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Veil Nebula SHO - processing in PixInsight to use all 3 filters


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Previous incarnations that I have done of the Veil are usually in HOO which is the traditional way of representing a supernova remnant or playing around in SHO and getting garish results.

The nebula is full of sulphur as well as Ha and oxygen III and I was looking for a new way to utilize the red of the S2 along with the Ha (which is also red) and mapping to RGB.

Then last night I was on a live stream where Adam Block happened to demonstrate a well known method (which I had forgotten) on how to do it.

So here is my SHO representation done in PixInsight.


  • William Optics Redcat 51
  • ZWO ASI 183MM Pro
  • Baader 3.5nm Ha filter and 4nm O3,S2 filters
  • 38x 360 seconds O3
  • 91x 360 seconds Ha
  • 43x 360 seconds S2
  • Gain 111 Offset 8

Total 17.2 hours from Bortle 7/8 26th August 2022 to 2nd September 2022





Here is my processing for anybody how might be interested


  • First of all working in linear mode use StarXTerminator to remove the stars from each of the monochrome images
  • Next do linear noise reduction using whatever method you choose. I use NoiseXTerminator
  • Then using PixelMath use this formula, after renaming the images to S, H and O respectively of course, to create a linear RGB image

// R:

// G:

// B:


  • Do some Dynamic Background Extraction as the colours might not be to your taste
  • Then do a histogram transform to change it to a non linear image.
  • Do whatever else processing to your own taste
  • I then went back to the original mono images, converted then to non linear after combination and extracted the stars.
  • Then simply added them back together with about 80% of the stars.
  • Did a star de-emphasize using the excellent AstroSwell script (Star De-Emphasizer) and here the above image is my results.




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  • TerryMcK changed the title to Veil Nebula SHO - processing in PixInsight to use all 3 filters

Terry, really like what you have done with the Veil and the processing.

I watched that video recording on YouTube  and Adam really explained the concept extremely clearly.

I agree with you that the veil has structural detail contributions from all three channels and a colour mix overlaid to a Ha luminance would not deliver the detail.


The teal/red combo you have presented  is very easy to interpret - wonder - are you temped to try out the modifier mixes that Adam presented in same video ?


Its definately got me thinking in a different way about how to process narrow band and if there is enough good data in each channel then I will try to stop using the Ha channel as a luminance - but the caveat akways here in UK do we get enough time (clear skies) on a single target to use the 3 channel flow......








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Thanks Bryan. I think I will have a go at the modifier mixes too. Adam certain presents really well.

I still like adding Ha into luminance but it does depend upon the subject. Experimentation is the key with PixInsight and it is a very powerful piece of software.

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Same data as before but processed with modifiers to bring out the sulphur. Garish, yes and probably needs taking back a bit (quite a lot actually if I'm honest) but a bit different from the traditional SHO combination.


My pixelmath combo on this was 

// R:

h_starless + s_starless*(hs_modifier+1)


// G:

h_starless*3 + 2*o_starless*ho_modifier


// B:



Really want to change the magenta to a deeper red so might do that in a different iteration.




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yes more tweaks I think - it took me quite a while to tailor the modifier images and also the mutiplier factors in the equations. Are you using linear or stretched images ? 
with stretched the 2*o_starless is way too much and the multiplication factor for ha_starless in the G channel I pushed back to 0.1 ( I don’t think you meant 3x there above it was 0.3 in the video)

I think every image will need custom values to achieve a pleasing colour mix with this technique


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