is interlaced, and you turned
2221 on the interlace handler, this function will
2222 be called for every row in every pass. Some
2223 of these rows will not be changed from the
2224 previous pass. When the row is not changed,
2225 the new_row variable will be NULL. The rows
2226 and passes are called in order, so you don't
2227 really need the row_num and pass, but I'm
2228 supplying them because it may make your life
2229 easier.
2230
2231 For the non-NULL rows of interlaced images,
2232 you must call png_progressive_combine_row()
2233 passing in the row and the old row. You can
2234 call this function for NULL rows (it will just
2235 return) and for non-interlaced images (it just
2236 does the memcpy for you) if it will make the
2237 code easier. Thus, you can just do this for
2238 all cases:
2239 */
2240
2241 png_progressive_combine_row(png_ptr, old_row,
2242 new_row);
2243
2244 /* where old_row is what was displayed for
2245 previously for the row. Note that the first
2246 pass (pass == 0, really) will completely cover
2247 the old row, so the rows do not have to be
2248 initialized. After the first pass (and only
2249 for interlaced images), you will have to pass
2250 the current row, and the function will combine
2251 the old row and the new row.
2252 */
2253 }
2254
2255 void
2256 end_callback(png_structp png_ptr, png_infop info)
2257 {
2258 /* This function is called after the whole image
2259 has been read, including any chunks after the
2260 image (up to and including the IEND). You
2261 will usually have the same info chunk as you
2262 had in the header, although some data may have
2263 been added to the comments and time fields.
2264
2265 Most people won't do much here, perhaps setting
2266 a flag that marks the image as finished.
2267 */
2268 }
2269
2270
2271
2272.SH IV. Writing
2273
2274Much of this is very similar to reading. However, everything of
2275importance is repeated here, so you won't have to constantly look
2276back up in the reading section to understand writing.
2277
4946a942
GD		 2278.SS Setup
2279
75b6e0a0
GD		 2280You will want to do the I/O initialization before you get into libpng,
2281so if it doesn't work, you don't have anything to undo. If you are not
2282using the standard I/O functions, you will need to replace them with
2283custom writing functions. See the discussion under Customizing libpng.
2284
2285 FILE *fp = fopen(file_name, "wb");
2286 if (!fp)
2287 {
4946a942 2288 return (ERROR);
75b6e0a0
GD		 2289 }
2290
2291Next, png_struct and png_info need to be allocated and initialized.
2292As these can be both relatively large, you may not want to store these
2293on the stack, unless you have stack space to spare. Of course, you
2294will want to check if they return NULL. If you are also reading,
2295you won't want to name your read structure and your write structure
2296both "png_ptr"; you can call them anything you like, such as
2297"read_ptr" and "write_ptr". Look at pngtest.c, for example.
2298
2299 png_structp png_ptr = png_create_write_struct
2300 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2301 user_error_fn, user_warning_fn);
2302 if (!png_ptr)
4946a942 2303 return (ERROR);
75b6e0a0
GD		 2304
2305 png_infop info_ptr = png_create_info_struct(png_ptr);
2306 if (!info_ptr)
2307 {
2308 png_destroy_write_struct(&png_ptr,
2309 (png_infopp)NULL);
4946a942 2310 return (ERROR);
75b6e0a0
GD		 2311 }
2312
2313If you want to use your own memory allocation routines,
2314define PNG_USER_MEM_SUPPORTED and use
4946a942 2315png_create_write_struct_2() instead of png_create_write_struct():
75b6e0a0
GD		 2316
2317 png_structp png_ptr = png_create_write_struct_2
2318 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2319 user_error_fn, user_warning_fn, (png_voidp)
2320 user_mem_ptr, user_malloc_fn, user_free_fn);
2321
2322After you have these structures, you will need to set up the
2323error handling. When libpng encounters an error, it expects to
2324longjmp() back to your routine. Therefore, you will need to call
4946a942 2325setjmp() and pass the png_jmpbuf(png_ptr). If you
75b6e0a0 2326write the file from different routines, you will need to update
4946a942
GD		 2327the png_jmpbuf(png_ptr) every time you enter a new routine that will
2328call a png_*() function. See your documentation of setjmp/longjmp
75b6e0a0
GD		 2329for your compiler for more information on setjmp/longjmp. See
2330the discussion on libpng error handling in the Customizing Libpng
2331section below for more information on the libpng error handling.
2332
4946a942 2333 if (setjmp(png_jmpbuf(png_ptr)))
75b6e0a0 2334 {
4946a942
GD		 2335 png_destroy_write_struct(&png_ptr, &info_ptr);
2336 fclose(fp);
2337 return (ERROR);
75b6e0a0
GD		 2338 }
2339 ...
2340 return;
2341
4946a942
GD		 2342If you would rather avoid the complexity of setjmp/longjmp issues,
2343you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2344errors will result in a call to PNG_ABORT() which defaults to abort().
2345
75b6e0a0
GD		 2346Now you need to set up the output code. The default for libpng is to
2347use the C function fwrite(). If you use this, you will need to pass a
2348valid FILE * in the function png_init_io(). Be sure that the file is
2349opened in binary mode. Again, if you wish to handle writing data in
2350another way, see the discussion on libpng I/O handling in the Customizing
2351Libpng section below.
2352
2353 png_init_io(png_ptr, fp);
2354
4946a942
GD		 2355.SS Write callbacks
2356
75b6e0a0
GD		 2357At this point, you can set up a callback function that will be
2358called after each row has been written, which you can use to control
2359a progress meter or the like. It's demonstrated in pngtest.c.
2360You must supply a function
2361
4946a942
GD		 2362 void write_row_callback(png_ptr, png_uint_32 row,
2363 int pass);
75b6e0a0
GD		 2364 {
2365 /* put your code here */
2366 }
2367
2368(You can give it another name that you like instead of "write_row_callback")
2369
2370To inform libpng about your function, use
2371
2372 png_set_write_status_fn(png_ptr, write_row_callback);
2373
2374You now have the option of modifying how the compression library will
2375run. The following functions are mainly for testing, but may be useful
2376in some cases, like if you need to write PNG files extremely fast and
2377are willing to give up some compression, or if you want to get the
2378maximum possible compression at the expense of slower writing. If you
2379have no special needs in this area, let the library do what it wants by
2380not calling this function at all, as it has been tuned to deliver a good
2381speed/compression ratio. The second parameter to png_set_filter() is
4946a942
GD		 2382the filter method, for which the only valid values are 0 (as of the
2383July 1999 PNG specification, version 1.2) or 64 (if you are writing
2384a PNG datastream that is to be embedded in a MNG datastream). The third
2385parameter is a flag that indicates which filter type(s) are to be tested
2386for each scanline. See the PNG specification for details on the specific filter
75b6e0a0
GD		 2387types.
2388
2389
2390 /* turn on or off filtering, and/or choose
4946a942
GD		 2391 specific filters. You can use either a single
2392 PNG_FILTER_VALUE_NAME or the logical OR of one
2393 or more PNG_FILTER_NAME masks. */
75b6e0a0 2394 png_set_filter(png_ptr, 0,
4946a942
GD		 2395 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2396 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2397 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2398 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2399 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2400 PNG_ALL_FILTERS);
2401
2402If an application
2403wants to start and stop using particular filters during compression,
2404it should start out with all of the filters (to ensure that the previous
2405row of pixels will be stored in case it's needed later), and then add
2406and remove them after the start of compression.
2407
2408If you are writing a PNG datastream that is to be embedded in a MNG
2409datastream, the second parameter can be either 0 or 64.
2410
2411The png_set_compression_*() functions interface to the zlib compression
75b6e0a0
GD		 2412library, and should mostly be ignored unless you really know what you are
2413doing. The only generally useful call is png_set_compression_level()
2414which changes how much time zlib spends on trying to compress the image
4946a942
GD		 2415data. See the Compression Library (zlib.h and algorithm.txt, distributed
2416with zlib) for details on the compression levels.
75b6e0a0
GD		 2417
2418 /* set the zlib compression level */
2419 png_set_compression_level(png_ptr,
2420 Z_BEST_COMPRESSION);
2421
2422 /* set other zlib parameters */
2423 png_set_compression_mem_level(png_ptr, 8);
2424 png_set_compression_strategy(png_ptr,
2425 Z_DEFAULT_STRATEGY);
2426 png_set_compression_window_bits(png_ptr, 15);
2427 png_set_compression_method(png_ptr, 8);
4946a942
GD		 2428 png_set_compression_buffer_size(png_ptr, 8192)
2429
2430extern PNG_EXPORT(void,png_set_zbuf_size)
2431
2432.SS Setting the contents of info for output
75b6e0a0
GD		 2433
2434You now need to fill in the png_info structure with all the data you
2435wish to write before the actual image. Note that the only thing you
2436are allowed to write after the image is the text chunks and the time
4946a942 2437chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
75b6e0a0
GD		 2438the latest PNG specification for more information on that. If you
2439wish to write them before the image, fill them in now, and flag that
2440data as being valid. If you want to wait until after the data, don't
2441fill them until png_write_end(). For all the fields in png_info and
2442their data types, see png.h. For explanations of what the fields
2443contain, see the PNG specification.
