1 .TH LIBPNG 3 "September 1, 2001"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.2.0
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_uint_32 png_get_asm_flags (png_structp \fIpng_ptr\fP\fB);\fP
107 \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
111 \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
115 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
119 \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
123 \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
127 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
135 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
143 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
147 \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
151 \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
155 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
159 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
163 \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
167 \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
171 \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
175 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
183 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
187 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
191 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
195 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
199 \fBpng_byte png_get_mmx_bitdepth_threshold (png_structp \fIpng_ptr\fP\fB);\fP
203 \fBpng_uint_32 png_get_mmx_flagmask (int \fP\fIflag_select\fP\fB, int \fI*compilerID\fP\fB);\fP
207 \fBpng_uint_32 png_get_mmx_rowbytes_threshold (png_structp \fIpng_ptr\fP\fB);\fP
211 \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
215 \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
219 \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
223 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
227 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
231 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
235 \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
239 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
241 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
245 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
249 \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
253 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
257 \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
261 \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
265 \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
269 \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
273 \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
277 \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
281 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
285 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
289 \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
293 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
297 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
301 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
305 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
309 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
313 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
317 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
321 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
325 \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
329 \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
333 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
337 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
341 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
345 \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
349 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
353 \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
357 \fBint png_mmx_support \fI(void\fP\fB);\fP
361 \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
365 \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
369 \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
373 \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
377 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
381 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
385 \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
389 \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
393 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
397 \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
401 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
405 \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
409 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
413 \fBpng_set_asm_flags (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIasm_flags\fP\fB);\fP
417 \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
421 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
425 \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
429 \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
433 \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
437 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
441 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
445 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
449 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
453 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
457 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
461 \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
465 \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
469 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
473 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
477 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
481 \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
485 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
489 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
493 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
497 \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
501 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
505 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
509 \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
513 \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
517 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
521 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
525 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
529 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
533 \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
537 \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
541 \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
545 \fBpng_set_mmx_thresholds (png_structp \fP\fIpng_ptr\fP\fB, png_byte \fP\fImmx_bitdepth_threshold\fP\fB, png_uint_32 \fImmx_rowbytes_threshold\fP\fB);\fP
549 \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
553 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
557 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
561 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
565 \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
569 \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
573 \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
577 \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
581 \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
585 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
589 \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
593 \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
597 \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
601 \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
605 \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
609 \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
613 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
617 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
621 \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
625 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
629 \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
633 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
637 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
641 \fBvoid png_set_strip_error_numbers (png_structp \fIpng_ptr,
643 \fBpng_uint_32 \fIstrip_mode\fP\fB);\fP
647 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
651 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
655 \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
659 \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
663 \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
667 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
671 \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
675 \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
679 \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
683 \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
687 \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
691 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
695 \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
699 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
703 \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
707 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
711 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
715 \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
719 \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
723 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
727 \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
731 \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
735 \fBvoid png_write_destroy_info (png_infop \fIinfo_ptr\fP\fB);\fP
739 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
743 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
747 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
751 \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
755 \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
759 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
763 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
767 \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
771 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
775 \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
782 library supports encoding, decoding, and various manipulations of
783 the Portable Network Graphics (PNG) format image files. It uses the
786 Following is a copy of the libpng.txt file that accompanies libpng.
788 libpng.txt - A description on how to use and modify libpng
790 libpng version 1.2.0 - September 1, 2001
791 Updated and distributed by Glenn Randers-Pehrson
792 <randeg@alum.rpi.edu>
793 Copyright (c) 1998-2001 Glenn Randers-Pehrson
794 For conditions of distribution and use, see copyright
799 libpng 1.0 beta 6 version 0.96 May 28, 1997
800 Updated and distributed by Andreas Dilger
801 Copyright (c) 1996, 1997 Andreas Dilger
803 libpng 1.0 beta 2 - version 0.88 January 26, 1996
804 For conditions of distribution and use, see copyright
805 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
806 Schalnat, Group 42, Inc.
808 Updated/rewritten per request in the libpng FAQ
809 Copyright (c) 1995, 1996 Frank J. T. Wojcik
810 December 18, 1995 & January 20, 1996
814 This file describes how to use and modify the PNG reference library
815 (known as libpng) for your own use. There are five sections to this
816 file: introduction, structures, reading, writing, and modification and
817 configuration notes for various special platforms. In addition to this
818 file, example.c is a good starting point for using the library, as
819 it is heavily commented and should include everything most people
820 will need. We assume that libpng is already installed; see the
821 INSTALL file for instructions on how to install libpng.
823 Libpng was written as a companion to the PNG specification, as a way
824 of reducing the amount of time and effort it takes to support the PNG
825 file format in application programs.
827 The PNG-1.2 specification is available at <http://www.libpng.org/pub/png>
828 and at <ftp://ftp.uu.net/graphics/png/documents/>.
830 The PNG-1.0 specification is available
831 as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
832 W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
833 additional chunks are described in the special-purpose public chunks
834 documents at <ftp://ftp.uu.net/graphics/png/documents/>.
837 about PNG, and the latest version of libpng, can be found at the PNG home
838 page, <http://www.libpng.org/pub/png/>
839 and at <ftp://ftp.uu.net/graphics/png/>.
841 Most users will not have to modify the library significantly; advanced
842 users may want to modify it more. All attempts were made to make it as
843 complete as possible, while keeping the code easy to understand.
844 Currently, this library only supports C. Support for other languages
847 Libpng has been designed to handle multiple sessions at one time,
848 to be easily modifiable, to be portable to the vast majority of
849 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
850 to use. The ultimate goal of libpng is to promote the acceptance of
851 the PNG file format in whatever way possible. While there is still
852 work to be done (see the TODO file), libpng should cover the
853 majority of the needs of its users.
855 Libpng uses zlib for its compression and decompression of PNG files.
856 Further information about zlib, and the latest version of zlib, can
857 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
858 The zlib compression utility is a general purpose utility that is
859 useful for more than PNG files, and can be used without libpng.
860 See the documentation delivered with zlib for more details.
861 You can usually find the source files for the zlib utility wherever you
862 find the libpng source files.
864 Libpng is thread safe, provided the threads are using different
865 instances of the structures. Each thread should have its own
866 png_struct and png_info instances, and thus its own image.
867 Libpng does not protect itself against two threads using the
868 same instance of a structure. Note: thread safety may be defeated
869 by use of some of the MMX assembler code in pnggccrd.c, which is only
870 compiled when the user defines PNG_THREAD_UNSAFE_OK.
875 There are two main structures that are important to libpng, png_struct
876 and png_info. The first, png_struct, is an internal structure that
877 will not, for the most part, be used by a user except as the first
878 variable passed to every libpng function call.
880 The png_info structure is designed to provide information about the
881 PNG file. At one time, the fields of png_info were intended to be
882 directly accessible to the user. However, this tended to cause problems
883 with applications using dynamically loaded libraries, and as a result
884 a set of interface functions for png_info (the png_get_*() and png_set_*()
885 functions) was developed. The fields of png_info are still available for
886 older applications, but it is suggested that applications use the new
887 interfaces if at all possible.
889 Applications that do make direct access to the members of png_struct (except
890 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
891 and applications that make direct access to the members of png_info must
892 be recompiled if they were compiled or loaded with libpng version 1.0.6,
893 in which the members were in a different order. In version 1.0.7, the
894 members of the png_info structure reverted to the old order, as they were
895 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
896 structures are going to be hidden, and the contents of the structures will
897 only be accessible through the png_get/png_set functions.
899 The png.h header file is an invaluable reference for programming with libpng.
900 And while I'm on the topic, make sure you include the libpng header file:
906 We'll now walk you through the possible functions to call when reading
907 in a PNG file sequentially, briefly explaining the syntax and purpose
908 of each one. See example.c and png.h for more detail. While
909 progressive reading is covered in the next section, you will still
910 need some of the functions discussed in this section to read a PNG
915 You will want to do the I/O initialization(*) before you get into libpng,
916 so if it doesn't work, you don't have much to undo. Of course, you
917 will also want to insure that you are, in fact, dealing with a PNG
918 file. Libpng provides a simple check to see if a file is a PNG file.
919 To use it, pass in the first 1 to 8 bytes of the file to the function
920 png_sig_cmp(), and it will return 0 if the bytes match the corresponding
921 bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
922 you pass in, the greater the accuracy of the prediction.
924 If you are intending to keep the file pointer open for use in libpng,
925 you must ensure you don't read more than 8 bytes from the beginning
926 of the file, and you also have to make a call to png_set_sig_bytes_read()
927 with the number of bytes you read from the beginning. Libpng will
928 then only check the bytes (if any) that your program didn't read.
930 (*): If you are not using the standard I/O functions, you will need
931 to replace them with custom functions. See the discussion under
935 FILE *fp = fopen(file_name, "rb");
940 fread(header, 1, number, fp);
941 is_png = !png_sig_cmp(header, 0, number);
948 Next, png_struct and png_info need to be allocated and initialized. In
949 order to ensure that the size of these structures is correct even with a
950 dynamically linked libpng, there are functions to initialize and
951 allocate the structures. We also pass the library version, optional
952 pointers to error handling functions, and a pointer to a data struct for
953 use by the error functions, if necessary (the pointer and functions can
954 be NULL if the default error handlers are to be used). See the section
955 on Changes to Libpng below regarding the old initialization functions.
956 The structure allocation functions quietly return NULL if they fail to
957 create the structure, so your application should check for that.
959 png_structp png_ptr = png_create_read_struct
960 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
961 user_error_fn, user_warning_fn);
965 png_infop info_ptr = png_create_info_struct(png_ptr);
968 png_destroy_read_struct(&png_ptr,
969 (png_infopp)NULL, (png_infopp)NULL);
973 png_infop end_info = png_create_info_struct(png_ptr);
976 png_destroy_read_struct(&png_ptr, &info_ptr,
981 If you want to use your own memory allocation routines,
982 define PNG_USER_MEM_SUPPORTED and use
983 png_create_read_struct_2() instead of png_create_read_struct():
985 png_structp png_ptr = png_create_read_struct_2
986 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
987 user_error_fn, user_warning_fn, (png_voidp)
988 user_mem_ptr, user_malloc_fn, user_free_fn);
990 The error handling routines passed to png_create_read_struct()
991 and the memory alloc/free routines passed to png_create_struct_2()
992 are only necessary if you are not using the libpng supplied error
993 handling and memory alloc/free functions.
995 When libpng encounters an error, it expects to longjmp back
996 to your routine. Therefore, you will need to call setjmp and pass
997 your png_jmpbuf(png_ptr). If you read the file from different
998 routines, you will need to update the jmpbuf field every time you enter
999 a new routine that will call a png_*() function.
1001 See your documentation of setjmp/longjmp for your compiler for more
1002 information on setjmp/longjmp. See the discussion on libpng error
1003 handling in the Customizing Libpng section below for more information
1004 on the libpng error handling. If an error occurs, and libpng longjmp's
1005 back to your setjmp, you will want to call png_destroy_read_struct() to
1008 if (setjmp(png_jmpbuf(png_ptr)))
1010 png_destroy_read_struct(&png_ptr, &info_ptr,
1016 If you would rather avoid the complexity of setjmp/longjmp issues,
1017 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1018 errors will result in a call to PNG_ABORT() which defaults to abort().
1020 Now you need to set up the input code. The default for libpng is to
1021 use the C function fread(). If you use this, you will need to pass a
1022 valid FILE * in the function png_init_io(). Be sure that the file is
1023 opened in binary mode. If you wish to handle reading data in another
1024 way, you need not call the png_init_io() function, but you must then
1025 implement the libpng I/O methods discussed in the Customizing Libpng
1028 png_init_io(png_ptr, fp);
1030 If you had previously opened the file and read any of the signature from
1031 the beginning in order to see if this was a PNG file, you need to let
1032 libpng know that there are some bytes missing from the start of the file.
1034 png_set_sig_bytes(png_ptr, number);
1036 .SS Setting up callback code
1038 You can set up a callback function to handle any unknown chunks in the
1039 input stream. You must supply the function
1041 read_chunk_callback(png_ptr ptr,
1042 png_unknown_chunkp chunk);
1044 /* The unknown chunk structure contains your
1049 /* Note that libpng has already taken care of
1052 /* put your code here. Return one of the
1055 return (-n); /* chunk had an error */
1056 return (0); /* did not recognize */
1057 return (n); /* success */
1060 (You can give your function another name that you like instead of
1061 "read_chunk_callback")
1063 To inform libpng about your function, use
1065 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1066 read_chunk_callback);
1068 This names not only the callback function, but also a user pointer that
1069 you can retrieve with
1071 png_get_user_chunk_ptr(png_ptr);
1073 At this point, you can set up a callback function that will be
1074 called after each row has been read, which you can use to control
1075 a progress meter or the like. It's demonstrated in pngtest.c.
1076 You must supply a function
1078 void read_row_callback(png_ptr ptr, png_uint_32 row,
1081 /* put your code here */
1084 (You can give it another name that you like instead of "read_row_callback")
1086 To inform libpng about your function, use
1088 png_set_read_status_fn(png_ptr, read_row_callback);
1090 .SS Unknown-chunk handling
1092 Now you get to set the way the library processes unknown chunks in the
1093 input PNG stream. Both known and unknown chunks will be read. Normal
1094 behavior is that known chunks will be parsed into information in
1095 various info_ptr members; unknown chunks will be discarded. To change
1098 png_set_keep_unknown_chunks(png_ptr, info_ptr, keep,
1099 chunk_list, num_chunks);
1100 keep - 0: do not keep
1101 1: keep only if safe-to-copy
1102 2: keep even if unsafe-to-copy
1103 chunk_list - list of chunks affected (a byte string,
1104 five bytes per chunk, NULL or '\0' if
1106 num_chunks - number of chunks affected; if 0, all
1107 unknown chunks are affected
1109 Unknown chunks declared in this way will be saved as raw data onto a
1110 list of png_unknown_chunk structures. If a chunk that is normally
1111 known to libpng is named in the list, it will be handled as unknown,
1112 according to the "keep" directive. If a chunk is named in successive
1113 instances of png_set_keep_unknown_chunks(), the final instance will
1116 .SS The high-level read interface
1118 At this point there are two ways to proceed; through the high-level
1119 read interface, or through a sequence of low-level read operations.
