[digikam] [Bug 339961] New: Hierarchical tags lost when sharing images from Digikam to Windows Photo Gallery / Windows Explorer

[Antoine Chauveau]

https://bugs.kde.org/show_bug.cgi?id=339961

            Bug ID: 339961
           Summary: Hierarchical tags lost when sharing images from
                    Digikam to Windows Photo Gallery / Windows Explorer
           Product: digikam
           Version: 4.4.0
          Platform: Ubuntu Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Metadata
          Assignee: [hidden email]
          Reporter: [hidden email]

There is an issue where Windows Photo Gallery / Windows Explorer can't read
hierarchical tags written by Digikam. Interoperability in the other direction
works fine.

Reproducible: Always

Steps to Reproduce:
1. Create a file with hierarchical tags in Windows Photo Gallery
2. Import into Digikam. This works just fine.
3. Execute "Write Metadata to Images" in Digikam.

Actual Results:  
Open the file from Step 3. in Windows Photo Gallery. The tag hierarchy is lost,
only leaf tags remain.
Look in Windows Explorer. The same information loss is visible in tooltips and
details view.

Expected Results:  
Hierarchical tags are still visible in Photo Gallery and Explorer.

Digikam stores only leaf nodes under XMP-dc "Subject", the field that Photo
Gallery and Explorer read in priority. The complete hierarchy is stored in
other fields but that doesn't help these apps.

Digikam also writes leaves-only data to a new field IPTC "Keywords", but I
assume that Photo Gallery doesn't care since XMP data is present too.

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[Antoine Chauveau]

https://bugs.kde.org/show_bug.cgi?id=339961

--- Comment #1 from Antoine Chauveau <[hidden email]> ---
Created attachment 89128
  --> https://bugs.kde.org/attachment.cgi?id=89128&action=edit
Sample image for step 1, photo tagged in Windows Photo Gallery

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[Antoine Chauveau]

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--- Comment #2 from Antoine Chauveau <[hidden email]> ---
Created attachment 89129
  --> https://bugs.kde.org/attachment.cgi?id=89129&action=edit
Sample image for step 3, photo edited in Digikam

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[Gilles Caulier-4]

https://bugs.kde.org/show_bug.cgi?id=339961

Gilles Caulier <[hidden email]> changed:

           What    |Removed                     |Added
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                 CC|                            |[hidden email]

--- Comment #3 from Gilles Caulier <[hidden email]> ---
Where Windows Photo Gallery / Windows Explorer store full tag hierarchies in
XMP ?

Gilles Caulier

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[Antoine Chauveau]

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--- Comment #4 from Antoine Chauveau <[hidden email]> ---
In the Step 1 example file Photo Gallery created these full hierarchies in
XMP-dc "Subject" and  XMP-microsoft "Last Keyword XMP". The app also updates
some other locations if they already exist.

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[Gilles Caulier-4]

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Gilles Caulier <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Hierarchical tags lost when |HUB : Hierarchical tags
                   |sharing images from Digikam |lost when sharing images
                   |to Windows Photo Gallery /  |from Digikam to Windows
                   |Windows Explorer            |Photo Gallery / Windows
                   |                            |Explorer

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Gilles Caulier <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|Metadata                    |Metadata-Hub

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[bugzilla_noreply]

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--- Comment #5 from [hidden email] ---
This entry is illegible for GSoC 2016 project  :

https://community.kde.org/GSoC/2016/Ideas#Project:_digiKam_MetadataHub_improvements

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[hidden email] changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |wishlist
            Summary|HUB : Hierarchical tags     |HUB : Add Windows Photo
                   |lost when sharing images    |Gallery / Windows Explorer
                   |from Digikam to Windows     |Hierarchical tags support
                   |Photo Gallery / Windows     |
                   |Explorer                    |

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Maik Qualmann <[hidden email]> changed:

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                 CC|                            |[hidden email]

--- Comment #6 from Maik Qualmann <[hidden email]> ---
Windows Photo Gallery stores tags path in "Exif.Image.XPKeywords". This field
is with libexiv2 read only. I have checked it, write to "Exif.Image.XPKeywords"
is not possible with libexiv2. DigiKam can do nothing here and it will probably
not change.

http://dev.exiv2.org/boards/3/topics/530

Maik

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--- Comment #7 from Antoine Chauveau <[hidden email]> ---
Thanks for looking into this Maik.

I don't think that the read-only status of "Exif.Image.XPKeywords" matters
here. As I stated in the bug description, the main field that Photo Gallery and
Explorer read is not XPKeywords but XMP-dc "Subject". This is already written
to by Digikam, and the main problem here is that Digikam only writes the node
leaves in this field, and not the full hierarchical view.

Note that Photo Gallery will be end-of-life'd by Microsoft in Jan 2017, but the
bug is still relevant since it also affects Windows 10's Explorer app.

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--- Comment #8 from Maik Qualmann <[hidden email]> ---
Created attachment 102624
  --> https://bugs.kde.org/attachment.cgi?id=102624&action=edit
Xmp.dc.subject.png

Ok, I understand now. With digiKam5 you can craete a new XMP namespace. See
screenshot.
1 disable default XMP.dc.subject
2 add new namespace
3 write XMP.dc.subject and set tags path seperator "/"
4 enable tags path

DigiKam now write a tags path to XMP.dc.subject.

Maik

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #9 from Antoine Chauveau <[hidden email]> ---
Thank you, configuring Digikam like you suggest (and also disabling reading and
writing tags for all other namespaces) allows good interoperability with
Explorer and Photo Gallery.

Note that the example in attachment 102624 wasn't complete, I also had to set
"Special Options" in this dialog to TAG_XMPBAG or nothing got written.

It is rather inconvenient that such advanced configuration is needed for my use
case, but the fault is in the lack of a widely adopted standard for
hierarchical tags and not in Digikam. I understand that Digikam defaults to
writing Xmp.dc.subject according to the MWG's standard
(http://www.metadataworkinggroup.org/specs), and that seems like a reasonable
choice.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
   Version Fixed In|                            |5.4.0
         Resolution|WONTFIX                     |FIXED

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         Resolution|FIXED                       |WONTFIX

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