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The Oxford Compendium of Visual Illusions$
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Arthur G. Shapiro and Dejan Todorovic

Print publication date: 2017

Print ISBN-13: 9780199794607

Published to Oxford Scholarship Online: June 2017

DOI: 10.1093/acprof:oso/9780199794607.001.0001

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The Staircase Gelb Illusion

The Staircase Gelb Illusion

Chapter:
(p.367) Chapter 46 The Staircase Gelb Illusion
Source:
The Oxford Compendium of Visual Illusions
Author(s):

Alan Gilchrist

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199794607.003.0046

Adhemar Gelb showed that if a piece of black paper is suspended in midair and illuminated by a projector, it appears white. However, when a white paper is brought into the projector beam and placed next to or surrounding the black paper, the black paper once again appears black. In the staircase Gelb illusion, a succession of increasingly lighter papers, dark gray, middle gray, light gray, and finally white, is brought into the projector beam. Each time a lighter paper is added it appears white, and this causes the prior paper to darken, due to the highest luminance rule of anchoring. When all five shades are present within the beam, the gamut of perceived values is compressed relative to the actual values. The compression requires the simultaneous juxtaposition of different illumination levels and illustrates the codetermination principle of Kardos.

Keywords:   lightness, illusion, Gelb illusion, codetermination, gamut, compression

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