[digiKam-users] Confused by tick boxes in "Edit Metadata" + how does "Captions" interact?

[Remco Viëtor]

On lundi 17 septembre 2018 09:21:13 CEST Chris Green wrote:
> Gilles Caulier <caulier.gilles at gmail.com> wrote:
> 
> [snip]
> 
> > > There are also the three extra tick boxes which I assume are the ones
> > > that copy metadata between Exif, IPTC and XMP.  However there is some
> > > confusion here too (for me anyway!), what is JFIF?
> > 
> > JPEG segment used to store comment and more. Look in wikipedia.
> 
> Ah, OK, thank you.
> 
> > https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format. This is not
> > Exif.
> > 
> > And yes, photo file format are puzzle...
> 
> Absolutely!  It's all a bit of a can of worms and I realise that
> Digikam is doing its best to handle it all in a reasonable way.
> 
> [snip]
> 
> > > What would also be really, really useful would be a listing of which
> > > Exif, IPTC and XMP fields correspond to each field in the "Edit
> > > Metadata" section as this would clear up any ambiguity between
> > > "Comment", "Caption", "Description" and similar.  Either this or give
> > > the actual field names in the "Edit Metadata", e.g. you could put
> > 
> > In fact no. This tool try to simplify the complixity of reduntant metadat
> > tags in files, something like the file properties in Photoshop.
> 
> OK, but it would still be very useful to be able to find this
> information.  I know some are described in detail in the
> Metadata->Advanced tab in Settings but it would be good to know how
> all are handled.  Maybe the section in Settings could be extended?
> 
> Anyway, thank you for your reply, I know this is a rather 'messy' area
> in handling image files so there is no easy answer.

Part of the problem for the XMP part is that Digikam tries to keep some 
compatibility with other programs. That means that some tag contents have to 
be duplicated over different XML tags. Worse, those tags can change without 
warning, as Digikam has no control over what those other programs do.

Depending on what you plan on doing with that information, you may or may not 
have to take into account all the different tags that store keywords. Best 
might be to take an image with typical (or worst-case) tagging and create a 
full dump of the metadata with exiftool or exiv2 (or both). That should show 
you how those tags are handled.

Or open an XMP sidecar file in a text editor, it's just a plain text file 
containing an XML tag structure (it's not XML, as it's missing the required 
headers). Working with the XML files is probably safer than working on image 
files in any case (and faster, as the files are a lot smaller).

Remco