1120 You can use the high-level interface if (a) you are willing to read
1121 the entire image into memory, and (b) the input transformations
1122 you want to do are limited to the following set:
1124 PNG_TRANSFORM_IDENTITY No transformation
1125 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1127 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1128 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1130 PNG_TRANSFORM_PACKSWAP Change order of packed
1132 PNG_TRANSFORM_EXPAND Perform set_expand()
1133 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1134 PNG_TRANSFORM_SHIFT Normalize pixels to the
1136 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1138 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1140 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1142 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1144 (This excludes setting a background color, doing gamma transformation,
1145 dithering, and setting filler.) If this is the case, simply do this:
1147 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1149 where png_transforms is an integer containing the logical OR of
1150 some set of transformation flags. This call is equivalent to png_read_info(),
1151 followed the set of transformations indicated by the transform mask,
1152 then png_read_image(), and finally png_read_end().
1154 (The final parameter of this call is not yet used. Someday it might point
1155 to transformation parameters required by some future input transform.)
1157 After you have called png_read_png(), you can retrieve the image data
1160 row_pointers = png_get_rows(png_ptr, info_ptr);
1162 where row_pointers is an array of pointers to the pixel data for each row:
1164 png_bytep row_pointers[height];
1166 If you know your image size and pixel size ahead of time, you can allocate
1167 row_pointers prior to calling png_read_png() with
1169 row_pointers = png_malloc(png_ptr,
1170 height*sizeof(png_bytep));
1171 for (int i=0; i<height, i++)
1172 row_pointers[i]=png_malloc(png_ptr,
1174 png_set_rows(png_ptr, info_ptr, &row_pointers);
1176 Alternatively you could allocate your image in one big block and define
1177 row_pointers[i] to point into the proper places in your block.
1179 If you use png_set_rows(), the application is responsible for freeing
1180 row_pointers (and row_pointers[i], if they were separately allocated).
1182 If you don't allocate row_pointers ahead of time, png_read_png() will
1183 do it, and it'll be free'ed when you call png_destroy_*().
1185 .SS The low-level read interface
1187 If you are going the low-level route, you are now ready to read all
1188 the file information up to the actual image data. You do this with a
1189 call to png_read_info().
1191 png_read_info(png_ptr, info_ptr);
1193 This will process all chunks up to but not including the image data.
1195 .SS Querying the info structure
1197 Functions are used to get the information from the info_ptr once it
1198 has been read. Note that these fields may not be completely filled
1199 in until png_read_end() has read the chunk data following the image.
1201 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1202 &bit_depth, &color_type, &interlace_type,
1203 &compression_type, &filter_method);
1205 width - holds the width of the image
1206 in pixels (up to 2^31).
1207 height - holds the height of the image
1208 in pixels (up to 2^31).
1209 bit_depth - holds the bit depth of one of the
1210 image channels. (valid values are
1211 1, 2, 4, 8, 16 and depend also on
1212 the color_type. See also
1213 significant bits (sBIT) below).
1214 color_type - describes which color/alpha channels
1217 (bit depths 1, 2, 4, 8, 16)
1218 PNG_COLOR_TYPE_GRAY_ALPHA
1220 PNG_COLOR_TYPE_PALETTE
1221 (bit depths 1, 2, 4, 8)
1224 PNG_COLOR_TYPE_RGB_ALPHA
1227 PNG_COLOR_MASK_PALETTE
1228 PNG_COLOR_MASK_COLOR
1229 PNG_COLOR_MASK_ALPHA
1231 filter_method - (must be PNG_FILTER_TYPE_BASE
1232 for PNG 1.0, and can also be
1233 PNG_INTRAPIXEL_DIFFERENCING if
1234 the PNG datastream is embedded in
1235 a MNG-1.0 datastream)
1236 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1238 interlace_type - (PNG_INTERLACE_NONE or
1239 PNG_INTERLACE_ADAM7)
1240 Any or all of interlace_type, compression_type, of
1241 filter_method can be NULL if you are
1242 not interested in their values.
1244 channels = png_get_channels(png_ptr, info_ptr);
1245 channels - number of channels of info for the
1246 color type (valid values are 1 (GRAY,
1247 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1248 4 (RGB_ALPHA or RGB + filler byte))
1249 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1250 rowbytes - number of bytes needed to hold a row
1252 signature = png_get_signature(png_ptr, info_ptr);
1253 signature - holds the signature read from the
1254 file (if any). The data is kept in
1255 the same offset it would be if the
1256 whole signature were read (i.e. if an
1257 application had already read in 4
1258 bytes of signature before starting
1259 libpng, the remaining 4 bytes would
1260 be in signature[4] through signature[7]
1261 (see png_set_sig_bytes())).
1264 width = png_get_image_width(png_ptr,
1266 height = png_get_image_height(png_ptr,
1268 bit_depth = png_get_bit_depth(png_ptr,
1270 color_type = png_get_color_type(png_ptr,
1272 filter_method = png_get_filter_type(png_ptr,
1274 compression_type = png_get_compression_type(png_ptr,
1276 interlace_type = png_get_interlace_type(png_ptr,
1280 These are also important, but their validity depends on whether the chunk
1281 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1282 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1283 data has been read, or zero if it is missing. The parameters to the
1284 png_get_<chunk> are set directly if they are simple data types, or a pointer
1285 into the info_ptr is returned for any complex types.
1287 png_get_PLTE(png_ptr, info_ptr, &palette,
1289 palette - the palette for the file
1290 (array of png_color)
1291 num_palette - number of entries in the palette
1293 png_get_gAMA(png_ptr, info_ptr, &gamma);
1294 gamma - the gamma the file is written
1297 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1298 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1299 The presence of the sRGB chunk
1300 means that the pixel data is in the
1301 sRGB color space. This chunk also
1302 implies specific values of gAMA and
1305 png_get_iCCP(png_ptr, info_ptr, &name,
1306 &compression_type, &profile, &proflen);
1307 name - The profile name.
1308 compression - The compression type; always
1309 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1310 You may give NULL to this argument to
1312 profile - International Color Consortium color
1313 profile data. May contain NULs.
1314 proflen - length of profile data in bytes.
1316 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1317 sig_bit - the number of significant bits for
1318 (PNG_INFO_sBIT) each of the gray,
1319 red, green, and blue channels,
1320 whichever are appropriate for the
1321 given color type (png_color_16)
1323 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1325 trans - array of transparent entries for
1326 palette (PNG_INFO_tRNS)
1327 trans_values - graylevel or color sample values of
1328 the single transparent color for
1329 non-paletted images (PNG_INFO_tRNS)
1330 num_trans - number of transparent entries
1333 png_get_hIST(png_ptr, info_ptr, &hist);
1335 hist - histogram of palette (array of
1338 png_get_tIME(png_ptr, info_ptr, &mod_time);
1339 mod_time - time image was last modified
1342 png_get_bKGD(png_ptr, info_ptr, &background);
1343 background - background color (PNG_VALID_bKGD)
1344 valid 16-bit red, green and blue
1345 values, regardless of color_type
1347 num_comments = png_get_text(png_ptr, info_ptr,
1348 &text_ptr, &num_text);
1349 num_comments - number of comments
1350 text_ptr - array of png_text holding image
1352 text_ptr[i].compression - type of compression used
1353 on "text" PNG_TEXT_COMPRESSION_NONE
1354 PNG_TEXT_COMPRESSION_zTXt
1355 PNG_ITXT_COMPRESSION_NONE
1356 PNG_ITXT_COMPRESSION_zTXt
1357 text_ptr[i].key - keyword for comment. Must contain
1359 text_ptr[i].text - text comments for current
1360 keyword. Can be empty.
1361 text_ptr[i].text_length - length of text string,
1362 after decompression, 0 for iTXt
1363 text_ptr[i].itxt_length - length of itxt string,
1364 after decompression, 0 for tEXt/zTXt
1365 text_ptr[i].lang - language of comment (empty
1366 string for unknown).
1367 text_ptr[i].translated_keyword - keyword in UTF-8
1368 (empty string for unknown).
1369 num_text - number of comments (same as
1370 num_comments; you can put NULL here
1371 to avoid the duplication)
1372 Note while png_set_text() will accept text, language,
1373 and translated keywords that can be NULL pointers, the
1374 structure returned by png_get_text will always contain
1375 regular zero-terminated C strings. They might be
1376 empty strings but they will never be NULL pointers.
1378 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1380 palette_ptr - array of palette structures holding
1381 contents of one or more sPLT chunks
1383 num_spalettes - number of sPLT chunks read.
1385 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1387 offset_x - positive offset from the left edge
1389 offset_y - positive offset from the top edge
1391 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1393 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1395 res_x - pixels/unit physical resolution in
1397 res_y - pixels/unit physical resolution in
1399 unit_type - PNG_RESOLUTION_UNKNOWN,
1400 PNG_RESOLUTION_METER
1402 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1404 unit - physical scale units (an integer)
1405 width - width of a pixel in physical scale units
1406 height - height of a pixel in physical scale units
1407 (width and height are doubles)
1409 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1411 unit - physical scale units (an integer)
1412 width - width of a pixel in physical scale units
1413 height - height of a pixel in physical scale units
1414 (width and height are strings like "2.54")
1416 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1417 info_ptr, &unknowns)
1418 unknowns - array of png_unknown_chunk
1419 structures holding unknown chunks
1420 unknowns[i].name - name of unknown chunk
1421 unknowns[i].data - data of unknown chunk
1422 unknowns[i].size - size of unknown chunk's data
1423 unknowns[i].location - position of chunk in file
1425 The value of "i" corresponds to the order in which the
1426 chunks were read from the PNG file or inserted with the
1427 png_set_unknown_chunks() function.
1429 The data from the pHYs chunk can be retrieved in several convenient
1432 res_x = png_get_x_pixels_per_meter(png_ptr,
1434 res_y = png_get_y_pixels_per_meter(png_ptr,
1436 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1438 res_x = png_get_x_pixels_per_inch(png_ptr,
1440 res_y = png_get_y_pixels_per_inch(png_ptr,
1442 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1444 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1447 (Each of these returns 0 [signifying "unknown"] if
1448 the data is not present or if res_x is 0;
1449 res_x_and_y is 0 if res_x != res_y)
1451 The data from the oFFs chunk can be retrieved in several convenient
1454 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1455 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1456 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1457 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1459 (Each of these returns 0 [signifying "unknown" if both
1460 x and y are 0] if the data is not present or if the
1461 chunk is present but the unit is the pixel)
1463 For more information, see the png_info definition in png.h and the
1464 PNG specification for chunk contents. Be careful with trusting
1465 rowbytes, as some of the transformations could increase the space
1466 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1467 See png_read_update_info(), below.
1469 A quick word about text_ptr and num_text. PNG stores comments in
1470 keyword/text pairs, one pair per chunk, with no limit on the number
1471 of text chunks, and a 2^31 byte limit on their size. While there are
1472 suggested keywords, there is no requirement to restrict the use to these
1473 strings. It is strongly suggested that keywords and text be sensible
1474 to humans (that's the point), so don't use abbreviations. Non-printing
1475 symbols are not allowed. See the PNG specification for more details.
1476 There is also no requirement to have text after the keyword.
1478 Keywords should be limited to 79 Latin-1 characters without leading or
1479 trailing spaces, but non-consecutive spaces are allowed within the
1480 keyword. It is possible to have the same keyword any number of times.
1481 The text_ptr is an array of png_text structures, each holding a
1482 pointer to a language string, a pointer to a keyword and a pointer to
1483 a text string. The text string, language code, and translated
1484 keyword may be empty or NULL pointers. The keyword/text
1485 pairs are put into the array in the order that they are received.
1486 However, some or all of the text chunks may be after the image, so, to
1487 make sure you have read all the text chunks, don't mess with these
1488 until after you read the stuff after the image. This will be
1489 mentioned again below in the discussion that goes with png_read_end().
1491 .SS Input transformations
1493 After you've read the header information, you can set up the library
1494 to handle any special transformations of the image data. The various
1495 ways to transform the data will be described in the order that they
1496 should occur. This is important, as some of these change the color
1497 type and/or bit depth of the data, and some others only work on
1498 certain color types and bit depths. Even though each transformation
1499 checks to see if it has data that it can do something with, you should
1500 make sure to only enable a transformation if it will be valid for the
1501 data. For example, don't swap red and blue on grayscale data.
1503 The colors used for the background and transparency values should be
1504 supplied in the same format/depth as the current image data. They
1505 are stored in the same format/depth as the image data in a bKGD or tRNS
1506 chunk, so this is what libpng expects for this data. The colors are
1507 transformed to keep in sync with the image data when an application
1508 calls the png_read_update_info() routine (see below).
1510 Data will be decoded into the supplied row buffers packed into bytes
1511 unless the library has been told to transform it into another format.
1512 For example, 4 bit/pixel paletted or grayscale data will be returned
1513 2 pixels/byte with the leftmost pixel in the high-order bits of the
1514 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1515 in RGB RGB RGB format unless png_set_filler() is called to insert filler
1516 bytes, either before or after each RGB triplet. 16-bit RGB data will
1517 be returned RRGGBB RRGGBB, with the most significant byte of the color
1518 value first, unless png_set_strip_16() is called to transform it to
1519 regular RGB RGB triplets, or png_set_filler() is called to insert
1520 filler bytes, either before or after each RRGGBB triplet. Similarly,
1521 8-bit or 16-bit grayscale data can be modified with png_set_filler()
1522 or png_set_strip_16().
