Help me learn Narrowband processing

[joelshort]

3 months in to PI and I feel as though I am getting the basics down for RGB processing.  Narrowband is a completely different story.  No matter what guides I follow the image I'm working on comes out looking horrible.  I'm working on Sh2-274 in Ha/OIII/SII.  I'm fairly happy with the individual channel data.  But when I try to combine and start working with the image and color and stretching it just really stinks.   

I would love it if someone could take my data and see what they can do with it, and then let me know how they did it.  Here is a link to download a zip folder containing Ha/OIII/SII master files.  I have applied DBE and MLT noise reduction on each channel. 
https://www.dropbox.com/s/fgxsm010vyd53nl/Sh2-274.zip?dl=0

I hope this isn't asking too much, but I really am at a loss.  I've stared at tutorials and guides and videos to the point my eyes are red!  Thanks in advance for helping me out. 

[Geoff]

This is what I got with:
1. LinearFit, using Ha as the reference image
2. Combine with ChannelCombination SII -> R, Ha ->G, OIII ->B
3. Adjust STF sliders then transfer STF settings to HistogramTransformation.
4. Finally tweak HistogramTransformation to line up the  red, green and blue peaks and raise the black point.


I'm not sure of the cause, but there are lots of dark spots on the greyscale images, which end up as colour splotches on the colour combination.

[msmythers]

Hi

Much like Geoff I used SII as red, Ha as Green and OIII as blue. I used PixelMath to combine to a new RGB image. I then used STF auto using the settings of -5 for shadow clipping, 0.09 for background and a Boost Background Factor of 1.00. This was applied through HistogramTransformation. I then created a structure map to use as a mask for ColorSaturation. I did this with StarAlignment using an extracted L image as the reference. This mask was applied and I then used ColorSaturation to increase the color slightly. I then used the ExponentailTransformation tool for a slight increase in the background. Finally I resampled to 50 percent and saved.

One more thing, you could make a star mask, apply it to the image and use SCNR to remove the green from the stars. This would make them a more pleasing yellow.


Mike

[joelshort]

Thank you Geoff and Mike.

"I'm not sure of the cause, but there are lots of dark spots on the greyscale images, which end up as colour splotches on the colour combination."
Yes, it is the background and star color that are giving me fits.  I now see the dark spots that you are referring to.  What I don't understand is that I did not see these dark spots on the original linear images after DBE with an automatic STF stretch (linear).  Even after I did the noise reduction with MLT I didn't see these spots with the first auto STF.  But now after the noise reduction when I use autostretch STF (still linear) the image comes out much brighter and I can clearly see the spots you are referring to.  I hope that all makes sense.  I don't understand how to correct for those dark spots during the noise reduction process if I can't see them in the first auto STF.