Very low bit-rate video coding using matching pursuits

The term matching pursuits refers to a greedy algorithm which matches signal structures to a large, diverse dictionary of functions. The technique was proposed by Mallat and Zhang with an application to signal analysis. In this paper, we show how matching pursuits can be used to effectively code the motion residual in a hybrid video coding system at bit rates below 20 kbit/s. One advantage of this technique at low bit rates is that bits are assigned progressively to high energy areas in the motion residual. The proper choice of a dictionary set can lead to other advantages. For instance, a large dictionary with a wide variety of structures can represent a residual signal using fewer coefficients than the DCT basis. Also, a dictionary which is not block-based can reduce block distortions common to low bit rate DCT systems. Experimental results are presented in which the DCT residual coder from a standard coding system is replaced by a matching pursuit coder. These results show a substantial improvement in both PSNR and perceived visual quality. Further improvements result when the matching pursuit coder is paired with a smooth motion model using overlapping motion blocks.