Hi, I am trying to customize image metadata with my own tags (I think I am a victim of ExifTool being too flexible ;) ), and there is one thing doesn't seem to work for me. I defined my own XMP sub-namespace for my tags, and it seems to work just fine, as in I can read/write these tags without issues. Here is an example of namespace definition:
%Image::ExifTool::UserDefined::xmpVM = (
GROUPS => { 0 => 'XMP', 1 => 'XMP-xmpVM', 2 => 'Image' },
NAMESPACE => { 'xmpVM' => 'http://ns.xxx.net/xmpVM/1.0/' },
WRITABLE => 'string',
vmIdNumber => { Writable => 'string' },
vmOriginalRawFilename => { Writable => 'string' },
vmTimeZoneOffset => { Writable => 'string' },
);
Now, vmOriginalRawFilename is populated only for sidecar XMP files (contains file name of the corresponding raw); this tag is not present in JPG/CR2/etc files. Now I wanted to define a composite tag that would return vmOriginalRawFilename if it is present, and FileName otherwise. Here is how I've done it:
'Image::ExifTool::Composite' => {
vmOriginalFileName => {
Desire => {
0 => 'FileName',
1 => 'XMP-xmpVM:vmOriginalRawFilename',
},
ValueConv => '(defined $val[1]) ? $val[1] : $val[0]',
},
}
This composite always returns FileName, i.e. the second (user-defined) tag is never defined, even though it certainly is in my XMP file. If I replace the second tag with something standard (e.g. XMP-xmp:CreateDate), the composite works as expected. But for user-defined namespace tag I was unable to get it to work, no matter what kind of qualifiers I put in front of the tag name. Is it supposed to work in the first place, and if yes, what am I doing wrong?
Thanks!
Your problem is that the Require/Desire tag names are case sensitive. You muse use "XMP-xmpVM:VmOriginalRawFilename".
If you will notice, ExifTool automaticallly capitalized the first letter in your tag name (use -s when extracting to see the exact tag name).
- Phil
Awesome, that worked. I thought I tried all the permutations, but apparently not ;) I never thought that capitalization in -s mattered as in the config I spelled it differently, and from the command line capitalization doesn't seem to matter at all.
Thanks!
Is there any particular reason for having it case-sensitive in this spot, while not in others?
I would prefer case insensitive everywhere, but unfortunately in some places (like in the Require/Desire tags) coding case insensitivity would be very inefficient. Also, case is sensitive everywhere else in the config file, so the rules are simple: The command line is not case sensitive, but the config file is. This is mentioned in the sample config file, but I can see how it would be easy to overlook:
# NOTE: All tag names used in the following tables are case sensitive.
I think the biggest source of confusion here may be that ExifTool automatically generates a tag Name from the capitalized tag ID for XMP tags if not otherwise specified. The algorithm for generating the tag Name is not well documented.
- Phil
Edit: I have just added a note about this to FAQ 11 (https://exiftool.org/faq.html#Q11).
You're right about the source of confusion - I did see the comment about case-sensitivity of this section, and made sure that I double checked (and finally just copy-pasted) tags as I spelled them in the config. But case-sensitivity was for tag names that were implicitly generated, not ids that I defined. To add to the confusion, I could see my tags in XMP file spelled exactly the way I specified it in the config (i.e. no capitalization). I always thought that capitalization was only for display purposes, so ignored it.
I'll probably just specify tag names explicitly:
vmOriginalRawFilename => { Writable => 'string', Name => 'vmOriginalRawFilename' },
Looks a bit redundant, but this way I won't need to worry about capitalization (at least for my own custom tags) - correct? I know that it seems to work, but are there any issues with doing it this way?
You can name them however you want. This will work. It is only an ExifTool convention to capitalize the first letter.
- Phil