1524 The following code transforms grayscale images of less than 8 to 8 bits,
1525 changes paletted images to RGB, and adds a full alpha channel if there is
1526 transparency information in a tRNS chunk. This is most useful on
1527 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1528 viewing application that wishes to treat all images in the same way.
1530 if (color_type == PNG_COLOR_TYPE_PALETTE)
1531 png_set_palette_to_rgb(png_ptr);
1533 if (color_type == PNG_COLOR_TYPE_GRAY &&
1534 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1536 if (png_get_valid(png_ptr, info_ptr,
1537 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1539 These three functions are actually aliases for png_set_expand(), added
1540 in libpng version 1.0.4, with the function names expanded to improve code
1541 readability. In some future version they may actually do different
1544 PNG can have files with 16 bits per channel. If you only can handle
1545 8 bits per channel, this will strip the pixels down to 8 bit.
1547 if (bit_depth == 16)
1548 png_set_strip_16(png_ptr);
1550 If, for some reason, you don't need the alpha channel on an image,
1551 and you want to remove it rather than combining it with the background
1552 (but the image author certainly had in mind that you *would* combine
1553 it with the background, so that's what you should probably do):
1555 if (color_type & PNG_COLOR_MASK_ALPHA)
1556 png_set_strip_alpha(png_ptr);
1558 In PNG files, the alpha channel in an image
1559 is the level of opacity. If you need the alpha channel in an image to
1560 be the level of transparency instead of opacity, you can invert the
1561 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1562 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1563 images) is fully transparent, with
1565 png_set_invert_alpha(png_ptr);
1567 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1568 they can, resulting in, for example, 8 pixels per byte for 1 bit
1569 files. This code expands to 1 pixel per byte without changing the
1570 values of the pixels:
1573 png_set_packing(png_ptr);
1575 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1576 stored in a PNG image have been "scaled" or "shifted" up to the next
1577 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1578 8 bits/sample in the range [0, 255]). However, it is also possible to
1579 convert the PNG pixel data back to the original bit depth of the image.
1580 This call reduces the pixels back down to the original bit depth:
1582 png_color_8p sig_bit;
1584 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1585 png_set_shift(png_ptr, sig_bit);
1587 PNG files store 3-color pixels in red, green, blue order. This code
1588 changes the storage of the pixels to blue, green, red:
1590 if (color_type == PNG_COLOR_TYPE_RGB ||
1591 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1592 png_set_bgr(png_ptr);
1594 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1595 into 4 or 8 bytes for windowing systems that need them in this format:
1597 if (color_type == PNG_COLOR_TYPE_RGB)
1598 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1600 where "filler" is the 8 or 16-bit number to fill with, and the location is
1601 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1602 you want the filler before the RGB or after. This transformation
1603 does not affect images that already have full alpha channels. To add an
1604 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1605 will generate RGBA pixels.
1607 If you are reading an image with an alpha channel, and you need the
1608 data as ARGB instead of the normal PNG format RGBA:
1610 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1611 png_set_swap_alpha(png_ptr);
1613 For some uses, you may want a grayscale image to be represented as
1614 RGB. This code will do that conversion:
1616 if (color_type == PNG_COLOR_TYPE_GRAY ||
1617 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1618 png_set_gray_to_rgb(png_ptr);
1620 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1623 if (color_type == PNG_COLOR_TYPE_RGB ||
1624 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1625 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1626 int red_weight, int green_weight);
1628 error_action = 1: silently do the conversion
1629 error_action = 2: issue a warning if the original
1630 image has any pixel where
1631 red != green or red != blue
1632 error_action = 3: issue an error and abort the
1633 conversion if the original
1634 image has any pixel where
1635 red != green or red != blue
1637 red_weight: weight of red component times 100000
1638 green_weight: weight of green component times 100000
1639 If either weight is negative, default
1640 weights (21268, 71514) are used.
1642 If you have set error_action = 1 or 2, you can
1643 later check whether the image really was gray, after processing
1644 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1645 It will return a png_byte that is zero if the image was gray or
1646 1 if there were any non-gray pixels. bKGD and sBIT data
1647 will be silently converted to grayscale, using the green channel
1648 data, regardless of the error_action setting.
1650 With red_weight+green_weight<=100000,
1651 the normalized graylevel is computed:
1653 int rw = red_weight * 65536;
1654 int gw = green_weight * 65536;
1655 int bw = 65536 - (rw + gw);
1656 gray = (rw*red + gw*green + bw*blue)/65536;
1658 The default values approximate those recommended in the Charles
1659 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1660 Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
1662 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1664 Libpng approximates this with
1666 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1668 which can be expressed with integers as
1670 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1672 The calculation is done in a linear colorspace, if the image gamma
1675 If you have a grayscale and you are using png_set_expand_depth() or
1676 png_set_expand() to change to
1677 a higher bit-depth, you must either supply the background color as a gray
1678 value at the original file bit-depth (need_expand = 1) or else supply the
1679 background color as an RGB triplet at the final, expanded bit depth
1680 (need_expand = 0). Similarly, if you are reading a paletted image, you
1681 must either supply the background color as a palette index (need_expand = 1)
1682 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1684 png_color_16 my_background;
1685 png_color_16p image_background;
1687 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1688 png_set_background(png_ptr, image_background,
1689 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1691 png_set_background(png_ptr, &my_background,
1692 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1694 The png_set_background() function tells libpng to composite images
1695 with alpha or simple transparency against the supplied background
1696 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1697 you may use this color, or supply another color more suitable for
1698 the current display (e.g., the background color from a web page). You
1699 need to tell libpng whether the color is in the gamma space of the
1700 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1701 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1702 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1703 know why anyone would use this, but it's here).
1705 To properly display PNG images on any kind of system, the application needs
1706 to know what the display gamma is. Ideally, the user will know this, and
1707 the application will allow them to set it. One method of allowing the user
1708 to set the display gamma separately for each system is to check for a
1709 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1712 Note that display_gamma is the overall gamma correction required to produce
1713 pleasing results, which depends on the lighting conditions in the surrounding
1714 environment. In a dim or brightly lit room, no compensation other than
1715 the physical gamma exponent of the monitor is needed, while in a dark room
1716 a slightly smaller exponent is better.
1718 double gamma, screen_gamma;
1720 if (/* We have a user-defined screen
1723 screen_gamma = user_defined_screen_gamma;
1725 /* One way that applications can share the same
1726 screen gamma value */
1727 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1730 screen_gamma = (double)atof(gamma_str);
1732 /* If we don't have another value */
1735 screen_gamma = 2.2; /* A good guess for a
1736 PC monitor in a bright office or a dim room */
1737 screen_gamma = 2.0; /* A good guess for a
1738 PC monitor in a dark room */
1739 screen_gamma = 1.7 or 1.0; /* A good
1740 guess for Mac systems */
1743 The png_set_gamma() function handles gamma transformations of the data.
1744 Pass both the file gamma and the current screen_gamma. If the file does
1745 not have a gamma value, you can pass one anyway if you have an idea what
1746 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1747 that file gammas are inverted from screen gammas. See the discussions
1748 on gamma in the PNG specification for an excellent description of what
1749 gamma is, and why all applications should support it. It is strongly
1750 recommended that PNG viewers support gamma correction.
1752 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1753 png_set_gamma(png_ptr, screen_gamma, gamma);
1755 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1757 If you need to reduce an RGB file to a paletted file, or if a paletted
1758 file has more entries then will fit on your screen, png_set_dither()
1759 will do that. Note that this is a simple match dither that merely
1760 finds the closest color available. This should work fairly well with
1761 optimized palettes, and fairly badly with linear color cubes. If you
1762 pass a palette that is larger then maximum_colors, the file will
1763 reduce the number of colors in the palette so it will fit into
1764 maximum_colors. If there is a histogram, it will use it to make
1765 more intelligent choices when reducing the palette. If there is no
1766 histogram, it may not do as good a job.
1768 if (color_type & PNG_COLOR_MASK_COLOR)
1770 if (png_get_valid(png_ptr, info_ptr,
1773 png_uint_16p histogram;
1775 png_get_hIST(png_ptr, info_ptr,
1777 png_set_dither(png_ptr, palette, num_palette,
1778 max_screen_colors, histogram, 1);
1782 png_color std_color_cube[MAX_SCREEN_COLORS] =
1785 png_set_dither(png_ptr, std_color_cube,
1786 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1791 PNG files describe monochrome as black being zero and white being one.
1792 The following code will reverse this (make black be one and white be
1795 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1796 png_set_invert_mono(png_ptr);
1798 This function can also be used to invert grayscale and gray-alpha images:
1800 if (color_type == PNG_COLOR_TYPE_GRAY ||
1801 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1802 png_set_invert_mono(png_ptr);
1804 PNG files store 16 bit pixels in network byte order (big-endian,
1805 ie. most significant bits first). This code changes the storage to the
1806 other way (little-endian, i.e. least significant bits first, the
1807 way PCs store them):
1809 if (bit_depth == 16)
1810 png_set_swap(png_ptr);
1812 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1813 need to change the order the pixels are packed into bytes, you can use:
1816 png_set_packswap(png_ptr);
1818 Finally, you can write your own transformation function if none of
1819 the existing ones meets your needs. This is done by setting a callback
1822 png_set_read_user_transform_fn(png_ptr,
1825 You must supply the function
1827 void read_transform_fn(png_ptr ptr, row_info_ptr
1828 row_info, png_bytep data)
1830 See pngtest.c for a working example. Your function will be called
1831 after all of the other transformations have been processed.
1833 You can also set up a pointer to a user structure for use by your
1834 callback function, and you can inform libpng that your transform
1835 function will change the number of channels or bit depth with the
1838 png_set_user_transform_info(png_ptr, user_ptr,
1839 user_depth, user_channels);
1841 The user's application, not libpng, is responsible for allocating and
1842 freeing any memory required for the user structure.
1844 You can retrieve the pointer via the function
1845 png_get_user_transform_ptr(). For example:
1847 voidp read_user_transform_ptr =
1848 png_get_user_transform_ptr(png_ptr);
1850 The last thing to handle is interlacing; this is covered in detail below,
1851 but you must call the function here if you want libpng to handle expansion
1852 of the interlaced image.
1854 number_of_passes = png_set_interlace_handling(png_ptr);
1856 After setting the transformations, libpng can update your png_info
1857 structure to reflect any transformations you've requested with this
1858 call. This is most useful to update the info structure's rowbytes
1859 field so you can use it to allocate your image memory. This function
1860 will also update your palette with the correct screen_gamma and
1861 background if these have been given with the calls above.
1863 png_read_update_info(png_ptr, info_ptr);
1865 After you call png_read_update_info(), you can allocate any
1866 memory you need to hold the image. The row data is simply
1867 raw byte data for all forms of images. As the actual allocation
1868 varies among applications, no example will be given. If you
1869 are allocating one large chunk, you will need to build an
1870 array of pointers to each row, as it will be needed for some
1871 of the functions below.
1873 .SS Reading image data
1875 After you've allocated memory, you can read the image data.
1876 The simplest way to do this is in one function call. If you are
1877 allocating enough memory to hold the whole image, you can just
1878 call png_read_image() and libpng will read in all the image data
1879 and put it in the memory area supplied. You will need to pass in
1880 an array of pointers to each row.
1882 This function automatically handles interlacing, so you don't need
1883 to call png_set_interlace_handling() or call this function multiple
1884 times, or any of that other stuff necessary with png_read_rows().
1886 png_read_image(png_ptr, row_pointers);
1888 where row_pointers is:
1890 png_bytep row_pointers[height];
1892 You can point to void or char or whatever you use for pixels.
1894 If you don't want to read in the whole image at once, you can
1895 use png_read_rows() instead. If there is no interlacing (check
1896 interlace_type == PNG_INTERLACE_NONE), this is simple:
1898 png_read_rows(png_ptr, row_pointers, NULL,
1901 where row_pointers is the same as in the png_read_image() call.
1903 If you are doing this just one row at a time, you can do this with
1904 a single row_pointer instead of an array of row_pointers:
1906 png_bytep row_pointer = row;
1907 png_read_row(png_ptr, row_pointer, NULL);
1909 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1910 get somewhat harder. The only current (PNG Specification version 1.2)
1911 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1912 is a somewhat complicated 2D interlace scheme, known as Adam7, that
1913 breaks down an image into seven smaller images of varying size, based
1916 libpng can fill out those images or it can give them to you "as is".
1917 If you want them filled out, there are two ways to do that. The one
1918 mentioned in the PNG specification is to expand each pixel to cover
1919 those pixels that have not been read yet (the "rectangle" method).
1920 This results in a blocky image for the first pass, which gradually
1921 smooths out as more pixels are read. The other method is the "sparkle"
1922 method, where pixels are drawn only in their final locations, with the
1923 rest of the image remaining whatever colors they were initialized to
1924 before the start of the read. The first method usually looks better,
1925 but tends to be slower, as there are more pixels to put in the rows.
1927 If you don't want libpng to handle the interlacing details, just call
1928 png_read_rows() seven times to read in all seven images. Each of the
1929 images is a valid image by itself, or they can all be combined on an
1930 8x8 grid to form a single image (although if you intend to combine them
1931 you would be far better off using the libpng interlace handling).
