https://bugs.kde.org/show_bug.cgi?id=477926
Bug ID: 477926
Summary: Fractional zoom causes 8-bit PNG to produce black
pixel artifacts.
Classification: Applications
Product: gwenview
Version: 23.08.3
Platform: Manjaro
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: gwenview-bugs-n...@kde.org
Reporter: vad....@vad.cx
Target Milestone: ---
Created attachment 163765
--> https://bugs.kde.org/attachment.cgi?id=163765&action=edit
pngquant-ed reproduction file
SUMMARY
***
Fractional zoom causes 8-bit PNG to produce black pixel artifacts.
***
STEPS TO REPRODUCE
1. Open the attached PNG in Gwenview
2. Use scroll wheel zoom
OBSERVED RESULT
Fractional zoom values are scaled without artifacting
EXPECTED RESULT
Black pixel artifacts.
WITHOUT artifacts are those zoom values: 100%, 400%, 800%, 1600%
SOFTWARE/OS VERSIONS
Linux/KDE Plasma:
(available in About System)
KDE Plasma Version: 5.27.9
KDE Frameworks Version: 5.112.0
Qt Version: 5.15.11
Gwenview: 23.08.3 on Manjaro and 22.04.1 on Fedora ELRepo
ADDITIONAL INFORMATION
I am not sure if it's paletted, probably yes. I got that image after
optimization with PNGaunglet.
`file` output: "PNG image data, 1307 x 304, 8-bit colormap, non-interlaced"
The effect seems to be stronger on 23.08.3 than on 22.04.1
I could reproduce this effect after running a similar image through `pngquant
--nofs path/to.png`
Other programs that work correctly:
gThumb, qView, KDE's Pix, Krita, GIMP, IrfanView, Firefox
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