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How can I remove just the small stars?

Processing Star Reduction Deep Sky
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Dan Brown avatar
Dan Brown avatar
My latest image has too many stars. It looks great without stars but as soon as I add them they totally obscure the nebulosity. What I would like to do is remove just the smaller stars from the image. I've tried the minimum filter in PS. When set to 1 pixel radius it works pretty good, just not enough for my needs. I have also tried Bill Blanshen's plugin and I'm still not getting the effect I wan't. Does anyone have any ideas?
Thanks,
Dan
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Tom Boyd avatar
Tom Boyd avatar
Separate the stars from the nebulosity while the image is still linear, stretch the stars and nebulosity separately and recombine. This way you can use your stretch of the stars as an effective size filter - more stretch, more smaller stars.
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Itto Ogami avatar
Itto Ogami avatar
Dan, If using phtotoshop, I use the brightness/contrast adjustment (specifically contrast) on the star layer. this will easily remove smaller "popcorn stars" and reduce the brightness of the others without significantly altering stars shapes. You can check my images to see if the star shapes are accceptable to you.

As Tom mentions above, I mask out the stars almost immediately after a couple of operations in photoshop. the more you stretch before you mask, the bigger, brighter and more bloated the stars will be. My process is usually open the image in PS > levels> color balance if needed > levels again > color balalnce if needed >  mask out stars

Hope this helps.

Regards,
Itto (Jim)
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HR_Maurer avatar
HR_Maurer avatar
Build a binary star mask, and use the morphological transformation tools (erode/dilate) to remove she small diameter ones. Pretty much like in star processing steps few years ago. The resulting mask might be further dilated, and miltiplied to the primary mask. Something like this…
Tony Gondola avatar
Tony Gondola avatar
The easiest way is to do your star removal directly after stacking. That way you can process the star plate separately and make them as unobtrusive as you like, simple. Do any more and you are getting pretty far from reality, if that matters in what you are trying to accomplish!
Doug Crowe avatar
Doug Crowe avatar
You should check out Seti Astro's programs. I use them all the time in Pixinsight, but now he has some standalone programs including star stretch and  NB to RGB stars that I use all the time. Just google "Seti Astro" for his website.
John Hayes avatar
John Hayes avatar
Dan Brown:
My latest image has too many stars. It looks great without stars but as soon as I add them they totally obscure the nebulosity. What I would like to do is remove just the smaller stars from the image. I've tried the minimum filter in PS. When set to 1 pixel radius it works pretty good, just not enough for my needs. I have also tried Bill Blanshen's plugin and I'm still not getting the effect I wan't. Does anyone have any ideas?
Thanks,
Dan

You are on the right track to create a better looking image but simply removing the faintest stars is not the best strategy.   The best way to handle this is to de-emphasize the star field.  The first step in that process is to reduce the size of the stars.  My two favorite tools for that are BlurXterminator and StarShrink.  That's often enough but for some fields you may want to further dim the stars.  In that case, it's best to separate the stars from the image or to use a star mask so that you can work on ONLY the stars.  The MorphologicalTranform rool in PixInsight is ideal for dimming the star field by any degree that you like before you put it all back together.  You can use layer filtering with the MultiScaleMedianTransform tool in PI on a pure star image to remove tiny stars if you really want to take that route.

John
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Dan Brown avatar
Dan Brown avatar
John Hayes:
Dan Brown:
My latest image has too many stars. It looks great without stars but as soon as I add them they totally obscure the nebulosity. What I would like to do is remove just the smaller stars from the image. I've tried the minimum filter in PS. When set to 1 pixel radius it works pretty good, just not enough for my needs. I have also tried Bill Blanshen's plugin and I'm still not getting the effect I wan't. Does anyone have any ideas?
Thanks,
Dan

You are on the right track to create a better looking image but simply removing the faintest stars is not the best strategy.   The best way to handle this is to de-emphasize the star field.  The first step in that process is to reduce the size of the stars.  My two favorite tools for that are BlurXterminator and StarShrink.  That's often enough but for some fields you may want to further dim the stars.  In that case, it's best to separate the stars from the image or to use a star mask so that you can work on ONLY the stars.  The MorphologicalTranform rool in PixInsight is ideal for dimming the star field by any degree that you like before you put it all back together.  You can use layer filtering with the MultiScaleMedianTransform tool in PI on a pure star image to remove tiny stars if you really want to take that route.

John

Thanks John, MSMT seems to work the best. Thank you all for your help, keep an eye out for this image this week.
David Russell avatar
David Russell avatar
in a layer based photo editor its not hard at all.

First you need to run Starnet and make a Starless image. subtract that from the Full image to create a Stars only image.

then you can Blend the two in Affinity, and use the opacity slider to adjust how bright and visible the stars  should be.

you can also run contrast and many other adjustment layers on the stars only image that can help.

lots of Affinity tutorials on You Tube.
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Tony Gondola avatar
Tony Gondola avatar
+1 for Affinity Photo
Ed Dixon avatar
Ed Dixon avatar
I use GIMP to do this, and it's a free tool.

I use the RC-Astto StarXTerminator to produce a starless image.  I then create two layers, one with all data and the second the starless one.  Place the starless one on top and then use the blend option to determine how much of the lower “all” image to include.
Dan Brown avatar
Dan Brown avatar
I ended up using MLT to make a star mask and then shrunk the stars with morphological transform tool. The end result can be seen here,
https://www.astrobin.com/jgi7ok/
Dan
John Hayes avatar
John Hayes avatar
Dan Brown:
I ended up using MLT to make a star mask and then shrunk the stars with morphological transform tool. The end result can be seen here,
https://www.astrobin.com/jgi7ok/
Dan

Good work!