The interplay between material qualities and lighting

In previous research we tested visual material perception in matching and discrimination tasks, and found multiple material and lighting dependent interactions. We used four basis surface scattering modes, namely diffuse, asperity, forward, and mesofacet scattering, which we represented by covering a same-shaped 3D object with "matte", "velvety", "specular", and "glittery" finishes, respectively. All four birds were photographed in so-called ambient, focus and brilliance lighting, three canonical modes that are commonly used in lighting design. In the current study, we asked observers to judge the 12 stimuli on 9 material qualities terms that are commonly used in material perception studies, namely "matte", "velvety", "specular", "glittery", "hard", "soft", "rough", "smooth", and "glossy", to test 1) whether the naming of the scattering modes we used is proper; 2) whether certain material qualities can be brought out or eliminated by certain canonical types of illuminations. For each term and each stimulus image, we first asked observers to judge whether it was applicable. If they answered "yes", they were asked to rate the term on a scale from 1 to 7. Three repetitions for 12 stimuli and 9 qualities, made 324 trials per observer. In preliminary results with 9 inexperienced observers, we found that 1) "matte" applied to all materials, while "velvety", "specular" and "glittery" specifically applied to those respective materials; 2) for "specular" and "glossy" we found similar judgments; 3) brilliance light brought out glitteriness, specularity, glossiness and smoothness the best; 4) focus light resulted in a small increase in the velvetiness, softness and roughness ratings compared to those for ambient and brilliance light. In further analysis, we will look into how the key stimuli image features can trigger certain perceived qualities and how to design lighting to optimize appearance.