RGB Channel Mixer

Is there a possibility in Siril to mix the RGB channels, like
Photoshop / Channel Mixer
Fitsworks / Color Functions / Color Corrections?

With my ASI 183 MC camera, the green and blue channel are a bit sensitive above 650nm and therefore it is a good solution to subtract some R (20%) from G channel in the case of nebula (h alpha).
The color saturation of the nebula is significantly better. (from orange to red)

Please have a look here: Siril - RGB composition

This is how we do in Siril.

Thank you for your prompt reply.
I know this Siril function “RGB composition”.
I am looking for a solution for a fast RGB Mixer inside a siril script.

The RGB composition in GUI is a overkill for my small problem.
First I have to split an RGB image into the three channels in order to put them back together again.
I was hoping to avoid that.

There is currently no way to do what you describe in simple operations, you have to split images, multiply them, subtract them and so on.

I’ve never seen the result of what you explain, would you share images to show us how much it improved the result? That could be another interesting way of improving the RGB composition tool.

would you share images to show us how much it improved the result?

The difference is of course relatively small. All methods of color shifting can compensate for this crosstalk between the red and green channels.
The later you tackle this, the more other colors are also attacked.

Siril’s phomotric color calibration does an excellent job of compensating for this crosstalk.

You can best see it in the RAW image.
As an attachment, an example in which only the stacked image was corrected with these two steps,
(a) Background extraction
(b) color calibration (no photometric calibration to show the difference!)

This picture is the original result.fit.

In the picture below, the channels of result.fit were mixed in Fitswork ( in the next step siril Background extraction and color calibration)

After some corrections in Photoshop

Another good use of a command line channels mixer in Siril are dual-channel filters on RGB cameras.

It can be useful to calculate a synthetic 3rd color channel from the dual-channel filter.
Keyword: Steve Cannistra and his Bicolor Narrowband Technique for synthetic green

I like to do something like that with Imagemagick
R/K: HA → R
G: (0.4HA)+(0.6OIII) → 0.2R+0.8G
B: OIII → 0.3B + 0.7G -0.1R

magick Autosave_001-259.tif -depth 32 -color-matrix “1 0 0 , 0.2 0.8 0 , -0.1 0.7 0.3” Autosave_001-259Green.tif

// the same command, but slow

magick Autosave_001-259.tif -write mpr:N2 +delete mpr:N2 -channel r -fx “u.r” mpr:N2 -channel g -fx “0.2u.r+0.8u.g” mpr:N2 -channel b -fx “0.7u.g+0.3u.b-0.1*u.r” Autosave_001-259Green.tif

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Thank you! Basically, compared to what I had in mind, I’ll have to allow for negative values, that’s a good idea! That’s nice!