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Michael S. Langer, Daria Gipsman; Elongations near intensity maxima: a cue for shading?. Journal of Vision 2005;5(8):565. doi: 10.1167/5.8.565.
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The term ‘shading’ typically refers to illuminance variations on a curved 3D surface. Familiar examples are a wrinkled shirt, or a snow pile. Shading is distinguished from ‘texture’ which refers to surface pigmentation variation only, familiar examples being marble or wood grain. A natural yet neglected issue in understanding perception of shading and texture is how the visual system distinguishes them from each other from a single image (Freeman and Viola NIPS 1998). We address this issue by studying a newly discovered signature for shading which occurs near intensity maxima, namely that isoluminance curves due to shading are significantly elongated near intensity maxima. We show that these elongations can produce large kurtosis in the outputs of Gabor filtered shading patterns. We show how this statistical property depends on the interaction of surface geometry and illuminant direction. We discuss conditions under which the elongations could be used as a cue for distinguishing shading from texture.
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