-.TH LIBPNG 3 "January 14, 1999"
-.SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.0.3 - January 14, 1999
-.SH SYNOPSIS
-
-#include <png.h>
-
-int png_check_sig (png_bytep sig, int num);
-
-void png_chunk_error (png_structp png_ptr, png_const_charp
-error);
-
-void png_chunk_warning (png_structp png_ptr, png_const_charp
-message);
-
-void png_convert_from_struct_tm (png_timep ptime, struct tm FAR
-* ttime);
-
-void png_convert_from_time_t (png_timep ptime, time_t ttime);
-
-png_charp png_convert_to_rfc1123 (png_structp png_ptr,
-png_timep ptime);
-
-png_infop png_create_info_struct (png_structp png_ptr);
-
-png_structp png_create_read_struct (png_const_charp
-user_png_ver, voidp error_ptr, png_error_ptr error_fn,
-png_error_ptr warn_fn);
-
-png_structp png_create_read_struct_2(png_const_charp user_png_ver,
-png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr
-warn_fn, png_voidp mem_ptr, png_malloc_ptr malloc_fn,
-png_free_ptr free_fn)
-
-png_structp png_create_write_struct (png_const_charp
-user_png_ver, voidp error_ptr, png_error_ptr error_fn,
-png_error_ptr warn_fn);
-
-png_structp png_create_write_struct_2(png_const_charp
-user_png_ver, png_voidp error_ptr, png_error_ptr error_fn,
-png_error_ptr warn_fn, png_voidp mem_ptr,
-png_malloc_ptr malloc_fn, png_free_ptr free_fn)
-
-int png_debug(int level, png_const_charp message)
-
-int png_debug1(int level, png_const_charp message, p1)
-
-int png_debug2(int level, png_const_charp message, p1, p2)
-
-void png_destroy_info_struct (png_structp png_ptr, png_infopp
-info_ptr_ptr);
-
-void png_destroy_read_struct (png_structpp png_ptr_ptr,
-png_infopp info_ptr_ptr, png_infopp end_info_ptr_ptr);
-
-void png_destroy_write_struct (png_structpp png_ptr_ptr,
-png_infopp info_ptr_ptr);
-
-void png_error (png_structp png_ptr, png_const_charp error);
-
-void png_free (png_structp png_ptr, png_voidp ptr);
-
-void png_free_default(png_structp png_ptr, png_voidp ptr)
-
-png_byte png_get_bit_depth (png_structp png_ptr, png_infop
-info_ptr);
-
-png_uint_32 png_get_bKGD (png_structp png_ptr, png_infop
-info_ptr, png_color_16p *background);
-
-png_byte png_get_channels (png_structp png_ptr, png_infop
-info_ptr);
-
-png_uint_32 png_get_cHRM (png_structp png_ptr, png_infop
-info_ptr, double *white_x, double *white_y, double *red_x,
-double *red_y, double *green_x, double *green_y, double
-*blue_x, double *blue_y);
-
-png_byte png_get_color_type (png_structp png_ptr, png_infop
-info_ptr);
-
-png_byte png_get_compression_type (png_structp png_ptr,
-png_infop info_ptr);
-
-png_byte png_get_copyright (png_structp png_ptr);
-
-png_voidp png_get_error_ptr (png_structp png_ptr);
-
-png_byte png_get_filter_type (png_structp png_ptr, png_infop
-info_ptr);
-
-png_uint_32 png_get_gAMA (png_structp png_ptr, png_infop
-info_ptr, double *file_gamma);
-
-png_byte png_get_header_version (png_structp png_ptr);
-
-png_uint_32 png_get_hIST (png_structp png_ptr, png_infop
-info_ptr, png_uint_16p *hist);
-
-png_uint_32 png_get_IHDR (png_structp png_ptr, png_infop
-info_ptr, png_uint_32 *width, png_uint_32 *height, int
-*bit_depth, int *color_type, int *interlace_type, int
-*compression_type, int *filter_type);
-
-png_uint_32 png_get_image_height (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_image_width (png_structp png_ptr, png_infop
-info_ptr);
-
-png_byte png_get_interlace_type (png_structp png_ptr, png_infop
-info_ptr);
-
-png_voidp png_get_io_ptr (png_structp png_ptr);
-
-png_voidp png_get_mem_ptr(png_structp png_ptr)
-
-png_uint_32 png_get_oFFs (png_structp png_ptr, png_infop
-info_ptr, png_uint_32 *offset_x, png_uint_32 *offset_y, int
-*unit_type);
-
-png_uint_32 png_get_pCAL (png_structp png_ptr, png_infop
-info_ptr, png_charp *purpose, png_int_32 *X0, png_int_32 *X1,
-int *type, int *nparams, png_charp *units, png_charpp *params);
-
-png_uint_32 png_get_pHYs (png_structp png_ptr, png_infop
-info_ptr, png_uint_32 *res_x, png_uint_32 *res_y, int
-*unit_type);
-
-float png_get_pixel_aspect_ratio (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_pixels_per_meter (png_structp png_ptr,
-png_infop info_ptr);
-
-png_voidp png_get_progressive_ptr (png_structp png_ptr);
-
-png_uint_32 png_get_PLTE (png_structp png_ptr, png_infop
-info_ptr, png_colorp *palette, int *num_palette);
-
-png_byte png_get_rgb_to_gray_status (png_structp png_ptr)
-
-png_uint_32 png_get_rowbytes (png_structp png_ptr, png_infop
-info_ptr);
-
-png_uint_32 png_get_sBIT (png_structp png_ptr, png_infop
-info_ptr, png_color_8p *sig_bit);
-
-png_bytep png_get_signature (png_structp png_ptr, png_infop
-info_ptr);
-
-png_uint_32 png_get_sRGB (png_structp png_ptr, png_infop
-info_ptr, int *intent);
-
-png_uint_32 png_get_text (png_structp png_ptr, png_infop
-info_ptr, png_textp *text_ptr, int *num_text);
-
-png_uint_32 png_get_tIME (png_structp png_ptr, png_infop
-info_ptr, png_timep *mod_time);
-
-png_uint_32 png_get_tRNS (png_structp png_ptr, png_infop
-info_ptr, png_bytep *trans, int *num_trans, png_color_16p
-*trans_values);
-
-png_uint_32 png_get_valid (png_structp png_ptr, png_infop
-info_ptr, png_uint_32 flag);
-
-png_uint_32 png_get_x_offset_microns (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_x_offset_pixels (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_x_pixels_per_meter (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_y_offset_microns (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_y_offset_pixels (png_structp png_ptr,
-png_infop info_ptr);
-
-png_uint_32 png_get_y_pixels_per_meter (png_structp png_ptr,
-png_infop info_ptr);
-
-void png_info_init (png_infop info_ptr);
-
-void png_init_io (png_structp png_ptr, FILE *fp);
-
-png_voidp png_malloc (png_structp png_ptr, png_uint_32 size);
-
-png_voidp png_malloc_default(png_structp png_ptr,
-png_uint_32 size)
-
-voidp png_memcpy (png_voidp s1, png_voidp s2, png_size_t size);
-
-png_voidp png_memcpy_check (png_structp png_ptr, png_voidp s1,
-png_voidp s2, png_uint_32 size);
-
-voidp png_memset (png_voidp s1, int value, png_size_t size);
-
-png_voidp png_memset_check (png_structp png_ptr, png_voidp
-s1, int value, png_uint_32 size);
-
-void png_process_data (png_structp png_ptr, png_infop info_ptr,
-png_bytep buffer, png_size_t buffer_size);
-
-void png_progressive_combine_row (png_structp png_ptr,
-png_bytep old_row, png_bytep new_row);
-
-void png_read_destroy (png_structp png_ptr, png_infop info_ptr,
-png_infop end_info_ptr);
-
-void png_read_end (png_structp png_ptr, png_infop info_ptr);
-
-void png_read_image (png_structp png_ptr, png_bytepp image);
-
-void png_read_info (png_structp png_ptr, png_infop info_ptr);
-
-void png_read_row (png_structp png_ptr, png_bytep row,
-png_bytep display_row);
-
-void png_read_rows (png_structp png_ptr, png_bytepp row,
-png_bytepp display_row, png_uint_32 num_rows);
-
-void png_read_update_info (png_structp png_ptr, png_infop
-info_ptr);
-
-void png_set_background (png_structp png_ptr, png_color_16p
-background_color, int background_gamma_code, int need_expand,
-double background_gamma);
-
-void png_set_bgr (png_structp png_ptr);
-
-void png_set_bKGD (png_structp png_ptr, png_infop info_ptr,
-png_color_16p background);
-
-void png_set_cHRM (png_structp png_ptr, png_infop info_ptr,
-double white_x, double white_y, double red_x, double red_y,
-double green_x, double green_y, double blue_x, double blue_y);
-
-void png_set_compression_level (png_structp png_ptr, int
-level);
-
-void png_set_compression_mem_level (png_structp png_ptr, int
-mem_level);
-
-void png_set_compression_method (png_structp png_ptr, int
-method);
-
-void png_set_compression_strategy (png_structp png_ptr, int
-strategy);
-
-void png_set_compression_window_bits (png_structp png_ptr, int
-window_bits);
-
-void png_set_crc_action (png_structp png_ptr, int crit_action,
-int ancil_action);
-
-void png_set_dither (png_structp png_ptr, png_colorp palette,
-int num_palette, int maximum_colors, png_uint_16p histogram,
-int full_dither);
-
-void png_set_error_fn (png_structp png_ptr, png_voidp
-error_ptr, png_error_ptr error_fn, png_error_ptr warning_fn);
-
-void png_set_expand (png_structp png_ptr);
-
-void png_set_filler (png_structp png_ptr, png_uint_32 filler,
-int flags);
-
-void png_set_filter (png_structp png_ptr, int method, int
-filters);
-
-void png_set_filter_heuristics (png_structp png_ptr, int
-heuristic_method, int num_weights, png_doublep filter_weights,
-png_doublep filter_costs);
-
-void png_set_flush (png_structp png_ptr, int nrows);
-
-void png_set_gamma (png_structp png_ptr, double screen_gamma,
-double default_file_gamma);
-
-void png_set_gAMA (png_structp png_ptr, png_infop info_ptr,
-double file_gamma);
-
-void png_set_gray_to_rgb (png_structp png_ptr);
-
-void png_set_hIST (png_structp png_ptr, png_infop info_ptr,
-png_uint_16p hist);
-
-int png_set_interlace_handling (png_structp png_ptr);
-
-void png_set_invert_alpha (png_structp png_ptr);
-
-void png_set_invert_mono (png_structp png_ptr);
-
-void png_set_IHDR (png_structp png_ptr, png_infop info_ptr,
-png_uint_32 width, png_uint_32 height, int bit_depth, int
-color_type, int interlace_type, int compression_type, int
-filter_type);
-
-void png_set_mem_fn(png_structp png_ptr, png_voidp mem_ptr,
-png_malloc_ptr malloc_fn, png_free_ptr free_fn)
-
-void png_set_oFFs (png_structp png_ptr, png_infop info_ptr,
-png_uint_32 offset_x, png_uint_32 offset_y, int unit_type);
-
-void png_set_packing (png_structp png_ptr);
-
-void png_set_packswap (png_structp png_ptr);
-
-void png_set_pCAL (png_structp png_ptr, png_infop info_ptr,
-png_charp purpose, png_int_32 X0, png_int_32 X1, int type, int
-nparams, png_charp units, png_charpp params);
-
-void png_set_pHYs (png_structp png_ptr, png_infop info_ptr,
-png_uint_32 res_x, png_uint_32 res_y, int unit_type);
-
-void png_set_progressive_read_fn (png_structp png_ptr,
-png_voidp progressive_ptr, png_progressive_info_ptr info_fn,
-png_progressive_row_ptr row_fn, png_progressive_end_ptr
-end_fn);
-
-void png_set_PLTE (png_structp png_ptr, png_infop info_ptr,
-png_colorp palette, int num_palette);
-
-void png_set_read_fn (png_structp png_ptr, png_voidp io_ptr,
-png_rw_ptr read_data_fn);
-
-void png_set_read_status_fn (png_structp png_ptr, png_read_status_ptr
-read_row_fn);
-
-void png_set_read_user_transform_fn (png_structp png_ptr,
-png_user_transform_ptr read_user_transform_fn);
-
-void png_set_rgb_to_gray (png_structp png_ptr, int error_action);
-
-void png_set_sBIT (png_structp png_ptr, png_infop info_ptr,
-png_color_8p sig_bit);
-
-void png_set_shift (png_structp png_ptr, png_color_8p
-true_bits);
-
-void png_set_sig_bytes (png_structp png_ptr, int num_bytes);
-
-void png_set_sRGB (png_structp png_ptr, png_infop info_ptr, int
-intent);
-
-void png_set_sRGB_gAMA_and_cHRM (png_structp png_ptr, png_infop
-info_ptr, int intent);
-
-void png_set_strip_16 (png_structp png_ptr);
-
-void png_set_strip_alpha (png_structp png_ptr);
-
-void png_set_swap (png_structp png_ptr);
-
-void png_set_swap_alpha (png_structp png_ptr);
-
-void png_set_text (png_structp png_ptr, png_infop info_ptr,
-png_textp text_ptr, int num_text);
-
-void png_set_tIME (png_structp png_ptr, png_infop info_ptr,
-png_timep mod_time);
-
-void png_set_tRNS (png_structp png_ptr, png_infop info_ptr,
-png_bytep trans, int num_trans, png_color_16p trans_values);
-
-void png_set_write_fn (png_structp png_ptr, png_voidp io_ptr,
-png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn);
-
-void png_set_write_status_fn (png_structp png_ptr, png_write_status_ptr
-write_row_fn);
-
-void png_set_write_user_transform_fn (png_structp png_ptr,
-png_user_transform_ptr write_user_transform_fn);
-
-int png_sig_cmp (png_bytep sig, png_size_t start, png_size_t
-num_to_check);
-
-void png_start_read_image (png_structp png_ptr);
-
-void png_warning (png_structp png_ptr, png_const_charp
-message);
-
-void png_write_chunk (png_structp png_ptr, png_bytep
-chunk_name, png_bytep data, png_size_t length);
-
-void png_write_chunk_data (png_structp png_ptr, png_bytep data,
-png_size_t length);
-
-void png_write_chunk_end (png_structp png_ptr);
-
-void png_write_chunk_start (png_structp png_ptr, png_bytep
-chunk_name, png_uint_32 length);
-
-void png_write_destroy (png_structp png_ptr);
-
-void png_write_destroy_info (png_infop info_ptr);
-
-void png_write_end (png_structp png_ptr, png_infop info_ptr);
-
-void png_write_flush (png_structp png_ptr);
-
-void png_write_image (png_structp png_ptr, png_bytepp image);
-
-void png_write_info (png_structp png_ptr, png_infop info_ptr);
-
-void png_write_row (png_structp png_ptr, png_bytep row);
-
-void png_write_rows (png_structp png_ptr, png_bytepp row,
-png_uint_32 num_rows);
-
-.SH DESCRIPTION
-The
-.I libpng
-library supports encoding, decoding, and various manipulations of
-the Portable Network Graphics (PNG) format image files. It uses the
-.IR zlib(3)
-compression library.
