https://bugs.kde.org/show_bug.cgi?id=521397
Bug ID: 521397
Summary: Low-resolution/pixelated thumbnail generated for JXL
images after internal editing (e.g., Local Contrast)
Classification: Applications
Product: digikam
Version First 9.0.0
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: ImageEditor-Save
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 193112
--> https://bugs.kde.org/attachment.cgi?id=193112&action=edit
Same image versionated in JXL but with low-resolution thumbnail
DESCRIPTION
When a JPEG XL (.jxl) image is edited internally using digiKam's built-in tools
(such as the Local Contrast filter) and saved, the thumbnail generated in the
Album/Thumbnail view becomes highly pixelated and loses its original high
resolution.
This behavior does not occur with JXL images created or edited in external
applications (e.g., GIMP, Darktable), which display crisp thumbnails in
digiKam. The underlying JXL image file itself is perfectly fine, maintaining
its proper dimensions and full resolution when opened in the Image Editor; only
the thumbnail cache/embedded preview generated by digiKam appears destroyed.
STEPS TO REPRODUCE
1. Open a standard image (JPEG or JXL) in digiKam's Image Editor.
2. Apply an internal filter (e.g., Enhance -> Local Contrast).
3. Save or export the image as a JPEG XL (.jxl) file.
4. Go back to the Thumbnails/Album view and look at the newly created JXL file.
OBSERVED RESULT
The thumbnail for the internally edited JXL file is extremely blurry,
pixelated, and looks like a low-res placeholder (as seen in the second
thumbnail of the attached screenshot, labeled "JXL").
EXPECTED RESULT
The thumbnail should be rendered with the same high quality and sharpness as
the original image or externally generated JXL files.
SOFTWARE/OS VERSIONS
Operating System: Ubuntu Studio 26.04 LTS
KDE Plasma Version: 6.6.4
KDE Frameworks Version: 6.24
Qt Version: 6.10.2
ADDITIONAL INFORMATION
Re-building thumbnails (Tools -> Maintenance -> Rebuild Thumbnails) does not
fix the issue for these specific internally saved JXL files.
Attached is a screenshot showing the comparison between the original JPG
thumbnail and the corrupted JXL thumbnail after applying Local Contrast inside
digiKam.
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