August 2010
Volume 10, Issue 7
Free
Vision Sciences Society Annual Meeting Abstract  |   August 2010
Lightness estimation errors in a 3D context
Author Affiliations
  • Yoana Dimitrova
    Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London
    Division of Psychology and Language Sciences, Department of Cognitive, Perceptual and Brain Sciences, University College London
  • Peter McOwan
    Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London
    School of Electronic Engineering and Computer Science, Department of Computer Science, Queen Mary, University of London
  • Alan Johnston
    Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London
    Division of Psychology and Language Sciences, Department of Cognitive, Perceptual and Brain Sciences, University College London
Journal of Vision August 2010, Vol.10, 453. doi:10.1167/10.7.453
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      Yoana Dimitrova, Peter McOwan, Alan Johnston; Lightness estimation errors in a 3D context. Journal of Vision 2010;10(7):453. doi: 10.1167/10.7.453.

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Abstract

The problem of recovering reflectance from a single image is inherently under-constrained. Therefore, the visual system must use heuristics or biases to recover reflectance, whilst discounting geometry and illumination. In a previous study, we investigated lightness perception in a 3D context (Dimitrova YD, McOwan P, Johnston A, 2009, Perception 38: ECVP Abstract supplement, p. 31). Participants systematically overestimated reflectance for vertically eccentric illuminant angles and underestimated for illuminant angles close to the horizontal plane. These errors were robust to additional cues to light source direction and depth as well as to the removal of local features. Errors rose significantly with the increase in the ratio of directional to ambient light. Modelling of the data indicated three possible causes of the reflectance misestimation: a light direction bias, a bias in the proportion of ambient to directional light or a simple brightness averaging over the image. To investigate perceived illuminant direction, participants were asked to adjust the illumination direction for a sphere until it matched the lighting direction for a dodecahedron rendered using a range of illuminant elevations. The pattern of light direction adjustments was consistent with a bias of perceived illuminant elevation that is both shifted away from vertically eccentric angles and away from the horizontal plane. These adjustments were similar the results of modelling reflectance errors with a light direction bias. This finding supports the view that the systematic errors in reflectance settings are at least in part caused by a bias in the assumed direction of illumination.

Dimitrova, Y. McOwan, P. Johnston, A. (2010). Lightness estimation errors in a 3D context [Abstract]. Journal of Vision, 10(7):453, 453a, http://www.journalofvision.org/content/10/7/453, doi:10.1167/10.7.453. [CrossRef]
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