Effects of Specular Highlights on Perceived Surface Convexity

Abstract

Shading is known to produce vivid perceptions of depth. However, the influence of specular highlights on perceived shape is unclear: some studies have shown that highlights improve quantitative shape perception while others have shown no effect. Here we ask how specular highlights combine with Lambertian shading cues to determine perceived surface curvature, and to what degree this is based upon a coherent model of the scene geometry. Observers viewed ambiguous convex/concave shaded surfaces, with or without highlights. We show that the presence/absence of specular highlights has an effect on qualitative shape, their presence biasing perception toward convex interpretations of ambiguous shaded objects. We also find that the alignment of a highlight with the Lambertian shading modulates its effect on perceived shape; misaligned highlights are less likely to be perceived as specularities, and thus have less effect on shape perception. Increasing the depth of the surface or the slant of the illuminant also modulated the effect of the highlight, increasing the bias toward convexity. The effect of highlights on perceived shape can be understood probabilistically in terms of scene geometry: for deeper objects and/or highly slanted illuminants, highlights will occur on convex but not concave surfaces, due to occlusion of the illuminant. Given uncertainty about the exact object depth and illuminant direction, the presence of a highlight increases the probability that the surface is convex.

The Southampton-York Natural Scenes (SYNS) dataset: Statistics of surface attitude

“…Multimodal probability densities reflect strong dominance of horizontal and vertical surfaces, and dependence on scene category and elevation suggests that conditioning on these variables will improve accuracy of surface estimation. We are currently quantifying psychophysical estimation of surface attitude64 to assess concordance with the statistics reported here and have been employing the Spheron HDR spherical images for light field modelling in 3D rendering65 and light adaptation models of the human retina37. We expect the SYNS dataset to be useful for a great diversity of future projects by laboratories around the world.…”

Can you see what you feel? Color and folding properties affect visual–tactile material discrimination of fabrics

“…Previous findings showed that the visual system used shading cues to estimate reflective properties of the surface and materials, and 3-D shape influenced material perception (Giesel & Zaidi, 2013;Ho, Landy, & Maloney, 2008;Kerrigan & Adams, 2013;, 2012Motoyoshi, 2010;Radonjic & Gilchrist, 2013;Vangorp, Laurijssen, & Dutré, 2007;Wijntjes, Doerschner, Kucukoglu, & Pont, 2012). A recent study also shows that presence of specular highlights also increased perceived surface convexity (Adams & Elder, 2014). It is possible that the presence of specular highlights helps recovering the 3-D shape of the fabrics, hence improving material understanding of the mechanical properties, such as softness and rigidity, of the fabrics.…”

Effect of Geometric Sharpness on Translucent Material Perception

“…Conversely, the perception of 3D shape is affected by the surface’s optical (i.e, reflectance) properties. For example, it has been shown that the same surface can be perceived to have different 3D geometry when its reflectance becomes more or less specular (Doerschner, Yilmaz, Kucukoglu, & Fleming, 2013; Adams & Elder, 2014; Sawayama & Nishida, 2018). This coupling between the perception of 3D shape and surface reflectance properties has also been demonstrated in objects with non-specular reflectance (Todd, Egan, & Phillips, 2014).…”