Once I have processed a raw image with darktable, I export to jpg format and store on disk in a hierarchy of folders organised by date and trip location. I then use digikam to review the images, giving a star rating and tagging with extra information such as precise location, and for wildlife the name and species group.
What I would like is a way to copy the rating and tagging information from the jpg file back to the raw file. exiv2 or exiftool can extract the rating information and raw filename from the jpg, and probably, with a bit of scripting, write the information into the raw file xmp. However, with thousands of images in dozens of subfolders it would be tricky to create a reliable batch process.
So my real question is whether there are any tools inside digikam or darktable that would make the job easier, or does anyone have a script already?
How would I use this? Well I could save a lot of disk space if I could selectively delete all raw files containing poor quality images - even with the latest darktable advances, its rarely worth fiddling with rubbish in the hope of finding a gem. A rough and ready calculation (including backups) shows that I could clean up 1Tb of storage - worth it if there is a good way to automate things.