2444
2445Some of the more important parts of the png_info are:
2446
2447 png_set_IHDR(png_ptr, info_ptr, width, height,
2448 bit_depth, color_type, interlace_type,
4946a942 2449 compression_type, filter_method)
75b6e0a0
GD		 2450 width - holds the width of the image
2451 in pixels (up to 2^31).
2452 height - holds the height of the image
2453 in pixels (up to 2^31).
2454 bit_depth - holds the bit depth of one of the
2455 image channels.
2456 (valid values are 1, 2, 4, 8, 16
2457 and depend also on the
2458 color_type. See also significant
2459 bits (sBIT) below).
2460 color_type - describes which color/alpha
2461 channels are present.
2462 PNG_COLOR_TYPE_GRAY
2463 (bit depths 1, 2, 4, 8, 16)
2464 PNG_COLOR_TYPE_GRAY_ALPHA
2465 (bit depths 8, 16)
2466 PNG_COLOR_TYPE_PALETTE
2467 (bit depths 1, 2, 4, 8)
2468 PNG_COLOR_TYPE_RGB
2469 (bit_depths 8, 16)
2470 PNG_COLOR_TYPE_RGB_ALPHA
2471 (bit_depths 8, 16)
2472
2473 PNG_COLOR_MASK_PALETTE
2474 PNG_COLOR_MASK_COLOR
2475 PNG_COLOR_MASK_ALPHA
2476
2477 interlace_type - PNG_INTERLACE_NONE or
2478 PNG_INTERLACE_ADAM7
2479 compression_type - (must be
2480 PNG_COMPRESSION_TYPE_DEFAULT)
4946a942
GD		 2481 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2482 or, if you are writing a PNG to
2483 be embedded in a MNG datastream,
2484 can also be
2485 PNG_INTRAPIXEL_DIFFERENCING)
75b6e0a0
GD		 2486
2487 png_set_PLTE(png_ptr, info_ptr, palette,
2488 num_palette);
2489 palette - the palette for the file
2490 (array of png_color)
2491 num_palette - number of entries in the palette
2492
2493 png_set_gAMA(png_ptr, info_ptr, gamma);
2494 gamma - the gamma the image was created
2495 at (PNG_INFO_gAMA)
2496
2497 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2498 srgb_intent - the rendering intent
2499 (PNG_INFO_sRGB) The presence of
2500 the sRGB chunk means that the pixel
2501 data is in the sRGB color space.
2502 This chunk also implies specific
2503 values of gAMA and cHRM. Rendering
2504 intent is the CSS-1 property that
2505 has been defined by the International
2506 Color Consortium
2507 (http://www.color.org).
2508 It can be one of
4946a942
GD		 2509 PNG_sRGB_INTENT_SATURATION,
2510 PNG_sRGB_INTENT_PERCEPTUAL,
2511 PNG_sRGB_INTENT_ABSOLUTE, or
2512 PNG_sRGB_INTENT_RELATIVE.
75b6e0a0
GD		 2513
2514
2515 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2516 srgb_intent);
2517 srgb_intent - the rendering intent
2518 (PNG_INFO_sRGB) The presence of the
2519 sRGB chunk means that the pixel
2520 data is in the sRGB color space.
2521 This function also causes gAMA and
2522 cHRM chunks with the specific values
2523 that are consistent with sRGB to be
2524 written.
2525
4946a942
GD		 2526 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2527 profile, proflen);
2528 name - The profile name.
2529 compression - The compression type; always
2530 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2531 You may give NULL to this argument to
2532 ignore it.
2533 profile - International Color Consortium color
2534 profile data. May contain NULs.
2535 proflen - length of profile data in bytes.
2536
75b6e0a0
GD		 2537 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2538 sig_bit - the number of significant bits for
2539 (PNG_INFO_sBIT) each of the gray, red,
2540 green, and blue channels, whichever are
2541 appropriate for the given color type
2542 (png_color_16)
2543
2544 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2545 trans_values);
2546 trans - array of transparent entries for
2547 palette (PNG_INFO_tRNS)
4946a942
GD		 2548 trans_values - graylevel or color sample values of
2549 the single transparent color for
2550 non-paletted images (PNG_INFO_tRNS)
75b6e0a0
GD		 2551 num_trans - number of transparent entries
2552 (PNG_INFO_tRNS)
2553
2554 png_set_hIST(png_ptr, info_ptr, hist);
2555 (PNG_INFO_hIST)
2556 hist - histogram of palette (array of
4946a942 2557 png_uint_16)
75b6e0a0
GD		 2558
2559 png_set_tIME(png_ptr, info_ptr, mod_time);
2560 mod_time - time image was last modified
2561 (PNG_VALID_tIME)
2562
2563 png_set_bKGD(png_ptr, info_ptr, background);
2564 background - background color (PNG_VALID_bKGD)
2565
2566 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2567 text_ptr - array of png_text holding image
2568 comments
4946a942
GD		 2569 text_ptr[i].compression - type of compression used
2570 on "text" PNG_TEXT_COMPRESSION_NONE
2571 PNG_TEXT_COMPRESSION_zTXt
2572 PNG_ITXT_COMPRESSION_NONE
2573 PNG_ITXT_COMPRESSION_zTXt
2574 text_ptr[i].key - keyword for comment. Must contain
2575 1-79 characters.
2576 text_ptr[i].text - text comments for current
2577 keyword. Can be NULL or empty.
2578 text_ptr[i].text_length - length of text string,
2579 after decompression, 0 for iTXt
2580 text_ptr[i].itxt_length - length of itxt string,
2581 after decompression, 0 for tEXt/zTXt
2582 text_ptr[i].lang - language of comment (NULL or
2583 empty for unknown).
2584 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2585 or empty for unknown).
2586 num_text - number of comments
2587
2588 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2589 num_spalettes);
2590 palette_ptr - array of png_sPLT_struct structures
2591 to be added to the list of palettes
2592 in the info structure.
2593 num_spalettes - number of palette structures to be
2594 added.
75b6e0a0
GD		 2595
2596 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2597 unit_type);
2598 offset_x - positive offset from the left
2599 edge of the screen
2600 offset_y - positive offset from the top
2601 edge of the screen
2602 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2603
2604 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2605 unit_type);
2606 res_x - pixels/unit physical resolution
2607 in x direction
2608 res_y - pixels/unit physical resolution
2609 in y direction
2610 unit_type - PNG_RESOLUTION_UNKNOWN,
2611 PNG_RESOLUTION_METER
2612
4946a942
GD		 2613 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2614 unit - physical scale units (an integer)
2615 width - width of a pixel in physical scale units
2616 height - height of a pixel in physical scale units
2617 (width and height are doubles)
2618
2619 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2620 unit - physical scale units (an integer)
2621 width - width of a pixel in physical scale units
2622 height - height of a pixel in physical scale units
2623 (width and height are strings like "2.54")
2624
2625 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2626 num_unknowns)
2627 unknowns - array of png_unknown_chunk
2628 structures holding unknown chunks
2629 unknowns[i].name - name of unknown chunk
2630 unknowns[i].data - data of unknown chunk
2631 unknowns[i].size - size of unknown chunk's data
2632 unknowns[i].location - position to write chunk in file
2633 0: do not write chunk
2634 PNG_HAVE_IHDR: before PLTE
2635 PNG_HAVE_PLTE: before IDAT
2636 PNG_AFTER_IDAT: after IDAT
2637
2638The "location" member is set automatically according to
2639what part of the output file has already been written.
2640You can change its value after calling png_set_unknown_chunks()
2641as demonstrated in pngtest.c. Within each of the "locations",
2642the chunks are sequenced according to their position in the
2643structure (that is, the value of "i", which is the order in which
2644the chunk was either read from the input file or defined with
2645png_set_unknown_chunks).
75b6e0a0
GD		 2646
2647A quick word about text and num_text. text is an array of png_text
2648structures. num_text is the number of valid structures in the array.
4946a942
GD		 2649Each png_text structure holds a language code, a keyword, a text value,
2650and a compression type.
2651
75b6e0a0
GD		 2652The compression types have the same valid numbers as the compression
2653types of the image data. Currently, the only valid number is zero.
2654However, you can store text either compressed or uncompressed, unlike
2655images, which always have to be compressed. So if you don't want the
2656text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
4946a942
GD		 2657Because tEXt and zTXt chunks don't have a language field, if you
2658specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2659any language code or translated keyword will not be written out.
2660
75b6e0a0
GD		 2661Until text gets around 1000 bytes, it is not worth compressing it.
2662After the text has been written out to the file, the compression type
2663is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2664so that it isn't written out again at the end (in case you are calling
2665png_write_end() with the same struct.
