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The perceived brightness of an object does not correspond in a simple way with its luminance, and two objects of equal lumi-nance can appear to have different levels of brightness if they are observed in different contexts. Such simultaneous bright-ness contrast (SBC) is observed, for example, when a gray circle appears brighter against a dark background than against a light background (Fig. 1a). Similarly, spatially distinct ele-ments of a visual scene can induce an illusory percept of lumi-nance contours if the organization of those elements induces the visual system to extrapolate the presence of an occluding surface (Fig. 1b), as in the Kanizsa triangle illusion (Kanizsa