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96 Chapter 4. Colour Management in the Graphic Technologies
Delta E
Figure 4.7 Lab Colour Space
Delta, the fourth letter of the Greek alphabet and symbolized as a triangle, is used in science to indicate
difference. Delta E is the difference between two colours designated as two points in the Lab colour
space. With values assigned to each of the L, a, and b attributes of two colours, we can use simple
geometry to calculate the distance between their two placements in the Lab colour space (see Figure
4.7).
How do we do that? It looks a lot like the formula used to determine the long side of a right triangle that
you may remember from high school geometry. We square the difference between each of the L, a, and
b values; add them all together; and take the square root of that sum. Written out as a formula it looks a
little more daunting: .
Let’s try a simple example to see what we get. Colour 1 has a Lab value of 51, 2, 2 and Colour 2 is 50,
0, 0 (right at the centre of the colour space):
