It is computed as:: formula_12where "K""b" is a coefficient that depends upon the illuminant (for D65, "K""b" is 67.20; see approximate formula below) and "Z""n" is the "Z" tristimulus value of the specified white object.
It is computed as:formula_66where formula_67 is a coefficient which depends upon the illuminant (for D65, formula_67 is 67.20; see approximate formula below) and Zn is the Z tristimulus value of the specified white object.