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| Research article summary (published 30 May 2002): |
Spatial frequency, phase, and the contrast of natural images.
Full 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.
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Author information
Author/s: Bex, Peter J (PJ); Makous, Walter (W);
Affiliation: Institute of Ophthalmology, London, UK. p.bex@ucl.ac.uk
Grants: EY-1319 (Agency:United States NEI) ; EY-4885 (Agency:United States NEI)
Journal and publication information
Publication Type: Journal Article; Research Support, U.S. Gov't, P.H.S.
Journal: Journal of the Optical Society of America. A, Optics, image science, and vision (J Opt Soc Am A Opt Image Sci Vis), published in United States. (Language: eng)
Reference: 2002-Jun; vol 19 (issue 6) : pp 1096-106
Dates: Created 2002/06/06; Completed 2002/06/26; Revised 2007/11/14;
PMID: 12049346, status: MEDLINE (last retrieval date: 11/6/2008)
Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.
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