Use of Group Numbers

[Archive]

[Originally posted by eixga on 2006-12-07 02:09:11-08]

I tried the following command:

Code:

exiftool -1xmp-dc:Subject=dogs -1iptc:keywords=dogs image.jpg

It claimed that there was no tags by those names. I thought this is the way to use the group number, per http://www.exiftool.org/exiftool_pod.html (Under the Options section, -Tag subsection).

Once I took out the 1 before the tags they worked fine. I guess I don't understand the use of the group numbers. Also, why is IPTC under group 0 and 1? What is the difference between the two?

Thanks.

[Archive]

[Originally posted by exiftool on 2006-12-07 14:42:59-08]

Hi,

You're right.  This should work according to the documentation.  I should
do something about this.

The leading family number is almost never used.  The only reason it is
needed is to distinguish between the rare cases where a group has the
same name but represents a different set of tags in family 0 and 1.  This
only happens in the case where there are multiple IPTC records in a single
file (which only happens when some proprietary information contiaining
IPTC has been written to the file).  In this rare case, the family 0 group
names of both IPTC records are "IPTC", while the family 1 group names
are "IPTC" and "IPTC2".  I hope this makes explains things a bit.

But the leading family number is not used for writing and all IPTC
records are currently updated if multiple records exist.  For this reason,
I hadn't added the code to parse the family number when writing.  But I
will do this to avoid future problems like yours in the future.

Thanks for pointing out this inconsistency.

- Phil