Poster Session I: Combining spatial and quantitative models to account for the relationship between luminance, context and brightness.

The apparent brightness of a target region is determined not only by its local luminance, but also by its surrounding context. This is well demonstrated by the many illusions where some surround context causes two physically identical targets to appear different in brightness (e.g. White's (1979) illusion). Here we use perceptual scales from Maximum Likelihood Conjoint Measurements to test the predictive power of computational brightness models as a function of surround context and local luminance. While the qualitative relationship between target brightness and surround context (i.e. direction of effect) is captured well by image-computable models of the spatial filtering type (e.g. Blakeslee and McCourt, 1997), these do not predict the quantitative aspects of that relationship (i.e. magnitude of effect). A different class of models (e.g. Whittle, 1992) makes quantitative predictions of brightness as a function of luminance, but requires labeling of target and background (i.e., is not image-computable), thus cannot by itself account for the spatial context. Hence we combine Whittle's model with spatial mechanisms to account for both spatial context and local luminance. A combined model using multiscale spatial filtering and calculating brightness at every spatial scale is able to provide both a correct qualitative prediction of direction of effect, as well as a quantitative prediction of apparent brightness that can be tested against perceptual scales for different stimuli.