Adaptive SPIHT for image coding based on curved wavelet transform

The curved wavelet transform performs 1-D filtering along curves and exploits orientation features of edges and lines in an image to improve the compactness of the wavelet transform. This paper investigates the issue of efficient data organization and representation of the curved wavelet coefficients. We present an adaptive zero-tree structure that exploits the cross-subband similarity of the curved wavelet transform. The child positions in the adaptive zero-tree structure are not restricted to a square of 2x2 pixels and they vary with the curves along which the WT is performed. Five child patterns have been determined according to different combination of curve orientations. A new image coder, using the curved wavelet transform, is then developed based on this adaptive zero-tree structure and the set partitioning technique. Experimental results using synthetic and natural images show the effectiveness of the proposed adaptive zero-tree structure for encoding of the curved wavelet coefficients. The coding gain of the proposed coder can be as higher as 1.2dB in terms of PSNR compared to the SPIHT coder.