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JPEG
Joint
Photographic Experts Group is one of the most popular file formats
for storing 8 and 24 bit continuous tone grayscale and color images
(which makes it one of the more popular web graphic formats.
It is a standardized image
compression mechanism designed for compressing either full-color or
gray-scale images. It works well on photographs, artwork, and
similar material. However, it does not work as well on lettering,
simple cartoons, or line drawings. JPEG works by exploiting known
limitations of the human eye, notably the fact that small color
changes are perceived less accurately than small changes in
brightness.
JPEG is lossy but it achieves much greater compression
than is possible with lossless methods. A major disadvantage of
lossy compression is that repeated compression and decompress will
continue to deteriorate image quality. The amount of "loss" can be
varied by adjusting compression parameters that determine image
quality and speed of decoding. This means that image size is offset
by image quality or the amount of time needed to decode the image
file for display. JPEG does not support transparency.
The highly
efficient JPEG compression modes are:
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Non-differential Huffman coding
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Differential
Huffman coding
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Non-differential arithmetic coding
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Differential
arithmetic coding
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