If a PDF has been created without bleed, or if the bleed is not sufficient, generating bleed out of page content is needed to avoid register problems.
To solve this task, pdfToolbox offers a variety of methods to add bleed from page content:
- Mirror content as image
- Repeat last pixel as image
- Mirror page objects
It is possible to define the width of the bleed per edge. The different methods can even become combined when using this feature as a Fixup.
Mirror content as image
Using the "Mirror as image" option will create an image for each edge (and if selected: corner) at the TrimBox from the content. This image will be place mirrored outside of the TrimBox.
The red rectangle shows a good example of the effect of this method.
Repeat last pixel as an image
The "Repeat last pixel as an image" method is rendering a thin strip inside the TrimBox and creates a wider image out of this last visible strip. This will result in an image, which "smears" out the last used color inside of the TrimBox outside as the bleed.
Mirror page objects
Yet another approach is to use all of the page objects, duplicate them (four times), flip them (two of them horizontally, the other two vertically), and then append them one by one to each of the four sides of the page. This will result in bleed with the same rendering accuracy and rendering quality as the page content itself. Different form what one may expect, the impact on file size is minimal (the page objects are not actually duplicated, but instead four references are created). The only real downside is that both a PDF viewer as well as a PDF output system will have to process – to a certain degree – five times as much page content data. This can lead to longer processing times during output, especially on systems with relatively small amounts of working memory.