Design of a Tree-Structured Bank with Allpass Polyphase Filters for Subband Image Coding via Time-Frequency Localization

Abstract

We discuss the optimization of filter coefficients in a tree-structured bank with allpass polyphase filters for subband image coding. First we show that the impulse response length and cutoff characteristics of the filter bank have a tradeoff relationship in terms of coding performance. Then we propose a method of designing a bank by minimizing the product ΔnΔw between the time and bandwidths of subband filters. Amplitude responses of the designed subband filters nearly approximate Gaussian functions and their ΔnΔw are little larger than the lower bound of the uncertainty principle. Coding simulations show that the coding performance of the designed bank compares favorably with that of image-optimized banks.