Rate/distortion in fractal compression: order of transform and block symmetries

The authors have evaluated two complexity options in fractal image coding, namely the order of the fractal approximation and the benefits of searching over block symmetries. This was done in terms of the the entropy and distortion for a range of quantizations of the fractal coefficients. The results question the current wisdom in this field. Most fractal block coding systems use a low order approximation, while the present results suggest that where the distortion and compression are similar, a higher order approximation gives a noticeably sharper image. Virtually all reported fractal coding algorithms search for the best block reflections and rotations, but the present authors demonstrate that extra bits required to code the symmetry options are not compensated for by the modest fidelity gained.< >