White's illusion is an optical illusion illustrating the fact that the same target luminance can elicit different perceptions of brightness in different contextes. (New World Encyclopedia)
Rectangle on the right, look much darker than the rectangle on the left. However, Both rectangles reflect the same amount of light.
Description: White's illusion is made up of a series of black and white horizontal bars. On one side, shorter gray bars cover the black bars; on the other side, they cover the white bars. When observing the image, it appears as though the gray bars surrounded by white stripes are definitively lighter than the gray bars surrounded by black stripes. In addition to appearing lighter, the gray bars surrounded by white also appear to be brighter, or of higher luminance. (New World Encyclopedia)
Munker illusion is a similar illusion that uses colors instead of grayscale.
Note, that although the blue rectangles are all of equal luminance, the brightness of the blue rectangles appear to shift toward the brightness of the top and bottom bordering stripes
The black bars are removed with the Photoshop Elements' Magic Wand tool.