1933 The first pass will return an image 1/8 as wide as the entire image
1934 (every 8th column starting in column 0) and 1/8 as high as the original
1935 (every 8th row starting in row 0), the second will be 1/8 as wide
1936 (starting in column 4) and 1/8 as high (also starting in row 0). The
1937 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
1938 1/8 as high (every 8th row starting in row 4), and the fourth pass will
1939 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1940 and every 4th row starting in row 0). The fifth pass will return an
1941 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1942 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1943 (starting in column 1 and row 0). The seventh and final pass will be as
1944 wide as the original, and 1/2 as high, containing all of the odd
1945 numbered scanlines. Phew!
1947 If you want libpng to expand the images, call this before calling
1948 png_start_read_image() or png_read_update_info():
1950 if (interlace_type == PNG_INTERLACE_ADAM7)
1952 = png_set_interlace_handling(png_ptr);
1954 This will return the number of passes needed. Currently, this
1955 is seven, but may change if another interlace type is added.
1956 This function can be called even if the file is not interlaced,
1957 where it will return one pass.
1959 If you are not going to display the image after each pass, but are
1960 going to wait until the entire image is read in, use the sparkle
1961 effect. This effect is faster and the end result of either method
1962 is exactly the same. If you are planning on displaying the image
1963 after each pass, the "rectangle" effect is generally considered the
1966 If you only want the "sparkle" effect, just call png_read_rows() as
1967 normal, with the third parameter NULL. Make sure you make pass over
1968 the image number_of_passes times, and you don't change the data in the
1969 rows between calls. You can change the locations of the data, just
1970 not the data. Each pass only writes the pixels appropriate for that
1971 pass, and assumes the data from previous passes is still valid.
1973 png_read_rows(png_ptr, row_pointers, NULL,
1976 If you only want the first effect (the rectangles), do the same as
1977 before except pass the row buffer in the third parameter, and leave
1978 the second parameter NULL.
1980 png_read_rows(png_ptr, NULL, row_pointers,
1983 .SS Finishing a sequential read
1985 After you are finished reading the image through either the high- or
1986 low-level interfaces, you can finish reading the file. If you are
1987 interested in comments or time, which may be stored either before or
1988 after the image data, you should pass the separate png_info struct if
1989 you want to keep the comments from before and after the image
1990 separate. If you are not interested, you can pass NULL.
1992 png_read_end(png_ptr, end_info);
1994 When you are done, you can free all memory allocated by libpng like this:
1996 png_destroy_read_struct(&png_ptr, &info_ptr,
1999 It is also possible to individually free the info_ptr members that
2000 point to libpng-allocated storage with the following function:
2002 png_free_data(png_ptr, info_ptr, mask, seq)
2003 mask - identifies data to be freed, a mask
2004 containing the logical OR of one or
2006 PNG_FREE_PLTE, PNG_FREE_TRNS,
2007 PNG_FREE_HIST, PNG_FREE_ICCP,
2008 PNG_FREE_PCAL, PNG_FREE_ROWS,
2009 PNG_FREE_SCAL, PNG_FREE_SPLT,
2010 PNG_FREE_TEXT, PNG_FREE_UNKN,
2011 or simply PNG_FREE_ALL
2012 seq - sequence number of item to be freed
2015 This function may be safely called when the relevant storage has
2016 already been freed, or has not yet been allocated, or was allocated
2017 by the user and not by libpng, and will in those
2018 cases do nothing. The "seq" parameter is ignored if only one item
2019 of the selected data type, such as PLTE, is allowed. If "seq" is not
2020 -1, and multiple items are allowed for the data type identified in
2021 the mask, such as text or sPLT, only the n'th item in the structure
2022 is freed, where n is "seq".
2024 The default behavior is only to free data that was allocated internally
2025 by libpng. This can be changed, so that libpng will not free the data,
2026 or so that it will free data that was allocated by the user with png_malloc()
2027 or png_zalloc() and passed in via a png_set_*() function, with
2029 png_data_freer(png_ptr, info_ptr, freer, mask)
2030 mask - which data elements are affected
2031 same choices as in png_free_data()
2033 PNG_DESTROY_WILL_FREE_DATA
2034 PNG_SET_WILL_FREE_DATA
2035 PNG_USER_WILL_FREE_DATA
2037 This function only affects data that has already been allocated.
2038 You can call this function after reading the PNG data but before calling
2039 any png_set_*() functions, to control whether the user or the png_set_*()
2040 function is responsible for freeing any existing data that might be present,
2041 and again after the png_set_*() functions to control whether the user
2042 or png_destroy_*() is supposed to free the data. When the user assumes
2043 responsibility for libpng-allocated data, the application must use
2044 png_free() to free it, and when the user transfers responsibility to libpng
2045 for data that the user has allocated, the user must have used png_malloc()
2046 or png_zalloc() to allocate it.
2048 If you allocated your row_pointers in a single block, as suggested above in
2049 the description of the high level read interface, you must not transfer
2050 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2051 because they would also try to free the individual row_pointers[i].
2053 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2054 separately, do not transfer responsibility for freeing text_ptr to libpng,
2055 because when libpng fills a png_text structure it combines these members with
2056 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2057 if you transfer responsibility for free'ing text_ptr from libpng to your
2058 application, your application must not separately free those members.
2060 The png_free_data() function will turn off the "valid" flag for anything
2061 it frees. If you need to turn the flag off for a chunk that was freed by your
2062 application instead of by libpng, you can use
2064 png_set_invalid(png_ptr, info_ptr, mask);
2065 mask - identifies the chunks to be made invalid,
2066 containing the logical OR of one or
2068 PNG_INFO_gAMA, PNG_INFO_sBIT,
2069 PNG_INFO_cHRM, PNG_INFO_PLTE,
2070 PNG_INFO_tRNS, PNG_INFO_bKGD,
2071 PNG_INFO_hIST, PNG_INFO_pHYs,
2072 PNG_INFO_oFFs, PNG_INFO_tIME,
2073 PNG_INFO_pCAL, PNG_INFO_sRGB,
2074 PNG_INFO_iCCP, PNG_INFO_sPLT,
2075 PNG_INFO_sCAL, PNG_INFO_IDAT
2077 For a more compact example of reading a PNG image, see the file example.c.
2079 .SS Reading PNG files progressively
2081 The progressive reader is slightly different then the non-progressive
2082 reader. Instead of calling png_read_info(), png_read_rows(), and
2083 png_read_end(), you make one call to png_process_data(), which calls
2084 callbacks when it has the info, a row, or the end of the image. You
2085 set up these callbacks with png_set_progressive_read_fn(). You don't
2086 have to worry about the input/output functions of libpng, as you are
2087 giving the library the data directly in png_process_data(). I will
2088 assume that you have read the section on reading PNG files above,
2089 so I will only highlight the differences (although I will show
2092 png_structp png_ptr;
2095 /* An example code fragment of how you would
2096 initialize the progressive reader in your
2099 initialize_png_reader()
2101 png_ptr = png_create_read_struct
2102 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2103 user_error_fn, user_warning_fn);
2106 info_ptr = png_create_info_struct(png_ptr);
2109 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2114 if (setjmp(png_jmpbuf(png_ptr)))
2116 png_destroy_read_struct(&png_ptr, &info_ptr,
2121 /* This one's new. You can provide functions
2122 to be called when the header info is valid,
2123 when each row is completed, and when the image
2124 is finished. If you aren't using all functions,
2125 you can specify NULL parameters. Even when all
2126 three functions are NULL, you need to call
2127 png_set_progressive_read_fn(). You can use
2128 any struct as the user_ptr (cast to a void pointer
2129 for the function call), and retrieve the pointer
2130 from inside the callbacks using the function
2132 png_get_progressive_ptr(png_ptr);
2134 which will return a void pointer, which you have
2135 to cast appropriately.
2137 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2138 info_callback, row_callback, end_callback);
2143 /* A code fragment that you call as you receive blocks
2146 process_data(png_bytep buffer, png_uint_32 length)
2148 if (setjmp(png_jmpbuf(png_ptr)))
2150 png_destroy_read_struct(&png_ptr, &info_ptr,
2155 /* This one's new also. Simply give it a chunk
2156 of data from the file stream (in order, of
2157 course). On machines with segmented memory
2158 models machines, don't give it any more than
2159 64K. The library seems to run fine with sizes
2160 of 4K. Although you can give it much less if
2161 necessary (I assume you can give it chunks of
2162 1 byte, I haven't tried less then 256 bytes
2163 yet). When this function returns, you may
2164 want to display any rows that were generated
2165 in the row callback if you don't already do
2168 png_process_data(png_ptr, info_ptr, buffer, length);
2172 /* This function is called (as set by
2173 png_set_progressive_read_fn() above) when enough data
2174 has been supplied so all of the header has been
2178 info_callback(png_structp png_ptr, png_infop info)
2180 /* Do any setup here, including setting any of
2181 the transformations mentioned in the Reading
2182 PNG files section. For now, you _must_ call
2183 either png_start_read_image() or
2184 png_read_update_info() after all the
2185 transformations are set (even if you don't set
2186 any). You may start getting rows before
2187 png_process_data() returns, so this is your
2188 last chance to prepare for that.
2192 /* This function is called when each row of image
2195 row_callback(png_structp png_ptr, png_bytep new_row,
2196 png_uint_32 row_num, int pass)
2198 /* If the image is interlaced, and you turned
2199 on the interlace handler, this function will
2200 be called for every row in every pass. Some
2201 of these rows will not be changed from the
2202 previous pass. When the row is not changed,
2203 the new_row variable will be NULL. The rows
2204 and passes are called in order, so you don't
2205 really need the row_num and pass, but I'm
2206 supplying them because it may make your life
2209 For the non-NULL rows of interlaced images,
2210 you must call png_progressive_combine_row()
2211 passing in the row and the old row. You can
2212 call this function for NULL rows (it will just
2213 return) and for non-interlaced images (it just
2214 does the memcpy for you) if it will make the
2215 code easier. Thus, you can just do this for
2219 png_progressive_combine_row(png_ptr, old_row,
2222 /* where old_row is what was displayed for
2223 previously for the row. Note that the first
2224 pass (pass == 0, really) will completely cover
2225 the old row, so the rows do not have to be
2226 initialized. After the first pass (and only
2227 for interlaced images), you will have to pass
2228 the current row, and the function will combine
2229 the old row and the new row.
2234 end_callback(png_structp png_ptr, png_infop info)
2236 /* This function is called after the whole image
2237 has been read, including any chunks after the
2238 image (up to and including the IEND). You
2239 will usually have the same info chunk as you
2240 had in the header, although some data may have
2241 been added to the comments and time fields.
2243 Most people won't do much here, perhaps setting
2244 a flag that marks the image as finished.
2252 Much of this is very similar to reading. However, everything of
2253 importance is repeated here, so you won't have to constantly look
2254 back up in the reading section to understand writing.
2258 You will want to do the I/O initialization before you get into libpng,
2259 so if it doesn't work, you don't have anything to undo. If you are not
2260 using the standard I/O functions, you will need to replace them with
2261 custom writing functions. See the discussion under Customizing libpng.
2263 FILE *fp = fopen(file_name, "wb");
2269 Next, png_struct and png_info need to be allocated and initialized.
2270 As these can be both relatively large, you may not want to store these
2271 on the stack, unless you have stack space to spare. Of course, you
2272 will want to check if they return NULL. If you are also reading,
2273 you won't want to name your read structure and your write structure
2274 both "png_ptr"; you can call them anything you like, such as
2275 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2277 png_structp png_ptr = png_create_write_struct
2278 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2279 user_error_fn, user_warning_fn);
2283 png_infop info_ptr = png_create_info_struct(png_ptr);
2286 png_destroy_write_struct(&png_ptr,
2291 If you want to use your own memory allocation routines,
2292 define PNG_USER_MEM_SUPPORTED and use
2293 png_create_write_struct_2() instead of png_create_write_struct():
2295 png_structp png_ptr = png_create_write_struct_2
2296 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2297 user_error_fn, user_warning_fn, (png_voidp)
2298 user_mem_ptr, user_malloc_fn, user_free_fn);
2300 After you have these structures, you will need to set up the
2301 error handling. When libpng encounters an error, it expects to
2302 longjmp() back to your routine. Therefore, you will need to call
2303 setjmp() and pass the png_jmpbuf(png_ptr). If you
2304 write the file from different routines, you will need to update
2305 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2306 call a png_*() function. See your documentation of setjmp/longjmp
2307 for your compiler for more information on setjmp/longjmp. See
2308 the discussion on libpng error handling in the Customizing Libpng
2309 section below for more information on the libpng error handling.
2311 if (setjmp(png_jmpbuf(png_ptr)))
2313 png_destroy_write_struct(&png_ptr, &info_ptr);
2320 If you would rather avoid the complexity of setjmp/longjmp issues,
2321 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2322 errors will result in a call to PNG_ABORT() which defaults to abort().
2324 Now you need to set up the output code. The default for libpng is to
2325 use the C function fwrite(). If you use this, you will need to pass a
2326 valid FILE * in the function png_init_io(). Be sure that the file is
2327 opened in binary mode. Again, if you wish to handle writing data in
2328 another way, see the discussion on libpng I/O handling in the Customizing
2329 Libpng section below.
2331 png_init_io(png_ptr, fp);
2335 At this point, you can set up a callback function that will be
2336 called after each row has been written, which you can use to control
2337 a progress meter or the like. It's demonstrated in pngtest.c.
