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].
|Publication status||Unpublished - 2007|
|Event||13th European Conference on Visual Perception - Arezzo (IT), Italy|
Duration: 27 Aug 2007 → 31 Aug 2007
|Conference||13th European Conference on Visual Perception|
|Period||27/08/07 → 31/08/07|
Bibliographical noteAbstract published in ECVP 2007 Abstract Supplement, in Perception, 2007, 36 (Suppl. S), pp.108-109, ISSN 0001-4966.
- sinusoidal shading patterns
- corrugated surfaces
- surface peaks
- luminance maxima
- grating orientation
- shading profile
- sinusoidal surface