UCR

UCR:
Short for undercolor removal; reducing the cyan, magenta, and yellow inks from the darkest neutral shadow areas in an image by replacing them with black ink.
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Gray Component Replacement is an extension of UCR in that it replaces the neutral colors in the image as well as the colored areas with equal amounts of cyan, magenta, and yellow throughout the tonal range of the image.
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undercolor removal (UCR)
a technique used to reduce the yellow, magenta, and cyan dot percentages in neutral tones by replacing them with an increased amount of black.

See also: Filter, Scale, Yellow, Exposure, Color