Delta xyY colour difference

Assessment of colour is more than a numeric expression. Usually it's an assessment of the colour difference (delta) from a known standard. CIELAB (L*a*b*) and CIELAB (L*C*h) are used to compare the colours of two objects.

The expressions for these colour differences are DL*, Da*, Db*, or DL* DC* DH* ("D" symbolises "delta," which indicates difference).

Note: DH* is usually used instead of Dh to enable DE* to be calculated.

DH* = 2(C ₁ *.C ₀ *) ^1/2 sin (Dh/2)

Where C₀* & C₁* are chromaticities of the colours being compared and Dh is in the range +180°. (If Dh is outside this range then 360° is added or /subtracted to bring it inside.)

Given DL*, Da* and Db*, or DL*, DC* and DH* the total difference or distance on the CIELAB diagram can be stated as a single value, known as DE*.

DE*ab = [(DL) ² + (Da) ² + (Db) ² ] ^1/2

DE*ab = [DE*) ² + (DC*) ² + (DH*) ² ] ^1/2

thus...

DL* = difference in lightness/darkness value (+ = lighter - = darker)
Da* = difference on red/green axis (+ = redder - = greener)
Db* = difference on yellow/blue axis (+ = yellower - = bluer)
DC* = difference in chroma (+ = brighter - = duller)
DH* = difference in hue
DE* = total colour difference value

Note: CIE stands for Commission Internationale de l´Eclairage (The International Commission on Illumination)