Processing tips - separating stars ** Tutorial Uploaded **

[multiweb]

I have a shot here (http://www.multiweb.com.au/astro/before_after.gif)that illustrates very clearly the point I'm trying to make. It's a timed animated GIF file. It will flip after a couple of seconds. There's nothing flash about this pic. It's a failed attempt to do some Ha from my light polluted backyard on the Xmas tree/cone nebula.

Never happened. Not one for the burbs. Too faint. Anyway I had a crack at it using that star removal method. Have a quick look at the before and after shot. Even if you tweak the levels in the original I started from you’ll see that it’s hard to get the contrast of the final. It obviously has some sharpening artifacts as the data was so poor to start with but you can see the technique has its advantages because without the stars in the way you can focus your processing on the nebulosity. It's easier from a user's point of view.

Here's a link (http://www.multiweb.com.au/astro/tut_01/)to the procedure I used.

[troypiggo]

The after looks fantastic. Great result. You use that astro anarchy guy's technique? His PS actions?

[multiweb]

I used a bit of the steps that were recorded in the actions combined with some other techniques in the tutorials for the tone mapping. Namely removing the stars with multiple iterations of the dust and scratches filter in PS with decreasing parameters each pass, then overlaying the original as a darken blend to put back the dark bits you might have left behind without putting the stars back in. Then what I really like is the difference blending between the starless version and the original to get the stars only. That's genius. With the appropriate Threshold and colour range selection and proper feathering on the selection you can truly isolate every single spec in the picture and move it to a separate star layer. Once you got that right you're 99% there. The rest is just standard stuff. When you're done you blend the stars back in with a lighten mode or other to suit your taste. I tried screen, pin light. Depends on the picture. I now also use the difference layer trick to isolate clipping in stars or nebulosity so I can then tweak the highlights back down. I did that on the tip of the cone and also on the planetary top right. Very very cool.

[troypiggo]

You should post these tips in the "ps tips" sticky. ;)

[allan gould]

More, more, more, Mark. Really interesting thread and procedures.
I agree with Troy - write an article for the rest of us dummies.

[multiweb]

Putting something together now with dialog screen grabs from PS so you can retrace steps in the layer stack. Will post a link when done.

[multiweb]

Here's a link (http://www.multiweb.com.au/astro/tut_01/)to the procedure I used as a few people showed some interest. This should give you a base to start from and an idea of the processing flow. Feel free to add your own stuff and experiment. That's what it's all about. :thumbsup:

[MrB]

Awesome, thanks Marc.
There should be more of this sorta stuff from our members, top stuff. :thumbsup:

[kamayok3]

Yeah....always waiting for that! Thanks Marc....

Regards,

Tommy

[multiweb]

Glad you find that helpful guys. :thumbsup: Now time to repo :)

[Terry B]

I like the little pic of the hubble variable neb that is in the image.

[TheDecepticon]

Hi Marc,:)
Great technique!!! I do not fully understand what you are doing with Noiseware. Are you just doing a noise clean up, or are you doing something else?:question:
Thanks!:thanx:

[multiweb]

Hi Gray. Just basic noise reduction. I like noiseware because it's subtle and has loads of parameters. John Glossop put me on it years ago (JohnG). Never looked back. It can sharpen also if you choose to but I turn that to the minimum. I also have noise ninja That Greg Bradley uses a lot and neatimage. They all do things differently and are good to have to.

[troypiggo]

Out of interest, what settings did you use in noiseware?

[multiweb]

What's on the snapshot (10% max). Depends on the picture or layer I'm working on at the time. I usually blink between before/after and do very small incremental passes. I also never sharpen while doing noise reduction. Highpass filter will always introduce noise so I do a noise reduction prior and after also.

There's only that many noise reductions you can do on a pic before starting to see artifacts so the idea is to "spread it" over multiple stages within your processing if that makes sense. If you blow the budget too early or too late it's no good.

[RobF]

You're the best Marc :)

Just came here with the intention to make a new post on techniques people use to process stars separately, and here you already have it all laid out!

Must get to and start trying next opportunity.

Thanks again,
R

[troypiggo]

G'day Marc, sorry about the thread resurrection. Was playing around on the weekend with some old data, looking at star removal etc. Came back to this thread, followed your method pretty much and it was all very clear. Even made an action for the star removal so it's kinda one click now. Refer attached :D Oh yeah, go the ED80.

Question time...

Adding the stars back in! I'm ending up with halos of dark around the stars because the starless nebula is stretched I guess. Got any tips/tricks on that one? Also finding the stars look a bit wrong, kinda too small. I don't want to blow them out, but they don't look proportionate to the nebulosity if that makes sense.

