I have been using Nebulosity to stack multiple images. Doing just that was not beyond me and lo! the noise level drops impressively. I then needed to get the colours to work. De-mosaicing (disgusting word) is necessary to produce a .fit file from .dng. Using the pre-sets in the dialogue (a 3x3 RGB Matrix) gives me greens when the original image of the Orion Nebula is violet (ish). Some random tinkering produces some random colour variations. I am presuming it's something to do with my (Brand New totally FAB) Pentax K2s's Bayer filtering. There must be a way to customise Nebulosity to handle this but I can't find any information - needless to say, the Neb manual never falls over backwards to help a chap. Anyone else been there and solved it?