A novel fast block motion estimation algorithm based on combined subsamplings on pixels and search candidates

Block motion estimation is one of the key technologies in video compression and has been widely adopted by several existing international standards of video coding. Many popular block motion estimation methods, including three-step search (TSS), new three-step search, and four-step search, have assumed that the error surface is unimodal over the search area or the motion vector is center-biased. However, these assumptions do not hold for most MPEG-1,2 video frames. As a result, schemes with these assumptions will exhibit degraded performance as they are applied to MPEG-1,2 video frames. In this paper, we propose a novel fast block motion estimation scheme based on an integration of pixels subsampling and search candidates subsampling. Compared with the well-known TSS algorithm, the proposed scheme visits more candidates so that it can significantly avoid being trapped into the local minima and therefore is more robust. Experimental results using typical MPEG-1 video frames show that the proposed algorithm can achieve better PSNR as well as higher speed-up ratios than the well-known TSS. In addition, the combined sub-sampling scheme has a regular structure that facilitates easy hardware implementation.