1
.TH LIBPNG 3 "September 12, 2004"
3
libpng \- Portable Network Graphics (PNG) Reference Library 1.2.7
11
\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15
\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
19
\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
23
\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
27
\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
31
\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
35
\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
39
\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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
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
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
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
59
\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
63
\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
67
\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
71
\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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
79
\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
83
\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
87
\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
91
\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
95
\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99
\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
103
\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
111
\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
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
123
\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
127
\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131
\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
135
\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
139
\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
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
151
\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
155
\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
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
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
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
171
\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
175
\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179
\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
183
\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
187
\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
191
\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
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
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
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
207
\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
211
\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
215
\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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
223
\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
225
\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
229
\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
237
\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
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
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
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
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
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
265
\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
269
\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
273
\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
277
\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
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
285
\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
289
\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
293
\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
297
\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
301
\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
305
\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
309
\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
313
\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
317
\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
321
\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
325
\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
329
\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
333
\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
337
\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
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
345
\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
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
353
\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
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
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
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
369
\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
373
\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
377
\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
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
385
\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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
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
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
401
\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
405
\fB#if \fI!defined(PNG_1_0_X)
407
\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
413
\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
417
\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
421
\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
425
\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
429
\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
433
\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
437
\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
441
\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
445
\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
449
\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
453
\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
457
\fBvoid png_set_dither (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_dither\fP\fB);\fP
461
\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
465
\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
469
\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
473
\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
477
\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
481
\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
485
\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
489
\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
493
\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
497
\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
501
\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
505
\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
509
\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
513
\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
517
\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
521
\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
525
\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
529
\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
533
\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
537
\fBvoid png_set_mem_fn(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
541
\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
545
\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
549
\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
553
\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
557
\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
561
\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
565
\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
569
\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
573
\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
577
\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
581
\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
585
\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
589
\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
593
\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
597
\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
601
\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
605
\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
609
\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
613
\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
617
\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
621
\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
625
\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
629
\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
633
\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
637
\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
641
\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
645
\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
649
\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
653
\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
657
\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
661
\fBvoid png_set_unknown_chunk_location(png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
665
\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
669
\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
673
\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
677
\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
681
\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
685
\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
689
\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
693
\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
697
\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
701
\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
705
\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
709
\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
713
\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
717
\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
721
\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
725
\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
729
\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
733
\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
737
\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
741
\fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
745
\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
749
\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
753
\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
757
\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
761
\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
765
\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
769
\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
776
library supports encoding, decoding, and various manipulations of
777
the Portable Network Graphics (PNG) format image files. It uses the
780
Following is a copy of the libpng.txt file that accompanies libpng.
782
libpng.txt - A description on how to use and modify libpng
784
libpng version 1.2.7 - September 12, 2004
785
Updated and distributed by Glenn Randers-Pehrson
786
<glennrp@users.sourceforge.net>
787
Copyright (c) 1998-2004 Glenn Randers-Pehrson
788
For conditions of distribution and use, see copyright
793
libpng 1.0 beta 6 version 0.96 May 28, 1997
794
Updated and distributed by Andreas Dilger
795
Copyright (c) 1996, 1997 Andreas Dilger
797
libpng 1.0 beta 2 - version 0.88 January 26, 1996
798
For conditions of distribution and use, see copyright
799
notice in png.h. Copyright (c) 1995, 1996 Guy Eric
800
Schalnat, Group 42, Inc.
802
Updated/rewritten per request in the libpng FAQ
803
Copyright (c) 1995, 1996 Frank J. T. Wojcik
804
December 18, 1995 & January 20, 1996
808
This file describes how to use and modify the PNG reference library
809
(known as libpng) for your own use. There are five sections to this
810
file: introduction, structures, reading, writing, and modification and
811
configuration notes for various special platforms. In addition to this
812
file, example.c is a good starting point for using the library, as
813
it is heavily commented and should include everything most people
814
will need. We assume that libpng is already installed; see the
815
INSTALL file for instructions on how to install libpng.
817
Libpng was written as a companion to the PNG specification, as a way
818
of reducing the amount of time and effort it takes to support the PNG
819
file format in application programs.
821
The PNG specification (second edition), November 2003, is available as
822
a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
823
<http://www.w3.org/TR/2003/REC-PNG-20031110/
824
The W3C and ISO documents have identical technical content.
826
The PNG-1.2 specification is available at
827
<http://www.libpng.org/pub/png/documents/>
829
The PNG-1.0 specification is available
830
as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
831
W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
832
additional chunks are described in the special-purpose public chunks
833
documents at <http://www.libpng.org/pub/png/documents/>.
836
about PNG, and the latest version of libpng, can be found at the PNG home
837
page, <http://www.libpng.org/pub/png/>.
839
Most users will not have to modify the library significantly; advanced
840
users may want to modify it more. All attempts were made to make it as
841
complete as possible, while keeping the code easy to understand.
842
Currently, this library only supports C. Support for other languages
845
Libpng has been designed to handle multiple sessions at one time,
846
to be easily modifiable, to be portable to the vast majority of
847
machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
848
to use. The ultimate goal of libpng is to promote the acceptance of
849
the PNG file format in whatever way possible. While there is still
850
work to be done (see the TODO file), libpng should cover the
851
majority of the needs of its users.
853
Libpng uses zlib for its compression and decompression of PNG files.
854
Further information about zlib, and the latest version of zlib, can
855
be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
856
The zlib compression utility is a general purpose utility that is
857
useful for more than PNG files, and can be used without libpng.
858
See the documentation delivered with zlib for more details.
859
You can usually find the source files for the zlib utility wherever you
860
find the libpng source files.
862
Libpng is thread safe, provided the threads are using different
863
instances of the structures. Each thread should have its own
864
png_struct and png_info instances, and thus its own image.
865
Libpng does not protect itself against two threads using the
866
same instance of a structure. Note: thread safety may be defeated
867
by use of some of the MMX assembler code in pnggccrd.c, which is only
868
compiled when the user defines PNG_THREAD_UNSAFE_OK.
872
There are two main structures that are important to libpng, png_struct
873
and png_info. The first, png_struct, is an internal structure that
874
will not, for the most part, be used by a user except as the first
875
variable passed to every libpng function call.
877
The png_info structure is designed to provide information about the
878
PNG file. At one time, the fields of png_info were intended to be
879
directly accessible to the user. However, this tended to cause problems
880
with applications using dynamically loaded libraries, and as a result
881
a set of interface functions for png_info (the png_get_*() and png_set_*()
882
functions) was developed. The fields of png_info are still available for
883
older applications, but it is suggested that applications use the new
884
interfaces if at all possible.
886
Applications that do make direct access to the members of png_struct (except
887
for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
888
and applications that make direct access to the members of png_info must
889
be recompiled if they were compiled or loaded with libpng version 1.0.6,
890
in which the members were in a different order. In version 1.0.7, the
891
members of the png_info structure reverted to the old order, as they were
892
in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
893
structures are going to be hidden, and the contents of the structures will
894
only be accessible through the png_get/png_set functions.
896
The png.h header file is an invaluable reference for programming with libpng.
897
And while I'm on the topic, make sure you include the libpng header file:
903
We'll now walk you through the possible functions to call when reading
904
in a PNG file sequentially, briefly explaining the syntax and purpose
905
of each one. See example.c and png.h for more detail. While
906
progressive reading is covered in the next section, you will still
907
need some of the functions discussed in this section to read a PNG
912
You will want to do the I/O initialization(*) before you get into libpng,
913
so if it doesn't work, you don't have much to undo. Of course, you
914
will also want to insure that you are, in fact, dealing with a PNG
915
file. Libpng provides a simple check to see if a file is a PNG file.
916
To use it, pass in the first 1 to 8 bytes of the file to the function
917
png_sig_cmp(), and it will return 0 if the bytes match the corresponding
918
bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
919
you pass in, the greater the accuracy of the prediction.
921
If you are intending to keep the file pointer open for use in libpng,
922
you must ensure you don't read more than 8 bytes from the beginning
923
of the file, and you also have to make a call to png_set_sig_bytes_read()
924
with the number of bytes you read from the beginning. Libpng will
925
then only check the bytes (if any) that your program didn't read.
927
(*): If you are not using the standard I/O functions, you will need
928
to replace them with custom functions. See the discussion under
932
FILE *fp = fopen(file_name, "rb");
937
fread(header, 1, number, fp);
938
is_png = !png_sig_cmp(header, 0, number);
945
Next, png_struct and png_info need to be allocated and initialized. In
946
order to ensure that the size of these structures is correct even with a
947
dynamically linked libpng, there are functions to initialize and
948
allocate the structures. We also pass the library version, optional
949
pointers to error handling functions, and a pointer to a data struct for
950
use by the error functions, if necessary (the pointer and functions can
951
be NULL if the default error handlers are to be used). See the section
952
on Changes to Libpng below regarding the old initialization functions.
953
The structure allocation functions quietly return NULL if they fail to
954
create the structure, so your application should check for that.
956
png_structp png_ptr = png_create_read_struct
957
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
958
user_error_fn, user_warning_fn);
962
png_infop info_ptr = png_create_info_struct(png_ptr);
965
png_destroy_read_struct(&png_ptr,
966
(png_infopp)NULL, (png_infopp)NULL);
970
png_infop end_info = png_create_info_struct(png_ptr);
973
png_destroy_read_struct(&png_ptr, &info_ptr,
978
If you want to use your own memory allocation routines,
979
define PNG_USER_MEM_SUPPORTED and use
980
png_create_read_struct_2() instead of png_create_read_struct():
982
png_structp png_ptr = png_create_read_struct_2
983
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
984
user_error_fn, user_warning_fn, (png_voidp)
985
user_mem_ptr, user_malloc_fn, user_free_fn);
987
The error handling routines passed to png_create_read_struct()
988
and the memory alloc/free routines passed to png_create_struct_2()
989
are only necessary if you are not using the libpng supplied error
990
handling and memory alloc/free functions.
992
When libpng encounters an error, it expects to longjmp back
993
to your routine. Therefore, you will need to call setjmp and pass
994
your png_jmpbuf(png_ptr). If you read the file from different
995
routines, you will need to update the jmpbuf field every time you enter
996
a new routine that will call a png_*() function.
998
See your documentation of setjmp/longjmp for your compiler for more
999
information on setjmp/longjmp. See the discussion on libpng error
1000
handling in the Customizing Libpng section below for more information
1001
on the libpng error handling. If an error occurs, and libpng longjmp's
1002
back to your setjmp, you will want to call png_destroy_read_struct() to
1005
if (setjmp(png_jmpbuf(png_ptr)))
1007
png_destroy_read_struct(&png_ptr, &info_ptr,
1013
If you would rather avoid the complexity of setjmp/longjmp issues,
1014
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1015
errors will result in a call to PNG_ABORT() which defaults to abort().
1017
Now you need to set up the input code. The default for libpng is to
1018
use the C function fread(). If you use this, you will need to pass a
1019
valid FILE * in the function png_init_io(). Be sure that the file is
1020
opened in binary mode. If you wish to handle reading data in another
1021
way, you need not call the png_init_io() function, but you must then
1022
implement the libpng I/O methods discussed in the Customizing Libpng
1025
png_init_io(png_ptr, fp);
1027
If you had previously opened the file and read any of the signature from
1028
the beginning in order to see if this was a PNG file, you need to let
1029
libpng know that there are some bytes missing from the start of the file.
1031
png_set_sig_bytes(png_ptr, number);
1033
.SS Setting up callback code
1035
You can set up a callback function to handle any unknown chunks in the
1036
input stream. You must supply the function
1038
read_chunk_callback(png_ptr ptr,
1039
png_unknown_chunkp chunk);
1041
/* The unknown chunk structure contains your
1046
/* Note that libpng has already taken care of
1049
/* put your code here. Return one of the
1052
return (-n); /* chunk had an error */
1053
return (0); /* did not recognize */
1054
return (n); /* success */
1057
(You can give your function another name that you like instead of
1058
"read_chunk_callback")
1060
To inform libpng about your function, use
1062
png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1063
read_chunk_callback);
1065
This names not only the callback function, but also a user pointer that
1066
you can retrieve with
1068
png_get_user_chunk_ptr(png_ptr);
1070
At this point, you can set up a callback function that will be
1071
called after each row has been read, which you can use to control
1072
a progress meter or the like. It's demonstrated in pngtest.c.
1073
You must supply a function
1075
void read_row_callback(png_ptr ptr, png_uint_32 row,
1078
/* put your code here */
1081
(You can give it another name that you like instead of "read_row_callback")
1083
To inform libpng about your function, use
1085
png_set_read_status_fn(png_ptr, read_row_callback);
1087
.SS Width and height limits
1089
The PNG specification allows the width and height of an image to be as
1090
large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1091
Since very few applications really need to process such large images,
1092
we have imposed an arbitrary 1-million limit on rows and columns.
1093
Larger images will be rejected immediately with a png_error() call. If
1094
you wish to override this limit, you can use
1096
png_set_user_limits(png_ptr, width_max, height_max);
1098
to set your own limits, or use width_max = height_max = 0x7fffffffL
1099
to allow all valid dimensions (libpng may reject some very large images
1100
anyway because of potential buffer overflow conditions).
1102
You should put this statement after you create the PNG structure and
1103
before calling png_read_info(), png_read_png(), or png_process_data().
1104
If you need to retrieve the limits that are being applied, use
1106
width_max = png_get_user_width_max(png_ptr);
1107
height_max = png_get_user_height_max(png_ptr);
1109
.SS Unknown-chunk handling
1111
Now you get to set the way the library processes unknown chunks in the
1112
input PNG stream. Both known and unknown chunks will be read. Normal
1113
behavior is that known chunks will be parsed into information in
1114
various info_ptr members; unknown chunks will be discarded. To change
1117
png_set_keep_unknown_chunks(png_ptr, keep,
1118
chunk_list, num_chunks);
1119
keep - 0: do not handle as unknown
1121
2: keep only if safe-to-copy
1122
3: keep even if unsafe-to-copy
1123
You can use these definitions:
1124
PNG_HANDLE_CHUNK_AS_DEFAULT 0
1125
PNG_HANDLE_CHUNK_NEVER 1
1126
PNG_HANDLE_CHUNK_IF_SAFE 2
1127
PNG_HANDLE_CHUNK_ALWAYS 3
1128
chunk_list - list of chunks affected (a byte string,
1129
five bytes per chunk, NULL or '\0' if
1131
num_chunks - number of chunks affected; if 0, all
1132
unknown chunks are affected. If nonzero,
1133
only the chunks in the list are affected
1135
Unknown chunks declared in this way will be saved as raw data onto a
1136
list of png_unknown_chunk structures. If a chunk that is normally
1137
known to libpng is named in the list, it will be handled as unknown,
1138
according to the "keep" directive. If a chunk is named in successive
1139
instances of png_set_keep_unknown_chunks(), the final instance will
1140
take precedence. The IHDR and IEND chunks should not be named in
1141
chunk_list; if they are, libpng will process them normally anyway.
