[avandonk]

The in camera noise reduction is better than any method in images plus. For a start there is virtually no colour noise with ICNR just tiny weak 'holes' which disappear if frames are dithered or shift slightly and stacked frames are averaged as median.
I tried using all uncompressed 16bit CFA fit files for bias,flat and dark frames and of course light (image). This gave the best noise reduction even noticeably better than lossless compressed fits. There was still some amp glow. there is none with ICNR. The selection of dark frames was also critical as I had dark frames taken before and after data I tried an average of both, just before and just after. Dark frames after worked best and this also corresponded better to the temperatures. I used the scale factor option (auto box ) in all cases as it worked better.

To get the same result as ICNR unless the temperature of the camera was the same all night dark frames would have to be taken before during and after and then work out which gives the best result. You may as well use ICNR and get it close to perfect.
The other option is to keep the camera temperature constant by enclosing it in a thermostatically controlled peltier cooled 'fridge'.

You can see the amp glow and colour noise in this pic ICNR off
9X7 min ISO 1000 darks bias and flats etc in IP.

This pic 17X6min frames at ISO1600 INCR ON only used flats for correction


Bert