Sorry for being unclear. Yes, the raw data in the NEF file is clamped at 588. There are no values below, and no way of recovering the missing values from the data - they are not there. As far as I know hacks to obtain true dark current and to disable star eater are available for D5100 and D7000, but you can reach out to nikon hacker community for more up-to-date info on the subject.
Dear Sir:
Sorry for being unclear. Yes, the raw data in the NEF file is clamped at 588. There are no values below, and no way of recovering the missing values from the data - they are not there. As far as I know hacks to obtain true dark current and to disable star eater are available for D5100 and D7000, but you can reach out to nikon hacker community for more up-to-date info on the subject.