Best way to add Ha data to LRGB in Pixinsight? - Forums

Topic starter

Nov 13, 2021

I'm new to PixInsight (one day in) and am trying to add Ha data to LRGB. The way I used so far was to use Pixelmath to work out the difference between the Ha data and the Red channel and create a a sudo-starless image like below:

I then used Pixelmath to add that back on top of the red channel in the original RGB image.

I also replaced the luminance channel with the Ha image by separating out channels and using LRGB combine.

Is there a better/more logical way of doing this stuff?; I would ultimately like to do HaOIIILRGB on the Crescent Nebula.

The result so far is:

Crescent Nebula - First attempt at HaRGB

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andrea tasselli

Frequent contributor

Nov 13, 2021

Use the NBRGBCombination script.

Andy Wray

Topic starter

Nov 13, 2021

andrea tasselli:
Use the NBRGBCombination script.

I just tried it and ... it's a great way of doing a quick and dirty combination, but left me with some ugly stars. I'll look at what the script is doing, because I'm sure it will give me some hints.

andrea tasselli

Frequent contributor

Nov 13, 2021

Weird. Never had issues with star shapes. Alternatively you could use LinearFit on the H-alpha image using the R channel as a reference and then add the two together in whatever proportion you find you prefer.

Roberto Marinoni

Nov 14, 2021

If you have an LRGB image and want to add Ha, I would add Ha to RGB by extracting R channel from RGB and then adding Ha data to reinforce the R signal.
If you have also OIII you can do the same by extracting G and B channel from RGB and use OII to reinforce G and B signal.
You can find a good and detailed tutorial here:

https://www.lightvortexastronomy.com/tutorial-combining-lrgb-with-narrowband.html

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Olly Barrett

Nov 15, 2021

I’ve just done my first Ha LRGB image (see below) and combined the Ha to the Red channel using pixelmath inside Pixinsight, the expression used is in this excellent YouTube tutorial, once I’d combined the Ha and Red then the rest was straightforwards…
Hope that helps …

https://youtu.be/CDBejs636hk

Brent Newton

Nov 16, 2021

Roberto Marinoni:
If you have an LRGB image and want to add Ha, I would add Ha to RGB by extracting R channel from RGB and then adding Ha data to reinforce the R signal.
If you have also OIII you can do the same by extracting G and B channel from RGB and use OII to reinforce G and B signal.
You can find a good and detailed tutorial here:

https://www.lightvortexastronomy.com/tutorial-combining-lrgb-with-narrowband.html

I second this, I use this method for all of my NB/BB combinations. However, I have also found to first run StarNet on the NB imagrey before isolating it from any interfering broadband continuum. This avoids any possible issue with stars having double contributions from each channel and makes the result cleaner

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