2666
2667The keywords that are given in the PNG Specification are:
2668
2669 Title Short (one line) title or
2670 caption for image
2671 Author Name of image's creator
2672 Description Description of image (possibly long)
2673 Copyright Copyright notice
2674 Creation Time Time of original image creation
2675 (usually RFC 1123 format, see below)
2676 Software Software used to create the image
2677 Disclaimer Legal disclaimer
2678 Warning Warning of nature of content
2679 Source Device used to create the image
2680 Comment Miscellaneous comment; conversion
2681 from other image format
2682
2683The keyword-text pairs work like this. Keywords should be short
2684simple descriptions of what the comment is about. Some typical
2685keywords are found in the PNG specification, as is some recommendations
2686on keywords. You can repeat keywords in a file. You can even write
2687some text before the image and some after. For example, you may want
2688to put a description of the image before the image, but leave the
2689disclaimer until after, so viewers working over modem connections
2690don't have to wait for the disclaimer to go over the modem before
2691they start seeing the image. Finally, keywords should be full
2692words, not abbreviations. Keywords and text are in the ISO 8859-1
2693(Latin-1) character set (a superset of regular ASCII) and can not
2694contain NUL characters, and should not contain control or other
2695unprintable characters. To make the comments widely readable, stick
2696with basic ASCII, and avoid machine specific character set extensions
2697like the IBM-PC character set. The keyword must be present, but
2698you can leave off the text string on non-compressed pairs.
2699Compressed pairs must have a text string, as only the text string
2700is compressed anyway, so the compression would be meaningless.
2701
2702PNG supports modification time via the png_time structure. Two
4946a942 2703conversion routines are provided, png_convert_from_time_t() for
75b6e0a0
GD		 2704time_t and png_convert_from_struct_tm() for struct tm. The
2705time_t routine uses gmtime(). You don't have to use either of
2706these, but if you wish to fill in the png_time structure directly,
2707you should provide the time in universal time (GMT) if possible
2708instead of your local time. Note that the year number is the full
2709year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2710that months start with 1.
2711
2712If you want to store the time of the original image creation, you should
2713use a plain tEXt chunk with the "Creation Time" keyword. This is
2714necessary because the "creation time" of a PNG image is somewhat vague,
2715depending on whether you mean the PNG file, the time the image was
2716created in a non-PNG format, a still photo from which the image was
2717scanned, or possibly the subject matter itself. In order to facilitate
2718machine-readable dates, it is recommended that the "Creation Time"
2719tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2720although this isn't a requirement. Unlike the tIME chunk, the
2721"Creation Time" tEXt chunk is not expected to be automatically changed
2722by the software. To facilitate the use of RFC 1123 dates, a function
2723png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2724time to an RFC 1123 format string.
2725
4946a942
GD		 2726.SS Writing unknown chunks
2727
2728You can use the png_set_unknown_chunks function to queue up chunks
2729for writing. You give it a chunk name, raw data, and a size; that's
2730all there is to it. The chunks will be written by the next following
2731png_write_info_before_PLTE, png_write_info, or png_write_end function.
2732Any chunks previously read into the info structure's unknown-chunk
2733list will also be written out in a sequence that satisfies the PNG
2734specification's ordering rules.
2735
2736.SS The high-level write interface
2737
2738At this point there are two ways to proceed; through the high-level
2739write interface, or through a sequence of low-level write operations.
2740You can use the high-level interface if your image data is present
2741in the info structure. All defined output
2742transformations are permitted, enabled by the following masks.
2743
2744 PNG_TRANSFORM_IDENTITY No transformation
2745 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2746 PNG_TRANSFORM_PACKSWAP Change order of packed
2747 pixels to LSB first
2748 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2749 PNG_TRANSFORM_SHIFT Normalize pixels to the
2750 sBIT depth
2751 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2752 to BGRA
2753 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2754 to AG
2755 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2756 to transparency
2757 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2758 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2759
2760If you have valid image data in the info structure (you can use
2761png_set_rows() to put image data in the info structure), simply do this:
2762
2763 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2764
2765where png_transforms is an integer containing the logical OR of some set of
2766transformation flags. This call is equivalent to png_write_info(),
2767followed the set of transformations indicated by the transform mask,
2768then png_write_image(), and finally png_write_end().
2769
2770(The final parameter of this call is not yet used. Someday it might point
2771to transformation parameters required by some future output transform.)
2772
2773.SS The low-level write interface
2774
2775If you are going the low-level route instead, you are now ready to
2776write all the file information up to the actual image data. You do
2777this with a call to png_write_info().
75b6e0a0
GD		 2778
2779 png_write_info(png_ptr, info_ptr);
2780
4946a942
GD		 2781Note that there is one transformation you may need to do before
2782png_write_info(). In PNG files, the alpha channel in an image is the
2783level of opacity. If your data is supplied as a level of
2784transparency, you can invert the alpha channel before you write it, so
2785that 0 is fully transparent and 255 (in 8-bit or paletted images) or
278665535 (in 16-bit images) is fully opaque, with
2787
2788 png_set_invert_alpha(png_ptr);
2789
2790This must appear before png_write_info() instead of later with the
2791other transformations because in the case of paletted images the tRNS
2792chunk data has to be inverted before the tRNS chunk is written. If
2793your image is not a paletted image, the tRNS data (which in such cases
2794represents a single color to be rendered as transparent) won't need to
2795be changed, and you can safely do this transformation after your
2796png_write_info() call.
2797
2798If you need to write a private chunk that you want to appear before
2799the PLTE chunk when PLTE is present, you can write the PNG info in
2800two steps, and insert code to write your own chunk between them:
2801
2802 png_write_info_before_PLTE(png_ptr, info_ptr);
2803 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2804 png_write_info(png_ptr, info_ptr);
2805
75b6e0a0
GD		 2806After you've written the file information, you can set up the library
2807to handle any special transformations of the image data. The various
2808ways to transform the data will be described in the order that they
2809should occur. This is important, as some of these change the color
2810type and/or bit depth of the data, and some others only work on
2811certain color types and bit depths. Even though each transformation
2812checks to see if it has data that it can do something with, you should
2813make sure to only enable a transformation if it will be valid for the
2814data. For example, don't swap red and blue on grayscale data.
2815
2816PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
4946a942
GD		 2817the library to strip input data that has 4 or 8 bytes per pixel down
2818to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2819bytes per pixel).
75b6e0a0
GD		 2820
2821 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2822
4946a942
GD		 2823where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2824PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2825is stored XRGB or RGBX.
75b6e0a0
GD		 2826
2827PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2828they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2829If the data is supplied at 1 pixel per byte, use this code, which will
2830correctly pack the pixels into a single byte:
2831
2832 png_set_packing(png_ptr);
2833
2834PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2835data is of another bit depth, you can write an sBIT chunk into the
4946a942 2836file so that decoders can recover the original data if desired.
75b6e0a0
GD		 2837
2838 /* Set the true bit depth of the image data */
2839 if (color_type & PNG_COLOR_MASK_COLOR)
2840 {
2841 sig_bit.red = true_bit_depth;
2842 sig_bit.green = true_bit_depth;
2843 sig_bit.blue = true_bit_depth;
2844 }
2845 else
2846 {
2847 sig_bit.gray = true_bit_depth;
2848 }
2849 if (color_type & PNG_COLOR_MASK_ALPHA)
2850 {
2851 sig_bit.alpha = true_bit_depth;
2852 }
2853
2854 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2855
2856If the data is stored in the row buffer in a bit depth other than
2857one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2858this will scale the values to appear to be the correct bit depth as
2859is required by PNG.
2860
2861 png_set_shift(png_ptr, &sig_bit);
2862
2863PNG files store 16 bit pixels in network byte order (big-endian,
2864ie. most significant bits first). This code would be used if they are
2865supplied the other way (little-endian, i.e. least significant bits
2866first, the way PCs store them):
2867
2868 if (bit_depth > 8)
2869 png_set_swap(png_ptr);
2870
2871If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2872need to change the order the pixels are packed into bytes, you can use:
2873
2874 if (bit_depth < 8)
2875 png_set_packswap(png_ptr);
2876
2877PNG files store 3 color pixels in red, green, blue order. This code
2878would be used if they are supplied as blue, green, red:
2879
2880 png_set_bgr(png_ptr);
2881
2882PNG files describe monochrome as black being zero and white being
2883one. This code would be used if the pixels are supplied with this reversed
2884(black being one and white being zero):
2885
2886 png_set_invert_mono(png_ptr);
2887
2888Finally, you can write your own transformation function if none of
2889the existing ones meets your needs. This is done by setting a callback
2890with
2891
2892 png_set_write_user_transform_fn(png_ptr,
2893 write_transform_fn);
2894
2895You must supply the function
2896
2897 void write_transform_fn(png_ptr ptr, row_info_ptr
2898 row_info, png_bytep data)
2899
2900See pngtest.c for a working example. Your function will be called
4946a942
GD		 2901before any of the other transformations are processed.
2902
2903You can also set up a pointer to a user structure for use by your
2904callback function.
2905
2906 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2907
2908The user_channels and user_depth parameters of this function are ignored
2909when writing; you can set them to zero as shown.
2910
2911You can retrieve the pointer via the function png_get_user_transform_ptr().
