臺灣博碩士論文加值系統

H.264是新一代的視訊編碼標準，其制定目的主要是為了在低位元率傳輸時能提供較高的影像品質。為了達到這個目的，H.264採用很多新的編碼技術來進一步壓縮視訊資料，但相對地，H.264也需付出相當高的編碼複雜度，使得編碼時間大幅增加，以至於難以達到即時的應用。
畫框內預測（intra prediction）是H.264新加入的編碼方法之一，它主要是利用自然影像空間域的關聯性（spatial correlation）來降低資訊冗餘量。然而，欲達到系統的最佳碼率-失真比（rate-distortion optimization: RDO），畫框內預測必須付出相當高的複雜度及編碼時間，以H.264的軟體測試平台JM 10.1而言，畫框內預測必須執行高達592次的RDO運算。因此，為了加速畫框內預測的編碼速度，近年來有相當多的研究與論文被發表，其中以Pan等學者於2005年所發表的演算法較著名，他們利用數位濾波器累積區塊內的預測方向以降低預測模式的運算數目，而此演算法也被納入H.264草案中。然而，Pan的演算法必須付出額外的的前處理時間導致無法達到即時編碼的要求。為了更進一步加速H.264的編碼時間，本論文提出一個新的快速演算法來加速畫框內預測的編碼速度。
我們提出利用區塊間關聯性（interblock correlation）的快速模式決策演算法作有效率的模式預測，並減少畫框內預測模式的測試數目。臨近四塊已編碼區塊的預測模式將優先作為待編碼區塊的測試模式，接著透過臨界值組合終止模式決策的流程來達到快速編碼的目的，論文中將臨界值組合區分為三個區間，分別定義為高R-D編碼效能（high R-D performance）、中R-D編碼效能（medium R-D performance）及低R-D編碼效能（low R-D performance）。實驗結果驗證本論文所提出的快速模式決策（fast mode decision）演算法的確可加速H.264的編碼速度。從實驗結果觀察，在高R-D編碼效能雖比原始RDO模式的畫面品質減少0.02 dB以下、位元率約增加11.15 Kbps，但編碼速度可比原始RDO模式加速1.95倍以上；在低R-D編碼效能，雖然畫面品質降低約0.09 dB、位元率增加90.37 Kbps，但編碼時間比原始RDO模式快3.1倍以上。

H.264 is the ITU-T’s newest video coding recommendation, which is also known as MPEG-4 Advanced Video Coding (AVC). The H.264 standard can achieve much higher coding efficiency than the previous standards such as MPEG-1/2/4 and H.261/H.263. This is mainly due to the fact that the H.264 encoder employs more complicated approaches in the coding procedure. One important approach is the technique of intra-prediction in the spatial domain. The H.264 standard exploits the directional spatial correlation between adjacent macroblocks (MBs) or blocks for intra prediction. In other words, the current MB/block is predicted by adjacent pixels in the upper and the left MBs/blocks that are previously decoded.
H.264 employs spatial intra prediction to achieve higher coding efficiency compared with existing video standards. Unfortunately, the performance gains of H.264 come at the cost in considerably increased complexity when RDO is adopted. According to the observation of intra prediction mode of any macroblocks/block and those of its four neighboring blocks from different real video sequences, we find that there are a high mode correlation exists in intramode map of H.264.
In this thesis, a fast intra-mode selection algorithm for H.264 that exploits the interblock correlation in the intra-mode domain is proposed to reduce computational complexity. Four modes of neighboring coded macroblocks/blocks are considered as the good candidate modes of the current block and terminated by threshold sets. The threshold sets are classified into three levels which are high R-D performance, medium R-D performance, and low R-D performance respectively. Experimental results show that the high R-D performance can speed up 1.95 times than JM 10.1 RDO with decreasing 0.02 dB in video quality and 11.15 Kbps increment in bitrate. On the other hand, the low R-D performance can speed up 3.10 times than JM 10.1 RDO with decreasing 0.09 dB in video quality and 90.37 Kbps increment in bitrate.

中文摘要i
英文摘要iii
誌謝v
目錄vi
圖目錄viii
表目錄x
第一章 緒論1
1.1 研究背景1
1.2 研究動機2
1.3 論文架構2
第二章 H.264編碼標準之畫框內預測演算法概述3
2.1 H.264簡介3
2.2 H.264編碼技巧簡介5
2.2.1 畫框間預測5
2.2.2 整數4×4離散餘弦轉換10
2.3 畫框內預測演算法11
2.3.1 畫框內預測模式介紹11
2.3.2 內插值的運算13
2.3.3 畫框內預測模式決策18
2.4 快速演算法之比較24
2.4.1 Pan演算法原理24
2.4.2 Pan畫框內預測演算法25
2.4.3 Pan演算法之實驗結果與討論30
第三章 H.264快速畫框內預測演算法36
3.1 原始決策流程改善36
3.2 畫框內預測模式相關性探討39
3.2.1 區塊模式分佈39
3.2.2 機率分析39
3.3 快速畫框內預測演算法43
3.4 臨界值的判定45
第四章 實驗結果與討論50
4.1 實驗條件50
4.2 實驗結果51
4.3 模式匹配度比較65
4.4 解碼影像分析65
第五章 結論72
參考文獻73

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