Composite RGB for astrophoto's

[AstroPhoto]

Hi all, 

 

I' reasonably new to imageprocessing, but have gained a little experience in Nebulosity and GIMP for creating and retouching astrophotography images.

 

In astrophotography you typically and up with 4 separate greyscale images; one for each RGB channel and one for luminosity. To create an RGB images in Nebulosity you select the function "composite RGB", assign the right greyscale image to the right channel and press "apply"... and there it is :-)

 

I've been trying this in Affinity, but can not find/comprehend a way to do this.

 

Can anyone point me out were to start and how to accomplish this?

 

Thanks!

 

Johan

 

[yakk]

Hi AstroPhoto

 

That's an interesting question. But I'm afraid it's not as straightforward as it can be in your other software.

 

My guess would be to mix a pure color layer to each R, G and B grey layer, using multiply blend mode. After you'll have to mix those three colored layers (screen blend mode ?) and finally do a last mix with the luminosity layer using a color blend mode.

 

Need to test all this to find the right workflow though.

[AstroPhoto]

Hi Yakk,

 

Would love to get some guidance, once you've tried it.

 

Have been experimenting with the following;

 

- Load the 4 greyscale images (LRGB)

- Change the color mode for each to RGB-16 bit

- Apply a (per color) curve layer to each RGB image, to remove the colors that shouldn't be there (R layer = curve -B and -G, etc) 

- Copy the RGB layers on top of each other, using add mode for the top two laters.

- Copy L layer on top of that with blend mode luminosity

- It sort of looked like expected, but it could be beter

 

Thanks in advance!