Abstract
The dimensions of early color coding are highly asymmetric (e.g. in the relative number of cones or in the signals available for luminance or chromatic contrast), yet perceptually the world seems to vary as much in color as lightness and seems balanced in hue. We examined the nature of this perceptual equivalence by measuring the subjective color balance in images. Stimuli were 1/f noise images formed by combining different noise sources for the RGB values. These allowed a full gamut of colors to be shown at different spatial scales without tying colors to familiar objects. Luminance contrast was fixed while observers adjusted the LvsM and SvsLM contrast to equate the perceived magnitude. Subjects reliably judged the relative salience of signals along the three axes, and LvsM and SvsLM contrasts scaled roughly proportionately to luminance contrast and to each other. We compare these subjectively equated contrasts to the range of contrasts for images of natural scenes. The perceived gamut of colors may be adapted to match the range of contrasts to which observers are exposed. Consistent with this, the perceived balance is altered after observers are adapted to images in which the gamut of colors is reduced or exaggerated.