Motion-Compensated Temporal Filtering and Motion Vector Coding Using Biorthogonal Filters
This paper investigates 3-D subband coding via motion-compensated temporal filtering (MCTF) using biorthogonal filters. While nonoverlapping Haar filter-based MCTF has a fixed size group of pictures (GOP) structure, for longer filters we need to use extensions at the GOP ends resulting in coding efficiency loss and/or significant peak signal-to-noise (PSNR) variation. We solve this problem by introducing a "sliding window" approach to MCTF. While we find the longer filters have higher coding gain and significant PSNR improvement at high bit rates, a necessary doubling of the number of motion vectors (MVs) causes a drop in PSNR at lower bit rates. The paper then concentrates on improving the efficiency of both the MV estimation and compression. We employ the MV estimate at higher temporal resolutions as the starting point for local MV refinement at the present temporal resolution thereby reducing the complexity of motion search and obtaining a more uniform motion field. We improve MV coding performance by adapting the context-based binary arithmetic coder (CABAC) from H.264. Instead of encoding MV residuals along a quadtree scanning path, we reduce the MV bit rate by prediction from both neighboring MV blocks and blocks in the previous or the next lower temporal level. Our proposed motion estimation and coding schemes can reduce the MV bit rate by 10%-20% for Haar and 15%-30% for 5/3 MCTF