Δ-E is essentially nothing more than the difference between two colors. It’s a mathematically derived product that represents a physical distance between two numbers in a Gamut. You already know what a Gamut is. Since we’re talking about a three dimensional distance from a point, you may have already recognized that Δ-E manifests as a spherical volume.
Normalized human vision can sense a difference in two colors that are about Δ-E = 5 distant, but this standard varies with the actual colors tested and their saturation. Human eyes are quite a bit more sensitive-in some matters-achromatically, meaning “relative to black and white.” In neutral (monochromatic, or achromatic, as you prefer…) tones, it is not unusual to document discernment of Δ-E < .8.
If your life simply can’t be complete without the math, here ya go.
Δ-E can also be affected by Metamerism, meaning it can (and often does) reflect perceptual error.
Obviously there are going to be several derivatives of Δ-E as it exists in a perceptually uniform Gamut. Δ-E can be calculated in a nonuniform Gamut, and it can be measured in the performance of any device that produces color such as your monitor/s and printer/s. The Δ-E that I’m explaining above, and the result values I quoted, are pertinent to a particular color model (CIEL*a*b* 1976) and Δ-E convention (Δ-E76, also from 1976). Metrics using those two models may be terribly inaccurate in other applications, so you do need to be careful! In some Δ-E models a value of 1 will represent normalized human acuity limits.
There are various other measurements of color variance, such as:
- Δ-L*, pure Luminance difference
- Δ-C*, pure Chromatic difference
- Δ-H*, pure Hue difference
They can be used to diagnose production problems or to impress your friends even further than Δ-E…as if that would ever be necessary.
Why on earth would I bother you with this? Obviously, because it can be important when you bubble up to the point that you’re producing high grade output. Here’s an article that combines what you now know about Metamerism and Δ-E, and actually applies that knowledge to print output with measured results. The various graphics on the page demonstrate how functional and efficacious a proper application of Color Management principles can be.
For further study:
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