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

Andrew Schofield, Paul Rock, Mark Georgeson, T. A. Yates

Research output: Contribution to journalConference abstract

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 ÃÙÆ 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 hemisphericalöthe `dark is deep' rule applies. For A, surface peaks will be offset by ÃÙÆ wavelength from the luminance maxima; for B, this offset will be zero. As the sum of two same-frequency sinusoids with different 108 Posters: Shape perception Wednesday 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 surfaceoffsets imply that gratings close to horizontal are taken to be lit by a point source; those close to vertical by a diffuse source.
Original languageEnglish
Pages (from-to)108-109
Number of pages2
JournalPerception
Volume36
DOIs
Publication statusPublished - 1 Aug 2007

Keywords

  • sinusoidal shading patterns
  • corrugated surfaces
  • surface peaks
  • luminance maxima
  • grating orientation
  • shading profile
  • sinusoidal surface

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