(v13) Knockouts and overprinting

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

A knockout is a white hole produced in one color separation by the presence of a colored object in another separation. If the hole were not there, the ink in the first separation would mix with the ink in the other to produce a mixture which is usually not the color originally intended.

Sometimes this mixing is intended, usually to cope with artifacts of the printing process. This method, namely not painting a separation white to produce a knockout, is called overprinting. Trapping in PostScript-language jobs is usually done this way—by putting an overprinted border around the knocked-out graphic. Then any misregistration in printing results in a mixture of the colors rather than a more obvious white hairline. A special case of this is black ink which is generally more opaque than other inks, so solid black can sometimes be safely over printed everywhere.

Overprinting is normally controlled by setoverprint, but this does not give enough control for some purposes; the Harlequin RIP has an extension, OverprintProcess, to cope with this, and further extensions for dealing specially with overprinting of solid black.