2912For example:
2913
2914 voidp write_user_transform_ptr =
2915 png_get_user_transform_ptr(png_ptr);
75b6e0a0
GD		 2916
2917It is possible to have libpng flush any pending output, either manually,
2918or automatically after a certain number of lines have been written. To
2919flush the output stream a single time call:
2920
2921 png_write_flush(png_ptr);
2922
2923and to have libpng flush the output stream periodically after a certain
2924number of scanlines have been written, call:
2925
2926 png_set_flush(png_ptr, nrows);
2927
2928Note that the distance between rows is from the last time png_write_flush()
2929was called, or the first row of the image if it has never been called.
2930So if you write 50 lines, and then png_set_flush 25, it will flush the
2931output on the next scanline, and every 25 lines thereafter, unless
2932png_write_flush() is called before 25 more lines have been written.
2933If nrows is too small (less than about 10 lines for a 640 pixel wide
2934RGB image) the image compression may decrease noticeably (although this
2935may be acceptable for real-time applications). Infrequent flushing will
2936only degrade the compression performance by a few percent over images
2937that do not use flushing.
2938
4946a942
GD		 2939.SS Writing the image data
2940
75b6e0a0 2941That's it for the transformations. Now you can write the image data.
4946a942 2942The simplest way to do this is in one function call. If you have the
75b6e0a0
GD		 2943whole image in memory, you can just call png_write_image() and libpng
2944will write the image. You will need to pass in an array of pointers to
2945each row. This function automatically handles interlacing, so you don't
2946need to call png_set_interlace_handling() or call this function multiple
2947times, or any of that other stuff necessary with png_write_rows().
2948
2949 png_write_image(png_ptr, row_pointers);
2950
2951where row_pointers is:
2952
2953 png_byte *row_pointers[height];
2954
2955You can point to void or char or whatever you use for pixels.
2956
2957If you don't want to write the whole image at once, you can
2958use png_write_rows() instead. If the file is not interlaced,
2959this is simple:
2960
2961 png_write_rows(png_ptr, row_pointers,
2962 number_of_rows);
2963
2964row_pointers is the same as in the png_write_image() call.
2965
2966If you are just writing one row at a time, you can do this with
4946a942 2967a single row_pointer instead of an array of row_pointers:
75b6e0a0
GD		 2968
2969 png_bytep row_pointer = row;
2970
4946a942 2971 png_write_row(png_ptr, row_pointer);
75b6e0a0
GD		 2972
2973When the file is interlaced, things can get a good deal more
4946a942
GD		 2974complicated. The only currently (as of the PNG Specification
2975version 1.2, dated July 1999) defined interlacing scheme for PNG files
75b6e0a0
GD		 2976is the "Adam7" interlace scheme, that breaks down an
2977image into seven smaller images of varying size. libpng will build
2978these images for you, or you can do them yourself. If you want to
2979build them yourself, see the PNG specification for details of which
2980pixels to write when.
2981
2982If you don't want libpng to handle the interlacing details, just
2983use png_set_interlace_handling() and call png_write_rows() the
2984correct number of times to write all seven sub-images.
2985
2986If you want libpng to build the sub-images, call this before you start
2987writing any rows:
2988
2989 number_of_passes =
2990 png_set_interlace_handling(png_ptr);
2991
2992This will return the number of passes needed. Currently, this
2993is seven, but may change if another interlace type is added.
2994
2995Then write the complete image number_of_passes times.
2996
2997 png_write_rows(png_ptr, row_pointers,
2998 number_of_rows);
2999
3000As some of these rows are not used, and thus return immediately,
3001you may want to read about interlacing in the PNG specification,
3002and only update the rows that are actually used.
3003
4946a942
GD		 3004.SS Finishing a sequential write
3005
75b6e0a0
GD		 3006After you are finished writing the image, you should finish writing
3007the file. If you are interested in writing comments or time, you should
3008pass an appropriately filled png_info pointer. If you are not interested,
3009you can pass NULL.
3010
3011 png_write_end(png_ptr, info_ptr);
3012
3013When you are done, you can free all memory used by libpng like this:
3014
3015 png_destroy_write_struct(&png_ptr, &info_ptr);
3016
4946a942
GD		 3017It is also possible to individually free the info_ptr members that
3018point to libpng-allocated storage with the following function:
3019
3020 png_free_data(png_ptr, info_ptr, mask, seq)
3021 mask - identifies data to be freed, a mask
3022 containing the logical OR of one or
3023 more of
3024 PNG_FREE_PLTE, PNG_FREE_TRNS,
3025 PNG_FREE_HIST, PNG_FREE_ICCP,
3026 PNG_FREE_PCAL, PNG_FREE_ROWS,
3027 PNG_FREE_SCAL, PNG_FREE_SPLT,
3028 PNG_FREE_TEXT, PNG_FREE_UNKN,
3029 or simply PNG_FREE_ALL
3030 seq - sequence number of item to be freed
3031 (-1 for all items)
3032
3033This function may be safely called when the relevant storage has
3034already been freed, or has not yet been allocated, or was allocated
3035by the user and not by libpng, and will in those
3036cases do nothing. The "seq" parameter is ignored if only one item
3037of the selected data type, such as PLTE, is allowed. If "seq" is not
3038-1, and multiple items are allowed for the data type identified in
3039the mask, such as text or sPLT, only the n'th item in the structure
3040is freed, where n is "seq".
3041
3042If you allocated data such as a palette that you passed
3043in to libpng with png_set_*, you must not free it until just before the call to
3044png_destroy_write_struct().
3045
3046The default behavior is only to free data that was allocated internally
3047by libpng. This can be changed, so that libpng will not free the data,
3048or so that it will free data that was allocated by the user with png_malloc()
3049or png_zalloc() and passed in via a png_set_*() function, with
3050
3051 png_data_freer(png_ptr, info_ptr, freer, mask)
3052 mask - which data elements are affected
3053 same choices as in png_free_data()
3054 freer - one of
3055 PNG_DESTROY_WILL_FREE_DATA
3056 PNG_SET_WILL_FREE_DATA
3057 PNG_USER_WILL_FREE_DATA
3058
3059For example, to transfer responsibility for some data from a read structure
3060to a write structure, you could use
3061
3062 png_data_freer(read_ptr, read_info_ptr,
3063 PNG_USER_WILL_FREE_DATA,
3064 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3065 png_data_freer(write_ptr, write_info_ptr,
3066 PNG_DESTROY_WILL_FREE_DATA,
3067 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3068
3069thereby briefly reassigning responsibility for freeing to the user but
3070immediately afterwards reassigning it once more to the write_destroy
3071function. Having done this, it would then be safe to destroy the read
3072structure and continue to use the PLTE, tRNS, and hIST data in the write
3073structure.
3074
3075This function only affects data that has already been allocated.
3076You can call this function before calling after the png_set_*() functions
3077to control whether the user or png_destroy_*() is supposed to free the data.
3078When the user assumes responsibility for libpng-allocated data, the
3079application must use
3080png_free() to free it, and when the user transfers responsibility to libpng
3081for data that the user has allocated, the user must have used png_malloc()
3082or png_zalloc() to allocate it.
3083
3084If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3085separately, do not transfer responsibility for freeing text_ptr to libpng,
3086because when libpng fills a png_text structure it combines these members with
3087the key member, and png_free_data() will free only text_ptr.key. Similarly,
3088if you transfer responsibility for free'ing text_ptr from libpng to your
3089application, your application must not separately free those members.
75b6e0a0
GD		 3090For a more compact example of writing a PNG image, see the file example.c.
3091
75b6e0a0
GD		 3092.SH V. Modifying/Customizing libpng:
3093
4946a942 3094There are three issues here. The first is changing how libpng does
75b6e0a0
GD		 3095standard things like memory allocation, input/output, and error handling.
3096The second deals with more complicated things like adding new chunks,
3097adding new transformations, and generally changing how libpng works.
4946a942
GD		 3098Both of those are compile-time issues; that is, they are generally
3099determined at the time the code is written, and there is rarely a need
3100to provide the user with a means of changing them. The third is a
3101run-time issue: choosing between and/or tuning one or more alternate
3102versions of computationally intensive routines; specifically, optimized
3103assembly-language (and therefore compiler- and platform-dependent)
3104versions.
3105
3106Memory allocation, input/output, and error handling
75b6e0a0
GD		 3107
3108All of the memory allocation, input/output, and error handling in libpng
4946a942
GD		 3109goes through callbacks that are user-settable. The default routines are
3110in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3111these functions, call the appropriate png_set_*_fn() function.
3112
3113Memory allocation is done through the functions png_malloc()
3114and png_free(). These currently just call the standard C functions. If
75b6e0a0
GD		 3115your pointers can't access more then 64K at a time, you will want to set
3116MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3117memory allocation on a platform will change between applications, these
4946a942
GD		 3118functions must be modified in the library at compile time. If you prefer
3119to use a different method of allocating and freeing data, you can use
3120png_create_read_struct_2() or png_create_write_struct_2() to register
3121your own functions as described above.
4946a942
GD		 3122These functions also provide a void pointer that can be retrieved via
3123
3124 mem_ptr=png_get_mem_ptr(png_ptr);
3125
3126Your replacement memory functions must have prototypes as follows:
3127
3128 png_voidp malloc_fn(png_structp png_ptr,
3129 png_size_t size);
3130 void free_fn(png_structp png_ptr, png_voidp ptr);
3131
5b02c8a1
VS		 3132Your malloc_fn() must return NULL in case of failure. The png_malloc()
3133function will normally call png_error() if it receives a NULL from the
3134system memory allocator or from your replacement malloc_fn().
