Does your press sheet match the customer-approved color proof? How far apart can two colors be and still be considered a “match”? These are questions that every printer must face every time they work with a new customer. Some might say that color matching is subjective, and to some extent this is true. Depending on a person’s color acuity (determined through color vision testing), they may be more critical of color difference. Some amount of color variance may be part of the process and the press can never match the proof exactly. For all of these reasons it is important to set up acceptable color tolerances in your shop.
Most people in the graphic arts have probably run across the term Delta E. Delta E provides an objective numerical value to represent the color difference between any two colors. Delta E can be calculated from the CIELab value provided by a color measurement device, known as a spectrophotometer. Unlike a densitometer which measures reflectance, a spectrophotometer (“spectro”) measures the spectrum of visible color and identifies a color using three points, L* (a measure of lightness), along with a* and b* (coordinates that represent hue and saturation of a specific color).
The original Delta E calculation was developed in 1976 (sometimes referred to as Delta EAB), however the standard Delta E calculation does not necessarily account for non-uniformities in the color space. The Delta E calculation has been retooled several times (1984, 1994, 2000) in attempts to find a more uniform metric for quantifying color difference. There are many opinions on which is the best version to use, but no clear standout has emerged.
A Delta-E value of less than 1 is considered to be a “color match” and represents an indistinguishable color difference between two samples. However due to the non-uniformities mentioned above, this rule does not always hold true. It is a good idea for a company to take the time to identify what level of tolerance is acceptable for color difference, but simply relying on a spectrophotometer for objective Delta-E values may be misleading. A more realistic way to establish color tolerance house-standards is to use a tool such as the Pilot Color Tolerance Exercise to associate a realistic tolerance with a subjective evaluation.
The Pilot Color Tolerance Exercise is an easy, foolproof way to determine tolerance for color acceptability that benefits your customers and offers your company the potential for increased profits. Using the exercise, a company can determine a company-wide standard for color tolerance. The kit includes six strips of color patches, instructions for administering the exercise, and a easy-to-follow guide that will provide a numerical tolerance.