H.264/AVC視頻編碼標準比以往的標準，如MPEG-2, MPEG-4, 以及H.263，編碼效率有顯著的提高。為增進編碼效率，H.264/AVC編碼器在畫面內編碼上運用了多種的預測模式以採用及率失真優化(RDO)來決定最佳的模式。因為編碼器要運算所有可能的模式，運算的複雜度也隨之劇烈地增加。 本研究針對在H.264/AVC中的畫面內編碼減少運算複雜度，提出階層式高效率畫面內編碼演算法。該演算法共有四個主要部分，即1.快速的畫面內過濾決策;2.基於量化的區塊大小選擇決策;3.基於方向的預測模式決策;與4.快速的畫面內部分過濾決策。 本研究的實驗結果顯示階層式高效率畫面內編碼演算法，其低解析的視訊編碼中可達到平均85%以上的時間節省，在高解析的視訊編碼中可達到平均90%以上的時間節省，同時在品質下降方面是可被忽略的，在編碼長度的上昇是非常微小的。 The H.264/AVC video coding standard can achieve higher coding efficiency than any other previous coding standards, such as MPEG-2, MPEG-4, and H.263. In order to improve the coding efficiency, the H.264/AVC encoder employs various prediction modes in the intra coding and adopts the rate-distortion optimization (RDO) method for selection of an optimum mode. Since the encoder computes the rate-distortion (RD) costs of all possible coding modes to decide the optimum mode, the computational complexity is dramatically increased. In this study, an efficient hierarchical approach which consists of the four algorithms: 1) fast intra skip decision; 2) quant-based block size selection decision; 3) direction-based prediction mode decision; and 4) fast partial intra skip decision for H.264/AVC intra encoding is proposed to reduce the computational complexity. Our experimental results have shown that the proposed algorithms outperform the previous methods. Our overall algorithm can significantly reduce above 85% encoding time for low-resolution video sequences on average, and reduce above 90% encoding time for high-resolution video sequences on average, while the PSNR degradation is negligible and the bit rate increment is minimal.
