Thank you Stratos for sharing your data with us 😉 I have had a go myself since I am actually working to improve HaRGB and LHaRGB composites for a future APP release.
The workflow to do star color calibration on a HaRGB (or a LHaRGB) is not recommended, in fact it is physically a wrong step. You need to do star color calibration on broadband data. If you add narrowband data in the mix and then try to perform star color calibration on a broadband+narrowband composite, it would be mere coincidence if the colors look good...
Star color calibration needs broadband data to make sense of the star color physics. Adding narrowband data in there will cause the R/G B/G ratio's of the stars in your data to be polluted by the narrowband emissions. Those narroband emissions don't follow the physics at all that we use for star color calibration.
So how to do this properly then?
1) create a RGB (or LRGB compositie), in this case I used formula RGB 2 in the RGB Combine tool
2) perform Remove Light Pollution and Background Calibration on the RGB composite ( ! if you perform Remove Light Pollution, you automatically perform Background Calibration, there is no need to do it again after Remove Light Pollution)
3) Perform Star Color Calibration on this RGB composite that is corrected for light pollution and is background calibrated:
4) We know open the RGB Combine tool and will add the H-alpha layer. Now, this next 2 steps are essential to preserve the RGB Star Color Calibrated colors in your composite:
set normalize to none in the RGB Combine tool.
Load the RGB star color calibrated result into the tool with the RGB 1 formula
These 2 steps will preserve the colors of the star color calibration 🙂 !
5) Add the H-alpha layer in the RGB Combine tool.
6) To preserve the colors and luminance of your star color calibrated result, set the luminance for the composite so that it is preserved. Normally you want Red to contribute for roughly 20%, Green for 70% and Blue for 10%.
7) And slightly add H-alpha to red, I added it for 23% to Red as can be seen in the below screenshot. Now to maintain the star colors, you need to gently adjust the multipliers for the R,G,B channels as can be seen as well. Red 1,15, Green 1,17, Blue 1,20. These factors do depend on the data, you need to do this carefully. Try to get the same colors as the star color calibrated result off course 😉
I am working to make this more automatic and easier for the user off course, but this is a proper workflow in which you can get good star colors with narrowband included to enhance the active regions in this case of M51 😉
This show the star color calibration result next to the final HaRGB composite: we see that star colors are still good and we also see much more enhanced active regions in M51 from the H-alpha data, top is the RGB composite after star color calibration, below is the finals HaRGB composite with the same star colors 🙂 :
Let me know if this is clear and/or if you have any questions about this workflow 😉
Crop of the field of view of the final HaRGB:
Cheers,
Mabula
This post was modified 3 years ago by Mabula-Admin
Owkee, well, I'm learning something as well there. 😉 I was assuming that, since there is broadband data, it would still work. But makes sense indeed, that's why I needed to fiddle around with the slopes apparently.
First of all I must thank you for this great explained workflow and saw us where was our mistake ...
This is great because we know now to process narrowband and broadband data ... The last years color cameras with narrowband and broadband filters are so popular and seems like the came to stay ...
This will be great tutorial for all people that use this kind of equipment...
I will try it this tutorial and I let you know how went ...
ps you can upload your version in server that can I take it to compare with mine ?
