How Does Lighting Direction Affect Shape Perception of Glossy and Matte Surfaces?

(a) matte (b) glossy Figure 1: Sample surfaces at a slant of θ = 60 ◦ and a light slant of φ = 120◦. Note the more detailed 3D shape percept of the glossy surface, where the specular highlights are located exactly at the tops of the hills and bottoms of the valleys. See Figure 3(a) for definition of φ, θ. To visualize the shape of 2D surface data, one often renders it using a simple model with matte or glossy reflectance and a light source at infinity. The parameter choices for this model are typically ad hoc, however, and previous studies have provided varying evidence on what this choice should be so that the shape is perceived as ac-curately as possible. Here we present an experiment that exam-ines local qualitative shape perception on matte and glossy surfaces where we vary both the overall slant of the surface with respect to the viewer and the slant of the distant light source. We find that increasing the slant of the light source to twice that of the surface slant angle improves subjects ’ perception of qualitative shape of glossy surfaces. Additionally, at these high slant angles the glossy surface percepts are better than those of matte surfaces. We argue that these improvements are due to the positioning of the highlights at the peaks and valleys of the terrain, where they demarcate the surface maxima. We also find that increasing the light slant pro-duces better and/or more consistent shape percepts than the default lighting in commercial visualization software such as Matlab and Mathematica