Kodak DCS 520c, issues with ISO

[PeterWem]

This camera is when shooting in raw truly ISO less. ISO 200 or ISO 1600 are just the same.
DCS 520c saves raw files in .TIF but darktable can't read those. Replacing .TIF with .DCR is a workaround.

Now the problem. darktable shows major sensor clipping in the raw file at ISO 1600. It should be identical to the raw file at ISO 200.

Raw files and how RawTherapee works without sensor clipping
https://discuss.pixls.us/t/darktable-increases-brightness-in-raw-file-with-no-way-back/27306

OS: Ubuntu 20.04
darktable 3.6.1

[kmilos]

Replacing .TIF with .DCR is a workaround

rawspeed actually thinks this is a Canon-style .CR2 file, DCRs are somewhat different... Perhaps something goes wrong w/ the GrayResponseCurve decoding (i.e. linearization), they are very different for the two files:

[PeterWem]

Canon EOS D2000/Kodak DCS 520c. It is a Canon 1N with a digital back from Kodak https://en.wikipedia.org/wiki/Canon_EOS_D2000

Canon created a software to convert Kodak DCS 520c raw files from Tiff to CR2. https://in.canon/en/support/0900000101
Edit: CR2 converter fails with Kodak DCS 520c but works with EOS D2000C even if they are the same camera. There are some differences in Exif and raw file size. I tried D2000C file from raw.pixls.us and compared.