RGB Stars and Narrowband

[Starwiz]

Can anyone direct me to a tutorial that shows how to replace narrowband stars with RGB?

I've searched but can't find what I'm looking for.

Thanks

John

[vlaiv]

3 hours ago, Starwiz said:

Can anyone direct me to a tutorial that shows how to replace narrowband stars with RGB?

I've searched but can't find what I'm looking for.

Thanks

John

Don't know any tutorial on how to do it, but I can describe sensible steps to perform the operation.

In principle, I would be able to do all steps but one - for which I'm not sure if I could do it without first searching the internet for some ideas or even small tutorial on that particular part.

Problematic step is layer mask of stars - you need to be able to isolate stars in one image, and that is basically it. DSS for example has the option to create star mask - that could be very helpful (have not tried it, but I know it's there). Other astro software probably has something similar.

Anyway, you get your LRGB/RGB image and create nice looking star field. There are couple of ways to do it, I prefer RGB ratio method since you don't have to worry about color being lost when doing stretch.

Next thing is to process your NB image as you would and in the end you take RGB image, apply star mask and layer on top of NB with 100% opacity where stars are (background should be transparent).

Just to point out something - your NB and RGB images need to be aligned / registered to same reference frame (that is sort of obvious, but just in case ...).

[sloz1664]

I use Stratton star removal software, very good at removing stars for the price £14.64.

https://order.shareit.com/product?vendorid=200042742&productid=300568169

Again, star removal can be done by other software programmes, it depends on what you already have.

Steve

[vlaiv]

Yep, one way of creating a star mask would be:

- take rgb image and make a copy of it.

- do star removal on that image (do something like http://www.astro-photography.net/Star-Removal.html )

- subtract two images (in PS put them in layers and do difference or similar as blend mode)

- flatten that image and do selection on background fill it with black, do inverse on selection and fill it with white.

[MarsG76]

1 hour ago, vlaiv said:

Yep, one way of creating a star mask would be:

- take rgb image and make a copy of it.

- do star removal on that image (do something like http://www.astro-photography.net/Star-Removal.html )

- subtract two images (in PS put them in layers and do difference or similar as blend mode)

- flatten that image and do selection on background fill it with black, do inverse on selection and fill it with white.

Providing that Starwiz uses photoshop.

[vlaiv]

1 minute ago, MarsG76 said:

Providing that Starwiz uses photoshop.

Gimp is also an option - I use it and it can do all of that (same as PS).

[MarsG76]

5 minutes ago, vlaiv said:

Gimp is also an option - I use it and it can do all of that (same as PS).

Very true...

I use either masking and range selection if I have the RGB stars data... or create a grey luma map and use the original narrowband image blured 5 pixes as color data.. usually fixes stars that have a purple halo that are normally present or a side effect in narrowband imaging.

[Starwiz]

Thanks all for the help.  I'll give it a go in PS.

John

[rickwayne]

You could also give starnet++ a try for star removal. I was able to get much better results with that right off the bat than from Photoshop tweaks. As vlaiv says, after you've registered your NB and RGB images and run starnet++ on the latter to get a no-stars layer, you can do a "difference" blend mode in Photoshop and "stamp visible" to create a stars-only layer. Process that and your NB stuff, then add the stars back on top and set blend mode to "lighten".

Edited July 28, 2019 by rickwayne

[carastro]

I have never found a tutorial on this so just used my initiative.  Still not sure if I am doing it right.

I register the NB image and the RGB image so that they match each other. 

In Photoshop I select the stars on the RGB image,  expand them a little and then feather them by half.  

I then copy and paste them onto the NB image,  Then use a blend mode such as Lighten to blend them into the NB image.

This method doesn't always work, and sometimes I have to reduce the size of the stars in in the RGB image before copying and pasting them as they will be bigger than the NB stars.  OR, Use Filter/Other/ Minimum on the RGB stars before blending them in.

If any-one knows a better method in Photoshop, I would be glad to hear it.   

Carole 

 

Edited July 28, 2019 by carastro

[carastro]

Here's one I did that worked using the method above:

 

[MarsG76]

11 minutes ago, carastro said:

Here's one I did that worked using the method above:

 

 

41 minutes ago, carastro said:

I have never found a tutorial on this so just used my initiative.  Still not sure if I am doing it right.

I register the NB image and the RGB image so that they match each other. 

In Photoshop I select the stars on the RGB image,  expand them a little and then feather them by half.  

I then copy and paste them onto the NB image,  Then use a blend mode such as Lighten to blend them into the NB image.

This method doesn't always work, and sometimes I have to reduce the size of the stars in in the RGB image before copying and pasting them as they will be bigger than the NB stars.  OR, Use Filter/Other/ Minimum on the RGB stars before blending them in.

If any-one knows a better method in Photoshop, I would be glad to hear it.   

Carole 

 

 

2 hours ago, rickwayne said:

You could also give starnet++ a try for star removal. I was able to get much better results with that right off the bat than from Photoshop tweaks. As vlaiv says, after you've registered your NB and RGB images and run starnet++ on the latter to get a no-stars layer, you can do a "difference" blend mode in Photoshop and "stamp visible" to create a stars-only layer. Process that and your NB stuff, then add the stars back on top and set blend mode to "lighten".

 

9 hours ago, vlaiv said:

Yep, one way of creating a star mask would be:

- take rgb image and make a copy of it.

- do star removal on that image (do something like http://www.astro-photography.net/Star-Removal.html )

- subtract two images (in PS put them in layers and do difference or similar as blend mode)

- flatten that image and do selection on background fill it with black, do inverse on selection and fill it with white.

As the saying goes, there's more than one way to skin a cat.

[carastro]

Quote

As the saying goes, there's more than one way to skin a cat.

 

[Starwiz]

On 28/07/2019 at 22:36, carastro said:

Here's one I did that worked using the method above:

 

Very nice Carole.

John

[Starwiz]

And here's the result......

John