Huffman encoding; Shannon-Fano encoding; arithmetic encoding
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input is sliced into fixed units while the corresponding output comes in chunks of variable size
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RLE -Run Length Encoding (TIFF, BMP)
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lossless: Replace upto 127 identical characters by two bytes -- first byte is number of identical characters in string, second byte is character itself
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For example: AAAAbbbbbccct ---> 4A5b3c1t
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LZW - Lepel-Ziv-Welch (TIFF, GIF)
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Directory based encoding algorithm
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compress, zoo, lha, pkzip. arj
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LZ77, LZ78
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input is divided into units of variable length (words) and coded in a fixed-length output code
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shorter bit patterns for most common characters
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DCT - Discrete Cosine Transform (MPEG, JPEG, H.261)
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lossy; converts the spatial image representation into a frequency map
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DCT scheme is effective only for compressing continuous-tone images (from "Graphics File Formats", O'Reilly and Associates Inc., page 162 in description of JPEG algorithm)
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