2338 You must supply a function
2340 void write_row_callback(png_ptr, png_uint_32 row,
2343 /* put your code here */
2346 (You can give it another name that you like instead of "write_row_callback")
2348 To inform libpng about your function, use
2350 png_set_write_status_fn(png_ptr, write_row_callback);
2352 You now have the option of modifying how the compression library will
2353 run. The following functions are mainly for testing, but may be useful
2354 in some cases, like if you need to write PNG files extremely fast and
2355 are willing to give up some compression, or if you want to get the
2356 maximum possible compression at the expense of slower writing. If you
2357 have no special needs in this area, let the library do what it wants by
2358 not calling this function at all, as it has been tuned to deliver a good
2359 speed/compression ratio. The second parameter to png_set_filter() is
2360 the filter method, for which the only valid values are 0 (as of the
2361 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2362 a PNG datastream that is to be embedded in a MNG datastream). The third
2363 parameter is a flag that indicates which filter type(s) are to be tested
2364 for each scanline. See the PNG specification for details on the specific filter
2368 /* turn on or off filtering, and/or choose
2369 specific filters. You can use either a single
2370 PNG_FILTER_VALUE_NAME or the logical OR of one
2371 or more PNG_FILTER_NAME masks. */
2372 png_set_filter(png_ptr, 0,
2373 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2374 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2375 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2376 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2377 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2381 wants to start and stop using particular filters during compression,
2382 it should start out with all of the filters (to ensure that the previous
2383 row of pixels will be stored in case it's needed later), and then add
2384 and remove them after the start of compression.
2386 If you are writing a PNG datastream that is to be embedded in a MNG
2387 datastream, the second parameter can be either 0 or 64.
2389 The png_set_compression_*() functions interface to the zlib compression
2390 library, and should mostly be ignored unless you really know what you are
2391 doing. The only generally useful call is png_set_compression_level()
2392 which changes how much time zlib spends on trying to compress the image
2393 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2394 with zlib) for details on the compression levels.
2396 /* set the zlib compression level */
2397 png_set_compression_level(png_ptr,
2398 Z_BEST_COMPRESSION);
2400 /* set other zlib parameters */
2401 png_set_compression_mem_level(png_ptr, 8);
2402 png_set_compression_strategy(png_ptr,
2403 Z_DEFAULT_STRATEGY);
2404 png_set_compression_window_bits(png_ptr, 15);
2405 png_set_compression_method(png_ptr, 8);
2406 png_set_compression_buffer_size(png_ptr, 8192)
2408 extern PNG_EXPORT(void,png_set_zbuf_size)
2410 .SS Setting the contents of info for output
2412 You now need to fill in the png_info structure with all the data you
2413 wish to write before the actual image. Note that the only thing you
2414 are allowed to write after the image is the text chunks and the time
2415 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2416 the latest PNG specification for more information on that. If you
2417 wish to write them before the image, fill them in now, and flag that
2418 data as being valid. If you want to wait until after the data, don't
2419 fill them until png_write_end(). For all the fields in png_info and
2420 their data types, see png.h. For explanations of what the fields
2421 contain, see the PNG specification.
2423 Some of the more important parts of the png_info are:
2425 png_set_IHDR(png_ptr, info_ptr, width, height,
2426 bit_depth, color_type, interlace_type,
2427 compression_type, filter_method)
2428 width - holds the width of the image
2429 in pixels (up to 2^31).
2430 height - holds the height of the image
2431 in pixels (up to 2^31).
2432 bit_depth - holds the bit depth of one of the
2434 (valid values are 1, 2, 4, 8, 16
2435 and depend also on the
2436 color_type. See also significant
2438 color_type - describes which color/alpha
2439 channels are present.
2441 (bit depths 1, 2, 4, 8, 16)
2442 PNG_COLOR_TYPE_GRAY_ALPHA
2444 PNG_COLOR_TYPE_PALETTE
2445 (bit depths 1, 2, 4, 8)
2448 PNG_COLOR_TYPE_RGB_ALPHA
2451 PNG_COLOR_MASK_PALETTE
2452 PNG_COLOR_MASK_COLOR
2453 PNG_COLOR_MASK_ALPHA
2455 interlace_type - PNG_INTERLACE_NONE or
2457 compression_type - (must be
2458 PNG_COMPRESSION_TYPE_DEFAULT)
2459 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2460 or, if you are writing a PNG to
2461 be embedded in a MNG datastream,
2463 PNG_INTRAPIXEL_DIFFERENCING)
2465 png_set_PLTE(png_ptr, info_ptr, palette,
2467 palette - the palette for the file
2468 (array of png_color)
2469 num_palette - number of entries in the palette
2471 png_set_gAMA(png_ptr, info_ptr, gamma);
2472 gamma - the gamma the image was created
2475 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2476 srgb_intent - the rendering intent
2477 (PNG_INFO_sRGB) The presence of
2478 the sRGB chunk means that the pixel
2479 data is in the sRGB color space.
2480 This chunk also implies specific
2481 values of gAMA and cHRM. Rendering
2482 intent is the CSS-1 property that
2483 has been defined by the International
2485 (http://www.color.org).
2487 PNG_sRGB_INTENT_SATURATION,
2488 PNG_sRGB_INTENT_PERCEPTUAL,
2489 PNG_sRGB_INTENT_ABSOLUTE, or
2490 PNG_sRGB_INTENT_RELATIVE.
2493 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2495 srgb_intent - the rendering intent
2496 (PNG_INFO_sRGB) The presence of the
2497 sRGB chunk means that the pixel
2498 data is in the sRGB color space.
2499 This function also causes gAMA and
2500 cHRM chunks with the specific values
2501 that are consistent with sRGB to be
2504 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2506 name - The profile name.
2507 compression - The compression type; always
2508 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2509 You may give NULL to this argument to
2511 profile - International Color Consortium color
2512 profile data. May contain NULs.
2513 proflen - length of profile data in bytes.
2515 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2516 sig_bit - the number of significant bits for
2517 (PNG_INFO_sBIT) each of the gray, red,
2518 green, and blue channels, whichever are
2519 appropriate for the given color type
2522 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2524 trans - array of transparent entries for
2525 palette (PNG_INFO_tRNS)
2526 trans_values - graylevel or color sample values of
2527 the single transparent color for
2528 non-paletted images (PNG_INFO_tRNS)
2529 num_trans - number of transparent entries
2532 png_set_hIST(png_ptr, info_ptr, hist);
2534 hist - histogram of palette (array of
2537 png_set_tIME(png_ptr, info_ptr, mod_time);
2538 mod_time - time image was last modified
2541 png_set_bKGD(png_ptr, info_ptr, background);
2542 background - background color (PNG_VALID_bKGD)
2544 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2545 text_ptr - array of png_text holding image
2547 text_ptr[i].compression - type of compression used
2548 on "text" PNG_TEXT_COMPRESSION_NONE
2549 PNG_TEXT_COMPRESSION_zTXt
2550 PNG_ITXT_COMPRESSION_NONE
2551 PNG_ITXT_COMPRESSION_zTXt
2552 text_ptr[i].key - keyword for comment. Must contain
2554 text_ptr[i].text - text comments for current
2555 keyword. Can be NULL or empty.
2556 text_ptr[i].text_length - length of text string,
2557 after decompression, 0 for iTXt
2558 text_ptr[i].itxt_length - length of itxt string,
2559 after decompression, 0 for tEXt/zTXt
2560 text_ptr[i].lang - language of comment (NULL or
2562 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2563 or empty for unknown).
2564 num_text - number of comments
2566 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2568 palette_ptr - array of png_sPLT_struct structures
2569 to be added to the list of palettes
2570 in the info structure.
2571 num_spalettes - number of palette structures to be
2574 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2576 offset_x - positive offset from the left
2578 offset_y - positive offset from the top
2580 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2582 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2584 res_x - pixels/unit physical resolution
2586 res_y - pixels/unit physical resolution
2588 unit_type - PNG_RESOLUTION_UNKNOWN,
2589 PNG_RESOLUTION_METER
2591 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2592 unit - physical scale units (an integer)
2593 width - width of a pixel in physical scale units
2594 height - height of a pixel in physical scale units
2595 (width and height are doubles)
2597 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2598 unit - physical scale units (an integer)
2599 width - width of a pixel in physical scale units
2600 height - height of a pixel in physical scale units
2601 (width and height are strings like "2.54")
2603 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2605 unknowns - array of png_unknown_chunk
2606 structures holding unknown chunks
2607 unknowns[i].name - name of unknown chunk
2608 unknowns[i].data - data of unknown chunk
2609 unknowns[i].size - size of unknown chunk's data
2610 unknowns[i].location - position to write chunk in file
2611 0: do not write chunk
2612 PNG_HAVE_IHDR: before PLTE
2613 PNG_HAVE_PLTE: before IDAT
2614 PNG_AFTER_IDAT: after IDAT
2616 The "location" member is set automatically according to
2617 what part of the output file has already been written.
2618 You can change its value after calling png_set_unknown_chunks()
2619 as demonstrated in pngtest.c. Within each of the "locations",
2620 the chunks are sequenced according to their position in the
2621 structure (that is, the value of "i", which is the order in which
2622 the chunk was either read from the input file or defined with
2623 png_set_unknown_chunks).
2625 A quick word about text and num_text. text is an array of png_text
2626 structures. num_text is the number of valid structures in the array.
2627 Each png_text structure holds a language code, a keyword, a text value,
2628 and a compression type.
2630 The compression types have the same valid numbers as the compression
2631 types of the image data. Currently, the only valid number is zero.
2632 However, you can store text either compressed or uncompressed, unlike
2633 images, which always have to be compressed. So if you don't want the
2634 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2635 Because tEXt and zTXt chunks don't have a language field, if you
2636 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2637 any language code or translated keyword will not be written out.
2639 Until text gets around 1000 bytes, it is not worth compressing it.
2640 After the text has been written out to the file, the compression type
2641 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2642 so that it isn't written out again at the end (in case you are calling
2643 png_write_end() with the same struct.
2645 The keywords that are given in the PNG Specification are:
2647 Title Short (one line) title or
2649 Author Name of image's creator
2650 Description Description of image (possibly long)
2651 Copyright Copyright notice
2652 Creation Time Time of original image creation
2653 (usually RFC 1123 format, see below)
2654 Software Software used to create the image
2655 Disclaimer Legal disclaimer
2656 Warning Warning of nature of content
2657 Source Device used to create the image
2658 Comment Miscellaneous comment; conversion
2659 from other image format
2661 The keyword-text pairs work like this. Keywords should be short
2662 simple descriptions of what the comment is about. Some typical
2663 keywords are found in the PNG specification, as is some recommendations
2664 on keywords. You can repeat keywords in a file. You can even write
2665 some text before the image and some after. For example, you may want
2666 to put a description of the image before the image, but leave the
2667 disclaimer until after, so viewers working over modem connections
2668 don't have to wait for the disclaimer to go over the modem before
2669 they start seeing the image. Finally, keywords should be full
2670 words, not abbreviations. Keywords and text are in the ISO 8859-1
2671 (Latin-1) character set (a superset of regular ASCII) and can not
2672 contain NUL characters, and should not contain control or other
2673 unprintable characters. To make the comments widely readable, stick
2674 with basic ASCII, and avoid machine specific character set extensions
2675 like the IBM-PC character set. The keyword must be present, but
2676 you can leave off the text string on non-compressed pairs.
2677 Compressed pairs must have a text string, as only the text string
2678 is compressed anyway, so the compression would be meaningless.
2680 PNG supports modification time via the png_time structure. Two
2681 conversion routines are provided, png_convert_from_time_t() for
2682 time_t and png_convert_from_struct_tm() for struct tm. The
2683 time_t routine uses gmtime(). You don't have to use either of
2684 these, but if you wish to fill in the png_time structure directly,
2685 you should provide the time in universal time (GMT) if possible
2686 instead of your local time. Note that the year number is the full
2687 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2688 that months start with 1.
2690 If you want to store the time of the original image creation, you should
2691 use a plain tEXt chunk with the "Creation Time" keyword. This is
2692 necessary because the "creation time" of a PNG image is somewhat vague,
2693 depending on whether you mean the PNG file, the time the image was
2694 created in a non-PNG format, a still photo from which the image was
2695 scanned, or possibly the subject matter itself. In order to facilitate
2696 machine-readable dates, it is recommended that the "Creation Time"
2697 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2698 although this isn't a requirement. Unlike the tIME chunk, the
2699 "Creation Time" tEXt chunk is not expected to be automatically changed
2700 by the software. To facilitate the use of RFC 1123 dates, a function
2701 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2702 time to an RFC 1123 format string.
2704 .SS Writing unknown chunks
2706 You can use the png_set_unknown_chunks function to queue up chunks
2707 for writing. You give it a chunk name, raw data, and a size; that's
2708 all there is to it. The chunks will be written by the next following
2709 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2710 Any chunks previously read into the info structure's unknown-chunk
2711 list will also be written out in a sequence that satisfies the PNG
2712 specification's ordering rules.
2714 .SS The high-level write interface
2716 At this point there are two ways to proceed; through the high-level
2717 write interface, or through a sequence of low-level write operations.
2718 You can use the high-level interface if your image data is present
2719 in the info structure. All defined output
2720 transformations are permitted, enabled by the following masks.
2722 PNG_TRANSFORM_IDENTITY No transformation
2723 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2724 PNG_TRANSFORM_PACKSWAP Change order of packed
2726 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2727 PNG_TRANSFORM_SHIFT Normalize pixels to the
2729 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2731 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2733 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2735 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2736 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2738 If you have valid image data in the info structure (you can use
2739 png_set_rows() to put image data in the info structure), simply do this:
2741 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2743 where png_transforms is an integer containing the logical OR of some set of
2744 transformation flags. This call is equivalent to png_write_info(),
2745 followed the set of transformations indicated by the transform mask,
2746 then png_write_image(), and finally png_write_end().
2748 (The final parameter of this call is not yet used. Someday it might point
2749 to transformation parameters required by some future output transform.)
2751 .SS The low-level write interface
2753 If you are going the low-level route instead, you are now ready to
2754 write all the file information up to the actual image data. You do
2755 this with a call to png_write_info().
