A Simple Way To Improve Perceived Quality Of Motion Compensated Prediction Images

Almost all current video codecs are of the hybrid type and thus use motion compensated prediction. The motion vectors are assigned to rectangular blocks rather than pixels, because vector search algorithms are rather calculation intensive and because transmitting vectors for all pixels requires a substantial bit rate all by itself. However, if we see the motion vectors we are willing to transmit as a sampling of an underlying motion vector eld, it is obvious that we can reconstruct this underlying eld better than by simply using the zeroth order approximation (block-wise constant assumption), which is generally taken. In this paper, a simple alternative for this block-wise constant assumption is made. Transmitted vectors are seen as samples of a rather smooth realistic motion eld. This assumes a more intelligent motion vector scheme than plain MAD. Vectors used for non sampling points are calculated by interpolation with vectors of neighboring blocks. Interpolation is done so that the transition between block boundaries is made as continuous as possible. This is achieved by a simple second order surface matching. To prove the validity of the scheme, several simulations were done. First, the perceived visual quality of the motion compensated prediction was evaluated. The scheme results in visually more acceptable predicted images, as their characteristic blocky appearance is greatly reduced. Secondly, the signal to noise ratio of the prediction was compared. Dierences with the standard scheme are relatively small, and in either direction. Finally, a complete codec was tested with both predictions schemes.