[Shotwell] EXIF/IPTC as well as XMP

[Lucas Beeler]

Hi Tim,

> It seems the feature only writes to XMP tags.

Shotwell will happily write metadata out to EXIF and IPTC in addition
to XMP, but only under certain conditions. Likewise, there are some
conditions under which Shotwell will not write out any XMP metadata.
Understanding when and why these conditions occur requires
understanding how Shotwell's metadata handling works. In general,
metadata handling in Shotwell works as follows.

Shotwell recognizes three separate metadata domains : EXIF, IPTC, and
XMP. For any given photo file, no, some, or all of these domains may
be present. For example, you can have a photo with only EXIF metadata
-- in this case, only one domain (the EXIF domain) is present.
Likewise, you can have a photo with both EXIF and XMP metadata -- in
this case, two domains (EXIF and XMP) are present.

One key feature of Shotwell's metadata handling is this: Shotwell will
write out metadata only to domains that are already present in the
photo. This is to say, if you have a photo that contains only EXIF and
IPTC metadata and you change that photo's title, only the EXIF and
IPTC title tags are updated. No new XMP domain is created. This is
because the photo had no XMP data in it to begin with, and Shotwell
will only write metadata out to pre-existing domains.

I admit that this behavior is not terribly intuitive, so I've created
a ticket reflecting this here: http://trac.yorba.org/ticket/3044

Regards,
Lucas