Search the FAQ Archives

3 - A - B - C - D - E - F - G - H - I - J - K - L - M
N - O - P - Q - R - S - T - U - V - W - X - Y - Z
faqs.org - Internet FAQ Archives

JPEG image compression FAQ, part 1/2
Section - [18] What about arithmetic coding?

( Part1 - Part2 - Single Page )
[ Usenet FAQs | Web FAQs | Documents | RFC Index | Zip codes ]


Top Document: JPEG image compression FAQ, part 1/2
Previous Document: [17] How does JPEG work?
Next Document: [19] Could an FPU speed up JPEG? How about a DSP chip?
See reader questions & answers on this topic! - Help others by sharing your knowledge
The JPEG spec defines two different "back end" modules for the final output
of compressed data: either Huffman coding or arithmetic coding is allowed.
The choice has no impact on image quality, but arithmetic coding usually
produces a smaller compressed file.  On typical images, arithmetic coding
produces a file 5 to 10 percent smaller than Huffman coding.  (All the
file-size numbers previously cited are for Huffman coding.)

Unfortunately, the particular variant of arithmetic coding specified by the
JPEG standard is subject to patents owned by IBM, AT&T, and Mitsubishi.
Thus *you cannot legally use JPEG arithmetic coding* unless you obtain
licenses from these companies.  (Patent law's "experimental use" exception
allows people to test a patented method in the context of scientific
research, but any commercial or routine personal use is infringement.)

I recommend that people not use JPEG arithmetic coding; the space savings
isn't great enough to justify the potential legal hassles.  In particular,
arithmetic coding *should not* be used for any images to be exchanged on
the Internet.  Even if you don't care about US patent law, other folks do.

User Contributions:

Comment about this article, ask questions, or add new information about this topic:

CAPTCHA




Top Document: JPEG image compression FAQ, part 1/2
Previous Document: [17] How does JPEG work?
Next Document: [19] Could an FPU speed up JPEG? How about a DSP chip?

Part1 - Part2 - Single Page

[ Usenet FAQs | Web FAQs | Documents | RFC Index ]

Send corrections/additions to the FAQ Maintainer:
jpeg-info@uunet.uu.net





Last Update March 27 2014 @ 02:11 PM