Keep RGB stars only after LRGB combination

[kirkster501]

Hi all is there a way to do this in PI or Photoshop for that matter?  I always seem to blow out my stars when I do LRGB combination

Only way I can think of is to use Starnet on the L image prior to doing LRGB combination?

Appreciate your thoughts.

[ollypenrice]

You could try running Starnet on the finished LRGB and then pasting the RGB-only on top of the de-starred image and choosing blend mode lighten. You ought to find that only the RGB stars will be visible in the output image because only the stars will be brighter than the base image now. If anything else is being applied from the RGB top layer you could manipulate it in curves so that only the stars did appear.

If you de-star the luminance and apply it in blend mode Luminosity it will make a mess of your stars by illuminating them from the starless lum. On the other hand you could try applying your starless Lum in Blend Mode Lighten over the RGB. I've never tried that.

Yet another way might be to paste the LRGB over the RGB and use Noel's actions, Select Brighter Stars, and expand/feather the selection being careful to keep the selection within the circumference of the stars. You could then erase, wholly or partially, the selected stellar cores of the luminance.

And yet another!! 🤣 I think I'd go for this first. Make a copy of your Lum and de-star it. Paste this on top of your starry Lum in Blend Mode Darken so that the stars disappear, then lower the opacity of that layer till the stars re-appear to some extent. They will be considerably subdued, particularly in their cores. With the right blend of starry and starless Lum you should find they won't blow out your RGB cores.

Olly

[kirkster501]

Typical example of my ongoing Abell 1656 Coma Cluster project (in progress and noisy still).  LRGB blows up the stars.

Thanks Olly I will try that.

[ollypenrice]

Just now, kirkster501 said:

Typical example of my ongoing Abell 1656 Coma Cluster project (in progress and noisy still).  LRGB blows up the stars.

Thanks Olly I will try that.

 

Blimey, I see what you mean. I've never had it as severe as that. How do you stretch the lum?

Just a wild thought, but are you sure that's a Lum filter you have in there? It couldn't be a clear or something that passes lots of UV? Or even a filterless slot in your filterwheel? Unlikely but those stars are bizarre. I never see anything like that with my own 460/TEC140.

Olly

[kirkster501]

Yes it's an Astrodon L filter.

Something else I have found.  HSV repair script pushes that light blue into the bright star core on the RGB giving my stars that blue tint.  I need to go back and re-evaluate.

[kirkster501]

I will check it again though but I am 99.999% sure the filters are in the right places.

[ollypenrice]

1 minute ago, kirkster501 said:

I will check it again though but I am 99.999% sure the filters are in the right places.

It's a quick check. Don't take the wheel off,  just look down the spout.

Olly

[kirkster501]

Just now, ollypenrice said:

It's a quick check. Don't take the wheel off,  just look down the spout.

Olly

Really?  How Olly?

[ollypenrice]

Just now, kirkster501 said:

Really?  How Olly?

Just look down the objective. As you change each filter you'll see the new one roll in. It should be easy to see that your Luminance slot isn't an accidental vacant one. It isn't likely but I'd be inclined to check.

Olly

[kirkster501]

Yeah it did have the L filter in. Good idea Olly.

I am trying the paste the RGB on top of the LRGB in PS but removing the two bright PITA stars first with patch tool and a blur then pasting the RGB on top again.  Will give it a go.  Those two large stars in this image are impossible to control otherwise.

[ollypenrice]

21 minutes ago, kirkster501 said:

Yeah it did have the L filter in. Good idea Olly.

I am trying the paste the RGB on top of the LRGB in PS but removing the two bright PITA stars first with patch tool and a blur then pasting the RGB on top again.  Will give it a go.  Those two large stars in this image are impossible to control otherwise.

If you like you can Dropbox me the linear Lum Tiff and I'll compare it with what I'm getting from a similar setup.

Olly