How to Keep the stars looking like they are supposed to look, help!

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How to Keep the stars looking like they are supposed to look, help!

#1

Post by chris_g »


Hello all,

Looking for some guidance on how to tame stars in Photoshop. I have about 8 hours of data on NGC 1893. I want the stars to look like the unprocessed version once I've gotten the nebula processed. I figure the best way to do that is to have two different images and layer them. A star only version and a nebula only version. I do all the processing on the nebula only version and once that is done, add the stars only version back in. How do I extract just the nebula from the image and end up with a star only image? I tried getting a nebula only image using StarNet before doing any processing, but it doesn't do anything. Afte processing and running StarNet on the processed version, the output was displeasing to say the least for the starless version.
NGC_1893 No Processing.jpg
NGC 1893_Processed.jpg
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Re: How to Keep the stars looking like they are supposed to look, help!

#2

Post by OzEclipse »


Hi Chris,

From this point and with existing data there are two ways to proceed.

1. Combine Starnet and Photoshop images you posted using an alpha channel mask

2. Abandon the starnet layer and use Photoshop itself to reduce the stars.


1. Combine Starnet and Photoshop images you posted using an alpha channel mask
Chris_G-TSS alpha-channel mix.jpg

2. Abandon the starnet layer and use Photoshop itself to reduce the stars.
Chris_G-TSS star red copy.jpg
This is a star reduction script I wrote for Photoshop and the one I used in the #2 example above.
Star reduction.atn.zip
(1.24 KiB) Downloaded 56 times
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Re: How to Keep the stars looking like they are supposed to look, help!

#3

Post by SkyHiker »


Hi Chris. Do you remember my recommendation about StarNet? Reduce to 2000xsomething before using it. Here's an example of a horrible looking Wizard, just about as ugly as yours.
wizard_dss3_small.jpg
I applied StarNet++ directly to it (resolution = 6298x4208) and got this starless image:
starless_small.jpg
Tonight I decided to revisit it and reduce the image to 2000x1336, stretched it - a bit better this time, before apoplying StarNet++.
wiz2000_small.jpg
Then I ran StarNet++ and got this much improved version:
starless2000_small.jpg
I added the original back in (the plain original, not star-extracted or anything like that), cranked up the saturation, curved it up a little for more brightness, then ran a slight Gaussian blur to make it look more real, before adding. I also sharpened the starless before adding.
wiz2000final_small.jpg
I was pleasantly surprised about how much better StarNet++ works at lower resolution! Another nice thing is that it runs in 5 minutes instead of an hour, on my ole laptoip.

So for the second time, try it on yours. It may still not work but your chances are better. Of course an F/7 ED80 adds extra blur because of Dawes' limit that is much worse than with my 12" Newt, so your stars have an extra bloat. Then of course you may want to think about filters, I don't know if you used your L-enhance if you have one although they tend to turn out red and blue, the green is clearly missing. Narrowband is a more radical way to fix it. In general mono imaging will give you better quality.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: How to Keep the stars looking like they are supposed to look, help!

#4

Post by chris_g »


OzEclipse wrote: Mon Jan 10, 2022 5:54 am Hi Chris,

From this point and with existing data there are two ways to proceed.

1. Combine Starnet and Photoshop images you posted using an alpha channel mask

2. Abandon the starnet layer and use Photoshop itself to reduce the stars.


1. Combine Starnet and Photoshop images you posted using an alpha channel mask

Image


2. Abandon the starnet layer and use Photoshop itself to reduce the stars.

Image

This is a star reduction script I wrote for Photoshop and the one I used in the #2 example above.
Star reduction.atn.zip

regards

Joe
Thanks for the script, I'll give it a try tonight after work. I didn't explain the two images very well, neither were the result of StarNet. It was too messed up to work with. The first image was the stacked image from DSS while the second was the result of my adjustments in Photoshop in trying to get the nebula to show up. I did run Carboni's Astronomy Tools, Make Stars Smaller, but it didn't do anything.
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Re: How to Keep the stars looking like they are supposed to look, help!

