Who says you have to have hours and hours of data with dozens of sub-frames to get a good image? This image is the result of just 20 minutes total imaging time, just one five-minute frame each of Red, Green, Blue and Luminance. Due to fast moving cumulus clouds I was lucky to get one frame of each color. Other than applying dark and flat frames I had nothing to stack. But I decided to see what could be done in PixInsight with a little help from Photoshop. 

The first discovery was that PixInsight needs at least three sub-frames to stack when applying the darks and flats (maybe there's another method other than the batch processing script?). So, I reverted to DeepSkyStacker to get four TIF files, one for each color, and then imported those to PixInsight.

Naturally after combining and stretching the data I had a very noisy image. I tried many different ways to get the noise out of the background without much success. Everything I tried messed up the stars and/or galaxy. But, finally I noticed something. The DynamicBackgroundExtractor process pulls out a noise-free background model. It occurred to me that I could use  PixelMath with a star mask to replace the noisy background with the DBE extracted background. It worked great! Here are my PixelMath expressions: Red channel:     (NGC3079_background[0]*0.7) + ($T[0]*0.3)
Green channel: ((NGC3079_background[1]*0.7)*0.95) + ($T[1]*0.3)
Blue channel:    (NGC3079_background[2]*0.7) + ($T[2]*0.3)

NGC3079_background is the background model from DynamicBackgroundExtractor.

At first I tried a straight replacement of the background but the result was so smooth it looked unnatural. So, as you can see in the expressions I added 70% of the DBE background with 30% of the noisy background. There was slight green tent in the DBE background so I reduced that a little in the green channel. 

I had to use Photoshop to touch-up the star mask. PixInsight got me 95% of the way there but I couldn't find a way to clean up the last few details in the mask so I used Photoshop for that. 

Comments welcome
Robertson Miller