Bug 521131 - File Picker and Dolphin shows the thumbnails of folders with images very pixelated
Summary: File Picker and Dolphin shows the thumbnails of folders with images very pixe...
Status: REPORTED
Alias: None
Product: kio-extras
Classification: Frameworks and Libraries
Component: Thumbnails and previews (other bugs)
Version First Reported In: 26.08.0
Platform: CachyOS Linux
: NOR minor
Target Milestone: ---
Assignee: Plasma Bugs List
URL:
Keywords:
Depends on:
Blocks: 522957
  Show dependency treegraph
 
Reported: 2026-06-06 10:05 UTC by Fernando Marcelino Muniz
Modified: 2026-09-12 19:19 UTC (History)
2 users (show)

See Also:
Latest Commit:
Version Fixed/Implemented In:
Sentry Crash Report:


Attachments
Issue in File Picker. (64.05 KB, image/png)
2026-06-06 10:05 UTC, Fernando Marcelino Muniz
Details
Issue in Dolphin (375.90 KB, image/png)
2026-08-21 19:17 UTC, Fernando Marcelino Muniz
Details

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Description Fernando Marcelino Muniz 2026-06-06 10:05:27 UTC
Created attachment 192939 [details]
Issue in File Picker.

STEPS TO REPRODUCE
1. See the icon of a folder with images with the File Picker.
2. See the icon of a folder with images with Dolphin.

OBSERVED RESULT
File Picker is showing the thumbnails very pixelated when compared to Dolphin, even though it has the same icon size.

EXPECTED RESULT
File Picker should show the thumbnails in the icon of folders with images with the same quality as Dolphin.

SOFTWARE/OS VERSIONS
Operating System: CachyOS Linux 
KDE Plasma Version: 6.6.5
KDE Frameworks Version: 6.26.0
Qt Version: 6.11.1
Kernel Version: 7.0.11-1-cachyos (64-bit)
Graphics Platform: Wayland
Processors: 8 × 11th Gen Intel® Core™ i5-11300H @ 3.10GHz
Memory: 9 GB of RAM (8.1 GB usable)
Graphics Processor 1: Intel® Iris® Xe Graphics
Graphics Processor 2: NVIDIA GeForce GTX 1650
Manufacturer: LENOVO
Product Name: 82MG
System Version: IdeaPad Gaming 3 15IHU6
Comment 1 Fernando Marcelino Muniz 2026-08-21 19:17:37 UTC
Created attachment 195345 [details]
Issue in Dolphin

Now the issue is also in Dolphin 26.08.0
Comment 2 Friedrich W. H. Kossebau 2026-09-12 19:19:18 UTC
Hi. The last days some issues with the scaling done inside the folder thumbnail rendering code were uncovered, which might explain the issue as documented in the screenshots, though under certain conditions only, which also would be a bit unexpected.

Which might need some more investigations into your system, so some questions:

a) can you tell the output of "kscreen-doctor -o", especially the "Scale" values shown for the respective outputs?
b) had you added/removed screens during the respective apps (the one where you used the file picker and Dolphin) were running?
c) had you moved the windows around between your screens?

As by your screenshots the pixellation is limited to the overlayed file thumbs, not seen with the folder itself, a possible cause currently can be if the thumbnail worker assumes (for unknown reasons) all screens have no scaling (or, have 1), while the apps run with scaling of e.g. 2 and request a scale-matching thumbnail.

In case you are experienced with running code from git, please check https://invent.kde.org/network/kio-extras/-/merge_requests/556, which has been merged to master as well the release branch already, so what will become 26.08.2 in October. 
And in case you have developer skills, please also consider adding 
    qDebug() << "APP devicePixelRatio" << QGuiApplication::devicePixelRatio();
to the begin of ThumbnailProtocol::thumbForDirectory() method in https://invent.kde.org/network/kio-extras/-/blob/master/thumbnail/thumbnail.cpp#L529 locally, so we can see what the worker thinks the scaling is.