System information

11. Overprint
11.1 The simple overprint and knockout theory
The basic rule
You may have overlapping colored objects in your PDF document, for example text or an image on
a colored background. If so, you can specify what should happen with these colors when they are
printed:
• Knockout, meaning that the colors of the object in the foreground cut out the area underneath.
In other words, the background color is erased and the resulting color will be the foreground
color.
• Overprint, meaning that the colors of the object are printed on top of the background colors.
The resulting color is a combination of the foreground and the background color.
A simple theoretical example
Let’s take a simple example (no need to worry, things will get complicated later, see The devil in
the overprint and knockout detail on page 210). Suppose you have a PDF file with two overlapping
objects. Their fill colors are as follows.
Foreground objectBackground objectInk
0 %40 %Cyan
0 %0 %Magenta
60 %0 %Yellow
0 %0 %Black
The table below shows what will “normally” happen when this PDF file is color-separated and
printed.
OverprintKnockout
Preview
Cyan plate
207
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