Changing timezone on CRW raw files

[aperturemode]

For JPG files, I have been adding timezones with the offset tags (exif:OffsetTimeDigitized, exif:OffsetTime, and -exif:OffsetTimeOriginal) using the shortcut command:

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exiftool '-exif:offsettime*=-05:00' *.JPG

It seems to me that raw files don't used these 'offset' tags either in the CRW or XMP (sidecar) files?

Interesting although I didn't set any time zones on camera, as the raw file itself shows 0 for the timezone Makernotes,

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[MakerNotes:CanonRaw] TimeZoneCode              : 0
[MakerNotes:CanonRaw] TimeZoneInfo              : 0

timezone still showed up in my XMP sidecar files (perhaps added by Lightroom?):

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[XMP:XMP-exif]  DateTimeOriginal                : 2007:07:23 17:19:42-05:00
[XMP:XMP-xmp]   CreateDate                      : 2007:07:23 17:19:42-05:00
[XMP:XMP-xmp]   ModifyDate                      : 2007:07:23 17:19:42-05:00
However, the timezones are wrong so I would like to correct them. How and in which tag would I do that?

[StarGeek]

XMP sidecar files can only hold XMP data, while the TimeZoneOffset* tags are EXIF data.

XMP time stamps don't use a separate tag to hold the time zone.  It is included in the tag, as shown in your output.

If you know the difference needed to correct the time zone, you can shift the time.  For example, if the time zone was set to -08:00 West Coast US, but the pictures were taken on the East Coast -05:00, you would have to add three hours.
exiftool -DateTimeOriginal+=+03:00 /path/to/files/
or if it was the reverse, -05:00 time zone but needed to be -08:00
exiftool -DateTimeOriginal+=-03:00 /path/to/files/

This does require exiftool ver 12.49+

Otherwise you could either rewrite the whole date.  Taking the value from your example output
exiftool -DateTimeOriginal="2007:07:23 17:19:42-08:00" /path/to/files/

A more complex command would be to use the -TagsFromFile option and a regular expression
exiftool -TagsFromFile @ "-DateTimeOriginal<${DateTimeOriginal;s/-05:00/-08:00/}" /path/to/files/

Personally, I'd recommend the shifting option.

Also, you can use the AllDates shortcut to modify the three most commonly used time stamps at once
exiftool -AllDates+=+03:00 /path/to/files/

You would have to add any other date/time tags to the command separately.  Use this command to see all the date/time tags in the file
exiftool -time:all -G1 -a -s /path/to/files/

You can ignore the MakerNotes tags if you want, as there are almost no programs that read that data.  I'm not sure what values those Canon time zone tags hold, so you'd have to experiment with that.

[aperturemode]

Thanks for the great explanation and various options to correct the dates.

I think in this instance, I may try the -TagsFromFile option and a regular expression as it seems the actual local time is correct  but the timezone is off. Is it possible to use the -alldates with this approach or better to change each date tag individually, per your example?

[Phil Harvey]

Is it possible to use the -alldates with this approach or better to change each date tag individually, per your example?

The string substitution won't when using a ShortCut tag as the source, so you need separate arguments for each tag you want to change.

- Phil

[StarGeek]

Ah, the -api Filter option works

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C:\>exiftool -G1 -a -s -alldates y:\!temp\Test4.jpg
[XMP-exif]      DateTimeOriginal                : 2023:11:20 12:00:00-05:00
[XMP-xmp]       CreateDate                      : 2023:11:20 12:00:00-05:00
[XMP-xmp]       ModifyDate                      : 2023:11:20 12:00:00-05:00

C:\>exiftool -P -overwrite_original -api "Filter=s/-05:00/-08:00/" -TagsFromFile @ -XMP:AllDates y:\!temp\Test4.jpg
    1 image files updated

C:\>exiftool -G1 -a -s -alldates y:\!temp\Test4.jpg
[XMP-exif]      DateTimeOriginal                : 2023:11:20 12:00:00-08:00
[XMP-xmp]       CreateDate                      : 2023:11:20 12:00:00-08:00
[XMP-xmp]       ModifyDate                      : 2023:11:20 12:00:00-08:00

[Phil Harvey]

Smart!

[aperturemode]

Neat solution. Thanks to you both!