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comp.compression Frequently Asked Questions (part 1/3)
Section - [19] What is JPEG?

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JPEG (pronounced "jay-peg") is a standardized image compression mechanism.
JPEG stands for Joint Photographic Experts Group, the original name of the
committee that wrote the standard.  JPEG is designed for compressing either
full-color or gray-scale digital images of "natural", real-world scenes.
It does not work very well on non-realistic images, such as cartoons or
line drawings.

JPEG does not handle black-and-white (1-bit-per-pixel) images, nor does it
handle motion picture compression.  Related standards for compressing those
types of images exist, and are called JBIG and MPEG respectively.

Regular JPEG is "lossy", meaning that the image you get out of decompression
isn't quite identical to what you originally put in.  The algorithm achieves
much of its compression by exploiting known limitations of the human eye,
notably the fact that small color details aren't perceived as well as small
details of light-and-dark.  Thus, JPEG is intended for compressing images that
will be looked at by humans.  If you plan to machine-analyze your images, the
small errors introduced by JPEG may be a problem for you, even if they are
invisible to the eye.  The JPEG standard includes a separate lossless mode,
but it is rarely used and does not give nearly as much compression as the
lossy mode.

Question 75 "Introduction to JPEG" (in part 2 of this FAQ) gives an overview
of how JPEG works and provides references for further reading.  Also see the
JPEG FAQ article, which covers JPEG software and usage hints.  The JPEG FAQ
http://www.faqs.org/faqs/jpeg-faq/part1/preamble.html is
posted regularly in news.answers by Tom Lane <tgl@netcom.com>.
(See also question 53 "Where are FAQ lists archived".)

For JPEG software, see item 15 above.  For JPEG hardware, see item 85
in part 3 of this FAQ.  The ISO JPEG standards committee's home page
is http://www.jpeg.org/public/welcome.htm

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