jpeg(4)                                                                jpeg(4)


NAME
     jpeg - 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.


SEE ALSO
     dm_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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