<title>Overlapped block motion compensation</title>

Abstract

Block motion compensation is a critical component of most efficient video compression algorithms. Applications range from real-time low bit rate teleconferencing codecs to moderate and high bit-rate coding standards currently being considered for CD-ROM video storage and packet video. Recent research has suggested that blocking artifacts can be reduced by applying block motion compensation on overlapped blocks in image frames. In this paper, we formulate overlapped block motion compensation as an optimal linear estimator of pixel intensities given the neighboring block motion estimate in the frame. Applying this framework, we propose a procedure for designing optimal windows for overlapped block motion compensation. When applying block motion compensation with overlapped blocks, the optimal motion vector to apply at each block in an image depends on values of motion vectors in a non-causal neighborhood of that block. Thus, unlike for standard block-based compensation, optimal motion estimates cannot be computed with exhaustive search block- matching algorithms, even with the overlap window incorporated. Instead, we defined a simple iterative procedure for computing optimal motion estimates for overlapped block motion compensation. The performance gains achieved by both optimal motion estimation and optimal overlapped windows are demonstrated in simulations. Together, reductions of up to 30% in displaced frame difference energy are demonstrated compared with standard block motion compensation.