Abstract
Previous results suggest that the glossiness of a surface is systematically underestimated when adjacent highlights from different light sources overlap to such an extent that they appear as a single, expanded highlight. Here we investigated how the availability of color- and motion-induced information, which may help to unravel such merged highlights, affects gloss constancy. We used images of computer-generated scenes where a complex 3D object made of glossy material was illuminated by three point light sources, which had varying distances to each other. The point lights were either all achromatic or they differed clearly in their color and the test object was either presented statically or rotating. The subjects had to adjust the smoothness of a match object illuminated by a single achromatic point light so that it appeared to have the same glossiness as the test object. The results show that color information contributes to gloss constancy in this situation: If it was available, the perceived glossiness remained almost invariant with changes in the degree of overlap between the highlights. This suggests that highlights of different color are processed separately. Motion information had no such effect but only led to a general increase in perceived glossiness.
Highlights
The present results suggest that color information is used by the visual system to analyze and demerge the complex highlight pattern and possibly even to decompose it into its causal components: A plausible interpretation of our findings is that the highlights are perceptually grouped according to their different colors, which leads to three separate highlight maps, each associated with one of the three light sources
The highlights produced by different light sources may overlap in the input image and it was found in a previous study that this can have a negative effect on gloss constancy
We investigated whether color and motion information can be used to separate the influence of different light sources and to increase constancy
Summary
2012; Nishida & Shinya, 1998; Olkkonen & Brainard, 2010, 2011; Pont & te Pas, 2006; Todd & Norman, 2018; Vangorp, Laurijssen, & Dutre , 2007; Wendt, Faul, Ekroll, & Mausfeld, 2010) Such cases of incomplete gloss constancy are due to the fact that the visual system bases its glossiness estimate on visual cues that are affected by the material properties of the surface and by other factors, such as the object’s shape and the illumination in the scene. According to physically based reflectance models, the specular reflection of a surface is determined by its microscale structure, more precisely by the distribution of the orientations of so-called microfacets that constitute the surface of the object (Cook & Torrance, 1982; Ngan, Durand, & Matusik, 2005). Properties of these highlights are used by the visual system as cues for the glossiness of the surface: The sharper, smaller, and more intense the highlights, the more glossy a surface generally appears (Beck & Prazdny, 1981; Fleming et al, 2003; Forbus, 1977; Kim, Marlow, & Anderson, 2012; Kim, Tan, & Chowdhury, 2016; Marlow & Anderson, 2013; Marlow, Kim, & Anderson, 2012; Qi, Chantler, Siebert, & Dong, 2014, 2015)
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