I've filed a bug at bugs.kde.org: https://bugs.kde.org/show_bug.cgi?id=274947 Meanwhile it seems to be related to "LibJPEG: 80". I have a kubuntu test system which uses "LibJPEG: 62" and works fine. I guess it's related to bug #306679 and https://bugs.kde.org/show_bug.cgi?id=228483 .
Created attachment 277705 [details] Output of "emerge --info"
I'm sorry, that the bug description looks very thin. There is a lot of information (including stack traces) about this bug over at bugs.kde.org, so I thought I don't have to copy it here. I've also done some debugging and located the bug as close as I could get. Summary: Digikam calls "jpegutils.cpp". The latter creates a struct "jpeg_transform_info transformoption". But there seems to be an error, because "transformoption.crop_yoffset_set" of type "Digikam::<anonymous enum>" is not initialized with "0" (= "Digikam::JCROP_UNSET") but with "134814873". This leads to premature termination of the transformation process. Hope this bug looks a bit more worthy to fix now.
Fixed in media-gfx/digikam-2.0.0