An analysis and efficient implementation of half-pel motion estimation

Subpixel motion compensation has become a main ingredient in many modern video compression standards due to its ability to provide accurate motion prediction. To obtain fine motion vector accuracy, video encoders incorporate a motion estimation process at the subpixel level. This process is generally limited to a small area around the integer pixel motion vector in order to keep complexity small. This paper proposes an efficient motion estimation method for video encoders to generate 8×8 half-pel motion vectors. By reusing the matching costs from a previous motion estimation task, the proposed method selectively ignores redundant candidate vectors that have already been searched, thereby reducing complexity without sacrificing search quality. An analysis of the redundancy is presented and simulation results are reported which show promising reductions in the number of 8×8 search point positions. Although this paper focuses on a specific problem of half-pel motion estimation for 8×8 blocks, the approach can be generalized for efficient motion estimation for other block sizes, pixel resolutions and search ranges.