  The present research was designed to examine how patterns of illumination
influence the perceptual categorization of metal, shiny black, and shiny white
materials. The stimuli depicted three possible objects that were illuminated by
five possible HDRI light maps, which varied in their overall distributions of
illuminant directions and intensities. The surfaces included a low roughness
chrome material, a shiny black material, and a shiny white material with both
diffuse and specular components. Observers rated each stimulus by adjusting
four sliders to indicate their confidence that the depicted material was metal,
shiny black, shiny white or something else, and these adjustments were
constrained so that the sum of all four settings was always 100%. The results
revealed that the metal and shiny black categories are easily confused. For
example, metal materials with low intensity light maps or a narrow range of
illuminant directions are often judged as shiny black, whereas shiny black
materials with high intensity light maps or a wide range of illuminant
directions are often judged as metal. A spherical harmonic analysis was
performed on the different light maps in an effort to quantitatively predict
how they would bias observers' judgments of metal and shiny black surfaces.
