Context-Based Entropy Coding of DCT Coefficients for Image Compression 洪毓懋、張世旭
E-mail: [email protected]
ABSTRACT
This paper proposes Context-based entropy coding of DCT coefficients for image compression. The main compression step is :(1) Divide the input image into the 8*8 block, use Discrete Cosine Transform (DCT) for every block; (2) Find out suitable quantization coefficient, quantize DCT coefficient; (3) Use the Direct Current coefficient (DC) to predict that Alternating Current (AC)
coefficient, get AC error coefficient, (4) Use the differential pulse code modulation (DPCM) to DC coefficient, get DC error coefficient; (5) Context coding is used in DCT coefficient. Models of Context Coding: (1)Zero Coding, (2) Refine Coding, (3)
Run-length Coding. When enter compression step,quantization coefficient will be recomputed. The performance which doesn't need extra quantization table is better than the performance which needs to use fixed quantization table.When using arithmetic coding, consider the relation of coefficient can improve the performance of compression. According to predict AC coefficient can improve the Transform, using DC coefficient to predict AC cocefficient can improve the performance of compression. Because coefficient transform is one kind of block-based coefficient transform. When image would be compressed overly, the restructure image will cause distinct Blocking Effect. Post-processing can improve the performance of compression.
Keywords : Discrete Cosine Transform, Progressive Compreesion, Embedded DCT, Context coding, AC Coefficient Predicted Table of Contents
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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