1README for libpng version 1.6.44 2================================ 3 4See the note about version numbers near the top of `png.h`. 5See `INSTALL` for instructions on how to install libpng. 6 7Libpng comes in several distribution formats. Get `libpng-*.tar.gz` 8or `libpng-*.tar.xz` if you want UNIX-style line endings in the text 9files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings. 10 11For a detailed description on using libpng, read `libpng-manual.txt`. 12For examples of libpng in a program, see `example.c` and `pngtest.c`. 13For usage information and restrictions (what little they are) on libpng, 14see `png.h`. For a description on using zlib (the compression library 15used by libpng) and zlib's restrictions, see `zlib.h`. 16 17You should use zlib 1.0.4 or later to run this, but it _may_ work with 18versions as old as zlib 0.95. Even so, there are bugs in older zlib 19versions which can cause the output of invalid compression streams for 20some images. 21 22You should also note that zlib is a compression library that is useful 23for more things than just PNG files. You can use zlib as a drop-in 24replacement for `fread()` and `fwrite()`, if you are so inclined. 25 26zlib should be available at the same place that libpng is, or at 27https://zlib.net . 28 29You may also want a copy of the PNG specification. It is available 30as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find 31these at http://www.libpng.org/pub/png/pngdocs.html . 32 33This code is currently being archived at https://libpng.sourceforge.io 34in the download area, and at http://libpng.download/src . 35 36This release, based in a large way on Glenn's, Guy's and Andreas' 37earlier work, was created and will be supported by myself and the PNG 38development group. 39 40Send comments, corrections and commendations to `png-mng-implement` 41at `lists.sourceforge.net`. (Subscription is required; visit 42https://lists.sourceforge.net/lists/listinfo/png-mng-implement 43to subscribe.) 44 45Send general questions about the PNG specification to `png-mng-misc` 46at `lists.sourceforge.net`. (Subscription is required; visit 47https://lists.sourceforge.net/lists/listinfo/png-mng-misc 48to subscribe.) 49 50Historical notes 51---------------- 52 53The libpng library has been in extensive use and testing since mid-1995. 54Version 0.89, published a year later, was the first official release. 55By late 1997, it had finally gotten to the stage where there hadn't 56been significant changes to the API in some time, and people have a bad 57feeling about libraries with versions below 1.0. Version 1.0.0 was 58released in March 1998. 59 60Note that some of the changes to the `png_info` structure render this 61version of the library binary incompatible with libpng-0.89 or 62earlier versions if you are using a shared library. The type of the 63`filler` parameter for `png_set_filler()` has changed from `png_byte` 64to `png_uint_32`, which will affect shared-library applications that 65use this function. 66 67To avoid problems with changes to the internals of the `info_struct`, 68new APIs have been made available in 0.95 to avoid direct application 69access to `info_ptr`. These functions are the `png_set_<chunk>` and 70`png_get_<chunk>` functions. These functions should be used when 71accessing/storing the `info_struct` data, rather than manipulating it 72directly, to avoid such problems in the future. 73 74It is important to note that the APIs did not make current programs 75that access the info struct directly incompatible with the new 76library, through libpng-1.2.x. In libpng-1.4.x, which was meant to 77be a transitional release, members of the `png_struct` and the 78`info_struct` can still be accessed, but the compiler will issue a 79warning about deprecated usage. Since libpng-1.5.0, direct access 80to these structs is not allowed, and the definitions of the structs 81reside in private `pngstruct.h` and `pnginfo.h` header files that are 82not accessible to applications. It is strongly suggested that new 83programs use the new APIs (as shown in `example.c` and `pngtest.c`), 84and older programs be converted to the new format, to facilitate 85upgrades in the future. 86 87The additions since 0.89 include the ability to read from a PNG stream 88which has had some (or all) of the signature bytes read by the calling 89application. This also allows the reading of embedded PNG streams that 90do not have the PNG file signature. As well, it is now possible to set 91the library action on the detection of chunk CRC errors. It is possible 92to set different actions based on whether the CRC error occurred in a 93critical or an ancillary chunk. 