Chromatic Adaptation to Image Displays

The human visual system has evolved with a sophisticated set of mechanisms to produce stable perceptions of object colors across changes in illumination. This phenomenon is typically referred to as chromatic adaptation or color constancy. When viewing scenes or hard-copy reproductions, it is generally assumed that one adapts almost completely to the color and luminance of the prevailing light source. This is likely not the case when soft-copy image displays are viewed. Differences in the degree of chromatic adaptation to hard-copy and soft-copy displays point to two types of chromatic-adaptation mechanisms: sensory and cognitive. Sensory mechanisms are those that act automatically in response to the stimulus, such as retinal gain control. Cognitive mechanisms are those that rely on observers' knowledge of scene content. For example, an observer knows the color of his own skin or a piece of paper and therefore can discount the effects of colored illuminants. A series of experiments that measured the spatial, temporal, and chromatic properties of sensory chromatic-adaptation mechanisms are discussed. The results show that these mechanisms are chromatically incomplete, spatially localized, and have a time course on the order of tens of seconds. In addition, the influence of cognitive factors is presented quantitatively through experiments that measured the state of chromatic adaptation to hard-copy and soft-copy displays with various amounts of recognizable scene content. A mathematical model for predicting these chromatic adaptation effects is presented along with some practical recommendations, based on psychophysical experiments, on how to approach these problems in typical cross-media color reproduction situations. displays with various amounts of recognizable scene content. A mathematical model for predicting these chromatic adaptation effects is presented along with some practical recommendations, based on psychophysical experiments, on how to approach these problems in typical cross-media color reproduction situations.