東南大學(xué)圖像處理-展示頁(yè)
2025-01-26 10:56本頁(yè)面
【正文】 的字符串 (不一定要求空間上相鄰 ) ? 每接收一個(gè)字符系列，判斷以前是否出現(xiàn)過(guò)，然后用出現(xiàn)過(guò)的字符串代替該重復(fù)的部分，輸出對(duì)應(yīng)的“ 指針 ”（位置） ? 例如： “ aabbccddee” 的指針是 0100，以后每次出現(xiàn)該字符串，就用 0100代替。 LZW Notes ? Dictionary is not null at first, single symbol ? Building depression dictionary is needed ? Application: GIF(graphic interchange format) TIFF(tagged image file format) PDF(portable document format) Huffman coding 灰度 0 1 2 3 4 5 6 7 概率 0 1 0 0 1 0 1 0 1 0 1 0 1 1 編碼 01100 01101 100 101 00 11 010 0111 編碼 : 從根節(jié)點(diǎn)開(kāi)始到葉子節(jié)點(diǎn) !! Standard Huffman coding Average bits : Entropy : efficiency: Standard Huffman disadvantages ? Even if 1 bit error, a series of errors , no solutions (example in next page) ? When decoding, fail to abstract contents from randomly position ? Computation: k2 source ranking ? To symbol with less probability: code length is too long (max: k1 bits) shifted Huffman Error decoding example of Huffman Code : 011, 1, 01010, 0100, 01011, 00 Gray : a1 a2 a3 a4 a5 a6 a3,a1,a2,a2,a6 ... 01010 011 1 1 00 * Encoding : Gray ? Code Decoding : Code ? Gray 010100111100.... 01010 00 1 1 1 1 00... 01010 01011 00... a3,a6,a2,a2,a2,a2,a6... a3,a5,a6... * Add 0 : error decoding * 011 010, Shifted Huffman encoding 1 ? Truncate: 90%(main) standard Huffman ? Divide blocks: assign a prefix to each
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