Inter-observer agreement on visual colour matches and the role of metamerism as a cause of disagreement

Abstract

The phenomenon is investigated, of ‘Observer Metamerism’ (one illuminant, two differing observers), as distinct from Illuminant Metamerism (one observer and two differing light sources). Difference in colour perception is quantified by the CIE Colour Matching Functions or CMFs which map response with respect to wavelength. The size of potential mismatches is quantified using calculations which compare co-ordinates, derived from the CMFs of 10 individual observers, with co-ordinates derived from the Standard Observer CMFs as a constant reference. The individual CMFs used are those of 10 of the observers whose colour matching responses were used in the 1964 Supplementary Standard Observer average. The colour-inconstancy results found on change of observer, suggest a level of observer-metameric effects that is likely to affect visual matching judgements by a high proportion of individual observers. The data suggest that, in practical situations, two individuals are likely to disagree on both the magnitude and direction of visible colour difference in metameric matches, and individual observers may also dispute the presence or absence of a visible metameric difference in many sample pair comparisons.