Curved wavelet transform and overlapped extension for image coding

The conventional 2D wavelet transform for image coding is performed using a symmetric extension and 1D filtering in the vertical and horizontal directions. In this paper, we present a curved wavelet transform and a method called overlapped extension. The curved wavelet transform is performed using 1D filtering along curves that are usually parallel to edges and lines in images. The pixels along these curves can be well represented using a small number of wavelet coefficients. The overlapped extension is proposed to prevent coding artifacts around the ends of the curves. Experimental results show that, compared with the conventional wavelet transform, the curved wavelet transform with overlapped extension significantly improves the subjective quality of decoded images, and the coding gain in PSNR can be up to 1.5 dB.