Under color removal
In four-color printing (or more) under color removal (UCR) is the process of eliminating amounts of yellow, magenta, and cyan that would have added to a dark neutral (black) and replacing them with black ink during the color separation process.
Why?
With current ink technology, the total CMYK ink in the shdows refuses to stick after it reaches the dark shadows. It begins to peel off. In order to prevent this, printers developed a system called UCR, in which the neutral shadows which would have normally been produced by printing the primaries cyan, magenta, and yellow in the shadows (high ink coverage) is replaced with black. There is no universal rule for under color removal. The amount required will depend on the printing press, paper, and ink in use. - Advantages: solves the ink not sticking problem (called ink trapping)
:Advantages: black ink is cheaper
:Possible disadvantages:Black ink by itself in a shadow may not be not dark enough, so they'd better put back a little of the CMY in the shadows (Called Under color addition UCA) to make a pleasing reproduction
See also
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