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README for libpng 1.0.1 (shared library 2.1)
See the note about version numbers near the top of png.h
See INSTALL for instructions on how to install libpng.
This is 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 for about two and a half years. However, it's
finally gotten to the stage where there haven't been significant
changes to the API in some time, and people have a bad feeling about
libraries with versions < 1.0.
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 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 do not make current programs
that access the info struct directly incompatible with the new
library. However, it is strongly suggested that new programs use
the new APIs (as shown in example.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
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 changes made to the library, and bugs fixed are based on discussions
on the PNG implementation mailing list <>
and not on material submitted to Guy.
For a detailed description on using libpng, read libpng.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 will definitely need zlib 1.0.4 or later if you are
taking advantage of the MS-DOS "far" structure allocation for the small
and medium memory models. 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.
If not, it should be at in /graphics/png
Eventually, it will be at in /pub/archiving/zip/zlib
You may also want a copy of the PNG specification. It is available
as an RFC and a W3C Recommendation. Failing
these resources you can try in the /graphics/png directory.
This code is currently being archived at in the
/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
at GO GRAPHSUP. If you can't find it in any of those places,
e-mail me, and I'll help you find it.
If you have any code changes, requests, problems, etc., please e-mail
them to me. Also, I'd appreciate any make files or project files,
and any modifications you needed to make to get libpng to compile,
along with a #define variable to tell what compiler/system you are on.
If you needed to add transformations to libpng, or wish libpng would
provide the image in a different way, drop me a note (and code, if
possible), so I can consider supporting the transformation.
Finally, if you get any warning messages when compiling libpng
(note: not zlib), and they are easy to fix, I'd appreciate the
fix. Please mention "libpng" somewhere in the subject line. Thanks.
This release was created and will be supported by myself (of course
based in a large way on Guy's and Andreas' earlier work), and the PNG group.
You can't reach Guy, the original libpng author, at the addresses
given in previous versions of this document. He and Andreas will read mail
addressed to the png-implement list, however.
Please do not send general questions about PNG. Send them to
the address in the specification ( At the same
time, please do not send libpng questions to that address, send them to me
or to I'll
get them in the end anyway. If you have a question about something
in the PNG specification that is related to using libpng, send it
to me. Send me any questions that start with "I was using libpng,
and ...". If in doubt, send questions to me. I'll bounce them
to others, if necessary.
Please do not send suggestions on how to change PNG. We have
been discussing PNG for three years now, and it is official and
finished. If you have suggestions for libpng, however, I'll
gladly listen. Even if your suggestion is not used for version
1.0, it may be used later.
Files in this distribution:
CHANGES => Description of changes between libpng versions
README => This file
TODO => Things not implemented in the current library
ansi2knr.1 => Manual page for ansi2knr
ansi2knr.c => Converts files to K&R style function declarations
build.bat => MS-DOS batch file for Borland compiler
descrip.mms => VMS project file
example.c => Example code for using libpng functions
libpng.3 => manual page for libpng
libpng.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
pngconf.h => System specific library configuration
pngerror.c => Error/warning message I/O functions
pngget.c => Functions for retrieving info from struct
pngmem.c => Memory handling functions
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
scripts => Directory containing scripts for building libpng:
descrip.mms => VMS makefile for MMS or MMK
makefile.std => Generic UNIX makefile
makefile.knr => Archaic UNIX Makefile that converts files with ansi2knr
makefile.dec => DEC Alpha UNIX makefile
makefile.sgi => Silicon Graphics IRIX makefile
makefile.sun => Sun makefile
makefile.s2x => Solaris 2.X makefile (gcc, creates
makefile.lnx => Linux/ELF makefile (gcc, creates
makefile.mip => MIPS makefile => Acorn makefile
makefile.ama => Amiga makefile
smakefile.ppc => AMIGA smakefile for SAS C V6.58/7.00 PPC compiler
(Requires SCOPTIONS, copied from scripts/SCOPTIONS.ppc)
makefile.atr => Atari makefile
makefile.bor => Borland makefile
build.bat => MS-DOS batch file for Borland compiler
makefile.dj2 => DJGPP 2 makefile
makefile.msc => Microsoft C makefile
makefile.tc3 => Turbo C 3.0 makefile
makefile.os2 => OS/2 Makefile (gcc and emx, requires pngos2.def)
makefile.wat => Watcom 10a+ Makefile, 32-bit flat memory model
pngos2.def => OS/2 module definition file used by makefile.os2 => VMS build script
Good luck, and happy coding.
-Glenn Randers-Pehrson
-Andreas Eric Dilger
-Guy Eric Schalnat
(formerly of Group 42, Inc)