If I understand correctly: you just wish to extract exif data into some external file, which can be later reused (for examining, writing back to image, etc.)?
If so, then I suggest you use MIE file:

exiftool -o exif.mie -exif:all --makernotes photo.jpg

-this will create exif.mie file, which will contain (only) all exif info from photo.jpg file. Think of mie file as being jpg (or any image file) without containing any image. So, you can read/edit mie using exiftool and even write it back into another image file.

Greetings,
Bogdan

Thanks Bogdan.

The YCbCrPositioning tag is considered "unsafe" to copy because it may affect the way the image is rendered. These "unsafe" tags are listed in the tag name documentation, and must be specified explicitly if you want them copied.

YCbCrPositioning is unique in that as well as being "unsafe", it is also a required tag according to the EXIF specification. Currently ExifTool sets this to "Centered" by default if not specified. This is why you get a different value for this tag.

Perhaps in a future release I will come up with a better way to handle this.

- Phil