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Figure 13.1. SIE L*a*b* color wheel and brightness axis 
The CIE LAB system allows you to determine the color gamut of a color print 
and the color difference ∆E of any pair of colors. For example, you can compare the 
colors of the reference copy and the reference copy. 
The simplest option for determining color coverage is CMY (Cyan, Yellow, 
Magenta) in a* and b* on the color wheel, that is, for magenta, yellow, and magenta 
printing ink colors, as well as two-color overlap red ( Red), green (Green) and blue 
(Blue) is to build a color gamut shape. For this, the indicated color points are placed on 
the color circle and combined into six circles. The colors that this system of color 
printing can produce are located in the work of the resulting color gamut pattern. 
Beyond that, there are colors that cannot be obtained with these printing inks on this 
printing equipment. An example of a color gamut shape is shown in Figure 13.2. 
To determine the color difference ∆E, the coordinates of the compared colors L*a*b* 
are determined and calculated according to the following formula:
∆Е=[(∆ L
*
)
2 
+ (∆b
*
)
2
+ (∆b
*
)
2
]
1/2
, 
where ∆ L*, ∆b*, ∆b* are the difference of the compared color coordinates. The 
value of the color difference allows you to think about the accuracy of color 
reproduction in this printing process. ∆E=3-4 units is an acceptable value. Experts 
notice a color difference even at smaller values of ∆E. The L*,S*,h* system is a 
derived system from CIE LAB, where L* represents luminance, S* represents 
saturation, and h* represents hue. S* and h* are determined from the following 
formulas: S*=[(a*)2+(b*)2]1/2 and h*=arstg(b/a) (see Figure 13.1). In this system, the 
color difference is determined by the following formula:
∆Е=[(∆ L
*
)
2 
+ (∆S
*
)
2
+ (∆h
*
)
2
]
1/2
Color coverage and accuracy of color reproduction of a color print depends on 

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the description of the dyes, capabilities of the raster processor used in the digital 
equipment, and the printing process. 
Ideal printing inks should absorb radiation from only one of the three areas of 
the spectrum (blue, green or red), where the color of the absorbed radiation is 
complementary to the color of the ink. Yellow paint should absorb only blue radiation, 
red paint should absorb green radiation, and orange paint should absorb red radiation.