src/png/README

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
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 implementation mailing list <png-implement@dworking.wustl.edu>
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 ftp.uu.net in /graphics/png
Eventually, it will be at ftp.uu.net 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 ftp.uu.net in the /graphics/png directory.

This code is currently being archived at ftp.uu.net 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.

randeg@alumni.rpi.edu
png-implement@dworkin.wustl.edu

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 (png-group@w3.org).  At the same
time, please do not send libpng questions to that address, send them to me
or to png-implement@dworkin.wustl.edu.  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 libpng.so.2.1.0)
        makefile.lnx  =>  Linux/ELF makefile (gcc, creates libpng.so.2.1.0)
        makefile.mip  =>  MIPS makefile
        makefile.aco  =>  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
        makevms.com   =>  VMS build script

Good luck, and happy coding.

-Glenn Randers-Pehrson
 Internet: randeg@alumni.rpi.edu
 Web: http://www.rpi.edu/~randeg/index.html

-Andreas Eric Dilger
 Internet: adilger@enel.ucalgary.ca
 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/

-Guy Eric Schalnat
 (formerly of Group 42, Inc)
 Internet: gschal@infinet.com
Commit	Line	Data
	1	README for libpng 1.0.1 (shared library 2.1)
	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	This is the first official release of libpng. Don't let the fact that
	7	it's the first release fool you. The libpng library has been in
	8	extensive use and testing for about two and a half years. However, it's
	9	finally gotten to the stage where there haven't been significant
	10	changes to the API in some time, and people have a bad feeling about
	11	libraries with versions < 1.0.
	12
	13	****
	14	Note that some of the changes to the png_info structure render this
	15	version of the library binary incompatible with libpng-0.89 or
	16	earlier versions if you are using a shared library. The type of the
	17	"filler" parameter for png_set_filler() has changed from png_byte to
	18	png_uint_32, which will affect shared-library applications that use
	19	this function.
	20
	21	To avoid problems with changes to the internals of png_info_struct,
	22	new APIs have been made available in 0.95 to avoid direct application
	23	access to info_ptr. These functions are the png_set_<chunk> and
	24	png_get_<chunk> functions. These functions should be used when
	25	accessing/storing the info_struct data, rather than manipulating it
	26	directly, to avoid such problems in the future.
	27
	28	It is important to note that the APIs do not make current programs
	29	that access the info struct directly incompatible with the new
	30	library. However, it is strongly suggested that new programs use
	31	the new APIs (as shown in example.c), and older programs be converted
	32	to the new format, to facilitate upgrades in the future.
	33	****
	34
	35	Additions since 0.90 include the ability to compile libpng as a
	36	Windows DLL, and new APIs for accessing data in the info struct.
	37	Experimental functions include the ability to set weighting and cost
	38	factors for row filter selection, direct reads of integers from buffers
	39	on big-endian processors that support misaligned data access, faster
	40	methods of doing alpha composition, and more accurate 16->8 bit color
	41	conversion.
	42
	43	The additions since 0.89 include the ability to read from a PNG stream
	44	which has had some (or all) of the signature bytes read by the calling
	45	application. This also allows the reading of embedded PNG streams that
	46	do not have the PNG file signature. As well, it is now possible to set
	47	the library action on the detection of chunk CRC errors. It is possible
	48	to set different actions based on whether the CRC error occurred in a
	49	critical or an ancillary chunk.
	50
	51	The changes made to the library, and bugs fixed are based on discussions
	52	on the PNG implementation mailing list <png-implement@dworking.wustl.edu>
	53	and not on material submitted to Guy.
	54
	55	For a detailed description on using libpng, read libpng.txt. For
	56	examples of libpng in a program, see example.c and pngtest.c. For usage
	57	information and restrictions (what little they are) on libpng, see
	58	png.h. For a description on using zlib (the compression library used by
	59	libpng) and zlib's restrictions, see zlib.h
	60
	61	I have included a general makefile, as well as several machine and
	62	compiler specific ones, but you may have to modify one for your own needs.
	63
	64	You should use zlib 1.0.4 or later to run this, but it MAY work with
	65	versions as old as zlib 0.95. Even so, there are bugs in older zlib
	66	versions which can cause the output of invalid compression streams for
	67	some images. You will definitely need zlib 1.0.4 or later if you are
	68	taking advantage of the MS-DOS "far" structure allocation for the small
	69	and medium memory models. You should also note that zlib is a
	70	compression library that is useful for more things than just PNG files.
	71	You can use zlib as a drop-in replacement for fread() and fwrite() if
	72	you are so inclined.
	73
	74	zlib should be available at the same place that libpng is.
	75	If not, it should be at ftp.uu.net in /graphics/png
	76	Eventually, it will be at ftp.uu.net in /pub/archiving/zip/zlib
	77
	78	You may also want a copy of the PNG specification. It is available
	79	as an RFC and a W3C Recommendation. Failing
