1 README for libpng version 1.6.37 - April 14, 2019
   2 =================================================
   4 See the note about version numbers near the top of png.h.
   5 See INSTALL for instructions on how to install libpng.
   7 Libpng comes in several distribution formats.  Get libpng-*.tar.gz or
   8 libpng-*.tar.xz or if you want UNIX-style line endings in the text
   9 files, or lpng*.7z or lpng*.zip if you want DOS-style line endings.
  11 Version 0.89 was the first official release of libpng.  Don't let the
  12 fact that it's the first release fool you.  The libpng library has been
  13 in extensive use and testing since mid-1995.  By late 1997 it had
  14 finally gotten to the stage where there hadn't been significant
  15 changes to the API in some time, and people have a bad feeling about
  16 libraries with versions < 1.0.  Version 1.0.0 was released in
  17 March 1998.
  19 ****
  20 Note that some of the changes to the png_info structure render this
  21 version of the library binary incompatible with libpng-0.89 or
  22 earlier versions if you are using a shared library.  The type of the
  23 "filler" parameter for png_set_filler() has changed from png_byte to
  24 png_uint_32, which will affect shared-library applications that use
  25 this function.
  27 To avoid problems with changes to the internals of the png info_struct,
  28 new APIs have been made available in 0.95 to avoid direct application
  29 access to info_ptr.  These functions are the png_set_<chunk> and
  30 png_get_<chunk> functions.  These functions should be used when
  31 accessing/storing the info_struct data, rather than manipulating it
  32 directly, to avoid such problems in the future.
  34 It is important to note that the APIs did not make current programs
  35 that access the info struct directly incompatible with the new
  36 library, through libpng-1.2.x.  In libpng-1.4.x, which was meant to
  37 be a transitional release, members of the png_struct and the
  38 info_struct can still be accessed, but the compiler will issue a
  39 warning about deprecated usage.  Since libpng-1.5.0, direct access
  40 to these structs is not allowed, and the definitions of the structs
  41 reside in private pngstruct.h and pnginfo.h header files that are not
  42 accessible to applications.  It is strongly suggested that new
  43 programs use the new APIs (as shown in example.c and pngtest.c), and
  44 older programs be converted to the new format, to facilitate upgrades
  45 in the future.
  46 ****
  48 Additions since 0.90 include the ability to compile libpng as a
  49 Windows DLL, and new APIs for accessing data in the info struct.
  50 Experimental functions include the ability to set weighting and cost
  51 factors for row filter selection, direct reads of integers from buffers
  52 on big-endian processors that support misaligned data access, faster
  53 methods of doing alpha composition, and more accurate 16->8 bit color
  54 conversion.
  56 The additions since 0.89 include the ability to read from a PNG stream
  57 which has had some (or all) of the signature bytes read by the calling
  58 application.  This also allows the reading of embedded PNG streams that
  59 do not have the PNG file signature.  As well, it is now possible to set
  60 the library action on the detection of chunk CRC errors.  It is possible
  61 to set different actions based on whether the CRC error occurred in a
  62 critical or an ancillary chunk.
  64 For a detailed description on using libpng, read libpng-manual.txt.
  65 For examples of libpng in a program, see example.c and pngtest.c.  For
  66 usage information and restrictions (what little they are) on libpng,
  67 see png.h.  For a description on using zlib (the compression library
  68 used by libpng) and zlib's restrictions, see zlib.h
  70 I have included a general makefile, as well as several machine and
  71 compiler specific ones, but you may have to modify one for your own
  72 needs.
  74 You should use zlib 1.0.4 or later to run this, but it MAY work with
  75 versions as old as zlib 0.95.  Even so, there are bugs in older zlib
  76 versions which can cause the output of invalid compression streams for
  77 some images.
  79 You should also note that zlib is a compression library that is useful
  80 for more things than just PNG files.  You can use zlib as a drop-in
  81 replacement for fread() and fwrite(), if you are so inclined.
  83 zlib should be available at the same place that libpng is, or at
  84 https://zlib.net.
  86 You may also want a copy of the PNG specification.  It is available
  87 as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
  88 these at http://www.libpng.org/pub/png/pngdocs.html .
  90 This code is currently being archived at libpng.sourceforge.io in the
  91 [DOWNLOAD] area, and at http://libpng.download/src .
  93 This release, based in a large way on Glenn's, Guy's and Andreas'
  94 earlier work, was created and will be supported by myself and the PNG
  95 development group.