1143
.SS The high-level read interface
1145
At this point there are two ways to proceed; through the high-level
1146
read interface, or through a sequence of low-level read operations.
1147
You can use the high-level interface if (a) you are willing to read
1148
the entire image into memory, and (b) the input transformations
1149
you want to do are limited to the following set:
1151
PNG_TRANSFORM_IDENTITY No transformation
1152
PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1154
PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1155
PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1157
PNG_TRANSFORM_PACKSWAP Change order of packed
1159
PNG_TRANSFORM_EXPAND Perform set_expand()
1160
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1161
PNG_TRANSFORM_SHIFT Normalize pixels to the
1163
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1165
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1167
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1169
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1171
(This excludes setting a background color, doing gamma transformation,
1172
dithering, and setting filler.) If this is the case, simply do this:
1174
png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1176
where png_transforms is an integer containing the logical OR of
1177
some set of transformation flags. This call is equivalent to png_read_info(),
1178
followed the set of transformations indicated by the transform mask,
1179
then png_read_image(), and finally png_read_end().
1181
(The final parameter of this call is not yet used. Someday it might point
1182
to transformation parameters required by some future input transform.)
1184
You must use png_transforms and not call any png_set_transform() functions
1185
when you use png_read_png().
1187
After you have called png_read_png(), you can retrieve the image data
1190
row_pointers = png_get_rows(png_ptr, info_ptr);
1192
where row_pointers is an array of pointers to the pixel data for each row:
1194
png_bytep row_pointers[height];
1196
If you know your image size and pixel size ahead of time, you can allocate
1197
row_pointers prior to calling png_read_png() with
1199
if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1201
"Image is too tall to process in memory");
1202
if (width > PNG_UINT_32_MAX/pixel_size)
1204
"Image is too wide to process in memory");
1205
row_pointers = png_malloc(png_ptr,
1206
height*png_sizeof(png_bytep));
1207
for (int i=0; i<height, i++)
1208
row_pointers[i]=png_malloc(png_ptr,
1210
png_set_rows(png_ptr, info_ptr, &row_pointers);
1212
Alternatively you could allocate your image in one big block and define
1213
row_pointers[i] to point into the proper places in your block.
1215
If you use png_set_rows(), the application is responsible for freeing
1216
row_pointers (and row_pointers[i], if they were separately allocated).
1218
If you don't allocate row_pointers ahead of time, png_read_png() will
1219
do it, and it'll be free'ed when you call png_destroy_*().
1221
.SS The low-level read interface
1223
If you are going the low-level route, you are now ready to read all
1224
the file information up to the actual image data. You do this with a
1225
call to png_read_info().
1227
png_read_info(png_ptr, info_ptr);
1229
This will process all chunks up to but not including the image data.
1231
.SS Querying the info structure
1233
Functions are used to get the information from the info_ptr once it
1234
has been read. Note that these fields may not be completely filled
1235
in until png_read_end() has read the chunk data following the image.
1237
png_get_IHDR(png_ptr, info_ptr, &width, &height,
1238
&bit_depth, &color_type, &interlace_type,
1239
&compression_type, &filter_method);
1241
width - holds the width of the image
1242
in pixels (up to 2^31).
1243
height - holds the height of the image
1244
in pixels (up to 2^31).
1245
bit_depth - holds the bit depth of one of the
1246
image channels. (valid values are
1247
1, 2, 4, 8, 16 and depend also on
1248
the color_type. See also
1249
significant bits (sBIT) below).
1250
color_type - describes which color/alpha channels
1253
(bit depths 1, 2, 4, 8, 16)
1254
PNG_COLOR_TYPE_GRAY_ALPHA
1256
PNG_COLOR_TYPE_PALETTE
1257
(bit depths 1, 2, 4, 8)
1260
PNG_COLOR_TYPE_RGB_ALPHA
1263
PNG_COLOR_MASK_PALETTE
1264
PNG_COLOR_MASK_COLOR
1265
PNG_COLOR_MASK_ALPHA
1267
filter_method - (must be PNG_FILTER_TYPE_BASE
1268
for PNG 1.0, and can also be
1269
PNG_INTRAPIXEL_DIFFERENCING if
1270
the PNG datastream is embedded in
1271
a MNG-1.0 datastream)
1272
compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1274
interlace_type - (PNG_INTERLACE_NONE or
1275
PNG_INTERLACE_ADAM7)
1276
Any or all of interlace_type, compression_type, of
1277
filter_method can be NULL if you are
1278
not interested in their values.
1280
channels = png_get_channels(png_ptr, info_ptr);
1281
channels - number of channels of info for the
1282
color type (valid values are 1 (GRAY,
1283
PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1284
4 (RGB_ALPHA or RGB + filler byte))
1285
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1286
rowbytes - number of bytes needed to hold a row
1288
signature = png_get_signature(png_ptr, info_ptr);
1289
signature - holds the signature read from the
1290
file (if any). The data is kept in
1291
the same offset it would be if the
1292
whole signature were read (i.e. if an
1293
application had already read in 4
1294
bytes of signature before starting
1295
libpng, the remaining 4 bytes would
1296
be in signature[4] through signature[7]
1297
(see png_set_sig_bytes())).
1300
width = png_get_image_width(png_ptr,
1302
height = png_get_image_height(png_ptr,
1304
bit_depth = png_get_bit_depth(png_ptr,
1306
color_type = png_get_color_type(png_ptr,
1308
filter_method = png_get_filter_type(png_ptr,
1310
compression_type = png_get_compression_type(png_ptr,
1312
interlace_type = png_get_interlace_type(png_ptr,
1316
These are also important, but their validity depends on whether the chunk
1317
has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1318
png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1319
data has been read, or zero if it is missing. The parameters to the
1320
png_get_<chunk> are set directly if they are simple data types, or a pointer
1321
into the info_ptr is returned for any complex types.
1323
png_get_PLTE(png_ptr, info_ptr, &palette,
1325
palette - the palette for the file
1326
(array of png_color)
1327
num_palette - number of entries in the palette
1329
png_get_gAMA(png_ptr, info_ptr, &gamma);
1330
gamma - the gamma the file is written
1333
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1334
srgb_intent - the rendering intent (PNG_INFO_sRGB)
1335
The presence of the sRGB chunk
1336
means that the pixel data is in the
1337
sRGB color space. This chunk also
1338
implies specific values of gAMA and
1341
png_get_iCCP(png_ptr, info_ptr, &name,
1342
&compression_type, &profile, &proflen);
1343
name - The profile name.
1344
compression - The compression type; always
1345
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1346
You may give NULL to this argument to
1348
profile - International Color Consortium color
1349
profile data. May contain NULs.
1350
proflen - length of profile data in bytes.
1352
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1353
sig_bit - the number of significant bits for
1354
(PNG_INFO_sBIT) each of the gray,
1355
red, green, and blue channels,
1356
whichever are appropriate for the
1357
given color type (png_color_16)
1359
png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1361
trans - array of transparent entries for
1362
palette (PNG_INFO_tRNS)
1363
trans_values - graylevel or color sample values of
1364
the single transparent color for
1365
non-paletted images (PNG_INFO_tRNS)
1366
num_trans - number of transparent entries
1369
png_get_hIST(png_ptr, info_ptr, &hist);
1371
hist - histogram of palette (array of
1374
png_get_tIME(png_ptr, info_ptr, &mod_time);
1375
mod_time - time image was last modified
1378
png_get_bKGD(png_ptr, info_ptr, &background);
1379
background - background color (PNG_VALID_bKGD)
1380
valid 16-bit red, green and blue
1381
values, regardless of color_type
1383
num_comments = png_get_text(png_ptr, info_ptr,
1384
&text_ptr, &num_text);
1385
num_comments - number of comments
1386
text_ptr - array of png_text holding image
1388
text_ptr[i].compression - type of compression used
1389
on "text" PNG_TEXT_COMPRESSION_NONE
1390
PNG_TEXT_COMPRESSION_zTXt
1391
PNG_ITXT_COMPRESSION_NONE
1392
PNG_ITXT_COMPRESSION_zTXt
1393
text_ptr[i].key - keyword for comment. Must contain
1395
text_ptr[i].text - text comments for current
1396
keyword. Can be empty.
1397
text_ptr[i].text_length - length of text string,
1398
after decompression, 0 for iTXt
1399
text_ptr[i].itxt_length - length of itxt string,
1400
after decompression, 0 for tEXt/zTXt
1401
text_ptr[i].lang - language of comment (empty
1402
string for unknown).
1403
text_ptr[i].lang_key - keyword in UTF-8
1404
(empty string for unknown).
1405
num_text - number of comments (same as
1406
num_comments; you can put NULL here
1407
to avoid the duplication)
1408
Note while png_set_text() will accept text, language,
1409
and translated keywords that can be NULL pointers, the
1410
structure returned by png_get_text will always contain
1411
regular zero-terminated C strings. They might be
1412
empty strings but they will never be NULL pointers.
1414
num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1416
palette_ptr - array of palette structures holding
1417
contents of one or more sPLT chunks
1419
num_spalettes - number of sPLT chunks read.
1421
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1423
offset_x - positive offset from the left edge
1425
offset_y - positive offset from the top edge
1427
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1429
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1431
res_x - pixels/unit physical resolution in
1433
res_y - pixels/unit physical resolution in
1435
unit_type - PNG_RESOLUTION_UNKNOWN,
1436
PNG_RESOLUTION_METER
1438
png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1440
unit - physical scale units (an integer)
1441
width - width of a pixel in physical scale units
1442
height - height of a pixel in physical scale units
1443
(width and height are doubles)
1445
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1447
unit - physical scale units (an integer)
1448
width - width of a pixel in physical scale units
1449
height - height of a pixel in physical scale units
1450
(width and height are strings like "2.54")
1452
num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1453
info_ptr, &unknowns)
1454
unknowns - array of png_unknown_chunk
1455
structures holding unknown chunks
1456
unknowns[i].name - name of unknown chunk
1457
unknowns[i].data - data of unknown chunk
1458
unknowns[i].size - size of unknown chunk's data
1459
unknowns[i].location - position of chunk in file
1461
The value of "i" corresponds to the order in which the
1462
chunks were read from the PNG file or inserted with the
1463
png_set_unknown_chunks() function.
1465
The data from the pHYs chunk can be retrieved in several convenient
1468
res_x = png_get_x_pixels_per_meter(png_ptr,
1470
res_y = png_get_y_pixels_per_meter(png_ptr,
1472
res_x_and_y = png_get_pixels_per_meter(png_ptr,
1474
res_x = png_get_x_pixels_per_inch(png_ptr,
1476
res_y = png_get_y_pixels_per_inch(png_ptr,
1478
res_x_and_y = png_get_pixels_per_inch(png_ptr,
1480
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1483
(Each of these returns 0 [signifying "unknown"] if
1484
the data is not present or if res_x is 0;
1485
res_x_and_y is 0 if res_x != res_y)
1487
The data from the oFFs chunk can be retrieved in several convenient
1490
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1491
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1492
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1493
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1495
(Each of these returns 0 [signifying "unknown" if both
1496
x and y are 0] if the data is not present or if the
1497
chunk is present but the unit is the pixel)
1499
For more information, see the png_info definition in png.h and the
1500
PNG specification for chunk contents. Be careful with trusting
1501
rowbytes, as some of the transformations could increase the space
1502
needed to hold a row (expand, filler, gray_to_rgb, etc.).
1503
See png_read_update_info(), below.
1505
A quick word about text_ptr and num_text. PNG stores comments in
1506
keyword/text pairs, one pair per chunk, with no limit on the number
1507
of text chunks, and a 2^31 byte limit on their size. While there are
1508
suggested keywords, there is no requirement to restrict the use to these
1509
strings. It is strongly suggested that keywords and text be sensible
1510
to humans (that's the point), so don't use abbreviations. Non-printing
1511
symbols are not allowed. See the PNG specification for more details.
1512
There is also no requirement to have text after the keyword.
1514
Keywords should be limited to 79 Latin-1 characters without leading or
1515
trailing spaces, but non-consecutive spaces are allowed within the
1516
keyword. It is possible to have the same keyword any number of times.
1517
The text_ptr is an array of png_text structures, each holding a
1518
pointer to a language string, a pointer to a keyword and a pointer to
1519
a text string. The text string, language code, and translated
1520
keyword may be empty or NULL pointers. The keyword/text
1521
pairs are put into the array in the order that they are received.
1522
However, some or all of the text chunks may be after the image, so, to
1523
make sure you have read all the text chunks, don't mess with these
1524
until after you read the stuff after the image. This will be
1525
mentioned again below in the discussion that goes with png_read_end().
1527
.SS Input transformations
1529
After you've read the header information, you can set up the library
1530
to handle any special transformations of the image data. The various
1531
ways to transform the data will be described in the order that they
1532
should occur. This is important, as some of these change the color
1533
type and/or bit depth of the data, and some others only work on
1534
certain color types and bit depths. Even though each transformation
1535
checks to see if it has data that it can do something with, you should
1536
make sure to only enable a transformation if it will be valid for the
1537
data. For example, don't swap red and blue on grayscale data.
1539
The colors used for the background and transparency values should be
1540
supplied in the same format/depth as the current image data. They
1541
are stored in the same format/depth as the image data in a bKGD or tRNS
1542
chunk, so this is what libpng expects for this data. The colors are
1543
transformed to keep in sync with the image data when an application
1544
calls the png_read_update_info() routine (see below).
1546
Data will be decoded into the supplied row buffers packed into bytes
1547
unless the library has been told to transform it into another format.
1548
For example, 4 bit/pixel paletted or grayscale data will be returned
1549
2 pixels/byte with the leftmost pixel in the high-order bits of the
1550
byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1551
in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1552
is called to insert filler bytes, either before or after each RGB triplet.