	80	these resources you can try ftp.uu.net in the /graphics/png directory.
	81
	82	This code is currently being archived at ftp.uu.net in the
	83	/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
	84	at GO GRAPHSUP. If you can't find it in any of those places,
	85	e-mail me, and I'll help you find it.
	86
	87	If you have any code changes, requests, problems, etc., please e-mail
	88	them to me. Also, I'd appreciate any make files or project files,
	89	and any modifications you needed to make to get libpng to compile,
	90	along with a #define variable to tell what compiler/system you are on.
	91	If you needed to add transformations to libpng, or wish libpng would
	92	provide the image in a different way, drop me a note (and code, if
	93	possible), so I can consider supporting the transformation.
	94	Finally, if you get any warning messages when compiling libpng
	95	(note: not zlib), and they are easy to fix, I'd appreciate the
	96	fix. Please mention "libpng" somewhere in the subject line. Thanks.
	97
	98	This release was created and will be supported by myself (of course
	99	based in a large way on Guy's and Andreas' earlier work), and the PNG group.
	100
	101	randeg@alumni.rpi.edu
	102	png-implement@dworkin.wustl.edu
	103
	104	You can't reach Guy, the original libpng author, at the addresses
	105	given in previous versions of this document. He and Andreas will read mail
	106	addressed to the png-implement list, however.
	107
	108	Please do not send general questions about PNG. Send them to
	109	the address in the specification (png-group@w3.org). At the same
	110	time, please do not send libpng questions to that address, send them to me
	111	or to png-implement@dworkin.wustl.edu. I'll
	112	get them in the end anyway. If you have a question about something
	113	in the PNG specification that is related to using libpng, send it
	114	to me. Send me any questions that start with "I was using libpng,
	115	and ...". If in doubt, send questions to me. I'll bounce them
	116	to others, if necessary.
	117
	118	Please do not send suggestions on how to change PNG. We have
	119	been discussing PNG for three years now, and it is official and
	120	finished. If you have suggestions for libpng, however, I'll
	121	gladly listen. Even if your suggestion is not used for version
	122	1.0, it may be used later.
	123
	124	Files in this distribution:
	125
	126	CHANGES => Description of changes between libpng versions
	127	README => This file
	128	TODO => Things not implemented in the current library
	129	ansi2knr.1 => Manual page for ansi2knr
	130	ansi2knr.c => Converts files to K&R style function declarations
	131	build.bat => MS-DOS batch file for Borland compiler
	132	descrip.mms => VMS project file
	133	example.c => Example code for using libpng functions
	134	libpng.3 => manual page for libpng
	135	libpng.txt => Description of libpng and its functions
	136	libpngpf.3 => manual page for libpng's private functions
	137	png.5 => manual page for the PNG format
	138	png.c => Basic interface functions common to library
	139	png.h => Library function and interface declarations
	140	pngconf.h => System specific library configuration
	141	pngerror.c => Error/warning message I/O functions
	142	pngget.c => Functions for retrieving info from struct
	143	pngmem.c => Memory handling functions
	144	pngpread.c => Progressive reading functions
	145	pngread.c => Read data/helper high-level functions
	146	pngrio.c => Lowest-level data read I/O functions
	147	pngrtran.c => Read data transformation functions
	148	pngrutil.c => Read data utility functions
	149	pngset.c => Functions for storing data into the info_struct
	150	pngtest.c => Library test program
	151	pngtest.png => Library test sample image
	152	pngtrans.c => Common data transformation functions
	153	pngwio.c => Lowest-level write I/O functions
	154	pngwrite.c => High-level write functions
	155	pngwtran.c => Write data transformations
	156	pngwutil.c => Write utility functions
	157	scripts => Directory containing scripts for building libpng:
	158	descrip.mms => VMS makefile for MMS or MMK
	159	makefile.std => Generic UNIX makefile
	160	makefile.knr => Archaic UNIX Makefile that converts files with ansi2knr
	161	makefile.dec => DEC Alpha UNIX makefile
	162	makefile.sgi => Silicon Graphics IRIX makefile
	163	makefile.sun => Sun makefile
	164	makefile.s2x => Solaris 2.X makefile (gcc, creates libpng.so.2.1.0)
	165	makefile.lnx => Linux/ELF makefile (gcc, creates libpng.so.2.1.0)
	166	makefile.mip => MIPS makefile
	167	makefile.aco => Acorn makefile
	168	makefile.ama => Amiga makefile
	169	smakefile.ppc => AMIGA smakefile for SAS C V6.58/7.00 PPC compiler
	170	(Requires SCOPTIONS, copied from scripts/SCOPTIONS.ppc)
	171	makefile.atr => Atari makefile
	172	makefile.bor => Borland makefile
	173	build.bat => MS-DOS batch file for Borland compiler
	174	makefile.dj2 => DJGPP 2 makefile
	175	makefile.msc => Microsoft C makefile
	176	makefile.tc3 => Turbo C 3.0 makefile
	177	makefile.os2 => OS/2 Makefile (gcc and emx, requires pngos2.def)
	178	makefile.wat => Watcom 10a+ Makefile, 32-bit flat memory model
	179	pngos2.def => OS/2 module definition file used by makefile.os2
	180	makevms.com => VMS build script
	181
	182	Good luck, and happy coding.
	183
	184	-Glenn Randers-Pehrson
	185	Internet: randeg@alumni.rpi.edu
	186	Web: http://www.rpi.edu/~randeg/index.html
	187
	188	-Andreas Eric Dilger
	189	Internet: adilger@enel.ucalgary.ca
	190	Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
	191
	192	-Guy Eric Schalnat
	193	(formerly of Group 42, Inc)
	194	Internet: gschal@infinet.com