Until recently Gwenview was able to display RAW camera files, orf,nef,cr2 etc. That is no longer the case.
It might be related to this:
Now we have this bug (huge regression):
Okulare removed photo support from ePub. (worth reading with comments). Something is going on.
not sure whether show_bug.cgi?id=462669 is related, but Gwenview no longer displays RAW files again. no previews, and fails to load RAW files too. bug already reported;
will be fixed in