What is trapping?
Prepress technique of slightly overlapping adjacent colors so press misregistration leaves no gaps
Trapping Definition
Trapping is the prepress technique of slightly overlapping adjacent colors so that small misregistration on press does not leave visible white gaps between them. It compensates for the mechanical tolerance of the printing process. In packaging, trapping protects the appearance of artwork where colors, text, and edges meet.
How trapping works
On press, each color prints from a separate plate, and the substrate can shift by a fraction of a millimeter between them. Where two colors meet, that shift can expose the unprinted stock as a thin white line. Trapping prevents this by expanding one color slightly into the other so they overlap. The lighter color is generally the one that moves, because it is less visible in the overlap. Trap values are set to the registration tolerance of the specific press and substrate.
Two basic trap directions:
Spread: a lighter foreground object expands outward into a darker background
Choke: a lighter background is pulled in around a darker foreground object
Why trapping matters in packaging
Packaging often combines bold solids, fine reversed-out type, and tight registration on absorbent or flexible substrates, all conditions where misregistration shows. Flexographic printing on film and board is especially prone to movement. Without trapping, a small shift produces white slivers around type and between color blocks that reach the shelf across the whole run. Correct trapping makes the print tolerant of normal press variation, so quality holds without demanding perfect registration.
Trapping In a Governed Workflow
Governed prepress sets trapping to defined values for the press and substrate and records them as part of the file preparation trail, so the choice is specified rather than left to a default. See ARTiViA's approach to Prepress.
Frequently asked questions
Both overlap adjacent colors to hide misregistration. A spread expands a lighter foreground object outward into a darker background. A choke shrinks a lighter background inward around a darker object. In both, the lighter color moves, because the overlap is less noticeable that way.
Each color prints from a separate plate, and the substrate can shift slightly between them. Without trapping, that shift leaves thin white gaps where colors meet. Trapping overlaps the colors so normal press movement does not expose the unprinted stock, protecting appearance across the run.
Digital printing registers all colors in one pass, so it needs far less trapping than offset or flexo. Some trapping may still be applied for safety, but the tight, built-in registration of digital output greatly reduces the gaps that trapping exists to prevent.