1553
16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1554
byte of the color value first, unless png_set_strip_16() is called to
1555
transform it to regular RGB RGB triplets, or png_set_filler|add alpha()
1556
is called to insert filler bytes, either before or after each RRGGBB
1557
triplet. Similarly, 8-bit or 16-bit grayscale data can be modified with
1558
png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1560
The following code transforms grayscale images of less than 8 to 8 bits,
1561
changes paletted images to RGB, and adds a full alpha channel if there is
1562
transparency information in a tRNS chunk. This is most useful on
1563
grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1564
viewing application that wishes to treat all images in the same way.
1566
if (color_type == PNG_COLOR_TYPE_PALETTE)
1567
png_set_palette_to_rgb(png_ptr);
1569
if (color_type == PNG_COLOR_TYPE_GRAY &&
1570
bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1572
if (png_get_valid(png_ptr, info_ptr,
1573
PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1575
These three functions are actually aliases for png_set_expand(), added
1576
in libpng version 1.0.4, with the function names expanded to improve code
1577
readability. In some future version they may actually do different
1580
PNG can have files with 16 bits per channel. If you only can handle
1581
8 bits per channel, this will strip the pixels down to 8 bit.
1583
if (bit_depth == 16)
1584
png_set_strip_16(png_ptr);
1586
If, for some reason, you don't need the alpha channel on an image,
1587
and you want to remove it rather than combining it with the background
1588
(but the image author certainly had in mind that you *would* combine
1589
it with the background, so that's what you should probably do):
1591
if (color_type & PNG_COLOR_MASK_ALPHA)
1592
png_set_strip_alpha(png_ptr);
1594
In PNG files, the alpha channel in an image
1595
is the level of opacity. If you need the alpha channel in an image to
1596
be the level of transparency instead of opacity, you can invert the
1597
alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1598
fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1599
images) is fully transparent, with
1601
png_set_invert_alpha(png_ptr);
1603
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1604
they can, resulting in, for example, 8 pixels per byte for 1 bit
1605
files. This code expands to 1 pixel per byte without changing the
1606
values of the pixels:
1609
png_set_packing(png_ptr);
1611
PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1612
stored in a PNG image have been "scaled" or "shifted" up to the next
1613
higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1614
8 bits/sample in the range [0, 255]). However, it is also possible to
1615
convert the PNG pixel data back to the original bit depth of the image.
1616
This call reduces the pixels back down to the original bit depth:
1618
png_color_8p sig_bit;
1620
if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1621
png_set_shift(png_ptr, sig_bit);
1623
PNG files store 3-color pixels in red, green, blue order. This code
1624
changes the storage of the pixels to blue, green, red:
1626
if (color_type == PNG_COLOR_TYPE_RGB ||
1627
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1628
png_set_bgr(png_ptr);
1630
PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1631
into 4 or 8 bytes for windowing systems that need them in this format:
1633
if (color_type == PNG_COLOR_TYPE_RGB)
1634
png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1636
where "filler" is the 8 or 16-bit number to fill with, and the location is
1637
either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1638
you want the filler before the RGB or after. This transformation
1639
does not affect images that already have full alpha channels. To add an
1640
opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1641
will generate RGBA pixels.
1643
Note that png_set_filler() does not change the color type. If you want
1644
to do that, you can add a true alpha channel with
1646
if (color_type == PNG_COLOR_TYPE_RGB ||
1647
color_type == PNG_COLOR_TYPE_GRAY)
1648
png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1650
where "filler" contains the alpha value to assign to each pixel.
1651
This function became available in libpng-1.2.7.
1653
If you are reading an image with an alpha channel, and you need the
1654
data as ARGB instead of the normal PNG format RGBA:
1656
if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1657
png_set_swap_alpha(png_ptr);
1659
For some uses, you may want a grayscale image to be represented as
1660
RGB. This code will do that conversion:
1662
if (color_type == PNG_COLOR_TYPE_GRAY ||
1663
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1664
png_set_gray_to_rgb(png_ptr);
1666
Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1669
if (color_type == PNG_COLOR_TYPE_RGB ||
1670
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1671
png_set_rgb_to_gray_fixed(png_ptr, error_action,
1672
int red_weight, int green_weight);
1674
error_action = 1: silently do the conversion
1675
error_action = 2: issue a warning if the original
1676
image has any pixel where
1677
red != green or red != blue
1678
error_action = 3: issue an error and abort the
1679
conversion if the original
1680
image has any pixel where
1681
red != green or red != blue
1683
red_weight: weight of red component times 100000
1684
green_weight: weight of green component times 100000
1685
If either weight is negative, default
1686
weights (21268, 71514) are used.
1688
If you have set error_action = 1 or 2, you can
1689
later check whether the image really was gray, after processing
1690
the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1691
It will return a png_byte that is zero if the image was gray or
1692
1 if there were any non-gray pixels. bKGD and sBIT data
1693
will be silently converted to grayscale, using the green channel
1694
data, regardless of the error_action setting.
1696
With red_weight+green_weight<=100000,
1697
the normalized graylevel is computed:
1699
int rw = red_weight * 65536;
1700
int gw = green_weight * 65536;
1701
int bw = 65536 - (rw + gw);
1702
gray = (rw*red + gw*green + bw*blue)/65536;
1704
The default values approximate those recommended in the Charles
1705
Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1706
Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1708
Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1710
Libpng approximates this with
1712
Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1714
which can be expressed with integers as
1716
Y = (6969 * R + 23434 * G + 2365 * B)/32768
1718
The calculation is done in a linear colorspace, if the image gamma
1721
If you have a grayscale and you are using png_set_expand_depth(),
1722
png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1723
a higher bit-depth, you must either supply the background color as a gray
1724
value at the original file bit-depth (need_expand = 1) or else supply the
1725
background color as an RGB triplet at the final, expanded bit depth
1726
(need_expand = 0). Similarly, if you are reading a paletted image, you
1727
must either supply the background color as a palette index (need_expand = 1)
1728
or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1730
png_color_16 my_background;
1731
png_color_16p image_background;
1733
if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1734
png_set_background(png_ptr, image_background,
1735
PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1737
png_set_background(png_ptr, &my_background,
1738
PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1740
The png_set_background() function tells libpng to composite images
1741
with alpha or simple transparency against the supplied background
1742
color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1743
you may use this color, or supply another color more suitable for
1744
the current display (e.g., the background color from a web page). You
1745
need to tell libpng whether the color is in the gamma space of the
1746
display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1747
(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1748
that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1749
know why anyone would use this, but it's here).
1751
To properly display PNG images on any kind of system, the application needs
1752
to know what the display gamma is. Ideally, the user will know this, and
1753
the application will allow them to set it. One method of allowing the user
1754
to set the display gamma separately for each system is to check for a
1755
SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1758
Note that display_gamma is the overall gamma correction required to produce
1759
pleasing results, which depends on the lighting conditions in the surrounding
1760
environment. In a dim or brightly lit room, no compensation other than
1761
the physical gamma exponent of the monitor is needed, while in a dark room
1762
a slightly smaller exponent is better.
1764
double gamma, screen_gamma;
1766
if (/* We have a user-defined screen
1769
screen_gamma = user_defined_screen_gamma;
1771
/* One way that applications can share the same
1772
screen gamma value */
1773
else if ((gamma_str = getenv("SCREEN_GAMMA"))
1776
screen_gamma = (double)atof(gamma_str);
1778
/* If we don't have another value */
1781
screen_gamma = 2.2; /* A good guess for a
1782
PC monitor in a bright office or a dim room */
1783
screen_gamma = 2.0; /* A good guess for a
1784
PC monitor in a dark room */
1785
screen_gamma = 1.7 or 1.0; /* A good
1786
guess for Mac systems */
1789
The png_set_gamma() function handles gamma transformations of the data.
1790
Pass both the file gamma and the current screen_gamma. If the file does
1791
not have a gamma value, you can pass one anyway if you have an idea what
1792
it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1793
that file gammas are inverted from screen gammas. See the discussions
1794
on gamma in the PNG specification for an excellent description of what
1795
gamma is, and why all applications should support it. It is strongly
1796
recommended that PNG viewers support gamma correction.
1798
if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1799
png_set_gamma(png_ptr, screen_gamma, gamma);
1801
png_set_gamma(png_ptr, screen_gamma, 0.45455);
1803
If you need to reduce an RGB file to a paletted file, or if a paletted
1804
file has more entries then will fit on your screen, png_set_dither()
1805
will do that. Note that this is a simple match dither that merely
1806
finds the closest color available. This should work fairly well with
1807
optimized palettes, and fairly badly with linear color cubes. If you
1808
pass a palette that is larger then maximum_colors, the file will
1809
reduce the number of colors in the palette so it will fit into
1810
maximum_colors. If there is a histogram, it will use it to make
1811
more intelligent choices when reducing the palette. If there is no
1812
histogram, it may not do as good a job.
1814
if (color_type & PNG_COLOR_MASK_COLOR)
1816
if (png_get_valid(png_ptr, info_ptr,
1819
png_uint_16p histogram = NULL;
1821
png_get_hIST(png_ptr, info_ptr,
1823
png_set_dither(png_ptr, palette, num_palette,
1824
max_screen_colors, histogram, 1);
1828
png_color std_color_cube[MAX_SCREEN_COLORS] =
1831
png_set_dither(png_ptr, std_color_cube,
1832
MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1837
PNG files describe monochrome as black being zero and white being one.
1838
The following code will reverse this (make black be one and white be
1841
if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1842
png_set_invert_mono(png_ptr);
1844
This function can also be used to invert grayscale and gray-alpha images:
1846
if (color_type == PNG_COLOR_TYPE_GRAY ||
1847
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1848
png_set_invert_mono(png_ptr);
1850
PNG files store 16 bit pixels in network byte order (big-endian,
1851
ie. most significant bits first). This code changes the storage to the
1852
other way (little-endian, i.e. least significant bits first, the
1853
way PCs store them):
1855
if (bit_depth == 16)
1856
png_set_swap(png_ptr);
1858
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1859
need to change the order the pixels are packed into bytes, you can use:
1862
png_set_packswap(png_ptr);
1864
Finally, you can write your own transformation function if none of
1865
the existing ones meets your needs. This is done by setting a callback
1868
png_set_read_user_transform_fn(png_ptr,
1871
You must supply the function
1873
void read_transform_fn(png_ptr ptr, row_info_ptr
1874
row_info, png_bytep data)
1876
See pngtest.c for a working example. Your function will be called
1877
after all of the other transformations have been processed.
1879
You can also set up a pointer to a user structure for use by your
1880
callback function, and you can inform libpng that your transform
1881
function will change the number of channels or bit depth with the
1884
png_set_user_transform_info(png_ptr, user_ptr,
1885
user_depth, user_channels);
1887
The user's application, not libpng, is responsible for allocating and
1888
freeing any memory required for the user structure.
1890
You can retrieve the pointer via the function
1891
png_get_user_transform_ptr(). For example:
1893
voidp read_user_transform_ptr =
1894
png_get_user_transform_ptr(png_ptr);
1896
The last thing to handle is interlacing; this is covered in detail below,
1897
but you must call the function here if you want libpng to handle expansion
1898
of the interlaced image.
1900
number_of_passes = png_set_interlace_handling(png_ptr);
1902
After setting the transformations, libpng can update your png_info
1903
structure to reflect any transformations you've requested with this
1904
call. This is most useful to update the info structure's rowbytes
1905
field so you can use it to allocate your image memory. This function
1906
will also update your palette with the correct screen_gamma and
1907
background if these have been given with the calls above.
1909
png_read_update_info(png_ptr, info_ptr);
1911
After you call png_read_update_info(), you can allocate any
1912
memory you need to hold the image. The row data is simply
1913
raw byte data for all forms of images. As the actual allocation
1914
varies among applications, no example will be given. If you
1915
are allocating one large chunk, you will need to build an
1916
array of pointers to each row, as it will be needed for some
1917
of the functions below.
1919
.SS Reading image data
1921
After you've allocated memory, you can read the image data.
1922
The simplest way to do this is in one function call. If you are
1923
allocating enough memory to hold the whole image, you can just
1924
call png_read_image() and libpng will read in all the image data
1925
and put it in the memory area supplied. You will need to pass in
1926
an array of pointers to each row.
1928
This function automatically handles interlacing, so you don't need
1929
to call png_set_interlace_handling() or call this function multiple
1930
times, or any of that other stuff necessary with png_read_rows().
1932
png_read_image(png_ptr, row_pointers);
1934
where row_pointers is:
1936
png_bytep row_pointers[height];
1938
You can point to void or char or whatever you use for pixels.
1940
If you don't want to read in the whole image at once, you can
1941
use png_read_rows() instead. If there is no interlacing (check
1942
interlace_type == PNG_INTERLACE_NONE), this is simple:
1944
png_read_rows(png_ptr, row_pointers, NULL,
1947
where row_pointers is the same as in the png_read_image() call.
1949
If you are doing this just one row at a time, you can do this with
1950
a single row_pointer instead of an array of row_pointers:
1952
png_bytep row_pointer = row;
1953
png_read_row(png_ptr, row_pointer, NULL);
1955
If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1956
get somewhat harder. The only current (PNG Specification version 1.2)
1957
interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1958
is a somewhat complicated 2D interlace scheme, known as Adam7, that
1959
breaks down an image into seven smaller images of varying size, based
1962
libpng can fill out those images or it can give them to you "as is".
1963
If you want them filled out, there are two ways to do that. The one
1964
mentioned in the PNG specification is to expand each pixel to cover
1965
those pixels that have not been read yet (the "rectangle" method).
1966
This results in a blocky image for the first pass, which gradually
1967
smooths out as more pixels are read. The other method is the "sparkle"
1968
method, where pixels are drawn only in their final locations, with the
1969
rest of the image remaining whatever colors they were initialized to
1970
before the start of the read. The first method usually looks better,
1971
but tends to be slower, as there are more pixels to put in the rows.
1973
If you don't want libpng to handle the interlacing details, just call
1974
png_read_rows() seven times to read in all seven images. Each of the
1975
images is a valid image by itself, or they can all be combined on an
1976
8x8 grid to form a single image (although if you intend to combine them
1977
you would be far better off using the libpng interlace handling).
