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    - DCT
    - Coefficient Quantization
    - Lossless Compression


Programs using complex graphics are showing up in virtually every area of computing applications including games, education, desktop publishing, graphical design, and most recently the World Wide Web. Although graphics do a great deal to enhance the usability and visual aesthetics of such applications, they consume prodigious amounts of disk storage.

When research into image compression began in the late 1970s, most compression concentrated on using conventional lossless techniques. However, such types of compression, which included statistical and dictionary methods of compression, did not tend to perform well on photographic, or continuous tone images. The primary problem with statistical techniques stemmed from the fact that pixels in photographic images tend to be well spread out over their entire range. If the colors in an image are plotted as a histogram based on frequency, the histogram is not as "spiky" as one would like for statistical compression to be effective. Each pixel code has approximately the same chance of appearing as any other, negating any opportunity for exploiting entropy differences (Nelson 349).

By the late 1980s, extensive research pushed the development of lossy compression algorithms that take advantage of known limitations of the human eye. Such algorithms play on the idea that slight modifications and loss of information during the compression/decompression process often do not affect the quality of the image as perceived by the human user. Eventually, the JPEG continuous tone image compression specification was standardized, named after the Joint Photographic Experts Group, the standards group consisting of members from both the CCITT and the ISO that wrote the specification. The JPEG specification includes separate lossy and lossless algorithms; however, the lossless algorithm is rarely used due to its poor compression ratios. Thus, when one mentions JPEG compression, it can almost be assumed that the reference is being made to the lossy algorithm, or the JPEG baseline algorithm. The baseline algorithm, which is capable of compressing continuous tone images to less that 10% of their original size without visible degradation of the image quality, is detailed below.


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