Handling big stars in OIII before combining with Ha

[Fordos Moon]

Morning all,

Would be grateful for any techniques in combining an OIII image with a Ha one in order to preserve the tightness of the latter one's stars.

Many thanks

Bob

[PhotoGav]

Hello Bob, what processing software do you use?

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[Fordos Moon]

Hello Bob, what processing software do you use?

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Hi Gav, I am currently stacking in Deep Sky Stacker and then in to Photoshop

[johnrt]

Hi Bob,

Open up in photoshop.....

On your OIII mono image duplicate the background layer. Erode the stars using dust and scratches tool, careful not to include any precious nebula detail. Clean up any left overs with clone / healing brush. Now change layer blending to difference. You should just see the stars. Use colour range select to select the stars, expand the selection a couple of pixels and then feather a couple. Click on background layer and go to new layer via copy selection. Delete or hide the layer you used dust and scratches on and you now have your background layer with a star layer on top. Run a minumum filter on the stars to reuce them in size to taste.

Hope that helps

[pete_l]

In photoshop, can you use the Hα layer as a luminosity mask

[Fordos Moon]

Hi Bob,

Open up in photoshop.....

On your OIII mono image duplicate the background layer. Erode the stars using dust and scratches tool, careful not to include any precious nebula detail. Clean up any left overs with clone / healing brush. Now change layer blending to difference. You should just see the stars. Use colour range select to select the stars, expand the selection a couple of pixels and then feather a couple. Click on background layer and go to new layer via copy selection. Delete or hide the layer you used dust and scratches on and you now have your background layer with a star layer on top. Run a minumum filter on the stars to reuce them in size to taste.

Hope that helps

That's helpful thanks John!

[Fordos Moon]

In photoshop, can you use the Hα layer as a luminosity mask

Thanks Pete, I have done that but the smaller Ha stars were overwhelmed by the larger OIII layer stars underneath, John's tip should sort it!

[PhotoGav]

John's approach should do it.

My technique is basically the same:

In your flattened OIII image

Duplicate the background layer and call Reduce Stars

Run Noel's Action 'Select Brighter Stars'

Expand the selection by 4 pixels

Feather the selection by 2 pixels

Hide the marching ants so you can see what is going on

Minimum filter with radius of 1 pixel

You can then do 'Fade Minimum' to alter the strength of the filter to taste

You can also change the opacity of the Reduce Stars layer to taste

If you have the Ha image open too, you can compare the two images until the stars look roughly similar.

Good luck

[Fordos Moon]

John's approach should do it.

My technique is basically the same:

In your flattened OIII image

Duplicate the background layer and call Reduce Stars

Run Noel's Action 'Select Brighter Stars'

Expand the selection by 4 pixels

Feather the selection by 2 pixels

Hide the marching ants so you can see what is going on

Minimum filter with radius of 1 pixel

You can then do 'Fade Minimum' to alter the strength of the filter to taste

You can also change the opacity of the Reduce Stars layer to taste

If you have the Ha image open too, you can compare the two images until the stars look roughly similar.

Good luck

Thanks Gav how do I hide the crawling ants?!

[lensman57]

Thanks Gav how do I hide the crawling ants?!

Try Ctrl H, it might work.

A.G