75b6e0a0
GD		 3135
3136Input/Output in libpng is done through png_read() and png_write(),
3137which currently just call fread() and fwrite(). The FILE * is stored in
3138png_struct and is initialized via png_init_io(). If you wish to change
3139the method of I/O, the library supplies callbacks that you can set
3140through the function png_set_read_fn() and png_set_write_fn() at run
3141time, instead of calling the png_init_io() function. These functions
3142also provide a void pointer that can be retrieved via the function
3143png_get_io_ptr(). For example:
3144
3145 png_set_read_fn(png_structp read_ptr,
3146 voidp read_io_ptr, png_rw_ptr read_data_fn)
3147
3148 png_set_write_fn(png_structp write_ptr,
3149 voidp write_io_ptr, png_rw_ptr write_data_fn,
3150 png_flush_ptr output_flush_fn);
3151
3152 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3153 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3154
4946a942 3155The replacement I/O functions must have prototypes as follows:
75b6e0a0
GD		 3156
3157 void user_read_data(png_structp png_ptr,
4946a942 3158 png_bytep data, png_size_t length);
75b6e0a0 3159 void user_write_data(png_structp png_ptr,
4946a942 3160 png_bytep data, png_size_t length);
75b6e0a0
GD		 3161 void user_flush_data(png_structp png_ptr);
3162
3163Supplying NULL for the read, write, or flush functions sets them back
3164to using the default C stream functions. It is an error to read from
3165a write stream, and vice versa.
3166
3167Error handling in libpng is done through png_error() and png_warning().
3168Errors handled through png_error() are fatal, meaning that png_error()
3169should never return to its caller. Currently, this is handled via
4946a942
GD		 3170setjmp() and longjmp() (unless you have compiled libpng with
3171PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3172but you could change this to do things like exit() if you should wish.
3173
3174On non-fatal errors, png_warning() is called
75b6e0a0
GD		 3175to print a warning message, and then control returns to the calling code.
3176By default png_error() and png_warning() print a message on stderr via
4946a942
GD		 3177fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3178(because you don't want the messages) or PNG_NO_STDIO defined (because
3179fprintf() isn't available). If you wish to change the behavior of the error
3180functions, you will need to set up your own message callbacks. These
3181functions are normally supplied at the time that the png_struct is created.
3182It is also possible to redirect errors and warnings to your own replacement
3183functions after png_create_*_struct() has been called by calling:
75b6e0a0
GD		 3184
3185 png_set_error_fn(png_structp png_ptr,
3186 png_voidp error_ptr, png_error_ptr error_fn,
3187 png_error_ptr warning_fn);
3188
3189 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3190
3191If NULL is supplied for either error_fn or warning_fn, then the libpng
3192default function will be used, calling fprintf() and/or longjmp() if a
3193problem is encountered. The replacement error functions should have
3194parameters as follows:
3195
3196 void user_error_fn(png_structp png_ptr,
3197 png_const_charp error_msg);
3198 void user_warning_fn(png_structp png_ptr,
3199 png_const_charp warning_msg);
3200
3201The motivation behind using setjmp() and longjmp() is the C++ throw and
3202catch exception handling methods. This makes the code much easier to write,
3203as there is no need to check every return code of every function call.
3204However, there are some uncertainties about the status of local variables
3205after a longjmp, so the user may want to be careful about doing anything after
3206setjmp returns non-zero besides returning itself. Consult your compiler
4946a942
GD		 3207documentation for more details. For an alternative approach, you may wish
3208to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3209
3210.SS Custom chunks
3211
3212If you need to read or write custom chunks, you may need to get deeper
3213into the libpng code. The library now has mechanisms for storing
3214and writing chunks of unknown type; you can even declare callbacks
3215for custom chunks. Hoewver, this may not be good enough if the
3216library code itself needs to know about interactions between your
3217chunk and existing `intrinsic' chunks.
3218
3219If you need to write a new intrinsic chunk, first read the PNG
3220specification. Acquire a first level of
3221understanding of how it works. Pay particular attention to the
3222sections that describe chunk names, and look at how other chunks were
3223designed, so you can do things similarly. Second, check out the
3224sections of libpng that read and write chunks. Try to find a chunk
3225that is similar to yours and use it as a template. More details can
3226be found in the comments inside the code. It is best to handle unknown
3227chunks in a generic method, via callback functions, instead of by
3228modifying libpng functions.
75b6e0a0
GD		 3229
3230If you wish to write your own transformation for the data, look through
3231the part of the code that does the transformations, and check out some of
3232the simpler ones to get an idea of how they work. Try to find a similar
3233transformation to the one you want to add and copy off of it. More details
3234can be found in the comments inside the code itself.
3235
4946a942 3236.SS Configuring for 16 bit platforms
75b6e0a0 3237
4946a942 3238You will want to look into zconf.h to tell zlib (and thus libpng) that
75b6e0a0
GD		 3239it cannot allocate more then 64K at a time. Even if you can, the memory
3240won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3241
4946a942 3242.SS Configuring for DOS
75b6e0a0
GD		 3243
3244For DOS users who only have access to the lower 640K, you will
3245have to limit zlib's memory usage via a png_set_compression_mem_level()
3246call. See zlib.h or zconf.h in the zlib library for more information.
3247
4946a942 3248.SS Configuring for Medium Model
75b6e0a0
GD		 3249
3250Libpng's support for medium model has been tested on most of the popular
3251compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3252defined, and FAR gets defined to far in pngconf.h, and you should be
3253all set. Everything in the library (except for zlib's structure) is
3254expecting far data. You must use the typedefs with the p or pp on
3255the end for pointers (or at least look at them and be careful). Make
4946a942 3256note that the rows of data are defined as png_bytepp, which is an
75b6e0a0
GD		 3257unsigned char far * far *.
3258
4946a942 3259.SS Configuring for gui/windowing platforms:
75b6e0a0
GD		 3260
3261You will need to write new error and warning functions that use the GUI
3262interface, as described previously, and set them to be the error and
4946a942 3263warning functions at the time that png_create_*_struct() is called,
75b6e0a0
GD		 3264in order to have them available during the structure initialization.
3265They can be changed later via png_set_error_fn(). On some compilers,
3266you may also have to change the memory allocators (png_malloc, etc.).
3267
4946a942 3268.SS Configuring for compiler xxx:
75b6e0a0
GD		 3269
3270All includes for libpng are in pngconf.h. If you need to add/change/delete
3271an include, this is the place to do it. The includes that are not
3272needed outside libpng are protected by the PNG_INTERNAL definition,
3273which is only defined for those routines inside libpng itself. The
3274files in libpng proper only include png.h, which includes pngconf.h.
3275
4946a942 3276.SS Configuring zlib:
75b6e0a0
GD		 3277
3278There are special functions to configure the compression. Perhaps the
3279most useful one changes the compression level, which currently uses
3280input compression values in the range 0 - 9. The library normally
3281uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3282have shown that for a large majority of images, compression values in
3283the range 3-6 compress nearly as well as higher levels, and do so much
3284faster. For online applications it may be desirable to have maximum speed
3285(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3286specify no compression (Z_NO_COMPRESSION = 0), but this would create
3287files larger than just storing the raw bitmap. You can specify the
3288compression level by calling:
3289
3290 png_set_compression_level(png_ptr, level);
3291
3292Another useful one is to reduce the memory level used by the library.
3293The memory level defaults to 8, but it can be lowered if you are
3294short on memory (running DOS, for example, where you only have 640K).
4946a942
GD		 3295Note that the memory level does have an effect on compression; among
3296other things, lower levels will result in sections of incompressible
3297data being emitted in smaller stored blocks, with a correspondingly
3298larger relative overhead of up to 15% in the worst case.
75b6e0a0
GD		 3299
3300 png_set_compression_mem_level(png_ptr, level);
3301
3302The other functions are for configuring zlib. They are not recommended
3303for normal use and may result in writing an invalid PNG file. See
3304zlib.h for more information on what these mean.
3305
3306 png_set_compression_strategy(png_ptr,
3307 strategy);
3308 png_set_compression_window_bits(png_ptr,
3309 window_bits);
3310 png_set_compression_method(png_ptr, method);
4946a942 3311 png_set_compression_buffer_size(png_ptr, size);
75b6e0a0 3312
4946a942 3313.SS Controlling row filtering
75b6e0a0
GD		 3314
3315If you want to control whether libpng uses filtering or not, which
3316filters are used, and how it goes about picking row filters, you
3317can call one of these functions. The selection and configuration
3318of row filters can have a significant impact on the size and
3319encoding speed and a somewhat lesser impact on the decoding speed
3320of an image. Filtering is enabled by default for RGB and grayscale
3321images (with and without alpha), but not for paletted images nor
3322for any images with bit depths less than 8 bits/pixel.
3323
3324The 'method' parameter sets the main filtering method, which is
4946a942 3325currently only '0' in the PNG 1.2 specification. The 'filters'
75b6e0a0
GD		 3326parameter sets which filter(s), if any, should be used for each
3327scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3328to turn filtering on and off, respectively.
