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Tree [d5515b] master libpng16 v1.6.56 / History
Filip Wasil 
Chris Blume 
Glenn Randers-Pehrson 
Cristian Rodríguez 
THE-Spellchecker 
ylwango613 Read Me
README for libpng version 1.6.56 ================================ See the note about version numbers near the top of `png.h`. See `INSTALL` for instructions on how to install libpng. Libpng comes in several distribution formats. Get `libpng-*.tar.gz` or `libpng-*.tar.xz` if you want UNIX-style line endings in the text files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings. For a detailed description on using libpng, read `libpng-manual.txt`. For examples of libpng in a program, see `example.c` and `pngtest.c`. For usage information and restrictions (what little they are) on libpng, see `png.h`. For a description on using zlib (the compression library used by libpng) and zlib's restrictions, see `zlib.h`. You should use zlib 1.0.4 or later to run this, but it _may_ work with versions as old as zlib 0.95. Even so, there are bugs in older zlib versions which can cause the output of invalid compression streams for some images. You should also note that zlib is a compression library that is useful for more things than just PNG files. You can use zlib as a drop-in replacement for `fread()` and `fwrite()`, if you are so inclined. zlib should be available at the same place that libpng is, or at <https://zlib.net>. You may also want a copy of the PNG specification. It is available as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find these at <http://www.libpng.org/pub/png/pngdocs.html>. This code is currently being archived at <https://libpng.sourceforge.io> in the download area, and at <http://libpng.download/src>. This release, based in a large way on Glenn's, Guy's and Andreas' earlier work, was created and will be supported by myself and the PNG development group. Send comments, corrections and commendations to `png-mng-implement` at `lists.sourceforge.net`. (Subscription is required; visit <https://lists.sourceforge.net/lists/listinfo/png-mng-implement> to subscribe.) Send general questions about the PNG specification to `png-mng-misc` at `lists.sourceforge.net`. (Subscription is required; visit <https://lists.sourceforge.net/lists/listinfo/png-mng-misc> to subscribe.) Historical notes ---------------- The libpng library has been in extensive use and testing since mid-1995. Version 0.89, published a year later, was the first official release. By late 1997, it had finally gotten to the stage where there hadn't been significant changes to the API in some time, and people have a bad feeling about libraries with versions below 1.0. Version 1.0.0 was released in March 1998. Note that some of the changes to the `png_info` structure render this version of the library binary incompatible with libpng-0.89 or earlier versions if you are using a shared library. The type of the `filler` parameter for `png_set_filler()` has changed from `png_byte` to `png_uint_32`, which will affect shared-library applications that use this function. To avoid problems with changes to the internals of the `info_struct`, new APIs have been made available in 0.95 to avoid direct application access to `info_ptr`. These functions are the `png_set_<chunk>` and `png_get_<chunk>` functions. These functions should be used when accessing/storing the `info_struct` data, rather than manipulating it directly, to avoid such problems in the future. It is important to note that the APIs did not make current programs that access the info struct directly incompatible with the new library, through libpng-1.2.x. In libpng-1.4.x, which was meant to be a transitional release, members of the `png_struct` and the `info_struct` can still be accessed, but the compiler will issue a warning about deprecated usage. Since libpng-1.5.0, direct access to these structs is not allowed, and the definitions of the structs reside in private `pngstruct.h` and `pnginfo.h` header files that are not accessible to applications. It is strongly suggested that new programs use the new APIs (as shown in `example.c` and `pngtest.c`), and older programs be converted to the new format, to facilitate upgrades in the future. The additions since 0.89 include the ability to read from a PNG stream which has had some (or all) of the signature bytes read by the calling application. This also allows