Overlays, underlays, watermarks, n-up¶
You can use pikepdf to overlay pages or other content on top of other pages.
This might be used to do watermarks (typically an underlay, drawn before everything else), n-up (compositing multiple individual pages on a large page, such as converting slides from a presentation to 4-up for reading and printing).
If you are looking to merge pages from different PDFs, see Merge (concatenate) PDF from several PDFs.
In this example we use pikepdf.Page.add_overlay()
to draw a thumbnail of
of the second page onto the first page.
In [1]: from pikepdf import Pdf, Page, Rectangle
In [2]: pdf = Pdf.open(...)
In [3]: destination_page = Page(pdf.pages[0])
In [4]: thumbnail = Page(pdf.pages[1])
In [5]: destination_page.add_overlay(thumbnail, Rectangle(0, 0, 300, 300))
In [6]: pdf.save("page1_with_page2_thumbnail.pdf")
The pikepdf.Rectangle
specifies the position on the target page into which
the other page can be drawn. The object will be drawn centered in a way that
fills as much space as possible while preserving aspect ratio.
Use pikepdf.Page.add_underlay()
instead if you want content drawn underneath.
It is possible content drawn this way will be overdrawn by other objects.
Use pikepdf.Page.trimbox
to get a page’s dimensions.
add_overlay
will copy content across Pdf
objects as needed, and can copy
other pages or other Form XObjects.
add_overlay
also preserves aspect ratio.
Use pikepdf.Page.as_form_xobject()
and
pikepdf.Page.calc_form_xobject_placement()
if you want more precise control
over placement.
Composition works using Form XObjects, which is how PDF captures of a group of related objects for drawing. Some very basic PDF software may not support them, or may fail to detect images contained within.
When perform n-up composition, it will work better to create your composition within the existing document, rather than in a new document. Transforming the existing document will ensure that metadata, annotations and hyperlinks are preserved. For example, to convert 16 slides to 4×4-up pages for printing, add four pages onto the end of the file, draw the slides onto the target pages, and then delete the slides.
By default, add_overlay
encapsulates the existing content stream in a way
that ensures the transformation matrix is first reset, since this behavior
aligns with user expectations. This adds a q/Q
pair to (push/pop graphics
stack) to existing content streams. To disable this (usually desired) behavior
use push_stack=False
.