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Daisuke Kondo, Hayato Fujita, Isamu Motoyoshi; Material rendering property of illumination: relationship between illumination statistics and perception. Journal of Vision 2020;20(11):647. doi: https://doi.org/10.1167/jov.20.11.647.
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© ARVO (1962-2015); The Authors (2016-present)
Recent psychophysical studies show that the perception of surface material properties such as glossiness and color strongly depend on the spatial structure of illumination statistics, or "lightfield". In the present study, we systematically investigated the relationships between illumination statistics and perceived surface qualities in order to determine the characteristics of the lightfield that enhance the material appearance of surfaces – a term we dub the ‘material rendering property’ of illumination. In a series of psychophysical matching experiments, 9 observers inspected computer-generated images of bumpy objects under 21 different natural lightfields (both outdoor and indoor scenes selected from a large database) and adjusted one of the test's perceived surface properties – glossiness, mesoscopic roughness, or bump sharpness (7 levels for each dimension) – to match the perceived surface property of the reference object. For example, on each trial in the 'glossiness' experiment, the observers freely viewed the reference object of a given specular reflectance (e.g., 0.5 %) under a particular lightfield and adjusted the specular reflectance of the test object under a fixed lightfield (Eucalyptus). For each lightfield, we computed two classes luminance subband image statistics, namely moment statistics (contrast, skewness, and kurtosis) and energy correlations across subbands. We then calculated correlations between class statistics on the one hand and variations in matched glossiness across different specular reflectances on the other. The analysis showed that variations in perceived glossiness were highly correlated with key statistical features of the lightfield including contrast, skewness, kurtosis, and cross-orientation energy correlation. Similar correlations were obtained for mesoscopic roughness and bump sharpness. Together, results suggest that light environments with high spatial contrast, skewness, kurtosis, and cross-orientation energy correlations (e.g., bright, sparse, and spotty features) tend to have a high material rendering property.
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