Here is the text I have posted on the Darktable Forum with images inserted.
I would like to try and find out why the RAW Images from my Nikon D100 are 'blown out' when viewed in Darktable. There is the same problem when using UFRAW. It must be to do with the RawSpeed Library https://github.com/darktable-org/rawspeed.
This is a RAW image (NEF) imported into Darktable, Sharpened, Levels and Red /Blue channels Swapped. Not nice!! No cloud to see and grass under the trees blown out,
These Histograms demonstrate the problem. From left to right we have the NEF Image as seen in Darktable before any corrections, The NEF Image in Nikon Capture NX-D and on the right the file exported by the Nikon Software as a TIFF in Darkroom before any corrections.
Nikon use NEF as the file extension for their RAW format images.
Here is a NEF image,straight out of the camera, with the Levels corrected and converted to TIFF showing the problem. I have selected two areas as an example.
The insets are from the same image converted to TIFF in the Nikon Capture NX-D Software provided free by nikon here https://www.nikonusa.com/en/nikon-products/product/imaging-software/capt... with the levels corrected in Darktable. The extra detail is very clear.
I was alerted to this problem recently by the excellent website LifePixel. I had a tutorial from Dan Wampler who was most insistent that I use the Nikon software first to get the extra detail. I did not believe him, but have found with my own testing that he is correct, and think this information is worth sharing.
On this page https://www.lifepixel.com/photo-tutorials/infrared-photoshop-videos there is a video titled 'Infrared RAW file white balance issues & solutions' which shows the problem with White Balance as well. However I have got my White Balance set up fine in the camera, so have no problem with this. Clearly Adobe cannot get it sorted either!
I am shooting InfraRed using the Super Color IR Filter from LifePixel, but I am sure if you are shooting in RAW on a Canon or Nikon without an IR Conversion the same problem will apply.
I would suggest therefore that anyone shooting RAW will run their images through the Nikon or Canon software first so pull out all the detail.
I use Linux for all my computing needs, but have not been able to get the Nikon Software to run under 'Wine', so have had to install Windows 7 in VirtualBox and then run the Nikon software from there. It does have a batch mode, so it is easy to convert the new images from my camera to TIFF and than back into Darktabe to sort them out.
I am not clever enough to work on the RawSpeed Library to try and improve the importing of NEF Images, but maybe there is someone who can.