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The Independent JPEG Group’s JPEG software
README for release 6b of 27-Mar
This distribution contains the sixth public release of the Independent JPEG Group’s
free JPEG software. You are welcome to redistribute this software and to use it for
any purpose, subject to the conditions under LEGAL ISSUES, below.
Serious users of this software (particularly those incorporating it into larger
programs) should contact IJG at jpeg-
electronic mailing list. Mailing list members are notified of updates and have a
chance to particip
This software is the work of Tom
Julian Minguillon, Luis Ortiz, George Phillipido Vollbeding, Ge’
Weijers, and other members of the Independent JPEG Group.
IJG is not affiliated with the official ISO JPEG standards co
DOCUMENTATION
This file contains the followin
OVERVIEW Genera
LEGAL ISSUES Copwarranty, terms of distribution.
REFERENCES Where to lear
ARCHIVE LOCATIONS Where to find newer versions of this software.
RELATED SOFTWARE Other stu
FILE FORMAT WARS Software *not* to get.
TO DO Plans for fut
Other documentation files in the distribution are:
User documentation:
install.doc How and install the IJG software.
usage.doc Usage instructions for cjpeg, djpeg, jpegtran, rdjpgcom,
and wrjpgcom.
*.1 Unix-style man pages for programs (same info
wizard.doc A
change.log V
Programmer and internal documentation:
libjpeg.doc How to use the JPEG library in your own programs.
example.c Sample code for calling the JPEG library.
structure.doc Overview of the JPEG libr
filelist.doc Road
coderules.doc Coding style rules --- please read if you contribute code.
Please read at least the files install.doc and usage.doc. Useful information can also
be found in the JPEG FAQ (Frequently Asked Questions) article. See A
LOCATIONS below to find out where to obtain the FAQ article.
If you want to understand how the JPEG code works, we s
more of the REFERENC
order listed) before diving into t
OVERVI
This package contains C software to implement JPE
decompression. JPEG (pronounced “jay-peg”) is a standardized compression
method for full-color and gray-scale images. JPEG is intended for compressing real-
world scenes; line drawings, cartoons and other non-realistic image
strong suit. JPEG is lossy, meaning that
the input image. Hence you mu
bits. However, on typical photographic images, very good compression levels can
be obtained with no visible change, and remarkably high compression levels are
possible if you can tolerate a low-quali
references, or just experiment with various compression settings.
This software implements JPEG baseline, extended-sequential, and progressive
compression processes. Provision is made for supporting a
processes, although some uncommon parameter settings aren’t implemented yet.
For legal reasons, we are not distributing code for the arithmetic-coding variants of
JPEG; see LEGAL ISSUES. We have made no provision for supportin
hierarchical or lossless processes defined in the standard.
We provide a set of library routines for reading and writing JPEG image files, plus
two sample applications “cjpeg” and “djpeg”, which use the library to perform
conversion between JPEG and some other popular image
intended to be reused
In order to support file conversion and viewing software, we have included
considerable functionality beyond the bare JPEG coding/decoding capability; for
example, the color quantization modules are not strictly part of JPEG decoding, but
they are essential for output to c
These extra functions can be compile
particular application. We have also include
transcoding between different JPEG processes, and “rdjpgcom” and “wrjpgcom”
two simple applications for inserting and extracting textual comments in JFIF files.
The emphasis in designing this software has been on achiev
flexibility, while also making it fast enough to be useful. In particular, the software
is not intended to be read as a tutorial on JPEG. (See
introductory material.) Rather, it is intended to be reliable, portable, industrial-
strength code. We do not claim to have achieved that goal in every aspect of the
software, but we strive for it.
We welcome the use of this software as a component of commercial products. N
royalty is required, but we do ask for an acknowledgement in product
documentation, as
LEGAL ISSUES
In plain English:
1. We
us know!)
2. You can use you want. You
3. You may not pretend that you wrote this software. If you use it
you must acknowledge somewhere in your documentation that you’ve used
the IJG code.
In legalese:
The authors make NO WAR
respect to this software, its quality, accurac
particular purpose. This software is provided “AS IS”, and you, its user, assume the
entire risk as to its quality and accuracy.
This software is copyright © 1991-1998, Thomas G. Lane. All Rights Reserved exce
as specified below.
Permission, modify, and distribute this software (or
portions thereof) for any purpose, without fee, subject to these
( I
file must be included, with this
and any additions, deletions, or changes to the original files must be clearly
indicated in accompanying documentation.
(2) If only executable code is distributed, then the accompanying documentation
must state that “this software is based
JPEG Group”.
(3) Permission for use of this software is granted only if t
responsibility for any undesirable consequences; the
LIABILITY for da
These conditions apply to a
just to the unmodified library. If you
Permission is NOT granted for the use of any IJG author's name or com
in advertising or publicity relating to this software or products derived from it. This
software may be referred to only as “the Independent JPEG Group's software”.
We specifically permit and encourage the use of this software as the basis of
commercial products, provide
the product vendor.
ansi2knr.c is included in this distribu
proprietor of its copyright holder, Aladdin Enterpris
is NOT covered by the above copyright and co
distribution terms of the Free Software Foundation; principally,
include source code if you redistribute it. (See the file ansi2knr.c for full details.)
However, since ansi2knr.c is not needed as part of any program generated from the
IJG code, this does not limit you more
The Unix configuration script
copyright by the Free Software Foundation but is freely distributable. The
holds for its supportin
Another support script, install-sh, is copyright by M.I.T. but is also freely
distributable.
It appears that the arithmetic coding option of the JPEG spec is covered by patents
owned by IBM, AT&T, and Mitsubishi. H
used without obtaining one or more licenses. For thi
coding has been removed from the free JPEG software. (Since arithmetic coding
provides only a marginal gain over the unpatented H
very many implementations will support it.) So far as we are aware, there are no
patent restrictions on the remaining code.
The IJG distr to read and write GIF files. To avoid
entanglement with the Unisys LZW patent, GIF reading support has been removed
altogether, and the GIF writer has been simplified to produce uncompressed GIFs.
This technique does notthm; the resulting GIF files are larger
than usual, but are readable by all standard GIF decoders.
We are required to state that
“The Graphics Interchange Format(c) is the Copyright property of CompuServe
Incorporated. GIF(sm) is a Service Mark property of CompuServe
Incorporated.”
REFERENCES
We highly recommend reading one or more of these references before trying to
understand the innards of the JPEG software.
The best short technical introduction to the JPEG compression algorithm is
Wallace, Gregory K. “The JPEG Still Picture Compression Standard”,
Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
(Adjacent articles in that issue disc
applications of JPEG, and related topics.) If you don’t have t
a PostScript file containing
/ftp.uu.net/graphics/jpeg/wallace.ps.gz. The a preprint for an article
that appeared in IEEE Trans. Consumer Electronics) omits the sample image
appeared in CACM, but it includes corrections and some added material. Note: the
