[Digikam-users] Metadata settings when using XMP sidecar files

[Jean-François Rabasse]

Hello,

A few comments about :

On Tue, 23 Oct 2012, Elle Stone wrote:

> Reading and Writing Metadata:
> "Read from sidecar files" is checked.
> "Write to sidecar files" is checked, and "Write to XMP sidecar only"
> is selected. "If possible, write to raw is unchecked, and "update file
> timestamp" is unchecked.
>
> I don't know what "Read from sidecar files" means. When digiKam
> created the sidecar files, obviously it read from the image file. So
> once the sidecar file is created, what is the effect of reading or not
> reading from the sidecar file? digiKam is the only application that
> will write to the sidecar files.

Well, « When digiKam created the sidecar files, obviously it read from 
the image file », not exactly !
We should consider there are two kinds of meta information :

- technical metadata, i.e. all technical infos left by the camera in the
original images files, date, focal length, shutter speed, and many other
Exif data.

- user supplied metadata. This is what you provide via the GUI, title,
caption, tagslist, rating, etc. And this information is obviously never
available in an original « out of camera » image file.

Digikam stores all metainformation in its database. Technical 
information is extracted from images files when scanning for new images.
User supplied information is edited from the GUI.

This works well, but in case of problems (e.g. you happen to loose your
database, disk crash or other), the technical information could be
regenerated from images files Exif sections, but the user supplied 
information, title, rating et al. is lost.

Should you want to save metainformation outside of the DK database,
you have the choice : either save it in the image file itself (DK 
creates or updates a XMP section), or in a separate sidecar file.

And « Re-read metadata » options, from image files or sidecar files,
is just a way to rebuild (or overwrite) current metainformation in
the DK database from external file saved information.

Regards,

Jean-François