The perception of hazy gloss

Abstract

Most previous work on gloss perception has examined the strength and sharpness of specular reflections in simple bidirectional reflectance distribution functions (BRDFs) having a single specular component. However, BRDFs can be substantially more complex and it is interesting to ask how many additional perceptual dimensions there could be in the visual representation of surface reflectance qualities. To address this, we tested materials with two specular components that elicit an impression of hazy gloss. Stimuli were renderings of irregularly shaped objects under environment illumination, with either a single Ward specular BRDF component (Ward, 1992), or two such components, with the same total specular reflectance but different sharpness parameters, yielding both sharp and blurry highlights simultaneously. Differently shaped objects were presented side by side in matching, discrimination, and rating tasks. Our results show that observers mainly attend to the sharpest reflections in matching tasks, but they can indeed discriminate between single-component and two-component specular materials in discrimination and rating tasks. The results reveal an additional perceptual dimension of gloss-beyond strength and sharpness-akin to "haze gloss" (Hunter & Harold, 1987). However, neither the physical measurements of Hunter and Harold nor the kurtosis of the specular term predict perception in our tasks. We suggest the visual system may use a decomposition of specular reflections in the perception of hazy gloss, and we compare two possible candidates: a physical representation made of two gloss components, and an alternative representation made of a central gloss component and a surrounding halo component.

A Composite BRDF Model for Hazy Gloss

“…One may want to use two different types of functions, but this would complicate the peak ratio formula p without adding much more expressivity to the model. We have also limited our composite BRDF to a pair of components to be in accordance with existing perceptual studies on hazy gloss [VBF17]. Adding a third component would bring two additional degrees of freedom, but it is not clear how they might affect perception: would the new component be perceived independently or as part of the halo?…”

“…Vangorp et al [VBF17] have suggested that the perception of hazy gloss relies on a decomposition of the specular BRDF into a specular core and a surrounding halo. In particular, they show that the energy of their halo component is strongly correlated to subjective haziness ratings obtained through a perceptual experiment.…”

“…Perception of haze Recent work in visual perception [VBF17] has shown that humans are visually sensitive to haziness in some specific configurations. The authors employ a specular BRDF based on two Ward BRDF components [War92], one of narrow extent (i.e., small roughness), the other of wide extent (i.e., large roughness).…”

“…Our approach Throughout the paper, we focus on specular BRDFs and leave the diffuse term untouched. Our approach takes inspiration from the core/halo decomposition of Vangorp et al [VBF17] to introduce a BRDF model that grants direct control over hazy effects in a physically‐correct manner. We introduce material parameters that manipulate not only the haze magnitude but also its extent, which in practice exposes an additional d‐o‐f compared to distributions with controllable tails [LKYU12, BSH12, Bur12, RBMS17].…”

“…The focus of this work is on artistic control and ease of implementation for real‐time and off‐line rendering. We propose relying on a composite material based on a pair of arbitrary BRDF models; however, instead of controlling their physical parameters, we expose perceptual parameters inspired by visual experiments [VBF17]. Our main contribution then consists in a mapping from perceptual to physical parameters that ensures the resulting composite BRDF is valid in terms of reciprocity, positivity and energy conservation.…”