IPTC semantically equivalent Exif fields - where do they go?

[carlseibert]

Hi,

I'm having some trouble figuring out where the heck the three Exif versions of IPTC fields are supposed to go. I'm talking about Artist, Copyright, and ImageDescription.

As best I can see, different software and different cameras put these things in different IFDs.

Where are they actually supposed to go?

And what happens if they are in an unexpected place when ExifTool reads the file? After an edit, does ExifTool write them back where it found them, or does it attempt to put them where they belong?

I'm pretty lost here. Any help you can throw my way will be appreciated.

-Carl

[StarGeek]

Where are they actually supposed to go?

Don't try for specific locations, let exiftool figure out the right place to put them
exiftool -Artist=Artist -Copyright=Copyright -ImageDescription=ImageDescription /path/to/files/

Exiftool will write these to the proper locations in the EXIF group by default.

If you feel the need to be specific, just put the general group name, EXIF.  There's no need to deal with the specific locations, especially for tags in the EXIF group.
exiftool -EXIF:Artist=Artist -EXIF:Copyright=Copyright -EXIF:ImageDescription=ImageDescription /path/to/files/

For images, I always use simply EXIF: IPTC: or XMP: unless I'm trying to write to a specific tag that is marked Avoid.  There's rarely any reason to do otherwise.

[carlseibert]

OK. That works. IFD0 is where ExifTool put them. Good enough for me.

I'm still scratching my head over the IFD thing. A quick trip to the Exif standard didn't shed much - any - light. If various software and firmware are writing values in seemingly random IFDs, how come the earth doesn't tip off its axis and spin into chaos? If this thing is explainable in a post, please do. Otherwise, I'll just wait until I'm absolutely forced to spend an evening curled up with the standard. (Which seems pretty opaque, even by the standard of metadata standards.)

Thanks!

[StarGeek]

I gave up on figuring out the details of the EXIF structure a while ago.  Exiftool just works so the results are what's important to me.  XMP is easier to deal with and much more flexible.

The only detail I really know is that IFD1 is related to the thumbnail in jpg images (see this old post).  And that some Sony cameras write the EXIF:ModifyDate to IFD1 instead of IFD0 where it's supposed to go.  The case is one of the rare exceptions when it comes to writing specific EXIF locations.

[carlseibert]

Indeed. Since Exif doesn't really have any cultural or rights significance, I'm mostly of a mind to ignore it. I mean, I use it when I process pictures I've shot, just like anybody else. And I certainly wouldn't delete it off an original image. But I haven't been motivated to learn much about it. By the time in the asset lifecycle anybody asks me about it, it's meaningless. I usually just advise people to delete it and move on ;-)

So I just suggested these people do it the ExifTool way :-)

[Phil Harvey]

The Exif specification indicates in which IFD tags should reside.  The ExifTool EXIF Tags documentation indicates this by the default family 1 Group where the tags are written.  But obviously not everyone reads the specification because they aren't always found in the correct location.

- Phil