ISO not recognized on CR3 files

[reox]

I tested CR3 from both Canon RP and Canon R7. In both cases, the ISO is always 100.
CR2 images from 350D / 60D / 5Dmkii work fine.
Looks like the problem is actually in the RawHandler Library:

>>> from RawHandler.RawHandler import RawHandler
>>> x = RawHandler("/home/reox/Darktable/2025/2025-12-27/BY4A0730.CR3")
File format not recognized.
>>> x.core_metadata
CoreRawMetadata(black_level_per_channel=[511, 511, 511, 511], white_level=16383, rgb_xyz_matrix=array([[ 1.0424, -0.3138, -0.13  ],
       [-0.4221,  1.1938,  0.2584],
       [-0.0547,  0.1658,  0.6183],
       [ 0.    ,  0.    ,  0.    ]], dtype=float32), raw_pattern=array([[0, 1],
       [3, 2]], dtype=uint8), camera_white_balance=array([ 1910.,  1024.,  1540.,  1024.]), iheight=4660, iwidth=6984)
>>> x.full_metadata
{}

Hence, I see this error message in the log:

RawRefinery/RawRefinery/application/dng_utils.py

Line 155 in 4428865

print("Could not save EXIF")

because the dict is empty.

related to #8 - as there is also no EXIF written for the CR3 (but for the CR2)

-> Actually, the culprit is exifread, as it does not know CR3: ianare/exif-py#133

>>> import exifread
>>> exifread.process_file(open("/home/reox/Darktable/2025/2025-12-27/BY4A0730.CR3", "rb"))
File format not recognized.
{}

[reox]

maybe a solution is to switch from exif-py to exiv2: https://github.com/jim-easterbrook/python-exiv2

I tested it and it can read Exif Data from CR3 without problems.