Sub-Band Coding Of Images Using Nonrectangular Filter Banks

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Abstract
A procedure for image coding using a non-rectangular subband decomposition is described in this paper. The procedure provides a hierarchical partition where at each stage a decomposition into two subbands is accomplished with no bias toward either the horizontal or the vertical high frequency content of the signal. The filters used in the processing are low order IIR filters with approximately linear phase and the analysis/synthesis filter banks provide exact reconstruction in the absence of quantization and coding. The filters are implemented using a generalized notion of separable processing. A two stage decomposition was investigated in which the subband signal with lowest frequency content was coded using Discrete Cosine Transform (DCT) and the outer bands were coded using runlength coding and pulse code modulation (PCM) . The coding scheme is demonstrated on some test images. The scheme provides a natural hierarchy of image resolution where the sampling is reduced by a factor of two at each stage. In this diamond shaped frequency subband analysis/synthesis scheme if the information of the outer band is lost, the reconstructed signal appears visually more acceptable than in the case where either the high vertical or high horizontal information in the rectangular subband analysis/synthesis is ignored.

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