在這篇論文裡，我們提供了兩種有效率的內部模式決策演算法。其一是使用影像內容中的影像結構張量，也就是區域性區塊梯度特徵。從影像結構張量，我們可以決定方向性模式，那最可以去表示在一個區塊中最主要的邊緣。在找出可能的方向性的模式後，我們只要拿這些模式當作我們在編碼現在區塊中的備用模式去改善內部模式決策中的運算複雜度。第二種方法是架構在假設給定它的簡易梯度特徵和它鄰近區塊的內部模式中去學習現在要編碼區塊的內部模式的模式環境機率。基於環境機率，我們可以在已給定的鄰近模式和現在區塊的影像梯度特徵中，決定最可能的內部模式。同樣地，我們取這些模式當作我們在編碼現在區塊中的備用模式。除此之外，最後我們使用模式交集的想法去整合上述兩種方法。在實驗中我們可以看到我們的演算法與其它先前的內部模式決策演算法比較起來可以有效地在可忽略的影像損失和較少的位元率增加以達到減少運算複雜度的效果。

In this thesis, we propose two efficient intra mode decision algorithms. One uses the image structure tensor, the local block gradient feature for image content. From the image structure tensor, we can determine the candidate directional modes that are most possible for representing the main edge direction in a block. After we find out the possible directional modes, we can just take these modes as our candidate modes for encoding the current block to improve the intra mode decision computation complexity. The second proposed algorithm is based on learning the mode conditional probability for the encoded intra mode for the current block given its simple gradient features and the encoded modes of its neighboring blocks. Based on this conditional probability, we can determine the most possible intra modes given the condition of the neighboring modes and the image gradient features of the current block. Similarly, we take these modes into our candidate modes for encoding the current block. In addition, we use the idea of intersection of candidate modes for combining these two proposed algorithms. Experimental results show our algorithms can efficiently reduce the computation complexity with negligible quality loss and with less bitrate increase compared to other previous intra mode decision algorithms.

[1] ITU-T Rec. H.264/SO/IEC 11496-10, ”‘Advanced Video Coding”, Final Committee Draft, Document IVT F100, December 2002.
[2] F. Pan, X. Lin, S. Rahardja, K. P. Lim, Z. G. Li, D. Wu, and S. Wu, “Fast Mode Decision Algorithm for Intraprediction in H.264/AVC Video Coding,” IEEE Trans. Circuits Systems for Video Technology, Vol. 15, No. 7, pp. 813-822, July 2005
[3] J.-F. Wang, J.-C. Wang, J.-T. Chen, A.-C. Tsai, and A. Paul, “A Novel Fast Algorithm for Intra Mode Decision in11.264/AVG Encoders,” Proc. IEEE Intern. Symp. Circuits and Systems, CD-ROM, May 2006.
[4] C.-C. Cheng and T.-S. Chang, “Fast Three Step Intra Prediction Algorithm for 4x4 blocks in H.264,” Proc. IEEE Intern. Symp. Circuits and Systems, Vol. 2, pp. 1509 – 1512, May 2005
[5] Yu-K. Lin and T.-S. Chang, “Fast Block Type Decision Algorithm for Intra Prediction in H.264 FRext,” IEEE Intern. Conf. Image Processing, Vol. 1, pp. I - 585-8, Sep 2005.
[6] J.-W. Chen, C.-H. Chang, C.-C. Lin, Yi-H. Ou Yang, J.-In Guo, and J.S. Wang, “A Condition-based Intra Prediction Algorithm for H.264/AVC,” IEEE Intern. Conf. Multimedia and Expo, pp. 1070-1080, July 2006.
[7] C.-C. Wang, T.-S. Chen and C.-W. Tung, “Fast Intra-Mode Decision in H.264 Using Interblock Correlation,” IEEE Intern. Conf. Image Processing, pp. 1345-1348, Oct 2006.
[8] J. Yang, B. Yin, Y. Sun and N. Zhang, “A Block-Matching Based Intra Frame Prediction for H.264/AVC,” IEEE Intern. Conf. Multimedia and Expo, pp. 705-708, July 2006.
[9] Y.-W. Huang, B.-Y. Hsieh, T.-C. Chen, L.-G. Chen, “Analysis, fast algorithm, and VLSI architecture design for H.264/AVC intra frame coder,” Vol. 15, Issue 3, pp. 378-401, March 2005.
[10] JVT Reference Software JM10.2
http://iphome.hhi.de/suehring/tml/download/old_jm/jm10.2.zip
[11] G. Bjontegaard, “Calculation of average PSNR differences betweenRD-curves,” presented at the 13th VCEG-M33 Meeting, Austin, TX, 2001.