臺灣博碩士論文加值系統

在數位影像處理中以區塊為基礎的影像編解碼系統，例如： JPEG、MPEG、VQ-coder、H.263、H.264等。當在高壓縮率(低位元率)情況下，影像經壓縮與解壓縮過後容易造成影像品質的失真，然而在區塊的邊界產生不連續的現象，稱為區塊效應。
　　
本論文中，我們提出兩種新的改善區塊效應的方法，分別是利用四點離散餘弦轉換法與異變量等化法。其中離散餘弦轉換具有能量集中的特性，能量主要集中在低頻係數，因為區塊效應的產生主要含有高頻成份，所以區塊效應會表現在高頻係數上，區塊效應主要產生在區塊和區塊之間，故邊界上有明顯的變化(高頻成分)，我們主要減少高頻係數以達到減少區塊效應且保留影像的品質。本論文中的第二個方法，我們主要是利用反強化影像的觀念，利用邊界上的差異量獲得一個均勻的異變量。異變量可表現出一組離散信號的分散程度，當在高對比度或異變量變化較大的區域，利用降低彼此差異程度來獲得適當的衰減，而達到減少對比度的效果，經由實驗證明，我們可以確定兩個方法都可以有效地改善存在於轉換編解碼的影像中的區塊效應。

Block-based image coding system, such as JPEG, MPEG, VQ-coder, H.263, and H.246, etc., easily causes the degradation of reconstruction image in high compression ratio (low bit-rate). So there is a discontinuous condition between block and block, which is called the blocking artifacts.
In this thesis, we propose two new methods to improve the blocking artifacts, including: the methods using four-point discrete cosine transform (DCT) and using standard deviation equalizer. The DCT has the property of energy compaction on low-frequency coefficients for real-world digital images. The production of the blocking artifacts is mainly to contain high frequency components, so we will recant on the high frequency coefficients in order to reduce the blocking effects. Because the blocking artifacts are produced between block and block, there are obvious changes at the block boundary (high frequency components). We adjust high-frequency coefficient to reduce the blocking effect and keep the quality of the reconstruction image. The second method in this thesis is conceived from the inverse enhancement of an image by reducing the difference value at the boundary to approximate one standard deviation of uniform distribution. The standard deviation can represent the scattered degree of the discrete signal. At the area of larger contrast region, decaying the degree of mutual difference can reduce the contrast of the boundary so that the blocking artifacts are reduced. In the experimental results, it is shown that the two methods proposed in this thesis can really and effectively improve the blocking artifacts of the reconstruction image in the block-based coding system.

Abstract (in Chinese)………………………………………………………………....i
Abstract (in English)…………………………………………………………………ii
Acknowledgment (in Chinese)………………………………………..………….…iv
Contents……………………………………………………………………………….v
List of Abbreviations……….………………………………………………………viii
List of Figures………………………………………………………………………..ix
List of Tables…………………………...……………………………………………xi
Chapter 1 Introduction…………………………………………………………….1
1.1 Background of Research…………………………………………………...1
1.2 Motivation of Research………………………………………………….…2
1.3 Organization of This Thesis………………………………………………..4
Chapter 2 JPEG Image Compression standard………………………………….5
2.1 Introduction………………………………………………………………...5
2.2 JPEG Encoder and Decoder………………………………………………..5
2.2.1 JPEG Encoder………………………………………………………6
2.2.1.1 8�e8 Discrete Cosine Transform (DCT)………………………7
2.2.1.2 Quantization………………………………………………….8
2.2.1.3 DC Coding and Zig-Zag Scan………………………………..9
2.2.2 JPEG Decoder………………………………..……………………10
2.3 Motion JPEG (M-JPEG)………………………………………………...12
2.4 Blocking Artifacts………………………………………………………...13
2.5 Performance Evaluation…………………………………………………..14
Chapter 3 Deblocking Algorithms……………………………………………….16
3.1 Introduction……………………………………………………………….16
3.2 Several Existing Deblocking Algorithms………………..………………..17
3.2.1 Gaussian Filtering…………………………………………………17
3.2.2 Adaptive Separable Median Filtering……………………………..18
3.2.3 Signal Adaptive Filtering………………………………………….20
3.2.4 Blocking-Shifted Discrete Cosine Transform……………………..25
3.3 The Proposed Deblocking Algorithms……..…………..………………..27
3.3.1 Our Method I: 1-D Four-Point DCT…………………………….27
3.3.2 Our Method II: Standard Deviation Equalizer………………...…32
Chapter 4 Simulation Results and Performance Comparisons…………..……34
4.1 Introduction………………………………………………………………..34
4.2 Simulation Results………………………………………………………...34
4.3 Performance Comparisons………………………………………………...38
Chapter 5 Conclusions and Future studies……………………………………...90
5.1 Conclusions………………………………………………………………90
5.2 Future Studies…………………………………………………...……….91
Appendix………..…………………………………………………………………...92
References………………………………………………………………………….94
Vita………………………………………………………………………………...…96

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