The Effect of Perceived Transparency on Brightness Judgments

Subjects matched the brightness of test patches located within a larger surround, where the surround was made to appear either different in reflectance from neighboring regions, or of the same reflectance but viewed beneath a transparent film. In both conditions the luminance and spatial extent of the immediate surround was equivalent, thus controlling for the effects of local contrast. Perceived transparency had a small but significant effect on brightness. Test patch brightness was most significantly elevated when the perception of transparency was supported by stereo depth cues. The effect was, however, mediated by the virtual transmittance of the transparent overlay, increasing in magnitude with decreasing transmittance. Further, the effect of transparency on brightness was greatest for test patch luminances near to those of their immediate backgrounds. The implications of these results for the understanding of configurational effects on brightness is discussed.