Matching pursuit video coding .I. Dictionary approximation

We have shown in previous works that overcomplete signal decomposition using matching pursuits is an efficient technique for coding motion-residual images in a hybrid video coder. Others have shown that alternate basis sets may improve the coding efficiency or reduce the encoder complexity. In this work, we introduce for the first time a design methodology which incorporates both coding efficiency and complexity in a systematic way. The key to the method is an algorithm which takes an arbitrary 2-D dictionary and generates approximations of the dictionary which have fast two-stage implementations according to the method of Redmill et al. (see Proc. IEEE Int. Conf. Image Processing, p.769-773, 1998). By varying the quality of the approximation, we can explore a systematic tradeoff between the coding efficiency and complexity of the resulting matching pursuit video encoder. As a practical result, we show that complexity reduction factors of up to 1000 are achievable with negligible coding efficiency losses of about 0.1-dB PSNR.