The Relationship between the Chroma Values of Neutral Gray and Important Print Attributes

Gray balance is the first important step undertaken by color separators, in determining the color content and contrast that the final printed piece will have. It is a significant factor in determining what the overall color gamut will be. Gray Balance is the measurement of an ink set's ability to produce neutral gray with cyan, magenta, and yellow when printed at standard densities. Proper gray balance ensures that a tone of appropriate Cyan (C), Magenta (M) and Yellow (Y) tint values is visually perceived as neutral gray.

This study was an experimental research in nature and funded by the National Science Council (NSC) of Taiwan (NSC 93-2212-E-144-001). The purposes of this research were (1) to identify the optimum CMY combinations that produce the most neutral gray, and (2) to explore the relationship between the chroma values of neutral gray and important print attributes such as solid ink density, tone value increase, ink trapping, and print contrast.

More than 35 high quality commercial sheetfed lithographic printers were invited to participate in the study. A GATF Gray Balance Chart was used as a process standardization target for determining the three-color dot requirements for CMY to reproduce a neutral scale at four different tone values (7%, 30%, 60%, 80% tints). A spectrophotometer was used for measuring the Gray Balance Chart to investigate the colorimetric values (L*a*b* color) of the squares selected as most neutral. In addition, the spectrophotometer was used to read commonly-measured print attributes for the purpose of exploring the relationship between the minimum chroma values and values of the print attributes. The results of the study can be used as the reference for offset printers to set the gray balance for their in-house color reproduction and make prediction on their print attributes.