A colorimetric investigation of color tolerances

The study was conducted to determine the relationships between a standard color and its visually chosen limits. Commonly, limits or tolerances are communicated to printers using an Allen Tolerance Chart. The Allen Chart, used extensively by package printers, provides a standard of the color to be reproduced along with corresponding light and dark limits. A second form of tolerance chart, used by printers of U. S. Department of Transportation hazardous materials warning labels, provides limits for colors three dimensionally. Both types of tolerance charts were used in this study. Three Department of Transportation tolerance charts were measured spectrophotometrically producing a family of curves for the red, green and blue tolerance charts. The curves were then subjected to Eigenvector analysis to determine the similarity among the tolerances for each color. The results suggest the red and green family of curves are somewhat similar, but very different than the blue. Five hundred five Allen Chart standard colors and their light and dark limits were measured with a small spot colorimeter to determine the relationships between the standard colors and their customer allowed limits. The samples were also subdivided into those representing spot color printing and those representing process color printing. The study suggests the average allowable tolerance for light and dark limits and spot and process color was approximately six C. I . E. L*,a*,b* delta E units. Statistically the resu1ts indicate the light allowable tolerance is greater than the dark tolerance and the process color tolerances are greater than the spot, but for all practical purposes the differences are not significant. The delta E values were also subdivided into their component parts to determine which attribute of color (i.e. hue, chroma and lightness) made up the largest portion of the delta E . These results indicate, for the most part, the delta E values are equally represented by hue, chroma, and lightness