Dealing with a Touch of Gray
Staff -- graphic arts online, 3/1/2001
Says Kevin Klein, quality supervisor for Perry Judds, "Color improvement starts with process control and measurement. The proofing color control bar offers a measurable sampling of a proofing system's capability to predict press color reproduction.
"A digital color proof communicates expectations for product color appearance and quality to the printer, and without a color control bar, there is no means to pre-qualify how well a printing system can meet those expectations. The value of digital color proofs with color control bars is the ability to enable process control and reduce the frustrating color variation we experience in the workflow before we get to the pressroom."
In development
The rewrite committee for GRACoL (General Requirements for Applications in Commercial Offset Lithography) Version 5.0 felt that there was a need to investigate this problem.
As a result of its analysis, the group is developing a proofing color control bar that will meet the needs of the graphic arts and be presented as an industrywide standard of reference. The concept was to keep it as a simple tool that could be easily visualized and remembered, and delivered tangible value as well.
Dr. Tony Stanton, director of graphic communications management at Carnegie Mellon University, Pittsburgh, volunteered to design the GRACoL proofing color control bar. Stanton, who also serves as senior research advisor for the Sewickley, Pa.-based Graphic Arts Technical Foundation, brought to light an inherent problem.
In the graphic arts, he says, a "touch of gray" assumes a position of measurable importance.
"Gray balance" refers to the dot values that a combination of cyan, magenta, and yellow inks will yield as a neutral gray at normal ink densities on a printed sheet (gray balance patches are included on color control bars for measurable printing); a halftone black gray scale is used as a reference to the neutral gray. Stanton explains that when gray balance is achieved, the separations are said to have reached correct color balance.
"It is critical to achieve good gray balance for the picture to look natural," Stanton asserts. "Gray balance influences the reproduction of all the colors in the picture. The human observer exacerbates the problem by having extraordinary sensitivities to hue shifts in near-neutral colors."
No universal ratio
As there exists no universal gray balance ratio, rather, a variety of ratios representing different industry segments, the need for recommended standards was obvious to the GRACoL committee, which wondered if it should recommend different standards for each segment or instead try to find a common ratio.
Veteran color management consultant Don Hutcheson argues for the latter.
"The industry needs a single, standardized set of gray balance numbers to make CMYK separations more interchangeable, reduce costs, and rationalize the whole process," states Hutcheson. "Take, for example, a plant with 18 presses running three different stocks. For scheduling reasons, the actual press is seldom known at the time CMYK separations are made, and thus the prepress department has no option but to assume constant gray balance for all presses. We need to filter our research into commercially practical recommendations."
Says Imation Color Technologies technical specialist Dick Presley, "The various digital proofing systems in use today are as varied in their color make-up as the conventional systems they are replacing. We need to formalize a given set of values that allows for wide application."
