Bug 448462

Summary: PDF images may display repeated rectangular artefacts in the background at certain zooms
Product: [Applications] okular Reporter: rgreen <greenandpleasant2000-support>
Component: printingAssignee: Okular developers <okular-devel>
Status: CONFIRMED ---    
Severity: normal CC: aacid
Priority: NOR    
Version First Reported In: 21.12.0   
Target Milestone: ---   
Platform: Mint (Ubuntu based)   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:
Attachments: PDF showing visual artefacts at certain zoom settings
Screenshot of Okular PDF artefacts at 120% zoom
Screenshot of part of original pdf showing artefacts at 120% zoom

Description rgreen 2022-01-14 14:07:12 UTC
Created attachment 145458 [details]
PDF showing visual artefacts at certain zoom settings

SUMMARY
***
At certain zoom levels pdf images may display repeating rectangual markings whose size is related to the zoom level.. 
***
STEPS TO REPRODUCE
1. Open the attached pdf ("artefact"). This is actually an image, although text is displayed.
2. Set zoom level to 100%, then 110%.
3. Now, set zoom to 120%, then 125%.

OBSERVED RESULT

The view is as expected up to 110%. However, at 120%, you can definately make out repeating, bluish, rectangles in the background. These become very much smaller at 125%, and gradually fade away at incrementally larger zooms up to 150% or so.

EXPECTED RESULT

Obviously, there should be no such visual artefacts at any zoom.

SOFTWARE/OS VERSIONS

Linux/KDE Plasma:  Linux Mint
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 5.89
Qt Version: 5.15.3

ADDITIONAL INFORMATION

No artefacts were visible when viewing the same document at similar zooms in Xreader.
Comment 1 Albert Astals Cid 2022-01-15 23:44:22 UTC
Please attach a screenshot of such artifact
Comment 2 rgreen 2022-01-16 10:47:32 UTC
Created attachment 145530 [details]
Screenshot of Okular PDF artefacts at 120% zoom

See attached. If you zoom the png image you will see the artefacts change in a similar way to how they zoom in the pdf. They are somewhat faint, but if viewing on a laptop they become clearer by changing the angle of the screen.
Comment 3 Albert Astals Cid 2022-01-16 11:29:23 UTC
That image doesn't match with the PDF you attached.
Comment 4 rgreen 2022-01-16 12:08:45 UTC
Created attachment 145535 [details]
Screenshot of part of original pdf showing artefacts at 120% zoom

OK, here it is.
Comment 5 Albert Astals Cid 2022-01-16 23:06:53 UTC
I can defenitely not see that kind of artifacts but i can reproduce some different ones, at much lower zoom levels though. Needs someone with time to investigate, most probably a poppler bug.