Usage of Exif "UserComment"?

[obetz]

Hi,

is there any guidance how to use Exif 0x9286 User Comment?

The MWG guidance mentions a phrase "user comment" in one place but according to the following paragraph(s) it seems that they meant 0x010e ImageDescription.

Am I right that the exiftool's MWG composite tags don't deal with 0x9286 User Comment?

Oliver

[Phil Harvey]

Hi Oliver,

Interesting.  I didn't notice that the MWG "Description" field uses the EXIF ImageDescription tag, but they say it is also known as "user comment".  They provide no guidance for how to use UserComment.

- Phil

[obetz]

Hi Phil,

sorry for chosing the wrong forum initially.

IMO it's pretty bad that mwg_guidance.pdf mentions a "user comment" field without telling from which universe this name is.

The Exif tag "UserComment" is mentioned repeatedly, but under 5.2 "Description" they only list 0x010e ImageDescription as a counterpart to "Description".

According to JEITA CP-3451, UserComment is rather special thing with a hairy character encoding hack in the first 8 bytes (shudder, didn't know this till now). It might be intended to hold an less restricted copy of ImageDescription: "A tag for Exif users to write keywords or comments on the image besides those in ImageDescription, and without the character code limitations of the ImageDescription tag."

IMNSHO, Exif is not a good place to hold user generated text and therefore the relevant fields simply should left empty, but MWG probably doesn't share my opinion.

Oliver

[Phil Harvey]

Hi Oliver,

sorry for chosing the wrong forum initially.

No worries.

The Exif tag "UserComment" is mentioned repeatedly, but under 5.2 "Description" they only list 0x010e ImageDescription as a counterpart to "Description".

Yes.  They talk about the character encoding for UserComment, but not what it is used for.

According to JEITA CP-3451, UserComment is rather special thing with a hairy character encoding hack in the first 8 bytes (shudder, didn't know this till now).

It isn't that hairy.  The main problem is that it doesn't support modern character sets like UTF-8, and the byte ordering for multi-byte characters is not specified.

- Phil

[obetz]

Thanks for the information. I didn't know that UCS-2 leaves the byte order undefined.

Can you just confirm that ExifTool does not write to 0x9286 User Comment by any built-in MWG translation?

I don't find such a translation in the current .args files, but software I'm using populates the "User Comment" field which I consider unexpected.

Before reporting this, I just want to be sure that this is not an ExifTool decision.

Oliver

[Phil Harvey]

Can you just confirm that ExifTool does not write to 0x9286 User Comment by any built-in MWG translation?

The only difference when the MWG module is enabled is that UTF-8 is assumed if the UserComment coding is ASCII.

- Phil

[filmaj]

It isn't that hairy.  The main problem is that it doesn't support modern character sets like UTF-8, and the byte ordering for multi-byte characters is not specified.

- Phil

Hi, long-time listener, first-time caller here. Love the fantastic tool. Big fan, thanks for all your work.
Came across this comment and was wondering what your thoughts are about using the first 8 bytes to specify whatever character encodings we could wish for? I'm sort of doing that now in one of my projects...

[Phil Harvey]

You could do that if you want, but only your software would be able to read these encodings.  It would be possible to get ExifTool to read/write this by overriding the UserComment definition with a user-defined tag.

- Phil