The role of chromatic variance in modulating color appearance

Chromatictarget patches embedded in a chromatically variegated surround appear less saturated than when they are embedded in an achromatic uniform surround (Brown & MacLeod, 1997), which can be construed as either a form of gamut expansion for targets on uniform surrounds or as a form of gamut compression for targets on variegated surrounds.Ekroll, Faul, and Niederée (2004) suggested that the difference in perceived chromaticity on the two surrounds is caused by a layered scene decomposition, wherein the increased saturation of targets on homogenous surrounds is attributed to a decomposition of a target patch into a chromatically saturated transparent layer overlying an achromatic background.Here, we report asymmetric matching data that show the perceived chromaticity difference observed on the two surrounds depends on the particular direction of chromatic variation applied to the variegated surround. If the chromatic variegated surround has the same or a similar hue to that of the target and the saturation variation of the surround is large compared to the saturation of the target the gamut expansion effect is also large. However, if the variegated surround has a different hue than the hue of the target, the perceived chromaticity difference is small and largely does not depend on the variation in saturation of the surround. These results suggest that a layered scene representation cannot fully explain the gamut expansion effect and suggest that a chromatically tuned contrast gain control mechanism may contribute to the difference in perceived color of targets on achromatic homogeneous surrounds and chromatically variegated surrounds.