Contrast sensitivity under natural states of adaptation

Michael A. Webster

doi:10.1117/12.348468

19 May 1999 Contrast sensitivity under natural states of adaptation

Michael A. Webster

Proceedings Volume 3644, Human Vision and Electronic Imaging IV; (1999) https://doi.org/10.1117/12.348468
Event: Electronic Imaging '99, 1999, San Jose, CA, United States

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.

Citation Download Citation

Michael A. Webster "Contrast sensitivity under natural states of adaptation", Proc. SPIE 3644, Human Vision and Electronic Imaging IV, (19 May 1999); https://doi.org/10.1117/12.348468

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