使用HEVC預測單元殘差值之分佈狀態降低編碼樹遞迴運算複雜度

HEVC CU Mode Early Termination using PU Residual Distributions

鄒其展(Chi-Chan Chou)

指導教授 ： 林鼎然

中原大學/電機資訊學院/電子工程研究所/碩士(2015年)

https://doi.org/10.6840/CYCU.2015.00488

摘要

高效率視訊編碼(HEVC)利用四元樹分割結構的CU(編碼單位)特性，以應對更多可能性的偵間偵內預測區塊尺寸大小。為了找到最佳的CU深度而進行徹底全搜尋的複雜度是非常高的，這將導致實時傳輸上的一大困難。在本文提出的方法中，利用PUs(預測單元)產生的殘差值所屬之編碼CU進行統計，目的是觸發CU四元樹遞迴提早終止。且從參考殘差值分佈直方圖所設計出最佳的ET(提早終止) zone，若PU殘差值運算結果落在ET zone當中，ET將會被觸發。目前ET zone所有參數都已經達成最佳化，是由查表以及外插法兩種方式進行判定。此外還有兩種利用相鄰SKIP模式資訊所提出的ET，主要是使用HEVC當中的鄰近CU是否為SKIP模式作為判斷條件。在有意義的使用鄰近SKIP模式資訊下，這兩種方法不僅實現優良的時間節省，甚至與HM相比更降低了位元率。靠著基於殘差值的ET演算法則又可以更進一步的提升時間節省效果，本文將上述以殘差值以及SKIP資訊為基礎的演算法與其他最先進的方法做結合。實驗結果表明在PSNR略有0.06 dB掉落，在編碼時間上可以節省平均達57%，領先其他現有方法達14%，此外提出的方法只有1.1%的位元率增幅同樣贏過該方法達0.5%。

關鍵字：HEVC (高效率視訊編碼)， CU (編碼單元) 遞迴提早終止， ET演算法 (Early-termination algorithm)，殘差值分佈 (Residual distribution)，SKIP 模式。

關鍵字

高效率視訊編碼

並列摘要

High Efficiency Video Coding (HEVC) utilizes a quadtree-structured CU (coding unit) for more possible sizes of basic blocks for later　INTER/INTRA prediction. The exhaustive search for optimal CU depth requires high complexity, which causes difficulties for real-time streaming. In the proposed method, we make use of the residual statistics of PUs (prediction units) in the current encoded CU to make a decision on CU early termination. The residual histogram is discussed, and the optimal ET (early termination) zone is designed; if the PU residual statistics fall in the ET zone, the early termination is triggered. The　optimal parameters for the ET zone are solved, and can be used by table lookup or extrapolation in the testing stage. Two other early terminations using the neighboring SKIP information are also proposed. We use SKIP information from more meaningful CU neighbors defined and used in HEVC. These two methods not only achieve great time saving but also even reduce the bitrate in all cases compared with HM software due to the meaningful use of neighboring SKIP information. The residual-based method has further improvement in time saving. We combine the proposed residual-based and SKIP-based algorithm with a state-of-the-art method. The experimental results show that with a slight loss in PSNR by 0.06dB, the encoding time reduction of our design can be as high as 57% on average, outperforming the existing work by 14%. Furthermore, we only increase bitrates by 1.1% from HM, which is better than the existing work by 0.5%.

並列關鍵字

HEVC

參考文獻

[2] T. Wiegand, J. R. Ohm, G. J. Sullivan, W.-J. Han, R. Joshi, T. K. Tan, and K. Ugur, “Special section on the joint call for proposals on high efficiency video coding (HEVC) standardization,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 20, pp. 1661- 1666, January 2010.

[3] B. Bross, W.-J. Han, J.-R. Ohm, G. J. Sullivan, and T. Wiegand, “ JCTVC- J1003: High efficiency video coding (HEVC) text specification draft 8,” 2012.

[5] Y. Zhang, H. Wang, and Z. Li, “Fast coding unit depth decision algorithm for interframe coding in HEVC,” Data Compression Conference (DCC), 2013.

[6] G. Correa, P. Assuncao, L. Agostini, and L. A. Cruz, “Coding tree depth estimation for complexity reduction of HEVC,” Data Compression Conference (DCC), 2013.

[8] H. L. Tan, F. Liu, Y. H. Tan, and C. Yeo, “On fast coding tree block and mode decision for high-efficiency video coding (HEVC),” IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2012.