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File too long (should be no more than 24 lines). Line too long (should be no more than 80 characters). Trailing empty lines. Trailing white-space. Trucated the long files as best as possible while preserving the most info contained in them.
24 lines
1.6 KiB
Text
24 lines
1.6 KiB
Text
In 1992, a joint ISO/CCITT committee known as JPEG (Joint Photographic Experts
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Group) established and published the first draft international standard (DIS)
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for compressing continuous-tone still images, both grayscale and color. JPEG has
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defined four mode of operations, summarized them as follows:
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(1) Sequential encoding: each image component is encoded in a single
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left-to-right, top-to-bottom scan;
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(2) Progressive encoding: the image is encoded in multiple scans for
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applications in which transmission time is long, and the viewer prefers to
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watch the image build up in multiple coarse-to-clear passes;
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(3) Lossless encoding: the images is encoded to guarantee exact recovery of
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every source image sample value (even though the result is low compression
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compared to the lossy modes);
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(4) Hierarchical encoding: the image is encoded at multiple resolutions so that
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lower-resolution versions may be accessed without first having to decompress
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the image at its full resolution.
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Our lossless JPEG encoding program has an automatic prediction selection value
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(PSV) selector which selects the best PSV among a user provided or default set
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of PSVs. This selector guarantees the best compression ratio for lossless JPEG.
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The encoding program "pnmtoljpg" compresses a Portable Pixmap or Portable
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Graymap image to a lossles JPEG (ljpg) image using the JPEG standard (DIS)
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lossless mode of operation. The decoding program "ljpgtopnm" decodes a ljpg
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image to either a Portable Pixmap or Portable Graymap image depending on the
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number of color components stored in the ljpg image file.
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