3329
3330Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3331PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4946a942
GD		 3332ORed together with '|' to specify one or more filters to use.
3333These filters are described in more detail in the PNG specification.
3334If you intend to change the filter type during the course of writing
75b6e0a0
GD		 3335the image, you should start with flags set for all of the filters
3336you intend to use so that libpng can initialize its internal
4946a942
GD		 3337structures appropriately for all of the filter types. (Note that this
3338means the first row must always be adaptively filtered, because libpng
3339currently does not allocate the filter buffers until png_write_row()
3340is called for the first time.)
75b6e0a0
GD		 3341
3342 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4946a942
GD		 3343 PNG_FILTER_UP | PNG_FILTER_AVE |
3344 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3345
75b6e0a0
GD		 3346 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3347 filters);
4946a942
GD		 3348 The second parameter can also be
3349 PNG_INTRAPIXEL_DIFFERENCING if you are
3350 writing a PNG to be embedded in a MNG
3351 datastream. This parameter must be the
3352 same as the value of filter_method used
3353 in png_set_IHDR().
75b6e0a0
GD		 3354
3355It is also possible to influence how libpng chooses from among the
4946a942
GD		 3356available filters. This is done in one or both of two ways - by
3357telling it how important it is to keep the same filter for successive
3358rows, and by telling it the relative computational costs of the filters.
75b6e0a0
GD		 3359
3360 double weights[3] = {1.5, 1.3, 1.1},
3361 costs[PNG_FILTER_VALUE_LAST] =
3362 {1.0, 1.3, 1.3, 1.5, 1.7};
3363
4946a942
GD		 3364 png_set_filter_heuristics(png_ptr,
3365 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
75b6e0a0
GD		 3366 weights, costs);
3367
3368The weights are multiplying factors that indicate to libpng that the
3369row filter should be the same for successive rows unless another row filter
3370is that many times better than the previous filter. In the above example,
3371if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3372"sum of absolute differences" 1.5 x 1.3 times higher than other filters
3373and still be chosen, while the NONE filter could have a sum 1.1 times
3374higher than other filters and still be chosen. Unspecified weights are
3375taken to be 1.0, and the specified weights should probably be declining
3376like those above in order to emphasize recent filters over older filters.
3377
3378The filter costs specify for each filter type a relative decoding cost
3379to be considered when selecting row filters. This means that filters
3380with higher costs are less likely to be chosen over filters with lower
3381costs, unless their "sum of absolute differences" is that much smaller.
3382The costs do not necessarily reflect the exact computational speeds of
3383the various filters, since this would unduly influence the final image
3384size.
3385
3386Note that the numbers above were invented purely for this example and
3387are given only to help explain the function usage. Little testing has
3388been done to find optimum values for either the costs or the weights.
3389
4946a942 3390.SS Removing unwanted object code
75b6e0a0
GD		 3391
3392There are a bunch of #define's in pngconf.h that control what parts of
3393libpng are compiled. All the defines end in _SUPPORTED. If you are
3394never going to use a capability, you can change the #define to #undef
3395before recompiling libpng and save yourself code and data space, or
3396you can turn off individual capabilities with defines that begin with
3397PNG_NO_.
3398
3399You can also turn all of the transforms and ancillary chunk capabilities
4946a942 3400off en masse with compiler directives that define
75b6e0a0
GD		 3401PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3402or all four,
3403along with directives to turn on any of the capabilities that you do
3404want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3405the extra transformations but still leave the library fully capable of reading
4946a942 3406and writing PNG files with all known public chunks
75b6e0a0
GD		 3407Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3408produces a library that is incapable of reading or writing ancillary chunks.
3409If you are not using the progressive reading capability, you can
3410turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3411this with the INTERLACING capability, which you'll still have).
3412
3413All the reading and writing specific code are in separate files, so the
3414linker should only grab the files it needs. However, if you want to
3415make sure, or if you are building a stand alone library, all the
3416reading files start with pngr and all the writing files start with
3417pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3418are used for both reading and writing, and always need to be included.
3419The progressive reader is in pngpread.c
3420
3421If you are creating or distributing a dynamically linked library (a .so
3422or DLL file), you should not remove or disable any parts of the library,
3423as this will cause applications linked with different versions of the
3424library to fail if they call functions not available in your library.
3425The size of the library itself should not be an issue, because only
3426those sections that are actually used will be loaded into memory.
3427
4946a942 3428.SS Requesting debug printout
75b6e0a0
GD		 3429
3430The macro definition PNG_DEBUG can be used to request debugging
3431printout. Set it to an integer value in the range 0 to 3. Higher
3432numbers result in increasing amounts of debugging information. The
3433information is printed to the "stderr" file, unless another file
3434name is specified in the PNG_DEBUG_FILE macro definition.
3435
3436When PNG_DEBUG > 0, the following functions (macros) become available:
3437
3438 png_debug(level, message)
3439 png_debug1(level, message, p1)
3440 png_debug2(level, message, p1, p2)
3441
3442in which "level" is compared to PNG_DEBUG to decide whether to print
3443the message, "message" is the formatted string to be printed,
3444and p1 and p2 are parameters that are to be embedded in the string
3445according to printf-style formatting directives. For example,
3446
3447 png_debug1(2, "foo=%d\n", foo);
3448
3449is expanded to
3450
3451 if(PNG_DEBUG > 2)
3452 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3453
3454When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3455can still use PNG_DEBUG to control your own debugging:
3456
3457 #ifdef PNG_DEBUG
3458 fprintf(stderr, ...
3459 #endif
3460
3461When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3462having level = 0 will be printed. There aren't any such statements in
3463this version of libpng, but if you insert some they will be printed.
3464
5b02c8a1
VS		 3465%-%.SH VI. Runtime optimization
3466%-%
3467%-%A new feature in libpng 1.2.0 is the ability to dynamically switch between
3468%-%standard and optimized versions of some routines. Currently these are
3469%-%limited to three computationally intensive tasks when reading PNG files:
3470%-%decoding row filters, expanding interlacing, and combining interlaced or
3471%-%transparent row data with previous row data. Currently the optimized
3472%-%versions are available only for x86 (Intel, AMD, etc.) platforms with
3473%-%MMX support, though this may change in future versions. (For example,
3474%-%the non-MMX assembler optimizations for zlib might become similarly
3475%-%runtime-selectable in future releases, in which case libpng could be
3476%-%extended to support them. Alternatively, the compile-time choice of
3477%-%floating-point versus integer routines for gamma correction might become
3478%-%runtime-selectable.)
3479%-%
3480%-%Because such optimizations tend to be very platform- and compiler-dependent,
3481%-%both in how they are written and in how they perform, the new runtime code
3482%-%in libpng has been written to allow programs to query, enable, and disable
3483%-%either specific optimizations or all such optimizations. For example, to
3484%-%enable all possible optimizations (bearing in mind that some "optimizations"
3485%-%may actually run more slowly in rare cases):
3486%-%
3487%-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3488%-% png_uint_32 mask, flags;
3489%-%
3490%-% flags = png_get_asm_flags(png_ptr);
3491%-% mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3492%-% png_set_asm_flags(png_ptr, flags | mask);
3493%-% #endif
3494%-%
3495%-%To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3496%-%by itself when calling png_get_asm_flagmask(); similarly for optimizing
3497%-%only writing. To disable all optimizations:
3498%-%
3499%-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3500%-% flags = png_get_asm_flags(png_ptr);
3501%-% mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3502%-% png_set_asm_flags(png_ptr, flags & ~mask);
3503%-% #endif
3504%-%
3505%-%To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3506%-%in place of png_get_asm_flagmask(). The mmx version takes one additional
3507%-%parameter:
3508%-%
3509%-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3510%-% int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3511%-% int compilerID;
3512%-%
3513%-% mask = png_get_mmx_flagmask(selection, &compilerID);
3514%-% #endif
3515%-%
3516%-%On return, compilerID will indicate which version of the MMX assembler
3517%-%optimizations was compiled. Currently two flavors exist: Microsoft
3518%-%Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3519%-%On non-x86 platforms or on systems compiled without MMX optimizations, a
3520%-%value of -1 is used.
3521%-%
3522%-%Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3523%-%all valid, settable optimization bits for the version of the library that's
3524%-%currently in use. In the case of shared (dynamically linked) libraries,
3525%-%this may include optimizations that did not exist at the time the code was
3526%-%written and compiled. It is also possible, of course, to enable only known,
3527%-%specific optimizations; for example:
3528%-%
3529%-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3530%-% flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3531%-% | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3532%-% | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3533%-% | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3534%-% | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3535%-% | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3536%-% png_set_asm_flags(png_ptr, flags);
3537%-% #endif
3538%-%
3539%-%This method would enable only the MMX read-optimizations available at the
3540%-%time of libpng 1.2.0's release, regardless of whether a later version of
3541%-%the DLL were actually being used. (Also note that these functions did not
3542%-%exist in versions older than 1.2.0, so any attempt to run a dynamically
3543%-%linked app on such an older version would fail.)
3544%-%
3545%-%To determine whether the processor supports MMX instructions at all, use
3546%-%the png_mmx_support() function:
3547%-%
3548%-% #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3549%-% mmxsupport = png_mmx_support();
3550%-% #endif
3551%-%
3552%-%It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3553%-%is compiled but MMX is not supported by the processor, or 1 if MMX support
3554%-%is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3555%-%and png_get_asm_flagmask() all may be called without allocating and ini-
3556%-%tializing any PNG structures (for example, as part of a usage screen or
3557%-%"about" box).
3558%-%
3559%-%The following code can be used to prevent an application from using the
3560%-%thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3561%-%defined:
3562%-%
3563%-%#if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3564%-% && defined(PNG_THREAD_UNSAFE_OK)
3565%-% /* Disable thread-unsafe features of pnggccrd */
3566%-% if (png_access_version() >= 10200)
3567%-% {
3568%-% png_uint_32 mmx_disable_mask = 0;
3569%-% png_uint_32 asm_flags;
3570%-%
3571%-% mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3572%-% | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3573%-% | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3574%-% | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3575%-% asm_flags = png_get_asm_flags(png_ptr);
3576%-% png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3577%-% }
3578%-%#endif
3579%-%
3580%-%For more extensive examples of runtime querying, enabling and disabling
3581%-%of optimized features, see contrib/gregbook/readpng2.c in the libpng
3582%-%source-code distribution.
3583%-%
3584.SH VI. MNG support
4946a942
GD		 3585
3586The MNG specification (available at http://www.libpng.org/pub/mng) allows
3587certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3588Libpng can support some of these extensions. To enable them, use the
3589png_permit_mng_features() function:
3590
3591 feature_set = png_permit_mng_features(png_ptr, mask)
3592 mask is a png_uint_32 containing the logical OR of the
3593 features you want to enable. These include
3594 PNG_FLAG_MNG_EMPTY_PLTE
3595 PNG_FLAG_MNG_FILTER_64
3596 PNG_ALL_MNG_FEATURES
5b02c8a1 3597 feature_set is a png_uint_32 that is the logical AND of
4946a942
GD		 3598 your mask with the set of MNG features that is
3599 supported by the version of libpng that you are using.
3600
3601It is an error to use this function when reading or writing a standalone
3602PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3603in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3604and the MHDR and MEND chunks. Libpng does not provide support for these
3605or any other MNG chunks; your application must provide its own support for
3606them. You may wish to consider using libmng (available at
3607http://www.libmng.com) instead.
3608
5b02c8a1 3609.SH VII. Changes to Libpng from version 0.88
75b6e0a0
GD		 3610
3611It should be noted that versions of libpng later than 0.96 are not
3612distributed by the original libpng author, Guy Schalnat, nor by
3613Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3614distributed versions 0.89 through 0.96, but rather by another member
3615of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3616still alive and well, but they have moved on to other things.
3617
3618The old libpng functions png_read_init(), png_write_init(),
4946a942
GD		 3619png_info_init(), png_read_destroy(), and png_write_destroy() have been
3620moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3621functions will be removed from libpng version 2.0.0.
3622
3623The preferred method of creating and initializing the libpng structures is
75b6e0a0
GD		 3624via the png_create_read_struct(), png_create_write_struct(), and
3625png_create_info_struct() because they isolate the size of the structures
3626from the application, allow version error checking, and also allow the
3627use of custom error handling routines during the initialization, which
3628the old functions do not. The functions png_read_destroy() and
3629png_write_destroy() do not actually free the memory that libpng
3630allocated for these structs, but just reset the data structures, so they
3631can be used instead of png_destroy_read_struct() and
3632png_destroy_write_struct() if you feel there is too much system overhead
3633allocating and freeing the png_struct for each image read.
3634
3635Setting the error callbacks via png_set_message_fn() before
3636png_read_init() as was suggested in libpng-0.88 is no longer supported
3637because this caused applications that do not use custom error functions
3638to fail if the png_ptr was not initialized to zero. It is still possible
3639to set the error callbacks AFTER png_read_init(), or to change them with
4946a942
GD		 3640png_set_error_fn(), which is essentially the same function, but with a new
3641name to force compilation errors with applications that try to use the old
3642method.
3643
3644Starting with version 1.0.7, you can find out which version of the library
3645you are using at run-time:
3646
3647 png_uint_32 libpng_vn = png_access_version_number();
3648
3649The number libpng_vn is constructed from the major version, minor
3650version with leading zero, and release number with leading zero,
3651(e.g., libpng_vn for version 1.0.7 is 10007).
3652
3653You can also check which version of png.h you used when compiling your
3654application:
3655
3656 png_uint_32 application_vn = PNG_LIBPNG_VER;
75b6e0a0 3657
5b02c8a1 3658.SH VII. Y2K Compliance in libpng
75b6e0a0 3659
5b02c8a1 3660August 15, 2004
75b6e0a0
GD		 3661
3662Since the PNG Development group is an ad-hoc body, we can't make
3663an official declaration.
3664
4946a942 3665This is your unofficial assurance that libpng from version 0.71 and
5b02c8a1 3666upward through 1.2.6 are Y2K compliant. It is my belief that earlier
4946a942 3667versions were also Y2K compliant.
75b6e0a0
GD		 3668
3669Libpng only has three year fields. One is a 2-byte unsigned integer that
3670will hold years up to 65535. The other two hold the date in text
3671format, and will hold years up to 9999.
3672
3673The integer is
3674 "png_uint_16 year" in png_time_struct.
3675
3676The strings are
3677 "png_charp time_buffer" in png_struct and
3678 "near_time_buffer", which is a local character string in png.c.
3679
3680There are seven time-related functions:
3681
4946a942 3682 png_convert_to_rfc_1123() in png.c
75b6e0a0 3683 (formerly png_convert_to_rfc_1152() in error)
4946a942
GD		 3684 png_convert_from_struct_tm() in pngwrite.c, called
3685 in pngwrite.c
75b6e0a0
GD		 3686 png_convert_from_time_t() in pngwrite.c
3687 png_get_tIME() in pngget.c
3688 png_handle_tIME() in pngrutil.c, called in pngread.c
3689 png_set_tIME() in pngset.c
3690 png_write_tIME() in pngwutil.c, called in pngwrite.c
3691
4946a942 3692All appear to handle dates properly in a Y2K environment. The
75b6e0a0
GD		 3693png_convert_from_time_t() function calls gmtime() to convert from system
3694clock time, which returns (year - 1900), which we properly convert to
3695the full 4-digit year. There is a possibility that applications using
3696libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
4946a942
GD		 3697function, or that they are incorrectly passing only a 2-digit year
3698instead of "year - 1900" into the png_convert_from_struct_tm() function,
3699but this is not under our control. The libpng documentation has always
3700stated that it works with 4-digit years, and the APIs have been
3701documented as such.
75b6e0a0
GD		 3702
3703The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3704integer to hold the year, and can hold years as large as 65535.
3705
4946a942
GD		 3706zlib, upon which libpng depends, is also Y2K compliant. It contains
3707no date-related code.
3708
75b6e0a0
GD		 3709
3710 Glenn Randers-Pehrson
3711 libpng maintainer
3712 PNG Development Group
3713
3714.SH NOTE
3715
3716Note about libpng version numbers:
3717
3718Due to various miscommunications, unforeseen code incompatibilities
3719and occasional factors outside the authors' control, version numbering
3720on the library has not always been consistent and straightforward.
3721The following table summarizes matters since version 0.89c, which was
3722the first widely used release:
3723
4946a942
GD		 3724 source png.h png.h shared-lib
3725 version string int version
3726 ------- ------ ----- ----------
3727 0.89c ("beta 3") 0.89 89 1.0.89
3728 0.90 ("beta 4") 0.90 90 0.90
3729 0.95 ("beta 5") 0.95 95 0.95
3730 0.96 ("beta 6") 0.96 96 0.96
3731 0.97b ("beta 7") 1.00.97 97 1.0.1
3732 0.97c 0.97 97 2.0.97
3733 0.98 0.98 98 2.0.98
3734 0.99 0.99 98 2.0.99
3735 0.99a-m 0.99 99 2.0.99
3736 1.00 1.00 100 2.1.0
3737 1.0.0 1.0.0 100 2.1.0
3738 1.0.0 (from here on, the 100 2.1.0
3739 1.0.1 png.h string is 10001 2.1.0
3740 1.0.1a-e identical to the 10002 from here on, the
3741 1.0.2 source version) 10002 shared library is 2.V
3742 1.0.2a-b 10003 where V is the source
3743 1.0.1 10001 code version except as
3744 1.0.1a-e 10002 2.1.0.1a-e noted.
