Adaptive search range algorithms for variable block size motion estimation in H.264/AVC

Comparing with search pattern motion estimation (ME) algorithms, adaptive search range (ASR) algorithms are more fundamental, regular and flexible. In variable block size motion estimation (VBSME), ASR algorithms can be applied whether on a whole frame (frame level), or on an entire macroblock which includes up to forty-one blocks (macroblock level), or just on a single block (block level). In the other hand, in H.264/AVC, not the motion vectors (MVs) but the motion vector differences (MVDs) are coded and the median motion vector predictors (median-MVPs) are used to place the search centers. In this sense, it can be thought that the search windows (SWs) are centered at the positions pointed by median-MVPs, the search ranges (SRs) play the role of limiting MVDs. Thus it is reasonable for considering using MVDs to predict SRs. In this paper, one of the MB level and two of the block level, at all three MVD based SR prediction algorithms are proposed. VBSME based experiments are carried out to assess the proposed algorithms. Comparisons between the proposed three algorithms and the previously proposed one given in [8] are done in terms of encoding quality and computational complexity.