Colorimetric implications of the standard observer (2◦) in metameric matches

Many works have shown colorimetric additivity failures in colour-matching experiments. Thus, in the present work, using the colour-matching functions (CMF) of three real observers, we have conducted five experiments in isomeric and metameric matching. The stimuli matched, using two modified Donaldson colorimeters, were two achromatic, one blue, one orange and one green. Afterwards, we determined both the isomeric and the metameric discrimination ellipsoids for all the matches and for each observer. The results reflected differences in chromaticity and luminance with respect to the results of the CIE-1931 Standard Observer. When we compared our results (of each observer with his CMF) for the isomeric and metameric matches, we found that, according to the differential colour thresholds, the prediction was acceptable for chromaticity but not for luminance. The experimental results revealed the need to revise some aspects of the CIE-1931 Standard Observer.