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The influence of shape cues on the perception of lighting direction
 

Summary: The influence of shape cues on the perception
of lighting direction
Vision Science Program, University of California,
Berkeley, CA, USAJames P. O'Shea
Department of Computer Science, University of California,
Berkeley, CA, USAManeesh Agrawala
Vision Science Program, Department of Psychology and
Wills Neuroscience Institute, University of California,
Berkeley, CA, USAMartin S. Banks
Three scene properties determine the luminances in the image of a shaded object: the material reflectance, the illuminant
position, and the object's shape. Because all three properties determine the image, one cannot solve for any one property
without knowing the other two. Nevertheless, people perceive consistent 3D shape and consistent lighting in shaded
images; they must therefore be making assumptions about the unknown properties. We conducted two psychophysical
experiments to determine how viewers use shape information to estimate the lighting direction from shaded images. In the
first experiment, we confirmed that observers use 3D shape information when estimating lighting direction. In the second
experiment, we investigated how different shape cues affect lighting direction estimates. Observers can accurately
determine lighting direction when a host of shape cues specify the objects. When shading is the only cue, observers always
set lighting direction to be from above. We modeled the results in a Bayesian framework that included a prior distribution
describing the assumed lighting direction. The estimated prior was slightly counterclockwise from above at a 30- slant.
Our model showed that an assumption of convexity provides an accurate estimate of lighting direction when the shape is

  

Source: Agrawala, Maneesh - Department of Electrical Engineering and Computer Sciences, University of California at Berkeley

 

Collections: Computer Technologies and Information Sciences