Motion-Compensated Wavelet Transform Coding for Color Video Compression

A video compression scheme based on the wavelet representation and multiresolution motion compensation (MRMC) is presented in this paper. The multiresolution/multifrequency nature of the discrete wavelet transform is an ideal tool for representing images and video signals. Wavelet transform decomposes a video frame into a set of subframes with different resolutions corresponding to different frequency bands. These multiresolution frames also provide a representation of the global motion structure of the video signal at different scales. The motion activities for a particular subframe at different resolutions are different but highly correlated since they actually specify the same motion structure at different scales. In the multiresolution motion compensation approach, motion vectors in higher resolution are predicted by the motion vectors in the lower resolution and are refined at each step. In this paper, we propose a variable block-size MRMC scheme in which the size of a block is adapted to its level in the wavelet pyramid. This scheme not only considerably reduces the searching and matching time but also provides a meaningful characterization of the intrinsic motion structure. The variable block-size MRMC approach also avoids the drawback of the constant-size MRMC in describing small object motion activities. After wavelet decomposition, each scaled subframe tends to have different statistical properties. An adaptive truncation process was implemented and a bit allocation scheme similar to that In the transform coding is examined by adapting to the local variance distribution in each scaled subframe. Based on the wavelet representation, variable block-size MRMC approach and a uniform quantization scheme, four variations of the proposed motion-compensated wavelet video compression system are identified. It is shown that the motion-compensated wavelet transform coding approach has a superior performance in terms of the peak-to-peak signal-to-noise ratio as well as the subjective quality.