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Doug I always use the in camera noise reduction (ICNR) as it beats subtracting darks later hands down. The major problem is that the thermal noise is very dependant on the temperature of the sensor so nothing beats taking a dark straight after the light exposure . In fact the mere act of taking a long exposure will heat up your sensor to a higher temperature than with the camera just simply "on". You do not need to do any other correction apart from flats when using ICNR.
Canon does something very cunning at the actual pixel level so there is a minimum of thermal noise and amp glow(none!) with ICNR. Doing a dark correction later with software is correcting for noise at the colour image level that is interpolated from the Bayer data. This will introduce artefacts ie coloured spots these are absent from ICNR images.
I have done exhaustive tests with my 5DH and ICNR is the way to go. I have even done dark correction at the Bayer level with ImagesPlus and ICNR still wins! It doubles data collection time but the results a far better.
Use of RAW to 16 bit TIFF of course! Manipulating JPG's is a waste of time as it is non linear 8 bit kludge full of artefact.
Bert
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