-Following is a copy of the libpng.txt file that accompanies libpng.
-.SH LIBPNG.TXT
-libpng.txt - A description on how to use and modify libpng
-
- libpng version 1.0.3 - January 14, 1999
- Updated and distributed by Glenn Randers-Pehrson
- <randeg@alumni.rpi.edu>
- Copyright (c) 1998, 1999 Glenn Randers-Pehrson
- For conditions of distribution and use, see copyright
- notice in png.h.
-
- based on:
-
- libpng 1.0 beta 6 version 0.96 May 28, 1997
- Updated and distributed by Andreas Dilger
- Copyright (c) 1996, 1997 Andreas Dilger
-
- libpng 1.0 beta 2 - version 0.88 January 26, 1996
- For conditions of distribution and use, see copyright
- notice in png.h. Copyright (c) 1995, 1996 Guy Eric
- Schalnat, Group 42, Inc.
-
- Updated/rewritten per request in the libpng FAQ
- Copyright (c) 1995 Frank J. T. Wojcik
- December 18, 1995 && January 20, 1996
-
-.SH I. Introduction
-
-This file describes how to use and modify the PNG reference library
-(known as libpng) for your own use. There are five sections to this
-file: introduction, structures, reading, writing, and modification and
-configuration notes for various special platforms. In addition to this
-file, example.c is a good starting point for using the library, as
-it is heavily commented and should include everything most people
-will need. We assume that libpng is already installed; see the
-INSTALL file for instructions on how to install libpng.
-
-Libpng was written as a companion to the PNG specification, as a way
-of reducing the amount of time and effort it takes to support the PNG
-file format in application programs. The PNG specification is available
-as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
-W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
-additional chunks are described in the special-purpose public chunks
-documents at <ftp://ftp.uu.net/graphics/png/documents/>. Other information
-about PNG, and the latest version of libpng, can be found at the PNG home
-page, <http://www.cdrom.com/pub/png/>.
-
-Most users will not have to modify the library significantly; advanced
-users may want to modify it more. All attempts were made to make it as
-complete as possible, while keeping the code easy to understand.
-Currently, this library only supports C. Support for other languages
-is being considered.
-
-Libpng has been designed to handle multiple sessions at one time,
-to be easily modifiable, to be portable to the vast majority of
-machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
-to use. The ultimate goal of libpng is to promote the acceptance of
-the PNG file format in whatever way possible. While there is still
-work to be done (see the TODO file), libpng should cover the
-majority of the needs of its users.
-
-Libpng uses zlib for its compression and decompression of PNG files.
-Further information about zlib, and the latest version of zlib, can
-be found at the zlib home page, <http://www.cdrom.com/pub/infozip/zlib/>.
-The zlib compression utility is a general purpose utility that is
-useful for more than PNG files, and can be used without libpng.
-See the documentation delivered with zlib for more details.
-You can usually find the source files for the zlib utility wherever you
-find the libpng source files.
-
-Libpng is thread safe, provided the threads are using different
-instances of the structures. Each thread should have its own
-png_struct and png_info instances, and thus its own image.
-Libpng does not protect itself against two threads using the
-same instance of a structure.
-
-
-.SH II. Structures
-
-There are two main structures that are important to libpng, png_struct
-and png_info. The first, png_struct, is an internal structure that
-will not, for the most part, be used by a user except as the first
-variable passed to every libpng function call.
-
-The png_info structure is designed to provide information about the
-PNG file. At one time, the fields of png_info were intended to be
-directly accessible to the user. However, this tended to cause problems
-with applications using dynamically loaded libraries, and as a result
-a set of interface functions for png_info was developed. The fields
-of png_info are still available for older applications, but it is
-suggested that applications use the new interfaces if at all possible.
-
-The png.h header file is an invaluable reference for programming with libpng.
-And while I'm on the topic, make sure you include the libpng header file:
-
-#include <png.h>
-
-.SH III. Reading
-
-Reading PNG files:
-
-We'll now walk you through the possible functions to call when reading
-in a PNG file, briefly explaining the syntax and purpose of each one.
-See example.c and png.h for more detail. While Progressive reading
-is covered in the next section, you will still need some of the
-functions discussed in this section to read a PNG file.
-
-You will want to do the I/O initialization(*) before you get into libpng,
-so if it doesn't work, you don't have much to undo. Of course, you
-will also want to insure that you are, in fact, dealing with a PNG
-file. Libpng provides a simple check to see if a file is a PNG file.
-To use it, pass in the first 1 to 8 bytes of the file, and it will
-return true or false (1 or 0) depending on whether the bytes could be
-part of a PNG file. Of course, the more bytes you pass in, the
-greater the accuracy of the prediction.
-
-If you are intending to keep the file pointer open for use in libpng,
-you must ensure you don't read more than 8 bytes from the beginning
-of the file, and you also have to make a call to png_set_sig_bytes_read()
-with the number of bytes you read from the beginning. Libpng will
-then only check the bytes (if any) that your program didn't read.
-
-(*): If you are not using the standard I/O functions, you will need
-to replace them with custom functions. See the discussion under
-Customizing libpng.
-
-
- FILE *fp = fopen(file_name, "rb");
- if (!fp)
- {
- return;
- }
- fread(header, 1, number, fp);
- is_png = !png_sig_cmp(header, 0, number);
- if (!is_png)
- {
- return;
- }
-
-
-Next, png_struct and png_info need to be allocated and initialized. In
-order to ensure that the size of these structures is correct even with a
-dynamically linked libpng, there are functions to initialize and
-allocate the structures. We also pass the library version, optional
-pointers to error handling functions, and a pointer to a data struct for
-use by the error functions, if necessary (the pointer and functions can
-be NULL if the default error handlers are to be used). See the section
-on Changes to Libpng below regarding the old initialization functions.
-
- png_structp png_ptr = png_create_read_struct
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
- user_error_fn, user_warning_fn);
- if (!png_ptr)
- return;
-
- png_infop info_ptr = png_create_info_struct(png_ptr);
- if (!info_ptr)
- {
- png_destroy_read_struct(&png_ptr,
- (png_infopp)NULL, (png_infopp)NULL);
- return;
- }
-
- png_infop end_info = png_create_info_struct(png_ptr);
- if (!end_info)
- {
- png_destroy_read_struct(&png_ptr, &info_ptr,
- (png_infopp)NULL);
- return;
- }
-
-If you want to use your own memory allocation routines,
-define PNG_USER_MEM_SUPPORTED and use
-png_create_read_struct_2() instead of png_create_read_struct():
-
- png_structp png_ptr = png_create_read_struct_2
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
- user_error_fn, user_warning_fn, (png_voidp)
- user_mem_ptr, user_malloc_fn, user_free_fn);
-
-The error handling routines passed to png_create_read_struct()
-and the memory alloc/free routines passed to png_create_struct_2()
-are only necessary if you are not using the libpng supplied error
-handling and memory alloc/free functions.
-
-When libpng encounters an error, it expects to longjmp back
-to your routine. Therefore, you will need to call setjmp and pass
-your png_ptr->jmpbuf. If you read the file from different
-routines, you will need to update the jmpbuf field every time you enter
-a new routine that will call a png_ function.
-
-See your documentation of setjmp/longjmp for your compiler for more
-handling in the Customizing Libpng section below for more information on
-the libpng error handling. If an error occurs, and libpng longjmp's
-back to your setjmp, you will want to call png_destroy_read_struct() to
-free any memory.
-
- if (setjmp(png_ptr->jmpbuf))
- {
- png_destroy_read_struct(&png_ptr, &info_ptr,
- &end_info);
- fclose(fp);
- return;
- }
-
-Now you need to set up the input code. The default for libpng is to
-use the C function fread(). If you use this, you will need to pass a
-valid FILE * in the function png_init_io(). Be sure that the file is
-opened in binary mode. If you wish to handle reading data in another
-way, you need not call the png_init_io() function, but you must then
-implement the libpng I/O methods discussed in the Customizing Libpng
-section below.
-
- png_init_io(png_ptr, fp);
-
-If you had previously opened the file and read any of the signature from
-the beginning in order to see if this was a PNG file, you need to let
-libpng know that there are some bytes missing from the start of the file.
-
- png_set_sig_bytes(png_ptr, number);
-
-At this point, you can set up a callback function that will be
-called after each row has been read, which you can use to control
-a progress meter or the like. It's demonstrated in pngtest.c.
