Diffuse IIIumination as a default assumption for shape- from-shading in the absence of shadows

摘要

Radial sinusoids (blurry spoke patterns) appear dramatically saturated toward the brigther regions. The saturation is not percepturally logarithmic but exhibits a hyperboic (Naka-Rushton) compression behavior at normal indoor liminance levels. The object interpretation of the spoke pattrns was no consistent with the default assumption of any unidirectional light source, but implied a diffuse illumination (as if the object were looming out of a fog). The depth interpretation was consistent with the hypothesis that the compressed brightness profile provided the neural signal for perceived shape, as an approximation to computing the diffuse Lambertian illumination function for the surface. The surface material of the images was perceived as non-Lambertain to varying degrees, ranging from a chalky matte to a lustrous metallic.