Thanx for replying Russ
Using PI:
Yes I do extract illuminance and then use LRGB combination.
Regards to how much Ha in M31:
I just looked at images found in Astrobin and there seems to be a lot of detail gained by using Ha.
Also there are a few PI tutorials (M31) that include Ha.
The process for extracting the Ha (using OSC) is a bit tedious and highly inefficient, but there seems to be a usable result.
In summary, I have to debayer, and then use channel extraction and throw away the G & B channels. The R (or Ha) channel is then combined with the R channel extracted from the RGB images.
I am in the process of designing a PI work flow that at this stage, has nearly 100 steps
When tested and I have a result, I will post it if anyone is interested.