How are hierarchycal tags/keywords stored in picture files?

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How are hierarchycal tags/keywords stored in picture files?

woenx
Hello,

My previous photo manager didn't have support for hierarchical tags or
keywords (I don't know what's the proper term), and it's awesome that
digikam supports them since they are incredibly useful.

One question though. Are these hierarchies stored in the picture files at
all? On one hand, I imported some files that already had some hierarchical
keywords (I guess they were edited with adobe lightroom by someone else), so
that makes me think the keywords and their relationship are indeed embedded
in each picture, but on the other hand, after creating some keyword
hierarchies on digikam, I can see the changes are immediate and they require
no network usage (my files are stored in a NAS), whereas adding a new tag
takes a few seconds for each picture. That makes me think nothing is being
saved in the pictures themselves, only in digikam's database.

So... are digikam hierarchical keywords stored in each picture? If I import
them in another photo manager (let's say lightroom or shotwell), will they
appear as a hierarchy or just as a list of keywords on the same level?

Thanks!



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Re: How are hierarchycal tags/keywords stored in picture files?

Noeck
Hi,

as far as I can tell, it's like this:

Assume you have a hierarchy:

  [x] tag1
   |-- [x] tag2
   '-- [ ] tag3
        '-- [x] tag4
  [ ] tag5


You will see in your file's metadata:

tag1
tag1/tag2
tag1/tag3/tag4

So the hierarchy is stored in the files, but the main question is: Will
your other software be able to interpret it accordingly. In most cases,
probably not.

Best,
Joram

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Re: How are hierarchycal tags/keywords stored in picture files?

woenx
I ran some tests. I created the keywords with the hierarchy you suggested
using four different pictures using four different editors: Digikam,
Lightroom, Picasa and ACDsee photo studio.

The hierarchy and the keywords are preserved between Digikam and Lightroom.
These two programs are fully compatible with each other.

Picasa and ACDsee do not support hierarchies, so the keywords from the two
previous programs are listed in a plain list. Keywords from these two
programs can be read in digikam and lightroom, but they'll place them using
a previous keyword hierarchy if it exists.

When creating conflicting hierarchies in digikam and lightroom, both
programs will try to integrate them, so both are preserved (therefore no
data is lost, but it's probably going to be a keyword mess if you use
different hierarchies for each picture...).

So, answering my own question, keywords and keyword hierarchies in digikam
are stored in each picture file and seem to be compatible with other
photography managing software.

PS: keywords in PNG files do not seem to be compatible with Picasa and
ACDsee, but were not a problem for digikam and Lightroom.



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