README
    README for libpng version 1.6.37 - April 14, 2019
    =================================================
    
    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 or if you want UNIX-style line endings in the text
    files, or lpng*.7z or lpng*.zip if you want DOS-style line endings.
    
    Version 0.89 was the first official release of libpng.  Don't let the
    fact that it's the first release fool you.  The libpng library has been
    in extensive use and testing since mid-1995.  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 < 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 png 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.
    ****
    
    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 include 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->8 bit color
    conversion.
    
    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.
    
    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
    
    I have included a general makefile, as well as several machine and
    compiler specific ones, but you may have to modify one for your own
    needs.
    
    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 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/commendations to png-mng-implement at
    lists.sourceforge.net (subscription 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 required; visit
    https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
    subscribe).
    
    Files in this distribution:
    
          ANNOUNCE      =>  Announcement of this version, with recent changes
          AUTHORS       =>  List of contributing authors
          CHANGES       =>  Description of changes between libpng versions
          KNOWNBUG      =>  List of known bugs and deficiencies
          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
          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           =>  Contains optimized code for the ARM platform
          powerpc       =>  Contains optimized code for the PowerPC platform
          contrib       =>  Contributions
           arm-neon         =>  Optimized code for ARM-NEON platform
           powerpc-vsx      =>  Optimized code for POWERPC-VSX platform
           examples         =>  Example programs
           gregbook         =>  source code for PNG reading and writing, from
                                Greg Roelofs' "PNG: The Definitive Guide",
                                O'Reilly, 1999
           libtests         =>  Test programs
           mips-msa         =>  Optimized code for MIPS-MSA platform
           pngminim         =>  Minimal decoder, encoder, and progressive decoder
                                programs demonstrating use of pngusr.dfa
           pngminus         =>  Simple pnm2png and png2pnm programs
           pngsuite         =>  Test images
           testpngs
           tools            =>  Various tools
           visupng          =>  Contains a MSVC workspace for VisualPng
          intel             =>  Optimized code for INTEL-SSE2 platform
          mips              =>  Optimized code for MIPS platform
          projects      =>  Contains project files and workspaces for
                            building a DLL
           owatcom          =>  Contains a WATCOM project for building libpng
           visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
                                workspace for building libpng and zlib
           vstudio          =>  Contains a Microsoft Visual C++ (MSVC)
                                workspace for building libpng and zlib
          scripts       =>  Directory containing scripts for building libpng:
                                (see scripts/README.txt for the list of 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.)
    

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