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Adding RGB stars to NB images in Photoshop

carastro
11 Oct, 2019 14:09
Does any-one have a good tutorial on how to do this in photoshop.  I have done it a few times in the past just using cut feather and paste, but the blending mode doesn't always seem to work.  It's probably not the authentic way of doing it anyway.

I don't use Pixinsight.

Thanks

Carole
Swanny
11 Oct, 2019 15:43
I place one over the other and move it around until the stars line up.
Godiex
11 Oct, 2019 15:48
This seems like a good one: https://www.youtube.com/watch?v=rcpAZpj0gBs&t=250s You'll need a starless narrowband image, and since you don't have Pix, maybe this can help with Tone Mapping in photoshop: https://www.youtube.com/watch?v=-NajE2n0_6I

I haven't tried it yet, but let me know if it works.
Cheers!
carastro
11 Oct, 2019 17:57
That seems to work better by putting the RGB image on top of the NB image, I was doing it the wrong way round.
Thanks

Carole
carastro
11 Oct, 2019 17:58
Swanny
I place one over the other and move it around until the stars line up.

How do you blend them?

Carole
Edited 11 Oct, 2019 23:12
Swanny
11 Oct, 2019 18:00
If Inwas home in front of my computer I could walk you through it.   Unfortunately I am gone for the weekend .
ruccdu
15 Oct, 2019 00:37
Carole,

I would try putting the rgb on the top and use color blending mode.  IIRC, that adds the color of the upper (rgb) layer to the lower layer.

HTH,
Ron
carastro
15 Oct, 2019 08:12
ruccdu
IIRC, that adds the color of the upper (rgb) layer to the lower layer.
Thanks for this, however where do I find IIRC?  Maybe I don't have it because I am using Photoshop CS3 and need a later version.

Carole
Edited 15 Oct, 2019 15:07
Hondo
15 Oct, 2019 17:31
Carastro
where do I find IIRC?

Hi Carole,

IIRC is modern lingo for "if I remember or recall correctly".  I use the colour mode when adding RGB stars in CS2.

Scott
DaveBoddington
15 Oct, 2019 17:46
Oops mis read the request
Edited 15 Oct, 2019 17:49
lucam_astro
15 Oct, 2019 19:43
Carole,

This is my approach when i want to replace NB stars with RGB:

1) Remove stars from NB with starnet++ and process starless image (stars get minimally process and stay tight and unbloated).
2) Create Ha star image by subtracting original Ha image and Ha starless image (Difference blending mode in PS or PixelMath in PI)
2) Stretch very lightly RGB  image to preserve star color (use Arcsinhstretch and masked stretch in PixInsight)
 3) add Ha stars back in the processed NB image with Color Dodge blending mode.
4) Add RGB color to the stars by placing the RGB image on top of the Ha star image as a Clipping Mask and setting blending mode to Color. If the core of the stars loses color, you can use the Maximum filter on the star RGB image. The color will not bleed outside of the star luminance set by the Ha star image.
carastro
15 Oct, 2019 22:07
Thanks for that, unfortunately I have always avoided Masks as up until now I have always managed to achieve what I wanted in other ways,, can you explain what a clipping mask is.

Carole
carastro
15 Oct, 2019 22:07
Thanks for that, unfortunately I have always avoided Masks as up until now I have always managed to achieve what I wanted in other ways,, can you explain what a clipping mask is.

Carole
carastro
15 Oct, 2019 22:38
Thanks for all your help guys, going to have to read up on clipping masks as up until now I have always avoided masks as I could do most things without.

I do find when I do a starless image that it has a tendency to ruin the nebula at the same time.  I have used Straton and Annies Actions.  So that is something else I avoid too.

Carole
Edited 15 Oct, 2019 22:39
ruccdu
16 Oct, 2019 00:25
Carole,
As mentioned, IIRC is "if I recall correctly".  By using the color blend mode, only the color of the layer will be used.

Ron
lucam_astro
16 Oct, 2019 01:09
Hi Carole,

Sometimes masks are indeed complex. Clipping masks are not and are a very powerful tool in Photoshop. Essentially, it's a way to modify a specific layer without affecting anything underneath it. Say you have your star layer on top  of  your starless image with Linear Dodge blending mode to add the two, now you want to change the color of the star layer without affecting the color of the narrowband nebula with the RGB color. You put the RGB stars on top of the narrowband stars, you select the RGB stars and Create Clipping Mask from the Layer menu. This tells photoshop that the RGB stars only modify the layer below them and not everything underneath. Then you set the blending mode to Color so that only the color property of the RGB star layer is mixed in, and not the luminance.

—Luca
carastro
16 Oct, 2019 08:30
Brilliant Luca that seems to work.  Thank you so much.  As you say the clipping mask in the layers menu is not so complicated.

Carole
weili616
17 Oct, 2019 17:59
Hi, Luca:
    I see one issue with the flow you described. The stars do have RGB colors and won't spill outside of ha stars. But the size of stars are also limited by ha stars, which is very small.  After combination, stars are hardly seen. Is there a good way to grow or increase size of ha stars?

Wei
lucam_astro
17 Oct, 2019 19:30
weili616
Hi, Luca:    I see one issue with the flow you described. The stars do have RGB colors and won't spill outside of ha stars. But the size of stars are also limited by ha stars, which is very small.  After combination, stars are hardly seen. Is there a good way to grow or increase size of ha stars?

Wei

Wei,

You are correct. If you look at my recent Bubble Nebula image you can see exactly the point you are raising.

Versions D and F differ by how much the stars are stretched. I originally kept the stars very tight and barely stretched beyond the initial histogram transformation. I liked the way the image was almost starless but not quite. In discussions with a few other imagers, the balance of stars size with the rest of the composition was raised and I simply went back and stretched  bit more the star luminance layer, extending the footprint of the stars. RGB star color filled the expanded stars nicely. Ultimately, I went back to the small star version because for this image I like it better but the method offers the flexibility. Also, if the RGB stars end up being too small, one can use the maximum filter in the RGB color star layer to extend the color radially.

An alternative workflow is to add the RGB stars (not just their color) with Screen blending mode and balance the narrowband and RGB stars. I find that it is more difficult to keep a natural look with this approach because the RGB background also blends in unless it's masked out, and that's always tough to achieve perfectly especially near bright stars.
Edited 17 Oct, 2019 19:34
 
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