Abstract
PURPOSE. Object surface reflectance can be approximated as arising from two components: the diffuse component, which correlates with perceived lightness and color, and the specular component, which correlates with perceived glossiness. In addition to the reflectance parameters, geometric and spectral properties of the illuminant as well as object shape affect the spectrum and geometry of the reflected light. We and others have shown that lightfield geometry affects the perceived glossiness of spheres. Here, we study the interaction between changing the lightfield and changing object shape on perceived glossiness. METHODS. The stimuli consisted of two different blob-shaped objects with both convex and concave regions. These were rendered under three different natural lightfields using the Radiance rendering software. On each trial, a pair of objects were presented side-by-side on a high-dynamic-range display. Observers indicated which object appeared glossier, and an adaptive staircase procedure adjusted the strength of the specular reflectance component over trials to determine the point of subjective equality. We examined the effect of changing lightfield and the effect of changing shape. Measurements were made for three levels of reference specular reflectance, and the effect of lightfield and shape was quantified by the slope of the line fit to the reference specularity versus PSE data. RESULTS. Changes in lightfield and shape both had substantial effects on perceived glossiness: measured slopes deviated from unity by an average (across subjects) of 51% (lightfield) and 66% (shape). In addition, there was a strong interaction between shape and the effect of lightfield. For one of the lightfield changes, the effect on perceived glossiness had opposite sign for the two shapes: the average slope for Shape A was 1.95 but for Shape B was 0.56. Thus to develop a theory of perceived glossiness, effects of lightfield and object shape must be considered jointly.
Supported by NIH Grants RO1 EY10016 and P30 EY001583.