Preventing Registration Errors | Printing

Trapping is a way of compensating for errors in registration on the press and is one of the ways that people judge the quality of the printed piece. It's the process of slightly overlapping colors so that slivers of white won't appear between colors, compensating for potential registration errors. Registration errors can be caused by a few different things like: Material problems, environmental issues, mechanical problems, and of course, human error, but most common problems usually stem from the press itself and the paper.


The goal of every printer is to print everything in perfect alignment or "in register." If anything becomes misaligned you'll be able to see gaps between colors or areas where one color is very pronounced instead of blending in with other inks to create a color. Trapping is designed to minimize the errors in registration by putting images with similar colors along a common edge and slightly overprinting.

Chokes and spreads

A spread traps a light foreground color to a dark background color and a choke traps a light background color to a dark foreground color. The dark color defines the edge of the object or text and slightly spreads into the darker lighter color to maintain the edge without any gaps.

Knocking Out and Overprinting

When you’re imaging color separations for a job with overlapping colors whatever image is on top should knock out the other colors (won’t print them) that are behind it. You can specify what colors and images you want to overprint. For your job to turn out the best it's better to have your full color images to be knocked out when the overprint would blend and create a funky color. But you can also use it to create cool effects on your background colors or to prevent any mis-registration.