Modelling the power spectra of natural images: statistics and information.

Power spectra of an extensive set of natural images were analysed. Both the total power in a spectrum (corresponding to image contrast) and its dependence on spatial frequency vary considerably between images, and also within images when considered as functions of orientation. A series of probabilistic models for power spectra enabled calculating the information obtained from prior knowledge of parameters describing spectra. Most information is gained from contrast, 1/f2 spatial frequency behaviour, and contrast as a function of orientation. Variations in spatial frequency behaviour are relatively unimportant. For oriented contrast, a bandwidth of 10-30 deg is sufficient to obtain most information.