Light direction from shad(ow)ed random Gaussian surfaces

Jan J. Koenderink, Andrea J. Van Doorn, Sylvia C. Pont

Research output: Contribution to journalArticleScientificpeer-review

32 Citations (Scopus)

Abstract

Three human observers estimated the illumination direction for samples of random Gaussian surfaces illuminated by a collimated beam from random directions. These stimuli appear as 'texture' due to shading and shadowing (the surface on the microscale was Lambertian of uniform albedo; thus texture appears only through shading and shadowing). We found that observers were able to estimate the azimuth of the source with remarkable accuracy. In the shading regime (no shadows) the observers committed 180° azimuth errors with 50% probability, whereas in the shadow-dominated regime they were able to avoid this convex/concave confusion to a large extent. They evidently relied on second-order statistics in the shading regime and used an unidentified first-order cue in the shadow regime. The elevations of the source were also estimated with remarkable precision. We attribute this to the statistical homogeneity of the sample which can apparently be exploited by the observers. Likely cues are the fraction of shadowed surface, average intensity and rms contrast. The ability of human observers to estimate the illumination direction from surface texture no doubt contributes to the ability to estimate the light field in scenes, which is a prerequisite to the photometric parsing of scenes (shape from shading, and so forth).

Original languageEnglish
Pages (from-to)1405-1420
Number of pages16
JournalPerception
Volume33
Issue number12
DOIs
Publication statusPublished - 2004
Externally publishedYes

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