When opening RAF files from my X-T2 in darktable 2.6.2 on Ubuntu 18.04, photos shot at ISO 400 - 640 are underexposed by about one stop, photos taken at ISO 800 or higher are underexposed by more than two stops.
I took a series of photos with ISO values from 200 to 12800 on my Fujifilm X-T2. The exposure was kept the same by adjusting the shutter speed, all other values (aperture, white balance, …) were unchanged.
When looking at the in-camera JPGs, the exposure stays pretty much the same for all ISO values / shutter speeds:
When importing the raw files into darktable, only the ISO values from 200 - 320 match the exposure of the in-camera JPG. From ISO 400 - ISO 640 all photos are about one stop underexposed, photos with ISO 800 or higher are more than two stops underexposed. To demonstrate the problem I exported the RAW files into JPG with the default settings applied by darktable:
I use darktable with files from the X-T2 and did not noticed this. But I changed darktable’s default behavior to not enable the base curve by default.
Did you used any DR settings on the X-T2? if these are used, I can see why you would have such differences between the camera JPG output and darktable default base curve output. You should not expect these two to look similar anyway, the camera does much more to the raw data than what darktable does by default (especially if you use the film simulations).
Since images below ISO 400 show correct brightness, the DR setting is probably the problem.
Another reason might be the ‘RAW exposure compensation’ flag in the Exif data. This flag tells the RAW converter how the exposure of a Fujifilm RAW should be pushed. However, I didn’t experienced a problem within this regard with darktable (I’m also not using the base curve).
Thanks for the replies, this was exactly the problem. When setting DR to 100, the issue disappears.
By the way, I didn’t expect Darktable to match exactly the in-camera JPEGs, but the difference in exposure was astonishing. I also loaded the same RAFs into RawTherapee and there they were all shown with the correct exposure.