Under color removal


In printing, under color removal is a process of eliminating overlapping yellow, magenta, and cyan that would have added to a dark neutral and replacing them with black ink only, called a Full Black, during the color separation process. Under color removal is used in four-color printing. Black ink used to add details and darkness in shadowed areas is called a Skeletal Black.
With current ink technology, the total CMYK ink in the shadows refuses to stick after it reaches the dark shadows, and begins to peel off. To prevent this, printers developed UCR, in which neutral shadows – which would have normally been produced by overprinting the four inks Cyan, Magenta, Yellow and Black on top of each other – are replaced with the single layer of Black. UCR removes the color inks under the Black, resulting in a single layer of ink which sticks to the sheet better, and saves on the consumption of ink.
There is no universal rule for UCR. The amount required will depend on the printing press, paper, and ink in use.
UCR is generally not recommended for use in printing, due to its tendency to produce dull-looking images and artwork. The main exception to this rule is that where working in newsprint, UCR is the best way to avoid the associated ink limit and registration issues. UCR is also recommended for some specific paper stocks, depending on the coloration and texture of the paper.