Abstract
The state-of-the-art video coding standard H.264/AVC achieves significant coding performance by adopting variable block sizes for motion estimation (ME) and mode decision. However, this technique brings out high computational complexity since the optimal mode is determined by exhaustively performing rate-distortion optimization (RDO) on each coding mode with different block sizes. In this paper, the fast intermode decision algorithm is proposed to reduce the computational complexity. Based on the high correlation between the residual error of ME and the optimal block size, general residual complexity (GRC) and local residual complexity (LRC) are defined. According to MB activity evaluated on GRC and LRC, candidate intermodes are determined and RDO processes are only performed on selected intermodes. The experimental results demonstrate that the proposed algorithm achieves time saving by 63% on average with negligible degradation of coding efficiency.
Highlights
The state-of-the-art video coding standard H.264/AVC [1] was developed by the Joint Video Team of ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group
Computational complexity increases with these tools, especially by several block sizes for motion estimation (ME) and mode decision [3]
In rate-distortion optimization (RDO), after the rate-distortion cost (RDcost) of each coding mode is calculated, the mode with the minimum RDcost is selected as the optimal mode
Summary
The state-of-the-art video coding standard H.264/AVC [1] was developed by the Joint Video Team of ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group. Zeng et al [13] proposed a method to select the candidate modes according to motion activity, generated by the MVs of spatially and temporally nearby MBs. Liu et al [14] proposed an efficient intermode decision algorithm based on motion homogeneity evaluated on a normalized MV field, as determined by the MVs from ME of 4 × 4 block. To determine MB activity, GRC and LRC are proposed based on the observation that smaller block sizes are likely to be selected as the optimal mode in MB with high residual error of ME. Since LRC is obtained in the process of ME for 16 × 16, additional computation is not needed These features contribute to the performance improvement for all sequences including ones with high motion or detailed regions.
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