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一套图像处理程序,支持三种图像文件格式,我调试过了,很好用

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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.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, published by M&T Books (Redwood
City, CA), 1991, ISBN 1-55851-216-0.  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.  (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 US,
copies of the standard may be ordered from ANSI Sales at [phone], or
from Global Engineering Documents at [phone].  (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 number ISO/IEC IS 10918-1.  As of mid-1994,
Part 2 is still at Draft International Standard status.  It is titled "Digital
Compression and Coding of Continuous-tone Still Images, Part 2: Compliance
testing" and has document number ISO/IEC DIS 10918-2.  (The document number
will change to IS 10918-2 when final approval is obtained.)  A Part 3,
covering extensions, is likely to appear in draft form in late 1994.

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 [phone],  fax [phone]
A PostScript version of this document is available at ftp.uu.net, file
graphics/jpeg/jfif.ps.gz.  It can also be obtained by e-mail from the C-Cube
mail server, [e-mail].  Send the message "send jfif_ps from jpeg"
to the server to obtain the JFIF document; send the message "help" if you have
trouble.

The TIFF 6.0 file format specification can be obtained by FTP from sgi.com
(192.48.153.1), file graphics/tiff/TIFF6.ps.Z; or you can order a printed copy
from Aldus Corp. at [phone].  It should be noted that the TIFF 6.0 spec
of 3-June-92 has a number of serious problems in its JPEG features.  A
redesign effort is currently underway to correct these problems; it is
expected to result in a new, incompatible, spec.  IJG intends to support the
corrected version of TIFF when the new spec is issued.


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 graphics/jpeg/jpegsrc.v5a.tar.gz.  If you are on the Internet, you
can retrieve files from ftp.uu.net by standard anonymous FTP.  If you don't
have FTP access, UUNET's archives are also available via UUCP; contact
[e-mail] for information on retrieving files that way.

Numerous Internet sites maintain copies of the UUNET files; in particular,
you can probably find a copy at any site that archives comp.sources.misc
submissions.  However, only ftp.uu.net is guaranteed to have the latest
official version.

You can also obtain this software from CompuServe, in the GRAPHSUPPORT
forum (GO GRAPHSUP), probably in library 15 (there are rumors of a pending
reorganization there).  Again, CompuServe is not guaranteed to have the
very latest version.

The JPEG FAQ (Frequently Asked Questions) article is a useful source of
general information about JPEG.  It is updated constantly and therefore is
not included in this distribution.  The FAQ is posted every two weeks to
Usenet newsgroups comp.graphics, news.answers, and other groups.  You can
always obtain the latest version from the news.answers archive at
rtfm.mit.edu.  By FTP, fetch /pub/usenet/news.answers/jpeg-faq/part1 and
.../part2.  If you don't have FTP, send e-mail to [e-mail]
with body
	send usenet/news.answers/jpeg-faq/part1
	send usenet/news.answers/jpeg-faq/part2


RELATED SOFTWARE
================

Numerous viewing and image manipulation programs now support JPEG.  (Quite a
few of them use this library to do so.)  The JPEG FAQ described above lists
some of the more popular free and shareware viewers, and tells where to
obtain them on Internet.

If you are on a Unix machine, we highly recommend Jef Poskanzer's free
PBMPLUS image software, which provides many useful operations on PPM-format
image files.  In particular, it can convert PPM images to and from a wide
range of other formats.  You can obtain this package by FTP from ftp.x.org
(contrib/pbmplus*.tar.Z) or ftp.ee.lbl.gov (pbmplus*.tar.Z).  There is also
a newer update of this package called NETPBM, available from
wuarchive.wustl.edu under directory /graphics/graphics/packages/NetPBM/.
Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software
is; you are likely to have difficulty making it work on any non-Unix machine.

A different free JPEG implementation, written by the PVRG group at Stanford,
is available from havefun.stanford.edu in directory pub/jpeg.  This program
is designed for research and experimentation rather than production use;
it is slower, harder to use, and less portable than the IJG code, but it
implements a larger subset of the JPEG standard.  In particular, it supports
lossless JPEG.


FILE FORMAT WARS
================

Some JPEG programs produce files that are not compatible with our library.
The root of the problem is that the ISO JPEG committee failed to specify a
concrete file format.  Some vendors "filled in the blanks" on their own,
creating proprietary formats that no one else could read.  (For example, none
of the early commercial JPEG implementations for the Macintosh were able to
exchange compressed files.)

The file format we have adopted is called JFIF (see REFERENCES).  This format
has been agreed to by a number of major commercial JPEG vendors, and it has
become the de facto standard.  JFIF is a minimal or "low end" representation.
Work is also going forward to incorporate JPEG compression into the TIFF
standard, for use in "high end" applications that need to record a lot of
additional data about an image.  We intend to support TIFF in the future.
We hope that these two formats will be sufficient and that other,
incompatible JPEG file formats will not proliferate.

Indeed, part of the reason for developing and releasing this free software is
to help force rapid convergence to de facto standards for JPEG file formats.
SUPPORT STANDARD, NON-PROPRIETARY FORMATS: demand JFIF or TIFF/JPEG!


TO DO
=====

In future versions, we are considering supporting progressive JPEG
compression, the upcoming JPEG Part 3 extensions, and other improvements.

As always, speeding things up is high on our priority list.

Please send bug reports, offers of help, etc. to [e-mail].