[Digikam-devel] Storage of digiKam Tags path (again)...

[Gilles Caulier]

Hi all,

I would to talk again about digiKam tags path to store in Metadata...

You will certainly remember than you have already talk about this subject
here in the past, especially with Daniel...

I will resume the problem : actually a digiKam path (for ex.
"Travel/City/Paris/Monuments/Notre-Dame") is stored in an IPTC keywords as
well.

This  way can be a problem because :

- IPTC string are size limited (64 ASCII char for Keywords)
- IPTC char encoding is the hell. USing UTF-8 is not possible easily.
-IPTC keywords are used only to store a unique word/phrase, not a path like
digiKam use. With my example,
the digiKAm tags must be decomposed as multiple keywords like this :

* "Travel"
* "City"
* "Paris"
* "Monuments"
* "Notre-Dame"

Each Keywords will be stored in an IPTC Keywords tags (IPTC keywords can be
multiple in metadata).

But digikam need to store somewhere in metadata the complete path to
dupplicate/backup the database content in pictures. Also the
place must support at leasr UTF-8 encoding and do not have a limited size.

Like you know, my old laptop have crashed recently, and i have buy a new
laptop where M$ Vista have been installed...

.. and i have played a little with M$ photo manager program installed by
default with Vista. When i said played, i want mean hacked of course,
and especially to find how this program manage picture metadata.

This program is very similar than digiKam. We can see a Tags mechanism,
Rating, Comments, Date, etc... but it very limited... I can only manage JPEG
file. Others pictures formats are not supported. There is no editor, and the
import interface is very very simplified...

After a lots of of investiguations, I have seen than all metadata are stored
like XMP and never in IPTC/IIM. But it's not all, all informations are
stored in private Exif/Image Tags.

XMP is the ultimate way to store metatada, but i digiKam this way cannot be
used now. Later, when Exiv2 will support XMP, it will be more easy to do
(:=)))... Andreas, please note than XMP is very high priority for me
(:=)))...

Well howx to solve the digiKam Tags storing in metadata actually. Well it's
simple. we can do exactly the same thing than M$ with private Exif.Imagetags.

I will resume what M$ store and where :

Exif Tag 0x4746 ==> Rating : a short value : 1 star == 1, 2 star == 2,
etc...
Exif Tag 0x4749 ==> Rating in percent : 5 star == 100%, 0 star == 0%, etc...
Exif Tag 0x9c9b ==> Picture Title : string encoded in UCS2.
Exif Tag 0x9c9c ==> Picture Comments : string encoded in UCS2.
Exif Tag 0x9c9d ==> Picture Author : string encoded in UCS2.
Exif Tag 0x9c9e ==> Picture Keywords : string encoded in UCS2.
Exif Tag 0x9c9f ==> Picture Subject : string encoded in UCS2.

I propose to drive this Exif tags to be compatible with M$ photo manager and
... to add a new private Exif.Image tag to store all digiKam Tags path of an
image using UTF8 (or UCS2 i cannot see the real advantage). Why not to use
the tag 0x9cff witch is not yet used. Look the ExifTool tag database :

http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/EXIF.html

What do you thing about ?

Andreas, there is no risk to do it ?

Thanks in advance for your comments.

Gilles Caulier
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