2757 png_write_info(png_ptr, info_ptr);
2759 Note that there is one transformation you may need to do before
2760 png_write_info(). In PNG files, the alpha channel in an image is the
2761 level of opacity. If your data is supplied as a level of
2762 transparency, you can invert the alpha channel before you write it, so
2763 that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2764 65535 (in 16-bit images) is fully opaque, with
2766 png_set_invert_alpha(png_ptr);
2768 This must appear before png_write_info() instead of later with the
2769 other transformations because in the case of paletted images the tRNS
2770 chunk data has to be inverted before the tRNS chunk is written. If
2771 your image is not a paletted image, the tRNS data (which in such cases
2772 represents a single color to be rendered as transparent) won't need to
2773 be changed, and you can safely do this transformation after your
2774 png_write_info() call.
2776 If you need to write a private chunk that you want to appear before
2777 the PLTE chunk when PLTE is present, you can write the PNG info in
2778 two steps, and insert code to write your own chunk between them:
2780 png_write_info_before_PLTE(png_ptr, info_ptr);
2781 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2782 png_write_info(png_ptr, info_ptr);
2784 After you've written the file information, you can set up the library
2785 to handle any special transformations of the image data. The various
2786 ways to transform the data will be described in the order that they
2787 should occur. This is important, as some of these change the color
2788 type and/or bit depth of the data, and some others only work on
2789 certain color types and bit depths. Even though each transformation
2790 checks to see if it has data that it can do something with, you should
2791 make sure to only enable a transformation if it will be valid for the
2792 data. For example, don't swap red and blue on grayscale data.
2794 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2795 the library to strip input data that has 4 or 8 bytes per pixel down
2796 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2799 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2801 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2802 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2803 is stored XRGB or RGBX.
2805 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2806 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2807 If the data is supplied at 1 pixel per byte, use this code, which will
2808 correctly pack the pixels into a single byte:
2810 png_set_packing(png_ptr);
2812 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2813 data is of another bit depth, you can write an sBIT chunk into the
2814 file so that decoders can recover the original data if desired.
2816 /* Set the true bit depth of the image data */
2817 if (color_type & PNG_COLOR_MASK_COLOR)
2819 sig_bit.red = true_bit_depth;
2820 sig_bit.green = true_bit_depth;
2821 sig_bit.blue = true_bit_depth;
2825 sig_bit.gray = true_bit_depth;
2827 if (color_type & PNG_COLOR_MASK_ALPHA)
2829 sig_bit.alpha = true_bit_depth;
2832 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2834 If the data is stored in the row buffer in a bit depth other than
2835 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2836 this will scale the values to appear to be the correct bit depth as
2839 png_set_shift(png_ptr, &sig_bit);
2841 PNG files store 16 bit pixels in network byte order (big-endian,
2842 ie. most significant bits first). This code would be used if they are
2843 supplied the other way (little-endian, i.e. least significant bits
2844 first, the way PCs store them):
2847 png_set_swap(png_ptr);
2849 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2850 need to change the order the pixels are packed into bytes, you can use:
2853 png_set_packswap(png_ptr);
2855 PNG files store 3 color pixels in red, green, blue order. This code
2856 would be used if they are supplied as blue, green, red:
2858 png_set_bgr(png_ptr);
2860 PNG files describe monochrome as black being zero and white being
2861 one. This code would be used if the pixels are supplied with this reversed
2862 (black being one and white being zero):
2864 png_set_invert_mono(png_ptr);
2866 Finally, you can write your own transformation function if none of
2867 the existing ones meets your needs. This is done by setting a callback
2870 png_set_write_user_transform_fn(png_ptr,
2871 write_transform_fn);
2873 You must supply the function
2875 void write_transform_fn(png_ptr ptr, row_info_ptr
2876 row_info, png_bytep data)
2878 See pngtest.c for a working example. Your function will be called
2879 before any of the other transformations are processed.
2881 You can also set up a pointer to a user structure for use by your
2884 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2886 The user_channels and user_depth parameters of this function are ignored
2887 when writing; you can set them to zero as shown.
2889 You can retrieve the pointer via the function png_get_user_transform_ptr().
2892 voidp write_user_transform_ptr =
2893 png_get_user_transform_ptr(png_ptr);
2895 It is possible to have libpng flush any pending output, either manually,
2896 or automatically after a certain number of lines have been written. To
2897 flush the output stream a single time call:
2899 png_write_flush(png_ptr);
2901 and to have libpng flush the output stream periodically after a certain
2902 number of scanlines have been written, call:
2904 png_set_flush(png_ptr, nrows);
2906 Note that the distance between rows is from the last time png_write_flush()
2907 was called, or the first row of the image if it has never been called.
2908 So if you write 50 lines, and then png_set_flush 25, it will flush the
2909 output on the next scanline, and every 25 lines thereafter, unless
2910 png_write_flush() is called before 25 more lines have been written.
2911 If nrows is too small (less than about 10 lines for a 640 pixel wide
2912 RGB image) the image compression may decrease noticeably (although this
2913 may be acceptable for real-time applications). Infrequent flushing will
2914 only degrade the compression performance by a few percent over images
2915 that do not use flushing.
2917 .SS Writing the image data
2919 That's it for the transformations. Now you can write the image data.
2920 The simplest way to do this is in one function call. If you have the
2921 whole image in memory, you can just call png_write_image() and libpng
2922 will write the image. You will need to pass in an array of pointers to
2923 each row. This function automatically handles interlacing, so you don't
2924 need to call png_set_interlace_handling() or call this function multiple
2925 times, or any of that other stuff necessary with png_write_rows().
2927 png_write_image(png_ptr, row_pointers);
2929 where row_pointers is:
2931 png_byte *row_pointers[height];
2933 You can point to void or char or whatever you use for pixels.
2935 If you don't want to write the whole image at once, you can
2936 use png_write_rows() instead. If the file is not interlaced,
2939 png_write_rows(png_ptr, row_pointers,
2942 row_pointers is the same as in the png_write_image() call.
2944 If you are just writing one row at a time, you can do this with
2945 a single row_pointer instead of an array of row_pointers:
2947 png_bytep row_pointer = row;
2949 png_write_row(png_ptr, row_pointer);
2951 When the file is interlaced, things can get a good deal more
2952 complicated. The only currently (as of the PNG Specification
2953 version 1.2, dated July 1999) defined interlacing scheme for PNG files
2954 is the "Adam7" interlace scheme, that breaks down an
2955 image into seven smaller images of varying size. libpng will build
2956 these images for you, or you can do them yourself. If you want to
2957 build them yourself, see the PNG specification for details of which
2958 pixels to write when.
2960 If you don't want libpng to handle the interlacing details, just
2961 use png_set_interlace_handling() and call png_write_rows() the
2962 correct number of times to write all seven sub-images.
2964 If you want libpng to build the sub-images, call this before you start
2968 png_set_interlace_handling(png_ptr);
2970 This will return the number of passes needed. Currently, this
2971 is seven, but may change if another interlace type is added.
2973 Then write the complete image number_of_passes times.
2975 png_write_rows(png_ptr, row_pointers,
2978 As some of these rows are not used, and thus return immediately,
2979 you may want to read about interlacing in the PNG specification,
2980 and only update the rows that are actually used.
2982 .SS Finishing a sequential write
2984 After you are finished writing the image, you should finish writing
2985 the file. If you are interested in writing comments or time, you should
2986 pass an appropriately filled png_info pointer. If you are not interested,
2989 png_write_end(png_ptr, info_ptr);
2991 When you are done, you can free all memory used by libpng like this:
2993 png_destroy_write_struct(&png_ptr, &info_ptr);
2995 It is also possible to individually free the info_ptr members that
2996 point to libpng-allocated storage with the following function:
2998 png_free_data(png_ptr, info_ptr, mask, seq)
2999 mask - identifies data to be freed, a mask
3000 containing the logical OR of one or
3002 PNG_FREE_PLTE, PNG_FREE_TRNS,
3003 PNG_FREE_HIST, PNG_FREE_ICCP,
3004 PNG_FREE_PCAL, PNG_FREE_ROWS,
3005 PNG_FREE_SCAL, PNG_FREE_SPLT,
3006 PNG_FREE_TEXT, PNG_FREE_UNKN,
3007 or simply PNG_FREE_ALL
3008 seq - sequence number of item to be freed
3011 This function may be safely called when the relevant storage has
3012 already been freed, or has not yet been allocated, or was allocated
3013 by the user and not by libpng, and will in those
3014 cases do nothing. The "seq" parameter is ignored if only one item
3015 of the selected data type, such as PLTE, is allowed. If "seq" is not
3016 -1, and multiple items are allowed for the data type identified in
3017 the mask, such as text or sPLT, only the n'th item in the structure
3018 is freed, where n is "seq".
3020 If you allocated data such as a palette that you passed
3021 in to libpng with png_set_*, you must not free it until just before the call to
3022 png_destroy_write_struct().
3024 The default behavior is only to free data that was allocated internally
3025 by libpng. This can be changed, so that libpng will not free the data,
3026 or so that it will free data that was allocated by the user with png_malloc()
3027 or png_zalloc() and passed in via a png_set_*() function, with
3029 png_data_freer(png_ptr, info_ptr, freer, mask)
3030 mask - which data elements are affected
3031 same choices as in png_free_data()
3033 PNG_DESTROY_WILL_FREE_DATA
3034 PNG_SET_WILL_FREE_DATA
3035 PNG_USER_WILL_FREE_DATA
3037 For example, to transfer responsibility for some data from a read structure
3038 to a write structure, you could use
3040 png_data_freer(read_ptr, read_info_ptr,
3041 PNG_USER_WILL_FREE_DATA,
3042 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3043 png_data_freer(write_ptr, write_info_ptr,
3044 PNG_DESTROY_WILL_FREE_DATA,
3045 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3047 thereby briefly reassigning responsibility for freeing to the user but
3048 immediately afterwards reassigning it once more to the write_destroy
3049 function. Having done this, it would then be safe to destroy the read
3050 structure and continue to use the PLTE, tRNS, and hIST data in the write
3053 This function only affects data that has already been allocated.
3054 You can call this function before calling after the png_set_*() functions
3055 to control whether the user or png_destroy_*() is supposed to free the data.
3056 When the user assumes responsibility for libpng-allocated data, the
3057 application must use
3058 png_free() to free it, and when the user transfers responsibility to libpng
3059 for data that the user has allocated, the user must have used png_malloc()
3060 or png_zalloc() to allocate it.
3062 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3063 separately, do not transfer responsibility for freeing text_ptr to libpng,
3064 because when libpng fills a png_text structure it combines these members with
3065 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3066 if you transfer responsibility for free'ing text_ptr from libpng to your
3067 application, your application must not separately free those members.
3068 For a more compact example of writing a PNG image, see the file example.c.
3070 .SH V. Modifying/Customizing libpng:
3072 There are three issues here. The first is changing how libpng does
3073 standard things like memory allocation, input/output, and error handling.
3074 The second deals with more complicated things like adding new chunks,
3075 adding new transformations, and generally changing how libpng works.
3076 Both of those are compile-time issues; that is, they are generally
3077 determined at the time the code is written, and there is rarely a need
3078 to provide the user with a means of changing them. The third is a
3079 run-time issue: choosing between and/or tuning one or more alternate
3080 versions of computationally intensive routines; specifically, optimized
3081 assembly-language (and therefore compiler- and platform-dependent)
3084 Memory allocation, input/output, and error handling
3086 All of the memory allocation, input/output, and error handling in libpng
3087 goes through callbacks that are user-settable. The default routines are
3088 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3089 these functions, call the appropriate png_set_*_fn() function.
3091 Memory allocation is done through the functions png_malloc(), png_zalloc(),
3092 and png_free(). These currently just call the standard C functions. If
3093 your pointers can't access more then 64K at a time, you will want to set
3094 MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3095 memory allocation on a platform will change between applications, these
3096 functions must be modified in the library at compile time. If you prefer
3097 to use a different method of allocating and freeing data, you can use
3099 png_set_mem_fn(png_structp png_ptr, png_voidp mem_ptr,
3100 png_malloc_ptr malloc_fn, png_free_ptr free_fn)
3102 This function also provides a void pointer that can be retrieved via
3104 mem_ptr=png_get_mem_ptr(png_ptr);
3106 Your replacement memory functions must have prototypes as follows:
3108 png_voidp malloc_fn(png_structp png_ptr,
3110 void free_fn(png_structp png_ptr, png_voidp ptr);
3112 Your malloc_fn() can return NULL in case of failure. The png_malloc()
3113 function will call png_error() if it receives a NULL from the system
3114 memory allocator or from your replacement malloc_fn().
3116 Input/Output in libpng is done through png_read() and png_write(),
3117 which currently just call fread() and fwrite(). The FILE * is stored in
3118 png_struct and is initialized via png_init_io(). If you wish to change
3119 the method of I/O, the library supplies callbacks that you can set
3120 through the function png_set_read_fn() and png_set_write_fn() at run
3121 time, instead of calling the png_init_io() function. These functions
3122 also provide a void pointer that can be retrieved via the function
3123 png_get_io_ptr(). For example:
3125 png_set_read_fn(png_structp read_ptr,
3126 voidp read_io_ptr, png_rw_ptr read_data_fn)
3128 png_set_write_fn(png_structp write_ptr,
3129 voidp write_io_ptr, png_rw_ptr write_data_fn,
3130 png_flush_ptr output_flush_fn);
3132 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3133 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3135 The replacement I/O functions must have prototypes as follows:
3137 void user_read_data(png_structp png_ptr,
3138 png_bytep data, png_uint_32 length);
3139 void user_write_data(png_structp png_ptr,
3140 png_bytep data, png_uint_32 length);
3141 void user_flush_data(png_structp png_ptr);
3143 Supplying NULL for the read, write, or flush functions sets them back
3144 to using the default C stream functions. It is an error to read from
3145 a write stream, and vice versa.
