Visually judging the accuracy of color between printed samples is a process that many printers use. Unfortunately, this method leads to downtime and waste. Here you
By Bruce Ridge
Some printing facilities base their color matching on printing to a Delta E tolerance of 3.0, 2.0, or some other magical number. Remember, the Pantone folks will tell you they print their specification guides to a Delta E of 3.0. They too need to print their books within a tolerancing specification; otherwise, a formulation book would cost $2500 or more if Pantone were required to match each page of each book to the point that a QC person could not visually see a difference in the colors.
If you do take L*a*b* readings of colors, you begin to find that one Delta E tolerancing number, such as 3.0, is not visually consistent with all colors. For example, a person with normal vision will probably be able to see a difference in a mid-tone neutral gray with a Delta E of 1.0. That same person will probably not be able to visually perceive much of a difference in a Delta E of 3.0 on a saturated color, such as a Pantone 185 Red. So using one Delta E tolerancing number for all co-lors may be causing you to reject colors that could be visually acceptable to your customer. You’re throwing money away!
The smart use of digital proofing
If there were a way to generate fast, accurate, low-cost visual representations of slight color variations for your customers prior to going to production, you would be creating color tolerances specific to your customer’s perception of those particular colors. How cool. How can this be done? You can do it by making smart use of today’s digital proofing methods (Figure 2).
When you start to create visual color variation with a digital proofing system, you begin to see how Delta E variations don’t always line up with visual variations. You also see another unusual variation—different colors demonstrate greater or fewer visual deviations depending on the axis in color space toward which they shift (Figure 3). Your understanding of color space is important here. Try to focus on L*a*b* color space, because it’s the only one of the three color spaces available in Photoshop and Illustrator that that you can measure on a printed sheet (Figure 4).
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