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: 
where ∆L^{*}, ∆a^{*}, ∆b^{*}: Difference in L^{*}, a^{*}, and b^{*} values between the specimen color and the target color. 
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: 
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: 
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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