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Color Control

Lithographic printing in itself is a rather startling miracle of science. The fact that it can be controlled and performed well is a tribute to the ingenuity of the machinery and the skill of the operator alike. If you are not familiar with the lithography concepts, see this brief outline of the science and principles behind modern printing.

There are many variables which can adversely affect lithographic printing:

Ink Density

If the ink is too heavy, excessive dot gain will make all the halftones and tints too dark and plug up fine type and fine lines in artwork. If it is too light, solid areas will become weak and in either case, severe shifts in color separations will occur.

Ink Coverage

Some areas will draw more ink from the rollers than others. This must be set up so that adequate levels of ink are distributed to the plate so that it has an even coating overall.

Dot Grain

animated dot gain
Tonal variations in printing are obtained by halftone dots. A matrix of rows and columns of equal spacing can contain larger or smaller dots to visually "mix" with the paper or other colors to fool the eye into seeing tones. Halftone dots are interpreted in terms of percentages. In actuality, a dot of any given percentage is what percent of area that dot covers, but it also means the visual density of the shade it creates. For example, a 20% dot covers 20% of the area of the sheet and appears to be one-fifth as dark as the solid color.

Whenever a halftone dot prints from a printing plate, a certain amount of dot gain occurs. The grain of the paper, the fact that the ink is a wet substance that gets pressed onto the paper under a great deal of pressure, the way the film or plates were created, all affect how much the dot will gain ("fatten up" or darken in value) on the press. Although dot gain can be affected by ink density, there are other factors, such as the amount of pressure applied to the paper during printing and handling of fountain solution (water) that can affect dot gain.



Registration

registration animation
Registration is the alignment of the cyan, magenta, yellow, and black portions of an image so that the composite image appears sharp and accurate.


Assessment

When a press operator begins a print run, he assesses the project's final state, using the DuPont Waterproof color proofs or actual product samples as a guide. This last task is possibly the most difficult and demands the most skill from an operator. Everyone sees color differently. What appears bluish to one person may seem like purple to another. Tints in the color of the paper, different light sources illuminating the print, and color gamut issues all affect the way an image is "supposed" to look. That's what makes the Tobias IQ 200 (Scanning Densitometer) an invaluable tool at Corporate Printers.

                                                      



Copyright © 2002 Corporate Printers All rights reserved.

Corporate Printers
83 Iber Road, Ottawa, Ontario, Canada K2S 1E7
Telephone: (613) 591-2335 Fax: (613) 591-1817
E-mail:admin@corporate.on.ca
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