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What are LAB values?

Answered by Dan Caldwell, Vice President of Operations, Integrated Color Solutions (ICS)

I am somewhat familiar with the color term, "L A B." I know L stands for luminance. What do the A and B stand for?

You are on the right track; L is the luminance while A and B are just values of a color and its saturation.

LAB values are the coordinates of a color within CIE color space. The CIE color space is a three dimensional volume that contains all the colors visible by the human eye. To visualize a model of this color space think of two cones one placed upside down on top of the other. The point at the top is white and the point at the bottom is black. A line down the center between the points would be the grey scale and is the 0 to 100 "L" value of LAB. A slice of this color space where the two cones meet is what most of us know as the apple color wheel with the hues around the circle fully saturated on the edge of the wheel going to grey or L*50 in the center. Now if you draw two lines across the color wheel -- one between yellow and blue and the second between green and red -- this would divide the wheel into equal quarters. The two lines would represent A and B of LAB. The line between yellow and blue is B. B=0 is the center. -B values go towards yellow and +B values go towards blue. The line between green and red is A with -A being green and +A being red.

Other measurements systems of the CIE color space are LCH and XYZ. You can think of these as different measurement scales in the same way Fahrenheit and Centigrade are two measurement scales of ambient temperature.

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