`PageObject.scale()` scales media box incorrectly

[dominik-korsa]

The file scaling example from the docs does not work. The content is scaled correctly, but the resulting page size is unexpected, as if the scaling got applied twice. See the reproduction example.

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
Linux-6.14.0-32-generic-x86_64-with-glibc2.41

$ python -c "import pypdf;print(pypdf._debug_versions)"
pypdf==6.1.1, crypt_provider=('cryptography', '45.0.7'), PIL=none

Code + PDF

This is a minimal, complete example that shows the issue:

# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "pypdf",
# ]
# ///
from pypdf import PdfReader, PdfWriter

reader = PdfReader("input.pdf") # A4 document
writer = PdfWriter()

for page in reader.pages:
    page.scale_by(0.5) # Expected A6
    writer.add_page(page)

# The output contains A8 pages instead,
# with the content scaled by the factor 0.5
writer.write("output.pdf")

The input PDF, A4:
input.pdf

The output contains A8 pages, not A6 as expected. The content is scaled correctly by the factor 0.5:

output.pdf

[stefan6419846]

Thanks for the report. You are of course invited to investigate this and propose a fix.

[Nid01]

I just tried the different releases.
Version 5.4.0 works fine and with version 5.5.0 the scaling is broken.

[Nid01]

@j-t-1 The order of the page boundaries has been changed by you, but the order seems to be essential, since the scaling issue is solved when undoing the marked change: d89fb78#diff-153e5cee71ddf471246ff5c0e198345f005942a540a8f39297736f0b620d631dR1587-R1592

[Nid01]

I opened a pull request, so we maybe get the issue fixed soon.

[j-t-1]

Apologies for this error.

The CropBox has default value of the MediaBox, and the others (apart from the MediaBox) have defaults value of the CropBox.

@Nid01 thanks for finding and fixing this. In your PR, it is unnecessary to move the ArtBox to fix this? I think the order should be
BleedBox, TrimBox, ArtBox, CropBox, MediaBox.

[dominik-korsa]

The resulting output.pdf is weirder than I thought:

• Okular, Chrome and Firefox (all on Kubuntu 25.04) all display the pages cropped like this:

• gs using the media box and the PDF preview in Dolphin (I'm not sure what rendering backend it uses) display the pages like this, for all boxes:

Below are all the images of the first pages rendered using this bash script on output.pdf:

#!/usr/bin/bash

mkdir mediabox bleedbox trimbox cropbox artbox
gs -sDEVICE=png16m -o mediabox/%02d.png $1
gs -dUseBleedBox -sDEVICE=png16m -o bleedbox/%02d.png $1
gs -dUseTrimBox -sDEVICE=png16m -o trimbox/%02d.png $1
gs -dUseCropBox -sDEVICE=png16m -o cropbox/%02d.png $1
gs -dUseArtBox -sDEVICE=png16m -o artbox/%02d.png $1

• artbox:

• cropbox:

• mediabox:

• trimbox:

• bleedbox:

[stefan6419846]

Usually, we shouldn't have to look into the dedicated boxes, but just the default rendering.

Nevertheless, looking into the corresponding code, we might have a similar side effect with the cropbox?

pypdf/pypdf/_page.py

Lines 2100 to 2130 in 2b2eca2

	mediabox = _create_rectangle_accessor(PG.MEDIABOX, ())
	"""A :class:`RectangleObject<pypdf.generic.RectangleObject>`, expressed in
	default user space units, defining the boundaries of the physical medium on
	which the page is intended to be displayed or printed."""
	cropbox = _create_rectangle_accessor("/CropBox", (PG.MEDIABOX,))
	"""
	A :class:`RectangleObject<pypdf.generic.RectangleObject>`, expressed in
	default user space units, defining the visible region of default user
	space.
	When the page is displayed or printed, its contents are to be clipped
	(cropped) to this rectangle and then imposed on the output medium in some
	implementation-defined manner. Default value: same as
	:attr:`mediabox<mediabox>`.
	"""
	bleedbox = _create_rectangle_accessor("/BleedBox", ("/CropBox", PG.MEDIABOX))
	"""A :class:`RectangleObject<pypdf.generic.RectangleObject>`, expressed in
	default user space units, defining the region to which the contents of the
	page should be clipped when output in a production environment."""
	trimbox = _create_rectangle_accessor("/TrimBox", ("/CropBox", PG.MEDIABOX))
	"""A :class:`RectangleObject<pypdf.generic.RectangleObject>`, expressed in
	default user space units, defining the intended dimensions of the finished
	page after trimming."""
	artbox = _create_rectangle_accessor("/ArtBox", ("/CropBox", PG.MEDIABOX))
	"""A :class:`RectangleObject<pypdf.generic.RectangleObject>`, expressed in
	default user space units, defining the extent of the page's meaningful
	content as intended by the page's creator."""

As far as I understand the current code, we should always end with cropbox and mediabox? Otherwise, the bleedbox, trimbox and artbox might be scaled twice as well.

[Nid01]

@Nid01 thanks for finding and fixing this. In your PR, it is unnecessary to move the ArtBox to fix this? I think the order should be BleedBox, TrimBox, ArtBox, CropBox, MediaBox.

@j-t-1 Yes, the visible scaling issue was caused by scaling the mediabox before the cropbox.
I'll add you proposed order to the pull request.