Figure 1.

Similarity of photometric maxima and minima generated by a curved surface and illusory Mach bands. (A) Digital photograph of a real-world cube manifesting a photometric highlight and lowlight (as indicated in the luminance profile beneath the photo). (B) A computer-generated image of a similar object, but lacking the highlight and lowlight. Despite the objective absence of these adornments, brightness maxima and minima (Mach bands) are apparent in the positions of their photometric counterparts in A.