How to uniquely identify tag ID

[mattburns]

Is there a way to format the output so that I can generate a tag ID that is globally unique? The Tag ID is only unique if you know the folder/group it's in.

For example, if I use :

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exiftool -j -U -G -H -a image

Then I get things like:

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  ...
  "EXIF:Make": {
    "id": "0x010f",
    "val": "NIKON"
  },
  ...
  "EXIF:GPSTimeStamp": {
    "id": "0x0007",
    "val": "00:00:00"
  },
  ...


In the example above, 0x0007 is only useful if you know I'm talking about the GPS tags. I can use the output above to get the group name and tag name, but I can't rely on that to be consistent as unknown tags are identified. For example:

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  "MakerNotes:Nikon_UnknownInfo_0x0003": {
    "id": "0x0003",
    "val": 0
  },


This may change in newer versions of ExifTool.

Ideally, I'd like a way to output the "fullID" or "fullPath" of the tag which effectively includes the address, or some kind of namespace. Something like this:

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  "MakerNotes:Nikon_UnknownInfo_0x0003": {
    "fullID": "0x8769:0x927c:0x002c:0x0003",
    "fullPath": "ExifOffset:MakerNoteNikon2:UnknownInfo:0x0003",
    "id": "0x0003",
    "val": 0
  },


Any ideas for how I could achieve anything like that?

[Phil Harvey]

A tag is uniquely identified in the -X -t output by a combination of the "et:id", "et:table" and "et:index" properties.

The -t feature doesn't yet work with the JSON output.

- Phil

Edit:  I'll add this feature to the -j and -php outputs for ExifTool 10.41

[mattburns]

Thanks Phil,

That's very helpful.

However, if I have the output:

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<Nikon:Nikon_UnknownInfo_0x0003 et:id='0x0003' et:table='Nikon::UnknownInfo'>0</Nikon:Nikon_UnknownInfo_0x0003>


Then I can concatenate et:table and et:id to make an ID, but wouldn't that be prone to changing in subsequent versions of ExifTool? eg:

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  Nikon::UnknownInfo::0x0003


"UnknownInfo" could be renamed later?

[Phil Harvey]

Ouch.  You want something that is consistent across ExifTool versions.  Not possible.  Tags may move into different tables as more information is decoded, which will change all of the coordinates for the tag (id, table and index).

- Phil

[mattburns]

OK, fair enough, thanks Phil. I'll just prefix my IDs with the ExifTool version number, that'll do for now.

Crazy idea: Would it be worth me attempting to write a script to try to do a reverse lookup of tag names to the tag IDs from the "-listx" xml database? Or is that also impossible?

Thanks again for your time

[Phil Harvey]

The design of the -X output is that you can use this information to find the exact tag in the -listx database.

I don't know exactly what you mean by a reverse lookup.  Maybe this is what you meant?

- Phil