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CMC colour difference formula.

Another, more complicated, colour difference formula which is better than DE* for evaluating small colour differences is the CMC colour difference formula.

CMC = [(DL* / lSL)^2 + (DC*ab / cSC)^2 + (DH*ab / SH)^2]^0.5
where:

 	SL = 0.040975L* / (1+0.01765L*) unless L < 16 when SL = 0.511
       	SC = 0.0638C*ab / (1+0.0131C*ab) + 0.638
       	SH = (fT + 1 - f)SC
where:

	f = [(C*ab)^4 / {(C*ab)^4 + 1900)}]^0.5
       	T = 0.36 + |0.4 cos(hab + 35)|
       		unless h is between 164 and 345 degrees when
	    	T = 0.56 + |0.2 cos(hab + 168)|
DL* is delta E star etc.

For predicting colour differences, the weights l and c are set to unity, and the colour difference is referred to as the CMC(1:1) difference.