Adelson's Squares

Simlar to the spirals sample, Adelson's squares demonstrate that human vision and perception is error prone for quantitative measurements. In the natural context in which humans evolved, it makes sense to compensate for shadows. However, this makes us believe that the two squares with the black diamonds have a different shade of grey, yet they are identical in brightness (RGB values). Since one is part of the "whites", and the other the "blacks", our brains, recognising the checkerboard pattern, fool our perception to believe the "white" square is lighter than the "black" square, because we unconciously correct for the darker shadow cast by the cylinder.