More advanced channel combination ideas/workflow (Ha added to L and RGB)

[xonefs]

I have some targets in mind that I think could benefit from this but I'm not sure the best way to approach it. It might be able to be done before bring to compose in ST but not sure the best way to do it.

For example I want to shoot M78 region wideish that will get some of barnard's loop. So it's a reflection nebula in a rich Ha region and I want natural RGB color.

See Sara wager's info and results shooting this with Ha, L, and RGB: https://www.swagastro.com/m78.html

So I would like to try something like that but I'm not sure on the channel combination with Ha and L, and adding Ha to R, and how to achieve that before compose in ST (I can use other programs as well if needed to add them before compose but main processing will be in ST if possible).

NBaccents doesn't apply for this use and it doesn't appear there is a straightforward method with compose for this, since I don't want to use only Ha as luminance but some sort of hybrid of Ha and Luminance as luminance, and possibly Ha and Red as red but this may be less critical.

I guess Ha could be loaded into red channel and added to luminance with compose? Not sure how that would work and if it would achieve what I'm thinking, but it would then be just using Ha for red data and not broadband red.

I have not shot it yet but plan to in a couple days so I'm trying to come up with a strategy of how much Ha and L to shoot each and how much RGB.

[Mike in Rancho]

Serious hours she put into that data!

She doesn't really give her detailed recipe, but does note I think that Ha was used for blending into both L and her R. That can certainly be done in the compose module I would think, saving them as mono files to then be recomposed once you have all your files ready.

I've done this sort of thing with Ha (stripped from a duoband) and combined it with my R (stripped from RGB), but have never had a luminance only file to try the fancier compositing that you are planning.

[xonefs]

I'm still curious about the best way to go about this

I have another project now with LRGB and Ha data (flaming star) I would like to combine

[hixx]

Hi,
you will need to create synthetic R first in Compose:
Create a red channel from (R+Ha):

• Launch Compose
  load R as red
  Load Ha as green.
  Keep the result (
  Save as red channel
  Relaunch the Compose module.

You then load the synthetic red as new R while loading G and B from RGB file
and create a synthetic luminance frame from R+G+B (for your detail)

• import new R, G and B as R, G and B
  Keep the result
  Save as luminance file

You'll end up with a Luminance and R channels that include both Ha and R
clear skies,
jochen

[admin]

Further to Jochen's exellent guidance, you can actually use the NBAccent module as well with some nice results, particularly if the narrowband mostly supportsd larger scale structures as seen in Sara's image.

[xonefs]

Ok thanks. So if I follow that then the Ha component gets added to Lum since it is added to the red channel which is then added. Is there any difference or benefit if it was added separately to L to contribute more or is it the same?

[hixx]

Hi,
Ha added to synth L will boost Ha vs other red spectrum contribution (such as S-II or N-II)
If you like the original R only instead, just use that.
Anyway, I would recommend to try NBA first, please check the User Notes or the Inofficial manual for more guidance
cheers,
jochen

[Mike in Rancho]

There is an interesting post (in an interesting thread) here: https://www.cloudynights.com/topic/7496 ... ry10849588, where Ivo got into the weeds a little bit on explaining how you can weight a Synth L when it has contributions from both L and the color channels. Check around the middle of the post, and he explains out the details of the sample being worked on as well.

The follow-up question, of course, is that while that covers the Synth L, what happens with the (required I believe) "L+Synth L" compositing, and should that be taken into account when setting up the weights for the Synth L. Since (in the case given) the L is the original Ha file.

How the L and Synth L are weighted and blended might be around here somewhere. I'm trying to remember if I have seen it in a thread or maybe documentation or user notes, but will have to go on a hunt.