  97 Send comments/corrections/commendations to png-mng-implement at
  98 lists.sourceforge.net (subscription required; visit
  99 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 100 to subscribe).
 102 Send general questions about the PNG specification to png-mng-misc
 103 at lists.sourceforge.net (subscription required; visit
 104 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
 105 subscribe).
 107 Files in this distribution:
 109       ANNOUNCE      =>  Announcement of this version, with recent changes
 110       AUTHORS       =>  List of contributing authors
 111       CHANGES       =>  Description of changes between libpng versions
 112       KNOWNBUG      =>  List of known bugs and deficiencies
 113       LICENSE       =>  License to use and redistribute libpng
 114       README        =>  This file
 115       TODO          =>  Things not implemented in the current library
 116       TRADEMARK     =>  Trademark information
 117       example.c     =>  Example code for using libpng functions
 118       libpng.3      =>  manual page for libpng (includes libpng-manual.txt)
 119       libpng-manual.txt  =>  Description of libpng and its functions
 120       libpngpf.3    =>  manual page for libpng's private functions
 121       png.5         =>  manual page for the PNG format
 122       png.c         =>  Basic interface functions common to library
 123       png.h         =>  Library function and interface declarations (public)
 124       pngpriv.h     =>  Library function and interface declarations (private)
 125       pngconf.h     =>  System specific library configuration (public)
 126       pngstruct.h   =>  png_struct declaration (private)
 127       pnginfo.h     =>  png_info struct declaration (private)
 128       pngdebug.h    =>  debugging macros (private)
 129       pngerror.c    =>  Error/warning message I/O functions
 130       pngget.c      =>  Functions for retrieving info from struct
 131       pngmem.c      =>  Memory handling functions
 132       pngbar.png    =>  PNG logo, 88x31
 133       pngnow.png    =>  PNG logo, 98x31
 134       pngpread.c    =>  Progressive reading functions
 135       pngread.c     =>  Read data/helper high-level functions
 136       pngrio.c      =>  Lowest-level data read I/O functions
 137       pngrtran.c    =>  Read data transformation functions
 138       pngrutil.c    =>  Read data utility functions
 139       pngset.c      =>  Functions for storing data into the info_struct
 140       pngtest.c     =>  Library test program
 141       pngtest.png   =>  Library test sample image
 142       pngtrans.c    =>  Common data transformation functions
 143       pngwio.c      =>  Lowest-level write I/O functions
 144       pngwrite.c    =>  High-level write functions
 145       pngwtran.c    =>  Write data transformations
 146       pngwutil.c    =>  Write utility functions
 147       arm           =>  Contains optimized code for the ARM platform
 148       powerpc       =>  Contains optimized code for the PowerPC platform
 149       contrib       =>  Contributions
 150        arm-neon         =>  Optimized code for ARM-NEON platform
 151        powerpc-vsx      =>  Optimized code for POWERPC-VSX platform
 152        examples         =>  Example programs
 153        gregbook         =>  source code for PNG reading and writing, from
 154                             Greg Roelofs' "PNG: The Definitive Guide",
 155                             O'Reilly, 1999
 156        libtests         =>  Test programs
 157        mips-msa         =>  Optimized code for MIPS-MSA platform
 158        pngminim         =>  Minimal decoder, encoder, and progressive decoder
 159                             programs demonstrating use of pngusr.dfa
 160        pngminus         =>  Simple pnm2png and png2pnm programs
 161        pngsuite         =>  Test images
 162        testpngs
 163        tools            =>  Various tools
 164        visupng          =>  Contains a MSVC workspace for VisualPng
 165       intel             =>  Optimized code for INTEL-SSE2 platform
 166       mips              =>  Optimized code for MIPS platform
 167       projects      =>  Contains project files and workspaces for
 168                         building a DLL
 169        owatcom          =>  Contains a WATCOM project for building libpng
 170        visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
 171                             workspace for building libpng and zlib
 172        vstudio          =>  Contains a Microsoft Visual C++ (MSVC)
 173                             workspace for building libpng and zlib
 174       scripts       =>  Directory containing scripts for building libpng:
 175                             (see scripts/README.txt for the list of scripts)
 177 Good luck, and happy coding!
 179  * Cosmin Truta (current maintainer, since 2018)
 180  * Glenn Randers-Pehrson (former maintainer, 1998-2018)
 181  * Andreas Eric Dilger (former maintainer, 1996-1997)
 182  * Guy Eric Schalnat (original author and former maintainer, 1995-1996)
 183    (formerly of Group 42, Inc.)