An Effective CU Size Decision Method for HEVC Encoders

• Published in: IEEE transactions on multimedia Vol. 15; no. 2; pp. 465 - 470
• Main Authors: Shen, Liquan, Liu, Zhi, Zhang, Xinpeng, Zhao, Wenqiang, Zhang, Zhaoyang
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2013; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithm design and analysis; Algorithmics. Computability. Computer arithmetics; Algorithms; Applied sciences; Artificial intelligence; Coders; Coding; Coding, codes; Complexity; Computation; Computer science; control theory; systems; Correlation; CU size decision; Encoders; Encoding; Exact sciences and technology; HEVC; Information, signal and communications theory; Materials; Mathematical models; motion estimation; Pattern recognition. Digital image processing. Computational geometry; Prediction algorithms; Signal and communications theory; Skips; Studies; Telecommunications and information theory; Theoretical computing; Video coding; Video coding; Motion estimation; Termination problem; Rate distortion theory; HEVC; Computational complexity; Modeling; Depth of field; Lagrange multiplier; Image coding; Efficiency; Homogeneity; CU size decision; Fast algorithm; Quad tree
• DOI: 10.1109/TMM.2012.2231060
• ISSN: 1520-9210

The emerging high efficiency video coding standard (HEVC) adopts the quadtree-structured coding unit (CU). Each CU allows recursive splitting into four equal sub-CUs. At each depth level (CU size), the test model of HEVC (HM) performs motion estimation (ME) with different sizes including 2N × 2N, 2N × N, N × 2N and N × N. ME process in HM is performed using all the possible depth levels and prediction modes to find the one with the least rate distortion (RD) cost using Lagrange multiplier. This achieves the highest coding efficiency but requires a very high computational complexity. In this paper, we propose a fast CU size decision algorithm for HM. Since the optimal depth level is highly content-dependent, it is not efficient to use all levels. We can determine CU depth range (including the minimum depth level and the maximum depth level) and skip some specific depth levels rarely used in the previous frame and neighboring CUs. Besides, the proposed algorithm also introduces early termination methods based on motion homogeneity checking, RD cost checking and SKIP mode checking to skip ME on unnecessary CU sizes. Experimental results demonstrate that the proposed algorithm can significantly reduce computational complexity while maintaining almost the same RD performance as the original HEVC encoder.