3147 Error handling in libpng is done through png_error() and png_warning().
3148 Errors handled through png_error() are fatal, meaning that png_error()
3149 should never return to its caller. Currently, this is handled via
3150 setjmp() and longjmp() (unless you have compiled libpng with
3151 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3152 but you could change this to do things like exit() if you should wish.
3154 On non-fatal errors, png_warning() is called
3155 to print a warning message, and then control returns to the calling code.
3156 By default png_error() and png_warning() print a message on stderr via
3157 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3158 (because you don't want the messages) or PNG_NO_STDIO defined (because
3159 fprintf() isn't available). If you wish to change the behavior of the error
3160 functions, you will need to set up your own message callbacks. These
3161 functions are normally supplied at the time that the png_struct is created.
3162 It is also possible to redirect errors and warnings to your own replacement
3163 functions after png_create_*_struct() has been called by calling:
3165 png_set_error_fn(png_structp png_ptr,
3166 png_voidp error_ptr, png_error_ptr error_fn,
3167 png_error_ptr warning_fn);
3169 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3171 If NULL is supplied for either error_fn or warning_fn, then the libpng
3172 default function will be used, calling fprintf() and/or longjmp() if a
3173 problem is encountered. The replacement error functions should have
3174 parameters as follows:
3176 void user_error_fn(png_structp png_ptr,
3177 png_const_charp error_msg);
3178 void user_warning_fn(png_structp png_ptr,
3179 png_const_charp warning_msg);
3181 The motivation behind using setjmp() and longjmp() is the C++ throw and
3182 catch exception handling methods. This makes the code much easier to write,
3183 as there is no need to check every return code of every function call.
3184 However, there are some uncertainties about the status of local variables
3185 after a longjmp, so the user may want to be careful about doing anything after
3186 setjmp returns non-zero besides returning itself. Consult your compiler
3187 documentation for more details. For an alternative approach, you may wish
3188 to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3192 If you need to read or write custom chunks, you may need to get deeper
3193 into the libpng code. The library now has mechanisms for storing
3194 and writing chunks of unknown type; you can even declare callbacks
3195 for custom chunks. Hoewver, this may not be good enough if the
3196 library code itself needs to know about interactions between your
3197 chunk and existing `intrinsic' chunks.
3199 If you need to write a new intrinsic chunk, first read the PNG
3200 specification. Acquire a first level of
3201 understanding of how it works. Pay particular attention to the
3202 sections that describe chunk names, and look at how other chunks were
3203 designed, so you can do things similarly. Second, check out the
3204 sections of libpng that read and write chunks. Try to find a chunk
3205 that is similar to yours and use it as a template. More details can
3206 be found in the comments inside the code. It is best to handle unknown
3207 chunks in a generic method, via callback functions, instead of by
3208 modifying libpng functions.
3210 If you wish to write your own transformation for the data, look through
3211 the part of the code that does the transformations, and check out some of
3212 the simpler ones to get an idea of how they work. Try to find a similar
3213 transformation to the one you want to add and copy off of it. More details
3214 can be found in the comments inside the code itself.
3216 .SS Configuring for 16 bit platforms
3218 You will want to look into zconf.h to tell zlib (and thus libpng) that
3219 it cannot allocate more then 64K at a time. Even if you can, the memory
3220 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3222 .SS Configuring for DOS
3224 For DOS users who only have access to the lower 640K, you will
3225 have to limit zlib's memory usage via a png_set_compression_mem_level()
3226 call. See zlib.h or zconf.h in the zlib library for more information.
3228 .SS Configuring for Medium Model
3230 Libpng's support for medium model has been tested on most of the popular
3231 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3232 defined, and FAR gets defined to far in pngconf.h, and you should be
3233 all set. Everything in the library (except for zlib's structure) is
3234 expecting far data. You must use the typedefs with the p or pp on
3235 the end for pointers (or at least look at them and be careful). Make
3236 note that the rows of data are defined as png_bytepp, which is an
3237 unsigned char far * far *.
3239 .SS Configuring for gui/windowing platforms:
3241 You will need to write new error and warning functions that use the GUI
3242 interface, as described previously, and set them to be the error and
3243 warning functions at the time that png_create_*_struct() is called,
3244 in order to have them available during the structure initialization.
3245 They can be changed later via png_set_error_fn(). On some compilers,
3246 you may also have to change the memory allocators (png_malloc, etc.).
3248 .SS Configuring for compiler xxx:
3250 All includes for libpng are in pngconf.h. If you need to add/change/delete
3251 an include, this is the place to do it. The includes that are not
3252 needed outside libpng are protected by the PNG_INTERNAL definition,
3253 which is only defined for those routines inside libpng itself. The
3254 files in libpng proper only include png.h, which includes pngconf.h.
3256 .SS Configuring zlib:
3258 There are special functions to configure the compression. Perhaps the
3259 most useful one changes the compression level, which currently uses
3260 input compression values in the range 0 - 9. The library normally
3261 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3262 have shown that for a large majority of images, compression values in
3263 the range 3-6 compress nearly as well as higher levels, and do so much
3264 faster. For online applications it may be desirable to have maximum speed
3265 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3266 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3267 files larger than just storing the raw bitmap. You can specify the
3268 compression level by calling:
3270 png_set_compression_level(png_ptr, level);
3272 Another useful one is to reduce the memory level used by the library.
3273 The memory level defaults to 8, but it can be lowered if you are
3274 short on memory (running DOS, for example, where you only have 640K).
3276 png_set_compression_mem_level(png_ptr, level);
3278 The other functions are for configuring zlib. They are not recommended
3279 for normal use and may result in writing an invalid PNG file. See
3280 zlib.h for more information on what these mean.
3282 png_set_compression_strategy(png_ptr,
3284 png_set_compression_window_bits(png_ptr,
3286 png_set_compression_method(png_ptr, method);
3287 png_set_compression_buffer_size(png_ptr, size);
3289 .SS Controlling row filtering
3291 If you want to control whether libpng uses filtering or not, which
3292 filters are used, and how it goes about picking row filters, you
3293 can call one of these functions. The selection and configuration
3294 of row filters can have a significant impact on the size and
3295 encoding speed and a somewhat lesser impact on the decoding speed
3296 of an image. Filtering is enabled by default for RGB and grayscale
3297 images (with and without alpha), but not for paletted images nor
3298 for any images with bit depths less than 8 bits/pixel.
3300 The 'method' parameter sets the main filtering method, which is
3301 currently only '0' in the PNG 1.2 specification. The 'filters'
3302 parameter sets which filter(s), if any, should be used for each
3303 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3304 to turn filtering on and off, respectively.
3306 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3307 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3308 ORed together with '|' to specify one or more filters to use.
3309 These filters are described in more detail in the PNG specification. If
3310 you intend to change the filter type during the course of writing
3311 the image, you should start with flags set for all of the filters
3312 you intend to use so that libpng can initialize its internal
3313 structures appropriately for all of the filter types.
3315 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3316 PNG_FILTER_UP | PNG_FILTER_AVE |
3317 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3319 filters = one of PNG_FILTER_VALUE_NONE,
3320 PNG_FILTER_VALUE_SUB, PNG_FILTER_VALUE_UP,
3321 PNG_FILTER_VALUE_AVE, PNG_FILTER_VALUE_PAETH
3323 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3325 The second parameter can also be
3326 PNG_INTRAPIXEL_DIFFERENCING if you are
3327 writing a PNG to be embedded in a MNG
3328 datastream. This parameter must be the
3329 same as the value of filter_method used
3332 It is also possible to influence how libpng chooses from among the
3333 available filters. This is done in two ways - by telling it how
3334 important it is to keep the same filter for successive rows, and
3335 by telling it the relative computational costs of the filters.
3337 double weights[3] = {1.5, 1.3, 1.1},
3338 costs[PNG_FILTER_VALUE_LAST] =
3339 {1.0, 1.3, 1.3, 1.5, 1.7};
3341 png_set_filter_selection(png_ptr,
3342 PNG_FILTER_SELECTION_WEIGHTED, 3,
3345 The weights are multiplying factors that indicate to libpng that the
3346 row filter should be the same for successive rows unless another row filter
3347 is that many times better than the previous filter. In the above example,
3348 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3349 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3350 and still be chosen, while the NONE filter could have a sum 1.1 times
3351 higher than other filters and still be chosen. Unspecified weights are
3352 taken to be 1.0, and the specified weights should probably be declining
3353 like those above in order to emphasize recent filters over older filters.
3355 The filter costs specify for each filter type a relative decoding cost
3356 to be considered when selecting row filters. This means that filters
3357 with higher costs are less likely to be chosen over filters with lower
3358 costs, unless their "sum of absolute differences" is that much smaller.
3359 The costs do not necessarily reflect the exact computational speeds of
3360 the various filters, since this would unduly influence the final image
3363 Note that the numbers above were invented purely for this example and
3364 are given only to help explain the function usage. Little testing has
3365 been done to find optimum values for either the costs or the weights.
3367 .SS Removing unwanted object code
3369 There are a bunch of #define's in pngconf.h that control what parts of
3370 libpng are compiled. All the defines end in _SUPPORTED. If you are
3371 never going to use a capability, you can change the #define to #undef
3372 before recompiling libpng and save yourself code and data space, or
3373 you can turn off individual capabilities with defines that begin with
3376 You can also turn all of the transforms and ancillary chunk capabilities
3377 off en masse with compiler directives that define
3378 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3380 along with directives to turn on any of the capabilities that you do
3381 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3382 the extra transformations but still leave the library fully capable of reading
3383 and writing PNG files with all known public chunks
3384 Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3385 produces a library that is incapable of reading or writing ancillary chunks.
3386 If you are not using the progressive reading capability, you can
3387 turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3388 this with the INTERLACING capability, which you'll still have).
3390 All the reading and writing specific code are in separate files, so the
3391 linker should only grab the files it needs. However, if you want to
3392 make sure, or if you are building a stand alone library, all the
3393 reading files start with pngr and all the writing files start with
3394 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3395 are used for both reading and writing, and always need to be included.
3396 The progressive reader is in pngpread.c
3398 If you are creating or distributing a dynamically linked library (a .so
3399 or DLL file), you should not remove or disable any parts of the library,
3400 as this will cause applications linked with different versions of the
3401 library to fail if they call functions not available in your library.
3402 The size of the library itself should not be an issue, because only
3403 those sections that are actually used will be loaded into memory.
3405 .SS Requesting debug printout
3407 The macro definition PNG_DEBUG can be used to request debugging
3408 printout. Set it to an integer value in the range 0 to 3. Higher
3409 numbers result in increasing amounts of debugging information. The
3410 information is printed to the "stderr" file, unless another file
3411 name is specified in the PNG_DEBUG_FILE macro definition.
3413 When PNG_DEBUG > 0, the following functions (macros) become available:
3415 png_debug(level, message)
3416 png_debug1(level, message, p1)
3417 png_debug2(level, message, p1, p2)
3419 in which "level" is compared to PNG_DEBUG to decide whether to print
3420 the message, "message" is the formatted string to be printed,
3421 and p1 and p2 are parameters that are to be embedded in the string
3422 according to printf-style formatting directives. For example,
3424 png_debug1(2, "foo=%d\n", foo);
3429 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3431 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3432 can still use PNG_DEBUG to control your own debugging:
3438 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3439 having level = 0 will be printed. There aren't any such statements in
3440 this version of libpng, but if you insert some they will be printed.
3442 .SH VI. Runtime optimization
3444 A new feature in libpng 1.2.0 is the ability to dynamically switch between
3445 standard and optimized versions of some routines. Currently these are
3446 limited to three computationally intensive tasks when reading PNG files:
3447 decoding row filters, expanding interlacing, and combining interlaced or
3448 transparent row data with previous row data. Currently the optimized
3449 versions are available only for x86 (Intel, AMD, etc.) platforms with
3450 MMX support, though this may change in future versions. (For example,
3451 the non-MMX assembler optimizations for zlib might become similarly
3452 runtime-selectable in future releases, in which case libpng could be
3453 extended to support them. Alternatively, the compile-time choice of
3454 floating-point versus integer routines for gamma correction might become
3455 runtime-selectable.)
3457 Because such optimizations tend to be very platform- and compiler-dependent,
3458 both in how they are written and in how they perform, the new runtime code
3459 in libpng has been written to allow programs to query, enable, and disable
3460 either specific optimizations or all such optimizations. For example, to
3461 enable all possible optimizations (bearing in mind that some "optimizations"
3462 may actually run more slowly in rare cases):
3464 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3465 png_uint_32 mask, flags;
3467 flags = png_get_asm_flags(png_ptr);
3468 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3469 png_set_asm_flags(png_ptr, flags | mask);
3472 To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3473 by itself when calling png_get_asm_flagmask(); similarly for optimizing
3474 only writing. To disable all optimizations:
3476 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3477 flags = png_get_asm_flags(png_ptr);
3478 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3479 png_set_asm_flags(png_ptr, flags & ~mask);
3482 To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3483 in place of png_get_asm_flagmask(). The mmx version takes one additional
3486 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3487 int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3490 mask = png_get_mmx_flagmask(selection, &compilerID);
3493 On return, compilerID will indicate which version of the MMX assembler
3494 optimizations was compiled. Currently two flavors exist: Microsoft
3495 Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3496 On non-x86 platforms or on systems compiled without MMX optimizations, a
3497 value of -1 is used.
3499 Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3500 all valid, settable optimization bits for the version of the library that's
3501 currently in use. In the case of shared (dynamically linked) libraries,
3502 this may include optimizations that did not exist at the time the code was
3503 written and compiled. It is also possible, of course, to enable only known,
3504 specific optimizations; for example:
3506 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3507 flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3508 | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3509 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3510 | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3511 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3512 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3513 png_set_asm_flags(png_ptr, flags);
3516 This method would enable only the MMX read-optimizations available at the
3517 time of libpng 1.2.0's release, regardless of whether a later version of
3518 the DLL were actually being used. (Also note that these functions did not
3519 exist in versions older than 1.2.0, so any attempt to run a dynamically
3520 linked app on such an older version would fail.)
