What is the CMC equation?

The CMC colour difference formula allows calculation of tolerance ellipsoids around the target standard where the dimensions of the ellipsoid is a function of the position in colour space of the target. The design of this formula allows for two user-definable coefficients l and c and the formula is thus normally specified as CMC(l:c). The values of l and c modify the relative importance that is given to differences in lightness and chroma respectively. The CMC(2:1) version of the formula has been shown to be useful for the estimation of the acceptability of colour difference evaluations.

The CMC(2:1) equation is a British Standard (BS:6923) for the assessment of small colour differences and is currently being considerd as an ISO standard.