YouTuber brusspup recreates MIT professor Edward H. Adelson’s incredible checker shadow illusion by using light and shadow to transform a gray square into a white square right before your very eyes!
So how does it work, exactly? The key lies in the shadow cast by the cylinder and how our brains process light. The shadow darkens the central square, but it still appears to be "light" in colour because of the contrast with its darker neighbours. Our brains are fooled by this local contrast making it difficult to perceive that the "light" square in the shadow has the same absolute shade as the "dark" square out of it.