On the relevance of the regularity constraint in subband image coding

Maximum regular wavelet filter banks have received much attention in the literature and it is a general conception that they enjoy some type of optimality for image coding purposes. To investigate this claim, this article focuses on one particular nonunitary filter bank, namely the two-channel 9/7. All possible combinations of having zeros at z=-1 for both analysis and synthesis lowpass filters rendering perfect reconstruction systems are studied. The best performance is obtained when the filter bank has 2/2 zeros at z=-1 for the analysis and synthesis lowpass filters, respectively. The competing wavelet 9/7 filter bank, which has 4/4 zeros at z=-1, is thus judged inferior both in terms of PSNR and visually.