-You must supply a function
-
- void read_row_callback(png_ptr, png_uint_32 row, int pass);
- {
- /* put your code here */
- }
-
-(You can give it another name that you like instead of "read_row_callback")
-
-To inform libpng about your function, use
-
- png_set_read_status_fn(png_ptr, read_row_callback);
-
-In PNG files, the alpha channel in an image is the level of opacity.
-If you need the alpha channel in an image to be the level of transparency
-instead of opacity, you can invert the alpha channel (or the tRNS chunk
-data) after it's read, so that 0 is fully opaque and 255 (in 8-bit or
-paletted images) or 65535 (in 16-bit images) is fully transparent, with
-
- png_set_invert_alpha(png_ptr);
-
-This has to appear here rather than later with the other transformations
-because the tRNS chunk data must be modified in the case of paletted images.
-If your image is not a paletted image, the tRNS data (which in such cases
-represents a single color to be rendered as transparent) won't be changed.
-
-Finally, you can write your own transformation function if none of
-the existing ones meets your needs. This is done by setting a callback
-with
-
- png_set_read_user_transform_fn(png_ptr,
- read_transform_fn);
-
-You must supply the function
-
- void read_transform_fn(png_ptr ptr, row_info_ptr
- row_info, png_bytep data)
-
-See pngtest.c for a working example. Your function will be called
-after all of the other transformations have been processed.
-
-You are now ready to read all the file information up to the actual
-image data. You do this with a call to png_read_info().
-
- png_read_info(png_ptr, info_ptr);
-
-Functions are used to get the information from the info_ptr:
-
- png_get_IHDR(png_ptr, info_ptr, &width, &height,
- &bit_depth, &color_type, &interlace_type,
- &compression_type, &filter_type);
-
- width - holds the width of the image
- in pixels (up to 2^31).
- height - holds the height of the image
- in pixels (up to 2^31).
- bit_depth - holds the bit depth of one of the
- image channels. (valid values are
- 1, 2, 4, 8, 16 and depend also on
- the color_type. See also
- significant bits (sBIT) below).
- color_type - describes which color/alpha channels
- are present.
- PNG_COLOR_TYPE_GRAY
- (bit depths 1, 2, 4, 8, 16)
- PNG_COLOR_TYPE_GRAY_ALPHA
- (bit depths 8, 16)
- PNG_COLOR_TYPE_PALETTE
- (bit depths 1, 2, 4, 8)
- PNG_COLOR_TYPE_RGB
- (bit_depths 8, 16)
- PNG_COLOR_TYPE_RGB_ALPHA
- (bit_depths 8, 16)
-
- PNG_COLOR_MASK_PALETTE
- PNG_COLOR_MASK_COLOR
- PNG_COLOR_MASK_ALPHA
-
- filter_type - (must be PNG_FILTER_TYPE_BASE
- for PNG 1.0)
- compression_type - (must be PNG_COMPRESSION_TYPE_BASE
- for PNG 1.0)
- interlace_type - (PNG_INTERLACE_NONE or
- PNG_INTERLACE_ADAM7)
- Any or all of interlace_type, compression_type, of
- filter_type can be
- NULL if you are not interested in their values.
-
- channels = png_get_channels(png_ptr, info_ptr);
- channels - number of channels of info for the
- color type (valid values are 1 (GRAY,
- PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
- 4 (RGB_ALPHA or RGB + filler byte))
- rowbytes = png_get_rowbytes(png_ptr, info_ptr);
- rowbytes - number of bytes needed to hold a row
-
- signature = png_get_signature(png_ptr, info_ptr);
- signature - holds the signature read from the
- file (if any). The data is kept in
- the same offset it would be if the
- whole signature were read (i.e. if an
- application had already read in 4
- bytes of signature before starting
- libpng, the remaining 4 bytes would
- be in signature[4] through signature[7]
- (see png_set_sig_bytes())).
-
-
- width = png_get_image_width(png_ptr,
- info_ptr);
- height = png_get_image_height(png_ptr,
- info_ptr);
- bit_depth = png_get_bit_depth(png_ptr,
- info_ptr);
- color_type = png_get_color_type(png_ptr,
- info_ptr);
- filter_type = png_get_filter_type(png_ptr,
- info_ptr);
- compression_type = png_get_compression_type(png_ptr,
- info_ptr);
- interlace_type = png_get_interlace_type(png_ptr,
- info_ptr);
-
-
-These are also important, but their validity depends on whether the chunk
-has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
-png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
-data has been read, or zero if it is missing. The parameters to the
-png_get_<chunk> are set directly if they are simple data types, or a pointer
-into the info_ptr is returned for any complex types.
-
- png_get_PLTE(png_ptr, info_ptr, &palette,
- &num_palette);
- palette - the palette for the file
- (array of png_color)
- num_palette - number of entries in the palette
-
- png_get_gAMA(png_ptr, info_ptr, &gamma);
- gamma - the gamma the file is written
- at (PNG_INFO_gAMA)
-
- png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
- srgb_intent - the rendering intent (PNG_INFO_sRGB)
- The presence of the sRGB chunk
- means that the pixel data is in the
- sRGB color space. This chunk also
- implies specific values of gAMA and
- cHRM.
-
- png_get_sBIT(png_ptr, info_ptr, &sig_bit);
- sig_bit - the number of significant bits for
- (PNG_INFO_sBIT) each of the gray,
- red, green, and blue channels,
- whichever are appropriate for the
- given color type (png_color_16)
-
- png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
- &trans_values);
- trans - array of transparent entries for
- palette (PNG_INFO_tRNS)
- trans_values - transparent pixel for non-paletted
- images (PNG_INFO_tRNS)
- num_trans - number of transparent entries
- (PNG_INFO_tRNS)
-
- png_get_hIST(png_ptr, info_ptr, &hist);
- (PNG_INFO_hIST)
- hist - histogram of palette (array of
- png_color_16)
-
- png_get_tIME(png_ptr, info_ptr, &mod_time);
- mod_time - time image was last modified
- (PNG_VALID_tIME)
-
- png_get_bKGD(png_ptr, info_ptr, &background);
- background - background color (PNG_VALID_bKGD)
-
- num_text = png_get_text(png_ptr, info_ptr, &text_ptr);
- text_ptr - array of png_text holding image
- comments
- text_ptr[i]->key - keyword for comment.
- text_ptr[i]->text - text comments for current
- keyword.
- text_ptr[i]->compression - type of compression used
- on "text" PNG_TEXT_COMPRESSION_NONE
- or PNG_TEXT_COMPRESSION_zTXt
- num_text - number of comments
-
- png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
- &unit_type);
- offset_x - positive offset from the left edge
- of the screen
- offset_y - positive offset from the top edge
- of the screen
- unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
-
- png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
- &unit_type);
- res_x - pixels/unit physical resolution in
- x direction
- res_y - pixels/unit physical resolution in
- x direction
- unit_type - PNG_RESOLUTION_UNKNOWN,
- PNG_RESOLUTION_METER
-
-The data from the pHYs chunk can be retrieved in several convenient
-forms:
-
- res_x = png_get_x_pixels_per_meter(png_ptr,
- info_ptr)
- res_y = png_get_y_pixels_per_meter(png_ptr,
- info_ptr)
- res_x_and_y = png_get_pixels_per_meter(png_ptr,
- info_ptr)
- aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
- info_ptr)
-
- (Each of these returns 0 [signifying "unknown"] if
- the data is not present or if res_x is 0;
- res_x_and_y is 0 if res_x != res_y)
-
-For more information, see the png_info definition in png.h and the
-PNG specification for chunk contents. Be careful with trusting
-rowbytes, as some of the transformations could increase the space
-needed to hold a row (expand, filler, gray_to_rgb, etc.).
-See png_read_update_info(), below.
-
-A quick word about text_ptr and num_text. PNG stores comments in
-keyword/text pairs, one pair per chunk, with no limit on the number
-of text chunks, and a 2^31 byte limit on their size. While there are
-suggested keywords, there is no requirement to restrict the use to these
-strings. It is strongly suggested that keywords and text be sensible
-to humans (that's the point), so don't use abbreviations. Non-printing
-symbols are not allowed. See the PNG specification for more details.
-There is also no requirement to have text after the keyword.
-
-Keywords should be limited to 79 Latin-1 characters without leading or
-trailing spaces, but non-consecutive spaces are allowed within the
-keyword. It is possible to have the same keyword any number of times.
-The text_ptr is an array of png_text structures, each holding pointer
-to a keyword and a pointer to a text string. Only the text string may
-be null. The keyword/text pairs are put into the array in the order
-that they are received. However, some or all of the text chunks may be
-after the image, so, to make sure you have read all the text chunks,
-don't mess with these until after you read the stuff after the image.
-This will be mentioned again below in the discussion that goes with
-png_read_end().
-
-After you've read the header information, you can set up the library
-to handle any special transformations of the image data. The various
-ways to transform the data will be described in the order that they
-should occur. This is important, as some of these change the color
-type and/or bit depth of the data, and some others only work on
-certain color types and bit depths. Even though each transformation
-checks to see if it has data that it can do something with, you should
-make sure to only enable a transformation if it will be valid for the
-data. For example, don't swap red and blue on grayscale data.
-
-The colors used for the background and transparency values should be
-supplied in the same format/depth as the current image data. They
-are stored in the same format/depth as the image data in a bKGD or tRNS
-chunk, so this is what libpng expects for this data. The colors are
-transformed to keep in sync with the image data when an application
-calls the png_read_update_info() routine (see below).
-
-Data will be decoded into the supplied row buffers packed into bytes
-unless the library has been told to transform it into another format.
-For example, 4 bit/pixel paletted or grayscale data will be returned
-2 pixels/byte with the leftmost pixel in the high-order bits of the
-byte, unless png_set_packing() is called. 8-bit RGB data will be stored
-in RGB RGB RGB format unless png_set_filler() is called to insert filler
-bytes, either before or after each RGB triplet. 16-bit RGB data will
-be returned RRGGBB RRGGBB, with the most significant byte of the color
-value first, unless png_set_strip_16() is called to transform it to
-regular RGB RGB triplets, or png_set_filler() is called to insert
-filler bytes, either before or after each RRGGBB triplet. Similarly,
-8-bit or 16-bit grayscale data can be modified with png_set_filler()
-or png_set_strip_16().
-
-The following code transforms grayscale images of less than 8 to 8 bits,
-changes paletted images to RGB, and adds a full alpha channel if there is
-transparency information in a tRNS chunk. This is most useful on
-grayscale images with bit depths of 2 or 4 or if there is a multiple-image
-viewing application that wishes to treat all images in the same way.
-
- if (color_type == PNG_COLOR_TYPE_PALETTE &&
- bit_depth <= 8) png_set_expand(png_ptr);
-
- if (color_type == PNG_COLOR_TYPE_GRAY &&
- bit_depth < 8) png_set_expand(png_ptr);
-
- if (png_get_valid(png_ptr, info_ptr,
- PNG_INFO_tRNS)) png_set_expand(png_ptr);
-
-PNG can have files with 16 bits per channel. If you only can handle
-8 bits per channel, this will strip the pixels down to 8 bit.
-
- if (bit_depth == 16)
- png_set_strip_16(png_ptr);
-
-The png_set_background() function tells libpng to composite images
-with alpha or simple transparency against the supplied background
-color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
-you may use this color, or supply another color more suitable for
-the current display (e.g., the background color from a web page). You
-need to tell libpng whether the color is in the gamma space of the
-display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
-(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
-that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
-know why anyone would use this, but it's here).
