A psychophysical experiment was carried out to examine the relationship between image contrast and overall perceived brightness. A second phase of the experiment looked at the relationship between the perceived brightness of variegated backgrounds and the simultaneous contrast effect produced by such backgrounds. These results have important ramifications for procedures used to calculate adapting chromaticities and luminances for image displays. The results suggest that the traditional concepts of linear luminance integration and equivalent background are satisfactory on average. However, results for individual observers show very striking, consistent, and significant trends with substantial inter-observer variability. These results help to reconcile differences between fundamental vision science experiments and practical experiences with color appearance models.