Physical Asymmetries and Brightness Perception

This paper considers the problem of estimating the brightness of visual stimuli. A number of physical asymmetries are seen to permit determination of brightness that is invariant to certain manipulations of the sensor responses, such as inversion. In particular, the light-dark range asymmetry is examined and is shown to result, over a certain range, in increased variability of sensor responses as scene brightness increases. Based on this observation we propose that brightness can be measured using variability statistics of conditional distributions of image patch values. We suggest that a process of statistical learning of these conditional distributions underlies the Stevens effect.