Hi, here is an example, taken from:
https://www.arciereceleste.it/tutorial- ... axy-ha-eng
1) Subtract from the HAlpha a fraction of the continuous spectrum of the Red image:
e.g. select the HAlpha, click "Merge" from Arithmetic menu, select the Red, copy the Background value of Red (1748 in the example, to subtract it), and find the coefficient which subtracts correctly the (non-saturated) stars, in this case 0.138, using the real time preview. Let's call this image "HaMod".
2) Subtract from HaMod its background value, so that it becomes zero, let's call this "HaMod_ZeroBkg", (menu Arithmetic/Add offset -1280).
3) Create a special RGB with the command Trichromy, where R = HaMod_ZeroBkg, G = 0 and B = 0 (or a small fraction of HaMod_ZeroBkg, it's 0.15 in the example below), let's call this image: TrichromyMod.
4) Now open the real RGB image you created in the past, and use the Merge window again to add the H-Alpha signal (the image TrichromyMod we just created).
Again, use the realtime preview to find a proper coefficient, in the example it's 2.15. Higher values will add more H_Alpha signal to the final image.
