Gray Balance - Part 1

Gray balance is a top requirement for overall color balance in the reproduction. The three process color inks - yellow, magenta, and cyan - most often will not produce a neutral. Nor will they always produce neutral light, medium, and dark grays in screened values. White light is made up of equal parts of red, green, and blue light. Black is achieved when all three have been completely absorbed. The full value range of neutral grays that lie between white and black can be achieved when balanced or equal levels of each of the three light primaries have been absorbed.

Gray balance refers to the ability of the set of process inks to absorb equal amounts of the three light primary colors across the range of light to dark when they are produced on the press. Ideally, this means that a 5% dot value in each process color would produce a very light gray. A 50% dot value in each would produce a medium value of gray, etc. In reality, equal screens of process inks do not absorb equal amounts of the primary colors and so, without correction, do not produce a value range of neutral grays. They are imperfect, out of balance.

An important aspect of color separation is to adjust the screen values or dot sizes to achieve gray balance. If this balance is not achieved throughout the possible spectrum of halftone dots, the neutral grays will be tinted yellow, red, or blue. Improper color balance also can cause the colors on the print other than gray to shift. The cyan ink is overpowered by the magenta and yellow, resulting in a brownish color where a neutral gray or black is desired.

This is controlled in color separation by "imbalancing" the three color printers. The cyan printer is allowed to print larger dot sizes of ink while the magenta and yellow printers are reduced in dot size by a controlled amount. A correct set of separations will be imbalanced to produce neutral values throughout the value scale from highlights to shadows. At that point, gray balance is achieved.

The potential causes of improper gray balance are numerous and include almost every variable in the process color system. Color separations often can be blamed for improper color balance, not necessarily because they are incorrect, but because they usually are adjusted to the reproduction characteristics of another printing process.

The following table is an example of gray balance values for CMY (from FTA's FIRST). This is just an example. These values will need to be figured based on the dot gain, density, color of process inks, and trapping characteristics for each set of printing conditions. Running a characterization can help the prepress supplier determine the best gray balance values for a given set of conditions. Running control targets, such as the one recommended by FIRST (also pictured below), can help the printer make sure nothing has changed in the printing process.

For more information on this issue, please contact: info@teamflexo.com

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