Lightroom to DigiKam: reading xmp files

[Remco Viëtor]

On dimanche 7 janvier 2018 13:56:19 CET Gilles Caulier wrote:
> yes, this can be done for reading, with a priority :
> 
> 1/ old naming scheme.
> 2/ new naming scheme (LR)
> 
> ... or vis versa.
> 
> But the problem is not here. Look well my comment #11
> 
> https://bugs.kde.org/show_bug.cgi?id=278935#c11
> 
> Gilles Caulier
> 

Oh, I realise that in the case of multiple existing sidecars with the same 
basenam you have a problem. Solvable in theory (XMP allows combining sidecar 
data for several image files/formats in one sidecar), but complicated to 
implement.

But, why do you have sidecar files in the first place?
In Digikam, as I see it, the main use is as an external place to save metadata 
linked to raw files (which are in principle unwritable safely). If you decide 
that you don't need to use a sidecar for jpeg, tiff, png, the problem would 
basically go away in a large part. So you could decide to have the 
<basename>.xmp scheme refer to raw files only. The more so as any information 
about editing operations is inherently non-portable to other programs anyway.

Basically, the problem seems to be adapting Digikam to play nice with other 
programs. While that's always a good thing, how many users are in that 
position, other than e.g. a one-time import from lightroom to Digikam?

And some other points:
- https://discuss.pixls.us/t/linux-applications-and-their-non-standard-xmp-sidecar-naming-convention/2688 gives rules about the naming of sidecar files, 
but those are specified for /each/ base format, /not/ in a general rule. That 
document deals principally with /embedding/ XMP data in other files, and 
sidecars are mentioned more or less in passing; when you have no other option
(e.g. MP2 files which don't provide for embedding XMP metadata).

I cannot conclude /from that document/ that the scheme "<basename>.XMP" is the 
*official* standard way of naming sidecar files (I don't have access to the ISO 
standard documents).

- LR seems to use sidecars for raw files *only*, not for .jpg, .dng and other 
writable formats.

Both seem to indicate that sidecars are considered a last option when the 
metadata cannot be embedded/added/modified, and in that case "<basename>.XMP" 
works (as most derived formats *can* embed the XML data)

Remco

> 2018-01-07 13:52 GMT+01:00 Remco Viëtor <remco.vietor at wanadoo.fr>:
<...>
> > 
> > Going to a naming scheme of "<basename>.xmp" instead of "<basename>.<orig-
> > ext>.xmp" could break compatibility with Darktable, a raw convertor/editor
> > that's used by several users active here.
> > 
> > But can't you have a system where "<basename>.xmp" is used when there is
> > no
> > eligible sidecar with the other possible name present? (i.e. first check
> > for
> > presence of a sidecar with current naming, if not found try
> > "<basename>.xmp")
> > 
> > Remco