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Color difference ∆E*ab in the L*a*b* color space,
which indicates the degree of color difference but not the direction,
is defined by the following equation:
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where
∆L*, ∆a*, ∆b*:
Difference in L*, a*, and b* values between the specimen color and the target color.
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The L*C*h color space uses the same diagram as the L*a*b*
color space, but uses cylindrical coordinates. Lightness L* is the same as L*
in the L*a*b* color space; Metric Chroma C* and
Metric Hue Angle h are defined by the following formulas:
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where
a*, b*:
Chromaticity coordinates in the L*a*b* color space
For difference measurements, Metric Hue Angle difference is not calculated;
instead, Metric Hue Difference ∆H* is calculated according to the following formula:
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The Metric Hue Difference is positive if the Metric Hue Angle h of the specimen is greater than that of the target
and negative if the Metric Hue Angle of the specimen is less than that of the target.
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