對離散餘弦轉換系數使用鄰近關係編碼之影像壓縮 洪毓懋、張世旭
E-mail: [email protected]
摘 要
本文提出一個對離散餘弦轉換係數使用鄰近關係編碼。主要 的壓縮步驟為：(1)將影像切割為8*8大小的區塊，分別對每一 個區塊作離散餘弦轉換(DCT)；(2)求出適合的量化係數，將 DCT係數量化；(3)利用直流係數(DC)預測交流係數(AC)， 得 到AC誤差係數；(4)對DC係數使用訊號誤差編碼(DPCM)， 得到DC誤差係數；(5)對DCT係數使用Context編碼。Context 編 碼的模式分別有：(1)零編碼(2)精練編碼(3)可變長度編 碼。由於進行壓縮時會重新計畫量化係數，不需要額外的量化表，
使得利用量化系數比使用固定量化表的壓縮效果好。在使用算數 編碼時配合鄰近關係能有效的提升壓縮的效率。並且根據 離散餘 弦轉換的特性，利用直流係數對交流系數預測可以提升壓縮的效 率。由於經過以區塊為基礎的函式轉換，因此當 影像過度壓縮後， 重建影像將會產生明顯的區塊效應(Blocking Effect)。而使用後 處裡的步驟能夠提高壓所的影像品質，並 且能提升視覺上的效果。
關鍵詞 : 離散餘弦轉換，漸進式壓縮，崁入式離散餘弦轉換， 鄰近關係編碼，交流係數預測 目錄
第1章 緒論... 1 1.1 影像壓縮簡介... 1 1.2 研究動機與目的... 2 1.3 文獻探 討... 3 1.4 論文架構... 5 第2章 相關研究... 6 2.1 EZDCT
和ezhdct... 6 2.2 EBCOT... 9 2.3 算數編碼... 12 第3章 演算法架 構... 15 3.1 編碼流程... 16 3.1.1 DCT轉換與係數分類... 16 3.1.2 DCT係數量 化... 17 3.1.3 交流係數預測... 17 3.1.4 直流係數預測... 19 3.1.5 嵌入式編碼流 程... 19 3.1.6 未重要係數編碼... 20 3.1.7 精煉編碼... 23 3.1.8 Run-length Coding... 23 3.2 解碼流程... 27 第4章 針對區塊效應進行後處理... 28 4.1 邊的探 測... 28 4.2 區塊契合... 29 第5章 實驗結果比較... 31 第6章 結論與未來工 作... 38 參考文獻... 39
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