Can anyone explain this change in Thumbnail Offset?

[Gary]

I took a copy of pristine JPG from a Canon camera and ran the following type of command that (I understand) should normally strip out data that one might typically add after ingestion. This was to check that the script would not affect a file that had not been altered after ingestion. (Now I should explain that I may not have gotten this command correct, since it is a melding of what I've read on the forum. If it's flawed, please let me know what needs to be done.)

exiftool -ext JPG -xmp:all= -iptc:all= -gps:all= -artist= -copyright= -exif:ownername= -makernotes:ownername="unknown" -overwrite_original -r <directory>

Then I dumped the metadata of the original and the one that had been through stripping using the following type of command.

exiftool <filename> -a -G1 -w txt

Nothing unusual so far that I know of...

Now I compared the before and after using:

FC IMG_0036_Master_Before_Stripping.txt IMG_0036_Master_After_Stripping.txt > Differences.txt

And got the following:

Code Select Expand

Comparing files IMG_0036_Master_Before_Stripping.txt and IMG_0036_MASTER_AFTER_STRIPPING.TXT
***** IMG_0036_Master_Before_Stripping.txt
[System]        File Size                       : 4.6 MB
[System]        File Modification Date/Time     : 2006:07:03 02:11:16-06:00
[System]        File Access Date/Time           : 2015:11:23 16:52:46-07:00
[System]        File Creation Date/Time         : 2015:11:23 16:42:18-07:00
***** IMG_0036_MASTER_AFTER_STRIPPING.TXT
[System]        File Size                       : 4.6 MB
[System]        File Modification Date/Time     : 2015:11:23 16:53:38-07:00
[System]        File Access Date/Time           : 2015:11:23 16:53:38-07:00
[System]        File Creation Date/Time         : 2015:11:23 16:42:18-07:00
*****

***** IMG_0036_Master_Before_Stripping.txt
[IFD1]          Resolution Unit                 : inches
[IFD1]          Thumbnail Offset                : 5120
[IFD1]          Thumbnail Length                : 8261
***** IMG_0036_MASTER_AFTER_STRIPPING.TXT
[IFD1]          Resolution Unit                 : inches
[IFD1]          Thumbnail Offset                : 4858
[IFD1]          Thumbnail Length                : 8261
*****

There ought to be no differences except for system times, but the Thumbnail offset has changed and I don't know why it should.

Can anyone explain this?

[StarGeek]

See FAQ 13.

[Gary]

Thanks, StarGeek. It's good to know that it's just a storage-efficiency thing and not anything to do with file corruption.