Suggested modification of CMC formula for acceptability

The Colour Measurement Committee [CMC] formulas for color‐difference acceptability do not describe ellipsoids in CIELAB space, but the literature describes the acceptability surfaces as ellipsoids. It turns out that the discrepancy does not affect computational results [as long as the CMC parameter c is 1]. However, if the ellipsoid equations were substituted for the existing quartic formulas, the possibility for conceptual confusion would be much reduced.