Fast directional search algorithm for fractional pixel motion estimation for H.264 AVC

Fractional pixel motion estimation (ME) is required to achieve more accurate motion vectors and higher compression efficiency. This results in an increase in the computational complexity of the ME process because of additional computational overheads such as interpolation and fractional pixel search. Fast algorithms for fractional ME in H.264/AVC are presented. To reduce the complexity of fractional pixel ME, unimodal error surface assumption is used to check only some points in the fractional pixel search window. The proposed algorithm employs motion prediction, directional quadrant and point-based search pattern and early termination to speed up the process. Hence, the proposed algorithm efficiently explores the neighborhood of integer pixel based on high correlation that exists between the neighboring fractional pixels and unimodal property of error surface. The proposed search pattern and early termination reduce computational time by almost 8% to 18% as compared to the hierarchical fractional pixel algorithm employed in the reference software with a negligible degradation in video quality and negligible increase in bit rate.