Humans assume a mixture of diffuse and point-source lighting when viewing sinusoidal shading patterns

Schofield, Andrew J., Rock, P.B., Georgeson, Mark A. and Yates, Timothy A. Humans assume a mixture of diffuse and point-source lighting when viewing sinusoidal shading patterns. IN: 13th European Conference on Visual Perception. 2007-08-27 - 2007-08-31. (Unpublished)

Abstract

Observers perceive sinusoidal shading patterns as being due to sinusoidally corrugated surfaces, and perceive surface peaks to be offset from luminance maxima by between zero and 1/4 wavelength. This offset varies with grating orientation. Physically, the shading profile of a sinusoidal surface will be approximately sinusoidal, with the same spatial frequency as the surface, only when: (A) it is lit suitably obliquely by a point source, or (B) the light source is diffuse and hemispherical--the 'dark is deep' rule applies. For A, surface peaks will be offset by 1/4 wavelength from the luminance maxima; for B, this offset will be zero. As the sum of two same-frequency sinusoids with different phases is a sinusoid of intermediate phase, our results suggest that observers assume a mixture of two light sources whose relative strength varies with grating orientation. The perceived surface offsets imply that gratings close to horizontal are taken to be lit by a point source; those close to vertical by a diffuse source. [Supported by EPSRC grants to AJS and MAG].

Divisions: Life & Health Sciences > Optometry
Additional Information: Abstract published in ECVP 2007 Abstract Supplement, in Perception, 2007, 36 (Suppl. S), pp.108-109, ISSN 0001-4966.
Event Title: 13th European Conference on Visual Perception
Event Type: Other
Event Dates: 2007-08-27 - 2007-08-31
Uncontrolled Keywords: sinusoidal shading patterns,corrugated surfaces,surface peaks,luminance maxima,grating orientation,shading profile,sinusoidal surface

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