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notes13 - 251Notes:4/12,4/14,4/16 DataCompression...

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251 Notes: 4/12,4/14,4/16 Data Compression Data encoding fixed length encoding o each character represent by same number of bits o Ex: ASCII 8bits/char, Unicode 16bits/char variable length encoding o different characters use different lengths o prefix rule to prevent ambiguities in variable length encoding, the code for every character  must not be the prefix of any other character if A is 010, B cannot be 0101 how would we interpret the string 0101. ....? o to enforce prefix rule, we present encoding using an encoding trie A = 010 B = 11 C = 00 D = 10 R = 011 01011011010000101001011011010 A B R A C A D A B R A 11 chars in 29 bits using this encoding, vs 88 bits using ASCII o if you can represent encoding using a trie, guaranteed not to break prefix rule o different encoding tries give different kind of compression: a good trie should give an  encoded text as short as possible Huffman trie
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o builds optimal encoding trie for a given string o starts by building a histogram of occurrences of each character
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notes13 - 251Notes:4/12,4/14,4/16 DataCompression...

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