Bright stars and processing

[Starwiz]

Does anyone know of any tutorials that deal with processing images that have a really bright star?

I've been searching the web but can't seem to find anything.

I'm processing some NB data for the witches broom NGC 6960, but the bright star is over-saturating.

Thanks

John

[Starwiz]

I guess that's a 'No' then.  🙂

[happy-kat]

What are you using to process your image?

Have other members mentioned what they did when processing this target?

[Aramcheck]

I haven't tried this properly yet, but there's a free script for Pixinsight called GAME which is very good for creating masks. You can use it to mask star halos by creating a Gradient mask and a Brightness mask; and then subtracting the Brightness Mask from the Gradient mask to create the Star Halo mask.

Here's a very rough example, which should have had intermediate steps added to exclude the dimmer stars & probably should have been done whilst the image was still linear.

Cheers
Ivor

[Starwiz]

13 hours ago, happy-kat said:

What are you using to process your image?

Have other members mentioned what they did when processing this target?

I'm processing in PS.

I've had a good search in the NGC6960 posts, but haven't been able to find anything useful.

John

[Starwiz]

8 hours ago, Aramcheck said:

I haven't tried this properly yet, but there's a free script for Pixinsight called GAME which is very good for creating masks. You can use it to mask star halos by creating a Gradient mask and a Brightness mask; and then subtracting the Brightness Mask from the Gradient mask to create the Star Halo mask.

Here's a very rough example, which should have had intermediate steps added to exclude the dimmer stars & probably should have been done whilst the image was still linear.

Cheers
Ivor

That's interesting, thanks.  I'm processing in PS, so there may be an equivalent way to do the same.

John

[Tommohawk]

On 25/06/2020 at 09:47, Starwiz said:

Does anyone know of any tutorials that deal with processing images that have a really bright star?

I've been searching the web but can't seem to find anything.

I'm processing some NB data for the witches broom NGC 6960, but the bright star is over-saturating.

Thanks

John

I think there may be two slightly separate issues here. NB data often has halos around bright stars - this seems to depend a lot on the filter brand. 

Also there are the usual issues when stretching data - you tend to bloat the brighter stars.

Last time I did NB I used Starnet to remove all stars, and then processed the star layer separately. You can see my effort here. It's not the best to be fair because by the time I got to that point I was going slightly gaga - but you get the idea. I think I also tried selecting the halo in PS, applied some feathering, and used curves to darken it to match the surrounding area.

Obviously masking bright stars somehow before stretching helps as per LRGB processing. Ivor's post above looks interesting.

[happy-kat]

I recall Ollypenrice doing something in PS (an older version of CS) for star tightening I'll see if I can find it.

[alacant]

On 25/06/2020 at 10:47, Starwiz said:

any tutorials

Hi

Do you mean without a dedicated processing app? There's a tried and tested method from way back which consists of stretching your image with an inverted star mask layer over the top of a duplicated image. This guy explains it.

Not very elegant, but it maybe worth a try.

Cheers and HTH.

 

 

[Starwiz]

47 minutes ago, alacant said:

Hi

Do you mean without a dedicated processing app? There's a tried and tested method from way back which consists of stretching your image with an inverted star mask layer over the top of a duplicated image. This guy explains it.

Not very elegant, but it maybe worth a try.

Cheers and HTH.

 

 

Thanks. 

I'm using Straton to remove the stars, but the brightness from the 'witch' star is such that much of the area surrounding it becomes brighter than the nebula when stretching.

John

[alacant]

On 25/06/2020 at 10:47, Starwiz said:

'witch' star

Ah, ok. Stretch the bottom layer less until the witch star is acceptable (the rest of the image will be too dark) then with your normallly stretched (but masked) layer on top, use a fuzzy black brush to punch through the mask directly on top of the offending star. Try different opacities until it's seasoned to your taste.

HTH

 

 

[happy-kat]

I like the episode 2 stargazine as that demo really showed the use of layers and tweaking a little in each step using different tools much I expect can be repeated in GIMP or similar.

[alacant]

1 minute ago, happy-kat said:

GIMP

Hi. Yeah, GIMP will do it. Also, if the op is ok with apps, there's Siril's (among many) sqrt or asinh stretching and StarTools'  FWOABW 'second-AutoDev' module. Then there's... aahgghh stop!

Cheers

[happy-kat]

The OP is using PS so easily covered.

[Starwiz]

So here's my attempt at controlling the 'witch' star.  I've still more work to do on correcting some of the coma and cropping out a few stacking artifacts.  I also want to alter the hue of the bright star as it's looking a little green.  Comments for improvements welcome as always.

John

 

[Tommohawk]

Looks pretty good to me!

Regarding correcting coma, are you using a coma corrector? In any event I think you might want to look at collimation - you seem to have quite a bit of coma bottom right and not much top left.

The bright star does look a bit green - easy fix though just select it and change hue/saturation. Hmmm.. just had a try at this and not so easy! Maybe careful use of clone stamp?

Edited July 2, 2020 by Tommohawk

[Starwiz]

1 hour ago, Tommohawk said:

Looks pretty good to me!

Regarding correcting coma, are you using a coma corrector? In any event I think you might want to look at collimation - you seem to have quite a bit of coma bottom right and not much top left.

The bright star does look a bit green - easy fix though just select it and change hue/saturation. Hmmm.. just had a try at this and not so easy! Maybe careful use of clone stamp?

Thanks.

Hopefully I'll be getting a coma corrector in late December.  I've written to Santa already.  😀

I last collimated a couple of weeks ago, but will re-check.

Green hue on star - I've used a lot of clone stamping on the mono images to removed the star, so will take another look.

Thanks for your help.

John