JPEG
(Joint Photographic Experts Group) An ISO/ITU standard for compressing still images that is becoming very popular due to its high compression capability. Using discrete cosine transform, it provides lossy compression (you lose some data from the original image) with ratios up to 100:1 and higher.
It depends on the image, but ratios of 10:1 to 20:1 may provide little noticeable loss. The more the loss can be tolerated, the more the image can be compressed. Compression is achieved by dividing the picture into tiny pixel blocks, which are halved over and over until the ratio is achieved.
    JPEG is implemented in software and hardware, with the latter providing sufficient speed for realtime, on-the-fly compression. C-Cube Microsystems introduced the first JPEG chip.
    JPEG++ is an extension to JPEG from Storm Technology, Mountain View, CA, that allows picture areas to be selectable for different ratios. For example, the background could be compressed higher than the foreground image.
    JPEG uses the JPEG File Interchange Format, or JFIF. File extensions are .JPG or .JFF. M-JPEG and MPEG are variations of JPEG used for full-motion digital video.


Glossary Index

Copyright  ©1998-2000 by Ultimate Systems, Inc. All Rights Reserved.