Missing thumbnails, maybe digikam4.db involved

[ShutterBug]

I recently encountered this problem, as well, using DigiKam 4.12 on Ubuntu
16.04.3.  Just for fun, I tried this (and it worked!):

1. Close DigiKam.
2. Open the file browser (Nautilus) and navigate to the folder that contains
the image files that DigiKam no longer displays thumbnails for.  Example: 
/Pictures/1973Pix
3. Open another file browser window and navigate to the folder above the
problem folder. Example:  /Pictures
4. Create another folder and move the files from the problem folder to the
new folder.  
Example:  
$mkdir 1973Pix-a
$cd 1973Pix-a
$mv /Pictures/1973Pix/* .
(Of course, you can do this all in Nautilus)
5. Launch DigiKam and let it scan the target Collection for new or deleted
files.  Look (in DigiKam) under the new Album folder.  You should now see
the missing thumbnail images, complete with any tag info you've added
previously!
Optional:  I wanted to retain the original folder names.  So, I reversed the
process:
6. Close DigiKam.
7. Move the files from the new folder back to the original folder (Example: 
1973Pix-a  > 1973Pix)
8. Delete the empty new folder (Example: $rm 1973Pix-a)
9. Launch DigiKam and wait for the rescan to complete.

I haven't tried this yet, but suspect that the entire target Collection root
folder could be renamed, the target Collection reset in the DigiKam
configuration settings, scanned by DigiKam, exit DigiKam, folder renamed
back, again reset the Collection target, launch DigiKam and allow it to
complete its scan.  I suspect this would catch any and all missing
thumbnails.

Caveat:
**Always keep a backup of your image files, just in case something goes
wrong!**


Hope this helps someone...DigiKam's a really great application!





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