Abstract
Introduction: The appearance of objects in natural scenes is determined by their reflectance, their surface roughness, their shape and by the nature of the illumination. Results of previous experiments suggested that illumination perception depends mainly on simple cues such as the location of the shadow edge. In the present study we investigate whether varying the complexity of illumination and shape influences the perception of illumination.
Method: We use a set of stimuli taken from the Amsterdam Library of Object Images (Geusebroek et al., International Journal of Computer Vision, 2005), containing photographs of complex shapes under a varying number and configuration of light sources.
Results: We find that perception of material, shape and illumination are basically confounded. Low spatial frequency manifestations of the illumination, such as average direction of the illumination and maybe an ambient term, can be discriminated, but high spatial frequency features, such as the number of light sources are almost impossible to distinguish. Introducing more complex shapes to the scene made the identification of such features of the light field even more difficult.
Conclusions: Shape, illumination, reflectance are perceptually confounded, and illumination discrimination is mainly based on low spatial frequency manifestations.