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Proceedings Paper

Detection of compressively sampled gratings
Author(s): Frederick A. Kingdom; Stephane J. M. Rainville
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Paper Abstract

Contrast thresholds for sine-wave gratings are increased when the gratings are compressively sampled into a set of narrow bright bars on a dark background, even though the mean luminance and contrast of the grating are unchanged by this sampling method. Burr, Ross and Morrone, who first demonstrated this phenomenon, suggested this was due to local luminance adaptation to the sample bars, whose average peak luminance necessarily increases with the degree of compressive sapling. However, the results could also be explained on the basis of either a luminance compressive non-linearity, or a local contrast-based non-linearity. Previously we reported results with decrement CSGs, which consist of dark sample bars on a bright background, which favored the local luminance adaptation hypothesis. However here we show that this hypothesis is untenable. Using increment CSGs (bright bars on a dark background) we found that raising background luminance while holding average peak sample bar luminance constant reduced thresholds by as much as a factor of ten. This demonstrates that it is the contrast of the bars, rather than their peak luminance, which is the important feature determining thresholds, at least with increment CSGs. We also provide evidence for the involvement of a gain control mechanism which serves to partially reduce the deleterious effects of the contrast-based non-linearity on CSG thresholds. Finally we show that CSG thresholds can be reduced by the presence of a low-contrast unsampled grating mask. This suggests that although local contrast processing is initially involved in CSG detection, the cortical mechanisms which ultimately detect CSGs are the same as those which detect the unsampled gratings from which they are derived.

Paper Details

Date Published: 22 April 1996
PDF: 11 pages
Proc. SPIE 2657, Human Vision and Electronic Imaging, (22 April 1996); doi: 10.1117/12.238717
Show Author Affiliations
Frederick A. Kingdom, McGill Vision Research Ctr. (Canada)
Stephane J. M. Rainville, McGill Vision Research Ctr. (Canada)

Published in SPIE Proceedings Vol. 2657:
Human Vision and Electronic Imaging
Bernice E. Rogowitz; Jan P. Allebach, Editor(s)

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