Fast Sub-pixel Motion Estimation for H.264

Abstract

Due to the variable block sizes and multi-reference frame used in the H.264/AVC standard; the motion estimation process becomes even more computationally intensive, resulting in a very low encoding speed. To overcome this low encoding speed, fast motion estimation algorithms such as UMHexagonS [1] and EPZS [2] have been proposed. Since the integer-pixel motion estimation speed has significantly decreased, the fractional or sub-pixel motion estimation speed is no longer non-negligible. We propose a fast sub-pixel motion estimation algorithm using an adaptive rood pattern based on the fractional motion vector of adjacent blocks and also a simplified small diamond search. Our algorithm is able to reduce the number of sub-pixel search points by more than 50%, while restricting the PSNR loss to less than 0.1 dB, compared to the hierarchical fractional pixel search.