﻿ Hunter L*a*b* Color model - EN

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# Hunter L*a*b* Color model

The Hunter L*a*b* color scale evolved during the 1950s and 1960s. At that time, many of the scientists involved with color measurement were working on uniform color scales. The X,Y,Z system was being used, but it did not give a good indication of sample color based solely on the numbers. The uniform color scales being investigated gave better indications of the color of a sample based solely on the numbers. There were several permutations of the Hunter L*a*b* color scale before the current formulas were released in 1966.

The Hunter L*a*b* color scale is more visually uniform than the X,Y,Z color scale. In a uniform color scale, the differences between points plotted in the color space correspond to visual differences between the colors plotted. The Hunter L,a,b color space is organized in a cube form similar to the CIE 1976 L*a*b* color model.

The L* axis runs from top to bottom. The maximum for L* is 100, which would be a perfect reflecting diffuser. The minimum for L* would be zero, which would be black. The a* and b* axes have no specific numerical limits. Positive a* is red. Negative a* is green. Positive b* is yellow. Negative b* is blue.

## Hunter L*a*b* color algorithm

The quantities L*, a*, and b* are obtained from the tristimulus values according to the following transformations:

where

X, Y, and Z are the CIE tristimulus values.
X
n, Yn, and Zn are the tristimulus values for the illuminant.
Y
n is 100.00.
K
a and Kb are chromaticity coefficients for the illuminant.

## Hunter L*a*b* color difference

There are delta values âL*, âa*, and âb* associated with the Hunter L*a*b* color model. These values indicate how much a standard and sample differ from one another in L*, a*, and b*.

The âL*, âa*, and âb* are calculated from the following equations:

âL* = L*sample - L*standard

positive âL means, the sample is lighter than the standard
negative âL means, the sample is darker than the standard

âa* = a*sample - a*standard

positive âa* means, the sample is redder than the standard
negative âa* means, the sample is greener than the standard

âb* = b*sample - b*standard

positive âb* means, the sample is yellower than the standard
negative âb* means, the sample is bluer than the standard

## References

The free dictionary.com

HunterLab