src/png/README

README for libpng version 1.5.6 - November 3, 2011 (shared library 15.0)
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,
libpng-*.tar.xz or libpng-*.tar.bz2 if you want UNIX-style line endings
in the text files, 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 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 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.

The changes made to the library, and bugs fixed are based on discussions
on the PNG-implement mailing list and not on material submitted
privately to Guy, Andreas, or Glenn.  They will forward any good
suggestions to the list.

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 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, or at.
ftp://ftp.info-zip.org/pub/infozip/zlib

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/documents/

This code is currently being archived at libpng.sf.net in the
[DOWNLOAD] area, 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
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) or to glennrp at users.sourceforge.net

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
png-mng-misc at lists.sf.net (subscription required; visit
https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
subscribe).  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 sixteen 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 immediately,
it may be used later.

Files in this distribution:

      ANNOUNCE      =>  Announcement of this version, with recent changes
      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
      Y2KINFO       =>  Statement of Y2K compliance
      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
      contrib       =>  Contributions
       gregbook         =>  source code for PNG reading and writing, from
                            Greg Roelofs' "PNG: The Definitive Guide",
                            O'Reilly, 1999
       msvctest     =>  Builds and runs pngtest using a MSVC workspace
       pngminus     =>  Simple pnm2png and png2pnm programs
       pngsuite     =>  Test images
       visupng      =>  Contains a MSVC workspace for VisualPng
      projects      =>  Contains project files and workspaces for
                        building a DLL
       cbuilder5        =>  Contains a Borland workspace for building
                            libpng and zlib
       visualc6         =>  Contains a Microsoft Visual C++ (MSVC)
                            workspace for building libpng and zlib
       visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
                            workspace for building libpng and zlib
       xcode            =>  Contains an Apple xcode
                            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.

-Glenn Randers-Pehrson (current maintainer, since 1998)
 Internet: glennrp at users.sourceforge.net

-Andreas Eric Dilger (former maintainer, 1996-1997)
 Internet: adilger at enel.ucalgary.ca
 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/

