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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 19, Iss. 6 — Jun. 1, 2002
  • pp: 1096–1106

Spatial frequency, phase, and the contrast of natural images

Peter J. Bex and Walter Makous  »View Author Affiliations


JOSA A, Vol. 19, Issue 6, pp. 1096-1106 (2002)
http://dx.doi.org/10.1364/JOSAA.19.001096


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Abstract

We examined contrast sensitivity and suprathreshold apparent contrast with natural images. The spatial-frequency components within single octaves of the images were removed (notch filtered), their phases were randomized, or the polarity of the images was inverted. Of Michelson contrast, root-mean-square (RMS) contrast, and band-limited contrast, RMS contrast was the best index of detectability. Negative images had lower apparent contrast than their positives. Contrast detection thresholds showed spatial-frequency-dependent elevation following both notch filtering and phase randomization. The peak of the spatial-frequency tuning function was approximately 0.5–2 cycles per degree (c/deg). Suprathreshold contrast matching functions also showed spatial-frequency-dependent contrast loss for both notch-filtered and phase-randomized images. The peak of the spatial-frequency tuning function was approximately 1–3 c/deg. There was no detectable difference between the effects of phase randomization and notch filtering on contrast sensitivity. We argue that these observations are consistent with changes in the activity within spatial-frequency channels caused by the higher-order phase structure of natural images that is responsible for the presence of edges and specularities.

© 2002 Optical Society of America

OCIS Codes
(330.1800) Vision, color, and visual optics : Vision - contrast sensitivity
(330.5510) Vision, color, and visual optics : Psychophysics
(330.6100) Vision, color, and visual optics : Spatial discrimination
(330.6110) Vision, color, and visual optics : Spatial filtering
(330.7310) Vision, color, and visual optics : Vision

History
Original Manuscript: September 28, 2001
Revised Manuscript: November 28, 2001
Manuscript Accepted: November 28, 2001
Published: June 1, 2002

Citation
Peter J. Bex and Walter Makous, "Spatial frequency, phase, and the contrast of natural images," J. Opt. Soc. Am. A 19, 1096-1106 (2002)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-19-6-1096

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