-
-If, for some reason, you don't need the alpha channel on an image,
-and you want to remove it rather than combining it with the background
-(but the image author certainly had in mind that you *would* combine
-it with the background, so that's what you should probably do):
-
- if (color_type & PNG_COLOR_MASK_ALPHA)
- png_set_strip_alpha(png_ptr);
-
-PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
-they can, resulting in, for example, 8 pixels per byte for 1 bit
-files. This code expands to 1 pixel per byte without changing the
-values of the pixels:
-
- if (bit_depth < 8)
- png_set_packing(png_ptr);
-
-PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
-stored in a PNG image have been "scaled" or "shifted" up to the next
-higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
-8 bits/sample in the range [0, 255]). However, it is also possible to
-convert the PNG pixel data back to the original bit depth of the image.
-This call reduces the pixels back down to the original bit depth:
-
- png_color_16p sig_bit;
-
- if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
- png_set_shift(png_ptr, sig_bit);
-
-PNG files store 3-color pixels in red, green, blue order. This code
-changes the storage of the pixels to blue, green, red:
-
- if (color_type == PNG_COLOR_TYPE_RGB ||
- color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_bgr(png_ptr);
-
-PNG files store RGB pixels packed into 3 bytes. This code expands them
-into 4 bytes for windowing systems that need them in this format:
-
- if (bit_depth == 8 && color_type ==
- PNG_COLOR_TYPE_RGB) png_set_filler(png_ptr,
- filler, PNG_FILLER_BEFORE);
-
-where "filler" is the 8 or 16-bit number to fill with, and the location is
-either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
-you want the filler before the RGB or after. This transformation
-does not affect images that already have full alpha channels.
-
-If you are reading an image with an alpha channel, and you need the
-data as ARGB instead of the normal PNG format RGBA:
-
- if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_swap_alpha(png_ptr);
-
-For some uses, you may want a grayscale image to be represented as
-RGB. This code will do that conversion:
-
- if (color_type == PNG_COLOR_TYPE_GRAY ||
- color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
- png_set_gray_to_rgb(png_ptr);
-
-Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
-with alpha. This is intended for conversion of images that really are
-gray (red == green == blue), so the function simply strips out the red
-and blue channels, leaving the green channel in the gray position.
-
- if (color_type == PNG_COLOR_TYPE_RGB ||
- color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_rgb_to_gray(png_ptr, error_action,
- float red_weight, float green_weight);
-
- error_action = 1: silently do the conversion
- error_action = 2: issue a warning if the original
- image has any pixel where
- red != green or red != blue
- error_action = 3: issue an error and abort the
- conversion if the original
- image has any pixel where
- red != green or red != blue
-
- red_weight: weight of red component
- (NULL -> default 54/256)
- green_weight: weight of green component
- (NULL -> default 183/256)
-
-If you have set error_action = 1 or 2, you can
-later check whether the image really was gray, after processing
-the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
-It will return a png_byte that is zero if the image was gray or
-1 if there were any non-gray pixels. bKGD and sBIT data
-will be silently converted to grayscale, using the green channel
-data, regardless of the error_action setting.
-
-With 0.0<=red_weight+green_weight<=1.0,
-the normalized graylevel is computed:
-
- int rw = red_weight * 256;
- int gw = green_weight * 256;
- int bw = 256 - (rw + gw);
- gray = (rw*red + gw*green + bw*blue)/256;
-
-The default values approximate those recommended in the Charles
-Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
-Copyright (c) 1998-01-04 Charles Poynton poynton@inforamp.net
-
- Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
-
-Libpng approximates this with
-
- Y = 0.211 * R + 0.715 * G + 0.074 * B
-
-which can be expressed with integers as
-
- Y = (54 * R + 183 * G + 19 * B)/256
-
-The calculation is done in a linear colorspace, if the image gamma
-is known.
-
-If you have a grayscale and you are using png_set_expand() to change to
-a higher bit-depth, you must either supply the background color as a gray
-value at the original file bit-depth (need_expand = 1) or else supply the
-background color as an RGB triplet at the final, expanded bit depth
-(need_expand = 0). Similarly, if you are reading a paletted image, you
-must either supply the background color as a palette index (need_expand = 1)
-or as an RGB triplet that may or may not be in the palette (need_expand = 0).
-
- png_color_16 my_background;
- png_color_16p image_background;
-
- if (png_get_bKGD(png_ptr, info_ptr, &image_background))
- png_set_background(png_ptr, image_background,
- PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
- else
- png_set_background(png_ptr, &my_background,
- PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
-
-To properly display PNG images on any kind of system, the application needs
-to know what the display gamma is. Ideally, the user will know this, and
-the application will allow them to set it. One method of allowing the user
-to set the display gamma separately for each system is to check for the
-DISPLAY_GAMMA and VIEWING_GAMMA environment variables or for a SCREEN_GAMMA
-environment variable, which will hopefully be correctly set.
-
-Note that display_gamma is the gamma of your display, while screen_gamma is
-the overall gamma correction required to produce pleasing results,
-which depends on the lighting conditions in the surrounding environment.
-Screen_gamma is display_gamma/viewing_gamma, where viewing_gamma is
-the amount of additional gamma correction needed to compensate for
-a (viewing_gamma=1.25) environment. In a dim or brightly lit room, no
-compensation other than the display_gamma is needed (viewing_gamma=1.0).
-
- if (/* We have a user-defined screen
- gamma value */)
- {
- screen_gamma = user_defined_screen_gamma;
- }
- /* One way that applications can share the same
- screen gamma value */
- else if ((gamma_str = getenv("SCREEN_GAMMA"))
- != NULL)
- {
- screen_gamma = atof(gamma_str);
- }
- /* If we don't have another value */
- else
- {
- screen_gamma = 2.2; /* A good guess for a
- PC monitor in a bright office or a dim room */
- screen_gamma = 2.0; /* A good guess for a
- PC monitor in a dark room */
- screen_gamma = 1.7 or 1.0; /* A good
- guess for Mac systems */
- }
-
-The png_set_gamma() function handles gamma transformations of the data.
-Pass both the file gamma and the current screen_gamma. If the file does
-not have a gamma value, you can pass one anyway if you have an idea what
-it is (usually 0.45455 is a good guess for GIF images on PCs). Note
-that file gammas are inverted from screen gammas. See the discussions
-on gamma in the PNG specification for an excellent description of what
-gamma is, and why all applications should support it. It is strongly
-recommended that PNG viewers support gamma correction.
-
- if (png_get_gAMA(png_ptr, info_ptr, &gamma))
- png_set_gamma(png_ptr, screen_gamma, gamma);
- else
- png_set_gamma(png_ptr, screen_gamma, 0.45455);
-
-If you need to reduce an RGB file to a paletted file, or if a paletted
-file has more entries then will fit on your screen, png_set_dither()
-will do that. Note that this is a simple match dither that merely
-finds the closest color available. This should work fairly well with
-optimized palettes, and fairly badly with linear color cubes. If you
-pass a palette that is larger then maximum_colors, the file will
-reduce the number of colors in the palette so it will fit into
-maximum_colors. If there is a histogram, it will use it to make
-more intelligent choices when reducing the palette. If there is no
-histogram, it may not do as good a job.
-
- if (color_type & PNG_COLOR_MASK_COLOR)
- {
- if (png_get_valid(png_ptr, info_ptr,
- PNG_INFO_PLTE))
- {
- png_color_16p histogram;
-
- png_get_hIST(png_ptr, info_ptr,
- &histogram);
- png_set_dither(png_ptr, palette, num_palette,
- max_screen_colors, histogram, 1);
- }
- else
- {
- png_color std_color_cube[MAX_SCREEN_COLORS] =
- { ... colors ... };
-
- png_set_dither(png_ptr, std_color_cube,
- MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
- NULL,0);
- }
- }
-
-PNG files describe monochrome as black being zero and white being one.
-The following code will reverse this (make black be one and white be
-zero):
-
- if (bit_depth == 1 && color_type == PNG_COLOR_GRAY)
- png_set_invert_mono(png_ptr);
-
-PNG files store 16 bit pixels in network byte order (big-endian,
-ie. most significant bits first). This code changes the storage to the
-other way (little-endian, i.e. least significant bits first, the
-way PCs store them):
-
- if (bit_depth == 16)
- png_set_swap(png_ptr);
-
-If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
-need to change the order the pixels are packed into bytes, you can use:
-
- if (bit_depth < 8)
- png_set_packswap(png_ptr);
-
-The last thing to handle is interlacing; this is covered in detail below,
-but you must call the function here if you want libpng to handle expansion
-of the interlaced image.
-
- number_of_passes = png_set_interlace_handling(png_ptr);
-
-After setting the transformations, libpng can update your png_info
-structure to reflect any transformations you've requested with this
-call. This is most useful to update the info structure's rowbytes
-field so you can use it to allocate your image memory. This function
-will also update your palette with the correct screen_gamma and
-background if these have been given with the calls above.
-
- png_read_update_info(png_ptr, info_ptr);
-
-After you call png_read_update_info(), you can allocate any
-memory you need to hold the image. The row data is simply
-raw byte data for all forms of images. As the actual allocation
-varies among applications, no example will be given. If you
-are allocating one large chunk, you will need to build an
-array of pointers to each row, as it will be needed for some
-of the functions below.
-
-After you've allocated memory, you can read the image data.
-The simplest way to do this is in one function call. If you are
-allocating enough memory to hold the whole image, you can just
-call png_read_image() and libpng will read in all the image data
-and put it in the memory area supplied. You will need to pass in
-an array of pointers to each row.
-
-This function automatically handles interlacing, so you don't need
-to call png_set_interlace_handling() or call this function multiple
-times, or any of that other stuff necessary with png_read_rows().
-
- png_read_image(png_ptr, row_pointers);
-
-where row_pointers is:
-
- png_bytep row_pointers[height];
-
-You can point to void or char or whatever you use for pixels.
-
-If you don't want to read in the whole image at once, you can
-use png_read_rows() instead. If there is no interlacing (check
-interlace_type == PNG_INTERLACE_NONE), this is simple:
-
- png_read_rows(png_ptr, row_pointers, NULL,
- number_of_rows);
-
-where row_pointers is the same as in the png_read_image() call.
-
-If you are doing this just one row at a time, you can do this with
-row_pointers:
-
- png_bytep row_pointers = row;
- png_read_row(png_ptr, &row_pointers, NULL);
-
-If the file is interlaced (info_ptr->interlace_type != 0), things get
-somewhat harder. The only current (PNG Specification version 1.0)
-interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
-is a somewhat complicated 2D interlace scheme, known as Adam7, that
-breaks down an image into seven smaller images of varying size, based
-on an 8x8 grid.
-
-libpng can fill out those images or it can give them to you "as is".
-If you want them filled out, there are two ways to do that. The one
-mentioned in the PNG specification is to expand each pixel to cover
-those pixels that have not been read yet (the "rectangle" method).
-This results in a blocky image for the first pass, which gradually
-smooths out as more pixels are read. The other method is the "sparkle"
-method, where pixels are drawn only in their final locations, with the
-rest of the image remaining whatever colors they were initialized to
-before the start of the read. The first method usually looks better,
-but tends to be slower, as there are more pixels to put in the rows.
-
-If you don't want libpng to handle the interlacing details, just call
-png_read_rows() seven times to read in all seven images. Each of the
-images is a valid image by itself, or they can all be combined on an
-8x8 grid to form a single image (although if you intend to combine them
-you would be far better off using the libpng interlace handling).
-
-The first pass will return an image 1/8 as wide as the entire image
-(every 8th column starting in column 0) and 1/8 as high as the original
-(every 8th row starting in row 0), the second will be 1/8 as wide
-(starting in column 4) and 1/8 as high (also starting in row 0). The
-third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
-1/8 as high (every 8th row starting in row 4), and the fourth pass will
-be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
-and every 4th row starting in row 0). The fifth pass will return an
-image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
-while the sixth pass will be 1/2 as wide and 1/2 as high as the original
-(starting in column 1 and row 0). The seventh and final pass will be as
-wide as the original, and 1/2 as high, containing all of the odd
-numbered scanlines. Phew!
