Photoshop

Create a color trap

A trap is an overlap that prevents tiny gaps in the printed image caused by a slight misregistration on press. Contact your service provider before you do any trapping. In most cases, your print shop determines whether trapping is needed. If so, the print shop staff will tell you what values to enter in the Trap dialog box.

Trapping to correct misalignment

A.
Misregistration with no trap

B.
Misregistration with trap

Trapping is intended to correct the misalignment of solid colors. In general, you don’t need traps for continuous-tone images such as photographs. Excessive trapping may produce an outline effect. These problems may not be visible on-screen and might show up only in print. Photoshop uses standard rules for trapping:

  • All colors spread under black.

  • Lighter colors spread under darker colors.

  • Yellow spreads under cyan, magenta, and black.

  • Pure cyan and pure magenta spread under each other equally.

  1. Save a version of the file in RGB mode, in case you want to reconvert the image later. Then choose Image > Mode > CMYK Color to convert the image to CMYK mode.
  2. Choose Image > Trap.
  3. For Width, enter the trapping value provided by your print shop. Then select a unit of measurement, and click OK. Consult your print shop to determine how much misregistration to expect.