CIELAB Uniform Color Space

The CIELAB uniform color space is a three-dimensional system, and the three-dimensional distribution of its colors is shown in the figure below. Since the introduction of CIELAB color space, it has been widely used in the industry, especially in the color quality control of products in dye and pigment manufacturing, paint, textile printing and dyeing, ink, plastic coloring and other industries. Among them, L* is the lightness coordinate, representing the brightness of the color; a*b* is the chromaticity coordinate.

The plane composed of chroma a and b represents the chroma of the color, and the lower left figure is the chroma plot, where +a represents red, -a represents green, +b represents yellow, and -b represents blue. And there is a relationship between red and green, and yellow and blue. The L lightness value in the lower right picture, the value range is 0-100.

CIELAB color difference formula

Its calculation formula is:
  

                            
In the formula
 

                    
    Among them, X, Y, and Z are the tristimulus values of the sample color;
    

is the tristimulus value obtained by the human eye after the surface of a completely diffuse reflection object passes through the CIE standard illuminant, where

=100.

If the L* a* b* value is known, and you want to get the X, Y, Z values, you can use the inverse equation:
   

 
    Fig. 2 is a schematic diagram of CIEL*a*b* uniform color space. The a* and b* in the figure indicate different hue directions. a* indicates the direction of red---green. +a* indicates the direction of red, -a* indicates the direction of green; b* indicates the direction of yellow---blue, +b* indicates the direction of yellow, -b* indicates the direction of blue. The vertical axis L* in the middle represents lightness, the lightness on the top is the largest, showing white; the lightness on the bottom is the smallest, showing black.

 
Figure 2 Schematic diagram of color space

While CIE suggested the CIELAB color space, it also suggested the corresponding color difference formula △Eab, in the following form:

The advantage of the △Eab color difference formula is that when the color difference of the color is greater than the recognition threshold of human vision (the value that can just be perceived), but smaller than the color difference value of the adjacent two levels in the Munsell system, it can better reflect The psychological effect of object color.