-
-If you want libpng to expand the images, call this before calling
-png_start_read_image() or png_read_update_info():
-
- if (interlace_type == PNG_INTERLACE_ADAM7)
- number_of_passes
- = png_set_interlace_handling(png_ptr);
-
-This will return the number of passes needed. Currently, this
-is seven, but may change if another interlace type is added.
-This function can be called even if the file is not interlaced,
-where it will return one pass.
-
-If you are not going to display the image after each pass, but are
-going to wait until the entire image is read in, use the sparkle
-effect. This effect is faster and the end result of either method
-is exactly the same. If you are planning on displaying the image
-after each pass, the "rectangle" effect is generally considered the
-better looking one.
-
-If you only want the "sparkle" effect, just call png_read_rows() as
-normal, with the third parameter NULL. Make sure you make pass over
-the image number_of_passes times, and you don't change the data in the
-rows between calls. You can change the locations of the data, just
-not the data. Each pass only writes the pixels appropriate for that
-pass, and assumes the data from previous passes is still valid.
-
- png_read_rows(png_ptr, row_pointers, NULL,
- number_of_rows);
-
-If you only want the first effect (the rectangles), do the same as
-before except pass the row buffer in the third parameter, and leave
-the second parameter NULL.
-
- png_read_rows(png_ptr, NULL, row_pointers,
- number_of_rows);
-
-After you are finished reading the image, you can finish reading
-the file. If you are interested in comments or time, which may be
-stored either before or after the image data, you should pass the
-separate png_info struct if you want to keep the comments from
-before and after the image separate. If you are not interested, you
-can pass NULL.
-
- png_read_end(png_ptr, end_info);
-
-When you are done, you can free all memory allocated by libpng like this:
-
- png_destroy_read_struct(&png_ptr, &info_ptr,
- &end_info);
-
-For a more compact example of reading a PNG image, see the file example.c.
-
-
-Reading PNG files progressively:
-
-The progressive reader is slightly different then the non-progressive
-reader. Instead of calling png_read_info(), png_read_rows(), and
-png_read_end(), you make one call to png_process_data(), which calls
-callbacks when it has the info, a row, or the end of the image. You
-set up these callbacks with png_set_progressive_read_fn(). You don't
-have to worry about the input/output functions of libpng, as you are
-giving the library the data directly in png_process_data(). I will
-assume that you have read the section on reading PNG files above,
-so I will only highlight the differences (although I will show
-all of the code).
-
-png_structp png_ptr;
-png_infop info_ptr;
-
- /* An example code fragment of how you would
- initialize the progressive reader in your
- application. */
- int
- initialize_png_reader()
- {
- png_ptr = png_create_read_struct
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
- user_error_fn, user_warning_fn);
- if (!png_ptr)
- return -1;
- info_ptr = png_create_info_struct(png_ptr);
- if (!info_ptr)
- {
- png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
- (png_infopp)NULL);
- return -1;
- }
-
- if (setjmp(png_ptr->jmpbuf))
- {
- png_destroy_read_struct(&png_ptr, &info_ptr,
- (png_infopp)NULL);
- return -1;
- }
-
- /* This one's new. You can provide functions
- to be called when the header info is valid,
- when each row is completed, and when the image
- is finished. If you aren't using all functions,
- you can specify NULL parameters. Even when all
- three functions are NULL, you need to call
- png_set_progressive_read_fn(). You can use
- any struct as the user_ptr (cast to a void pointer
- for the function call), and retrieve the pointer
- from inside the callbacks using the function
-
- png_get_progressive_ptr(png_ptr);
-
- which will return a void pointer, which you have
- to cast appropriately.
- */
- png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
- info_callback, row_callback, end_callback);
-
- return 0;
- }
-
- /* A code fragment that you call as you receive blocks
- of data */
- int
- process_data(png_bytep buffer, png_uint_32 length)
- {
- if (setjmp(png_ptr->jmpbuf))
- {
- png_destroy_read_struct(&png_ptr, &info_ptr,
- (png_infopp)NULL);
- return -1;
- }
-
- /* This one's new also. Simply give it a chunk
- of data from the file stream (in order, of
- course). On machines with segmented memory
- models machines, don't give it any more than
- 64K. The library seems to run fine with sizes
- of 4K. Although you can give it much less if
- necessary (I assume you can give it chunks of
- 1 byte, I haven't tried less then 256 bytes
- yet). When this function returns, you may
- want to display any rows that were generated
- in the row callback if you don't already do
- so there.
- */
- png_process_data(png_ptr, info_ptr, buffer, length);
- return 0;
- }
-
- /* This function is called (as set by
- png_set_progressive_read_fn() above) when enough data
- has been supplied so all of the header has been
- read.
- */
- void
- info_callback(png_structp png_ptr, png_infop info)
- {
- /* Do any setup here, including setting any of
- the transformations mentioned in the Reading
- PNG files section. For now, you _must_ call
- either png_start_read_image() or
- png_read_update_info() after all the
- transformations are set (even if you don't set
- any). You may start getting rows before
- png_process_data() returns, so this is your
- last chance to prepare for that.
- */
- }
-
- /* This function is called when each row of image
- data is complete */
- void
- row_callback(png_structp png_ptr, png_bytep new_row,
- png_uint_32 row_num, int pass)
- {
- /* If the image is interlaced, and you turned
- on the interlace handler, this function will
- be called for every row in every pass. Some
- of these rows will not be changed from the
- previous pass. When the row is not changed,
- the new_row variable will be NULL. The rows
- and passes are called in order, so you don't
- really need the row_num and pass, but I'm
- supplying them because it may make your life
- easier.
-
- For the non-NULL rows of interlaced images,
- you must call png_progressive_combine_row()
- passing in the row and the old row. You can
- call this function for NULL rows (it will just
- return) and for non-interlaced images (it just
- does the memcpy for you) if it will make the
- code easier. Thus, you can just do this for
- all cases:
- */
-
- png_progressive_combine_row(png_ptr, old_row,
- new_row);
-
- /* where old_row is what was displayed for
- previously for the row. Note that the first
- pass (pass == 0, really) will completely cover
- the old row, so the rows do not have to be
- initialized. After the first pass (and only
- for interlaced images), you will have to pass
- the current row, and the function will combine
- the old row and the new row.
- */
- }
-
- void
- end_callback(png_structp png_ptr, png_infop info)
- {
- /* This function is called after the whole image
- has been read, including any chunks after the
- image (up to and including the IEND). You
- will usually have the same info chunk as you
- had in the header, although some data may have
- been added to the comments and time fields.
-
- Most people won't do much here, perhaps setting
- a flag that marks the image as finished.
- */
- }
-
-
-
-.SH IV. Writing
-
-Much of this is very similar to reading. However, everything of
-importance is repeated here, so you won't have to constantly look
-back up in the reading section to understand writing.
-
-You will want to do the I/O initialization before you get into libpng,
-so if it doesn't work, you don't have anything to undo. If you are not
-using the standard I/O functions, you will need to replace them with
-custom writing functions. See the discussion under Customizing libpng.
-
- FILE *fp = fopen(file_name, "wb");
- if (!fp)
- {
- return;
- }
-
-Next, png_struct and png_info need to be allocated and initialized.
-As these can be both relatively large, you may not want to store these
-on the stack, unless you have stack space to spare. Of course, you
-will want to check if they return NULL. If you are also reading,
-you won't want to name your read structure and your write structure
-both "png_ptr"; you can call them anything you like, such as
-"read_ptr" and "write_ptr". Look at pngtest.c, for example.
-
- png_structp png_ptr = png_create_write_struct
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
- user_error_fn, user_warning_fn);
- if (!png_ptr)
- return;
-
- png_infop info_ptr = png_create_info_struct(png_ptr);
- if (!info_ptr)
- {
- png_destroy_write_struct(&png_ptr,
- (png_infopp)NULL);
- return;
- }
-
-If you want to use your own memory allocation routines,
-define PNG_USER_MEM_SUPPORTED and use
-png_create_write_struct_2() instead of png_create_read_struct():
-
- png_structp png_ptr = png_create_write_struct_2
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
- user_error_fn, user_warning_fn, (png_voidp)
- user_mem_ptr, user_malloc_fn, user_free_fn);
-
-After you have these structures, you will need to set up the
-error handling. When libpng encounters an error, it expects to
-longjmp() back to your routine. Therefore, you will need to call
-setjmp() and pass the png_ptr->jmpbuf. If you
-write the file from different routines, you will need to update
-the jmpbuf field every time you enter a new routine that will
-call a png_ function. See your documentation of setjmp/longjmp
-for your compiler for more information on setjmp/longjmp. See
-the discussion on libpng error handling in the Customizing Libpng
-section below for more information on the libpng error handling.
-
- if (setjmp(png_ptr->jmpbuf))
- {
- png_destroy_write_struct(&png_ptr, &info_ptr);
- fclose(fp);
- return;
- }
- ...
- return;
-
-Now you need to set up the output code. The default for libpng is to
-use the C function fwrite(). If you use this, you will need to pass a
-valid FILE * in the function png_init_io(). Be sure that the file is
-opened in binary mode. Again, if you wish to handle writing data in
-another way, see the discussion on libpng I/O handling in the Customizing
-Libpng section below.
-
- png_init_io(png_ptr, fp);
-
-At this point, you can set up a callback function that will be
-called after each row has been written, which you can use to control
-a progress meter or the like. It's demonstrated in pngtest.c.
-You must supply a function
-
- void write_row_callback(png_ptr, png_uint_32 row, int pass);
- {
- /* put your code here */
- }
-
-(You can give it another name that you like instead of "write_row_callback")
-
-To inform libpng about your function, use
-
- png_set_write_status_fn(png_ptr, write_row_callback);
-
-You now have the option of modifying how the compression library will
-run. The following functions are mainly for testing, but may be useful
-in some cases, like if you need to write PNG files extremely fast and
-are willing to give up some compression, or if you want to get the
-maximum possible compression at the expense of slower writing. If you
-have no special needs in this area, let the library do what it wants by
-not calling this function at all, as it has been tuned to deliver a good
-speed/compression ratio. The second parameter to png_set_filter() is
-the filter method, for which the only valid value is '0' (as of the
-October 1996 PNG specification, version 1.0). The third parameter is a
-flag that indicates which filter type(s) are to be tested for each
-scanline. See the Compression Library for details on the specific filter
-types.
-
-
- /* turn on or off filtering, and/or choose
- specific filters */
- png_set_filter(png_ptr, 0,
- PNG_FILTER_NONE | PNG_FILTER_SUB |
- PNG_FILTER_PAETH);
-
-The png_set_compression_???() functions interface to the zlib compression
-library, and should mostly be ignored unless you really know what you are
-doing. The only generally useful call is png_set_compression_level()
-which changes how much time zlib spends on trying to compress the image
-data. See the Compression Library for details on the compression levels.
-
- /* set the zlib compression level */
- png_set_compression_level(png_ptr,
- Z_BEST_COMPRESSION);
-
- /* set other zlib parameters */
- png_set_compression_mem_level(png_ptr, 8);
- png_set_compression_strategy(png_ptr,
- Z_DEFAULT_STRATEGY);
- png_set_compression_window_bits(png_ptr, 15);
- png_set_compression_method(png_ptr, 8);
-
-You now need to fill in the png_info structure with all the data you
-wish to write before the actual image. Note that the only thing you
-are allowed to write after the image is the text chunks and the time
-chunk (as of PNG Specification 1.0, anyway). See png_write_end() and
-the latest PNG specification for more information on that. If you
-wish to write them before the image, fill them in now, and flag that
-data as being valid. If you want to wait until after the data, don't
-fill them until png_write_end(). For all the fields in png_info and
-their data types, see png.h. For explanations of what the fields
-contain, see the PNG specification.
