Step 1: Create the naturaly coloured Stars layer.
1) stack R, G and B subs (short exposure f.ex. 20 sec, low gain).
2) Create a RGB composite
3) SinH stretch with a value of 50. Background must stay dark.
3) Remove noise.
4) Save as a TIFF file (stars_rgb.tif)
Step 2: Create the booster from a narrowband stack
1) Select a Narrowband stack full of stars with little nebulosity.
2) Remove noise.
3) SinH stretch to reveal faint stars, keep nebulosity as low as possible.
4) Save as a TIFF file (stars_nb.tif)
Step 3: Blend together
1) In Affinity photo, open stars_rgb.tif
2) Place stars_nb.tif on top.
3) Blend it as ‘Glow’. Set opacity as wanted.
4) Save as a TIFF file (stars.tif)
Step 4: Mix it with the Starless
1) In Siril convert stars.tif to FITS
2) Open PixelMath
3) Import stars.fits, name it STARS
4) Import starless.fits, name it STARLESS
5) Set the following formula in the RGB/K field
(STARS * 0.8) + STARLESS – ((STARS * 0.8) * STARLESS)
6) In the ‘Output’ section, activate the ‘rescale result’ option
7) Press the <Apply> button