The distribution of reflectances within the visual environment.

The statistics of natural images have often been used to account for various properties of animal visual systems. However, for most visual tasks, the images themselves are not important; it is the physical properties of the surfaces which generated them that guide behaviour. Here, we present statistical characterisations of the surface reflectances encountered within four different visual environments (woodland, beach, urban and interior), sampled using a systematic, survey-based method. Of the distributions fitted to the data, the beta distribution provides the best description per number of free parameters. Such distributions may be used as priors in Bayesian models of lightness constancy, or to generate ecologically valid reflectance distributions for simulated environments. The implications of this for models of reflectance extraction within visual systems are discussed.