Human interpretation of light diffuseness

The light diffuseness (Xia, Pont et al. 2016, Xia, Pont et al. 2016) can strongly influence the appearance of scenes and objects inside it. There are numerous studies investigating how to measure the light diffuseness or modelling index. However, there are few studies about how light diffuseness is interpreted by human observers. We use an appearancematching experiment to investigate observers' visual interpretation of light diffuseness from object appearance and its potential interactions with viewing angles, light probe type, etcetera. The results indicate that, generally, the observers are able to distinguish different diffuseness levels for both the smooth and rough white spherical probes. The “diffuseness-direction ambiguity” (Pont and Koenderink 2007) is obvious especially for the smooth probe and it can be largely corrected for by the “effective vector to scalar ratio” (Cuttle 1971). Moreover, the results showed that the use of a probe with mesorelief can at least partly resolve the “diffuseness-direction ambiguity”.