What is trapping in printing?
On a multi-colour press, each ink prints from a separate plate, and those plates can shift against each other by a hair — misregistration. Where two colours meet, that shift can open a thin white gap. Trapping is the deliberate, tiny overlap added between adjacent colours so a small shift never shows. It's the safety margin of colour printing.
The problem trapping solves
Imagine red text on a blue background, each a separate ink. If the plates register perfectly, the edges meet cleanly. But if the blue plate drifts even 0.1 mm, a sliver of white paper peeks out along one edge where neither ink lands. Across a page of fine detail, those white gaps are glaring. Trapping prevents them by making the colours overlap slightly so there's always ink, even if a plate moves.
Spread and choke
Trapping works by expanding one colour slightly into the other. The rule of thumb is that the lighter colour spreads under the darker one, because the darker colour defines the visible edge. Two directions:
- Spread — the lighter foreground object is enlarged slightly so it laps under the darker background.
- Choke — the lighter background is contracted into the darker foreground object.
Either way the overlap is tiny — typically a fraction of a millimetre — invisible to the eye but enough to cover any registration shift.
Trapping vs overprint
They're related but different. Overprint decides whether one colour prints over or knocks out another (see overprint and knockout). Trapping adds a small overlap at the boundary so misregistration doesn't show. Trapping often uses overprint along that thin overlap zone.
When you do — and don't — need it
Trapping matters most where two solid, distinct colours meet with hard edges — spot-colour jobs, bold graphics, text on contrasting fields. It matters less for full-colour photographic work, where adjacent CMYK areas usually share some ink, so a small shift blends rather than gaps. Jobs printed in a single ink need no trapping at all.
Who actually does the trapping
Good news: you usually don't trap by hand any more. Modern RIPs and the printer's prepress workflow apply trapping automatically, tuned to that press's real registration tolerance — they know it better than you do. Your job is mostly to not fight it: avoid building artwork that makes trapping impossible, keep fine coloured detail from sitting on busy contrasting backgrounds, and ask the printer whether they want you to leave trapping to them (almost always yes). Where inks overlap, just keep an eye on combined ink coverage.
Frequently asked questions
What is trapping in simple terms?
Trapping is a tiny deliberate overlap between two adjacent colours so that if the printing plates shift slightly, no white gap appears at the edge where they meet. It's a safety margin against misregistration.
What's the difference between spread and choke?
Both create the trap overlap. A spread enlarges the lighter foreground object into the darker background; a choke shrinks the lighter background into the darker object. The lighter colour usually moves, so the darker one keeps its visible edge.
Do I need to trap my files myself?
Usually not. Modern RIPs and the printer's prepress system apply trapping automatically, calibrated to that press. Manual trapping is rarely needed today — ask your printer, and in almost all cases they prefer to handle it.
Is trapping the same as overprint?
No, but they're related. Overprint controls whether a colour prints over or knocks out the one beneath. Trapping adds a small overlap at a colour boundary to hide misregistration, and it often uses overprint along that thin overlap.
Let the RIP handle it
Hand-trapping is mostly history; modern workflows tune it to the actual press far better than we can by eye. Your job is to not build artwork that makes trapping impossible. Reviewed June 14, 2026.