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A good result there. Perhaps a bit too red. The spine has more blue in it.
Ha+ red together and then G and B added leaves you no control.
There are several ways to add Ha. I like the Ha as a lighten blend mode with the green and blue channel deleted leaving only the red.
Lighten blend means only those pixels that are lighter than the layers above will show through.
So your curve at 45 degree straight line is neutral and if you push up the curve you start adding red.
You also make a duplicate layer before you delete the green and blue and this time delete the red and green channels giving blue. Add about 10% of this to the image and it adds the Hbeta colour to the nebula which is bluish. Also in lighten mode for the layer. Now you can control these Ha layers with curves.
There are other methods but I think they largely add up to the same thing in the end. Its which one gives you the most control and the most pleasing result.
Adding Ha to the luminance channel is the tricky bit. Not entirely needed unless you are doing HaRGB. Ha washes out the RGB badly and gives the dreaded salmon colour. A small amount may help the image but in small doses usually.
Perhaps that Arizona site technique for adding Ha as luminance may be helpful there.
Greg.
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