Trap (printing)

However, in the era of prepress software, the term came to refer to compensation for misregistration (when two layers of ink are not perfectly aligned) that was traditionally known as "chokes and spreads".

Correcting this involves creating overlaps (spreads) or underlaps (chokes) of objects during the print process.

Misregistration in the graphical workflow may be caused by human error, inaccuracies in the image setter, the film-to-plate or film-to-film copying steps or instability of the image carrier (e.g., stretch in film or plate), the press or the final medium.

The choice depends on the type of output (packaging applications including flexo-printing have other requirements than commercial printing on offset systems) and the degree of interactivity or automation.

Therefore, the trap width is set to a strict minimum, dictated by the maximum amount of misregistration of the entire workflow up to the press.

For the same reason, in many cases, black ink is set to "overprint" colors in the background, eliminating the more complex process of spreading or choking.

In that case, reduction would cause the spot color in the trap to be printed, not as a solid, but as a screened tint.

If a trap over the full length of the blend is needed, this produces a visible ‘staircase’ effect.

Often, the sliding factor is set to a point where the neutral densities of blend and background reach an appropriate difference.