Black trapping rules include:
- Traps to objects defined as black are affected by the black width scaling.
- Colors placed underneath overprinting black solid objects form rich blacks. In areas where a rich black borders an unpainted object such as the substrate, the color under the black will be kept back from the border.
Rich Blacks—a designer or printer often wants black objects to have more impact, that is, to look as black as possible, so one or more additional colors are added. Commonly, 40 percent cyan or 30 percent each of cyan, magenta, and yellow are added to the 100 percent black. The extra ink makes objects look darker than 100 percent black when printed.
These rich black objects need a reverse trap to pull the extra inks, often called booster colors, in from the edges of the object, to avoid having them appear along the edges if there is a misregistration on press. These reverse traps are sometimes called stayaway or keepaway traps.
Note: The rules above do not apply unless the tint of the black object is greater than, or equal to, the black color limit.
See Also