Trapping and separations for press in Layout by Zaweba
Set trap presets for page ranges, ink densities and trapped separations in Layout by Zaweba, then export greyscale TIFF plates and check them on screen.
On a printing press, each ink goes down from a separate plate, and the plates never line up perfectly. Where two colours meet, a hairline of white paper can appear if one plate is a fraction out. Trapping fixes this by making colours overlap very slightly at their edges, so a small misregister is hidden. Layout by Zaweba can work out traps itself, using presets you control, and show you the result before anything goes to press.
For many jobs the print shop handles trapping. When it falls to you, or when you are producing separations yourself, these are the controls.
What a trap preset sets
A trap preset holds the rules for how traps are made. Trap width sets how far colours spread into each other, and a separate black width sets how far traps go when black is involved, since black is usually handled differently. The step limit decides how different two colours need to be before a trap is made at all, so near identical colours aren't trapped for nothing.
Black colour and black density tell Layout what counts as black for trapping purposes. Sliding trap controls how the trap moves towards the centre line between colours of similar strength. Trap colour strength affects the colour of the trap itself. Placement decides where a trap goes when an object meets a picture, and the corners setting controls how traps meet at the corners of shapes.
These are technical settings, and the right values depend on the press, the paper and the print shop's preferences. Ask the printer what they want and build a preset to match.
Assigning presets to page ranges
Presets are assigned to page ranges, so one document can use different trapping on different pages. A brochure with a cover on heavy stock and an inner section on lighter paper, or a section printed on a different press, can each get suitable settings. Pages without trapping, such as those that are mostly single colour text, can be left out.
Ink densities and the ink manager
Trapping depends on how dark each ink is, because traps generally spread the lighter colour into the darker one. Ink densities are set in the ink manager, alongside its other jobs such as turning spot colours into process. If the document uses unusual spot inks, check their densities there so traps go the right way.
Seeing traps and exporting separations
Show traps displays the traps on screen, so you can see what has been built. Look closely at small type on coloured backgrounds, thin rules and the edges of logos, which are where traps show most.
When printing separations, Layout can apply trapping to them. Export > Separations writes one greyscale TIFF per plate, which is how you hand finished, trapped separations to a workflow that expects them, or check each plate's content in detail. Each TIFF shows exactly what will be on that plate, traps included.
Mistakes people make with trapping
Trapping twice is the big one. If you trap the document and the print shop also traps it, colours overlap too much and edges look heavy. Agree who does it before export.
Using one preset for everything ignores the differences between papers and presses. Use page ranges when the job has distinct parts.
Trapping very fine detail, such as small serif text in a colour on a colour, can thicken it noticeably. Look at Show traps at high zoom on these areas.
Ignoring ink densities for spot colours can make traps spread the wrong way. Check the ink manager.
Where trapping sits in prepress
Trapping comes after colour is settled. The separations preview and overprint preview show how the plates and overprints will behave, and the ink limit warning catches areas with too much ink. Live preflight checks the technical side as you work. Once all of that is right, trapping is the final adjustment for the press itself.
