Same color illusion

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Squares A and B are the same color.

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

The same color illusion — also known as Adelson’s checker shadow illusion, checker shadow illusion and checker shadow — is an optical illusion published by Ted Adelson in 1995. The squares A and B on the illusion are of the same color (or shade), although they seem to be different.

"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."^[1]

Note, the two pictures to the right actually use techniques that are slightly different in order to create the illusion. The animated gif on the bottom actually shows Adelson's checker in its most pure form, where boxes A and B are exactly the same. In the still gif on the top, the effect is more pronounced, not only because the picture is not animated, but because in the picture on top, the "B" label inscripted on the box in the shade is darker than the color of the box, whereas the "A" label in the box in direct light is lighter than the color of its box. In the animated gif on the bottom, this is not the case: the "A" and "B" labels are the same shade. The pictures on the top and bottom are not the same, and the Adelson's checker image on the bottom can be said to be a purer demonstration of the principle.