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Minjung Kim, Richard F. Murray; 3D surface shape and the appearance of glow. Journal of Vision 2011;11(11):399. doi: 10.1167/11.11.399.
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© ARVO (1962-2015); The Authors (2016-present)
Why do objects appear to glow? Previous studies on perception of glow have focused on simple 2D stimuli, largely neglecting the contribution of 3D shape cues. Here we show that 3D surface shape plays a crucial role in glow perception, and advance a theory of what luminance and shape patterns induce a percept of glow. HYPOTHESIS. For non-glowing objects under diffuse light, the luminance of a surface patch depends on the amount of the light source visible from the patch; thus, patches are dark in valleys and bright on peaks (Langer & Bülthoff, 2000). For glowing objects, the luminance depends on the amount of light received from neighboring glowing surfaces; thus, patches are bright in valleys, and dark on peaks. That is, brightness and depth are negatively correlated for diffusely lit objects, and positively correlated for glowing objects. In our experiment, we examined whether manipulating this shape-and-luminance relationship could generate apparent glow. METHODS. We rendered objects with complex, wavy surfaces under purely direct and purely diffuse lighting, and then inverted the luminance of the diffuse image to obtain the inverted diffuse image. The stimulus was a weighted sum of the three components (direct, diffuse, and inverted diffuse). Observers viewed pairs of stimuli generated with different inverted diffuse weights, and chose the object with stronger perceived glow. RESULTS. A Thurstone scaling analysis of the paired comparison responses revealed that diffuse inversion can induce apparent glow, and that higher inverted diffuse weights lead to stronger glow. Our results show that the perceived relationship between surface depth and luminance is relevant to perceived glow in complex objects, and further suggests the possibility that glow may be modulated by higher-order 3D shape cues (e.g., curvature).
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