Fidelity enhancement of transform based image coding using non-orthogonal basis images

Existing mixed transform based image coders been formulated for use with separable two-dimensional (2-D) orthogonal transforms such as the discrete cosine transform (DCT) and Haar transform. In this paper, we demonstrate that the mixed transform technique may also be applied to more general collections of non-orthogonal and non-separable basis images. To illustrate the effectiveness of the technique, image representations are constructed from an over-complete set which includes the DCT basis images plus basis images specifically designed to efficiently represent edges. The resulting representations are shown to provide much better visual quality and energy compaction than those constructed from the DCT alone when an equal number of basis images are employed.