Gray Balance - Part 2

The theory of color printing suggests that acceptable results can be achieved by using the three secondary colors or primary absorbers. This is often true, and the addition of a poor black printer often will hinder more than help. The black's purpose is twofold. First, it allows for a less than perfect color balance because it contributes to neutrality in color areas that are slightly out of balance and which should be neutral. Second, it allows for a darker shadow or contrast, which often isn't possible simply by overprinting the three process colors.

Black does what cyan, magenta, and yellow do independently, that is it absorbs all of the green, red, and blue light that strikes it. Black does this all at once, so it can be substituted where all three primaries need to be absorbed. Black can be used where unequal, but not necessarily dark, colors are needed. Since black does the primary absorption, it can substitute for the other colors.

For example, in a section of a print that is expected to reproduce a specific color on the original, 80% magenta, 70% cyan, and 50% yellow is required. If a black printer were used, the separator would take this into account and reduce the level of the three colors to an equal amount and allow the black to make up the difference to reproduce the same density on the print. Subtraction of each of the three color printers from neutral tones in the reproduction and substituting black for them is called "under color removal" (UCR). When done correctly, UCR reduces the amount of expensive process color ink used and increases the less expensive black ink without seriously affecting the color quality of the reproduction.

Often, a "skeleton black" is used. In this case, only the extreme dark areas of the print receive black ink. The reality of dot gain makes any gain of the black printer three times as troublesome because of its absorption in three different wavelengths. So the restricted area of the skeleton black is very popular because dot gain will occur only where added density is required.

The FTA FIRST organization states UCR is not always the best solution for flexographic printing. It is important to maintain definition, contrast, and shadow detail when using under color removal.

Go to: Part 1, Part 3

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

Back To Technical Articles