臺灣博碩士論文加值系統

本論文提出一個低計算量，且適用於在低位元率時，以方塊為基底（block-based）的視訊編碼系統（例如MPEG-4及H.264）之去除方塊效應演算法。此演算法包括四個濾波器，其中三種情況為平滑模式（smooth mode）、中間模式（intermediate mode）及複雜模式（complex mode），分別對應到低頻、中頻及高頻區域。而當相鄰方塊之間落差太大時，必須利用其它方法來消除方塊效應，陡峭模式（steep mode）即是為此而設計的。藉由觀察方塊邊綠附近像素的變化情形，可決定此區域適用於何種濾波器。在濾波器設計上，考慮到人眼對平滑區域的方塊效應較為敏感，平滑模式濾波器的效力也比複雜模式濾波器的效力來得強大。實驗結果顯示，在大部份情況下，本演算法比MPEG-4及H.264可移除更多的方塊效應，並且在主觀及客觀的判斷上皆有所提升；在計算量上，本演算法也比MPEG-4的計算量來得少，且可適用於多種以方塊為基底的影像及視訊編碼系統中。

This Thesis presents a new method to remove blocking artifacts in low bit-rate block-based video coding, such as MPEG-4 and H.264. A low computational deblocking filter with four modes is proposed, including three frequency-related modes (smooth modes, intermediate mode, and complex mode for low-frequency, mid-frequency, and high-frequency regions, respectively) and one special mode (steep mode for a large offset between two blocks). A mode decision procedure is also needed to decide which mode is given by observing pixel behavior around the block boundary. To take the masking effect of Human Visual System (HVS) into consideration, the filter for smooth mode is designed much stronger than that for complex mode, because the human eyes are more sensitive to smooth regions. Experimental results show that, in most cases, the proposed algorithm removes more blocking artifacts than MPEG-4 and H.264 deblocking filter, and improves both subjective and objective image quality. Also the proposed algorithm keeps the computation lower than MPEG-4 and is suitable for most block-based image and video coding systems.

CHAPTER 1 Introduction 1
CHAPTER 2 Introduction to Blocking Effect and Existing Deblocking Methods4
2.1 What is Blocking Effect 4
2.2 Existing Methods for the Reduction of Blocking Effect 6
2.3 Deblocking Method of Video Standards 7
2.3.1 MPEG-4 7
2.3.1.1 Overview of MPEG-4 Coding Technique 7
2.3.1.2 Intra-coded Frame 9
2.3.1.3 Inter-coded Frame 9
2.3.1.4 Deblocking Filter of MPEG-4 10
2.3.1.5 Default Mode 12
2.3.1.6 DC Offset Mode 13
2.3.2 H.264 14
2.3.2.1 Overview of H.264 Coding Technique 14
2.3.2.2 H.264 Codec 15
2.3.2.3 H.264 Encoder 16
2.3.2.4 H.264 Decoder 17
2.3.2.5 Inter Prediction 17
2.3.2.6 Intra Prediction 19
2.3.2.7 4×4 Intra Prediction Modes 19
2.3.2.8 16×16 Luminance Prediction Modes 21
2.3.2.9 Reconstruction Filter (Loop Filter) 21
2.3.2.10 Boundary Strength 23
2.3.2.11 Filtering of Boundaries with Bs=1,2, or 3 25
2.3.2.12 Filtering of Boundaries with Bs=4 26
CHAPTER 3 The Proposed Deblocking Algorithm 28
3.1 Observation 28
3.2 Overview of the Proposed Algorithm 29
3.3 Mode Decision Stage 31
3.4 Filtering Stage 33
3.4.1 Filter for Smooth Mode 33
3.4.2 Filter for Complex Mode 35
3.4.3 Filter for Intermediate Mode 37
3.4.4 Filter for Steep Mode 38
CHAPTER 4 Experimental Results 40
4.1 Assessment 40
4.2 Experimental Results of MPEG-4 Encoded Video 43
4.3 Experimental Results of H.264 52
CHAPTER 5 Conclusions and Future Works 57
REFERENCES 58
BIOGRAPHY 66

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