What the Heck is Delta-E?

Measuring color on printed output makes sense, but what do you do with the data collected? Also, how do you know when you have a problem? The term Delta-E, (dE) is commonly used in discussing color management and answers these questions.

Delta-E is a single number or metric that represents the “distance” between two colors.

It helps users identify the limits of their workflows and to work within these expectations. The idea is that a dE of 1.0 is the smallest color difference the human eye can see. So any dE less than 1.0 is imperceptible.

Delta-E can help constituents in the Color work flow measure differences between a proof and the final printed product or to monitor whether or not color produced by a specific printing device has drifted. It allows us to measure how far away we are from our ideal. It also helps to remove any subjectivity from the color matching process.

It also can help users determine how effective a particular profile is for printing or proofing, how closely it matches the color original.

If difference is a number showing how 'far apart' two colors are, tolerance is the meaning of the number. Determining a tolerance number defines how much variance is acceptable depending on the printing environment, how color-critical the job is, and other factors.

It should be noted that there are a variety of Delta-E types, including DEab, DE94, DE_CMc and DE2000. It is important to be aware of which Delta-E measurement is being utilized in order to make accurate comparisons. Apples to apples, after all.

DE76 was first created in 1976, the year L*a*b* was created, and is a simple calculation to determine the distance between two colors. While the math is simple, it does suffer from some limitation.

One problem with dE76 is that L*a*b* itself is not perceptually uniform as its creators had intended. So different amounts of visual color shift in different color areas of L*a*b* might have the same dE76 number.

Conversely, the same amount of color shift might result in different dE76 values.

Another issue is that the eye is most sensitive to hue differences, then chroma and finally lightness and dE76 does not take this into account

DE2000 takes into account hue, lightness and chroma factors instead of being simply a raw calculation. As a result it is much more difficult to calculate. But it is also much more accurate and a better representation of how your engine is performing.

It should be noted that the human eye cannot detect differences in Delta-E below a measurement of approximately 2.2.

In environments such as laser printers, a Delta-E of 6 to 8 is perfectly satisfactory and is the level that is often achievable on laser based devices.

Most commercial printers consider a Delta-E range of 2 to 4 acceptable.

A few important points about delta-E calculations in general:

Remember, dE calculations are based on colorimetry which means they are illuminant-dependent. Don't try comparing numbers calculated from colors viewed / measured under different illuminants.

Differing dE due to illuminant is metamerism. If colors are 'adapted' to the same white point then you have a metamerism index.

Always remember that nobody accepts or rejects color because of numbers - it's the way it looks that counts.

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