Strange problem when page.cropbox changed

[mlove4u]

OS: macOS 10.15.7
PyMuPDF: 1.18.17
Python: 3.7.4

My use case:

1. change the value of page.cropbox to trimbox
2. render a image from pdf page. Rendering area -->page.cropbox(trimbox)

Problem:

page.get_pixmap(clip=page.mediabox) and page.get_pixmap(clip=page.cropbox) does not crop the right area as expected.
Please take a look at the attached png file. Sorry for my poor English. Thanks.
Here is my code:

import fitz
from PIL import Image


def show_pm(pm, file_name):
    pil = Image.frombuffer('RGB', (pm.width, pm.height), pm.samples)
    pil.save(file_name)
    pil.show()


doc = fitz.open("trimbox.pdf")
page = doc[0]
#mat1 = page.transformation_matrix
#
print("old page.cropbox: ", page.cropbox)
# >> old page.cropbox:  Rect(0.0, 0.0, 400.0, 200.0)
pm = page.get_pixmap()  # clip(default)=page.cropbox
show_pm(pm, "0_page.cropbox.png")
#
pm = page.get_pixmap(clip=page.mediabox)
show_pm(pm, "0_page.mediabox.png")
#
#
doc.xref_set_key(page.xref, "CropBox", '[50 50 350 150]')  # change cropbox
print("new page.cropbox: ", page.cropbox)
# >> new page.cropbox:  Rect(50.0, 50.0, 350.0, 150.0)
#mat2 = page.transformation_matrix
pm = page.get_pixmap(clip=page.mediabox)  # page.mediabox.irect
show_pm(pm, "1_page.mediabox.png")
#
pm = page.get_pixmap(clip=page.cropbox)
show_pm(pm, "1_page.cropbox.png")
#
pm = page.get_pixmap()
show_pm(pm, "1_.png")

trimbox.pdf

[JorjMcKie]

I will have a look.
Meanwhile I will convert htis to a discussion.

[JorjMcKie]

It is early in the morning here, but to me everything works as expected - nothing is strange.
If you specify a clip parameter, then its intersection with the page rectangle will be taken. In so far, the formulation in the documentation is a bit misleading: I should have written "page rectangle".

[mlove4u]

Thank you for your reply.
What do you mean by "page rectangle"? Does it means Page.rect?
I noticed that the value of Page.rect changed from (0.0, 0.0, 400.0, 200.0) to (0.0, 0.0, 300.0, 100.0) (-->A_0-0.png) after I replaced the value of Page.cropbox.
But, what is the area of new Page.rect? It seems to be the pink area of B_50-50.png but not A_0-0.png.
B_50-50.png

A_0-0.png

Does the origin(0,0) of Page.rect changes depending on coordinate of Page.cropbox ?
Thanks.

[JorjMcKie]

Please consult the documentation!
Potntially except for page rotation and the top-left value, page.rect equals CropBox. The page may be rotated, but the CropBox never is. Width and height of the unrotated page always equal those of cropbox.
The top-left of page.rect always is (0,0).
So if you change the cropbox, you also change page.rect.

[mlove4u]

I got. Thank you very much.

[JorjMcKie]

CropBox is also the default for TrimBox, ArtBox and BleedBox. If CropBox is missing then MediaBox is used. See Adobe PDF guide.