Pioneer BDP-LX91 - Manuel (Page 57)

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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 © 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:
(1) If any part of the source code for this software is distributed, then this
README file must be included, with this copyright and no-warranty notice
unaltered; 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 in part on the work of the Independent
JPEG Group”.
(3) Permission for use of this software is granted only if the user accepts full
responsibility for any undesirable consequences; the authors accept NO
LIABILITY for damages of any kind.
These conditions apply to any software derived from or based on the IJG code, not
just to the unmodified library. If you use our work, you ought to acknowledge us.
Permission is NOT granted for the use of any IJG author's name or company name
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, provided that all warranty or liability claims are assumed by the product vendor.
ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, sole
proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
ansi2knr.c is NOT covered by the above copyright and conditions, but instead by
the usual distribution terms of the Free Software Foundation; principally, that you
must 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 than the foregoing paragraphs do.
The Unix configuration script “configure” was produced with GNU Autoconf. It is
copyright by the Free Software Foundation but is freely distributable. The same holds
for its supporting scripts (config.guess, config.sub, ltconfig, ltmain.sh). 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. Hence arithmetic coding cannot legally be
used without obtaining one or more licenses. For this reason, support for
arithmetic coding has been removed from the free JPEG software. (Since
arithmetic coding provides only a marginal gain over the unpatented Huffman
mode, it is unlikely that very many implementations will support it.) So far as we are
aware, there are no patent restrictions on the remaining code.
The IJG distribution formerly included code 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 not use the LZW algorithm; 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 discuss MPEG motion picture compression,
applications of JPEG, and related topics.) If you don’t have the CACM issue handy,
a PostScript file containing a revised version of Wallace’s article is available at ftp:/
/ftp.uu.net/graphics/jpeg/wallace.ps.gz. The file (actually a preprint for an article
that appeared in IEEE Trans. Consumer Electronics) omits the sample images that
appeared in CACM, but it includes corrections and some added material. Note: the
Wallace article is copyright ACM and IEEE, and it may not be used for commercial
purposes.
A somewhat less technical, more leisurely introduction to JPEG can be found in
The Data Compression Book by Mark Nelson and Jean-loup Gailly, published by
M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides good
explanations and example C code for a multitude of compression methods
including JPEG. It is an excellent source if you are comfortable reading C code but
don’t know much about data compression in general. The book’s JPEG sample
code is far from industrial-strength, but when you are ready to look at a full
implementation, you’ve got one here...
The best full description of JPEG is the textbook “JPEG Still Image Data Compression
Standard” by William B. Pennebaker and Joan L. Mitchell, published by Van Nostrand
Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. The book includes the
complete text of the ISO JPEG standards (DIS 10918-1 and draft DIS 10918-2). This is
by far the most complete exposition of JPEG in existence, and we highly recommend it.
The JPEG standard itself is not available electronically; you must order a paper copy
through ISO or ITU. (Unless you feel a need to own a certified official copy, we
recommend buying the Pennebaker and Mitchell book instead; it’s much cheaper
and includes a great deal of useful explanatory material.) In the USA, copies of the
standard may be ordered from ANSI Sales at (212) 642-4900, or from Global
Engineering Documents at (800) 854-7179. (ANSI doesn’t take credit card orders,
but Global does.) It’s not cheap: as of 1992, ANSI was charging $95 for Part 1 and
$47 for Part 2, plus 7% shipping/handling. The standard is divided into two parts,
Part 1 being the actual specification, while Part 2 covers compliance testing
methods. Part 1 is titled “Digital Compression and Coding of Continuous-tone Still
Images, Part 1: Requirements and guidelines” and has document numbers ISO/
IEC IS 10918-1, ITU-T T.81. Part 2 is titled “Digital Compression and Coding of
Continuous-tone Still Images, Part 2: Compliance testing” and has document
numbers ISO/IEC IS 10918-2, ITU-T T.83.
Some extensions to the original JPEG standard are defined in JPEG Part 3, a newer
ISO standard numbered ISO/IEC IS 10918-3 and ITU-T T.84. IJG currently does not
support any Part 3 extensions.
The JPEG standard does not specify all details of an interchangeable file format.
For the omitted details we follow the “JFIF” conventions, revision 1.02. A copy of the
JFIF spec is available from:
Literature Department
C-Cube Microsystems, Inc.
1778 McCarthy Blvd.
Milpitas, CA 95035
phone (408) 944-6300, fax (408) 944-6314
A PostScript version of this document is available by FTP at ftp://ftp.uu.net/
graphics/jpeg/jfif.ps.gz. There is also a plain text version at ftp://ftp.uu.net/
graphics/jpeg/jfif.txt.gz, but it is missing the figures.
The TIFF 6.0 file format specification can be obtained by FTP from ftp://ftp.sgi.com/
graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme found in the TIFF 6.0 spec of
3-June-92 has a number of serious problems. IJG does not recommend use of the TIFF
6.0 design (TIFF Compression tag 6). Instead, we recommend the JPEG design proposed
by TIFF Technical Note #2 (Compression tag 7). Copies of this Note can be obtained from
ftp.sgi.com or from ftp://ftp.uu.net/graphics/jpeg/. It is expected that the next revision of
the TIFF spec will replace the 6.0 JPEG design with the Note's design. Although IJG's own
code does not support TIFF/JPEG, the free libtiff library uses our library to implement
TIFF/JPEG per the Note. libtiff is available from ftp://ftp.sgi.com/graphics/tiff/.
ARCHIVE LOCATIONS
The “official” archive site for this software is ftp.uu.net (Internet address
192.48.96.9). The most recent released version can always be found there in
directory graphics/jpeg. This particular version will be archived as ftp://ftp.uu.net/
graphics/jpeg/jpegsrc.v6b.tar.gz. If you don’t have direct Internet access, UUNET’s