3745 1.0.2 10002 2.1.0.2
3746 1.0.2a-b 10003 2.1.0.2a-b
3747 1.0.3 10003 2.1.0.3
3748 1.0.3a-d 10004 2.1.0.3a-d
3749 1.0.4 10004 2.1.0.4
3750 1.0.4a-f 10005 2.1.0.4a-f
3751 1.0.5 (+ 2 patches) 10005 2.1.0.5
3752 1.0.5a-d 10006 2.1.0.5a-d
3753 1.0.5e-r 10100 2.1.0.5e-r
3754 1.0.5s-v 10006 2.1.0.5s-v
3755 1.0.6 (+ 3 patches) 10006 2.1.0.6
3756 1.0.6d-g 10007 2.1.0.6d-g
3757 1.0.6h 10007 10.6h
3758 1.0.6i 10007 10.6i
3759 1.0.6j 10007 2.1.0.6j
3760 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3761 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3762 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3763 1.0.7 1 10007 2.1.0.7
3764 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3765 1.0.8rc1 1 10008 2.1.0.8rc1
3766 1.0.8 1 10008 2.1.0.8
3767 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3768 1.0.9rc1 1 10009 2.1.0.9rc1
3769 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3770 1.0.9rc2 1 10009 2.1.0.9rc2
3771 1.0.9 1 10009 2.1.0.9
3772 1.0.10beta1 1 10010 2.1.0.10beta1
3773 1.0.10rc1 1 10010 2.1.0.10rc1
3774 1.0.10 1 10010 2.1.0.10
3775 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3776 1.0.11rc1 1 10011 2.1.0.11rc1
3777 1.0.11 1 10011 2.1.0.11
3778 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3779 1.0.12rc1 2 10012 2.1.0.12rc1
3780 1.0.12 2 10012 2.1.0.12
3781 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3782 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3783 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3784 1.2.0rc1 3 10200 3.1.2.0rc1
3785 1.2.0 3 10200 3.1.2.0
3786 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3787 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3788 1.2.1 3 10201 3.1.2.1
3789 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3790 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3791 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3792 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3793 1.0.13 10 10013 10.so.0.1.0.13
3794 1.2.2 12 10202 12.so.0.1.2.2
3795 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3796 1.2.3 12 10203 12.so.0.1.2.3
3797 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3798 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3799 1.0.14 10 10014 10.so.0.1.0.14
3800 1.2.4 13 10204 12.so.0.1.2.4
5b02c8a1
VS		 3801 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3802 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3803 1.0.15 10 10015 10.so.0.1.0.15
3804 1.2.5 13 10205 12.so.0.1.2.5
3805 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3806 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3807 1.0.16 10 10016 10.so.0.1.0.16
3808 1.2.6 13 10206 12.so.0.1.2.6
4946a942
GD		 3809
3810Henceforth the source version will match the shared-library minor
3811and patch numbers; the shared-library major version number will be
3812used for changes in backward compatibility, as it is intended. The
3813PNG_PNGLIB_VER macro, which is not used within libpng but is available
3814for applications, is an unsigned integer of the form xyyzz corresponding
3815to the source version x.y.z (leading zeros in y and z). Beta versions
3816were given the previous public release number plus a letter, until
3817version 1.0.6j; from then on they were given the upcoming public
3818release number plus "betaNN" or "rcN".
3819
75b6e0a0
GD		 3820.SH "SEE ALSO"
3821libpngpf(3), png(5)
3822.LP
3823.IR libpng :
3824.IP
3825ftp://ftp.uu.net/graphics/png
4946a942 3826http://www.libpng.org/pub/png
75b6e0a0
GD		 3827
3828.LP
3829.IR zlib :
3830.IP
3831(generally) at the same location as
3832.I libpng
3833or at
3834.br
3835ftp://ftp.uu.net/pub/archiving/zip/zlib
3836.br
4946a942 3837ftp://ftp.info-zip.org/pub/infozip/zlib
75b6e0a0
GD		 3838
3839.LP
3840.IR PNG specification: RFC 2083
3841.IP
3842(generally) at the same location as
3843.I libpng
3844or at
3845.br
3846ftp://ds.internic.net/rfc/rfc2083.txt
3847.br
3848or (as a W3C Recommendation) at
3849.br
3850http://www.w3.org/TR/REC-png.html
3851
3852.LP
3853In the case of any inconsistency between the PNG specification
3854and this library, the specification takes precedence.
3855
3856.SH AUTHORS
3857This man page: Glenn Randers-Pehrson
5b02c8a1 3858<glennrp@users.sourceforge.net>
75b6e0a0
GD		 3859
3860The contributing authors would like to thank all those who helped
3861with testing, bug fixes, and patience. This wouldn't have been
3862possible without all of you.
3863
3864Thanks to Frank J. T. Wojcik for helping with the documentation.
4946a942 3865
5b02c8a1 3866Libpng version 1.2.6 - August 15, 2004:
75b6e0a0 3867Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5b02c8a1 3868Currently maintained by Glenn Randers-Pehrson (glennrp@users.sourceforge.net).
75b6e0a0
GD		 3869
3870Supported by the PNG development group
3871.br
4946a942 3872(png-implement@ccrc.wustl.edu).
75b6e0a0 3873
4946a942 3874.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
75b6e0a0 3875
4946a942
GD		 3876(This copy of the libpng notices is provided for your convenience. In case of
3877any discrepancy between this copy and the notices in the file png.h that is
3878included in the libpng distribution, the latter shall prevail.)
3879
3880If you modify libpng you may insert additional notices immediately following
3881this sentence.
3882
5b02c8a1
VS		 3883libpng version 1.2.6, August 15, 2004, is
3884Copyright (c) 2004 Glenn Randers-Pehrson, and is
3885distributed according to the same disclaimer and license as libpng-1.2.5
3886with the following individual added to the list of Contributing Authors
3887
3888 Cosmin Truta
3889
3890libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
4946a942
GD		 3891Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3892distributed according to the same disclaimer and license as libpng-1.0.6
3893with the following individuals added to the list of Contributing Authors
3894
3895 Simon-Pierre Cadieux
3896 Eric S. Raymond
3897 Gilles Vollant
3898
3899and with the following additions to the disclaimer:
3900
3901 There is no warranty against interference with your
3902 enjoyment of the library or against infringement.
3903 There is no warranty that our efforts or the library
3904 will fulfill any of your particular purposes or needs.
3905 This library is provided with all faults, and the entire
3906 risk of satisfactory quality, performance, accuracy, and
3907 effort is with the user.
3908
3909libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
75b6e0a0 3910Copyright (c) 1998, 1999 Glenn Randers-Pehrson
4946a942
GD		 3911Distributed according to the same disclaimer and license as libpng-0.96,
3912with the following individuals added to the list of Contributing Authors:
3913
3914 Tom Lane
3915 Glenn Randers-Pehrson
3916 Willem van Schaik
75b6e0a0 3917
4946a942
GD		 3918libpng versions 0.89, June 1996, through 0.96, May 1997, are
3919Copyright (c) 1996, 1997 Andreas Dilger
3920Distributed according to the same disclaimer and license as libpng-0.88,
3921with the following individuals added to the list of Contributing Authors:
3922
3923 John Bowler
3924 Kevin Bracey
3925 Sam Bushell
3926 Magnus Holmgren
3927 Greg Roelofs
3928 Tom Tanner
3929
3930libpng versions 0.5, May 1995, through 0.88, January 1996, are
3931Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3932
3933For the purposes of this copyright and license, "Contributing Authors"
3934is defined as the following set of individuals:
3935
3936 Andreas Dilger
3937 Dave Martindale
3938 Guy Eric Schalnat
3939 Paul Schmidt
3940 Tim Wegner
3941
3942The PNG Reference Library is supplied "AS IS". The Contributing Authors
3943and Group 42, Inc. disclaim all warranties, expressed or implied,
75b6e0a0
GD		 3944including, without limitation, the warranties of merchantability and of
3945fitness for any purpose. The Contributing Authors and Group 42, Inc.
3946assume no liability for direct, indirect, incidental, special, exemplary,
3947or consequential damages, which may result from the use of the PNG
3948Reference Library, even if advised of the possibility of such damage.
3949
3950Permission is hereby granted to use, copy, modify, and distribute this
3951source code, or portions hereof, for any purpose, without fee, subject
3952to the following restrictions:
3953
4946a942 39541. The origin of this source code must not be misrepresented.
75b6e0a0 3955
4946a942
GD		 39562. Altered versions must be plainly marked as such and
3957 must not be misrepresented as being the original source.
75b6e0a0 3958
4946a942
GD		 39593. This Copyright notice may not be removed or altered from
3960 any source or altered source distribution.
75b6e0a0
GD		 3961
3962The Contributing Authors and Group 42, Inc. specifically permit, without
3963fee, and encourage the use of this source code as a component to
3964supporting the PNG file format in commercial products. If you use this
3965source code in a product, acknowledgment is not required but would be
3966appreciated.
3967
4946a942
GD		 3968
3969A "png_get_copyright" function is available, for convenient use in "about"
3970boxes and the like:
3971
3972 printf("%s",png_get_copyright(NULL));
3973
3974Also, the PNG logo (in PNG format, of course) is supplied in the
3975files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
3976
3977Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
3978certification mark of the Open Source Initiative.
3979
3980Glenn Randers-Pehrson
5b02c8a1
VS		 3981glennrp@users.sourceforge.net
3982August 15, 2004
4946a942 3983
75b6e0a0
GD		 3984.\" end of man page
3985
wxWidgets (Impactor)