-
-Some of the more important parts of the png_info are:
-
- png_set_IHDR(png_ptr, info_ptr, width, height,
- bit_depth, color_type, interlace_type,
- compression_type, filter_type)
- width - holds the width of the image
- in pixels (up to 2^31).
- height - holds the height of the image
- in pixels (up to 2^31).
- bit_depth - holds the bit depth of one of the
- image channels.
- (valid values are 1, 2, 4, 8, 16
- and depend also on the
- color_type. See also significant
- bits (sBIT) below).
- color_type - describes which color/alpha
- channels are present.
- PNG_COLOR_TYPE_GRAY
- (bit depths 1, 2, 4, 8, 16)
- PNG_COLOR_TYPE_GRAY_ALPHA
- (bit depths 8, 16)
- PNG_COLOR_TYPE_PALETTE
- (bit depths 1, 2, 4, 8)
- PNG_COLOR_TYPE_RGB
- (bit_depths 8, 16)
- PNG_COLOR_TYPE_RGB_ALPHA
- (bit_depths 8, 16)
-
- PNG_COLOR_MASK_PALETTE
- PNG_COLOR_MASK_COLOR
- PNG_COLOR_MASK_ALPHA
-
- interlace_type - PNG_INTERLACE_NONE or
- PNG_INTERLACE_ADAM7
- compression_type - (must be
- PNG_COMPRESSION_TYPE_DEFAULT)
- filter_type - (must be PNG_FILTER_TYPE_DEFAULT)
-
- png_set_PLTE(png_ptr, info_ptr, palette,
- num_palette);
- palette - the palette for the file
- (array of png_color)
- num_palette - number of entries in the palette
-
- png_set_gAMA(png_ptr, info_ptr, gamma);
- gamma - the gamma the image was created
- at (PNG_INFO_gAMA)
-
- png_set_sRGB(png_ptr, info_ptr, srgb_intent);
- srgb_intent - the rendering intent
- (PNG_INFO_sRGB) The presence of
- the sRGB chunk means that the pixel
- data is in the sRGB color space.
- This chunk also implies specific
- values of gAMA and cHRM. Rendering
- intent is the CSS-1 property that
- has been defined by the International
- Color Consortium
- (http://www.color.org).
- It can be one of
- PNG_SRGB_INTENT_SATURATION,
- PNG_SRGB_INTENT_PERCEPTUAL,
- PNG_SRGB_INTENT_ABSOLUTE, or
- PNG_SRGB_INTENT_RELATIVE.
-
-
- png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
- srgb_intent);
- srgb_intent - the rendering intent
- (PNG_INFO_sRGB) The presence of the
- sRGB chunk means that the pixel
- data is in the sRGB color space.
- This function also causes gAMA and
- cHRM chunks with the specific values
- that are consistent with sRGB to be
- written.
-
- png_set_sBIT(png_ptr, info_ptr, sig_bit);
- sig_bit - the number of significant bits for
- (PNG_INFO_sBIT) each of the gray, red,
- green, and blue channels, whichever are
- appropriate for the given color type
- (png_color_16)
-
- png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
- trans_values);
- trans - array of transparent entries for
- palette (PNG_INFO_tRNS)
- trans_values - transparent pixel for non-paletted
- images (PNG_INFO_tRNS)
- num_trans - number of transparent entries
- (PNG_INFO_tRNS)
-
- png_set_hIST(png_ptr, info_ptr, hist);
- (PNG_INFO_hIST)
- hist - histogram of palette (array of
- png_color_16)
-
- png_set_tIME(png_ptr, info_ptr, mod_time);
- mod_time - time image was last modified
- (PNG_VALID_tIME)
-
- png_set_bKGD(png_ptr, info_ptr, background);
- background - background color (PNG_VALID_bKGD)
-
- png_set_text(png_ptr, info_ptr, text_ptr, num_text);
- text_ptr - array of png_text holding image
- comments
- text_ptr[i]->key - keyword for comment.
- text_ptr[i]->text - text comments for current
- keyword.
- text_ptr[i]->compression - type of compression used
- on "text" PNG_TEXT_COMPRESSION_NONE or
- PNG_TEXT_COMPRESSION_zTXt
- num_text - number of comments in text_ptr
-
- png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
- unit_type);
- offset_x - positive offset from the left
- edge of the screen
- offset_y - positive offset from the top
- edge of the screen
- unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
-
- png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
- unit_type);
- res_x - pixels/unit physical resolution
- in x direction
- res_y - pixels/unit physical resolution
- in y direction
- unit_type - PNG_RESOLUTION_UNKNOWN,
- PNG_RESOLUTION_METER
-
-In PNG files, the alpha channel in an image is the level of opacity.
-If your data is supplied as a level of transparency, you can invert the
-alpha channel before you write it, so that 0 is fully transparent and 255
-(in 8-bit or paletted images) or 65535 (in 16-bit images) is fully opaque,
-with
-
- png_set_invert_alpha(png_ptr);
-
-This must appear here instead of later with the other transformations
-because in the case of paletted images the tRNS chunk data has to
-be inverted before the tRNS chunk is written. If your image is not a
-paletted image, the tRNS data (which in such cases represents a single
-color to be rendered as transparent) won't be changed.
-
-A quick word about text and num_text. text is an array of png_text
-structures. num_text is the number of valid structures in the array.
-If you want, you can use max_text to hold the size of the array, but
-libpng ignores it for writing (it does use it for reading). Each
-png_text structure holds a keyword-text value, and a compression type.
-The compression types have the same valid numbers as the compression
-types of the image data. Currently, the only valid number is zero.
-However, you can store text either compressed or uncompressed, unlike
-images, which always have to be compressed. So if you don't want the
-text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
-Until text gets around 1000 bytes, it is not worth compressing it.
-After the text has been written out to the file, the compression type
-is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
-so that it isn't written out again at the end (in case you are calling
-png_write_end() with the same struct.
-
-The keywords that are given in the PNG Specification are:
-
- Title Short (one line) title or
- caption for image
- Author Name of image's creator
- Description Description of image (possibly long)
- Copyright Copyright notice
- Creation Time Time of original image creation
- (usually RFC 1123 format, see below)
- Software Software used to create the image
- Disclaimer Legal disclaimer
- Warning Warning of nature of content
- Source Device used to create the image
- Comment Miscellaneous comment; conversion
- from other image format
-
-The keyword-text pairs work like this. Keywords should be short
-simple descriptions of what the comment is about. Some typical
-keywords are found in the PNG specification, as is some recommendations
-on keywords. You can repeat keywords in a file. You can even write
-some text before the image and some after. For example, you may want
-to put a description of the image before the image, but leave the
-disclaimer until after, so viewers working over modem connections
-don't have to wait for the disclaimer to go over the modem before
-they start seeing the image. Finally, keywords should be full
-words, not abbreviations. Keywords and text are in the ISO 8859-1
-(Latin-1) character set (a superset of regular ASCII) and can not
-contain NUL characters, and should not contain control or other
-unprintable characters. To make the comments widely readable, stick
-with basic ASCII, and avoid machine specific character set extensions
-like the IBM-PC character set. The keyword must be present, but
-you can leave off the text string on non-compressed pairs.
-Compressed pairs must have a text string, as only the text string
-is compressed anyway, so the compression would be meaningless.
-
-PNG supports modification time via the png_time structure. Two
-conversion routines are proved, png_convert_from_time_t() for
-time_t and png_convert_from_struct_tm() for struct tm. The
-time_t routine uses gmtime(). You don't have to use either of
-these, but if you wish to fill in the png_time structure directly,
-you should provide the time in universal time (GMT) if possible
-instead of your local time. Note that the year number is the full
-year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
-that months start with 1.
-
-If you want to store the time of the original image creation, you should
-use a plain tEXt chunk with the "Creation Time" keyword. This is
-necessary because the "creation time" of a PNG image is somewhat vague,
-depending on whether you mean the PNG file, the time the image was
-created in a non-PNG format, a still photo from which the image was
-scanned, or possibly the subject matter itself. In order to facilitate
-machine-readable dates, it is recommended that the "Creation Time"
-tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
-although this isn't a requirement. Unlike the tIME chunk, the
-"Creation Time" tEXt chunk is not expected to be automatically changed
-by the software. To facilitate the use of RFC 1123 dates, a function
-png_convert_to_rfc1123(png_timep) is provided to convert from PNG
-time to an RFC 1123 format string.
-
-You are now ready to write all the file information up to the actual
-image data. You do this with a call to png_write_info().
-
- png_write_info(png_ptr, info_ptr);
-
-After you've written the file information, you can set up the library
-to handle any special transformations of the image data. The various
-ways to transform the data will be described in the order that they
-should occur. This is important, as some of these change the color
-type and/or bit depth of the data, and some others only work on
-certain color types and bit depths. Even though each transformation
-checks to see if it has data that it can do something with, you should
-make sure to only enable a transformation if it will be valid for the
-data. For example, don't swap red and blue on grayscale data.
-
-PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
-the library to expand the input data to 4 or 8 bytes per pixel
-(or expand 1 or 2-byte grayscale data to 2 or 4 bytes per pixel).
-
- png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
-
-where the 0 is the value that will be put in the 4th byte, and the
-location is either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending
-upon whether the filler byte is stored XRGB or RGBX.
-
-PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
-they can, resulting in, for example, 8 pixels per byte for 1 bit files.
-If the data is supplied at 1 pixel per byte, use this code, which will
-correctly pack the pixels into a single byte:
-
- png_set_packing(png_ptr);
-
-PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
-data is of another bit depth, you can write an sBIT chunk into the
-file so that decoders can get the original data if desired.
-
- /* Set the true bit depth of the image data */
- if (color_type & PNG_COLOR_MASK_COLOR)
- {
- sig_bit.red = true_bit_depth;
- sig_bit.green = true_bit_depth;
- sig_bit.blue = true_bit_depth;
- }
- else
- {
- sig_bit.gray = true_bit_depth;
- }
- if (color_type & PNG_COLOR_MASK_ALPHA)
- {
- sig_bit.alpha = true_bit_depth;
- }
-
- png_set_sBIT(png_ptr, info_ptr, &sig_bit);
-
-If the data is stored in the row buffer in a bit depth other than
-one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
-this will scale the values to appear to be the correct bit depth as
-is required by PNG.
-
- png_set_shift(png_ptr, &sig_bit);
-
-PNG files store 16 bit pixels in network byte order (big-endian,
-ie. most significant bits first). This code would be used if they are
-supplied the other way (little-endian, i.e. least significant bits
-first, the way PCs store them):
-
- if (bit_depth > 8)
- png_set_swap(png_ptr);
-
-If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
-need to change the order the pixels are packed into bytes, you can use:
-
- if (bit_depth < 8)
- png_set_packswap(png_ptr);
-
-PNG files store 3 color pixels in red, green, blue order. This code
-would be used if they are supplied as blue, green, red:
-
- png_set_bgr(png_ptr);
-
-PNG files describe monochrome as black being zero and white being
-one. This code would be used if the pixels are supplied with this reversed
-(black being one and white being zero):
-
- png_set_invert_mono(png_ptr);
-
-Finally, you can write your own transformation function if none of
-the existing ones meets your needs. This is done by setting a callback
-with
-
- png_set_write_user_transform_fn(png_ptr,
- write_transform_fn);
-
-You must supply the function
-
- void write_transform_fn(png_ptr ptr, row_info_ptr
- row_info, png_bytep data)
-
-See pngtest.c for a working example. Your function will be called
-before any of the other transformations have been processed.
-
-It is possible to have libpng flush any pending output, either manually,
-or automatically after a certain number of lines have been written. To
-flush the output stream a single time call:
-
- png_write_flush(png_ptr);
-
-and to have libpng flush the output stream periodically after a certain
-number of scanlines have been written, call:
-
- png_set_flush(png_ptr, nrows);
-
-Note that the distance between rows is from the last time png_write_flush()
-was called, or the first row of the image if it has never been called.
