Hierarchical backward motion compensation for wavelet video coding using optimized interpolation filters
We describe a spatially scalable video coding framework in which motion correspondences between successive video frames are exploited in the wavelet transform domain in a purely backward fashion. The basic motivation for our coder is that motion fields are typically smooth and therefore can be efficiently captured through a multiresolutional framework. A wavelet decomposition is applied on each video frame and the coefficients at each level are predicted from the coarser level through backward motion compensation. To remove the aliasing effects caused by downsampling in the transform, a special interpolation filter is designed with the weighted aliasing energy as part of the optimization goal, and motion estimation is carried out with lowpass filtering and interpolation in the estimation loop. A novel adaptive quantization scheme is then applied to code the motion predicted residue wavelet coefficients in each band. Experimental results reveal typically a 0.5-2 dB increase on coded PSNR at 24-48 kb/s over the state-of-the-art H.263 standard, with also a considerable improvement in subjective reconstruction quality.