Progressive fractal coding

Progressive coding is an important feature of compression schemes. Wavelet coders are well suited for this purpose because the wavelet coefficients can be naturally ordered according to decreasing importance. Progressive fractal coding is feasible, but it was proposed only for hybrid fractal-wavelet schemes. We introduce a progressive fractal image coder in the spatial domain. A Lagrange optimization based on rate-distortion performance estimates determines an optimal ordering of the code bits. The optimality is in the sense that the reconstruction error is monotonically decreasing and minimum at intermediate rates. The decoder recovers this ordering without side information. As a side effect, our work motivates improved bit allocation strategies for fractal coding.