Star mask processing

[TiffsAndAstro]

Any know a good tutorial for processing my star masks before recombing in siril?

I have a basic grasp of processing the starless and can practice, but after recombining the two my stars look a bit goggle eyed. Also not so much colour left.

I think problem is in how I stretch the stars?

 

Looks like I missed a video by Deep space Astro 

Edited May 6 by TiffsAndAstro

[WolfieGlos]

Personally, I never had much luck recombining in Siril with Starnet. The stars always lost their brightness and often the brighter stars had a transparency about them. Those stars also came back in with artifacts, like a colour checkerboard pattern. This pattern would also be repeated on the starless image, a real pain.

I would also find this would happen using Starnet in the standalone version, so I came up with a different routine using GIMP.

I used the following:

1. Process your image as normal (with the stars) to a point in the non-linear (i.e. after stretching) and then SAVE. Ensure the stars are as you would want them in your final image.
2. Run Starnet in Siril.
3. Immediately save the resulting Starless image under a different name (call it stars2).
4. Reopen the starless image, and further process it as required.
5. Open GIMP, and load the original image BEFORE starnet, and then add stars2 as a new layer, and set the layer mode to Subtract. This should leave you with a perfect image of just the stars, no artifacts, etc.
6. Create a New Layer from Visible.
7. Open the processed starless image, and overlay the starless image on a SCREEN mode. Sometimes lighten only works, but mostly it's screen.

If you then want to reduce star sizes (if not using Deep Sky Astro's script in Siril), you can use Value Propagate in GIMP on the stars layer. Change the mode from More White to More Black, and adjust the sliders to suit. You can even change the Blending Mode (at the bottom) from Normal to Multiply to really cut the stars out drastically, if you so wish, and control it with the Opacity slider.

HTH.

Edited May 7 by WolfieGlos
Typo

[Ags]

So much information there! Many thanks @WolfieGlos!

[Swillis]

8 hours ago, WolfieGlos said:

Those stars also came back in with artifacts, like a colour checkerboard pattern.

Thanks @WolfieGlos I just thought that was due to my DSLR (and not having enough data) and reaching the limit of where I can stretch before bringing out the noise

I'll have to give it another go and try your method.

Thanks again

[TiffsAndAstro]

9 hours ago, WolfieGlos said:

Personally, I never had much luck recombining in Siril with Starnet. The stars always lost their brightness and often the brighter stars had a transparency about them. Those stars also came back in with artifacts, like a colour checkerboard pattern. This pattern would also be repeated on the starless image, a real pain.

I would also find this would happen using Starnet in the standalone version, so I came up with a different routine using GIMP.

I used the following:

1. Process your image as normal (with the stars) to a point in the non-linear (i.e. after stretching) and then SAVE. Ensure the stars are as you would want them in your final image.
2. Run Starnet in Siril.
3. Immediately save the resulting Starless image under a different name (call it stars2).
4. Reopen the starless image, and further process it as required.
5. Open the original image BEFORE starnet, and then add stars2 as a new layer, and set the layer mode to Subtract. This should leave you with a perfect image of just the stars, no artifacts, etc.
6. Create a New Layer from Visible.
7. Open the processed starless image, and overlay the starless image on a SCREEN mode. Sometimes lighten only works, but mostly it's screen.

If you then want to reduce star sizes (if not using Deep Sky Astro's script in Siril), you can use Value Propagate in GIMP on the stars layer. Change the mode from More White to More Black, and adjust the sliders to suit. You can even change the Blending Mode (at the bottom) from Normal to Multiply to really cut the stars out drastically, if you so wish, and control it with the Opacity slider.

HTH.

This is a really interesting way to do it Ty 

[WolfieGlos]

You're all welcome, hope it helps 🙂 There's always more than one way to do these things, but I found this most effective.

I came across the Subtract method on CN a while back, so I tried it and adapted it to fit into a workflow with Siril. It sometimes gives issues if you have large halo's on very bright stars across a nebulous region, in that the blending might be a bit off and look artificial, but some masking and local tweaking can always be applied.

47 minutes ago, Swillis said:

Thanks @WolfieGlos I just thought that was due to my DSLR (and not having enough data) and reaching the limit of where I can stretch before bringing out the noise

I'll have to give it another go and try your method.

Thanks again

 I never had an issue with noise, mostly just the checkerboard and transparency problem, and I suspected it might be related to varying FWHM values between subs 🤷‍♂️ I'm now on PI and trialing that, and I get the same issue with Starnet2 and the DSLR, so it must be Starnet related. No issue though with StarXT, which is also on trial, but it does cost £70 to purchase (on top of PI) and that doesn't include any of the other XT tools....

Edited May 7 by WolfieGlos

[AstroMuni]

On 06/05/2024 at 22:15, TiffsAndAstro said:

Also not so much colour left.

The trick to bring out colour in stars is use Asinh stretches. Photometric colour calibration also helps.

[Elp]

The key to star colour is usually a saturation boost (like a lot of you want nice blue red stars in the field) without clipping the data, if you move the white point you'll certainly wash them out into bright white.