-So if you write 50 lines, and then png_set_flush 25, it will flush the
-output on the next scanline, and every 25 lines thereafter, unless
-png_write_flush() is called before 25 more lines have been written.
-If nrows is too small (less than about 10 lines for a 640 pixel wide
-RGB image) the image compression may decrease noticeably (although this
-may be acceptable for real-time applications). Infrequent flushing will
-only degrade the compression performance by a few percent over images
-that do not use flushing.
-
-That's it for the transformations. Now you can write the image data.
-The simplest way to do this is in one function call. If have the
-whole image in memory, you can just call png_write_image() and libpng
-will write the image. You will need to pass in an array of pointers to
-each row. This function automatically handles interlacing, so you don't
-need to call png_set_interlace_handling() or call this function multiple
-times, or any of that other stuff necessary with png_write_rows().
-
- png_write_image(png_ptr, row_pointers);
-
-where row_pointers is:
-
- png_byte *row_pointers[height];
-
-You can point to void or char or whatever you use for pixels.
-
-If you don't want to write the whole image at once, you can
-use png_write_rows() instead. If the file is not interlaced,
-this is simple:
-
- png_write_rows(png_ptr, row_pointers,
- number_of_rows);
-
-row_pointers is the same as in the png_write_image() call.
-
-If you are just writing one row at a time, you can do this with
-row_pointers:
-
- png_bytep row_pointer = row;
-
- png_write_row(png_ptr, &row_pointer);
-
-When the file is interlaced, things can get a good deal more
-complicated. The only currently (as of February 1998 -- PNG Specification
-version 1.0, dated October 1996) defined interlacing scheme for PNG files
-is the "Adam7" interlace scheme, that breaks down an
-image into seven smaller images of varying size. libpng will build
-these images for you, or you can do them yourself. If you want to
-build them yourself, see the PNG specification for details of which
-pixels to write when.
-
-If you don't want libpng to handle the interlacing details, just
-use png_set_interlace_handling() and call png_write_rows() the
-correct number of times to write all seven sub-images.
-
-If you want libpng to build the sub-images, call this before you start
-writing any rows:
-
- number_of_passes =
- png_set_interlace_handling(png_ptr);
-
-This will return the number of passes needed. Currently, this
-is seven, but may change if another interlace type is added.
-
-Then write the complete image number_of_passes times.
-
- png_write_rows(png_ptr, row_pointers,
- number_of_rows);
-
-As some of these rows are not used, and thus return immediately,
-you may want to read about interlacing in the PNG specification,
-and only update the rows that are actually used.
-
-After you are finished writing the image, you should finish writing
-the file. If you are interested in writing comments or time, you should
-pass an appropriately filled png_info pointer. If you are not interested,
-you can pass NULL.
-
- png_write_end(png_ptr, info_ptr);
-
-When you are done, you can free all memory used by libpng like this:
-
- png_destroy_write_struct(&png_ptr, &info_ptr);
-
-You must free any data you allocated for info_ptr, such as comments,
-palette, or histogram, before the call to png_destroy_write_struct();
-
-For a more compact example of writing a PNG image, see the file example.c.
-
-
-.SH V. Modifying/Customizing libpng:
-
-There are two issues here. The first is changing how libpng does
-standard things like memory allocation, input/output, and error handling.
-The second deals with more complicated things like adding new chunks,
-adding new transformations, and generally changing how libpng works.
-
-All of the memory allocation, input/output, and error handling in libpng
-goes through callbacks that are user settable. The default routines are
-in pngmem.c, pngrio.c, pngwio.c, and pngerror.c respectively. To change
-these functions, call the appropriate png_set_???_fn() function.
-
-Memory allocation is done through the functions png_large_malloc(),
-png_malloc(), png_realloc(), png_large_free(), and png_free(). These
-currently just call the standard C functions. The large functions must
-handle exactly 64K, but they don't have to handle more than that. If
-your pointers can't access more then 64K at a time, you will want to set
-MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
-memory allocation on a platform will change between applications, these
-functions must be modified in the library at compile time.
-
-Input/Output in libpng is done through png_read() and png_write(),
-which currently just call fread() and fwrite(). The FILE * is stored in
-png_struct and is initialized via png_init_io(). If you wish to change
-the method of I/O, the library supplies callbacks that you can set
-through the function png_set_read_fn() and png_set_write_fn() at run
-time, instead of calling the png_init_io() function. These functions
-also provide a void pointer that can be retrieved via the function
-png_get_io_ptr(). For example:
-
- png_set_read_fn(png_structp read_ptr,
- voidp read_io_ptr, png_rw_ptr read_data_fn)
-
- png_set_write_fn(png_structp write_ptr,
- voidp write_io_ptr, png_rw_ptr write_data_fn,
- png_flush_ptr output_flush_fn);
-
- voidp read_io_ptr = png_get_io_ptr(read_ptr);
- voidp write_io_ptr = png_get_io_ptr(write_ptr);
-
-The replacement I/O functions should have prototypes as follows:
-
- void user_read_data(png_structp png_ptr,
- png_bytep data, png_uint_32 length);
- void user_write_data(png_structp png_ptr,
- png_bytep data, png_uint_32 length);
- void user_flush_data(png_structp png_ptr);
-
-Supplying NULL for the read, write, or flush functions sets them back
-to using the default C stream functions. It is an error to read from
-a write stream, and vice versa.
-
-Error handling in libpng is done through png_error() and png_warning().
-Errors handled through png_error() are fatal, meaning that png_error()
-should never return to its caller. Currently, this is handled via
-setjmp() and longjmp(), but you could change this to do things like
-exit() if you should wish. On non-fatal errors, png_warning() is called
-to print a warning message, and then control returns to the calling code.
-By default png_error() and png_warning() print a message on stderr via
-fprintf() unless the library is compiled with PNG_NO_STDIO defined. If
-you wish to change the behavior of the error functions, you will need to
-set up your own message callbacks. These functions are normally supplied
-at the time that the png_struct is created. It is also possible to change
-these functions after png_create_???_struct() has been called by calling:
-
- png_set_error_fn(png_structp png_ptr,
- png_voidp error_ptr, png_error_ptr error_fn,
- png_error_ptr warning_fn);
-
- png_voidp error_ptr = png_get_error_ptr(png_ptr);
-
-If NULL is supplied for either error_fn or warning_fn, then the libpng
-default function will be used, calling fprintf() and/or longjmp() if a
-problem is encountered. The replacement error functions should have
-parameters as follows:
-
- void user_error_fn(png_structp png_ptr,
- png_const_charp error_msg);
- void user_warning_fn(png_structp png_ptr,
- png_const_charp warning_msg);
-
-The motivation behind using setjmp() and longjmp() is the C++ throw and
-catch exception handling methods. This makes the code much easier to write,
-as there is no need to check every return code of every function call.
-However, there are some uncertainties about the status of local variables
-after a longjmp, so the user may want to be careful about doing anything after
-setjmp returns non-zero besides returning itself. Consult your compiler
-documentation for more details.
-
-If you need to read or write custom chunks, you will need to get deeper
-into the libpng code, as a mechanism has not yet been supplied for user
-callbacks with custom chunks. First, read the PNG specification, and have
-a first level of understanding of how it works. Pay particular attention
-to the sections that describe chunk names, and look at how other chunks
-were designed, so you can do things similarly. Second, check out the
-sections of libpng that read and write chunks. Try to find a chunk that
-is similar to yours and copy off of it. More details can be found in the
-comments inside the code. A way of handling unknown chunks in a generic
-method, potentially via callback functions, would be best.
-
-If you wish to write your own transformation for the data, look through
-the part of the code that does the transformations, and check out some of
-the simpler ones to get an idea of how they work. Try to find a similar
-transformation to the one you want to add and copy off of it. More details
-can be found in the comments inside the code itself.
-
-Configuring for 16 bit platforms:
-
-You may need to change the png_large_malloc() and png_large_free()
-routines in pngmem.c, as these are required to allocate 64K, although
-there is already support for many of the common DOS compilers. Also,
-you will want to look into zconf.h to tell zlib (and thus libpng) that
-it cannot allocate more then 64K at a time. Even if you can, the memory
-won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
-
-Configuring for DOS:
-
-For DOS users who only have access to the lower 640K, you will
-have to limit zlib's memory usage via a png_set_compression_mem_level()
-call. See zlib.h or zconf.h in the zlib library for more information.
-
-Configuring for Medium Model:
-
-Libpng's support for medium model has been tested on most of the popular
-compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
-defined, and FAR gets defined to far in pngconf.h, and you should be
-all set. Everything in the library (except for zlib's structure) is
-expecting far data. You must use the typedefs with the p or pp on
-the end for pointers (or at least look at them and be careful). Make
-note that the row's of data are defined as png_bytepp, which is an
-unsigned char far * far *.
-
-Configuring for gui/windowing platforms:
-
-You will need to write new error and warning functions that use the GUI
-interface, as described previously, and set them to be the error and
-warning functions at the time that png_create_???_struct() is called,
-in order to have them available during the structure initialization.
-They can be changed later via png_set_error_fn(). On some compilers,
-you may also have to change the memory allocators (png_malloc, etc.).
-
-Configuring for compiler xxx:
-
-All includes for libpng are in pngconf.h. If you need to add/change/delete
-an include, this is the place to do it. The includes that are not
-needed outside libpng are protected by the PNG_INTERNAL definition,
-which is only defined for those routines inside libpng itself. The
-files in libpng proper only include png.h, which includes pngconf.h.
-
-Configuring zlib:
-
-There are special functions to configure the compression. Perhaps the
-most useful one changes the compression level, which currently uses
-input compression values in the range 0 - 9. The library normally
-uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
-have shown that for a large majority of images, compression values in
-the range 3-6 compress nearly as well as higher levels, and do so much
-faster. For online applications it may be desirable to have maximum speed
-(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
-specify no compression (Z_NO_COMPRESSION = 0), but this would create
-files larger than just storing the raw bitmap. You can specify the
-compression level by calling:
-
- png_set_compression_level(png_ptr, level);
-
-Another useful one is to reduce the memory level used by the library.
-The memory level defaults to 8, but it can be lowered if you are
-short on memory (running DOS, for example, where you only have 640K).
-
- png_set_compression_mem_level(png_ptr, level);
-
-The other functions are for configuring zlib. They are not recommended
-for normal use and may result in writing an invalid PNG file. See
-zlib.h for more information on what these mean.
-
- png_set_compression_strategy(png_ptr,
- strategy);
- png_set_compression_window_bits(png_ptr,
- window_bits);
- png_set_compression_method(png_ptr, method);
-
-Controlling row filtering:
-
-If you want to control whether libpng uses filtering or not, which
-filters are used, and how it goes about picking row filters, you
-can call one of these functions. The selection and configuration
-of row filters can have a significant impact on the size and
-encoding speed and a somewhat lesser impact on the decoding speed
-of an image. Filtering is enabled by default for RGB and grayscale
-images (with and without alpha), but not for paletted images nor
-for any images with bit depths less than 8 bits/pixel.
-
-The 'method' parameter sets the main filtering method, which is
-currently only '0' in the PNG 1.0 specification. The 'filters'
-parameter sets which filter(s), if any, should be used for each
-scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
-to turn filtering on and off, respectively.
-
-Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
-PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
-ORed together '|' to specify one or more filters to use. These
-filters are described in more detail in the PNG specification. If
-you intend to change the filter type during the course of writing
-the image, you should start with flags set for all of the filters
-you intend to use so that libpng can initialize its internal
-structures appropriately for all of the filter types.
-
- filters = PNG_FILTER_NONE | PNG_FILTER_SUB
- | PNG_FILTER_UP;
- png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
- filters);
-
-It is also possible to influence how libpng chooses from among the
-available filters. This is done in two ways - by telling it how
-important it is to keep the same filter for successive rows, and
-by telling it the relative computational costs of the filters.
