Checker Shadow Illusion

The checker shadow illusion is an optical illusion published in 1995 by Edward H. Adelson, a professor of vision science at MIT, that demonstrates how strongly context shapes human color perception. The image shows a checkerboard made of light and dark squares, part of which is covered by the cast shadow of another object; a square labeled A appears distinctly darker than a square labeled B, yet within the two-dimensional image itself the two squares are exactly the same shade, meaning they would be printed with identical ink mixtures or displayed with pixels of identical color. The illusion arises because the visual system automatically compensates for what it interprets as a shadow falling across part of the board, adjusting its judgment of a square's brightness based on the surrounding context rather than reading the raw pixel value directly.