A midtone three color gray can be comprised of 50% yellow; 50% Magenta and 60% Cyan. This will render a neutral gray tone. All other midtone process color values will be dependent upon this setting. If the "gray balance" settings are altered; then the color balance will also be altered. Because of the limitations of the pigments in the process inks, when equal amounts of cyan, magenta, and yellow are printed on white paper, they do not reflect equal amounts of red, green and blue to produce gray (See Figure 1). Each of the process inks absorbs or reflects an unequal amount of its share of the red, green, and blue of the spectrum. As such, if equal amounts of cyan, magenta, and yellow are printed, they would make a brownish color rather than a neutral gray.
The second most important control the scanner operator has at his disposal is the choice of gradation. The choice of gradation dictates how "full" a job prints. In other words the scanner determines or influences the amount of dot gain a job will have.
The third most important control the scanner has is the %UCR setting. This setting dictates how much Yellow, Magenta and Cyan are printed in order to make up a three color shadow neutral (Grays and Browns). This will affect how well inks will trap or overprint and what shadow colors can be reproduced.
With scanning having this much influence and control over color, it is imperative that the prepress and press operations attempt to reproduce the scanner "gray balance" set up. Otherwise we are only guessing at correct color during a make ready on press.
Gray Balance agreement occurs when the proper proportions of yellow, magenta, and cyan that were blended together at the scanner; are reproduced at the press. Gray Balance is a significant factor in determining what the over all color gamut will be.
Proper color reproduction at press can only occur when the press has achieved the same "gray balance proportions" as were present in the color separations. Proper assessment of a printing ink's performance can be made only after the press has been "Gray Balanced."
"Proper Gray Balance" is achieved when the values put in at the scanner are reproduced on the pre-press proof and the printing press: with little to no color difference between the two.
One area that complicates the gray balance process and sometimes requires some interpretation, is the prepress proof. Some proofs are manufactured with a color bias or cast. This will force the scanner operator to "alter his gray balance setup" in order to get a better proof for his sales staff or the print buyer. In this case, the final films having been prejudiced will not yield proper color on a balanced printing process. Furthermore, if the press is pushed to an imbalanced condition; the inks will be compromised and not allowed to perform to peak ability.
We need to measure for Gray Balance because each person's individual perception of color is different. Each person has subconscious preferences that influence their color judgement. The human eye can detect any shift in neutrality when neutral areas are compared side by side. Comparing just by looking at the neutrality of two gray scales is much easier than comparing the purity of the reproduced process inks with a color in the original. The eyes can quickly detect if there is any color cast in the neutral area. In this respect, the eyes become the most sensitive instrument for checking gray balance. We are all influenced by variables in our environment that we are usually not aware they exist. To illustrate this, compare the two greens in Figure 2.