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Copyright 2005 Psychonomic Society, Inc. 120 Perception & Psychophysics

Summary: Copyright 2005 Psychonomic Society, Inc. 120
Perception & Psychophysics
2005, 67 (1), 120-128
In order to achieve lightness constancy, it is necessary
to discount the luminance variations resulting from
changes of the illumination falling on a surface, because
the luminance is the product of both the reflectance and
the illumination. Illumination can vary globally--that is,
the overall level can change from time to time--and it
can also vary locally in space, as occurs when a shadow
is cast on a surface. It is still unclear how the human vi-
sual system manages to evaluate illumination changes
separately from reflectance changes, since information
about the two are mixed in the retinal image. It is gener-
ally considered that the visual system uses various cues
to distinguish whether a local luminance change should
be discounted, as if it were due to illumination, or kept,
as if it were due to reflectance (albedo). For example, the
soft penumbra of a shadow is a cue that it is caused by il-
lumination rather than pigment. Gilchrist et al. have de-


Source: Adelson, Edward - Computer Science and Artificial Intelligence Laboratory, Department of Brain and Cognitive Science, Massachusetts Institute of Technology (MIT)


Collections: Biology and Medicine