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This product uses the following software.
For information (copyright, etc) about each software, read the original sentences stated below.
■ About The Independent JPEG Group’s JPEG
software
The Independent JPEG Group’s JPEG software
README for release 6b of 27-Mar-1998
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-info@uunet.uu.net to be added to our electronic mailing list.
Mailing list members are notified of updates and have a chance to participate in
technical discussions, etc.
This software is the work of Tom Lane, Philip Gladstone, Jim Boucher, Lee Crocker,
Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Guido Vollbeding,
Ge’ Weijers, and other members of the Independent JPEG Group.
IJG is not affiliated with the official ISO JPEG standards committee.
DOCUMENTATION ROADMAP
This file contains the following sections:
OVERVIEW General description of JPEG and the IJG software.
LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
REFERENCES Where to learn more about JPEG.
ARCHIVE LOCATIONS Where to find newer versions of this software.
RELATED SOFTWARE Other stuff you should get.
FILE FORMAT WARS Software *not* to get.
TO DO Plans for future IJG releases.
Other documentation files in the distribution are:
User documentation:
install.doc How to configure 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 as
usage.doc).
wizard.doc Advanced usage instructions for JPEG wizards only.
change.log Version-to-version change highlights.
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 library’s internal structure.
filelist.doc Road map of IJG files.
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 ARCHIVE
LOCATIONS below to find out where to obtain the FAQ article.
If you want to understand how the JPEG code works, we suggest reading one or more of
the REFERENCES, then looking at the documentation files (in roughly the order listed)
before diving into the code.
OVERVIEW
This package contains C software to implement JPEG image compression and
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 images are not its strong suit. JPEG is
lossy, meaning that the output image is not exactly identical to the input image. Hence
you must not use JPEG if you have to have identical output 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-
quality image. For more details, see the references, or just experiment with various
compression settings.
This software implements JPEG baseline, extended-sequential, and progressive
compression processes. Provision is made for supporting all variants of these 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 supporting the 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 file formats. The library is intended to be
reused in other applications.
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 colormapped file formats or colormapped displays. These extra functions can
be compiled out of the library if not required for a particular application. We have also
included “jpegtran”, a utility for lossless 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 achieving portability and
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 the REFERENCES section for
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. No
royalty is required, but we do ask for an acknowledgement in product documentation, as
described under LEGAL ISSUES.
LEGAL ISSUES
In plain English:
1. We don’t promise that this software works. (But if you find any bugs, please let us
know!)
2. You can use this software for whatever you want. You don’t have to pay us.
3. You may not pretend that you wrote this software. If you use it in a program, you
must acknowledge somewhere in your documentation that you’ve used the IJG
code.
In legalese:
The authors make NO WARRANTY or representation, either express or implied, with
respect to this software, its quality, accuracy, merchantability, or fitness for a 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 (C) 1991-1998, Thomas G. Lane.
All Rights Reserved except as specified below.
Permission is hereby granted to use, copy, modify, and distribute this software (or
portions thereof) for any purpose, without fee, subject to these conditions:
