Image statistics and lightness perception
Edward H. Adelson
The luminance of a matte surface is determined by a combination of
factors, notably the illumination striking the surface and the
reflectance of the surface. Both factors vary from point to point and
scene to scene. Humans are quite good at achieving "lightness
constancy," the discounting of viewing conditions in order to estimate
reflectance. Psychophysical evidence points to several heuristics,
one of which is gathering local luminance statistics in order to
estimate the illumination. This process assumes that illumination is
contant over a window, and assumes priors for the reflectance and
illuminant distributions. Larger windows provide more samples, but
they increase the chance that multiple conditions will be mixed. I
will discuss the heuristics that the visual system uses to avoid this
mixing, using grouping rules involving proximity, contours, and
junctions. I will also discuss assumptions about reflectance
distributions.
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