jpeg(4)jpeg(4)NAMEjpeg - JPEG compression format
DESCRIPTION
JPEG (Joint Photographic Experts Group) is a ``lossy'' compression scheme
based on psycho-visual studies of human perception. Picture information
which is generally not noticeable is dropped out in varying amounts
producing anywhere from a 2 to 100 times reduction in data needed to
store it.
The source image is processed in three basic steps. First, the data is
mathematically transformed from spatial to frequency form in eight by
eight blocks using the Discrete Cosine Transform (DCT). The frequency
coefficients are then filtered down by a linear quantization. Finally,
the coefficients are Huffman encoded into a bit stream. To decompress,
the process is simply reversed.
The quantization step is where the image quality/size trade-off is
controlled. A table called the ``quantization table'' is used to
variously scale each of the 64 DCT coefficients. A separate table is
used for the luminance (Y), and the chrominance (Cr and Cb) components.
PRODUCTS
The JPEG compression format is supported by several developer and end-
user products.
Digital Media Image Converter -- dmIC
Provides JPEG compression and decompression using either a
software codec or real-time hardware device (O2 ICE and
Octane Compression).
Compression Library
Provides JPEG compression and decompression using either a
software codec or a real-time hardware device (Cosmo Compress).
Movie Library
Provides editing and playback capabilities for movies of various
formats, including those that are JPEG compressed.
ImageVision Library
Provides reading and writing of JPEG compressed files in the
JFIF file format.
Digital Media Tools
Several tools enable end-users to create, manipulate, and view JPEG
compressed images and movies. Please refer to the man pages listed
in the final section.
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jpeg(4)jpeg(4)SEE ALSOdm_jpeg(3dm), dmIC(4), dmBuffer(4),
CLintro(3dm), mvIntro(3dm), ilJFIFImg(3il),
compview(1), dmrecord(1), dmconvert(1), dmplay(1),
capture(1), moviemaker(1), makemovie(1), movieplayer(1)
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