用 PyPDF2 裁剪 pdf

Question

I've been working on a project in which I extract table data from a pdf with neural network, I successfuly detect tables and get their coordinate (x,y,width,height), I've been trying to crop the pdf with pypdf2 to isolate the table but for some reason cropping never matches the desired outcome. After running inference i get these coordinates

[[5.0948269e+01, 1.5970685e+02, 1.1579385e+03, 2.7092386e+02 9.9353129e-01]]

the 5th number is my neural network precision, we can safely ignore it

trying them in pyplot works, so there's no problem with them:

However using the same coords in pypdf2 is always off

from PyPDF2 import PdfFileWriter, PdfFileReader

with open("mypdf.pdf", "rb") as in_f:
    input1 = PdfFileReader(in_f)
    output = PdfFileWriter()

    numPages = input1.getNumPages()

    for i in range(numPages):
        page = input1.getPage(i)
        page.cropBox.upperLeft = (5.0948269e+01,1.5970685e+02)
        page.cropBox.upperLeft = (1.1579385e+03, 2.7092386e+02)
     
        
        output.addPage(page)
        with open("out.pdf", "wb") as out_f:
          output.write(out_f)

This is the output I get:

Am i missing something?

thank you !

Answer 1

Here you go:

from PyPDF2 import PdfFileWriter, PdfFileReader

with open("mypdf.pdf", "rb") as in_f:
    input1 = PdfFileReader(in_f)
    output = PdfFileWriter()

    numPages = input1.getNumPages()

    x, y, w, h = (5.0948269e+01, 1.5970685e+02, 1.1579385e+03, 2.7092386e+02)

    page_x, page_y = input1.getPage(0).cropBox.getUpperLeft()
    upperLeft = [page_x.as_numeric(), page_y.as_numeric()] # convert PyPDF2.FloatObjects into floats
    new_upperLeft  = (upperLeft[0] + x, upperLeft[1] - y)
    new_lowerRight = (new_upperLeft[0] + w, new_upperLeft[1] - h)

    for i in range(numPages):
        page = input1.getPage(i)
        page.cropBox.upperLeft  = new_upperLeft
        page.cropBox.lowerRight = new_lowerRight

        output.addPage(page)

    with open("out.pdf", "wb") as out_f:
        output.write(out_f)

Note: in PyPDF2 the origin of coordinates placed in the lower left corner of a page. And the Y-axis is directed from the bottom to up. Not like on the screen. So if you want to get a PDF-coordinate of top edge of your crop area you need to subtract y-coordinate of the top edge of the crop area from the height of the page.