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Journal of the Optical Society of America A

Journal of the Optical Society of America A


  • Editor: Stephen A. Burns
  • Vol. 22, Iss. 10 — Oct. 1, 2005
  • pp: 2039–2049

Contrast statistics for foveated visual systems: fixation selection by minimizing contrast entropy

Raghu Raj, Wilson S. Geisler, Robert A. Frazor, and Alan C. Bovik  »View Author Affiliations

JOSA A, Vol. 22, Issue 10, pp. 2039-2049 (2005)

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The human visual system combines a wide field of view with a high-resolution fovea and uses eye, head, and body movements to direct the fovea to potentially relevant locations in the visual scene. This strategy is sensible for a visual system with limited neural resources. However, for this strategy to be effective, the visual system needs sophisticated central mechanisms that efficiently exploit the varying spatial resolution of the retina. To gain insight into some of the design requirements of these central mechanisms, we have analyzed the effects of variable spatial resolution on local contrast in 300 calibrated natural images. Specifically, for each retinal eccentricity (which produces a certain effective level of blur), and for each value of local contrast observed at that eccentricity, we measured the probability distribution of the local contrast in the unblurred image. These conditional probability distributions can be regarded as posterior probability distributions for the “true” unblurred contrast, given an observed contrast at a given eccentricity. We find that these conditional probability distributions are adequately described by a few simple formulas. To explore how these statistics might be exploited by central perceptual mechanisms, we consider the task of selecting successive fixation points, where the goal on each fixation is to maximize total contrast information gained about the image (i.e., minimize total contrast uncertainty). We derive an entropy minimization algorithm and find that it performs optimally at reducing total contrast uncertainty and that it also works well at reducing the mean squared error between the original image and the image reconstructed from the multiple fixations. Our results show that measurements of local contrast alone could efficiently drive the scan paths of the eye when the goal is to gain as much information about the spatial structure of a scene as possible.

© 2005 Optical Society of America

OCIS Codes
(110.2960) Imaging systems : Image analysis
(330.0330) Vision, color, and visual optics : Vision, color, and visual optics
(330.1800) Vision, color, and visual optics : Vision - contrast sensitivity
(330.2210) Vision, color, and visual optics : Vision - eye movements
(330.4060) Vision, color, and visual optics : Vision modeling
(330.6110) Vision, color, and visual optics : Spatial filtering

ToC Category:
Visual Coding and Natural Scene Statistics

Original Manuscript: January 7, 2005
Manuscript Accepted: February 24, 2005
Published: October 1, 2005

Raghu Raj, Wilson S. Geisler, Alan C. Bovik, and Robert A. Frazor, "Contrast statistics for foveated visual systems: fixation selection by minimizing contrast entropy," J. Opt. Soc. Am. A 22, 2039-2049 (2005)

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