Vector‐based modelling of colour difference: a pilot study of theDE2000 colour difference model

A novel approach to colour difference modelling is presented whereby for any givenCMC(1:1) orCIE DE2000 ∆E, ∆C, ∆H, and ∆Lcolour difference, the equivalentCIEXYZ,L*a*b*, andL*C*hcoordinate changes are derived by optimising the inputRGBstimuli from which they are all calculated. Single‐dimensionLorCorHdifference loci expressed inDE2000 difference units are thus generated, and the additive equivalence of tristimulus values is likewise projected forward onto each locus and also onto a set ofCIE DE2000 three‐unit ellipse boundaries. Using the datasets thus generated, it is then shown firstly that the derived ellipses have well‐defined semi‐axes, which explain the detailed orientation of the MacAdam ellipses inx,y,Yspace. UnitCIE DE2000 difference is confirmed as a successful quantifying constant of visual difference over a wide range of chroma, hue, and lightness differences. As a constant,CIE DE2000 unit difference is shown to have a significantly variable value at high and low chroma: evidence is established for systematic changes in both chroma and hue difference sensitivity. A hitherto unresolved non‐linearity is revealed in theC*dimension ofL*C*hspace that is not replicated in theCIE DE2000 model. The derived difference loci appear to specify physically reproducible experimental stimuli that could be used in the estimation of visual difference magnitude. Overall, the data derived by the new approach and presented in this paper increase the probability that a true vector model of the visual difference response may eventually be derived.