本論文針對H.264/AVC的內部預測編碼方式，提出數個演算法來改善其效能。首先提出一個快速決定編碼模式的機制來減少運算的複雜度。藉由圖像的邊界資訊，就可以達到這個目的。而這些邊界資訊，只須經由部份的轉換係數即可求得，藉此來減少編碼器的計算量。實驗證明我們所提出的演算法，只要損失少許PSNR的品質，可以縮短許多編碼時間。
其次，當H.264在執行CAVLC時，必須先將二維的係數掃描成一維。我們提出一種適應性的掃描方式來改變傳統的zig-zag掃描。這種方式是根據不同的內部預測模式來採用不同的掃描次序。藉由分析預測編碼後的殘值，我們發覺不同內部預測模式會造成殘值有不同的統計特性。所以，透過馬可夫模型的應用，可以推導出適當的掃描次序。實驗證明，我們所提出的方法，確實可以提高編碼效能。
第三，針對無失真編碼，我們也提出取代zig-zag掃描的方法。H.264/AVC無失真編碼可以利用DPCM的方式來完成。針對DPCM的編碼方式，採用統計每一個係數的平均能量。藉由能量的排序，來決定不同內部預測模式的掃描次序。
最後，我們提出一個稱之為以條件區塊及內文為基礎的算術編碼(BCAE)方式，來提升形狀編碼(Shape Coding)的效能。藉由條件機率模型的建立，形狀編碼採用CAE方法的壓縮效果可以有效的提升。我們可以將BCAE用在H.264/AVC的視訊物件編碼應用上。實驗證明，我們所提出的BCAE比MPEG-4標準的CAE還要更好。

In this dissertation, we propose several coding algorithms to improve the coding efficiency for intra-prediction coding scheme defined in H.264/AVC. First, a fast mode decision method for intra-prediction is proposed to reduce the computational complexity of H.264/AVC encoders. With edge information, we propose a novel fast estimation algorithm for mode selection, where the edge direction of each coding block is detected from only part of the transformed coefficients. Hence, the computation complexity is greatly reduced. Experimental results show that the proposed fast mode decision method can efficiently reduce the encoding time for all test sequences with acceptable degradation of PSNR and bitrates.
Secondly, instead of traditional zig-zag scan when performing CAVLC in H.264, an adaptive scan method is proposed, which uses the best fitted scan order for each intra-prediction mode. In H.264/AVC, the residuals after various intra-prediction modes have different statistical characteristics. After analyses of the transformed residuals, we derive an adaptive scan order scheme based on Markov model, which could match up with the intra-prediction mode, to further improve the efficiency of intra coding. Simulation results show that the proposed adaptive scan scheme can aid the context-adaptive variable length coding (CAVLC) to achieve better rate-distortion performances in H.264/AVC video coders. When the zig-zag scan order is replaced with the derived adaptive scan order, the coding performance can be improved with PSNR increased and no extra bits required.
Thirdly, for lossless intra coding included in H.264/AVC FRExt, the so-called fidelity range extension, we propose an adaptive scan order method to improve the coding efficiency. In image/video coding standards, the zig-zag scan, which transfers the coefficients of a two-dimensional transformed matrix from low-frequency to high-frequency components, successfully help to achieve an effective entropy encoder. Generally, the optimal scan of two-dimensional residual samples should be scanned in the descending order of their statistically-averaged power levels such that we can achieve more efficient variable length coding. For H.264/AVC with sample-wise DPCM lossless intra coding, which is included in the FRExt, the so-called fidelity range extension, the residuals after different directional prediction modes should have different statistical characteristics. After analyzing the power of the residuals, an adaptive scan order method to optimally match up with each intra-prediction mode for improving coding efficiency is proposed.
Finally, an efficient shape coding scheme, called block-conditioned context-based arithmetic-encoding (BCAE) is proposed to improve the coding efficiency of video object shape coding. By performing simple block detection, we first setup an efficient conditional source model in a block-by-block fashion and then derive the probability modes based on context-based arithmetic-encoding (CAE), by training various test video sequences. CAE is an efficiency coding scheme defined in MPEG-4 shape coding, and could be exploited by H.264/AVC for the applications of video object coding. With re-trained probability tables derived by our proposal, the coding efficiency of the proposed BCAE algorithm is better than that of the standardized CAE.

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