CIE L*, a*, b* color values provide a complete numerical descriptor of the color, in a rectangular coordinate system.
- L* represents lightness with 0 being a perfect black of 0% reflectance or transmission; 50 a middle gray; 100 a perfect white of 100% reflectance or a perfect clear of 100% transmission.
- a* represents redness-greenness of the color. Positive values of a* are red; negative values of a* are green; 0 is neutral.
- b* represents yellowness-blueness of the color. Positive values of b* are yellow; negative values of b* are blue; 0 is neutral.
Delta L*, delta a* and delta b* values provide a complete numerical descriptor of the color differences between a Sample or lot and a Standard or target color.
- dL* represents a lightness difference between sample and standard colors.
- da* represents a redness or greenness difference between sample and standard colors.
- db* represents blueness-yellowness difference between sample and standard colors.
In the case of dL*, da*, db*, the higher the value, the greater the difference in that dimension.
Delta E* (Total Color Difference) is calculated based on delta L*, a*, b* color differences and represents the distance of a line between the sample and standard.
In addition to quantifying the overall color difference between a sample and standard color, delta E* was intended to be a single number metric for Pass/Fail tolerance decisions. Effectively a delta E* tolerance value defines an acceptance sphere around the standard or target color.
The lower the delta E* value is, the closer the sample is to the standard. A delta E* value of 0.00 means the color of the sample is identical to the color of the standard.
Please note that while CIE L*, a*, b* are being used in this example, delta E (no star) represents the overall sample difference in Hunter L, a, b coordinates.
FAQ: What does the “E” in delta E or E* stand for?
All colorimetric terminology has a basis, usually related to light and perception, but some terms can be a little arbitrary.
The "E" in delta E or delta E* is derived from "Empfindung", the German word for sensation. Delta E means a "difference in sensation" for any delta E-type metric, CIE or Hunter.