1979
The first pass will return an image 1/8 as wide as the entire image
1980
(every 8th column starting in column 0) and 1/8 as high as the original
1981
(every 8th row starting in row 0), the second will be 1/8 as wide
1982
(starting in column 4) and 1/8 as high (also starting in row 0). The
1983
third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
1984
1/8 as high (every 8th row starting in row 4), and the fourth pass will
1985
be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1986
and every 4th row starting in row 0). The fifth pass will return an
1987
image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1988
while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1989
(starting in column 1 and row 0). The seventh and final pass will be as
1990
wide as the original, and 1/2 as high, containing all of the odd
1991
numbered scanlines. Phew!
1993
If you want libpng to expand the images, call this before calling
1994
png_start_read_image() or png_read_update_info():
1996
if (interlace_type == PNG_INTERLACE_ADAM7)
1998
= png_set_interlace_handling(png_ptr);
2000
This will return the number of passes needed. Currently, this
2001
is seven, but may change if another interlace type is added.
2002
This function can be called even if the file is not interlaced,
2003
where it will return one pass.
2005
If you are not going to display the image after each pass, but are
2006
going to wait until the entire image is read in, use the sparkle
2007
effect. This effect is faster and the end result of either method
2008
is exactly the same. If you are planning on displaying the image
2009
after each pass, the "rectangle" effect is generally considered the
2012
If you only want the "sparkle" effect, just call png_read_rows() as
2013
normal, with the third parameter NULL. Make sure you make pass over
2014
the image number_of_passes times, and you don't change the data in the
2015
rows between calls. You can change the locations of the data, just
2016
not the data. Each pass only writes the pixels appropriate for that
2017
pass, and assumes the data from previous passes is still valid.
2019
png_read_rows(png_ptr, row_pointers, NULL,
2022
If you only want the first effect (the rectangles), do the same as
2023
before except pass the row buffer in the third parameter, and leave
2024
the second parameter NULL.
2026
png_read_rows(png_ptr, NULL, row_pointers,
2029
.SS Finishing a sequential read
2031
After you are finished reading the image through either the high- or
2032
low-level interfaces, you can finish reading the file. If you are
2033
interested in comments or time, which may be stored either before or
2034
after the image data, you should pass the separate png_info struct if
2035
you want to keep the comments from before and after the image
2036
separate. If you are not interested, you can pass NULL.
2038
png_read_end(png_ptr, end_info);
2040
When you are done, you can free all memory allocated by libpng like this:
2042
png_destroy_read_struct(&png_ptr, &info_ptr,
2045
It is also possible to individually free the info_ptr members that
2046
point to libpng-allocated storage with the following function:
2048
png_free_data(png_ptr, info_ptr, mask, seq)
2049
mask - identifies data to be freed, a mask
2050
containing the logical OR of one or
2052
PNG_FREE_PLTE, PNG_FREE_TRNS,
2053
PNG_FREE_HIST, PNG_FREE_ICCP,
2054
PNG_FREE_PCAL, PNG_FREE_ROWS,
2055
PNG_FREE_SCAL, PNG_FREE_SPLT,
2056
PNG_FREE_TEXT, PNG_FREE_UNKN,
2057
or simply PNG_FREE_ALL
2058
seq - sequence number of item to be freed
2061
This function may be safely called when the relevant storage has
2062
already been freed, or has not yet been allocated, or was allocated
2063
by the user and not by libpng, and will in those
2064
cases do nothing. The "seq" parameter is ignored if only one item
2065
of the selected data type, such as PLTE, is allowed. If "seq" is not
2066
-1, and multiple items are allowed for the data type identified in
2067
the mask, such as text or sPLT, only the n'th item in the structure
2068
is freed, where n is "seq".
2070
The default behavior is only to free data that was allocated internally
2071
by libpng. This can be changed, so that libpng will not free the data,
2072
or so that it will free data that was allocated by the user with png_malloc()
2073
or png_zalloc() and passed in via a png_set_*() function, with
2075
png_data_freer(png_ptr, info_ptr, freer, mask)
2076
mask - which data elements are affected
2077
same choices as in png_free_data()
2079
PNG_DESTROY_WILL_FREE_DATA
2080
PNG_SET_WILL_FREE_DATA
2081
PNG_USER_WILL_FREE_DATA
2083
This function only affects data that has already been allocated.
2084
You can call this function after reading the PNG data but before calling
2085
any png_set_*() functions, to control whether the user or the png_set_*()
2086
function is responsible for freeing any existing data that might be present,
2087
and again after the png_set_*() functions to control whether the user
2088
or png_destroy_*() is supposed to free the data. When the user assumes
2089
responsibility for libpng-allocated data, the application must use
2090
png_free() to free it, and when the user transfers responsibility to libpng
2091
for data that the user has allocated, the user must have used png_malloc()
2092
or png_zalloc() to allocate it.
2094
If you allocated your row_pointers in a single block, as suggested above in
2095
the description of the high level read interface, you must not transfer
2096
responsibility for freeing it to the png_set_rows or png_read_destroy function,
2097
because they would also try to free the individual row_pointers[i].
2099
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2100
separately, do not transfer responsibility for freeing text_ptr to libpng,
2101
because when libpng fills a png_text structure it combines these members with
2102
the key member, and png_free_data() will free only text_ptr.key. Similarly,
2103
if you transfer responsibility for free'ing text_ptr from libpng to your
2104
application, your application must not separately free those members.
2106
The png_free_data() function will turn off the "valid" flag for anything
2107
it frees. If you need to turn the flag off for a chunk that was freed by your
2108
application instead of by libpng, you can use
2110
png_set_invalid(png_ptr, info_ptr, mask);
2111
mask - identifies the chunks to be made invalid,
2112
containing the logical OR of one or
2114
PNG_INFO_gAMA, PNG_INFO_sBIT,
2115
PNG_INFO_cHRM, PNG_INFO_PLTE,
2116
PNG_INFO_tRNS, PNG_INFO_bKGD,
2117
PNG_INFO_hIST, PNG_INFO_pHYs,
2118
PNG_INFO_oFFs, PNG_INFO_tIME,
2119
PNG_INFO_pCAL, PNG_INFO_sRGB,
2120
PNG_INFO_iCCP, PNG_INFO_sPLT,
2121
PNG_INFO_sCAL, PNG_INFO_IDAT
2123
For a more compact example of reading a PNG image, see the file example.c.
2125
.SS Reading PNG files progressively
2127
The progressive reader is slightly different then the non-progressive
2128
reader. Instead of calling png_read_info(), png_read_rows(), and
2129
png_read_end(), you make one call to png_process_data(), which calls
2130
callbacks when it has the info, a row, or the end of the image. You
2131
set up these callbacks with png_set_progressive_read_fn(). You don't
2132
have to worry about the input/output functions of libpng, as you are
2133
giving the library the data directly in png_process_data(). I will
2134
assume that you have read the section on reading PNG files above,
2135
so I will only highlight the differences (although I will show
2138
png_structp png_ptr;
2141
/* An example code fragment of how you would
2142
initialize the progressive reader in your
2145
initialize_png_reader()
2147
png_ptr = png_create_read_struct
2148
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2149
user_error_fn, user_warning_fn);
2152
info_ptr = png_create_info_struct(png_ptr);
2155
png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2160
if (setjmp(png_jmpbuf(png_ptr)))
2162
png_destroy_read_struct(&png_ptr, &info_ptr,
2167
/* This one's new. You can provide functions
2168
to be called when the header info is valid,
2169
when each row is completed, and when the image
2170
is finished. If you aren't using all functions,
2171
you can specify NULL parameters. Even when all
2172
three functions are NULL, you need to call
2173
png_set_progressive_read_fn(). You can use
2174
any struct as the user_ptr (cast to a void pointer
2175
for the function call), and retrieve the pointer
2176
from inside the callbacks using the function
2178
png_get_progressive_ptr(png_ptr);
2180
which will return a void pointer, which you have
2181
to cast appropriately.
2183
png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2184
info_callback, row_callback, end_callback);
2189
/* A code fragment that you call as you receive blocks
2192
process_data(png_bytep buffer, png_uint_32 length)
2194
if (setjmp(png_jmpbuf(png_ptr)))
2196
png_destroy_read_struct(&png_ptr, &info_ptr,
2201
/* This one's new also. Simply give it a chunk
2202
of data from the file stream (in order, of
2203
course). On machines with segmented memory
2204
models machines, don't give it any more than
2205
64K. The library seems to run fine with sizes
2206
of 4K. Although you can give it much less if
2207
necessary (I assume you can give it chunks of
2208
1 byte, I haven't tried less then 256 bytes
2209
yet). When this function returns, you may
2210
want to display any rows that were generated
2211
in the row callback if you don't already do
2214
png_process_data(png_ptr, info_ptr, buffer, length);
2218
/* This function is called (as set by
2219
png_set_progressive_read_fn() above) when enough data
2220
has been supplied so all of the header has been
2224
info_callback(png_structp png_ptr, png_infop info)
2226
/* Do any setup here, including setting any of
2227
the transformations mentioned in the Reading
2228
PNG files section. For now, you _must_ call
2229
either png_start_read_image() or
2230
png_read_update_info() after all the
2231
transformations are set (even if you don't set
2232
any). You may start getting rows before
2233
png_process_data() returns, so this is your
2234
last chance to prepare for that.
2238
/* This function is called when each row of image
2241
row_callback(png_structp png_ptr, png_bytep new_row,
2242
png_uint_32 row_num, int pass)
2244
/* If the image is interlaced, and you turned
2245
on the interlace handler, this function will
2246
be called for every row in every pass. Some
2247
of these rows will not be changed from the
2248
previous pass. When the row is not changed,
2249
the new_row variable will be NULL. The rows
2250
and passes are called in order, so you don't
2251
really need the row_num and pass, but I'm
2252
supplying them because it may make your life
2255
For the non-NULL rows of interlaced images,
2256
you must call png_progressive_combine_row()
2257
passing in the row and the old row. You can
2258
call this function for NULL rows (it will just
2259
return) and for non-interlaced images (it just
2260
does the memcpy for you) if it will make the
2261
code easier. Thus, you can just do this for
2265
png_progressive_combine_row(png_ptr, old_row,
2268
/* where old_row is what was displayed for
2269
previously for the row. Note that the first
2270
pass (pass == 0, really) will completely cover
2271
the old row, so the rows do not have to be
2272
initialized. After the first pass (and only
2273
for interlaced images), you will have to pass
2274
the current row, and the function will combine
2275
the old row and the new row.
2280
end_callback(png_structp png_ptr, png_infop info)
2282
/* This function is called after the whole image
2283
has been read, including any chunks after the
2284
image (up to and including the IEND). You
2285
will usually have the same info chunk as you
2286
had in the header, although some data may have
2287
been added to the comments and time fields.
2289
Most people won't do much here, perhaps setting
2290
a flag that marks the image as finished.
2298
Much of this is very similar to reading. However, everything of
2299
importance is repeated here, so you won't have to constantly look
2300
back up in the reading section to understand writing.
2304
You will want to do the I/O initialization before you get into libpng,
2305
so if it doesn't work, you don't have anything to undo. If you are not
2306
using the standard I/O functions, you will need to replace them with
2307
custom writing functions. See the discussion under Customizing libpng.
2309
FILE *fp = fopen(file_name, "wb");
2315
Next, png_struct and png_info need to be allocated and initialized.
2316
As these can be both relatively large, you may not want to store these
2317
on the stack, unless you have stack space to spare. Of course, you
2318
will want to check if they return NULL. If you are also reading,
2319
you won't want to name your read structure and your write structure
2320
both "png_ptr"; you can call them anything you like, such as
2321
"read_ptr" and "write_ptr". Look at pngtest.c, for example.
2323
png_structp png_ptr = png_create_write_struct
2324
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2325
user_error_fn, user_warning_fn);
2329
png_infop info_ptr = png_create_info_struct(png_ptr);
2332
png_destroy_write_struct(&png_ptr,
2337
If you want to use your own memory allocation routines,
2338
define PNG_USER_MEM_SUPPORTED and use
2339
png_create_write_struct_2() instead of png_create_write_struct():
2341
png_structp png_ptr = png_create_write_struct_2
2342
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2343
user_error_fn, user_warning_fn, (png_voidp)
2344
user_mem_ptr, user_malloc_fn, user_free_fn);
2346
After you have these structures, you will need to set up the
2347
error handling. When libpng encounters an error, it expects to
2348
longjmp() back to your routine. Therefore, you will need to call
2349
setjmp() and pass the png_jmpbuf(png_ptr). If you
2350
write the file from different routines, you will need to update
2351
the png_jmpbuf(png_ptr) every time you enter a new routine that will
2352
call a png_*() function. See your documentation of setjmp/longjmp
2353
for your compiler for more information on setjmp/longjmp. See
2354
the discussion on libpng error handling in the Customizing Libpng
2355
section below for more information on the libpng error handling.
2357
if (setjmp(png_jmpbuf(png_ptr)))
2359
png_destroy_write_struct(&png_ptr, &info_ptr);
2366
If you would rather avoid the complexity of setjmp/longjmp issues,
2367
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2368
errors will result in a call to PNG_ABORT() which defaults to abort().
2370
Now you need to set up the output code. The default for libpng is to
2371
use the C function fwrite(). If you use this, you will need to pass a
2372
valid FILE * in the function png_init_io(). Be sure that the file is
2373
opened in binary mode. Again, if you wish to handle writing data in
2374
another way, see the discussion on libpng I/O handling in the Customizing
2375
Libpng section below.
2377
png_init_io(png_ptr, fp);
2381
At this point, you can set up a callback function that will be
2382
called after each row has been written, which you can use to control
2383
a progress meter or the like. It's demonstrated in pngtest.c.
