HunterLab SpectraTrend HT, User Manual

Page: 103 / 109

SpectraTrend HT User’s Guide 3.2
103
Colorant Strength
When SMA is selected as the index, color values are adjusted based on the wavelength of maximum
absorbance (minimum reflectance) of the standard. The strength value is displayed as a percentage.
SMA = (K/S)

where
 
) S - (K * ) S - (1.0 * 2.0
) K - (1.0
(K/S)
2
  


=
K

= the absorption coefficient of the specimen (the %R value normally measured by a
spectrophotometer and normalized to 1.0)
S

= the scattering coefficient of the specimen (assumed to be 0.0 for most applications).
SW is K/S weighted by the visual function (such as the XYZ observer functions and the D65 illuminant
energy function) and summed over a wavelength interval within the visible spectrum.

=

  

d S * (K/S) * E SW
where

= wavelength over the available range of the spectrophotometer
E = energy distribution of the illuminant being used
S = observer functions.
dEcand CMC Autotolerancing
The equation for dEc describes an ellipsoidal volume with axes in the direction of lightness, chroma, and
hue centered about a standard. When the semi-axis lengths for the

Ec formula equal the calculated lSL,
cSc, and SH values for the standard, the resulting ellipsoid describes a 1.0 dEc unit volume/tolerance.
This volume and the size of its component parts become the basis for the establishment of an
appropriately-sized volume of acceptability for a given commercial situation by the application of a
commercial factor (cf). The cf equals the dEc tolerance.
When l = 2.0 and c = 1.0, the equation fixes the ratio of the three components (SL:SC:SH) to correlate
with visible assessment of typical textile samples. Other values of l may be required in cases where the
surface characteristics change dramatically. The value of c is always left at 1.0.
2 2 2
SH
* dH
+
cSC
* dC
+
lSL
* dL
= dEc


















Absolute
lSL
* dL
= c * dL
cSC
* dC
= c * dC
SH
* dH
= c * dH