Topmost pixels of Big PNG object gets black using insert_image() function

[LasseStaeglichPP]

Description of the bug

When using PyMuPDF's insert_image function to insert a transparent PNG into a PDF, certain areas of the image (notably the topmost pixels) appear as solid black in the generated PDF. This issue is most noticeable in large PNG images (~300 DPI, dimensions such as 56 cm x 100 cm)
I tried the insert_image() function with the Image parameter as a File, Pixmap and stream. All had the same result

Here the resulting PDF file:
23511_1_No.pdf
Screenshot of the PNG wihtout the issue

Screenshot of the PDF with the issue

The PNG was sadly to big for uploading so i here is a wetransfer link:
https://we.tl/t-1VdSrVImwP

How to reproduce the bug

use insert_image() function with a large PNG with transparency and semi transparency

PyMuPDF version

1.24.12

Operating system

Windows

Python version

3.12

[julian-smith-artifex-com]

Apologies for taking time to look at this. The above link https://we.tl/t-1VdSrVImwP has expired - could you create a new link?

[LasseStaeglichPP]

Hello Julian, Sure here is an updated Link. It will expire in 7 days again :(
https://we.tl/t-0UP2c6uadP

I did some further testing and i got a work around in reducing the DPI to exactly 300DPI or below, I did not get this issue since. But i prefer to not alter the images and reduce quality if i dont have to

[LasseStaeglichPP]

Hi, just the morning after i said we did not get this issue since scaling down to 300dpi i got this issue again.

It is here the last image on this gangsheet
28258_1_No.pdf

This is my code snippet on how i use the insert_image()

image = Image.open(path).convert("RGBA")

img_bytes = io.BytesIO()
image.save(img_bytes, format="PNG")
img_bytes.seek(0)

page.insert_image(placings_rect, stream=img_bytes.getvalue(), rotate=rotate)

[LasseStaeglichPP]

Hello,

Here is the new Wetransfer link, the one above should expire today https://we.tl/t-nrGpQYSu11

[julian-smith-artifex-com]

Thanks for the third link, actually i downloaded from the second link, so i now have the file. I can reproduce the problem, but i don't yet understand what's going wrong.

[LasseStaeglichPP]

Hi Julian, good to know you are able to reproduce the issue! If i can be of any help, sadly i am new to programming so i probably cannot help with this. But maybe more files where i find this exact issue might help, what do you think?

[julian-smith-artifex-com]

Apologies for the delay in getting back to this.

The black pixels seem to be in the original PNG file. I've attached a screenshot of the image manipulation application Gimp after loading the original PNG, showing a 16x zoomed-in view of the red character in the top-left of the image. [The checkerboard pattern indicates transparent pixels.]

I've also used Imagemagick's convert tool to extract just the top-left 500x500 region of the PNG, and this also shows black pixels.

[julian-smith-artifex-com]

Here's a link to the screenshot: https://ghostscript.com/~julian/4128_gimp.png

[julian-smith-artifex-com]

Closing this as no response for a while.

Please comment/reopen when more information is available.