2384
You must supply a function
2386
void write_row_callback(png_ptr, png_uint_32 row,
2389
/* put your code here */
2392
(You can give it another name that you like instead of "write_row_callback")
2394
To inform libpng about your function, use
2396
png_set_write_status_fn(png_ptr, write_row_callback);
2398
You now have the option of modifying how the compression library will
2399
run. The following functions are mainly for testing, but may be useful
2400
in some cases, like if you need to write PNG files extremely fast and
2401
are willing to give up some compression, or if you want to get the
2402
maximum possible compression at the expense of slower writing. If you
2403
have no special needs in this area, let the library do what it wants by
2404
not calling this function at all, as it has been tuned to deliver a good
2405
speed/compression ratio. The second parameter to png_set_filter() is
2406
the filter method, for which the only valid values are 0 (as of the
2407
July 1999 PNG specification, version 1.2) or 64 (if you are writing
2408
a PNG datastream that is to be embedded in a MNG datastream). The third
2409
parameter is a flag that indicates which filter type(s) are to be tested
2410
for each scanline. See the PNG specification for details on the specific filter
2414
/* turn on or off filtering, and/or choose
2415
specific filters. You can use either a single
2416
PNG_FILTER_VALUE_NAME or the logical OR of one
2417
or more PNG_FILTER_NAME masks. */
2418
png_set_filter(png_ptr, 0,
2419
PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2420
PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2421
PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2422
PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2423
PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2427
wants to start and stop using particular filters during compression,
2428
it should start out with all of the filters (to ensure that the previous
2429
row of pixels will be stored in case it's needed later), and then add
2430
and remove them after the start of compression.
2432
If you are writing a PNG datastream that is to be embedded in a MNG
2433
datastream, the second parameter can be either 0 or 64.
2435
The png_set_compression_*() functions interface to the zlib compression
2436
library, and should mostly be ignored unless you really know what you are
2437
doing. The only generally useful call is png_set_compression_level()
2438
which changes how much time zlib spends on trying to compress the image
2439
data. See the Compression Library (zlib.h and algorithm.txt, distributed
2440
with zlib) for details on the compression levels.
2442
/* set the zlib compression level */
2443
png_set_compression_level(png_ptr,
2444
Z_BEST_COMPRESSION);
2446
/* set other zlib parameters */
2447
png_set_compression_mem_level(png_ptr, 8);
2448
png_set_compression_strategy(png_ptr,
2449
Z_DEFAULT_STRATEGY);
2450
png_set_compression_window_bits(png_ptr, 15);
2451
png_set_compression_method(png_ptr, 8);
2452
png_set_compression_buffer_size(png_ptr, 8192)
2454
extern PNG_EXPORT(void,png_set_zbuf_size)
2456
.SS Setting the contents of info for output
2458
You now need to fill in the png_info structure with all the data you
2459
wish to write before the actual image. Note that the only thing you
2460
are allowed to write after the image is the text chunks and the time
2461
chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2462
the latest PNG specification for more information on that. If you
2463
wish to write them before the image, fill them in now, and flag that
2464
data as being valid. If you want to wait until after the data, don't
2465
fill them until png_write_end(). For all the fields in png_info and
2466
their data types, see png.h. For explanations of what the fields
2467
contain, see the PNG specification.
2469
Some of the more important parts of the png_info are:
2471
png_set_IHDR(png_ptr, info_ptr, width, height,
2472
bit_depth, color_type, interlace_type,
2473
compression_type, filter_method)
2474
width - holds the width of the image
2475
in pixels (up to 2^31).
2476
height - holds the height of the image
2477
in pixels (up to 2^31).
2478
bit_depth - holds the bit depth of one of the
2480
(valid values are 1, 2, 4, 8, 16
2481
and depend also on the
2482
color_type. See also significant
2484
color_type - describes which color/alpha
2485
channels are present.
2487
(bit depths 1, 2, 4, 8, 16)
2488
PNG_COLOR_TYPE_GRAY_ALPHA
2490
PNG_COLOR_TYPE_PALETTE
2491
(bit depths 1, 2, 4, 8)
2494
PNG_COLOR_TYPE_RGB_ALPHA
2497
PNG_COLOR_MASK_PALETTE
2498
PNG_COLOR_MASK_COLOR
2499
PNG_COLOR_MASK_ALPHA
2501
interlace_type - PNG_INTERLACE_NONE or
2503
compression_type - (must be
2504
PNG_COMPRESSION_TYPE_DEFAULT)
2505
filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2506
or, if you are writing a PNG to
2507
be embedded in a MNG datastream,
2509
PNG_INTRAPIXEL_DIFFERENCING)
2511
png_set_PLTE(png_ptr, info_ptr, palette,
2513
palette - the palette for the file
2514
(array of png_color)
2515
num_palette - number of entries in the palette
2517
png_set_gAMA(png_ptr, info_ptr, gamma);
2518
gamma - the gamma the image was created
2521
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2522
srgb_intent - the rendering intent
2523
(PNG_INFO_sRGB) The presence of
2524
the sRGB chunk means that the pixel
2525
data is in the sRGB color space.
2526
This chunk also implies specific
2527
values of gAMA and cHRM. Rendering
2528
intent is the CSS-1 property that
2529
has been defined by the International
2531
(http://www.color.org).
2533
PNG_sRGB_INTENT_SATURATION,
2534
PNG_sRGB_INTENT_PERCEPTUAL,
2535
PNG_sRGB_INTENT_ABSOLUTE, or
2536
PNG_sRGB_INTENT_RELATIVE.
2539
png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2541
srgb_intent - the rendering intent
2542
(PNG_INFO_sRGB) The presence of the
2543
sRGB chunk means that the pixel
2544
data is in the sRGB color space.
2545
This function also causes gAMA and
2546
cHRM chunks with the specific values
2547
that are consistent with sRGB to be
2550
png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2552
name - The profile name.
2553
compression - The compression type; always
2554
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2555
You may give NULL to this argument to
2557
profile - International Color Consortium color
2558
profile data. May contain NULs.
2559
proflen - length of profile data in bytes.
2561
png_set_sBIT(png_ptr, info_ptr, sig_bit);
2562
sig_bit - the number of significant bits for
2563
(PNG_INFO_sBIT) each of the gray, red,
2564
green, and blue channels, whichever are
2565
appropriate for the given color type
2568
png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2570
trans - array of transparent entries for
2571
palette (PNG_INFO_tRNS)
2572
trans_values - graylevel or color sample values of
2573
the single transparent color for
2574
non-paletted images (PNG_INFO_tRNS)
2575
num_trans - number of transparent entries
2578
png_set_hIST(png_ptr, info_ptr, hist);
2580
hist - histogram of palette (array of
2583
png_set_tIME(png_ptr, info_ptr, mod_time);
2584
mod_time - time image was last modified
2587
png_set_bKGD(png_ptr, info_ptr, background);
2588
background - background color (PNG_VALID_bKGD)
2590
png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2591
text_ptr - array of png_text holding image
2593
text_ptr[i].compression - type of compression used
2594
on "text" PNG_TEXT_COMPRESSION_NONE
2595
PNG_TEXT_COMPRESSION_zTXt
2596
PNG_ITXT_COMPRESSION_NONE
2597
PNG_ITXT_COMPRESSION_zTXt
2598
text_ptr[i].key - keyword for comment. Must contain
2600
text_ptr[i].text - text comments for current
2601
keyword. Can be NULL or empty.
2602
text_ptr[i].text_length - length of text string,
2603
after decompression, 0 for iTXt
2604
text_ptr[i].itxt_length - length of itxt string,
2605
after decompression, 0 for tEXt/zTXt
2606
text_ptr[i].lang - language of comment (NULL or
2608
text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2609
or empty for unknown).
2610
num_text - number of comments
2612
png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2614
palette_ptr - array of png_sPLT_struct structures
2615
to be added to the list of palettes
2616
in the info structure.
2617
num_spalettes - number of palette structures to be
2620
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2622
offset_x - positive offset from the left
2624
offset_y - positive offset from the top
2626
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2628
png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2630
res_x - pixels/unit physical resolution
2632
res_y - pixels/unit physical resolution
2634
unit_type - PNG_RESOLUTION_UNKNOWN,
2635
PNG_RESOLUTION_METER
2637
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2638
unit - physical scale units (an integer)
2639
width - width of a pixel in physical scale units
2640
height - height of a pixel in physical scale units
2641
(width and height are doubles)
2643
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2644
unit - physical scale units (an integer)
2645
width - width of a pixel in physical scale units
2646
height - height of a pixel in physical scale units
2647
(width and height are strings like "2.54")
2649
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2651
unknowns - array of png_unknown_chunk
2652
structures holding unknown chunks
2653
unknowns[i].name - name of unknown chunk
2654
unknowns[i].data - data of unknown chunk
2655
unknowns[i].size - size of unknown chunk's data
2656
unknowns[i].location - position to write chunk in file
2657
0: do not write chunk
2658
PNG_HAVE_IHDR: before PLTE
2659
PNG_HAVE_PLTE: before IDAT
2660
PNG_AFTER_IDAT: after IDAT
2662
The "location" member is set automatically according to
2663
what part of the output file has already been written.
2664
You can change its value after calling png_set_unknown_chunks()
2665
as demonstrated in pngtest.c. Within each of the "locations",
2666
the chunks are sequenced according to their position in the
2667
structure (that is, the value of "i", which is the order in which
2668
the chunk was either read from the input file or defined with
2669
png_set_unknown_chunks).
2671
A quick word about text and num_text. text is an array of png_text
2672
structures. num_text is the number of valid structures in the array.
2673
Each png_text structure holds a language code, a keyword, a text value,
2674
and a compression type.
2676
The compression types have the same valid numbers as the compression
2677
types of the image data. Currently, the only valid number is zero.
2678
However, you can store text either compressed or uncompressed, unlike
2679
images, which always have to be compressed. So if you don't want the
2680
text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2681
Because tEXt and zTXt chunks don't have a language field, if you
2682
specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2683
any language code or translated keyword will not be written out.
2685
Until text gets around 1000 bytes, it is not worth compressing it.
2686
After the text has been written out to the file, the compression type
2687
is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2688
so that it isn't written out again at the end (in case you are calling
2689
png_write_end() with the same struct.
2691
The keywords that are given in the PNG Specification are:
2693
Title Short (one line) title or
2695
Author Name of image's creator
2696
Description Description of image (possibly long)
2697
Copyright Copyright notice
2698
Creation Time Time of original image creation
2699
(usually RFC 1123 format, see below)
2700
Software Software used to create the image
2701
Disclaimer Legal disclaimer
2702
Warning Warning of nature of content
2703
Source Device used to create the image
2704
Comment Miscellaneous comment; conversion
2705
from other image format
2707
The keyword-text pairs work like this. Keywords should be short
2708
simple descriptions of what the comment is about. Some typical
2709
keywords are found in the PNG specification, as is some recommendations
2710
on keywords. You can repeat keywords in a file. You can even write
2711
some text before the image and some after. For example, you may want
2712
to put a description of the image before the image, but leave the
2713
disclaimer until after, so viewers working over modem connections
2714
don't have to wait for the disclaimer to go over the modem before
2715
they start seeing the image. Finally, keywords should be full
2716
words, not abbreviations. Keywords and text are in the ISO 8859-1
2717
(Latin-1) character set (a superset of regular ASCII) and can not
2718
contain NUL characters, and should not contain control or other
2719
unprintable characters. To make the comments widely readable, stick
2720
with basic ASCII, and avoid machine specific character set extensions
2721
like the IBM-PC character set. The keyword must be present, but
2722
you can leave off the text string on non-compressed pairs.
2723
Compressed pairs must have a text string, as only the text string
2724
is compressed anyway, so the compression would be meaningless.
2726
PNG supports modification time via the png_time structure. Two
2727
conversion routines are provided, png_convert_from_time_t() for
2728
time_t and png_convert_from_struct_tm() for struct tm. The
2729
time_t routine uses gmtime(). You don't have to use either of
2730
these, but if you wish to fill in the png_time structure directly,
2731
you should provide the time in universal time (GMT) if possible
2732
instead of your local time. Note that the year number is the full
2733
year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2734
that months start with 1.
2736
If you want to store the time of the original image creation, you should
2737
use a plain tEXt chunk with the "Creation Time" keyword. This is
2738
necessary because the "creation time" of a PNG image is somewhat vague,
2739
depending on whether you mean the PNG file, the time the image was
2740
created in a non-PNG format, a still photo from which the image was
2741
scanned, or possibly the subject matter itself. In order to facilitate
2742
machine-readable dates, it is recommended that the "Creation Time"
2743
tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2744
although this isn't a requirement. Unlike the tIME chunk, the
2745
"Creation Time" tEXt chunk is not expected to be automatically changed
2746
by the software. To facilitate the use of RFC 1123 dates, a function
2747
png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2748
time to an RFC 1123 format string.
2750
.SS Writing unknown chunks
2752
You can use the png_set_unknown_chunks function to queue up chunks
2753
for writing. You give it a chunk name, raw data, and a size; that's
2754
all there is to it. The chunks will be written by the next following
2755
png_write_info_before_PLTE, png_write_info, or png_write_end function.
2756
Any chunks previously read into the info structure's unknown-chunk
2757
list will also be written out in a sequence that satisfies the PNG
2758
specification's ordering rules.
2760
.SS The high-level write interface
2762
At this point there are two ways to proceed; through the high-level
2763
write interface, or through a sequence of low-level write operations.
2764
You can use the high-level interface if your image data is present
2765
in the info structure. All defined output
2766
transformations are permitted, enabled by the following masks.
2768
PNG_TRANSFORM_IDENTITY No transformation
2769
PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2770
PNG_TRANSFORM_PACKSWAP Change order of packed
2772
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2773
PNG_TRANSFORM_SHIFT Normalize pixels to the
2775
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2777
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2779
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2781
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2782
PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2784
If you have valid image data in the info structure (you can use
2785
png_set_rows() to put image data in the info structure), simply do this:
2787
png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2789
where png_transforms is an integer containing the logical OR of some set of
2790
transformation flags. This call is equivalent to png_write_info(),
2791
followed the set of transformations indicated by the transform mask,
2792
then png_write_image(), and finally png_write_end().
2794
(The final parameter of this call is not yet used. Someday it might point
2795
to transformation parameters required by some future output transform.)
2797
You must use png_transforms and not call any png_set_transform() functions
2798
when you use png_write_png().
2800
.SS The low-level write interface
2802
If you are going the low-level route instead, you are now ready to
2803
write all the file information up to the actual image data. You do
2804
this with a call to png_write_info().
2806
png_write_info(png_ptr, info_ptr);
2808
Note that there is one transformation you may need to do before
2809
png_write_info(). In PNG files, the alpha channel in an image is the
2810
level of opacity. If your data is supplied as a level of
2811
transparency, you can invert the alpha channel before you write it, so
2812
that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2813
65535 (in 16-bit images) is fully opaque, with
2815
png_set_invert_alpha(png_ptr);
2817
This must appear before png_write_info() instead of later with the
2818
other transformations because in the case of paletted images the tRNS
2819
chunk data has to be inverted before the tRNS chunk is written. If
2820
your image is not a paletted image, the tRNS data (which in such cases
2821
represents a single color to be rendered as transparent) won't need to
2822
be changed, and you can safely do this transformation after your
2823
png_write_info() call.
