Invariant cone-excitation ratios may predict transparency

Cone-excitation ratios for pairs of surfaces are almost invariant under cha nges in illumination and offer a possible basis for color constancy [Proc. R. Sec. London Ser. B 257, 115 (1994)]. We extend this idea to the per cept ion of transparency on the basis of the close analogy between the changes i n color signals that occur for surfaces when the illumination changes and t he changes in color signals when the surfaces are covered by a filter. This study presents measurements and simulations to investigate the conditions under which cone-excitation ratios are statistically invariant for physical ly transparent systems. The invariance breaks down when the spectral transm ission of the filters is low at some or all wavelengths. We suggest that co ne-excitation ratios might be useful to define the stimulus conditions nece ssary for the perception of transparency. (C) 2000 Optical Society of Ameri ca. [S0740-3232(00)00602-5] OCIS codes: 330.1690, 330.1720, 330.7310, 330.1 710.