Fast Motion Estimation and Intermode Selection for H.264
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Fast Motion Estimation and Intermode Selection for H.264 Byeong-Doo Choi, Ju-Hun Nam, Min-Cheol Hwang, and Sung-Jea Ko Department of Electronics Engineering, Korea University, Anam-Dong, Sungbuk-Ku, Seoul 136-701, South Korea Received 1 August 2005; Revised 5 June 2006; Accepted 11 June 2006 H.264/AVC provides various useful features such as improved coding efficiency and error robustness. These features enable mobile devices to adopt H.264 standard to achieve effective video communications. However, the encoder complexity is greatly increased mainly due to motion estimation (ME) and mode decision. In this paper, we propose a new scheme to jointly optimize intermode selection and ME using the multiresolution analysis. Experimental results show that the proposed method is over 3 times faster than other existing methods while maintaining the coding efficiency. Copyright © 2006 Byeong-Doo Choi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Recent advances in wireless communication technology have introduced various mobile services such as multimedia message services, video on demand, and mobile video communications. Especially, there are increasing demands on mobile video communications with prevailing demands of the mobile devices equipped with camera module. To realize this service, video sequences have to be compressed with high coding efficiency and error robustness. The H.264/AVC is the state-of-the-art video compression standard recently developed by the ITU-T/ISO/IEC Joint Video Team [1]. The H.264/AVC provides various useful features such as improved coding efficiency, error robust data partitioning, and network friendliness with the network abstraction layer (NAL). These features enable mobile devices to adopt the H.264/AVC standard to achieve effective video communications [2]. H.264/AVC supports multiple reference frames and various block sizes for ME. It uses tree-structured hierarchical macroblock (MB) partitions. There are 7 different block sizes (16 × 16, 16 × 8, 8 × 16, 8 × 8, 8 × 4, 4 × 8, and 4 × 4 blocks) that are used in a macroblock. The current H.264/AVC reference software is based on a rate-distortion optimization (RDO) framework for both ME and mode decision. Among all modules in the H.264/AVC encoder, ME and mode decision require a heavy computation, especially when RDO is used. ME has to be performed for every MB coding mode to find the best matching block. For mode decision, all possible combinations of coding modes are considered to obtain the MB with minimum cost. Moreover, since these
operations are performed in multiple reference frames, the computational load significantly increases at the encoder. The computational burden of ME can be reduced by applying fast ME methods, such as the three-step search [3], the four-step search [4], the diamond search [5], and the hexagon search [6]. Recently, uneven multihex
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