An Investigation of the Relationship between Gray Balance and Printed Dot Area

This study reports the findings of a series of press tests designed to gain more precise knowledge about the nature of gray balance. Given the importance of gray balance for good quality printing and its seemingly unpredictable nature, the authors sought to determine if useful gray balance specifications could be established for sheetfed lithography. During the 1999 GATF Sheetfed Lithographic Print Attribute Study (Stanton and Hutton, 1999) it was found that traditional gray balance curves were well modeled by a second-order polynomial relationship between the cyan and the magenta/yellow printed dot areas. Effectively, we found that gray balance was predictable across screen rulings if total printed dot areas of cyan, magenta, and yellow were considered. The current study has used more precision to examine the interrelationship of gray balance and printed dot areas. For any neutral area with a given cyan dot area, the magenta dot area can be calculated by the second-order polynomial: Mag DotArea = 0.0028(Cyan DotArea)2 + 0.69(Cyan DotArea) The yellow dot area can then be calculated by the linear relationship: YelDotArea = 0.095 (MagDotArea) These relationships were relatively stable across the full range of solid ink density settings and with several paper/ink combinations. When these relationships were applied to the average sheetfed lithographic printing conditions determined from the 1999 study, the 25%, 50%, and 75% C/M/Y combinations that yield neutral grays on gloss coated paper at 150 lpi are 25/18/17, 50/41/39, and 75/66/62, respectively.