2825
If you need to write a private chunk that you want to appear before
2826
the PLTE chunk when PLTE is present, you can write the PNG info in
2827
two steps, and insert code to write your own chunk between them:
2829
png_write_info_before_PLTE(png_ptr, info_ptr);
2830
png_set_unknown_chunks(png_ptr, info_ptr, ...);
2831
png_write_info(png_ptr, info_ptr);
2833
After you've written the file information, you can set up the library
2834
to handle any special transformations of the image data. The various
2835
ways to transform the data will be described in the order that they
2836
should occur. This is important, as some of these change the color
2837
type and/or bit depth of the data, and some others only work on
2838
certain color types and bit depths. Even though each transformation
2839
checks to see if it has data that it can do something with, you should
2840
make sure to only enable a transformation if it will be valid for the
2841
data. For example, don't swap red and blue on grayscale data.
2843
PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2844
the library to strip input data that has 4 or 8 bytes per pixel down
2845
to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2848
png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2850
where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2851
PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2852
is stored XRGB or RGBX.
2854
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2855
they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2856
If the data is supplied at 1 pixel per byte, use this code, which will
2857
correctly pack the pixels into a single byte:
2859
png_set_packing(png_ptr);
2861
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2862
data is of another bit depth, you can write an sBIT chunk into the
2863
file so that decoders can recover the original data if desired.
2865
/* Set the true bit depth of the image data */
2866
if (color_type & PNG_COLOR_MASK_COLOR)
2868
sig_bit.red = true_bit_depth;
2869
sig_bit.green = true_bit_depth;
2870
sig_bit.blue = true_bit_depth;
2874
sig_bit.gray = true_bit_depth;
2876
if (color_type & PNG_COLOR_MASK_ALPHA)
2878
sig_bit.alpha = true_bit_depth;
2881
png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2883
If the data is stored in the row buffer in a bit depth other than
2884
one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2885
this will scale the values to appear to be the correct bit depth as
2888
png_set_shift(png_ptr, &sig_bit);
2890
PNG files store 16 bit pixels in network byte order (big-endian,
2891
ie. most significant bits first). This code would be used if they are
2892
supplied the other way (little-endian, i.e. least significant bits
2893
first, the way PCs store them):
2896
png_set_swap(png_ptr);
2898
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2899
need to change the order the pixels are packed into bytes, you can use:
2902
png_set_packswap(png_ptr);
2904
PNG files store 3 color pixels in red, green, blue order. This code
2905
would be used if they are supplied as blue, green, red:
2907
png_set_bgr(png_ptr);
2909
PNG files describe monochrome as black being zero and white being
2910
one. This code would be used if the pixels are supplied with this reversed
2911
(black being one and white being zero):
2913
png_set_invert_mono(png_ptr);
2915
Finally, you can write your own transformation function if none of
2916
the existing ones meets your needs. This is done by setting a callback
2919
png_set_write_user_transform_fn(png_ptr,
2920
write_transform_fn);
2922
You must supply the function
2924
void write_transform_fn(png_ptr ptr, row_info_ptr
2925
row_info, png_bytep data)
2927
See pngtest.c for a working example. Your function will be called
2928
before any of the other transformations are processed.
2930
You can also set up a pointer to a user structure for use by your
2933
png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2935
The user_channels and user_depth parameters of this function are ignored
2936
when writing; you can set them to zero as shown.
2938
You can retrieve the pointer via the function png_get_user_transform_ptr().
2941
voidp write_user_transform_ptr =
2942
png_get_user_transform_ptr(png_ptr);
2944
It is possible to have libpng flush any pending output, either manually,
2945
or automatically after a certain number of lines have been written. To
2946
flush the output stream a single time call:
2948
png_write_flush(png_ptr);
2950
and to have libpng flush the output stream periodically after a certain
2951
number of scanlines have been written, call:
2953
png_set_flush(png_ptr, nrows);
2955
Note that the distance between rows is from the last time png_write_flush()
2956
was called, or the first row of the image if it has never been called.
2957
So if you write 50 lines, and then png_set_flush 25, it will flush the
2958
output on the next scanline, and every 25 lines thereafter, unless
2959
png_write_flush() is called before 25 more lines have been written.
2960
If nrows is too small (less than about 10 lines for a 640 pixel wide
2961
RGB image) the image compression may decrease noticeably (although this
2962
may be acceptable for real-time applications). Infrequent flushing will
2963
only degrade the compression performance by a few percent over images
2964
that do not use flushing.
2966
.SS Writing the image data
2968
That's it for the transformations. Now you can write the image data.
2969
The simplest way to do this is in one function call. If you have the
2970
whole image in memory, you can just call png_write_image() and libpng
2971
will write the image. You will need to pass in an array of pointers to
2972
each row. This function automatically handles interlacing, so you don't
2973
need to call png_set_interlace_handling() or call this function multiple
2974
times, or any of that other stuff necessary with png_write_rows().
2976
png_write_image(png_ptr, row_pointers);
2978
where row_pointers is:
2980
png_byte *row_pointers[height];
2982
You can point to void or char or whatever you use for pixels.
2984
If you don't want to write the whole image at once, you can
2985
use png_write_rows() instead. If the file is not interlaced,
2988
png_write_rows(png_ptr, row_pointers,
2991
row_pointers is the same as in the png_write_image() call.
2993
If you are just writing one row at a time, you can do this with
2994
a single row_pointer instead of an array of row_pointers:
2996
png_bytep row_pointer = row;
2998
png_write_row(png_ptr, row_pointer);
3000
When the file is interlaced, things can get a good deal more
3001
complicated. The only currently (as of the PNG Specification
3002
version 1.2, dated July 1999) defined interlacing scheme for PNG files
3003
is the "Adam7" interlace scheme, that breaks down an
3004
image into seven smaller images of varying size. libpng will build
3005
these images for you, or you can do them yourself. If you want to
3006
build them yourself, see the PNG specification for details of which
3007
pixels to write when.
3009
If you don't want libpng to handle the interlacing details, just
3010
use png_set_interlace_handling() and call png_write_rows() the
3011
correct number of times to write all seven sub-images.
3013
If you want libpng to build the sub-images, call this before you start
3017
png_set_interlace_handling(png_ptr);
3019
This will return the number of passes needed. Currently, this
3020
is seven, but may change if another interlace type is added.
3022
Then write the complete image number_of_passes times.
3024
png_write_rows(png_ptr, row_pointers,
3027
As some of these rows are not used, and thus return immediately,
3028
you may want to read about interlacing in the PNG specification,
3029
and only update the rows that are actually used.
3031
.SS Finishing a sequential write
3033
After you are finished writing the image, you should finish writing
3034
the file. If you are interested in writing comments or time, you should
3035
pass an appropriately filled png_info pointer. If you are not interested,
3038
png_write_end(png_ptr, info_ptr);
3040
When you are done, you can free all memory used by libpng like this:
3042
png_destroy_write_struct(&png_ptr, &info_ptr);
3044
It is also possible to individually free the info_ptr members that
3045
point to libpng-allocated storage with the following function:
3047
png_free_data(png_ptr, info_ptr, mask, seq)
3048
mask - identifies data to be freed, a mask
3049
containing the logical OR of one or
3051
PNG_FREE_PLTE, PNG_FREE_TRNS,
3052
PNG_FREE_HIST, PNG_FREE_ICCP,
3053
PNG_FREE_PCAL, PNG_FREE_ROWS,
3054
PNG_FREE_SCAL, PNG_FREE_SPLT,
3055
PNG_FREE_TEXT, PNG_FREE_UNKN,
3056
or simply PNG_FREE_ALL
3057
seq - sequence number of item to be freed
3060
This function may be safely called when the relevant storage has
3061
already been freed, or has not yet been allocated, or was allocated
3062
by the user and not by libpng, and will in those
3063
cases do nothing. The "seq" parameter is ignored if only one item
3064
of the selected data type, such as PLTE, is allowed. If "seq" is not
3065
-1, and multiple items are allowed for the data type identified in
3066
the mask, such as text or sPLT, only the n'th item in the structure
3067
is freed, where n is "seq".
3069
If you allocated data such as a palette that you passed
3070
in to libpng with png_set_*, you must not free it until just before the call to
3071
png_destroy_write_struct().
3073
The default behavior is only to free data that was allocated internally
3074
by libpng. This can be changed, so that libpng will not free the data,
3075
or so that it will free data that was allocated by the user with png_malloc()
3076
or png_zalloc() and passed in via a png_set_*() function, with
3078
png_data_freer(png_ptr, info_ptr, freer, mask)
3079
mask - which data elements are affected
3080
same choices as in png_free_data()
3082
PNG_DESTROY_WILL_FREE_DATA
3083
PNG_SET_WILL_FREE_DATA
3084
PNG_USER_WILL_FREE_DATA
3086
For example, to transfer responsibility for some data from a read structure
3087
to a write structure, you could use
3089
png_data_freer(read_ptr, read_info_ptr,
3090
PNG_USER_WILL_FREE_DATA,
3091
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3092
png_data_freer(write_ptr, write_info_ptr,
3093
PNG_DESTROY_WILL_FREE_DATA,
3094
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3096
thereby briefly reassigning responsibility for freeing to the user but
3097
immediately afterwards reassigning it once more to the write_destroy
3098
function. Having done this, it would then be safe to destroy the read
3099
structure and continue to use the PLTE, tRNS, and hIST data in the write
3102
This function only affects data that has already been allocated.
3103
You can call this function before calling after the png_set_*() functions
3104
to control whether the user or png_destroy_*() is supposed to free the data.
3105
When the user assumes responsibility for libpng-allocated data, the
3106
application must use
3107
png_free() to free it, and when the user transfers responsibility to libpng
3108
for data that the user has allocated, the user must have used png_malloc()
3109
or png_zalloc() to allocate it.
3111
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3112
separately, do not transfer responsibility for freeing text_ptr to libpng,
3113
because when libpng fills a png_text structure it combines these members with
3114
the key member, and png_free_data() will free only text_ptr.key. Similarly,
3115
if you transfer responsibility for free'ing text_ptr from libpng to your
3116
application, your application must not separately free those members.
3117
For a more compact example of writing a PNG image, see the file example.c.
3119
.SH V. Modifying/Customizing libpng:
3121
There are three issues here. The first is changing how libpng does
3122
standard things like memory allocation, input/output, and error handling.
3123
The second deals with more complicated things like adding new chunks,
3124
adding new transformations, and generally changing how libpng works.
3125
Both of those are compile-time issues; that is, they are generally
3126
determined at the time the code is written, and there is rarely a need
3127
to provide the user with a means of changing them. The third is a
3128
run-time issue: choosing between and/or tuning one or more alternate
3129
versions of computationally intensive routines; specifically, optimized
3130
assembly-language (and therefore compiler- and platform-dependent)
3133
Memory allocation, input/output, and error handling
3135
All of the memory allocation, input/output, and error handling in libpng
3136
goes through callbacks that are user-settable. The default routines are
3137
in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3138
these functions, call the appropriate png_set_*_fn() function.
3140
Memory allocation is done through the functions png_malloc()
3141
and png_free(). These currently just call the standard C functions. If
3142
your pointers can't access more then 64K at a time, you will want to set
3143
MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3144
memory allocation on a platform will change between applications, these
3145
functions must be modified in the library at compile time. If you prefer
3146
to use a different method of allocating and freeing data, you can use
3147
png_create_read_struct_2() or png_create_write_struct_2() to register
3148
your own functions as described above.
3149
These functions also provide a void pointer that can be retrieved via
3151
mem_ptr=png_get_mem_ptr(png_ptr);
3153
Your replacement memory functions must have prototypes as follows:
3155
png_voidp malloc_fn(png_structp png_ptr,
3157
void free_fn(png_structp png_ptr, png_voidp ptr);
3159
Your malloc_fn() must return NULL in case of failure. The png_malloc()
3160
function will normally call png_error() if it receives a NULL from the
3161
system memory allocator or from your replacement malloc_fn().
3163
Input/Output in libpng is done through png_read() and png_write(),
3164
which currently just call fread() and fwrite(). The FILE * is stored in
3165
png_struct and is initialized via png_init_io(). If you wish to change
3166
the method of I/O, the library supplies callbacks that you can set
3167
through the function png_set_read_fn() and png_set_write_fn() at run
3168
time, instead of calling the png_init_io() function. These functions
3169
also provide a void pointer that can be retrieved via the function
3170
png_get_io_ptr(). For example:
3172
png_set_read_fn(png_structp read_ptr,
3173
voidp read_io_ptr, png_rw_ptr read_data_fn)
3175
png_set_write_fn(png_structp write_ptr,
3176
voidp write_io_ptr, png_rw_ptr write_data_fn,
3177
png_flush_ptr output_flush_fn);
3179
voidp read_io_ptr = png_get_io_ptr(read_ptr);
3180
voidp write_io_ptr = png_get_io_ptr(write_ptr);
3182
The replacement I/O functions must have prototypes as follows:
3184
void user_read_data(png_structp png_ptr,
3185
png_bytep data, png_size_t length);
3186
void user_write_data(png_structp png_ptr,
3187
png_bytep data, png_size_t length);
3188
void user_flush_data(png_structp png_ptr);
3190
Supplying NULL for the read, write, or flush functions sets them back
3191
to using the default C stream functions. It is an error to read from
3192
a write stream, and vice versa.
3194
Error handling in libpng is done through png_error() and png_warning().
3195
Errors handled through png_error() are fatal, meaning that png_error()
3196
should never return to its caller. Currently, this is handled via
3197
setjmp() and longjmp() (unless you have compiled libpng with
3198
PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3199
but you could change this to do things like exit() if you should wish.
3201
On non-fatal errors, png_warning() is called
3202
to print a warning message, and then control returns to the calling code.
3203
By default png_error() and png_warning() print a message on stderr via
3204
fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3205
(because you don't want the messages) or PNG_NO_STDIO defined (because
3206
fprintf() isn't available). If you wish to change the behavior of the error
3207
functions, you will need to set up your own message callbacks. These
3208
functions are normally supplied at the time that the png_struct is created.
