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Proceedings Paper

Contrast sensitivity under natural states of adaptation
Author(s): Michael A. Webster
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Paper Abstract

The contrast sensitivity function (csf) is central to describing spatial vision and to models of visual coding, yet little is known about the form of the function under natural viewing conditions. We examined how contrast sensitivity is affected by adaption states that should arise in the course of normal viewing. Webster and Miyahara showed that adaptation to the low-frequency biases in natural scenes selectively reduces sensitivity at low frequencies. Here we examine how these sensitivity changes depend on the properties of observers, by varying subjects' refractive state or by measuring adaptation to chromatic contrast rather than luminance contrast. Defocus and physical blurring have similar effects, altering the adaptation only for strongly blurred images. Switching to chromatic contrast induces larger sensitivity changes at low frequencies, consistent with the different csf's for color and luminance. Thus natural viewing may lead to characteristic adaptation states that differ for luminance and color. To examine the basis for these sensitivity changes, we adapted to 1/f patterns filtered over different frequency bands. Adding lower frequencies to images reduces the adaption induced by higher frequencies. Thus in natural-image adaptation, the low-frequency bias may result - not from the bias in the input spectra - but because the adaptation at different spatial scales is not independent.

Paper Details

Date Published: 19 May 1999
PDF: 13 pages
Proc. SPIE 3644, Human Vision and Electronic Imaging IV, (19 May 1999); doi: 10.1117/12.348468
Show Author Affiliations
Michael A. Webster, Univ. of Nevada/Reno (United States)

Published in SPIE Proceedings Vol. 3644:
Human Vision and Electronic Imaging IV
Bernice E. Rogowitz; Thrasyvoulos N. Pappas, Editor(s)

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