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Jan J. Koenderink, Andrea J. van Doorn, Astrid M. L. Kappers, Susan F. Pas, Sylvia C. Pont; Perceiving illumination direction in 3D texture. Journal of Vision 2002;2(7):87. doi: 10.1167/2.7.87.
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© ARVO (1962-2015); The Authors (2016-present)
Image texture due to 3D surface corrugations (“3D texture”) differs fundamentally from image texture due to pigmentation variations of a smooth surface (“flat texture”). Flat texture yields no information concerning the way the surface is illuminated, whereas 3D texture is highly dependent upon the illumination.
Question: Is the human observer able to perceive the illumination direction from 3D texture?
Method: In order to address this question we extracted over sixty 3D textures due to natural materials from the Curet database. Fiducial illumination directions were 22.5°, 45° and 67.5° from the normal direction, all viewing directions were normal. The samples were clipped to circular discs and were randomly rotated in the picture plane. Observers indicated perceived illumination direction by way of an indicator panel showing a hemispherical boss on a plane, viewed normally to the plane. The simulated illumination direction was under the observer's control. Five observers viewed all samples in six different orientations.
Result: We find that the azimuth of the illumination direction can be perceived quite veridically except for the fact that 180° confusions are frequent. The elevation cannot be perceived with great certainty (deviations up to 45° occurring frequently) though the increase of perceived elevation with true elevation is significant. We find a number of interesting variations on this pattern that depend critically upon the type of texture.
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