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jpeg(4)								       jpeg(4)

NAME    [Toc]    [Back]

     jpeg - JPEG compression format

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     The JPEG compression format is supported by several developer and enduser

     Digital Media Image Converter -- dmIC    [Toc]    [Back]
	 Provides JPEG compression and decompression using either a
	 software codec	or real-time hardware device (O2 ICE and
	 Octane	Compression).

     Compression Library    [Toc]    [Back]
	 Provides JPEG compression and decompression using either a
	 software codec	or a real-time hardware	device (Cosmo Compress).

     Movie Library    [Toc]    [Back]
	 Provides editing and playback capabilities for	movies of various
	 formats, including those that are JPEG	compressed.

     ImageVision Library    [Toc]    [Back]
	 Provides reading and writing of JPEG compressed files in the
	 JFIF file format.

     Digital Media Tools    [Toc]    [Back]
	 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.

									Page 1

jpeg(4)								       jpeg(4)

SEE ALSO    [Toc]    [Back]

     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)

									PPPPaaaaggggeeee 2222
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