A low bit-rate video codec based on two-dimensional mesh motion compensation with adaptive interpolation
Visual communication over low bandwidth channels, such as the telephone line, requires high compression. Motion estimation and compensation techniques play an important role in achieving high compression by reducing the temporal redundancy inherent in video sequences. Current video coding standards employ the block-matching algorithm to perform motion estimation that produces visually annoying blocking artifacts at low bit-rate. In contrast, 2-D mesh motion compensation produces blocking free prediction by generating a smooth full motion field from the set of node motion vectors using spatial interpolation. However, the assumption of a globally smooth motion field is not valid for most natural occurring scenes, where motion discontinuities exist due to moving objects. We propose a post-processing scheme that refines the set of node motion vectors obtained by the 2-D mesh motion estimation. The approach is to selectively break the smoothness constraint of 2-D mesh for patches that contain motion boundaries by changing the interpolation patterns. Experimental results show improvements in both PSNR and perceptual quality over the 2-D mesh motion compensation and a block-based standard video-coding standard H.263.