Bug 402554

Summary: Gwenview upscales image on high-DPI monitors when scaling factor (in display settings) is set to >1
Product: [Applications] gwenview Reporter: tamius.han
Component: generalAssignee: Gwenview Bugs <gwenview-bugs-null>
Status: RESOLVED DUPLICATE    
Severity: normal    
Priority: NOR    
Version First Reported In: 18.08.3   
Target Milestone: ---   
Platform: Manjaro   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: Screenshot demo of the issue.

Description tamius.han 2018-12-25 13:05:37 UTC 
SUMMARY

On high-DPI monitors where scaling factor is set to more than one, gwenview seems to upscale the image by scaling factor. Image appears pixelizated. Issue is demonstrated in the screenshot.

STEPS TO REPRODUCE
1. Set scaling factor in settings > display settings to more than one (I use 1.3)
2. Open any image in gwenview

OBSERVED RESULT

Image is pixelizated, with jagged edges everywhere and generally looks pretty atrocious. (Right side of the screenshot/Gwenview window)

EXPECTED RESULT

Image is displayed normally, with no scaling applied (Left side of the screenshot/GIMP)


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 4.19.8-2-MANJARO
KDE Plasma Version: 5.14.4
KDE Frameworks Version: 5.52.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION

Judging by the image quality, it appears that gwenview rescales image twice. It seems the following happens:

1. Gwenview calculates how big the window would be if the scaling factor was set to 1
2. Gwenview rescales the image to fit inside a window of dimensions calculated in step 1
3. Gwenview then upscales the image to fit inside the actual window, using nearest neighbour (upscaling the image from step 2)
Comment 1 tamius.han 2018-12-25 13:09:39 UTC 
Created attachment 117099 [details]
Screenshot demo of the issue.

Same image opened in GIMP (left) and Gwenview (right), both at 100%. GIMP displays image correctly, Gwenview upscales and completely ruins it.
Comment 2 Christoph Feck 2018-12-25 14:34:02 UTC 

*** This bug has been marked as a duplicate of bug 373178 ***