#5

Post by chris_g »


SkyHiker wrote: Mon Jan 10, 2022 7:33 am
So for the second time, try it on yours. It may still not work but your chances are better. Of course an F/7 ED80 adds extra blur because of Dawes' limit that is much worse than with my 12" Newt, so your stars have an extra bloat. Then of course you may want to think about filters, I don't know if you used your L-enhance if you have one although they tend to turn out red and blue, the green is clearly missing. Narrowband is a more radical way to fix it. In general mono imaging will give you better quality.
You're talking about reducing the resolution of the image not cropping the image itself, correct? I am hoping to find a solution that doesn't require lowering the resolution of the image, you lose detail that way. I'll give it a go tonight and see what StarNet churns out. It was total garbage the first time around. I ran HLVG to remove the green and Astroflat Pro to remove any other gradients.

Below is what I got when I reduced the resolution as you suggested, definitely a lot better than the first piece of ugly that came out but still not anything I could work with. I need to figure out how to keep the stars tight as in the original stacked data and merge them into the final product after I've processed the nebula
starless.jpg
I used the L-Pro filter that night because the Moon wasn't out, and I was trying to get more color out of it. I also have just invested in a set of 7nm SHO Optolong filters, a UV/IR cut filter and 2" L-Pro filter to replace the clip filter I have now, along with a 2" filter wheel, waiting for them to show up. Nothing yet on a monochrome camera though, the one I want I just don't have the money for yet. I've seen DSLR images on Astrobin that have good tight stars at what appears to be the native resolution using NB filters. You also mention Dawes's limit, while it's a term I've seen in researching scopes in the beginning, I'm not sure what it is. Quick research shows that it's the ability of the telescope to resolve between two stars close together. Is that really the issue I have here?
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Re: How to Keep the stars looking like they are supposed to look, help!

#6

Post by SkyHiker »


chris_g wrote: Mon Jan 10, 2022 4:31 pm
Below is what I got when I reduced the resolution as you suggested, definitely a lot better than the first piece of ugly that came out but still not anything I could work with. I need to figure out how to keep the stars tight as in the original stacked data and merge them into the final product after I've processed the nebula
Why not? It looks pretty good. Just fix the giant star blob remnants. You can simply edit the original image and stretch it slightly to bring the stars out, then add it in.
chris_g wrote: Mon Jan 10, 2022 4:31 pm I used the L-Pro filter that night because the Moon wasn't out, and I was trying to get more color out of it. I also have just invested in a set of 7nm SHO Optolong filters, a UV/IR cut filter and 2" L-Pro filter to replace the clip filter I have now, along with a 2" filter wheel, waiting for them to show up. Nothing yet on a monochrome camera though, the one I want I just don't have the money for yet. I've seen DSLR images on Astrobin that have good tight stars at what appears to be the native resolution using NB filters. You also mention Dawes's limit, while it's a term I've seen in researching scopes in the beginning, I'm not sure what it is. Quick research shows that it's the ability of the telescope to resolve between two stars close together. Is that really the issue I have here?
It's a noticeable part of it when you start stretching it. Aperture always wins.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: How to Keep the stars looking like they are supposed to look, help!

#7

Post by chris_g »


SkyHiker wrote: Tue Jan 11, 2022 2:30 am Why not? It looks pretty good. Just fix the giant star blob remnants. You can simply edit the original image and stretch it slightly to bring the stars out, then add it in.
{/quote]

You make it sound so easy! :lol: I'll work with it and see what I can manage, thanks for the pointer with StarNet. This kind of processing is truly a challenge for me. Even though I've been into digital photography since 19987, I've always been a point and shoot photographer, family events, stuff like that.
SkyHiker wrote: Tue Jan 11, 2022 2:30 am It's a noticeable part of it when you start stretching it. Aperture always wins.
I was wanting a C9.25 eventually but I'm learning that the non-Edge version won't fully illuminate a full frame sensor, whereas the Edge version will. At least so I've read so far.
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Re: How to Keep the stars looking like they are supposed to look, help!

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Post by chris_g »


SkyHiker wrote: Tue Jan 11, 2022 2:30 am Why not? It looks pretty good. Just fix the giant star blob remnants. You can simply edit the original image and stretch it slightly to bring the stars out, then add it in.
Ok, how do you fix remnants like that? I know you use Gimp, but your workflow should be really similar to PS for this. You help is much appreciated and anyone else who wouldn't mind throwing in their process for fixing blobs... :lol:
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Re: How to Keep the stars looking like they are supposed to look, help!

