Overprinting

If you are producing color documents that will be printed on litho printing presses, you may 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.

A black circle knocks-out out the cyan background

If the two plates do not line up exactly during printing, the circle will slightly offset from the knock-out (known as "out of register") and a small white gap can appear.

This example is exaggerated to illustrate the out of register printing, but even thin lines can be noticeable with dark colors.

Overprinting compensates for this problem. Xara has two types of overprinting: object level and ink level.

Object level overprinting

You can separately specify overprint for the line and fill colors of an object.

To overprint the line on an object, select the object then:

Right click and choose "Imagesetting" > "Overprint Line"
Or choose "Utilities -> Imagesetting -> Overprint Line".

Or right click the object, then choose "Imagesetting -> Overprint Line".

To overprint the fill on an object, select the object then:

Right click and choose "Imagesetting" > "Overprint Fill"
Or choose "Utilities -> Imagesetting -> Overprint Fill".

Or right click the object, then choose "Imagesetting -> Overprint Fill".

To turn off overprint on an object, just select the relevant option again. You can overprint both the line and a fill on an object if required. The object's fill and/or line will then not knock-out the colors any colors below it. Overprinting the fill is most commonly used to overprint dark colored text.

Overprinting the line is the normal way of avoiding out of register printing. The print company can tell you the tolerance to allow (usually 0.5pt to lpt). The line color depends on the background and object colors. Unless you want a specific line color, set the line to the lighter color.

Ink-level overprinting

Xara has two ink-level overprint options:

Overprint everything, including tints, in the specified ink color. Set in the Separations dialog box (see above). This option is rarely useful, but works in the reverse of object-level overprinting. For example if you select Cyan to be overprinted, it will cause cyan to not be knocked-out.

Always overprint black (everything over 95% Key). Set in the Imagesetting dialog box. Black is a relatively opaque ink and overprinting reduces registration problems. This option is particularly useful if you have a lot of black text. If your document has large areas of solid black, overprinting all black can cause problems with over-inking on the press.