Luminance-dependent long-term chromatic adaptation.

There is theoretical and empirical support for long-term adaptation of human vision to chromatic regularities in the environment. The current study investigates whether relationships of luminance and chromaticity in the natural environment could drive chromatic adaptation independently and differently for bright and dark colors. This is motivated by psychophysical evidence of systematic difference shifts in red-green chromatic sensitivities between contextually bright- versus dark-colored stimuli. For some broad classes of scene content, consistent shifts in chromaticity are found between high and low light levels within images. Especially in those images in which sky and terrain are juxtaposed, this shift has direction and magnitude consistent with the observed psychophysical shifts in the red-green balance between bright and dark colors. Taken together, these findings suggest that relative weighting of M- and L-cone signals could be adapted, in a luminance-dependent fashion, to regularities in the natural environment.