The effect of diffuseness and direction of light on perceived texture visibility

The diffuseness of light and its angle of incidence influence the way we perceive material properties like roughness and shininess, but whether it influences our ability to discriminate between differently textured materials is unclear. Therefore we examined the effect of diffuseness and direction of light on the perceived texture visibility of images of different materials. Images were made under strongly collimated or strongly diffuse lighting and superimposed to obtain mixed images with varying diffuseness levels. Participants rated texture visibility pairs of images using a 2-alternative forced choice task (AFC). We found that overall the perceived texture visibility was best for the most diffuse light source and worst for intermediate diffuseness levels. Texture visibility improved with angle of incidence for collimated lighting. The effect of the diffuseness level of the illuminant was strongly dependent the material. Our results confirm that the diffuseness of light is an important factor for discriminating textures of real materials.