the reading of embedded PNG streams that do not have the PNG file signature. As well, it is now possible to set the library action on the detection of chunk CRC errors. It is possible to set different actions based on whether the CRC error occurred in a critical or an ancillary chunk. The additions since 0.90 include the ability to compile libpng as a Windows DLL, and new APIs for accessing data in the `info_struct`. Experimental functions included the ability to set weighting and cost factors for row filter selection, direct reads of integers from buffers on big-endian processors that support misaligned data access, faster methods of doing alpha composition, and more accurate 16-to-8 bit color conversion. Some of these experimental functions, such as the weighted filter heuristics, have since been removed. Files included in this distribution ----------------------------------- ANNOUNCE => Announcement of this version, with recent changes AUTHORS => List of contributing authors CHANGES => Description of changes between libpng versions INSTALL => Instructions to install libpng LICENSE => License to use and redistribute libpng README => This file TODO => Things not implemented in the current library TRADEMARK => Trademark information example.c => Example code for using libpng functions libpng.3 => Manual page for libpng (includes libpng-manual.txt) libpng-manual.txt => Description of libpng and its functions libpngpf.3 => Manual page for libpng's private functions (deprecated) png.5 => Manual page for the PNG format png.c => Basic interface functions common to library png.h => Library function and interface declarations (public) pngpriv.h => Library function and interface declarations (private) pngconf.h => System specific library configuration (public) pngstruct.h => png_struct declaration (private) pnginfo.h => png_info struct declaration (private) pngdebug.h => debugging macros (private) pngerror.c => Error/warning message I/O functions pngget.c => Functions for retrieving info from struct pngmem.c => Memory handling functions pngbar.png => PNG logo, 88x31 pngnow.png => PNG logo, 98x31 pngpread.c => Progressive reading functions pngread.c => Read data/helper high-level functions pngrio.c => Lowest-level data read I/O functions pngrtran.c => Read data transformation functions pngrutil.c => Read data utility functions pngset.c => Functions for storing data into the info_struct pngtest.c => Library test program pngtest.png => Library test sample image pngtrans.c => Common data transformation functions pngwio.c => Lowest-level write I/O functions pngwrite.c => High-level write functions pngwtran.c => Write data transformations pngwutil.c => Write utility functions arm/ => Optimized code for ARM Neon intel/ => Optimized code for INTEL SSE2 loongarch/ => Optimized code for LoongArch LSX mips/ => Optimized code for MIPS MSA and MIPS MMI powerpc/ => Optimized code for PowerPC VSX riscv/ => Optimized code for the RISC-V platform ci/ => Scripts for continuous integration contrib/ => External contributions arm-neon/ => Optimized code for the ARM-NEON platform mips-msa/ => Optimized code for the MIPS-MSA platform powerpc-vsx/ => Optimized code for the POWERPC-VSX platform examples/ => Examples of libpng usage gregbook/ => Source code for PNG reading and writing, from "PNG: The Definitive Guide" by Greg Roelofs, O'Reilly, 1999 libtests/ => Test programs pngexif/ => Program to inspect the EXIF information in PNG files pngminim/ => Minimal decoder, encoder, and progressive decoder programs demonstrating the use of pngusr.dfa pngminus/ => Simple pnm2png and png2pnm programs pngsuite/ => Test images riscv-rvv/ => Optimized code for the RISC-V Vector platform testpngs/ => Test images tools/ => Various tools visupng/ => VisualPng, a Windows viewer for PNG images projects/ => Project files and workspaces for various IDEs owatcom/ => OpenWatcom project visualc71/ => Microsoft Visual C++ 7.1 workspace vstudio/ => Microsoft Visual Studio workspace scripts/ => Scripts and makefiles for building libpng (see scripts/README.txt for the complete list) tests/ => Test scripts Good luck, and happy coding! * Cosmin Truta (current maintainer, since 2018) * Glenn Randers-Pehrson (former maintainer, 1998-2018) * Andreas Eric Dilger (former maintainer, 1996-1997) * Guy Eric Schalnat (original author and former maintainer, 1995-1996) (formerly of Group 42, Inc.)
