https://bugzilla.wikimedia.org/show_bug.cgi?id=24545
Summary: ImageMagick generated Thumbnails get messed up (wrong
colors) in some cases
Product: MediaWiki
Version: 1.15.1
Platform: All
OS/Version: Linux
Status: NEW
Severity: minor
Priority: Normal
Component: Images and files
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected],
[email protected]
Created an attachment (id=7592)
--> (https://bugzilla.wikimedia.org/attachment.cgi?id=7592)
Generated with: "convert -background white -size 120 testcase.jpg -thumbnail
'120x' -depth 8 -sharpen '0x0.4' thumb_wrong.jpg
I've found that ImageMagick/convert generates messed-up thumbnails from some
kinds of images (mainly truecolor, high-resolution but other kinds may be
affected as well).
The thumbnails show wrong color portions that might result from wrong (or no)
dithering. I tracked down the problem to the "-depth 8" parameter to convert in
"includes/media/Bitmap.php", without it, everything looks just fine.
A quick possible solution would be, to make this parameter optional. Maybe a
dedicated analysis of this bug could result in checking the uploaded
image-properties and selectively applying the "-depth 8" option to images where
it doesn't harm thumbnail generation.
Hope that helps.
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