| Title: |
Gray Balance - Part 3 |
| Date Submitted: |
09/06/03 |
| Author: |
Catherine Haynes, Manager of Training Services |
Gray Balance - Part 3
Standard Color Separations vs. Achromatic Color [Gray Component Removal (GCR)]
The standard color separation halftone printing process is based on the combined effects of additive and subtractive color-mixing principles. In chromatic process-color printing, all hues, as well as black and neutral gray, essentially are made with the three basic inks. Black is used to stabilize dark gray and add depth to shadows as indicated above. When three colors are overprinted, the two dominant ones determine the color, with the third, lesser color contributing to the color printing and grayness.
In recent years, a different approach to process-color printing has caught people's attention. This approach has been called achromatic process color or gray component removal, among other terms. In GCR process color printing, the primary and secondary colors are the same as in chromatic printing, but black replaces the gray component of the third color. Tertiary colors* now are composed of two colors and black. Now black is the dominant color in gray and black. Modern electronic scanners allow the unwanted color to be selectively removed from the yellow, magenta, and cyan, and a portion of the removed color is replaced by black (refer to table below).
| |
Chromatic Process |
GCR Process |
| Primary Color Space |
| Yellow, Magenta, Cyan |
Darkening is accomplished with equal quantities of the other two primary colors. |
Darkening is accomplished with black. |
| Secondary Color Space |
Red
Green
Blue |
Yellow + Magenta
Yellow + Cyan
Magenta + Cyan |
Yellow + Magenta
Yellow + Cyan
Magenta + Cyan |
| Tertiary Color Space |
Brown
Dark Blue
Dark Green |
All 3 basic colors arranged according to chromatic values. Two predominant primary colors, one darkening color; black is sometimes added for depth. |
Two basic colors + Black
Brown = yellow + magenta + black
Dk. Blue = magenta + cyan + black
Dk. Green = yellow + cyan + black |
| Black and Neutrals |
| |
Three basic colors in their respective percentages with the addtion of black for depth. |
Theoretically: black only
Components of the 3 basic colors, depending on printing conditions. |
Advantages claimed for GCR include sharper printing (because all detail is in the black), better color consistency, stable gray balance, less sensitivity to color-ink fluctuations, reduced ink usage and fewer trapping problems.
On the negative side: this process is unique and requires a major re-learning of process color for those used to the chromatic method. Proofs will be different and progressions will be obsolete.
Intermixing of standard and chromatic separations is not a good idea. Also, the black ink must have a higher density, must be neutral and must give adequate coverage. Dot-gain control of the black printer is essential.
The FTA FIRST organization recommends GCR be restricted to a single unwanted color. FIRST also states GCR should not be used when the printer is printing line black and process black on the same plate. In this situation a skeleton black (or a short black) may be preferred to allow the printer greater tolerance in setting impression.
*Tertiary Colors Ð Those obtained by mixing two secondary colors.
- Foundation of Flexographic Technical Association. Flexography Principles and Practices Fourth Edition. Ronkonkoma: Foundation of FTA, 1995.
UCA (under color addition) increases the dot sizes of the three process colors in the dark neutral areas. This compensates when the GCR process reduces cyan, magenta, and yellow dot sizes too much. Without UCA, dark areas may be lighter than desired. On the other hand, UCR (under color removal) may be used to compensate for this same issue.
- Miles Southworth and Donna Southworth. Color Separation On The Desktop. Livonia: Graphic Arts Publishing, 1993.
Go to: Part 1, Part 2
For more information on this issue, please contact: info@teamflexo.com
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