Saving a TIFF with EXIF sub-IFDs: compressed save raises "Error setting from dictionary", uncompressed save drops a GPS IFD #10460

What did you do?

Saved a TIFF with the EXIF from a camera-style JPEG (it has an Exif sub-IFD), using compression:

from PIL import Image, ExifTags

exif = Image.Exif()
exif[ExifTags.Base.Make] = "Canon"
exif.get_ifd(ExifTags.IFD.Exif)[ExifTags.Base.ISOSpeedRatings] = 400
Image.new("RGB", (8, 8)).save("photo.jpg", exif=exif)

with Image.open("photo.jpg") as im:
    im.save("photo.tif", compression="tiff_lzw", exif=im.getexif())

And saved an Image.Exif with a GPS IFD created through get_ifd() as an uncompressed TIFF:

exif = Image.Exif()
exif[ExifTags.Base.Make] = "Canon"
exif.get_ifd(ExifTags.IFD.GPSInfo)[ExifTags.GPS.GPSLatitudeRef] = "N"
for fmt in ("JPEG", "TIFF"):
    Image.new("RGB", (8, 8)).save("out." + fmt.lower(), fmt, exif=exif)
    with Image.open("out." + fmt.lower()) as im:
        print(fmt, im.getexif().get_ifd(ExifTags.IFD.GPSInfo))

What did you expect to happen?

The compressed TIFF saves, and its Exif IFD reads back as {34855: 400}, as it does without compression.

The GPS IFD reads back as {1: 'N'} from the TIFF, as it does from JPEG, PNG and WebP.

What actually happened?

The compressed save fails:

_TIFFVSetField: photo.tif: Bad LONG8 or IFD8 value 18446744073709551615 for "EXIFIFDOffset" tag 34665 in ClassicTIFF. Tag won't be written to file.
RuntimeError: Error setting from dictionary

The same happens with tiff_deflate, tiff_adobe_deflate and jpeg compression. 11.0.0 saved the file (without the Exif IFD), so this started in 11.1.0.

The uncompressed TIFF prints TIFF {} while JPEG prints JPEG {1: 'N'}.

For the libtiff path, _save puts the sub-IFD into ifd as a dict (ifd[key] = info.get_ifd(key)), then gives every tag in TAGS_V2_GROUPS the type LONG8, so encode.c calls PyLong_AsLongLong() on the dict and TIFFSetField fails. That type was added in #8529.

For the second case, _save only loops over the Exif keys, and a sub-IFD created with get_ifd() lives in _ifds until a pointer tag is set. Exif.tobytes() handles this since #8635, but the TIFF writer does not.

What are your OS, Python and Pillow versions?

• OS: Linux
• Python: 3.14
• Pillow: 13.0.0, also main (b2c077b)