Uniform Colour Space Based on the CMC(l:c) Colour‐difference Formula

Abstract

The CMC(c) colour‐difference formula agrees more closely with visual assessments than does the CIE L*a*b* formula, but hitherto there has been no associated ‘uniform colour space’. A new colour space similar in form to CIE L*a*b* space has been derived in which distances agree closely with the corresponding ΔE(CMC) values. The new space was extensively tested using real and hypothetical pairs of samples. In each case the distance, in the space, between a pair of samples was compared with the ΔE(CMC) value. The disagreement rarely exceeded 20%, while discrepancies between distances in CIE L*a*b* space and those implied by the CMC formula can exceed 500%.It is easy to construct ‘micro‐spaces’ apparently corresponding to the CMC formula which should be applicable to small regions of colour space and hence useful for applications such as colour sorting. Such micro‐spaces did not agree with the CMC formula as well as did the new space.The new space represents a substantial improvement over CIE L*a*b* space with respect to uniformity; its form is similar to CIE L*a*b* and so is easy to use.