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