Motion estimation with multiple matching criteria

Abstract

Block-based motion estimation is the method of choice in most video codecs to exploit temporal redundancy for compression. Since true rate-distortion evaluation for every candidate block is usually impractical, simple estimates are used instead as a matching criterion, e.g., the Sum of Absolute Differences (SAD) between the target and the candidate blocks weighted by its respective motion vector cost in bits. We show that different matching criteria may differ not only in the quality of the resulting motion estimation but may actually offer diverse motion estimates that can be locally selected to better suit the local data characteristics. As a proof of concept, we propose the Double Matching Criteria Algorithm (DMCA), a two-pass algorithm which performs two independent motion estimations for each block with different matching criteria and then locally selects the better one in a true rate-distortion sense. The algorithm is easily parallelizable and out-of-the-box compliant to any coding standard with support for block-based motion compensation. We also propose the Total Absolute Deviation from the Mean (TADM) as a matching criterion to be used along with the SAD in the DMCA framework. Unlike the SAD, which measures the size of the residue in a sense, the TADM is a measure of its dispersion. For demonstration purposes, we implemented the DMCA with the SAD and the TADM as matching criteria in a modified HM reference software encoder for the HEVC standard. We observed significant BD-rate gains with a fully compliant HEVC stream.