Double 'Date/Time Original' value with/without timezone

[squeak]

I'm struggling to understand some intricacies about the Date/Time Original field. Let's use a sample file generated via magick -size 50x50 xc:#0000ff test.jpg as a reference.

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> exiftool -Time:all '/var/home/squeak/Desktop/test.jpg' | sort
File Access Date/Time           : 2025:02:25 22:08:35+01:00
File Inode Change Date/Time     : 2025:02:25 22:08:34+01:00
File Modification Date/Time     : 2025:02:25 22:08:34+01:00

Let's write timezone information:

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> exiftool -DateTimeOriginal="2020:01:01 12:34:56+02:00" -OffsetTimeOriginal="+02:00" -o test_from_terminal.jpg test.jpg
    1 image files created

Now I add a timezone-aware timestamp:

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> exiftool -Time:all '/var/home/squeak/Desktop/test_from_terminal.jpg' | sort
Date/Time Original              : 2020:01:01 12:34:56
Date/Time Original              : 2020:01:01 12:34:56+02:00
File Access Date/Time           : 2025:02:25 22:36:15+01:00
File Inode Change Date/Time     : 2025:02:25 22:36:14+01:00
File Modification Date/Time     : 2025:02:25 22:36:14+01:00
Offset Time Original            : +02:00

Note the duplicated Date/Time Original field, once containing a timezoneless timestamp and once containing a timezone-aware value. I wanted to be able to do something like this from Python so I made this with pyexiftool:

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from exiftool import ExifToolHelper

with ExifToolHelper() as eh:
    eh.set_tags(
        "/var/home/squeak/Desktop/test.jpg",
        {
            "DateTimeOriginal": "2020:01:01 12:34:56+02:00",
            "OffsetTimeOriginal": "+02:00",
        },
        params=[
            "-o",
            "/var/home/squeak/Desktop/test_from_pyexiftool.jpg",
        ],
    )

The resulting file doesn't have the duplicated Date/Time Original field:

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> exiftool -Time:all '/var/home/squeak/Desktop/test_from_pyexiftool.jpg' | sort
Date/Time Original              : 2020:01:01 12:34:56+02:00
File Access Date/Time           : 2025:02:25 22:39:02+01:00
File Inode Change Date/Time     : 2025:02:25 22:39:01+01:00
File Modification Date/Time     : 2025:02:25 22:39:01+01:00
Offset Time Original            : +02:00

A tool I'm working with can ingest files with the duplicate Date/Time Original value correctly, but not files with only the timezone-aware value. So I wanted to find out why pyexiftool isn't doing the same thing. Under the hood, it seems to execute with sane-looking parameters:

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(Pdb)
> /var/home/squeak/.cache/pypoetry/virtualenvs/test-Wt2haxSr-py3.13/lib/python3.13/site-packages/exiftool/helper.py(484)set_tags()
-> return self.execute(*exec_params)
(Pdb) print(exec_params)
['-o', '/var/home/squeak/Desktop/test_from_pyexiftool.jpg', '-DateTimeOriginal=2020:01:01 12:34:56+02:00', '-OffsetTimeOriginal=+02:00', '/var/home/squeak/Desktop/test.jpg']

This was on line https://github.com/sylikc/pyexiftool/blob/master/exiftool/helper.py#L484.

What's the purpose of the double Date/Time Original field? Are the parameters pyexiftool runs exiftool with correct?

[StarGeek]

Use the command in FAQ #3. That will show you tags with duplicated names and the groups they belong too, as well as the actual tag names. Without the -s (-short) option, you will see tag descriptions (see FAQ #2) not tag names.

Take note that the DateTimeOriginal cannot contain a time zone unless it is the XMP group, e.g. XMP:DateTimeOriginal. See FAQ #5, How do I format date and time information for writing.

Example

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C:\>exiftool -P -overwrite_original -all= -subsecDateTimeOriginal="2020:01:01 12:34:56+02:00" y:\!temp\Test4.jpg
    1 image files updated

C:\>exiftool -time:all --system:all y:\!temp\Test4.jpg
Date/Time Original              : 2020:01:01 12:34:56
Offset Time Original            : +02:00
Date/Time Original              : 2020:01:01 12:34:56+02:00

C:\>exiftool -a -g -time:all --system:all y:\!temp\Test4.jpg
---- EXIF ----
Date/Time Original              : 2020:01:01 12:34:56
Offset Time Original            : +02:00
---- Composite ----
Date/Time Original              : 2020:01:01 12:34:56+02:00

C:\>exiftool -a -g -s -time:all --system:all y:\!temp\Test4.jpg
---- EXIF ----
DateTimeOriginal                : 2020:01:01 12:34:56
OffsetTimeOriginal              : +02:00
---- Composite ----
SubSecDateTimeOriginal          : 2020:01:01 12:34:56+02:00
PyExiftool is a third party tool. We cannot provide support for it.

[squeak]

Aha, the timezone info is indeed coming from XMP and not EXIF itself.

No need to talk about pyexiftool, I was just wondering whether invoking exiftool with ['-o', '/var/home/squeak/Desktop/test_from_pyexiftool.jpg', '-DateTimeOriginal=2020:01:01 12:34:56+02:00', '-OffsetTimeOriginal=+02:00', '/var/home/squeak/Desktop/test.jpg'] is correct (that's what the library was doing). The parameters were being fed to exiftool in -stay_open mode with -execute, so perhaps that triggers different tag resolution behavior.

Either way, passing EXIF:DateTimeOriginal and XMP:DateTimeOriginal explicitly solves the problem for me. Thanks for your help!

[Phil Harvey]

There should be no difference in behaviour with and without -stay_open running.

- Phil

[squeak]

Upon closer inspection, there was no XMP:DateTimeOffset present in test_from_terminal.jpg:

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> exiftool -time:all --system:all -a -g ~/Desktop/test_from_terminal.jpg
---- EXIF ----
Date/Time Original              : 2020:01:01 12:34:56
Offset Time Original            : +02:00
---- Composite ----
Date/Time Original              : 2020:01:01 12:34:56+02:00


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> exiftool -time:all --system:all -a -g ~/Desktop/test_from_pyexiftool.jpg
---- EXIF ----
Date/Time Original              : 2020:01:01 12:34:56+02:00
Offset Time Original            : +02:00

I ran the exiftool command that pyexiftool invoked:

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> exiftool -o ~/Desktop/test_from_terminal_2.jpg -DateTimeOriginal='2020:01:01 12:34:56+02:00' -OffsetTimeOriginal='+02:00' ~/Desktop/test.jpg
    1 image files created


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> exiftool -time:all --system:all -a -g ~/Desktop/test_from_terminal_2.jpg
---- EXIF ----
Date/Time Original              : 2020:01:01 12:34:56
Offset Time Original            : +02:00
---- Composite ----
Date/Time Original              : 2020:01:01 12:34:56+02:00

Why could the 'Composite' tag be missing?

[Phil Harvey]

The Composite:SubSecDateTimeOriginal tag is generated only if EXIF:DateTimeOriginal and (EXIF:SubSecTimeOriginal or EXIF:OffsetTimeOriginal) exists.

- Phil