94 95The additions since 0.90 include the ability to compile libpng as a 96Windows DLL, and new APIs for accessing data in the `info_struct`. 97Experimental functions included the ability to set weighting and cost 98factors for row filter selection, direct reads of integers from buffers 99on big-endian processors that support misaligned data access, faster 100methods of doing alpha composition, and more accurate 16-to-8 bit color 101conversion. Some of these experimental functions, such as the weighted 102filter heuristics, have since been removed. 103 104Files included in this distribution 105----------------------------------- 106 107 ANNOUNCE => Announcement of this version, with recent changes 108 AUTHORS => List of contributing authors 109 CHANGES => Description of changes between libpng versions 110 INSTALL => Instructions to install libpng 111 LICENSE => License to use and redistribute libpng 112 README => This file 113 TODO => Things not implemented in the current library 114 TRADEMARK => Trademark information 115 example.c => Example code for using libpng functions 116 libpng.3 => Manual page for libpng (includes libpng-manual.txt) 117 libpng-manual.txt => Description of libpng and its functions 118 libpngpf.3 => Manual page for libpng's private functions (deprecated) 119 png.5 => Manual page for the PNG format 120 png.c => Basic interface functions common to library 121 png.h => Library function and interface declarations (public) 122 pngpriv.h => Library function and interface declarations (private) 123 pngconf.h => System specific library configuration (public) 124 pngstruct.h => png_struct declaration (private) 125 pnginfo.h => png_info struct declaration (private) 126 pngdebug.h => debugging macros (private) 127 pngerror.c => Error/warning message I/O functions 128 pngget.c => Functions for retrieving info from struct 129 pngmem.c => Memory handling functions 130 pngbar.png => PNG logo, 88x31 131 pngnow.png => PNG logo, 98x31 132 pngpread.c => Progressive reading functions 133 pngread.c => Read data/helper high-level functions 134 pngrio.c => Lowest-level data read I/O functions 135 pngrtran.c => Read data transformation functions 136 pngrutil.c => Read data utility functions 137 pngset.c => Functions for storing data into the info_struct 138 pngtest.c => Library test program 139 pngtest.png => Library test sample image 140 pngtrans.c => Common data transformation functions 141 pngwio.c => Lowest-level write I/O functions 142 pngwrite.c => High-level write functions 143 pngwtran.c => Write data transformations 144 pngwutil.c => Write utility functions 145 arm/ => Optimized code for ARM Neon 146 intel/ => Optimized code for INTEL SSE2 147 loongarch/ => Optimized code for LoongArch LSX 148 mips/ => Optimized code for MIPS MSA and MIPS MMI 149 powerpc/ => Optimized code for PowerPC VSX 150 ci/ => Scripts for continuous integration 151 contrib/ => External contributions 152 arm-neon/ => Optimized code for the ARM-NEON platform 153 mips-msa/ => Optimized code for the MIPS-MSA platform 154 powerpc-vsx/ => Optimized code for the POWERPC-VSX platform 155 examples/ => Examples of libpng usage 156 gregbook/ => Source code for PNG reading and writing, from 157 "PNG: The Definitive Guide" by Greg Roelofs, 158 O'Reilly, 1999 159 libtests/ => Test programs 160 oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing 161 libpng 162 pngexif/ => Program to inspect the EXIF information in PNG files 163 pngminim/ => Minimal decoder, encoder, and progressive decoder 164 programs demonstrating the use of pngusr.dfa 165 pngminus/ => Simple pnm2png and png2pnm programs 166 pngsuite/ => Test images 167 testpngs/ => Test images 168 tools/ => Various tools 169 visupng/ => VisualPng, a Windows viewer for PNG images 170 projects/ => Project files and workspaces for various IDEs 171 owatcom/ => OpenWatcom project 172 visualc71/ => Microsoft Visual C++ 7.1 workspace 173 vstudio/ => Microsoft Visual Studio workspace 174 scripts/ => Scripts and makefiles for building libpng 175 (see scripts/README.txt for the complete list) 176 tests/ => Test scripts 177 178Good luck, and happy coding! 179 180 * Cosmin Truta (current maintainer, since 2018) 181 * Glenn Randers-Pehrson (former maintainer, 1998-2018) 182 * Andreas Eric Dilger (former maintainer, 1996-1997) 183 * Guy Eric Schalnat (original author and former maintainer, 1995-1996) 184 (formerly of Group 42, Inc.) 185
