EXIF pointer tags cause other tag changes to be reset?

[FRbrt]

Hello,

I'm completely new to Python / Pillow, sorry if my question isn't appropriate.
I've observed a behaviour, and I'm not sure if is that a bug, or I'm doing something wrong. Most probably I'm doing something wrong :-). I'm just very curious to find out an answer / explanation.

The situation is:

• I have a photo with EXIF data: dateTimeOriginal, GPS Info, etc.
• using the Image module I've retrieved the exif and changed the dateTimeOriginal tag

with Image.open(imageFilePath) as image:
        imgExif = image.getexif()

        imgExif[0x0132] = '2022:10:05 17:00:30'   # DateTime
        imgExif[0x9003] = '2022:10:05 17:00:30'   # DateTimeOriginal
        imgExif[0x9004] = '2022:10:05 17:00:30'   # DateTimeDigitized
        image.save(outputImagePath, exif=imgExif.tobytes())

• after saving the file and checking the EXIF using an image viewer I see the original values for the fields above, and not the ones set by me

I've looked a bit into the tobytes() function in the Image.py file. I've noticed that, when any of these (0x8825 (decimal: 34853) = GPS Tag pointer, 0x8769 (decimal: 34665) = Exif Tag pointer, 0x8225) tags exists, then the EXIF is read again from the image file and added to ifd return value (ifd is TiffImagePlugin.ImageFileDirectory_v2). Hence, the ifd dictionary will contain an entry like:

    ifd[34853] = { 0x9003 : '2022:09:19 15:32:27', etc. } # the original value from the image file

I suppose, when it is converted to bytes, it overrides the values set previously.

Please let me know if am I doing something wrong, is this intended?

Have a great day,
Robert

[radarhere]

I feel like you're halfway to figuring out the solution from the code.

In terms of the specification, the problem is that while DateTime is a top-level tag, DateTimeOriginal and DateTimeDigitized are not. See https://www.awaresystems.be/imaging/tiff/tifftags/exififd.html, or look at the Group column of https://exiftool.org/TagNames/EXIF.html.

It's not that your values are being overwritten as such. It's that you are setting them in the wrong place.

The following code should save those values correctly.

from PIL import Image
with Image.open(imageFilePath) as image:
    imgExif = image.getexif()

    imgExif[0x0132] = '2022:10:05 17:00:30'   # DateTime

    exif_ifd = imgExif.get_ifd(0x8769)
    exif_ifd[0x9003] = '2022:10:05 17:00:30'   # DateTimeOriginal
    exif_ifd[0x9004] = '2022:10:05 17:00:30'   # DateTimeDigitized
    imgExif[0x8769] = exif_ifd
    
    image.save(outputImagePath, exif=imgExif.tobytes())

[FRbrt]

Works perfectly!!! Thank you very much for your quick answer!