#9

Post by SkyHiker »


chris_g wrote: Tue Jan 11, 2022 7:29 pm
SkyHiker wrote: Tue Jan 11, 2022 2:30 am Why not? It looks pretty good. Just fix the giant star blob remnants. You can simply edit the original image and stretch it slightly to bring the stars out, then add it in.
Ok, how do you fix remnants like that? I know you use Gimp, but your workflow should be really similar to PS for this. You help is much appreciated and anyone else who wouldn't mind throwing in their process for fixing blobs... :lol:
I didn't do that for the example it because it takes some time.

To do it roughly you could select the area to be darkened, use curves to darken it (in my case I would use the blue one mostly) then follow with a generous Gaussian blur if it's far enough away from the nebulosity.

To do a better job at that it would be nice to mask the boundaries with a white/black mask, apply a Gaussian blur, then produce a negative mask. You use one mask for the darkening, the other for the nebulosity. Sum it all up when you're done and the boundaries should be smooth/unnoticeable. Too much work to go into detail but you get the picture. Gimp has 3 different ways of inverting, it matters which one you choose. Practice is golden.

YOu could also first try a gradient removal from the center of nebulosity towards the where the blob is. Gradients work nicely for that and don't do too much damage. The nature of the slope may help (linear or sinusoidal, or...).

Folding the stars back in also takes some effort. In my wizard example the stars look a bit unnatural, it can be improved with some more attention to detail. It was just a quick job.

Photoshop has plugins for that, maybe gradientXterminator knows how to do it. I think gradientXterminator and the recent starXtterminator would help tremendously and avoid the need for PI. Gradient removal and star reduction are the two big items that are hard, for everything else PS and Gimp seem good enough. I find tools like PS and Gimp much more user friendly than PI. I just started my trial license and need to gather up enthusiasm before trying it again.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: How to Keep the stars looking like they are supposed to look, help!

#10

Post by Sky »


Ok, how do you fix remnants like that? I know you use Gimp, but your workflow should be really similar to PS for this. You help is much appreciated and anyone else who wouldn't mind throwing in their process for fixing blobs... ]

I've used Photoshop for all my astro-image processing for the past 10 years. You can get spectacular results and very quickly when you use "Actions" to speed up the process.

Looking at your image of NGC1893, it's an easy task to remove the stars ... using a free Photoshop "star removing" action. The one I use is at least as good as StarNet++ and in some cases even faster with better results.

Starless_Image.jpg
This image also had some star removal artifacts similar to the StarNet++ image. They are easy and quick to remove using Photoshop. Just take the "Lasso" tool and circle all the individual defects you want to remove. Next, go-to "Edit" - "Fill" and choose the "Content-Aware" option and hit "OK" ... defects gone! Content-Aware looks at the data around a "defect" and replaces it with extrapolated data to provide a seamless repair. It even works to remove bad data (stars) from inside a nebula with a seamless substitution.

The next step is to place the stars in the unprocessed image into the starless image ... again, a simple PS task. Open both the star and starless images into PS and on the starless image "Select" - "All" - "Copy". "Paste" it onto the star image. Open the "Layers" info screen and scroll down the "Normal" mode to "Lighten" and the stars are now blended into the starless image. "Flatten the image and we're done.
Stars-_added_to_image.jpg
Here are two free PS "star removing" actions ... sometimes one might work better than the other and a free "Star Bloat Removal" action that just reduces the size of bloated stars (your choice) while leaving the remaining stars untouched:
StarRemoving.zip
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Re: How to Keep the stars looking like they are supposed to look, help!

#11

Post by chris_g »


@Sky, Thank you! Exactly what I was looking for, you are awesome!
Image Cam: Canon 6D (Ha mod), 600D (Stock), SVBony SV405CC
Image OTA: EvoStar ED80, WO Z73, C8-A XLT
Mount: EQ6-R Pro Pier, AZ-EQ5 Pro Pier
Guide OTA: Orion 60mm, WO 32mm, ZWO OAG, SV501P
Guide Cam: ZWO 120mm, 290mm mini
EAA OTA: Orion ST80
EAA Cam: SVBony SV705C
EP: Baader Hyperion Modular Set
Filters: L-Pro Canon EOS C, L-eNhance, L-Pro, Optolong Ha 7mm, Optolong Oiii 6.5mm, Optolong Sii 6.5mm, ES H-Beta
Session Control: Mini PC/Win11 Pro, APT 4.1, PHD2 2.6.10
Processing: PixInsight, DSS 4.2.6, Adobe PS CC, Astronomy Tools Action Set, Star Spikes Pro
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