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JPEG

The images in this archive are all in jpg [JPEG - Joint Photography Experts Group] format. The National Imagery Transmission format [NITF] standards have been designated by the US intelligence community for the exchange of digital imagery, and JPEG serves as the still imagery compression standard in the NITFS suite.

The JPEG designed an image compression methodology based on the Discrete Cosine Transform algorithm -- the file format itself is now commonly referred to as JPEG, and usually carries the extension .JPG or .JPEG. JPEG is a lossy algorithm -- the compressed image differs from the original, which allows for greater compression ratios. The Discrete Cosine Transform algorithm was designed to make these losses in quality difficult to notice. Depending on image type and compression amount, it can be very difficult for a human to tell the difference between the original and compressed images. JPEG Compression does very well on natural sources such as photographs. Artificial sources such as line art usually display visible pixellation and quality loss when compressed by JPEG.

There are a number of benefits of using JPEG, in particular the superior JPEG compression algorithms and their better performance with respect to those of Tape Format Requirements Document (TFRD) DCT. Studies based on imagery analyst (IA) analysis on DCT, JPEG, and other Bandwidth Compression/Expansion (BWC/E) algorithms indicates that at equal levels of bit per pixel compression rates, reconstructed DCT and JPEG images are of equal quality on a range of scenes from three different image sources.

The Central Imagery Office [CIO] has chosen JPEG as the still imagery compression standard for the United States Imagery System [USIS] architecture because the wide commercial acceptance of the ISO standard, coupled with its good imagery quality, will enhance interoperability. The Intelligence Community (IC), DOD, and other agencies have a large installed base of JPEG capable systems, though there are some high-end systems in use which may be expensive to convert.

Compared with commercially pervasive formats, such as GIF and TIFF, JPEG images typically require anywhere from one third to one tenth the badwidth and storage capacity.


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Updated Sunday, February 02, 1997