I took 2 raw photos with the lens cap on: One with Long Exposure Noise Reduction turned on, one with LENR turned off.
Checking the tags in the Raw file, BOTH report black levels of [200, 200, 200, 200] (One for each pixel in the Bayer pattern, I suppose). Total range is 4095 counts (12-bit)
I would expect this to be the case for the LENR=OFF photo, but not for the LENR=ON, since it subtracts a dark frame from the (also dark) photo, removing any offsets. Why does the black level stay the same?
EDIT: Exposure was 10 seconds in both cases. I have also added the histogram of both images, which might help. Granted, at 10 seconds, even with LENR turned off a second exposure is taken of ~3 seconds, but I'm not sure what happens there. The biggest question for me now is why the black level remains 200 after frame subtraction.