HunterLab SpectraTrend HT, Руководство пользователя

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SpectraTrend HT User’s Guide 3.2
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Whiteness is associated with a region or volume in color space in which objects are recognized as white.
Degree of whiteness is measured by the degree of departure of the object from a
perfect white.
Whiteness Index E313 (displayed as WIE) is the whiteness index published in ASTM Method E313.
WI CIE = Y + 800 (x
n
- x) + 1700 (y
n
- y) = WI-E313
where Y, x, and y are the luminance factor and chromaticity coordinates of the specimen, and x
n
and y
n
are the chromaticity coordinates for the CIE illuminant and standard observer used. These values are
provided in the table given in ASTM E313. This index is only displayed when the data view is configured
for either the C or the D65 illuminant, as these are the only relevant illuminants.
Refer to ASTM Method E313, “Standard Practice for Calculating Yellowness and Whiteness Indices from
Instrumentally Measured Color Coordinates,” for more information.
Y Brightness
Y Brightness (Y) is also known as luminosity or light intensity. This index is calculated in the same way as
(and is equivalent to) the Y of the XYZ tristimulus scale.
Yellowness Indices
Visually, yellowness is associated with scorching, soiling, and general product degradation by light,
chemical exposure, and processing. Yellowness indices are used chiefly to measure these types of
degradation.
Yellowness Index per ASTM Method E313 (displayed as YIE) is calculated as follows:
( )
Y
Z C - X C 100
= 96 - E313 YI
Z x
Where X, Y, and Z are the CIE tristimulus values and the coefficients depend on the illuminant and
observer as indicated in the table given in ASTM E313. This index is only displayed when the data view is
configured for either the C or the D65 illuminant, as these are the only relevant illuminants.
Refer to ASTM Method E313, “Standard Practice for Calculating Yellowness and Whiteness Indices from
Instrumentally Measured Color Coordinates,” for more information.
Yellowness Index per ASTM Method D1925 (displayed as YID) is defined in the ColorFlex EZ as follows:
( )
Y
Z 2 1.05743409 - 6X 1.27464150 100
= D1925 YI
under C/2° conditions.
The yellowness index formula is shown in ASTM D1925 as:
( )
YI D1925 =
100 1.28 X - 1.06 Z
Y
CIE CIE
CIE
under C/2° conditions.
The tristimulus values of clear air (for CIE illuminant C and the 1931 CIE 2° standard observer) are X =
98.041, Y = 100.000, Z = 118.103. Using these values, the ASTM formula yields YI = 0.303 for clear air
because the factors are truncated to three significant figures. In order to set the yellowness index for air
equal to 0.0, the constant multipliers for X
CIE
and Z
CIE
have been expanded slightly in the ColorFlex EZ.