Color Separation
Introduction
You may have an opportunity to create artwork intended for color printing
using the traditional offset lithographic process. The three types of color
separation processes are process color, spot color, and fake color. The
format of the master artwork determines the type of separation process you
use.
Process color
When you create the master artwork in a continuous tone medium, such as a
watercolor or a photograph, the color separation process is left to the camera
operator. This is process color. Very close reproductions result from using
color in the artwork similar to the color available to press inks.
How process
color works
The printer makes four separate negatives and four separate press plates for
each piece of continuous tone color artwork. Since colors photograph as
black or shades of grey, the printer uses regular black-and-white film. A
grey scale, photographed along side the artwork will assist the photographer
in comparing densities and contrast for each negative. The negatives must
have the same contrast and density or the resultant print will be out of
balance. Shooting through a halftone filter and a series of color filters
separates the colors of the original copy and breaks the image into a dot
pattern. The printer changes the angle of the halftone screen for each
negative to cause the dot pattern to overlap or print side by side in the final
print. A blue filter records yellow, a red filter records cyan (blue), a green
filter records magenta (red), and no filter or a combination of the three filters
records the black in the original. Conventionally develop the film. Hand
correct any negative aberrations. Expose and develop the press plates. Pull
a proof from the press plate in the appropriate color. This is known as a
progressive proof. The colors of the original artwork reproduce when the
plates are run on the press in the proper colors of ink. Overprinting
produces the color sensations of secondary and tertiary colors. Overlapping
three or more colors produce black.
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