[Octane]

That's like some kind of surrealist art. Beautiful work, Troy. Print that and hang on wall.

I've found processing this object to be a pain in the arse. It's got a very limited dynamic range to work with in the nebulosity itself.

I captured this for 2 hours at Snake Valley this year (it was somewhat low in the sky), but, I might need to remove the stars and see if I can turn it into a work of art such as you have here. I doubt it, though, I was imaging with the 40D with the 127ED at 952mm focal length. A bit too in your face, whereas this has the much needed empty space around it.

Damn, that looks so good.

H

[SkyViking]

When adding the stars back in, try adding them as a separate layer on top of the nebula and setting the star layer's blend mode to 'Lighten'. That way only the portion of the layer that is lighter than the underlying layer is added in. Before doing that you can try sharpening the stars, and/or adjusting levels & curves for them if you think they don't quite fit the appearance of the stretched nebula.

Great thread by the way Marc! Thanks for sharing :)

[multiweb]

The star layer should be set as lighten or lighter color so you don't get black ringing. Another trick is to select the stars with eyedropper and colour range then do a slight shadow/highlight filter on them. That gets rid of black outline. I use that per channel some time on blue channel when doing RGB.

If the stars are too small then the original selection was too tight. Try to increase the expand to 4px and feather more so you have more area to play with and blend in around the stars.

Very cool shot BTW. :thumbsup:

[multiweb]

You beat me to it.
What he said. :thumbsup:

Thanks.

[troypiggo]

D'oh. Shoulda thought of that. Obvious but didn't occur to me. Thanks guys!

Still some remnants of stars in my shot after the dust n scratches removal. Just need to finesse that out now. :)

[multiweb]

There are always abit of left over stars yes. The only person who can remove them all that I know of would be Fred. But I reckon it's beyond processing skills. He hates them so much they just fade away :P ;)

[troypiggo]

I've written what I think is a nifty little PS action that puts the stars back onto a starless layer. I think it's cool, but maybe everyone has already done this and it's nothing new. :shrug:

So I've got an action that removes stars, I have a bit of a methodology to tidy up the starless image that seemed to work on my test image (not sure if it's practical to be in the star removal action), and now an action to add the stars back as a separate layer so they can be turned on and off. It's all coming together for me. I haven't reverse-engineered the AstroAnarchy way of adding and removing stars, so I don't know if my methodology is similar or different, but it seems to work and I think his actions need a bit of work as sometimes they fall over if your layer naming isn't quite right. (Actually I might email him with fixes for that. :D)

When I get a chance I'll put it all together in a bit of a tutorial with downloads and screenshots etc.

[gregbradley]

Hey Troy.

That sounds useful.

Do have a place to download the action?

Greg.

[troypiggo]

This might be a bit premature, but would be handy to get some feedback. All of the actions should be non-destructive (ie they create and work on copies of the current layer only).

I use the threshold crop one to trim off alignment/stacking rubbish around the outside of images first thing after bringing into PS from Nebulosity. Tried to include a dialogue box to explain usage.

Big stretch and small stretch are just some curve adjustments to bring out some detail. I use big stretch typically first, maybe a couple of times, then small stretch sometimes helps but often don't and just use manual curves. Feedback on better curves appreciated.

Remove stars does still leave some artifacts that need cloning out manually. I'm working on a methodology of getting rid of those. Still not happy at this stage.

Star selection is probably a misnomer. Just put a duplicate of the original image with stars on top of your starless image, making sure there isn't any visible layers between them. Run the action and you can blink the stars/no stars versions by turning that top layer off.

Feedback appreciated. :)

Troy's Astro Actions v0.9.1 (http://piggo.com/%7Etroy/files/actions/Troy%27s%20Astro%20Actions%20v0_9_1 .atn)

[multiweb]

That sounds great Troy! Will have to try it. :thumbsup:

[troypiggo]

This is fun. Just updated the link above to version 0.9.1. Now included one action that separates the stars and the background with one click. Also made the action names a little more obvious.

[Andy01]

Hi guys, found this very interesting old thread and wanted to see if there were any other updates for this? I have downloaded Troys astro actions, thanks Troy, but Marc's links don't seem to work anymore?

Anyone else got a star removal action/tips to add?

Cheers
Andy

[coldlegs]

+1 for me too

Cheers
Stephen

[multiweb]

Just saw this now. Updated link above. Troy should have a link to the action somewhere.

PS: found it. See attached zip file.