HunterLab EasyMatch QC, User Manual

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EasyMatch QC User’s Manual Version 2.1
Measurement Values A-1
APPENDIX A
Measurement Values
Color values calculated using EasyMatch QC are relative to the absolute value of a perfect reflecting
diffuser as measured under the same geometric conditions, according to the January 1, 1969
recommendation of the International Commission on Illumination, CIE. These values are traceable to
measurements made at the National Institute of Standards and Technology.
All of the data types available for display within EasyMatch QC’s Spectral Data Table view are
described in the “Spectral Data Types” section at the end of this appendix. The remaining sections
describe the color scales, color difference scales, indices, and read methods available for display in your
Color Data Table view.
Color Scales and Related Color Difference Scales
CIE Tristimulus XYZ Scale
EasyMatch QC performs integration of reflectance/transmittance values over the visible spectrum to
arrive at tristimulus X, Y, and Z values. These values simulate the color matching response functions of
the human observer as defined by the 1931 2° Standard Observer or the 1964 CIE 10° Standard
Observer (as selected). Tristimulus integrations based on any or all of the illuminants may be selected.
For a complete description of how to calculate tristimulus values, refer to the publication CIE 15.2 and
to ASTM Method E308.
The related color difference values are defined as follows:
dX = X
SMP
- X
STD
dY = Y
SMP
- Y
STD
dZ = Z
SMP
- Z
STD
.
CIE Chromaticity Coordinates, Yxy
The relationship between CIE XYZ values and the x,y chromaticity coordinates is as follows:
Y = CIE Tristimulus Y (as above)
x =
X
X Y + Z
+
y =
Y
X + Y + Z
The related color difference values are defined as follows:
dY = Y
SMP
- Y
STD
dx = x
SMP
- x
STD
dy = y
SMP
- y
STD
.