Fast directional fractal coding of subbands using decision-directed clustering for block classification

We propose a new image compression scheme based on fractal coding of wavelet transform coefficients using a fast non-iterative algorithm for the codebook generation. The original image is first decomposed into subbands containing information in different spatial directions and different scales, using an orthogonal wavelet filter bank. Subbands are encoded using local iterated function systems (LIFS) with range and domain blocks presenting horizontal or vertical directionalities. Their sizes are estimated according to the correlation lengths and resolution of each subband. The computational complexity is greatly decreased by using subband decomposition. In addition a fast non-iterative algorithm is implemented for block classification. This algorithm progressively creates the codebook during only one scanning of the training set. We prove the efficiency of the proposed approach both in terms of PSNR/bit rate and computation time