No / Image gradients - smooth changes in color and luminance - may be caused by intrinsic surface reflectance properties or
extrinsic illumination phenomena, including shading, shadowing, and inter-reflections. In turn, image gradients may
provide the visual system with information concerning the origin of these factors, such as the orientation of surfaces with
respect to the light source. Color gradients induced by mutual illumination (MI) may play a similar role to that of
luminance gradients in shape-from-shading algorithms; it has been shown that 3D shape perception modulates the
influence of MI on surface color perception (M. G. Bloj, D. Kersten, & A. C. Hurlbert, 1999). In this study, we assess
human sensitivity to changes in color and luminance gradients that arise from changes in the light source position, within a
complex scene. In Experiment 1, we tested whether observers were able to discriminate between gradients due to different
light source positions. We found that observers reliably detected a change in the gradient information when the light source
position differed by only 4 deg from the reference scene. This sensitivity was mainly based on the luminance information in
the gradient (Experiments 2 and 3). Some observers make use of the spatial distribution of chromaticity and luminance
values within gradients when discriminating between them (Experiment 4). The high sensitivity to gradient differences
supports the notion that gradients contain information that may assist in the recovery of 3D shape and scene
configuration properties.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/4770 |
| Date | January 2008 |
| Creators | Ruppertsberg, Alexa I., Bloj, Marina, Hurlbert, A.C. |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Article, No full-text in the repository |
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