1 README for libpng version 1.6.34 - September 29, 2017 (shared library 16.0)
   2 See the note about version numbers near the top of png.h
   4 See INSTALL for instructions on how to install libpng.
   6 Libpng comes in several distribution formats.  Get libpng-*.tar.gz or
   7 libpng-*.tar.xz or if you want UNIX-style line endings in the text files,
   8 or lpng*.7z or lpng*.zip if you want DOS-style line endings.
  10 Version 0.89 was the first official release of libpng.  Don't let the
  11 fact that it's the first release fool you.  The libpng library has been in
  12 extensive use and testing since mid-1995.  By late 1997 it had
  13 finally gotten to the stage where there hadn't been significant
  14 changes to the API in some time, and people have a bad feeling about
  15 libraries with versions < 1.0.  Version 1.0.0 was released in
  16 March 1998.
  18 ****
  19 Note that some of the changes to the png_info structure render this
  20 version of the library binary incompatible with libpng-0.89 or
  21 earlier versions if you are using a shared library.  The type of the
  22 "filler" parameter for png_set_filler() has changed from png_byte to
  23 png_uint_32, which will affect shared-library applications that use
  24 this function.
  26 To avoid problems with changes to the internals of the png info_struct,
  27 new APIs have been made available in 0.95 to avoid direct application
  28 access to info_ptr.  These functions are the png_set_<chunk> and
  29 png_get_<chunk> functions.  These functions should be used when
  30 accessing/storing the info_struct data, rather than manipulating it
  31 directly, to avoid such problems in the future.
  33 It is important to note that the APIs did not make current programs
  34 that access the info struct directly incompatible with the new
  35 library, through libpng-1.2.x.  In libpng-1.4.x, which was meant to
  36 be a transitional release, members of the png_struct and the
  37 info_struct can still be accessed, but the compiler will issue a
  38 warning about deprecated usage.  Since libpng-1.5.0, direct access
  39 to these structs is not allowed, and the definitions of the structs
  40 reside in private pngstruct.h and pnginfo.h header files that are not
  41 accessible to applications.  It is strongly suggested that new
  42 programs use the new APIs (as shown in example.c and pngtest.c), and
  43 older programs be converted to the new format, to facilitate upgrades
  44 in the future.
  45 ****
  47 Additions since 0.90 include the ability to compile libpng as a
  48 Windows DLL, and new APIs for accessing data in the info struct.
  49 Experimental functions include the ability to set weighting and cost
  50 factors for row filter selection, direct reads of integers from buffers
  51 on big-endian processors that support misaligned data access, faster
  52 methods of doing alpha composition, and more accurate 16->8 bit color
  53 conversion.
  55 The additions since 0.89 include the ability to read from a PNG stream
  56 which has had some (or all) of the signature bytes read by the calling
  57 application.  This also allows the reading of embedded PNG streams that
  58 do not have the PNG file signature.  As well, it is now possible to set
  59 the library action on the detection of chunk CRC errors.  It is possible
  60 to set different actions based on whether the CRC error occurred in a
  61 critical or an ancillary chunk.
  63 The changes made to the library, and bugs fixed are based on discussions
  64 on the PNG-implement mailing list and not on material submitted
  65 privately to Guy, Andreas, or Glenn.  They will forward any good
  66 suggestions to the list.
  68 For a detailed description on using libpng, read libpng-manual.txt.  For
  69 examples of libpng in a program, see example.c and pngtest.c.  For usage
  70 information and restrictions (what little they are) on libpng, see
  71 png.h.  For a description on using zlib (the compression library used by
  72 libpng) and zlib's restrictions, see zlib.h
  74 I have included a general makefile, as well as several machine and
  75 compiler specific ones, but you may have to modify one for your own needs.
  77 You should use zlib 1.0.4 or later to run this, but it MAY work with
  78 versions as old as zlib 0.95.  Even so, there are bugs in older zlib
  79 versions which can cause the output of invalid compression streams for
  80 some images.  You will definitely need zlib 1.0.4 or later if you are
  81 taking advantage of the MS-DOS "far" structure allocation for the small
  82 and medium memory models.  You should also note that zlib is a
  83 compression library that is useful for more things than just PNG files.
  84 You can use zlib as a drop-in replacement for fread() and fwrite() if
  85 you are so inclined.
  87 zlib should be available at the same place that libpng is, or at zlib.net.
  89 You may also want a copy of the PNG specification.  It is available
  90 as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
  91 these at http://www.libpng.org/pub/png/pngdocs.html .
  93 This code is currently being archived at libpng.sourceforge.io in the
  94 [DOWNLOAD] area, and at http://libpng.download/src .  If you
  95 can't find it in any of those places, e-mail me, and I'll help you find it.
  97 I am not a lawyer, but I believe that the Export Control Classification
  98 Number (ECCN) for libpng is EAR99, which means not subject to export
  99 controls or International Traffic in Arms Regulations (ITAR) because it
 100 is open source, publicly available software, that does not contain any
 101 encryption software.  See the EAR, paragraphs 734.3(b)(3) and 734.7(b).
 103 If you have any code changes, requests, problems, etc., please e-mail
 104 them to me.  Also, I'd appreciate any make files or project files,
 105 and any modifications you needed to make to get libpng to compile,
 106 along with a #define variable to tell what compiler/system you are on.
 107 If you needed to add transformations to libpng, or wish libpng would
 108 provide the image in a different way, drop me a note (and code, if
 109 possible), so I can consider supporting the transformation.
