Overprinting Overview

If you are producing color documents that will be printed on litho printing presses, you will often find overprint useful. Printing presses are mechanical devices with the inevitable slight misalignments when they are running. Overprinting lets you overcome these misalignments. For example, your job may have a black circle on a cyan background. When the document is imageset, the circle appears on the black separation and the cyan separation has a non-printing area under the circle. (The technical term is that the circle 'knocks-out' the background.) The knock-out is the same size as the circle.

If the two plates do not line up exactly during printing, the circle will slightly offset from the knock-out. The technical term is that the printing is 'out of register'. A small white gap appears at one edge. (Exaggerated in this example but even thin lines can be noticeable with dark colors.)

Overprinting compensates for this. Use overprinting with care. Overprinting large areas can flood the printing press with excess ink. Xara LX has two type of overprint:

Object level

You can separately specify overprint for the line and fill colors. Right-click on the object to open the pop-up menu. Then choose Overprint line or Overprint fill from the Imagesetting submenu.

To cancel object level overprint, click again on Overprint line or Overprint fill.

Overprinting the fill is most commonly used to overprint dark colored text on a light background.

Overprinting the line is the normal way of avoiding mis-registration. The print shop can tell you the tolerance to allow (usually 0.5pt to 1pt).If you add a 1pt line to the black circle and set it to overprint, it extends onto the background by 0.5pt. The line color depends on the background and object colors. Unless you want a specific line color, set the line to the lighter color (Cyan in this case.) The illustration uses a red line around part of the circle so you can see it.

Note that you can only check overprint by examining the films produced by the service bureau
. Ordinary desktop printers ignore any overprint settings.

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Related Topics

Printing