HunterLab EasyMatch QC, User Manual

Page: 295 / 366

EasyMatch QC User’s Manual Version 2.1
Measurement Values A-5
b* = ) - Blue(-) axis =








3
n
3
n
Z
Z
-
Y
Y
200
C*
ab
= CIE 1976 a,b chroma=
2 2
* b * a
+
h° = CIE 1976 a,b hue-angle = arctan (b*/a*)
dh* = h°
Std
- h°
Sam
dH*
ab
= CIE 1976 a,b hue-difference =
2 2 2
* dC * dL * dE
− −
Note: Since hue angle changes dramatically for small differences in neutral and near-neutral
colors, use of dH*
ab
hue difference is not recommended when C* < 5. In this case, use dL*, da*,
and db* instead to define color differences.
dC* = Chromaticity difference in the a*b* plane = C*
smp
- C*
std
dE*
ab
= CIE 1976 L*a*b* color difference formula =
2 2 2
* db + * da * dL
+
d = Difference between Sample and Standard.
Reference: Commission International de l’Eclairage (CIE): “Recommendations on Uniform Color
Spaces, Color Difference Equations, Psychometric Color Terms,” Supplement No. 2 to
CIE Publication
No. 15 , Colorimetry, Bureau Central de la CIE, Paris, 1978. For more information, see AATCC Test
Method 173: Calculation of Small Color Differences .
Hunter Rdab Color Scale
The relationship between the Hunter Rd,a,b values and the CIE XYZ values for any illuminant is as
follows:
L(Rd) = Y
( )






=
n n
a
Y
Y
-
X
X
Y f K a(Rd)
( )






=
n n
b
Z
Z
-
Y
Y
Y f K b(Rd)
where
( )
f Y = 0.51
21 + 0.2Y
1 + 0.2Y
.
X, Y, and Z are the CIE tristimulus values obtained for the sample.