臺灣博碩士論文加值系統

在有限的網路頻寬和資料位元率下，為了得到較佳的視覺品質而增加頻寬或要求較高的位元率通常是困難而且代價昂貴的。對壓縮後的視訊做後處理(Post-processing)的方法似乎是較有效的解決方案，而且也不會更動現有的視訊編碼標準。換言之，如果視訊經過壓縮所產生的方塊效應雜訊能夠有效的抑制，我們能以更低的位元率壓縮此視訊，或是在相同的位元率下能夠得到更好的影像品質。
在本篇論文中，依據重建視訊影像中8 ×8方塊邊緣附近像素變化的情形，我們提出去除方塊效應(deblocking)演算法來減低視訊壓縮後視覺品質的不適。藉由考慮人類視覺系統(HVS)中的遮蔽效應對方塊效應的影響，在去除方塊效應處理中適應性區分為三種不同情況。此去除方塊效應的方法針對不同特性的方塊效應運用了三種不同處理，包含了平滑區域(smooth region)、複雜區域(complex region)和介於前面兩者的中間區域(intermediate region)。經由適合邊緣區域特性的去除方塊處理，視覺上的品質以及客觀上的評量(PSNR)都能獲得改善，同時能夠避免在影像特性複雜的區域產生過度的模糊或是在平滑區域中方塊效應去除的不夠理想。最後，根據實驗之PSNR數據的比較，此去塊效應的方法均比MPEG-4和H.26L表現佳，同時視覺上的品質也達到顯著的改善。

Increasing the bandwidth or bit rate in real-time video application to obtain better images quality is usually not possible or too costly. Post-processing appears to be the most practical solution because it does not require any change to existing standards. If the blocking effects can be significantly reduced, higher compression ratios at the same image quality or better quality at the same compression performance can be achieved.
In this Thesis, we proposed a deblocking algorithm based on three filtering modes in terms of the activity across block boundaries. By given proper consideration of the masking effect of the HVS (Human Visual System), an adaptive filtering decision is integrated into deblocking processing. Based on three different deblocking modes appropriate for the characteristic of local region, the perceptual quality as well as the objective quality is improved without over smoothing the image details and insufficient reducing the strong blocking effect on flat region. According to the simulation results, the proposed method shows better performance than those deblocking methods by H.26L and MPEG-4 in terms of PSNR. Noticeable perceptual improvements of image quality are achievable.

LIST OF TABLES i
LIST OF FIGURES ii

CHAPTER 1 Introduction 1
CHAPTER 2 Introduction to Video Coding and Blocking Effect 4
2.1 What is Blocking Effect 4
2.2 Existing Methods for the Reduction of Blocking Effect 5
2.3 Deblocking Method of Video Standards 7
2.3.1 H.263+ 7
2.3.2 H.26L 15
2.3.3 MPEG-4 21
CHAPTER 3 The Proposed Deblocking Algorithm 29
3.1 An Overview of the Proposed Deblocking Algorithm 29
3.2 Observation 32
3.3 Mode Decision 35
3.4 Deblocking for the Smooth Region 38
3.5 Deblocking for the Complex Region 42
3.6 Deblocking for the Intermediate Region 46
CHAPTER 4 Experimental Results 49
4.1 Experimental Environment 49
4.2 Experimental Results of the H.26L 50
4.3 Experimental Results of the MPEG-4 57
CHAPTER 5 Conclusions and Future Works 62
REFERENCES 63
PUBLICATION LIST 65
BIOGRAPHY 66

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