METHODS FOR QUANTIFYING METAMERISM .1. VISUAL ASSESSMENT

This work forms part of the Society of Dyers and Colourists' CMC Worki ng Group 1 project on metamerism and colour constancy. The aim of the project is to derive reliable indices for predicting metamerism and co lour constancy. Some 76 metamers were prepared by dyeing wool with aci d dyes. Two experiments were conducted to quantify the degree of metam erism using a grey-scale method. In the first experiment each metamer' s colour difference was assessed against a grey scale by a panel of ob servers under seven light sources. The second experiment was carried o ut under three sources: D-65, A and TL(84). Each observer assessed not only the total colour difference as in the first experiment but also the separate lightness, chroma, and hue components. Observer variation s were investigated in terms of observer precision, and within- and be tween- observer errors. Cross-over wavelengths for each metamer were a lso examined. It was found that intersections tend to converge on thre e wavelengths for almost all metamers used here, in agreement with pre vious findings.