-
- double weights[3] = {1.5, 1.3, 1.1},
- costs[PNG_FILTER_VALUE_LAST] =
- {1.0, 1.3, 1.3, 1.5, 1.7};
-
- png_set_filter_selection(png_ptr,
- PNG_FILTER_SELECTION_WEIGHTED, 3,
- weights, costs);
-
-The weights are multiplying factors that indicate to libpng that the
-row filter should be the same for successive rows unless another row filter
-is that many times better than the previous filter. In the above example,
-if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
-"sum of absolute differences" 1.5 x 1.3 times higher than other filters
-and still be chosen, while the NONE filter could have a sum 1.1 times
-higher than other filters and still be chosen. Unspecified weights are
-taken to be 1.0, and the specified weights should probably be declining
-like those above in order to emphasize recent filters over older filters.
-
-The filter costs specify for each filter type a relative decoding cost
-to be considered when selecting row filters. This means that filters
-with higher costs are less likely to be chosen over filters with lower
-costs, unless their "sum of absolute differences" is that much smaller.
-The costs do not necessarily reflect the exact computational speeds of
-the various filters, since this would unduly influence the final image
-size.
-
-Note that the numbers above were invented purely for this example and
-are given only to help explain the function usage. Little testing has
-been done to find optimum values for either the costs or the weights.
-
-Removing unwanted object code:
-
-There are a bunch of #define's in pngconf.h that control what parts of
-libpng are compiled. All the defines end in _SUPPORTED. If you are
-never going to use a capability, you can change the #define to #undef
-before recompiling libpng and save yourself code and data space, or
-you can turn off individual capabilities with defines that begin with
-PNG_NO_.
-
-You can also turn all of the transforms and ancillary chunk capabilities
-off en masse with compiler directives that define
-PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
-or all four,
-along with directives to turn on any of the capabilities that you do
-want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
-the extra transformations but still leave the library fully capable of reading
-and writing PNG files with all known public chunks [except for sPLT].
-Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
-produces a library that is incapable of reading or writing ancillary chunks.
-If you are not using the progressive reading capability, you can
-turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
-this with the INTERLACING capability, which you'll still have).
-
-All the reading and writing specific code are in separate files, so the
-linker should only grab the files it needs. However, if you want to
-make sure, or if you are building a stand alone library, all the
-reading files start with pngr and all the writing files start with
-pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
-are used for both reading and writing, and always need to be included.
-The progressive reader is in pngpread.c
-
-If you are creating or distributing a dynamically linked library (a .so
-or DLL file), you should not remove or disable any parts of the library,
-as this will cause applications linked with different versions of the
-library to fail if they call functions not available in your library.
-The size of the library itself should not be an issue, because only
-those sections that are actually used will be loaded into memory.
-
-Requesting debug printout:
-
-The macro definition PNG_DEBUG can be used to request debugging
-printout. Set it to an integer value in the range 0 to 3. Higher
-numbers result in increasing amounts of debugging information. The
-information is printed to the "stderr" file, unless another file
-name is specified in the PNG_DEBUG_FILE macro definition.
-
-When PNG_DEBUG > 0, the following functions (macros) become available:
-
- png_debug(level, message)
- png_debug1(level, message, p1)
- png_debug2(level, message, p1, p2)
-
-in which "level" is compared to PNG_DEBUG to decide whether to print
-the message, "message" is the formatted string to be printed,
-and p1 and p2 are parameters that are to be embedded in the string
-according to printf-style formatting directives. For example,
-
- png_debug1(2, "foo=%d\n", foo);
-
-is expanded to
-
- if(PNG_DEBUG > 2)
- fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
-
-When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
-can still use PNG_DEBUG to control your own debugging:
-
- #ifdef PNG_DEBUG
- fprintf(stderr, ...
- #endif
-
-When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
-having level = 0 will be printed. There aren't any such statements in
-this version of libpng, but if you insert some they will be printed.
-
-.SH VI. Changes to Libpng from version 0.88
-
-It should be noted that versions of libpng later than 0.96 are not
-distributed by the original libpng author, Guy Schalnat, nor by
-Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
-distributed versions 0.89 through 0.96, but rather by another member
-of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
-still alive and well, but they have moved on to other things.
-
-The old libpng functions png_read_init(), png_write_init(),
-png_info_init(), png_read_destroy(), and png_write_destory() have been
-moved to PNG_INTERNAL in version 0.95 to discourage their use. The
-preferred method of creating and initializing the libpng structures is
-via the png_create_read_struct(), png_create_write_struct(), and
-png_create_info_struct() because they isolate the size of the structures
-from the application, allow version error checking, and also allow the
-use of custom error handling routines during the initialization, which
-the old functions do not. The functions png_read_destroy() and
-png_write_destroy() do not actually free the memory that libpng
-allocated for these structs, but just reset the data structures, so they
-can be used instead of png_destroy_read_struct() and
-png_destroy_write_struct() if you feel there is too much system overhead
-allocating and freeing the png_struct for each image read.
-
-Setting the error callbacks via png_set_message_fn() before
-png_read_init() as was suggested in libpng-0.88 is no longer supported
-because this caused applications that do not use custom error functions
-to fail if the png_ptr was not initialized to zero. It is still possible
-to set the error callbacks AFTER png_read_init(), or to change them with
-png_set_error_fn(), which is essentially the same function, but with a
-new name to force compilation errors with applications that try to use
-the old method.
-
-.SH VII. Y2K Compliance in libpng
-
-January 13, 1999
-
-Since the PNG Development group is an ad-hoc body, we can't make
-an official declaration.
-
-This is your unofficial assurance that libpng from version 0.81 and
-upward are Y2K compliant. It is my belief that earlier versions were
-also Y2K compliant.
-
-Libpng only has three year fields. One is a 2-byte unsigned integer that
-will hold years up to 65535. The other two hold the date in text
-format, and will hold years up to 9999.
-
-The integer is
- "png_uint_16 year" in png_time_struct.
-
-The strings are
- "png_charp time_buffer" in png_struct and
- "near_time_buffer", which is a local character string in png.c.
-
-There are seven time-related functions:
-
- png_convert_to_rfc_1123() in png.c
- (formerly png_convert_to_rfc_1152() in error)
- png_convert_from_struct_tm() in pngwrite.c, called in pngwrite.c
- png_convert_from_time_t() in pngwrite.c
- png_get_tIME() in pngget.c
- png_handle_tIME() in pngrutil.c, called in pngread.c
- png_set_tIME() in pngset.c
- png_write_tIME() in pngwutil.c, called in pngwrite.c
-
-All appear to handle dates properly in a Y2K environment. The
-png_convert_from_time_t() function calls gmtime() to convert from system
-clock time, which returns (year - 1900), which we properly convert to
-the full 4-digit year. There is a possibility that applications using
-libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
-function, or incorrectly passing only a 2-digit year instead of
-"year - 1900" into the png_convert_from_struct_tm() function, but this
-is not under our control. The libpng documentation has always stated
-that it works with 4-digit years, and the APIs have been documented as
-such.
-
-The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
-integer to hold the year, and can hold years as large as 65535.
-
-
- Glenn Randers-Pehrson
- libpng maintainer
- PNG Development Group
-
-.SH NOTE
-
-Note about libpng version numbers:
-
-Due to various miscommunications, unforeseen code incompatibilities
-and occasional factors outside the authors' control, version numbering
-on the library has not always been consistent and straightforward.
-The following table summarizes matters since version 0.89c, which was
-the first widely used release:
-
- source png.h png.h shared-lib
- version string int version
- ------- ------ ------ ----------
- 0.89c 0.89 89 1.0.89
- 0.90 0.90 90 0.90 [should be 2.0.90]
- 0.95 0.95 95 0.95 [should be 2.0.95]
- 0.96 0.96 96 0.96 [should be 2.0.96]
- 0.97b 1.00.97 97 1.0.1 [should be 2.0.97]
- 0.97c 0.97 97 2.0.97
- 0.98 0.98 98 2.0.98
- 0.99 0.99 98 2.0.99
- 0.99a-m 0.99 99 2.0.99
- 1.00 1.00 100 2.1.0 [int should be 10000]
- 1.0.0 1.0.0 100 2.1.0 [int should be 10000]
- 1.0.1 1.0.1 10001 2.1.0
-
-Henceforth the source version will match the shared-library
-minor and patch numbers; the shared-library major version number will be
-used for changes in backward compatibility, as it is intended.
-The PNG_PNGLIB_VER macro, which is not used within libpng but
-is available for applications, is an unsigned integer of the form
-xyyzz corresponding to the source version x.y.z (leading zeros in y and z).
-
-.SH "SEE ALSO"
-libpngpf(3), png(5)
-.LP
-.IR libpng :
-.IP
-ftp://ftp.uu.net/graphics/png
-http://www.cdrom.com/pub/png
-
-.LP
-.IR zlib :
-.IP
-(generally) at the same location as
-.I libpng
-or at
-.br
-ftp://ftp.uu.net/pub/archiving/zip/zlib
-.br
-http://www.cdrom.com/pub/infozip/zlib
-
-.LP
-.IR PNG specification: RFC 2083
-.IP
-(generally) at the same location as
-.I libpng
-or at
-.br
-ftp://ds.internic.net/rfc/rfc2083.txt
-.br
-or (as a W3C Recommendation) at
-.br
-http://www.w3.org/TR/REC-png.html
-
-.LP
-In the case of any inconsistency between the PNG specification
-and this library, the specification takes precedence.
-
-.SH AUTHORS
-This man page: Glenn Randers-Pehrson
-<randeg@alumni.rpi.edu>
-
-Contributing Authors: John Bowler, Kevin Bracey, Sam Bushell, Andreas Dilger,
-Magnus Holmgren, Tom Lane, Dave Martindale, Glenn Randers-Pehrson,
-Greg Roelofs, Guy Eric Schalnat, Paul Schmidt, Tom Tanner, Willem van
-Schaik, Tim Wegner.
-<png-implement@dworkin.wustl.edu>
-
-The contributing authors would like to thank all those who helped
-with testing, bug fixes, and patience. This wouldn't have been
-possible without all of you.
-
-Thanks to Frank J. T. Wojcik for helping with the documentation.
-
-Libpng version 1.0.3 - January 14, 1999:
-Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
-Currently maintained by Glenn Randers-Pehrson (randeg@alumni.rpi.edu).
-
-Supported by the PNG development group
-.br
-(png-implement@dworkin.wustl.edu).
-
-.SH COPYRIGHT NOTICE:
-
-Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-Copyright (c) 1996, 1997 Andreas Dilger
-Copyright (c) 1998, 1999 Glenn Randers-Pehrson
-
-The PNG Reference Library (libpng) is supplied "AS IS". The Contributing
-Authors and Group 42, Inc. disclaim all warranties, expressed or implied,
-including, without limitation, the warranties of merchantability and of
-fitness for any purpose. The Contributing Authors and Group 42, Inc.
-assume no liability for direct, indirect, incidental, special, exemplary,
-or consequential damages, which may result from the use of the PNG
-Reference Library, even if advised of the possibility of such damage.
-
-Permission is hereby granted to use, copy, modify, and distribute this
-source code, or portions hereof, for any purpose, without fee, subject
-to the following restrictions:
-
- 1. The origin of this source code must not be
- misrepresented.
-
- 2. Altered versions must be plainly marked as such
- and must not be misrepresented as being the
- original source.
-
- 3. This Copyright notice may not be removed or
- altered from any source or altered source
- distribution.
-
-The Contributing Authors and Group 42, Inc. specifically permit, without
-fee, and encourage the use of this source code as a component to
-supporting the PNG file format in commercial products. If you use this
-source code in a product, acknowledgment is not required but would be
-appreciated.
-
-.\" end of man page
-
projects / wxWidgets.git / commitdiff
