Copying DateTimeOriginal to FileModifyDate drops the DST offset

[Exifdude]

I'm trying to update the FileModifyDate using the DateTimeOriginal on this type of JPG.  The two methods I have tried below remove the -01:00 UTC which is in effect due to Daylight Savings Time.  Is there anything that can be done to prevent this from happening?  If DTS is not in effect the value copies over fine.  With that being said a command that somehow arbitrarily adds an hour to the FileModifyDate wouldn't work in my case as this needs to be applied to files taken during and outside of DTS.

C:\Users\XYZ>exiftool -a -G1 -s -time:all E:\IMG_0001.JPG
[System]        FileModifyDate                  : 2019:07:08 16:45:52-04:00   <=Accurate hour due to DTS
[System]        FileAccessDate                  : 2019:01:08 00:00:00-05:00
[System]        FileCreateDate                  : 2019:01:08 16:07:39-05:00
[IFD0]          ModifyDate                      : 2019:07:08 15:45:50
[ExifIFD]       DateTimeOriginal                : 2019:07:08 15:45:50            <=DateTimeOriginal was taken in -05:00
[ExifIFD]       CreateDate                      : 2019:07:08 15:45:50

C:\Users\XYZ>exiftool "-filemodifydate<${DateTimeOriginal;s/ DST//}" -v "E:\IMG_0001.JPG"
======== E:\IMG_0001.JPG
Setting new values from E:\IMG_0001.JPG
    1 image files updated

C:\Users\XYZ>exiftool "-filemodifydate<datetimeoriginal" -v "E:\IMG_0001.JPG"
======== E:\IMG_0001.JPG
Setting new values from E:\IMG_0001.JPG
    1 image files updated

C:\Users\XYZ>exiftool -a -G1 -s -time:all E:\IMG_0001.JPG
[System]        FileModifyDate                  : 2019:07:08 15:45:50-04:00 <= Copies over as -05:00 thereby causing a difference of an hour from when the photo was originally taken
[System]        FileAccessDate                  : 2019:07:08 01:00:00-04:00
[System]        FileCreateDate                  : 2019:01:08 16:07:39-05:00
[IFD0]          ModifyDate                      : 2019:07:08 15:45:50
[ExifIFD]       DateTimeOriginal                : 2019:07:08 15:45:50
[ExifIFD]       CreateDate                      : 2019:07:08 15:45:50

[StarGeek]

Try the GlobalTimeShift option.  As an example, try
exiftool -globalTimeShift 1 "-filemodifydate<datetimeoriginal" E:\IMG_0001.JPG

Example output:

Code Select Expand

C:\>exiftool -g1 -a -s -FileModifyDate -DateTimeOriginal y:\!temp\Test4.jpg
---- System ----
FileModifyDate                  : 2019:07:08 16:45:52-07:00
---- ExifIFD ----
DateTimeOriginal                : 2019:07:08 15:45:50

C:\>exiftool -P -overwrite_original -globalTimeShift 1 "-filemodifydate<datetimeoriginal" y:\!temp\Test4.jpg
    1 image files updated

C:\>exiftool -g1 -a -s -FileModifyDate -DateTimeOriginal y:\!temp\Test4.jpg
---- System ----
FileModifyDate                  : 2019:07:08 16:45:50-07:00
---- ExifIFD ----
DateTimeOriginal                : 2019:07:08 15:45:50

One thing to remember is that the System timestamps will automatically correct for time zones.  Those dates are controlled by the underlying OS. 

[Phil Harvey]

Note there is a known "feature" (ie. bug) in the way that Windows handles time zones, mentioned in this post.

- Phil