-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
 (formerly of Group 42, Inc)
 Internet: gschal at infinet.com
Commit	Line	Data
	1	README for libpng version 1.5.6 - November 3, 2011 (shared library 15.0)
	2	See the note about version numbers near the top of png.h
	3
	4	See INSTALL for instructions on how to install libpng.
	5
	6	Libpng comes in several distribution formats. Get libpng-*.tar.gz,
	7	libpng-.tar.xz or libpng-.tar.bz2 if you want UNIX-style line endings
	8	in the text files, or lpng*.zip if you want DOS-style line endings.
	9
	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.
	17
	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.
	25
	26	To avoid problems with changes to the internals of 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.
	32
	33	It is important to note that the APIs do not make current programs
	34	that access the info struct directly incompatible with the new
	35	library. However, it is strongly suggested that new programs use
	36	the new APIs (as shown in example.c and pngtest.c), and older programs
	37	be converted to the new format, to facilitate upgrades in the future.
	38	****
	39
	40	Additions since 0.90 include the ability to compile libpng as a
	41	Windows DLL, and new APIs for accessing data in the info struct.
	42	Experimental functions include the ability to set weighting and cost
	43	factors for row filter selection, direct reads of integers from buffers
	44	on big-endian processors that support misaligned data access, faster
	45	methods of doing alpha composition, and more accurate 16->8 bit color
	46	conversion.
	47
	48	The additions since 0.89 include the ability to read from a PNG stream
	49	which has had some (or all) of the signature bytes read by the calling
	50	application. This also allows the reading of embedded PNG streams that
	51	do not have the PNG file signature. As well, it is now possible to set
	52	the library action on the detection of chunk CRC errors. It is possible
	53	to set different actions based on whether the CRC error occurred in a
	54	critical or an ancillary chunk.
	55
	56	The changes made to the library, and bugs fixed are based on discussions
	57	on the PNG-implement mailing list and not on material submitted
	58	privately to Guy, Andreas, or Glenn. They will forward any good
	59	suggestions to the list.
	60
	61	For a detailed description on using libpng, read libpng-manual.txt. For
	62	examples of libpng in a program, see example.c and pngtest.c. For usage
	63	information and restrictions (what little they are) on libpng, see
	64	png.h. For a description on using zlib (the compression library used by
	65	libpng) and zlib's restrictions, see zlib.h
	66
	67	I have included a general makefile, as well as several machine and
	68	compiler specific ones, but you may have to modify one for your own needs.
	69
	70	You should use zlib 1.0.4 or later to run this, but it MAY work with
	71	versions as old as zlib 0.95. Even so, there are bugs in older zlib
	72	versions which can cause the output of invalid compression streams for
	73	some images. You will definitely need zlib 1.0.4 or later if you are
	74	taking advantage of the MS-DOS "far" structure allocation for the small
	75	and medium memory models. You should also note that zlib is a
	76	compression library that is useful for more things than just PNG files.
	77	You can use zlib as a drop-in replacement for fread() and fwrite() if
	78	you are so inclined.
	79
	80	zlib should be available at the same place that libpng is, or at.
	81	ftp://ftp.info-zip.org/pub/infozip/zlib
	82
	83	You may also want a copy of the PNG specification. It is available
	84	as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
	85	these at http://www.libpng.org/pub/png/documents/
	86
	87	This code is currently being archived at libpng.sf.net in the
	88	[DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT)
	89	at GO GRAPHSUP. If you can't find it in any of those places,
	90	e-mail me, and I'll help you find it.
	91
	92	If you have any code changes, requests, problems, etc., please e-mail
	93	them to me. Also, I'd appreciate any make files or project files,
	94	and any modifications you needed to make to get libpng to compile,
	95	along with a #define variable to tell what compiler/system you are on.
	96	If you needed to add transformations to libpng, or wish libpng would
	97	provide the image in a different way, drop me a note (and code, if
	98	possible), so I can consider supporting the transformation.
	99	Finally, if you get any warning messages when compiling libpng
	100	(note: not zlib), and they are easy to fix, I'd appreciate the
	101	fix. Please mention "libpng" somewhere in the subject line. Thanks.
	102
	103	This release was created and will be supported by myself (of course
	104	based in a large way on Guy's and Andreas' earlier work), and the PNG
	105	development group.
	106
	107	Send comments/corrections/commendations to png-mng-implement at
	108	lists.sourceforge.net (subscription required; visit
	109	https://lists.sourceforge.net/lists/listinfo/png-mng-implement
	110	to subscribe) or to glennrp at users.sourceforge.net
	111
	112	You can't reach Guy, the original libpng author, at the addresses
	113	given in previous versions of this document. He and Andreas will
	114	read mail addressed to the png-implement list, however.
	115
	116	Please do not send general questions about PNG. Send them to
	117	png-mng-misc at lists.sf.net (subscription required; visit
	118	https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
	119	subscribe). If you have a question about something
	120	in the PNG specification that is related to using libpng, send it
	121	to me. Send me any questions that start with "I was using libpng,
	122	and ...". If in doubt, send questions to me. I'll bounce them
	123	to others, if necessary.
	124
	125	Please do not send suggestions on how to change PNG. We have
	126	been discussing PNG for sixteen years now, and it is official and
	127	finished. If you have suggestions for libpng, however, I'll
	128	gladly listen. Even if your suggestion is not used immediately,
	129	it may be used later.
	130
	131	Files in this distribution:
	132
	133	ANNOUNCE => Announcement of this version, with recent changes
	134	CHANGES => Description of changes between libpng versions
	135	KNOWNBUG => List of known bugs and deficiencies
	136	LICENSE => License to use and redistribute libpng
	137	README => This file
	138	TODO => Things not implemented in the current library
	139	Y2KINFO => Statement of Y2K compliance
	140	example.c => Example code for using libpng functions
	141	libpng.3 => manual page for libpng (includes libpng-manual.txt)
	142	libpng-manual.txt => Description of libpng and its functions
	143	libpngpf.3 => manual page for libpng's private functions
	144	png.5 => manual page for the PNG format
	145	png.c => Basic interface functions common to library
	146	png.h => Library function and interface declarations (public)
	147	pngpriv.h => Library function and interface declarations (private)
	148	pngconf.h => System specific library configuration (public)
	149	pngstruct.h => png_struct declaration (private)
	150	pnginfo.h => png_info struct declaration (private)
	151	pngdebug.h => debugging macros (private)
	152	pngerror.c => Error/warning message I/O functions
	153	pngget.c => Functions for retrieving info from struct
	154	pngmem.c => Memory handling functions
	155	pngbar.png => PNG logo, 88x31
	156	pngnow.png => PNG logo, 98x31
	157	pngpread.c => Progressive reading functions
	158	pngread.c => Read data/helper high-level functions
	159	pngrio.c => Lowest-level data read I/O functions
	160	pngrtran.c => Read data transformation functions
	161	pngrutil.c => Read data utility functions
	162	pngset.c => Functions for storing data into the info_struct
	163	pngtest.c => Library test program
	164	pngtest.png => Library test sample image
	165	pngtrans.c => Common data transformation functions
	166	pngwio.c => Lowest-level write I/O functions
	167	pngwrite.c => High-level write functions
	168	pngwtran.c => Write data transformations
	169	pngwutil.c => Write utility functions
	170	contrib => Contributions
	171	gregbook => source code for PNG reading and writing, from
	172	Greg Roelofs' "PNG: The Definitive Guide",
	173	O'Reilly, 1999
	174	msvctest => Builds and runs pngtest using a MSVC workspace
	175	pngminus => Simple pnm2png and png2pnm programs
	176	pngsuite => Test images
	177	visupng => Contains a MSVC workspace for VisualPng
	178	projects => Contains project files and workspaces for
	179	building a DLL
	180	cbuilder5 => Contains a Borland workspace for building
	181	libpng and zlib
	182	visualc6 => Contains a Microsoft Visual C++ (MSVC)
	183	workspace for building libpng and zlib
	184	visualc71 => Contains a Microsoft Visual C++ (MSVC)
	185	workspace for building libpng and zlib
	186	xcode => Contains an Apple xcode
	187	workspace for building libpng and zlib
	188	scripts => Directory containing scripts for building libpng:
	189	(see scripts/README.txt for the list of scripts)
	190
	191	Good luck, and happy coding.
	192
	193	-Glenn Randers-Pehrson (current maintainer, since 1998)
	194	Internet: glennrp at users.sourceforge.net
	195
	196	-Andreas Eric Dilger (former maintainer, 1996-1997)
	197	Internet: adilger at enel.ucalgary.ca
	198	Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
	199
	200	-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
	201	(formerly of Group 42, Inc)
	202	Internet: gschal at infinet.com