3209
It is also possible to redirect errors and warnings to your own replacement
3210
functions after png_create_*_struct() has been called by calling:
3212
png_set_error_fn(png_structp png_ptr,
3213
png_voidp error_ptr, png_error_ptr error_fn,
3214
png_error_ptr warning_fn);
3216
png_voidp error_ptr = png_get_error_ptr(png_ptr);
3218
If NULL is supplied for either error_fn or warning_fn, then the libpng
3219
default function will be used, calling fprintf() and/or longjmp() if a
3220
problem is encountered. The replacement error functions should have
3221
parameters as follows:
3223
void user_error_fn(png_structp png_ptr,
3224
png_const_charp error_msg);
3225
void user_warning_fn(png_structp png_ptr,
3226
png_const_charp warning_msg);
3228
The motivation behind using setjmp() and longjmp() is the C++ throw and
3229
catch exception handling methods. This makes the code much easier to write,
3230
as there is no need to check every return code of every function call.
3231
However, there are some uncertainties about the status of local variables
3232
after a longjmp, so the user may want to be careful about doing anything after
3233
setjmp returns non-zero besides returning itself. Consult your compiler
3234
documentation for more details. For an alternative approach, you may wish
3235
to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3239
If you need to read or write custom chunks, you may need to get deeper
3240
into the libpng code. The library now has mechanisms for storing
3241
and writing chunks of unknown type; you can even declare callbacks
3242
for custom chunks. Hoewver, this may not be good enough if the
3243
library code itself needs to know about interactions between your
3244
chunk and existing `intrinsic' chunks.
3246
If you need to write a new intrinsic chunk, first read the PNG
3247
specification. Acquire a first level of
3248
understanding of how it works. Pay particular attention to the
3249
sections that describe chunk names, and look at how other chunks were
3250
designed, so you can do things similarly. Second, check out the
3251
sections of libpng that read and write chunks. Try to find a chunk
3252
that is similar to yours and use it as a template. More details can
3253
be found in the comments inside the code. It is best to handle unknown
3254
chunks in a generic method, via callback functions, instead of by
3255
modifying libpng functions.
3257
If you wish to write your own transformation for the data, look through
3258
the part of the code that does the transformations, and check out some of
3259
the simpler ones to get an idea of how they work. Try to find a similar
3260
transformation to the one you want to add and copy off of it. More details
3261
can be found in the comments inside the code itself.
3263
.SS Configuring for 16 bit platforms
3265
You will want to look into zconf.h to tell zlib (and thus libpng) that
3266
it cannot allocate more then 64K at a time. Even if you can, the memory
3267
won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3269
.SS Configuring for DOS
3271
For DOS users who only have access to the lower 640K, you will
3272
have to limit zlib's memory usage via a png_set_compression_mem_level()
3273
call. See zlib.h or zconf.h in the zlib library for more information.
3275
.SS Configuring for Medium Model
3277
Libpng's support for medium model has been tested on most of the popular
3278
compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3279
defined, and FAR gets defined to far in pngconf.h, and you should be
3280
all set. Everything in the library (except for zlib's structure) is
3281
expecting far data. You must use the typedefs with the p or pp on
3282
the end for pointers (or at least look at them and be careful). Make
3283
note that the rows of data are defined as png_bytepp, which is an
3284
unsigned char far * far *.
3286
.SS Configuring for gui/windowing platforms:
3288
You will need to write new error and warning functions that use the GUI
3289
interface, as described previously, and set them to be the error and
3290
warning functions at the time that png_create_*_struct() is called,
3291
in order to have them available during the structure initialization.
3292
They can be changed later via png_set_error_fn(). On some compilers,
3293
you may also have to change the memory allocators (png_malloc, etc.).
3295
.SS Configuring for compiler xxx:
3297
All includes for libpng are in pngconf.h. If you need to add/change/delete
3298
an include, this is the place to do it. The includes that are not
3299
needed outside libpng are protected by the PNG_INTERNAL definition,
3300
which is only defined for those routines inside libpng itself. The
3301
files in libpng proper only include png.h, which includes pngconf.h.
3303
.SS Configuring zlib:
3305
There are special functions to configure the compression. Perhaps the
3306
most useful one changes the compression level, which currently uses
3307
input compression values in the range 0 - 9. The library normally
3308
uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3309
have shown that for a large majority of images, compression values in
3310
the range 3-6 compress nearly as well as higher levels, and do so much
3311
faster. For online applications it may be desirable to have maximum speed
3312
(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3313
specify no compression (Z_NO_COMPRESSION = 0), but this would create
3314
files larger than just storing the raw bitmap. You can specify the
3315
compression level by calling:
3317
png_set_compression_level(png_ptr, level);
3319
Another useful one is to reduce the memory level used by the library.
3320
The memory level defaults to 8, but it can be lowered if you are
3321
short on memory (running DOS, for example, where you only have 640K).
3322
Note that the memory level does have an effect on compression; among
3323
other things, lower levels will result in sections of incompressible
3324
data being emitted in smaller stored blocks, with a correspondingly
3325
larger relative overhead of up to 15% in the worst case.
3327
png_set_compression_mem_level(png_ptr, level);
3329
The other functions are for configuring zlib. They are not recommended
3330
for normal use and may result in writing an invalid PNG file. See
3331
zlib.h for more information on what these mean.
3333
png_set_compression_strategy(png_ptr,
3335
png_set_compression_window_bits(png_ptr,
3337
png_set_compression_method(png_ptr, method);
3338
png_set_compression_buffer_size(png_ptr, size);
3340
.SS Controlling row filtering
3342
If you want to control whether libpng uses filtering or not, which
3343
filters are used, and how it goes about picking row filters, you
3344
can call one of these functions. The selection and configuration
3345
of row filters can have a significant impact on the size and
3346
encoding speed and a somewhat lesser impact on the decoding speed
3347
of an image. Filtering is enabled by default for RGB and grayscale
3348
images (with and without alpha), but not for paletted images nor
3349
for any images with bit depths less than 8 bits/pixel.
3351
The 'method' parameter sets the main filtering method, which is
3352
currently only '0' in the PNG 1.2 specification. The 'filters'
3353
parameter sets which filter(s), if any, should be used for each
3354
scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3355
to turn filtering on and off, respectively.
3357
Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3358
PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3359
ORed together with '|' to specify one or more filters to use.
3360
These filters are described in more detail in the PNG specification.
3361
If you intend to change the filter type during the course of writing
3362
the image, you should start with flags set for all of the filters
3363
you intend to use so that libpng can initialize its internal
3364
structures appropriately for all of the filter types. (Note that this
3365
means the first row must always be adaptively filtered, because libpng
3366
currently does not allocate the filter buffers until png_write_row()
3367
is called for the first time.)
3369
filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3370
PNG_FILTER_UP | PNG_FILTER_AVE |
3371
PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3373
png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3375
The second parameter can also be
3376
PNG_INTRAPIXEL_DIFFERENCING if you are
3377
writing a PNG to be embedded in a MNG
3378
datastream. This parameter must be the
3379
same as the value of filter_method used
3382
It is also possible to influence how libpng chooses from among the
3383
available filters. This is done in one or both of two ways - by
3384
telling it how important it is to keep the same filter for successive
3385
rows, and by telling it the relative computational costs of the filters.
3387
double weights[3] = {1.5, 1.3, 1.1},
3388
costs[PNG_FILTER_VALUE_LAST] =
3389
{1.0, 1.3, 1.3, 1.5, 1.7};
3391
png_set_filter_heuristics(png_ptr,
3392
PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3395
The weights are multiplying factors that indicate to libpng that the
3396
row filter should be the same for successive rows unless another row filter
3397
is that many times better than the previous filter. In the above example,
3398
if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3399
"sum of absolute differences" 1.5 x 1.3 times higher than other filters
3400
and still be chosen, while the NONE filter could have a sum 1.1 times
3401
higher than other filters and still be chosen. Unspecified weights are
3402
taken to be 1.0, and the specified weights should probably be declining
3403
like those above in order to emphasize recent filters over older filters.
3405
The filter costs specify for each filter type a relative decoding cost
3406
to be considered when selecting row filters. This means that filters
3407
with higher costs are less likely to be chosen over filters with lower
3408
costs, unless their "sum of absolute differences" is that much smaller.
3409
The costs do not necessarily reflect the exact computational speeds of
3410
the various filters, since this would unduly influence the final image
3413
Note that the numbers above were invented purely for this example and
3414
are given only to help explain the function usage. Little testing has
3415
been done to find optimum values for either the costs or the weights.
3417
.SS Removing unwanted object code
3419
There are a bunch of #define's in pngconf.h that control what parts of
3420
libpng are compiled. All the defines end in _SUPPORTED. If you are
3421
never going to use a capability, you can change the #define to #undef
3422
before recompiling libpng and save yourself code and data space, or
3423
you can turn off individual capabilities with defines that begin with
3426
You can also turn all of the transforms and ancillary chunk capabilities
3427
off en masse with compiler directives that define
3428
PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3430
along with directives to turn on any of the capabilities that you do
3431
want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3432
the extra transformations but still leave the library fully capable of reading
3433
and writing PNG files with all known public chunks
3434
Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3435
produces a library that is incapable of reading or writing ancillary chunks.
3436
If you are not using the progressive reading capability, you can
3437
turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3438
this with the INTERLACING capability, which you'll still have).
3440
All the reading and writing specific code are in separate files, so the
3441
linker should only grab the files it needs. However, if you want to
3442
make sure, or if you are building a stand alone library, all the
3443
reading files start with pngr and all the writing files start with
3444
pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3445
are used for both reading and writing, and always need to be included.
3446
The progressive reader is in pngpread.c
3448
If you are creating or distributing a dynamically linked library (a .so
3449
or DLL file), you should not remove or disable any parts of the library,
3450
as this will cause applications linked with different versions of the
3451
library to fail if they call functions not available in your library.
3452
The size of the library itself should not be an issue, because only
3453
those sections that are actually used will be loaded into memory.
3455
.SS Requesting debug printout
3457
The macro definition PNG_DEBUG can be used to request debugging
3458
printout. Set it to an integer value in the range 0 to 3. Higher
3459
numbers result in increasing amounts of debugging information. The
3460
information is printed to the "stderr" file, unless another file
3461
name is specified in the PNG_DEBUG_FILE macro definition.
3463
When PNG_DEBUG > 0, the following functions (macros) become available:
3465
png_debug(level, message)
3466
png_debug1(level, message, p1)
3467
png_debug2(level, message, p1, p2)
3469
in which "level" is compared to PNG_DEBUG to decide whether to print
3470
the message, "message" is the formatted string to be printed,
3471
and p1 and p2 are parameters that are to be embedded in the string
3472
according to printf-style formatting directives. For example,
3474
png_debug1(2, "foo=%d\n", foo);
3479
fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3481
When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3482
can still use PNG_DEBUG to control your own debugging:
3488
When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3489
having level = 0 will be printed. There aren't any such statements in
3490
this version of libpng, but if you insert some they will be printed.
3492
.SH VI. Runtime optimization
3494
A new feature in libpng 1.2.0 is the ability to dynamically switch between
3495
standard and optimized versions of some routines. Currently these are
3496
limited to three computationally intensive tasks when reading PNG files:
3497
decoding row filters, expanding interlacing, and combining interlaced or
3498
transparent row data with previous row data. Currently the optimized
3499
versions are available only for x86 (Intel, AMD, etc.) platforms with
3500
MMX support, though this may change in future versions. (For example,
3501
the non-MMX assembler optimizations for zlib might become similarly
3502
runtime-selectable in future releases, in which case libpng could be
3503
extended to support them. Alternatively, the compile-time choice of
3504
floating-point versus integer routines for gamma correction might become
3505
runtime-selectable.)
3507
Because such optimizations tend to be very platform- and compiler-dependent,
3508
both in how they are written and in how they perform, the new runtime code
3509
in libpng has been written to allow programs to query, enable, and disable
3510
either specific optimizations or all such optimizations. For example, to
3511
enable all possible optimizations (bearing in mind that some "optimizations"
3512
may actually run more slowly in rare cases):
3514
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3515
png_uint_32 mask, flags;
3517
flags = png_get_asm_flags(png_ptr);
3518
mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3519
png_set_asm_flags(png_ptr, flags | mask);
3522
To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3523
by itself when calling png_get_asm_flagmask(); similarly for optimizing
3524
only writing. To disable all optimizations:
3526
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3527
flags = png_get_asm_flags(png_ptr);
3528
mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3529
png_set_asm_flags(png_ptr, flags & ~mask);
3532
To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3533
in place of png_get_asm_flagmask(). The mmx version takes one additional
3536
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3537
int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3540
mask = png_get_mmx_flagmask(selection, &compilerID);
3543
On return, compilerID will indicate which version of the MMX assembler
3544
optimizations was compiled. Currently two flavors exist: Microsoft
3545
Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3546
On non-x86 platforms or on systems compiled without MMX optimizations, a
3547
value of -1 is used.
3549
Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3550
all valid, settable optimization bits for the version of the library that's
3551
currently in use. In the case of shared (dynamically linked) libraries,
3552
this may include optimizations that did not exist at the time the code was
3553
written and compiled. It is also possible, of course, to enable only known,
3554
specific optimizations; for example:
3556
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3557
flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3558
| PNG_ASM_FLAG_MMX_READ_INTERLACE \
3559
| PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3560
| PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3561
| PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3562
| PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3563
png_set_asm_flags(png_ptr, flags);
3566
This method would enable only the MMX read-optimizations available at the
3567
time of libpng 1.2.0's release, regardless of whether a later version of
3568
the DLL were actually being used. (Also note that these functions did not
3569
exist in versions older than 1.2.0, so any attempt to run a dynamically
3570
linked app on such an older version would fail.)
3572
To determine whether the processor supports MMX instructions at all, use
3573
the png_mmx_support() function:
3575
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3576
mmxsupport = png_mmx_support();
3579
It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3580
is compiled but MMX is not supported by the processor, or 1 if MMX support
3581
is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3582
and png_get_asm_flagmask() all may be called without allocating and ini-
3583
tializing any PNG structures (for example, as part of a usage screen or
3586
The following code can be used to prevent an application from using the
3587
thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3590
#if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3591
&& defined(PNG_THREAD_UNSAFE_OK)
3592
/* Disable thread-unsafe features of pnggccrd */
3593
if (png_access_version() >= 10200)
3595
png_uint_32 mmx_disable_mask = 0;
3596
png_uint_32 asm_flags;
3598
mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3599
| PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3600
| PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3601
| PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3602
asm_flags = png_get_asm_flags(png_ptr);
3603
png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3607
For more extensive examples of runtime querying, enabling and disabling
3608
of optimized features, see contrib/gregbook/readpng2.c in the libpng
3609
source-code distribution.