3522 To determine whether the processor supports MMX instructions at all, use
3523 the png_mmx_support() function:
3525 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3526 mmxsupport = png_mmx_support();
3529 It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3530 is compiled but MMX is not supported by the processor, or 1 if MMX support
3531 is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3532 and png_get_asm_flagmask() all may be called without allocating and ini-
3533 tializing any PNG structures (for example, as part of a usage screen or
3536 The following code can be used to prevent an application from using the
3537 thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3540 #if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3541 && defined(PNG_THREAD_UNSAFE_OK)
3542 /* Disable thread-unsafe features of pnggccrd */
3543 if (png_access_version() >= 10200)
3545 png_uint_32 mmx_disable_mask = 0;
3546 png_uint_32 asm_flags;
3548 mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3549 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3550 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3551 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3552 asm_flags = png_get_asm_flags(png_ptr);
3553 png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3557 For more extensive examples of runtime querying, enabling and disabling
3558 of optimized features, see contrib/gregbook/readpng2.c in the libpng
3559 source-code distribution.
3562 .SH VII. MNG support
3564 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3565 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3566 Libpng can support some of these extensions. To enable them, use the
3567 png_permit_mng_features() function:
3569 feature_set = png_permit_mng_features(png_ptr, mask)
3570 mask is a png_uint_32 containing the logical OR of the
3571 features you want to enable. These include
3572 PNG_FLAG_MNG_EMPTY_PLTE
3573 PNG_FLAG_MNG_FILTER_64
3574 PNG_ALL_MNG_FEATURES
3575 feature_set is a png_32_uint that is the logical AND of
3576 your mask with the set of MNG features that is
3577 supported by the version of libpng that you are using.
3579 It is an error to use this function when reading or writing a standalone
3580 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3581 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3582 and the MHDR and MEND chunks. Libpng does not provide support for these
3583 or any other MNG chunks; your application must provide its own support for
3584 them. You may wish to consider using libmng (available at
3585 http://www.libmng.com) instead.
3587 .SH VIII. Changes to Libpng from version 0.88
3589 It should be noted that versions of libpng later than 0.96 are not
3590 distributed by the original libpng author, Guy Schalnat, nor by
3591 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3592 distributed versions 0.89 through 0.96, but rather by another member
3593 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3594 still alive and well, but they have moved on to other things.
3596 The old libpng functions png_read_init(), png_write_init(),
3597 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3598 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3599 functions will be removed from libpng version 2.0.0.
3601 The preferred method of creating and initializing the libpng structures is
3602 via the png_create_read_struct(), png_create_write_struct(), and
3603 png_create_info_struct() because they isolate the size of the structures
3604 from the application, allow version error checking, and also allow the
3605 use of custom error handling routines during the initialization, which
3606 the old functions do not. The functions png_read_destroy() and
3607 png_write_destroy() do not actually free the memory that libpng
3608 allocated for these structs, but just reset the data structures, so they
3609 can be used instead of png_destroy_read_struct() and
3610 png_destroy_write_struct() if you feel there is too much system overhead
3611 allocating and freeing the png_struct for each image read.
3613 Setting the error callbacks via png_set_message_fn() before
3614 png_read_init() as was suggested in libpng-0.88 is no longer supported
3615 because this caused applications that do not use custom error functions
3616 to fail if the png_ptr was not initialized to zero. It is still possible
3617 to set the error callbacks AFTER png_read_init(), or to change them with
3618 png_set_error_fn(), which is essentially the same function, but with a new
3619 name to force compilation errors with applications that try to use the old
3622 Starting with version 1.0.7, you can find out which version of the library
3623 you are using at run-time:
3625 png_uint_32 libpng_vn = png_access_version_number();
3627 The number libpng_vn is constructed from the major version, minor
3628 version with leading zero, and release number with leading zero,
3629 (e.g., libpng_vn for version 1.0.7 is 10007).
3631 You can also check which version of png.h you used when compiling your
3634 png_uint_32 application_vn = PNG_LIBPNG_VER;
3636 .SH IX. Y2K Compliance in libpng
3640 Since the PNG Development group is an ad-hoc body, we can't make
3641 an official declaration.
3643 This is your unofficial assurance that libpng from version 0.71 and
3644 upward through 1.2.0 are Y2K compliant. It is my belief that earlier
3645 versions were also Y2K compliant.
3647 Libpng only has three year fields. One is a 2-byte unsigned integer that
3648 will hold years up to 65535. The other two hold the date in text
3649 format, and will hold years up to 9999.
3652 "png_uint_16 year" in png_time_struct.
3655 "png_charp time_buffer" in png_struct and
3656 "near_time_buffer", which is a local character string in png.c.
3658 There are seven time-related functions:
3660 png_convert_to_rfc_1123() in png.c
3661 (formerly png_convert_to_rfc_1152() in error)
3662 png_convert_from_struct_tm() in pngwrite.c, called
3664 png_convert_from_time_t() in pngwrite.c
3665 png_get_tIME() in pngget.c
3666 png_handle_tIME() in pngrutil.c, called in pngread.c
3667 png_set_tIME() in pngset.c
3668 png_write_tIME() in pngwutil.c, called in pngwrite.c
3670 All appear to handle dates properly in a Y2K environment. The
3671 png_convert_from_time_t() function calls gmtime() to convert from system
3672 clock time, which returns (year - 1900), which we properly convert to
3673 the full 4-digit year. There is a possibility that applications using
3674 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3675 function, or that they are incorrectly passing only a 2-digit year
3676 instead of "year - 1900" into the png_convert_from_struct_tm() function,
3677 but this is not under our control. The libpng documentation has always
3678 stated that it works with 4-digit years, and the APIs have been
3681 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3682 integer to hold the year, and can hold years as large as 65535.
3684 zlib, upon which libpng depends, is also Y2K compliant. It contains
3685 no date-related code.
3688 Glenn Randers-Pehrson
3690 PNG Development Group
3694 Note about libpng version numbers:
3696 Due to various miscommunications, unforeseen code incompatibilities
3697 and occasional factors outside the authors' control, version numbering
3698 on the library has not always been consistent and straightforward.
3699 The following table summarizes matters since version 0.89c, which was
3700 the first widely used release:
3702 source png.h png.h shared-lib
3703 version string int version
3704 ------- ------ ----- ----------
3705 0.89c ("beta 3") 0.89 89 1.0.89
3706 0.90 ("beta 4") 0.90 90 0.90
3707 0.95 ("beta 5") 0.95 95 0.95
3708 0.96 ("beta 6") 0.96 96 0.96
3709 0.97b ("beta 7") 1.00.97 97 1.0.1
3710 0.97c 0.97 97 2.0.97
3713 0.99a-m 0.99 99 2.0.99
3715 1.0.0 1.0.0 100 2.1.0
3716 1.0.0 (from here on, the 100 2.1.0
3717 1.0.1 png.h string is 10001 2.1.0
3718 1.0.1a-e identical to the 10002 from here on, the
3719 1.0.2 source version) 10002 shared library is 2.V
3720 1.0.2a-b 10003 where V is the source
3721 1.0.1 10001 code version except as
3722 1.0.1a-e 10002 2.1.0.1a-e noted.
3724 1.0.2a-b 10003 2.1.0.2a-b
3726 1.0.3a-d 10004 2.1.0.3a-d
3728 1.0.4a-f 10005 2.1.0.4a-f
3729 1.0.5 (+ 2 patches) 10005 2.1.0.5
3730 1.0.5a-d 10006 2.1.0.5a-d
3731 1.0.5e-r 10100 2.1.0.5e-r
3732 1.0.5s-v 10006 2.1.0.5s-v
3733 1.0.6 (+ 3 patches) 10006 2.1.0.6
3734 1.0.6d-g 10007 2.1.0.6d-g
3737 1.0.6j 10007 2.1.0.6j
3738 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3739 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3740 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3741 1.0.7 1 10007 2.1.0.7
3742 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3743 1.0.8rc1 1 10008 2.1.0.8rc1
3744 1.0.8 1 10008 2.1.0.8
3745 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3746 1.0.9rc1 1 10009 2.1.0.9rc1
3747 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3748 1.0.9rc2 1 10009 2.1.0.9rc2
3749 1.0.9 1 10009 2.1.0.9
3750 1.0.10beta1 1 10010 2.1.0.10beta1
3751 1.0.10rc1 1 10010 2.1.0.10rc1
3752 1.0.10 1 10010 2.1.0.10
3753 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3754 1.0.11rc1 1 10011 2.1.0.11rc1
3755 1.0.11 1 10011 2.1.0.11
3756 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3757 1.0.12rc1 2 10012 2.1.0.12rc1
3758 1.0.12 2 10012 2.1.0.12
3759 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3760 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3761 1.2.0beta3-4 3 10200 3.1.2.0beta3-4
3763 Henceforth the source version will match the shared-library minor
3764 and patch numbers; the shared-library major version number will be
3765 used for changes in backward compatibility, as it is intended. The
3766 PNG_PNGLIB_VER macro, which is not used within libpng but is available
3767 for applications, is an unsigned integer of the form xyyzz corresponding
3768 to the source version x.y.z (leading zeros in y and z). Beta versions
3769 were given the previous public release number plus a letter, until
3770 version 1.0.6j; from then on they were given the upcoming public
3771 release number plus "betaNN" or "rcN".
3778 ftp://ftp.uu.net/graphics/png
3779 http://www.libpng.org/pub/png
3784 (generally) at the same location as
3788 ftp://ftp.uu.net/pub/archiving/zip/zlib
3790 ftp://ftp.info-zip.org/pub/infozip/zlib
3793 .IR PNG specification: RFC 2083
3795 (generally) at the same location as
3799 ftp://ds.internic.net/rfc/rfc2083.txt
3801 or (as a W3C Recommendation) at
3803 http://www.w3.org/TR/REC-png.html
3806 In the case of any inconsistency between the PNG specification
3807 and this library, the specification takes precedence.
3810 This man page: Glenn Randers-Pehrson
3811 <randeg@alum.rpi.edu>
3813 The contributing authors would like to thank all those who helped
3814 with testing, bug fixes, and patience. This wouldn't have been
3815 possible without all of you.
3817 Thanks to Frank J. T. Wojcik for helping with the documentation.
3819 Libpng version 1.2.0 - September 1, 2001:
3820 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3821 Currently maintained by Glenn Randers-Pehrson (randeg@alum.rpi.edu).
3823 Supported by the PNG development group
3825 (png-implement@ccrc.wustl.edu).
3827 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3829 (This copy of the libpng notices is provided for your convenience. In case of
3830 any discrepancy between this copy and the notices in the file png.h that is
3831 included in the libpng distribution, the latter shall prevail.)
3833 If you modify libpng you may insert additional notices immediately following
3836 libpng versions 1.0.7, July 1, 2000, through 1.2.0, September 1, 2001, are
3837 Copyright (c) 2000-2001 Glenn Randers-Pehrson, and are
3838 distributed according to the same disclaimer and license as libpng-1.0.6
3839 with the following individuals added to the list of Contributing Authors
3841 Simon-Pierre Cadieux
3845 and with the following additions to the disclaimer:
3847 There is no warranty against interference with your
3848 enjoyment of the library or against infringement.
3849 There is no warranty that our efforts or the library
3850 will fulfill any of your particular purposes or needs.
3851 This library is provided with all faults, and the entire
3852 risk of satisfactory quality, performance, accuracy, and
3853 effort is with the user.
3855 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3856 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3857 Distributed according to the same disclaimer and license as libpng-0.96,
3858 with the following individuals added to the list of Contributing Authors:
3861 Glenn Randers-Pehrson
3864 libpng versions 0.89, June 1996, through 0.96, May 1997, are
3865 Copyright (c) 1996, 1997 Andreas Dilger
3866 Distributed according to the same disclaimer and license as libpng-0.88,
3867 with the following individuals added to the list of Contributing Authors:
3876 libpng versions 0.5, May 1995, through 0.88, January 1996, are
3877 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3879 For the purposes of this copyright and license, "Contributing Authors"
3880 is defined as the following set of individuals:
3888 The PNG Reference Library is supplied "AS IS". The Contributing Authors
3889 and Group 42, Inc. disclaim all warranties, expressed or implied,
3890 including, without limitation, the warranties of merchantability and of
3891 fitness for any purpose. The Contributing Authors and Group 42, Inc.
3892 assume no liability for direct, indirect, incidental, special, exemplary,
3893 or consequential damages, which may result from the use of the PNG
3894 Reference Library, even if advised of the possibility of such damage.
3896 Permission is hereby granted to use, copy, modify, and distribute this
3897 source code, or portions hereof, for any purpose, without fee, subject
3898 to the following restrictions:
3900 1. The origin of this source code must not be misrepresented.
3902 2. Altered versions must be plainly marked as such and
3903 must not be misrepresented as being the original source.
3905 3. This Copyright notice may not be removed or altered from
3906 any source or altered source distribution.
3908 The Contributing Authors and Group 42, Inc. specifically permit, without
3909 fee, and encourage the use of this source code as a component to
3910 supporting the PNG file format in commercial products. If you use this
3911 source code in a product, acknowledgment is not required but would be
3915 A "png_get_copyright" function is available, for convenient use in "about"
3918 printf("%s",png_get_copyright(NULL));
3920 Also, the PNG logo (in PNG format, of course) is supplied in the
3921 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
3923 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
3924 certification mark of the Open Source Initiative.
3926 Glenn Randers-Pehrson
projects / rrdtool.git / blob