HunterLab EasyMatch QC, User Manual

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EasyMatch QC User’s Manual Version 2.1
Measurement Values A-19
b*/a* Ratio
b*/a* Ratio is simply the b* of CIEL*a*b* divided by the a* of CIEL*a*b*.
b*/a* Difference is also available, and is defined as follows:
db*/a* = (b*/a*)
sample
- (b*/a*)
standard.
Brightness 457
457 nm Brightness can be used to measure the relative brightness of paper. 457 nm brightness is
calculated over the range of 400 nm to 510 nm in accordance with TAPPI document T452. While
HunterLab’s spectrophotometer geometries do not conform exactly to those specified by TAPPI, the
measurements correlate closely with those made on TAPPI-compliant instruments.
457 nm Brightness Difference is also available, and is defined as follows:
d457nm Brightness = (457nm Brightness)
sample
- (457nm Brightness)
standard.
Color Value
Color Value is a single numerical value related to the amount of light-absorbing material (colorant)
contained in a sample and is usually based on spectral data. It is most often used to calculate the
difference in strength (% Strength) between a standard and a sample. Color Value may be calculated by
any one of three acceptable methods. The color value which results from one method may not agree
with any other method. The choice of method is usually dependent on the nature of the sample and the
need to obtain a color value. The Spectrophotometric methods for obtaining color value are labeled as
Color Value SUM, Color Value SWL, and Color Value WSUM, as described below.
Color Value SUM
Color Value SUM is calculated as the sum of the K/S values for the sample read across the spectrum for
reflectance measurements, and from the sum of the absorbances for the sample read across the spectrum
for transmittance measurements.
points #
S
K
= SUM Value Color
points #
1 =
∑
λ
λ
for reflectance
points #
Absorbance
= SUM Value Color
points #
1 =
∑
λ
λ
for transmittance.
K/S and Absorbance are described in the Spectral Data Types section of this appendix.
Color Value SUM Difference is also available, and is defined as follows:
dColor Value SUM = (Color Value SUM)
sample
- (Color Value SUM)
standard.