Foundations in Graphic Communications: Checking Color Proofs

New York City College Of Technology
Advertising Design & Graphic Arts: NYCCT

The Course At A Glance

Foundations In Graphic Communications
Patrick Henry     (718) 718.847.9430     (c) 917.647.0590     (e)

  PRODUCTION VARIABLES (II): Controlling Image Quality On Press  

TOTAL INK COVERAGE: no press-paper combination can handle four "wet" inks applied one over another at 100 percent of each color: 400 percent coverage is a "recipe for disaster" guaranteeing color contamination, plugged-up images, etc.

SWOP, therefore, specifies a total ink limit of 300 percent with only color printing at 100 percent. In practice, the limit runs from about 260 to 330 percent, depending on requirements, printing process, and type of paper.

BLACK-CHANNEL GENERATION: i.e., how much black ink to use, depending on color quality requirements, prepress image correction, etc. These adjustments can made as part of image processing in Photoshop. Methods:

GCR (gray component replacement) replaces the image's neutral colorant (C, Y, or M) with a percentage of black ink. Benefit: sharper, more stable colors without excess coverage

UCA (under color addition): replaces black ink in shadow areas with percentages of C, Y, and M. Benefit: richer colors in low-key ("nighttime") images.

UCR (under color removal): black substitution for the neutral colorant in shadow areas only. Benefit: better detail in shadows that might otherwise "plug up."

DOT GAIN: the tendency of halftone dots to expand in size as the ink is absorbed into the paper. Dot gain is higher on uncoated stocks than on coated stocks because uncoated stocks are more absorbent. To "leave room" for dot gain, Photoshop can scale back image characteristics by the amount of gain anticipated for the press-paper-ink combination that will be used.

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