Software to implement JPEG image compression and decompression. JPEG
(pronounced "jay-peg") is a standardized compression method for
full-color and grayscale images. JPEG is intended for compressing
"real-world" scenes (most of the time these are pictures that have been
scanned-in with a scanner or taken with a digital camera). Cartoons and
other nonrealistic images are not its strong suit. It should be noted
that JPEG output is not necessarily the same as its input. If this is a
factor for you, do not use it. With typical real-world scenes, JPEG can
achieve high compression rates without noticeable differences. If you
can accept pictures of lower quality, JPEG can achieve amazingly high
compression rates.

There are some library functions available for reading and writing JPEG
files. The 'cjpeg' and 'djpeg' applications use the library to make
conversions between JPEG and other popular graphic file formats
possible. The JPEG library is meant to be used within other
applications.

Cjpeg compresses the input file, or standard input if no filename is
given, and produces a JPEG/JFIF file as standard output. Currently
supported input file formats include: PPM (PBMPLUS color format), PGM
(PBMPLUS Grayscale format), BMP, GIF, Targa, and RLE (Utah Raster
Toolkit Format) (RLE is only supported if the RLE library is
available). Djpeg decompresses a JPEG file into one of the above
mentioned formats.