 110 Finally, if you get any warning messages when compiling libpng
 111 (note: not zlib), and they are easy to fix, I'd appreciate the
 112 fix.  Please mention "libpng" somewhere in the subject line.  Thanks.
 114 This release was created and will be supported by myself (of course
 115 based in a large way on Guy's and Andreas' earlier work), and the PNG
 116 development group.
 118 Send comments/corrections/commendations to png-mng-implement at
 119 lists.sourceforge.net (subscription required; visit
 120 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 121 to subscribe) or to glennrp at users.sourceforge.net
 123 You can't reach Guy, the original libpng author, at the addresses
 124 given in previous versions of this document.  He and Andreas will
 125 read mail addressed to the png-implement list, however.
 127 Please do not send general questions about PNG.  Send them to
 128 png-mng-misc at lists.sf.net (subscription required; visit
 129 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
 130 subscribe).  If you have a question about something
 131 in the PNG specification that is related to using libpng, send it
 132 to me.  Send me any questions that start with "I was using libpng,
 133 and ...".  If in doubt, send questions to me.  I'll bounce them
 134 to others, if necessary.
 136 Please do not send suggestions on how to change PNG.  We have
 137 been discussing PNG for twenty years now, and it is official and
 138 finished.  If you have suggestions for libpng, however, I'll
 139 gladly listen.  Even if your suggestion is not used immediately,
 140 it may be used later.
 142 Files in this distribution:
 144       ANNOUNCE      =>  Announcement of this version, with recent changes
 145       CHANGES       =>  Description of changes between libpng versions
 146       KNOWNBUG      =>  List of known bugs and deficiencies
 147       LICENSE       =>  License to use and redistribute libpng
 148       README        =>  This file
 149       TODO          =>  Things not implemented in the current library
 150       Y2KINFO       =>  Statement of Y2K compliance
 151       example.c     =>  Example code for using libpng functions
 152       libpng.3      =>  manual page for libpng (includes libpng-manual.txt)
 153       libpng-manual.txt  =>  Description of libpng and its functions
 154       libpngpf.3    =>  manual page for libpng's private functions
 155       png.5         =>  manual page for the PNG format
 156       png.c         =>  Basic interface functions common to library
 157       png.h         =>  Library function and interface declarations (public)
 158       pngpriv.h     =>  Library function and interface declarations (private)
 159       pngconf.h     =>  System specific library configuration (public)
 160       pngstruct.h   =>  png_struct declaration (private)
 161       pnginfo.h     =>  png_info struct declaration (private)
 162       pngdebug.h    =>  debugging macros (private)
 163       pngerror.c    =>  Error/warning message I/O functions
 164       pngget.c      =>  Functions for retrieving info from struct
 165       pngmem.c      =>  Memory handling functions
 166       pngbar.png    =>  PNG logo, 88x31
 167       pngnow.png    =>  PNG logo, 98x31
 168       pngpread.c    =>  Progressive reading functions
 169       pngread.c     =>  Read data/helper high-level functions
 170       pngrio.c      =>  Lowest-level data read I/O functions
 171       pngrtran.c    =>  Read data transformation functions
 172       pngrutil.c    =>  Read data utility functions
 173       pngset.c      =>  Functions for storing data into the info_struct
 174       pngtest.c     =>  Library test program
 175       pngtest.png   =>  Library test sample image
 176       pngtrans.c    =>  Common data transformation functions
 177       pngwio.c      =>  Lowest-level write I/O functions
 178       pngwrite.c    =>  High-level write functions
 179       pngwtran.c    =>  Write data transformations
 180       pngwutil.c    =>  Write utility functions
 181       arm           =>  Contains optimized code for the ARM platform
 182       powerpc       =>  Contains optimized code for the PowerPC platform
 183       contrib       =>  Contributions
 184        arm-neon         =>  Optimized code for ARM-NEON platform
 185        powerpc-vsx      =>  Optimized code for POWERPC-VSX platform
 186        examples         =>  Example programs
 187        gregbook         =>  source code for PNG reading and writing, from
 188                             Greg Roelofs' "PNG: The Definitive Guide",
 189                             O'Reilly, 1999
 190        libtests         =>  Test programs
 191        mips-msa         =>  Optimized code for MIPS-MSA platform
 192        pngminim         =>  Minimal decoder, encoder, and progressive decoder
 193                             programs demonstrating use of pngusr.dfa
 194        pngminus         =>  Simple pnm2png and png2pnm programs
 195        pngsuite         =>  Test images
 196        testpngs
 197        tools            =>  Various tools
 198        visupng          =>  Contains a MSVC workspace for VisualPng
 199       intel             =>  Optimized code for INTEL-SSE2 platform
 200       mips              =>  Optimized code for MIPS platform
 201       projects      =>  Contains project files and workspaces for
 202                         building a DLL
 203        owatcom          =>  Contains a WATCOM project for building libpng
 204        visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
 205                             workspace for building libpng and zlib
 206        vstudio          =>  Contains a Microsoft Visual C++ (MSVC)
 207                             workspace for building libpng and zlib
 208       scripts       =>  Directory containing scripts for building libpng:
 209                             (see scripts/README.txt for the list of scripts)
 211 Good luck, and happy coding.
 213 -Glenn Randers-Pehrson (current maintainer, since 1998)
 214  Internet: glennrp at users.sourceforge.net
 216 -Andreas Eric Dilger (former maintainer, 1996-1997)
 217  Internet: adilger at enel.ucalgary.ca
 218  Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
 220 -Guy Eric Schalnat (original author and former maintainer, 1995-1996)
 221  (formerly of Group 42, Inc)
 222  Internet: gschal at infinet.com