SOME ASPECTS OF THE VISUAL SCALING OF LARGE COLOR DIFFERENCES

The formulation of a metric to provide numbers that correlates with vi sually perceived colour differences has proved a very difficult task. Most early experimental work was concerned with just-perceptible colou r differences. Later the concept of perceptibility was expanded to acc eptability, it being argued that many industrial tolerances were large r than just-perceptible. This led naturally to the concept of large co lour differences and the question as to whether the current CIE colour -difference formulae, specified as appropriate for just-perceptible di fferences, can be applied to larger differences than those concerned w ith, for instance, colour matches experienced in the fabric dyeing ind ustry. This article investigates the application of four colour-differ ence formulae to visual scaling of large colour differences between ph otographically prepared reflection colour samples at approximately con stant lightness. It is shown that the scaling of colour differences de pends on the directions of hue and chroma difference of a test sample when compared with a reference. It is also shown that, of the four can didate colour-difference, referred to as CIE 1976 L a *b* colour diff erence, referred to as CIE1994 or Delta E-94, correlates best with vi sual scaling. (C) 1997 John Wiley & Sons, Inc.