Brightness contrast: cube scene

As can be seen by masking out the context, the gray diamonds on the upper and lower front face of the cubes are identical, but look very different in the unmasked scene. When the information in a scene indicates that, on statistical grounds, two targets are differently reflective surfaces under different illuminants, they look differently bright (or light).

(Image from: An empirical explanation of brightness. Williams, SM, McCoy AN, Purves D. Proc. Natl. Acad. Sci. 95: 13301-13306 [1998])