The Ultimate Guide for RGB Star Recombination in PixInsight Article by Caleb
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(Fig 1.)
It was this star (Fig 1.), Lambda Centauri that drove me to find the best way to reintegrate stars back into a starless image. Some will give you simple pixel math scripts that will clip and ruin your stars. This article will show you the best way to get your nebulosity perfected with no compromise to your beautiful star colours. This tutorial is suitable if you have multiple datasets (Dual band, broadband, etc, etc) or a single dataset. As long as there are stars, it will work.
Please keep in mind this tutorial is designed for those with some knowledge of PixInsight workflows.
To begin you are going to need some icons, download these three icons created by Bill Blanshan and drag them into your pix workspace.
https://drive.google.com/file/d/1ndJTVWkZgOVyhp03kOgl1ADPfYD48osO/view?usp=sharing
Upon completing this step, your workspace should appear like this (Fig 2.)
The ball is now in your court as you will need to complete (in general order)
Colour Calibration
Dynamic Background Extraction
Deconvolution
Screen Transfer Function unlinked autostretch (applied to image)
Light SCNR removal
Now that you have a cleaned up image and prepare for the next stage of processing, involving more stretching, saturation, star reduction/colours and noise reduction you will want maximum control over what you are changing, this is where this article will come in handy.
(Fig 2.)
Don't fret if your workspace is cluttered, simply close what you don't need, for now you just need your image.
The next step is to duplicate your image, this will later become your RGB star reference image, but you can minimise it for now. Next, run Starnet++ or Star Xterminator, either or. With your starless image now at hand (you can close any star layers/masks produced by the chosen software, they are not needed) we need to once again duplicate and minimise it, this will later become your RGB_Starless reference image.
Now with all your images ready, and your original starless image at hand, process to your hearts content, you may want to check out our "Penultimate Guide to Curves Adjustments" article to maximise your images potential, pulling out colour and detail previously unseen.
Your image, now finalised and ready for recombination is about to be assembled. If you are not happy with your natural star colours or want to saturate more, feel free to use curve adjustments in your RGB star reference image, but most importantly, whatever adjustments are applied to that image, must also be applied to your Starless_RGB image. This is essential to the normalisation process, and if not done, will result in artefacts littering the image.
Your images must be named correctly, your "narrowband" (or curves adjusted in this case) starless image must be named "Starless_NB" and your starless image of your starred image must be "Starless_RGB". There are icons included to simplify this process. The name of your starred image does not matter. Simply drag and drop the last icon over your starred image and watch as your image is perfectly assembled leaving no trace of artifacted stars, preserving every detail you indented.
The process was used with this image (although there are some optical aberrations visible to a keen eye) and every captured detail has been preserved, star colours and brightness external and internal to the nebula are kept within limits.
Clear Skies!
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