[gregbradley]

This also opens up the question what point is best in the workflow to do noise reduction?

I have tended to do it late in the workflow but it makes sense to do it earlier so the noise does not get stretched and boosted.

My workflow has traditionally used CCDstack 2 and Photoshop. I have a few plug ins and Carboni actions in Photoshop that are useful but basically its mostly Photoshop basic tools that I use:

CCDStack2 :
1. Callibrate (often trial and error to make sure I get the best calibration). Dark subtract with a bias and flat with a flat with no bias subtracted when I made the master but rather click the bias in the flat menu box in CCDstack 2. It would seem to do the same but it sometimes doesn't and with a tricky scope to flat field I find this works best.
Part of this step is to check each sub and see if its useable. I reject cloud damaged subs (they bloat the final combine) or bad eggy star images. If I have enough data I would reject enlarged star subs with bad FWHM. Sometimes I don't get that luxury of excess data.
2. Register (align).
3. Normalise bright and dim areas.
4. Data reject hot and cold pixels and interpolate the result. I don't use any of the other data reject tools as I have never seen them improve an image but others may see a result.
5. Combine I use Median as it gets rid of satellite trails etc. Perhaps Average gets slightly better results in PI but I don't see any gain in CCDstack 2.
6. I may do some gentle Decon on the luminance at this point or on a colour R G or Blue that has larger stars to get them to be more or less the same size between RGB masters. As Mike has pointed out Decon is a touchy tool so I usually only use it lightly but also have done multi layered decon as per Ken Crawford to get extra sharpness out of galaxy shots. Not usually though.
6. Save as a master file as 32bit floating. I reregister the masters using the luminance as the base image.
7. Do the above for all LRGB or Ha O111 S11 files. Sometimes I save the resulting master as a scaled TIFF. If I do that I always open the histogram and make sure the background is boosted slighty as the auto button in CCDstack 2 tends to clip the black point.
8. Do a colour combine in CCDStack 2 using the LRGB. Sometimes I find I need to normalise the RGB if I get a whacky result (seems like a lottery ticket sometimes). Save the resulting colour image in 16 bit TIFF ready for Photoshop.

Photoshop:

9. Stetch the image using curves and levels. Leave some room to the left of the histogram so no black point clipping occurs.
10. Do whatever processing to tweak the colours etc. Selective high pass filtering to sharpen bright areas, here I would probably do some noise reduction or a little later once colour is to taste and saturation etc is good and after any Ha blend. Ha blends I use the Don Goldman screen technique although I don't use Screen but soft light blend instead. Screen mode is too harsh.

Greg.