throughmirrorA different way of seeing
Craik–O’Brien–Cornsweet Illusion — Equal fields look different because of a narrow gradient at their boundary.
Look closely. Let the image settle.
Light & contrast / 1959–1970

Craik–O’Brien–Cornsweet Illusion

Equal fields look different because of a narrow gradient at their boundary.

TRY THIS

Cover the central transition and compare the flat areas on either side.

FOLLOW THE SOURCES

History, evidence & image credit

THE IMAGE IN THIS ARCHIVE

Lord Belbury

Original file & attribution · CC BY-SA 4.0

Original image downloaded from Wikimedia Commons; the downloaded file is unchanged. Gallery previews may be resized or converted to WebP; animated previews show the first frame.

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Frequently asked questions

What is Craik–O’Brien–Cornsweet Illusion?

Equal fields look different because of a narrow gradient at their boundary.

What should I look for in Craik–O’Brien–Cornsweet Illusion?

Cover the central transition and compare the flat areas on either side.

What explains Craik–O’Brien–Cornsweet Illusion?

A small brightness transition at the edge influences the apparent tone of larger adjoining regions. The flat parts can have equal luminance despite their different appearance.

Another way to see it

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Checkerboard and cylinder casting a shadow, with squares A and B labeled.

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Edward H. Adelson

Two squares. One shade of gray. A shadow changes everything.

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Ludimar Hermann

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White disks at gray grid intersections over black squares.

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James R. Bergen; later Bernd & Elke Lingelbach, Michael Schrauf & E. R. Wist

Black dots flicker across a grid of white dots.

Craik–O’Brien–Cornsweet Illusion — Equal fields look different because of a narrow gradient at their boundary.

Craik–O’Brien–Cornsweet Illusion