Digital Color Management: Encoding Solutions, 2nd Edition

D

Adaptation

The term adaptation refers to various processes by which the visual mechanism adjusts to the conditions under which the eyes are exposed to radiant energy. The relationship between the physical characteristics of a given color stimulus and the perception of its color is strongly influenced by effects produced by a number of different forms of adaptation.

In this book, three types of visual adaptation of particular importance in color-imaging applications are considered: general-brightness adaptation, lateral-brightness adaptation, and chromatic adaptation.

General-Brightness Adaptation

General-brightness adaptation refers to the adjustments of the visual mechanism in response to the average luminance of the stimuli to which the eyes are exposed. General-brightness adaptation must be considered in the encoding of images displayed in viewing conditions in which the observer fully or partially adapts to the displayed image itself. Such adaptation will occur when images are viewed under conditions that eliminate or minimize other visual cues that might influence the adaptive state of the observer.

The following describes one procedure that can be used to transform the colorimetry of an image to brightness-adapted colorimetry. The procedure accounts for general-brightness adaptation effects.

First, the XYZ tristimulus values for each image pixel are determined, using standard colorimetric methods. Each Y tristimulus value then is adjusted by an experimentally determined ...