Studies On Sub-pixel Motion Compensation Optimization

H. 264/AVC is published jointly by ITU-T VCEG and ISO/I EC MPEG. Compared with the previous standards, H. 264/AVC provides gain in compression efficiency over a wide range of bit rates and video resolutions, error robustness and network friendness. H. 264/AVC can be applied to nearly all fields of video communications such as wireless conversation, stream service over IP network, Digital Video Disk, and High Definition TV, etc. This new standard is widely concerned by companies and research groups, and the related papers and products are issued continuously. Sub-pixel motion compensation contributes the most coding gain, but it may increase great complexity both in computing and memory accessing. This paper focuses on optimization of sub-pixel motion compensation module in H. 264/AVC from these three aspects: complexity, coding efficiency, and VLSI architecture design. The main contributions are shown as following.(1)Low decoding complexity sub-pixel interpolation method: Sub-pixel motion compensation is adopted by H. 264/AVC, and one fourth sub-pixel precision motion vector is allowed in luma component. Compared with half-pixel precision motion vector and bilinear interpolation filter scheme, the 6-tap FIR interpolation and quarter pixel precision scheme improve compression efficiency by nearly 20%. On the other hand, the complexity both in memory accessing and computing is increased greatly. In the field of HDTV sequence decoding, motion compensation memory accessing is the main source of decoding delay and power consumption. Long tap filter and high precision motion vector make its computing and memory accessing load even heavier, which makes motion compensation become the bottleneck of decoding.This paper provides a Two-Step Four-Tap (TSFT) sub-pixel interpolation method based on the correlation analysis of the high def ination video sequences. And this method combines the cubic convolution interpolation function and cubic B spline interpolation method for he half-pixel and quarter-pixel interpolation. Athough The coding performance is still the same as the methods used for interpolation in H.264/AVC, the memory accessing and the computing complexity can be reduced by nearly 10% and 40% respectively in decoder.In October of 2003, TSFT has been adopted by China Audio Video coding Standards (AVS1.0).