I started this project in August with a limited amount of Ha data previously posted to AB and decided to get some more and add the SII and OIII. August weather closed me out but September was kinder.
Depicted in ForaxX SHO palette as described in general at,
https://thecoldestnights.com/2020/06/pixinsight-dynamic-narrowband-combinations-with-pixelmath/and I followed SarahMaths Astro YouTube video tutorial with her process of creating "o" and "ho" intermediary images prior to the final ForaxX PixelMath blend,
https://youtu.be/PfdOJZzyLEsfollowed by adjustments to taste with HT and CT trims to arrive at the starless background. In this case I also created a starless synthetic L from the sum of all three narrowband signals then sharpened it with a little deconvolution, stretched it and adding it back in via LRGBCombination.
With ForaxX SHO there is an extra level of effort to interpret the image for what atomic species are where in the field of view. But for this image, blue is pure OIII as "usual" for a SHO rendering. For the reds, it's sulfur unless that signal is weak, in which case hydrogen alpha is blended in dominantly. For the green channel, it's the hydrogen unless that's weak, in which case it's the oxygen. I let the green channel "bend" the tonality of the other colors, but for this image I removed overtly green content via PI's SCNR.
This field is almost the entire ASI6200MM-Pro full frame sensor FOV other than cropping for dithering. The Hocus Focus plugin for N.I.N.A. greatly assisted in sensor tilt tuning.
Star color data are derived from the narrowband stacks and processed separately via PI's PhotometricColorCalibration process in its narrowband mode, but again needed a green removal pass with SCNR afterward to arrive at what you see here.
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