Metadata settings when using XMP sidecar files

[Elle Stone]

I'm trying to set digiKam up so that it always and only writes to an
xmp sidecar file (never to the actual image file). I have all the
image files set to 'read only."

I'm a little confused about some of the settings options. Here's what
I have for the Metadata Settings:

Under Behavior tab:
Write this information: image tags, captions and titles, rating, pick
label, color label (but don't write timestamps or metadata templates -
these are not checked).

Reading and Writing Metadata:
"Read from sidecar files" is checked.
"Write to sidecar files" is checked, and "Write to XMP sidecar only"
is selected. "If possible, write to raw is unchecked, and "update file
timestamp" is unchecked.

I don't know what "Read from sidecar files" means. When digiKam
created the sidecar files, obviously it read from the image file. So
once the sidecar file is created, what is the effect of reading or not
reading from the sidecar file? digiKam is the only application that
will write to the sidecar files.

On the Rotation page, I have "rotate by only setting a flag" checked,
along with "write flag to metadata if possible". Does this mean the
flag is written to the XMP sidecar? Or does it mean that digiKam tries
to write to the image file (but will fail because the image file is
"read only").

Thanks in advance for any assistance!
Elle Stone
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[Jean-François Rabasse]

Hello,

A few comments about :

On Tue, 23 Oct 2012, Elle Stone wrote:

> Reading and Writing Metadata:
> "Read from sidecar files" is checked.
> "Write to sidecar files" is checked, and "Write to XMP sidecar only"
> is selected. "If possible, write to raw is unchecked, and "update file
> timestamp" is unchecked.
>
> I don't know what "Read from sidecar files" means. When digiKam
> created the sidecar files, obviously it read from the image file. So
> once the sidecar file is created, what is the effect of reading or not
> reading from the sidecar file? digiKam is the only application that
> will write to the sidecar files.

Well, « When digiKam created the sidecar files, obviously it read from
the image file », not exactly !
We should consider there are two kinds of meta information :

- technical metadata, i.e. all technical infos left by the camera in the
original images files, date, focal length, shutter speed, and many other
Exif data.

- user supplied metadata. This is what you provide via the GUI, title,
caption, tagslist, rating, etc. And this information is obviously never
available in an original « out of camera » image file.

Digikam stores all metainformation in its database. Technical
information is extracted from images files when scanning for new images.
User supplied information is edited from the GUI.

This works well, but in case of problems (e.g. you happen to loose your
database, disk crash or other), the technical information could be
regenerated from images files Exif sections, but the user supplied
information, title, rating et al. is lost.

Should you want to save metainformation outside of the DK database,
you have the choice : either save it in the image file itself (DK
creates or updates a XMP section), or in a separate sidecar file.

And « Re-read metadata » options, from image files or sidecar files,
is just a way to rebuild (or overwrite) current metainformation in
the DK database from external file saved information.

Regards,

Jean-François
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[Marcel Wiesweg]

> I'm trying to set digiKam up so that it always and only writes to an
> xmp sidecar file (never to the actual image file). I have all the
> image files set to 'read only."
>
> I'm a little confused about some of the settings options. Here's what
> I have for the Metadata Settings:
>
> Under Behavior tab:
> Write this information: image tags, captions and titles, rating, pick
> label, color label (but don't write timestamps or metadata templates -
> these are not checked).
>
> Reading and Writing Metadata:
> "Read from sidecar files" is checked.
> "Write to sidecar files" is checked, and "Write to XMP sidecar only"
> is selected. "If possible, write to raw is unchecked, and "update file
> timestamp" is unchecked.
>
> I don't know what "Read from sidecar files" means.

If unchecked, digikam will only read from the file and ignore any sidecar.
(it's not the most needed and necessary option as you see)

> When digiKam
> created the sidecar files, obviously it read from the image file. So
> once the sidecar file is created, what is the effect of reading or not
> reading from the sidecar file? digiKam is the only application that
> will write to the sidecar files.

You can have it write to sidecars, but not read from them. Sense? Not much.

>
> On the Rotation page, I have "rotate by only setting a flag" checked,
> along with "write flag to metadata if possible". Does this mean the
> flag is written to the XMP sidecar? Or does it mean that digiKam tries
> to write to the image file (but will fail because the image file is
> "read only").

That depends on your metadata settings. As above, it will only write to the
sidecars.
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[Elle Stone]

On 10/24/12, Marcel Wiesweg <[hidden email]> wrote:
>
>> When digiKam
>> created the sidecar files, obviously it read from the image file. So
>> once the sidecar file is created, what is the effect of reading or not
>> reading from the sidecar file? digiKam is the only application that
>> will write to the sidecar files.
>
> You can have it write to sidecars, but not read from them. Sense? Not much.
>

Is there any plan to change this behavior? Because not reading from
the sidecar files seems to preclude keeping the sidecar files in synch
with the database. Which pretty much makes the sidecar files useless
to me (perhaps useful to someone else, though how/why I can't
imagine).

If this behavior is permanent and won't be changed very soon, is there
some place in the code I can make an easy modification so that my own
copy of digiKam writes to the sidecar file? I've compiled digiKam from
source before.
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[Marcel Wiesweg]

> Is there any plan to change this behavior? Because not reading from
> the sidecar files seems to preclude keeping the sidecar files in synch
> with the database. Which pretty much makes the sidecar files useless
> to me (perhaps useful to someone else, though how/why I can't
> imagine).
>
> If this behavior is permanent and won't be changed very soon, is there
> some place in the code I can make an easy modification so that my own
> copy of digiKam writes to the sidecar file? I've compiled digiKam from
> source before.

You dont really need to change the source, just set the options as you need.
The initial question was why we have an option that you can switch off reading
sidecars. You can do that, but you dont need to.

There are other options with "historic" background like the one which makes
digikam ignore the Exif rotation of a picture. IMO as much needed as an option
to ignore a sidecar file.
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