Image Printing to Commercial Printing Machines (5)

Create color traps

Trapping is an overprinting technique that avoids the appearance of small gaps in the printed image due to slight misalignment during printing. It is important to contact your service provider to determine if any traps should be created. In most cases, the printer will determine if trapping is required; if necessary, it will tell you the value entered in the Trap dialog box.

Misaligned misalignment is not used, and trapped misalignment is used.
Trapping is used to correct misalignment of solid colors. In general, you do not need to create traps for continuous-tone images such as photos. Excessive trapping will produce a contour effect. These problems may not be visible on the screen, but may only appear when printing. Photoshop uses standard trapping rules:

All colors expand under black.
Bright colors expand in dark colors.
Yellow expands under cyan, magenta, and black.
Pure green and pure magenta expand equally under each other.
Create traps:

Stores a version of the file in RGB mode for later conversion. Then choose Image> Mode> CMYK Colors to convert the image to CMYK mode.
Choose Image > Trapping.
For Width, enter the trapping value provided by the printer. Then select the unit of measure and click the OK button. Consult the printer to determine the expected alignment error.




Source: China University Student Network