How to add Ha to M31

[blinky]

Hi,

 

I got about 7 hrs of L and an hour each of R,G,B as well as an hour of Ha but for the life of my I cant get it to add the Ha properly to the galaxy!  I get horrible colour casts, also my Ha seems noisy when stretched, tried to do a low stretch and just keep what I want by making the background black but that also does not work! Can anybody assist?  I've attached the XISF files from Pixinsight, would appreciate a little help/advice 🙂

HA.xisf M31_LRGB.xisf

[wimvb]

Here's a very quick try

Set equal weights to R, G and B in RGBWorksspace

Extracted R, G, and B from M31_LRGB

Linear Fit of HA to R

Clone of HA, took away layers 1 - 7 in MLT, only large scale structure left.

Did the same with R (removed layers 1 - 7)

PixelMath: R + (HA - HA_clone)    (this combines the large scale structures of R to the small scale structures of Ha)

Named the new image HaR

Channel combination of HaR with original G and B

In retrospect, I should have masked off M32, M110 and the stars, because they got a blue cast.

Edited September 13, 2021 by wimvb

[blinky]

Brilliant - thanks for doing that and also providing the details of how you did it!  Will go give it a try myself.

 

Cheers

[wimvb]

You could try combining R and Ha in the linear stage. Just linear fit Ha to R.