[Digikam-users] XMP metadata interoperability

Jean-François Rabasse jean-francois.rabasse at wanadoo.fr
Tue Jul 24 11:48:18 BST 2012


Hello,

I have a problem with the way Digikam seems to handle XMP metadata.
(My Digikam is a 2.2.0)

My problem :

1. I have imported some new images into a DK album. These images have
already a title, stored into the XMP Dublin Core title standard field.
After import (followed by « Reread Metadata From Image »), I can see the
title as expected in the XMP part of the Metadata folder (right part of
the GUI).
But the title doesn't appear on thumbnails, in the folder icons view,
as it should do. Seems that DK ignores it.

2. I've edited the title on some test images, using the DK
« Caption/Tags » right folder.
Say, I've replaced « Original title » text with « Edited title ».
After that I've « Write Metadata to Image ».

An now the strange things :
- On the album icons view, DK shows the correct new title,
   « Edited title ».
- In the Metadata folder, XMP section, DK still shows the original
   Dublin Core « Original title » (even after « Reread Metadata ... »).
- When I use some external programs, e.g. web album builders, that read
   images titles from the XMP.dc data, only original titles are read and
   never titles written by DK.


My investigations :

I have dumped an image XMP section to examine what what actually written
and I can see I have two titles ! One is XML tagged with <dc:Title> and
contains the « Original title » text, the other (written by Digikam) is
tagged <dc:title> and contains the « Edited title » text.
Hu hu...

Well, XMP section is an xml structure and names are expected to be case
sensitive and the Dublin Core Metadata Initiative defines the title
field with an initial uppercase 'T'. Changing case obviously breaks
interoperability with some other applications.

DK handles metadata via the libexiv2, and the exiv2 API is case
sensitive. It seems that DK writes xmp.dc.title, but when importing
images reads xmp.dc.title to obtain the image title for the icons view
but reads xmp.dc.Title to display text in the Metadata folder.
And when the two exist, obviously, inconsistency arises.
(When I view the image with some other viewer, e.g. Gwenview, and display
the Metainformations, I can see the two different titles, as two different
DC properties.)

I really need to have DK cope with other software and I can't see how
I could handle that in a simple way. (Simple way is NOT writing extra
tools to parse XMP sections and rewrite/rename dc:title into dc:Title
and vice versa, according to what I want to do with images and with
which software.)

Any ideas ? Is this a known issue ? Do other users face similar
interchange problems when using Digikam plus other metadata aware
software, readers or writers ? What can be done ?

Thanks in advance,

Regards,
Jean-François


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