COLOR DIFFERENCES UNDER ILLUMINANT-D65 AND ILLUMINANT-A

Some previous experimental results on color discrimination using objec t colors under illuminants D65 and A have been analyzed. From these re sults, the color-difference responses under D65 and A appear to be hig hly similar; leading to the conclusion that the CIE94 color-difference formula can be employed under illuminant A. The hue-angle dependences of Delta H-ab after corrections for C-ab*, are also similar for both illuminants, showing only a weak trend with two minima. However, the performance of the CIE94 formula clearly improves when different linea r functions of L are used, as new weighting functions of the lightnes s difference, for each illuminant. The usefulness of the CIE94 formula under D65 and A illuminants can also be understood bearing in mind th at the differences between color-discrimination thresholds obtained un der both illuminants are of the same order of magnitude, or only sligh tly higher, than those associated with the observer variability.