Douglas G. Walker

Effects of illuminant spectra on desktop color reproduction

With the advent of color management systems, and other methods of controlling the color reproduction of computer systems and their imaging peripherals, the use of colorimetric techniques to encode color information is gaining prominence. The calculation of colorimetric quantities to describe reflective materials always involves the use of an illuminant spectrum. This paper examines how the results of these calculations differ as the illuminant is changed from the standard CIE D50 daylight spectrum to a more realistic fluorescent viewing booth lamp intended to simulate D50. Color difference formulae are used to quantify the difference for a wide variety of color printing devices. In the case of certain colors, differences of greater than 6 (Delta) E*ab units are found for virtually all of the devices considered. The interaction of the illuminant spectra with the spectral reflectance of printer colorants is analyzed in some detail. Also, a method is presented which allows for the device specific transformation of colorimetric variables appropriate for one of the illuminants into those appropriate for another illuminant. Finally, recommendations are made concerning the standardization of practical D50 illuminants and their importance to the digital communication of color images.