EXIF tag InteropVersion has wrong type

[AdrienF]

What did you do?

Open an image with Pillow and save it with its exif data.

What did you expect to happen?

The content of the exif field InteropVersion must be the same in both files.

What actually happened?

The type of InteropVersion field value is set to TiffTags.BYTE (1) by Pillow where it should be of type TiffTags.UNDEFINED (7) to conform to standard. Some software might rely on that field to assess the validity of the file.

What are your OS, Python and Pillow versions?

• OS: Ubuntu 20.04
• Python: 3.8.5
• Pillow: 8.2.0 + fix from Incorrect JPEG EXIF write #5490

from PIL import Image
#open a jpeg image
im = Image.open("original.jpg")
# save it with original parameters, but it doesn't change the problem to use default values
im.save("copy.jpg", exif=im.getexif(), quality=95, progressive=True, subsampling="4:4:4")

Original image:

Result image:

Extract of the EXIF data from the original file (using exiftool -D -s original.jpg):

40962 ExifImageWidth                  : 1920
40963 ExifImageHeight                 : 692
    1 InteropIndex                    : R98 - DCF basic file (sRGB)
    2 InteropVersion                  : 0100

In the saved file (using exiftool -D -s copy.jpg):

40962 ExifImageWidth                  : 1920
40963 ExifImageHeight                 : 692
    1 InteropIndex                    : R98 - DCF basic file (sRGB)
    2 InteropVersion                  : 48 49 48 48

[AdrienF]

A workaround, from a user perspective, is to save file to a buffer, then seek and change the type of the IFD tag, and save the file.

[radarhere]

I created #5554 to resolve this, by adding tag data for specific tag groups.

[AdrienF]

I tested the fix and it does the job.
Thanks for the quick dev time!