3611
.SH VII. MNG support
3613
The MNG specification (available at http://www.libpng.org/pub/mng) allows
3614
certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3615
Libpng can support some of these extensions. To enable them, use the
3616
png_permit_mng_features() function:
3618
feature_set = png_permit_mng_features(png_ptr, mask)
3619
mask is a png_uint_32 containing the logical OR of the
3620
features you want to enable. These include
3621
PNG_FLAG_MNG_EMPTY_PLTE
3622
PNG_FLAG_MNG_FILTER_64
3623
PNG_ALL_MNG_FEATURES
3624
feature_set is a png_uint_32 that is the logical AND of
3625
your mask with the set of MNG features that is
3626
supported by the version of libpng that you are using.
3628
It is an error to use this function when reading or writing a standalone
3629
PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3630
in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3631
and the MHDR and MEND chunks. Libpng does not provide support for these
3632
or any other MNG chunks; your application must provide its own support for
3633
them. You may wish to consider using libmng (available at
3634
http://www.libmng.com) instead.
3636
.SH VIII. Changes to Libpng from version 0.88
3638
It should be noted that versions of libpng later than 0.96 are not
3639
distributed by the original libpng author, Guy Schalnat, nor by
3640
Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3641
distributed versions 0.89 through 0.96, but rather by another member
3642
of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3643
still alive and well, but they have moved on to other things.
3645
The old libpng functions png_read_init(), png_write_init(),
3646
png_info_init(), png_read_destroy(), and png_write_destroy() have been
3647
moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3648
functions will be removed from libpng version 2.0.0.
3650
The preferred method of creating and initializing the libpng structures is
3651
via the png_create_read_struct(), png_create_write_struct(), and
3652
png_create_info_struct() because they isolate the size of the structures
3653
from the application, allow version error checking, and also allow the
3654
use of custom error handling routines during the initialization, which
3655
the old functions do not. The functions png_read_destroy() and
3656
png_write_destroy() do not actually free the memory that libpng
3657
allocated for these structs, but just reset the data structures, so they
3658
can be used instead of png_destroy_read_struct() and
3659
png_destroy_write_struct() if you feel there is too much system overhead
3660
allocating and freeing the png_struct for each image read.
3662
Setting the error callbacks via png_set_message_fn() before
3663
png_read_init() as was suggested in libpng-0.88 is no longer supported
3664
because this caused applications that do not use custom error functions
3665
to fail if the png_ptr was not initialized to zero. It is still possible
3666
to set the error callbacks AFTER png_read_init(), or to change them with
3667
png_set_error_fn(), which is essentially the same function, but with a new
3668
name to force compilation errors with applications that try to use the old
3671
Starting with version 1.0.7, you can find out which version of the library
3672
you are using at run-time:
3674
png_uint_32 libpng_vn = png_access_version_number();
3676
The number libpng_vn is constructed from the major version, minor
3677
version with leading zero, and release number with leading zero,
3678
(e.g., libpng_vn for version 1.0.7 is 10007).
3680
You can also check which version of png.h you used when compiling your
3683
png_uint_32 application_vn = PNG_LIBPNG_VER;
3685
.SH IX. Y2K Compliance in libpng
3689
Since the PNG Development group is an ad-hoc body, we can't make
3690
an official declaration.
3692
This is your unofficial assurance that libpng from version 0.71 and
3693
upward through 1.2.7 are Y2K compliant. It is my belief that earlier
3694
versions were also Y2K compliant.
3696
Libpng only has three year fields. One is a 2-byte unsigned integer that
3697
will hold years up to 65535. The other two hold the date in text
3698
format, and will hold years up to 9999.
3701
"png_uint_16 year" in png_time_struct.
3704
"png_charp time_buffer" in png_struct and
3705
"near_time_buffer", which is a local character string in png.c.
3707
There are seven time-related functions:
3709
png_convert_to_rfc_1123() in png.c
3710
(formerly png_convert_to_rfc_1152() in error)
3711
png_convert_from_struct_tm() in pngwrite.c, called
3713
png_convert_from_time_t() in pngwrite.c
3714
png_get_tIME() in pngget.c
3715
png_handle_tIME() in pngrutil.c, called in pngread.c
3716
png_set_tIME() in pngset.c
3717
png_write_tIME() in pngwutil.c, called in pngwrite.c
3719
All appear to handle dates properly in a Y2K environment. The
3720
png_convert_from_time_t() function calls gmtime() to convert from system
3721
clock time, which returns (year - 1900), which we properly convert to
3722
the full 4-digit year. There is a possibility that applications using
3723
libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3724
function, or that they are incorrectly passing only a 2-digit year
3725
instead of "year - 1900" into the png_convert_from_struct_tm() function,
3726
but this is not under our control. The libpng documentation has always
3727
stated that it works with 4-digit years, and the APIs have been
3730
The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3731
integer to hold the year, and can hold years as large as 65535.
3733
zlib, upon which libpng depends, is also Y2K compliant. It contains
3734
no date-related code.
3737
Glenn Randers-Pehrson
3739
PNG Development Group
3743
Note about libpng version numbers:
3745
Due to various miscommunications, unforeseen code incompatibilities
3746
and occasional factors outside the authors' control, version numbering
3747
on the library has not always been consistent and straightforward.
3748
The following table summarizes matters since version 0.89c, which was
3749
the first widely used release:
3751
source png.h png.h shared-lib
3752
version string int version
3753
------- ------ ----- ----------
3754
0.89c ("beta 3") 0.89 89 1.0.89
3755
0.90 ("beta 4") 0.90 90 0.90
3756
0.95 ("beta 5") 0.95 95 0.95
3757
0.96 ("beta 6") 0.96 96 0.96
3758
0.97b ("beta 7") 1.00.97 97 1.0.1
3759
0.97c 0.97 97 2.0.97
3762
0.99a-m 0.99 99 2.0.99
3764
1.0.0 1.0.0 100 2.1.0
3765
1.0.0 (from here on, the 100 2.1.0
3766
1.0.1 png.h string is 10001 2.1.0
3767
1.0.1a-e identical to the 10002 from here on, the
3768
1.0.2 source version) 10002 shared library is 2.V
3769
1.0.2a-b 10003 where V is the source
3770
1.0.1 10001 code version except as
3771
1.0.1a-e 10002 2.1.0.1a-e noted.
3773
1.0.2a-b 10003 2.1.0.2a-b
3775
1.0.3a-d 10004 2.1.0.3a-d
3777
1.0.4a-f 10005 2.1.0.4a-f
3778
1.0.5 (+ 2 patches) 10005 2.1.0.5
3779
1.0.5a-d 10006 2.1.0.5a-d
3780
1.0.5e-r 10100 2.1.0.5e-r
3781
1.0.5s-v 10006 2.1.0.5s-v
3782
1.0.6 (+ 3 patches) 10006 2.1.0.6
3783
1.0.6d-g 10007 2.1.0.6d-g
3786
1.0.6j 10007 2.1.0.6j
3787
1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3788
1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3789
1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3790
1.0.7 1 10007 2.1.0.7
3791
1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3792
1.0.8rc1 1 10008 2.1.0.8rc1
3793
1.0.8 1 10008 2.1.0.8
3794
1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3795
1.0.9rc1 1 10009 2.1.0.9rc1
3796
1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3797
1.0.9rc2 1 10009 2.1.0.9rc2
3798
1.0.9 1 10009 2.1.0.9
3799
1.0.10beta1 1 10010 2.1.0.10beta1
3800
1.0.10rc1 1 10010 2.1.0.10rc1
3801
1.0.10 1 10010 2.1.0.10
3802
1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3803
1.0.11rc1 1 10011 2.1.0.11rc1
3804
1.0.11 1 10011 2.1.0.11
3805
1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3806
1.0.12rc1 2 10012 2.1.0.12rc1
3807
1.0.12 2 10012 2.1.0.12
3808
1.1.0a-f - 10100 2.1.1.0a-f abandoned
3809
1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3810
1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3811
1.2.0rc1 3 10200 3.1.2.0rc1
3812
1.2.0 3 10200 3.1.2.0
3813
1.2.1beta-4 3 10201 3.1.2.1beta1-4
3814
1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3815
1.2.1 3 10201 3.1.2.1
3816
1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3817
1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3818
1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3819
1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3820
1.0.13 10 10013 10.so.0.1.0.13
3821
1.2.2 12 10202 12.so.0.1.2.2
3822
1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3823
1.2.3 12 10203 12.so.0.1.2.3
3824
1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3825
1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3826
1.0.14 10 10014 10.so.0.1.0.14
3827
1.2.4 13 10204 12.so.0.1.2.4
3828
1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3829
1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3830
1.0.15 10 10015 10.so.0.1.0.15
3831
1.2.5 13 10205 12.so.0.1.2.5
3832
1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3833
1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3834
1.0.16 10 10016 10.so.0.1.0.16
3835
1.2.6 13 10206 12.so.0.1.2.6
3836
1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3837
1.0.17rc1 10 10017 12.so.0.1.0.17rc1
3838
1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3839
1.0.17 10 10017 12.so.0.1.0.17
3840
1.2.7 13 10207 12.so.0.1.2.7
3842
Henceforth the source version will match the shared-library minor
3843
and patch numbers; the shared-library major version number will be
3844
used for changes in backward compatibility, as it is intended. The
3845
PNG_PNGLIB_VER macro, which is not used within libpng but is available
3846
for applications, is an unsigned integer of the form xyyzz corresponding
3847
to the source version x.y.z (leading zeros in y and z). Beta versions
3848
were given the previous public release number plus a letter, until
3849
version 1.0.6j; from then on they were given the upcoming public
3850
release number plus "betaNN" or "rcN".
3857
http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3858
http://www.libpng.org/pub/png
3863
(generally) at the same location as
3867
ftp://ftp.info-zip.org/pub/infozip/zlib
3870
.IR PNG specification: RFC 2083
3872
(generally) at the same location as
3876
ftp://ds.internic.net/rfc/rfc2083.txt
3878
or (as a W3C Recommendation) at
3880
http://www.w3.org/TR/REC-png.html
3883
In the case of any inconsistency between the PNG specification
3884
and this library, the specification takes precedence.
3887
This man page: Glenn Randers-Pehrson
3888
<glennrp@users.sourceforge.net>
3890
The contributing authors would like to thank all those who helped
3891
with testing, bug fixes, and patience. This wouldn't have been
3892
possible without all of you.
3894
Thanks to Frank J. T. Wojcik for helping with the documentation.
3896
Libpng version 1.2.7 - September 12, 2004:
3897
Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3898
Currently maintained by Glenn Randers-Pehrson (glennrp@users.sourceforge.net).
3900
Supported by the PNG development group
3902
png-implement@ccrc.wustl.edu (subscription required; write to
3903
majordomo@ccrc.wustl.edu with "subscribe png-implement" in the message).
3905
.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3907
(This copy of the libpng notices is provided for your convenience. In case of
3908
any discrepancy between this copy and the notices in the file png.h that is
3909
included in the libpng distribution, the latter shall prevail.)
3911
If you modify libpng you may insert additional notices immediately following
3914
libpng version 1.2.6, September 12, 2004, is
3915
Copyright (c) 2004 Glenn Randers-Pehrson, and is
3916
distributed according to the same disclaimer and license as libpng-1.2.5
3917
with the following individual added to the list of Contributing Authors
3921
libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
3922
Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3923
distributed according to the same disclaimer and license as libpng-1.0.6
3924
with the following individuals added to the list of Contributing Authors
3926
Simon-Pierre Cadieux
3930
and with the following additions to the disclaimer:
3932
There is no warranty against interference with your
3933
enjoyment of the library or against infringement.
3934
There is no warranty that our efforts or the library
3935
will fulfill any of your particular purposes or needs.
3936
This library is provided with all faults, and the entire
3937
risk of satisfactory quality, performance, accuracy, and
3938
effort is with the user.
3940
libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3941
Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3942
Distributed according to the same disclaimer and license as libpng-0.96,
3943
with the following individuals added to the list of Contributing Authors:
3946
Glenn Randers-Pehrson
3949
libpng versions 0.89, June 1996, through 0.96, May 1997, are
3950
Copyright (c) 1996, 1997 Andreas Dilger
3951
Distributed according to the same disclaimer and license as libpng-0.88,
3952
with the following individuals added to the list of Contributing Authors:
3961
libpng versions 0.5, May 1995, through 0.88, January 1996, are
3962
Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3964
For the purposes of this copyright and license, "Contributing Authors"
3965
is defined as the following set of individuals:
3973
The PNG Reference Library is supplied "AS IS". The Contributing Authors
3974
and Group 42, Inc. disclaim all warranties, expressed or implied,
3975
including, without limitation, the warranties of merchantability and of
3976
fitness for any purpose. The Contributing Authors and Group 42, Inc.
3977
assume no liability for direct, indirect, incidental, special, exemplary,
3978
or consequential damages, which may result from the use of the PNG
3979
Reference Library, even if advised of the possibility of such damage.
3981
Permission is hereby granted to use, copy, modify, and distribute this
3982
source code, or portions hereof, for any purpose, without fee, subject
3983
to the following restrictions:
3985
1. The origin of this source code must not be misrepresented.
3987
2. Altered versions must be plainly marked as such and
3988
must not be misrepresented as being the original source.
3990
3. This Copyright notice may not be removed or altered from
3991
any source or altered source distribution.
3993
The Contributing Authors and Group 42, Inc. specifically permit, without
3994
fee, and encourage the use of this source code as a component to
3995
supporting the PNG file format in commercial products. If you use this
3996
source code in a product, acknowledgment is not required but would be
4000
A "png_get_copyright" function is available, for convenient use in "about"
4003
printf("%s",png_get_copyright(NULL));
4005
Also, the PNG logo (in PNG format, of course) is supplied in the
4006
files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4008
Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4009
certification mark of the Open Source Initiative.
4011
Glenn Randers-Pehrson
4012
glennrp@users.sourceforge.net
added
removed
src/png/libpng.3
