Image content matched directional filters for image coding based on contourlet transform

Due to the separability of its filters, the wavelet transform is suboptimal for transform coding of natural images. The contourlet transform is an approach to overcome this problem by employing directional filters. In contrast to the great number of filters available for the wavelet transform, few filters exist for use with contourlets. We describe a method for the design of directional filters, which can be tailored to specific image contents. The method numerically optimizes the coding gain of directional filters within the lifting framework. Thereto, a link is derived between the coefficients of directional filters and coding gain. An example of an optimized filter is presented and its superiority over a standard filter for contourlet based image coding is shown.