Unless you are well versed in how the physical qualities of the printing process effects the hue of CMYK color builds, you probably have no idea what Delta E is, if you have heard the term at all.
It’s actually a very simple concept that just needs a little exploration to understand. Essentially Delta E is a description of the amount of difference between the color target and the hue of CMYK build meant to replicate the color target. It’s measured on a scale of 0 to 100 in which zero is an exact match to the target and 100 is complete visual distortion of the color. In order to understand the implications of how this scale effects the color match, you need to understand the way the visual spectrum of light color gamut is laid out.
In the above example you can see a representation of the visible color spectrum along with the colors able to be reproduced by photographs, RGB displays, CMYK printing, and a color target within the gamut with the acceptable Delta E, where a circle describes the range of acceptable color variation within the Delta E, and the radius of the circle describing the numeric value of Delta E. Delta E is essentially a circular area described by the length of it’s radius. The idea is that a color farther away from the center of this area is also farther hue-wise away from the color target, with Delta E acting as a measurable numeric description of the difference.
In a perfect world all printed products would be able to reproduce their target colors with complete accuracy. In practical use no printing press is perfect regardless of preparation or skill of the press operator, thus the importance of the measure of Delta E. It give the printer a way to measure the amount of hue deviation in their color builds between the target and the final product without relying on the eyes of the press operator or QC department. There is also usually a negotiated amount of Deviation, usually under a Delta E of 4 or 5 for photographic printing, that the end user will accept. Anything outside of spec is thrown away as waste or shown to the buyer and accepted manually. A Delta E above 2 is generally visible with the naked eye if viewed under proper lighting, so 4-5 is actually a fairly large amount of deviation.
Hopefully this quick blog on Delta E helps you understand the concept and why it is important to the printing process.