The Perception of Surface Material

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How the visual properties of an object or scene affect human visual perception is a fundamental question in cognitive science. The proposed research is concerned with the visual properties of surfaces, which can reveal many characteristics important to decision-making, such as the identity of a substance, the cleanliness of an item, or the authenticity of a photograph. Humans make these judgments by analyzing the light reflected from surface materials. The proposed research examines how this is accomplished. Shiny materials like polished metal, gloss paint, smooth plastic, and varnished wood yield bright reflections of the light sources that illuminate them. Humans are quite adept at distinguishing those reflections from other causes of bright spots, such as white matte paint. Reflections are view dependent, meaning that their apparent position on the surface changes depending on the location of the viewing eye. Because of this view dependence, the reflection usually appears to lie beneath the surface. The proposed research will examine how the apparent position of reflections affects human judgments of material. The investigators will conduct theoretical work on the properties of reflections from many types of materials and experimental work on how well humans are able to use these properties to identify material. The investigators will also develop new computer graphics algorithms and a new display technique to allow realistic presentation of reflections from realistic materials. The work will contribute significantly to basic science and to several applications. One important application concerns how industry describes the visual properties of materials. Currently, manufacturers of paint, plastics, and furniture use one-dimensional scales of appearance, such as gloss, and inexpensive appearance measurement devices, such as glossmeters, to categorize finishes by "gloss level." Very different materials can have the same gloss level even though they produce very different reflections. The investigators will determine whether materials with the same gloss level actually look the same. The results could affect the way industry measures and assesses material. Another important application concerns how people distinguish between computer-generated and real images. This has important implications, not only for the motion picture and computer graphics industries, but also for forensic sciences. The principal investigator, in collaboration with an expert in digital forensics, will explore whether the pattern of light dispersal from human skin in computer-generated and real people, and the associated parallax properties, can aid in distinguishing fake from real images.