M31 Andromeda

Split into channels. Then register the R channel with Ha so that the sizes and positions of the stars match. Next, do pixel math. Load these files and use formulas: either median Red + (Halpha - med(Halpha)) * 1.5, or continuum $T + (H_Starless - (R * 0.1)) * 2. Sometimes you can also blend it into the L channel. If using continuum, it's better to remove stars from Ha before the math. You'll figure it out.