An hour or two capturing LRGB stars is usually enough to use as star only data. Also don't use a light pollution filter, luminence filter only to minimise IR bloat.

 

[TiffsAndAstro]

49 minutes ago, AstroMuni said:

The trick to bring out colour in stars is use Asinh stretches. Photometric colour calibration also helps.

I do a PCC before I separate. Asinh I messed a while back but not specifically on the star mask. Will have another play with it ty

Edited May 8 by TiffsAndAstro

[TiffsAndAstro]

So asinh helps, but I seem to need to stretch the star mask slot when recombining.

That seems white out the star colour. I think.

[900SL]

I use Starnet 2 on the linear stack, after DBE and PCC, but before any stretching.

You have to be careful stretching the Star mask,  It doesn't need much to blow out the brighter stars. I increase the colour saturation of the starmask  a touch before stretching

Helps to have good data without too much noise or star halo

The GHS in Siril has a highlight protection slider, which reduces the S curve and thus highlight clipping

You can see whether stars are oversaturated by using the selection box and right clicking, there is an enquiry option which will tell you min and max ADU

Edited May 11 by 900SL

[ollypenrice]

I do it in Photoshop and follow the WolfieGlos method until I have the finally stretched starless image as a bottom layer and the less-stretched normal image as a top layer.

At this point you could use blend mode subtract in Ps but I think there's a slightly better way. Whether these blend modes are available in Siril I don't know, but in Ps it goes like this:

Invert both layers

Change blend mode to divide.

Flatten.

Invert.

This gives a stars only image which can be pasted onto the starless, as WolfieGlos says, with the blend mode screen.

We are now in exactly the same situation again. With your stars only on top you can simply use the mid point slider in levels to brighten or dim the stars to taste. You can also use the contrast slider, or Curves, to increase contrast. This will reduce the outer glow around brighter stars. In Ps the very bright stars can be lassoed and their contrast further increased to bring any bloat down still further.

This control over stars is a dream come true!

Olly

[TiffsAndAstro]

On 11/05/2024 at 07:19, 900SL said:

I use Starnet 2 on the linear stack, after DBE and PCC, but before any stretching.

You have to be careful stretching the Star mask,  It doesn't need much to blow out the brighter stars. I increase the colour saturation of the starmask  a touch before stretching

Helps to have good data without too much noise or star halo

The GHS in Siril has a highlight protection slider, which reduces the S curve and thus highlight clipping

You can see whether stars are oversaturated by using the selection box and right clicking, there is an enquiry option which will tell you min and max ADU

Cheers for the reply. I do starnet before stretching and now also add some colour to the star mask before and after stretching. It does seem to help.

Will give the highlight protection slider a go see what happens:)

[TiffsAndAstro]

22 hours ago, ollypenrice said:

I do it in Photoshop and follow the WolfieGlos method until I have the finally stretched starless image as a bottom layer and the less-stretched normal image as a top layer.

At this point you could use blend mode subtract in Ps but I think there's a slightly better way. Whether these blend modes are available in Siril I don't know, but in Ps it goes like this:

Invert both layers

Change blend mode to divide.

Flatten.

Invert.

This gives a stars only image which can be pasted onto the starless, as WolfieGlos says, with the blend mode screen.

We are now in exactly the same situation again. With your stars only on top you can simply use the mid point slider in levels to brighten or dim the stars to taste. You can also use the contrast slider, or Curves, to increase contrast. This will reduce the outer glow around brighter stars. In Ps the very bright stars can be lassoed and their contrast further increased to bring any bloat down still further.

This control over stars is a dream come true!

Olly

Don't think all that can be done in siril. Probably gimp though. Or combination of both.

Bit advanced for me right now I think though. 

[ollypenrice]

31 minutes ago, TiffsAndAstro said:

Don't think all that can be done in siril. Probably gimp though. Or combination of both.

Bit advanced for me right now I think though. 

Well, the 'subtract' method will work. Assuming you have blend mode lighten in your layers menu, there is another easy way which sometimes works nicely. Place the less-stretched original with stars on top of the highly stretched starless and set the blend mode to Lighten. Only the stars should be visible from this layer because the nebulosity and background are not lighter than the bottom layer image. You can adjust the brightness of the stars using levels. You can also bring in the black point on the top layer to make the stars tighter.

Honestly, this is simple stuff in a Layers programme.

Olly

[TiffsAndAstro]

50 minutes ago, ollypenrice said:

Well, the 'subtract' method will work. Assuming you have blend mode lighten in your layers menu, there is another easy way which sometimes works nicely. Place the less-stretched original with stars on top of the highly stretched starless and set the blend mode to Lighten. Only the stars should be visible from this layer because the nebulosity and background are not lighter than the bottom layer image. You can adjust the brightness of the stars using levels. You can also bring in the black point on the top layer to make the stars tighter.

Honestly, this is simple stuff in a Layers programme.

Olly

Yeah gimp and layers are on my list to learn stuff, but not gotten around to it yet.