Abstract

This thesis deals with SubBand Coding (SBC) of still images at low bit rates, where the emphasis is on designing the SBC to be robust in the sense that the perceived image quality degrades gracefully as the bit rate is reduced. At low bit rates the subband data are coarsely approximated, and this results in visible distortions in the reconstructed image. The distortion characteristics depend on the filter bank applied. Blocking effects and ringing noise are the artifacts experienced using the Discrete Cosine Transform (DCT) and classical SBC, respectively. More recent filter banks, such as the Lapped Orthogonal Transforms (LOTs), utilize relatively short filter lengths. The noise characteristics are a cross between that of DCT and SBC: Less ringing noise than SBC, and smoother blocking artifacts than DCT. Much work has been done to develop clever quantization strategies for reducing the noise's influence on the reconstructed image. In this work we adopt a different strategy: Design the...

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