Thanks to the work by Nikon Hackers, it is possible to get the original unprocessed raw data from selected Nikon cameras. This hack is available for the previous generation of Nikon cameras (sorry, no D810 or D7200) apparently due to a recent hardware change in the new bodies.
There are three known manipulation performed to NEF files which could not be overridden by the user:
- Black level - truncation of negative values (not performed in new bodies such as the D810)
- White Balance Preconditioning
- Hot pixel suppression (usually for speeds below 1/4 sec)
The hack bypasses those processes, storing basically a raw dump from the sensor
There are two versions of this:
1) Temporary change which stores a hack in the camera RAM and it is reset when the camera turns off, and
2) Hacked firmware
I have tried option 1, since I thought it would be safer
I took a couple of samples with and without the hack with a Nikon D800:
a) Dark frame, 30 Sec @ ISO 100
b) Intentional blow out of all channels
c) Regular exposure at 1/5 sec @ ISO 100
Here are the resulting histograms using rawdigger
Dark Frame
These two images are with the hack, note how the lower values are centered around 600 and negative (relative) values are present. The difference between the images is just the level of detail
The following set of images show the effect of the Hot pixel suppression (HPS) algorithm. Without the hack, the HPS has suppressed any value above 349, while in the hacked file there are values up to maximum (16383)
Blown channels:
In regular NEF files, the channels max out at different values, due to the WB Preconditioning, that multiplies the R and B channels. In the case of the hacked file, all channels max out at exactly the same level
WB Preconditioning
The following set shows first the effect of the WB Preconditioning, with empty slots at regular intervals in the R and B channels while in the hacked file this does not happen
Is it worth to use this? For general photography maybe not (further testing is necessary) but for scientific purposes or astrophotography it is definitely useful. The guys at Nikon Hacker have some impressive samples of astrophotograpies using these hacks.