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File:Optical.greysquares.arp.gif

As the cyclinder's shadow forms square B appears to lighten.

Same color illusion, also known as Adelson’s "Checker shadow illusion" or Checker shadow illusion or just Checker shadow, is a visual illusion. The squares A and B on the illusion are of the same color (or shade), although they seem not to be. You can check it out with an eyedropper in a graphic program. By moving a copied fragment of B with mouse you can even see live how the shade changes in front of your eyes (animation of this effect in WMV, AVI_XVID, SWF formats, as well as EXE file can be downloaded from this page).

"When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material." [quotation from this page]

It was first published by Ted Adelson in 1995. The original figure. Ted Adelson's explanation.

You can also see the illusion at [1] and [2] and [3]

Other illusions involving color

External links

Three small squares are the same colour

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-[[Image:Optical.greysquares.arp.jpg|thumb|right|250px|Squares A and B are the same color.]]
+[[Image:Optical.greysquares.arp.jpg|thumb|right|Squares A and B are the same color.]]
+[[Image:Optical.greysquares.arp.gif|thumb|right|As the cyclinder's shadow forms square B appears to lighten.]]
 '''Same color illusion''', also known as '''Adelson’s  "Checker shadow illusion"''' or '''Checker shadow illusion''' or just '''Checker shadow''', is a [[visual illusion]]. The squares A and B on the illusion are of the same color (or shade), although they seem not to be.
 You can check it out with an eyedropper in a graphic program. By moving a copied fragment of B with mouse you can even see live how the shade changes in front of your eyes (animation of this effect in WMV, AVI_XVID, SWF formats, as well as EXE file can be downloaded from [http://naukiniekonwencjonalne.feedle.com/materialy/NaukiNieKonwencjonalne_ak.html this page]).