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graemlourens

M106 (abused as RGB vs LRGB target)

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Hi everybody.

The RGB vs LRGB-Discussions have always been in my head. I decided to take the last 4 clear nights (4 clear moonless nights, a beauty) and do both on a rather dim object. Capture enough RGB data to do a pure RGB and then capture additional Lum files to then be able to compare (24 x 600s each LRGB). But first here's the result (this one is the LRGB-Version)

M106.jpg

Please excuse the horribly bloated stars. I really hate them every time i look at my picture. My ED80 doesn't help me much on reducing that, and i've pulled every genie out of the box i know to reduce the effect, without much success.

I haven't posted the RGB-Version as its pretty much identical. I would say though that i was able to get LESS details on M106 as i could not deconvolve as much as in the Luminance without causing artefacts.
My conclusion is that in my setup with very small aperture of 80mm, and limited amount of sky-time (even with an remote automated obsy) considering that i can not get much sharper images compared to using L (that will be more blurry with the ED80, but i can get much more signal and deconvolve) i will be going for LRGB in future, except for very bright targets.

I'd love to hear you're comments on my conclusion of going consistantly LRGB, but also about the image in general. It felt as a very difficult one to process compared to other images i've done.

Kind regards, Graem

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You're killing me.... :) Please tell me how the heck you did that in such a short time. Somehow star control just doesn't want to work for me. I'm using Pixinsight for everything, but got Photoshop at hand if necessary.

Would you share your process?

Kind regards, Graem

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That's a really nice M106.

11 minutes ago, pyrasanth said:

There you go sorted-

How did you do that????

Chris

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I'm relieved i'm not the only one blown out of his mind :D ....

My suspicion is some kind of magic photoshop plugin. We'll see what he replies :)

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It can be done with noels "make stars smaller" action, or done properly as part of your workflow in Ps as described here:

Bear in mind that for LRGB it will need to be done for both lum and the combined RGB master ;)

 

 

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Thx for the revealing :) I'll check it out first thing tomorrow morning. 

And it will not let me peace until i went over all my old images one by one and fixed those horrible stars :)

We went way off topic, but i'm so grateful we did! Feedback to the original post obviously still greatly appreciated.

Kind regards, Graem

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8 minutes ago, graemlourens said:

Thx for the revealing :) I'll check it out first thing tomorrow morning. 

And it will not let me peace until i went over all my old images one by one and fixed those horrible stars :)

We went way off topic, but i'm so grateful we did! Feedback to the original post obviously still greatly appreciated.

Kind regards, Graem

I have the same issue with my C11 it gives bloated stars so the tool if used carefully is amazing- I use it all my images where stars are blown out. It costs $50.00 after the 30 day trial but it's a great purchase!

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Sorry to jump in, but is that a similar effect to the Morphological Transformation available in Pixinsight? Only played with it a little, but it seems to help - although it can also easily be pushed too far and look unnatural.

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Hi Marky.

I haven't tested the Photoshop plugin mentioned here yet (just checked out a few reviews) but i've had extensive practise with Morpho-transform of pixinsight. I don't like that script at all, as it just seems to reduce the brightness of the stars, not really the size (has been mentioned here i think as well in this forum a few times). And i haven't found a process in PI to do this. Only other way is masked stretching and thats - for me - one of the most difficult things to do to keep background levels same between the layers you're stretching.

Kind regards, Graem

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Cheers Graem - might be worth me looking at the PS plug-in as well! AS I said, I've only "toyed" with the script in PI as I am very much at the novice end, so not had much chance to really play around - but I have seen how easy it is to over-do it - although I think that is the case for all the scripts/techniques in any processing programme!

Love the image by the way!

 

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Well i reckon it looks amazing, even without the star shrinkage :)

 

Really lovely image Graem, well done.

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Thank you Aenima!

I know i should not get to hung up with the defects of my system, but as there are ways to deal with them in post processing, it bugs me so much that i can't let it rest!

Kind regards, Graem

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Hi Graem

An impressive image.   

Since you asked for comments:

I'd always go down the path of LRGB and sharpen the L layer with deconvolution/sharpening/high pass filter etc - if you apply these techniques to the RGB layer you will increase the chromatic noise and the results will not be as optimal.

The bright stars get bloated simply because they are stretched too much. To avoid the bloat you can do two things: Option 1) don't streach them as much or Option 2) shrink them once you have "overstretched" them.  

Option 1 - The way to implement the first option is to process the star layer separately, this allows you to effectively choose the size and number of your stars in the starfield. What you then need to do is to blend the result into the image. In PS you can do this with masks, the more nebulosity you have in your image the more effort you will need to create the optimum mask. For an image such as your own, the mask can be quite simple since you only have M106 and a few other galaxies. Rob's video link describes this process well. 

Option 2 - shrink the (overstreached) stars. I use the Starshrink plugin which I found to be very effective. However, do not apply this to your entire image because it will also shrink your object(s) of interest !  To use the tool effectively you need to use if with a hide all mask, you then paint on the mask with white at the points you want stars to the shrunk.  For optimum results I've found that it is useful to process large and small stars separately since the tool gives you the option of how much you want to shrink the stars.

The options are not mutually exclusive, so experiment away !

Alan

 

 

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Sorry to jump in, but is that a similar effect to the Morphological Transformation available in Pixinsight? Only played with it a little, but it seems to help - although it can also easily be pushed too far and look unnatural.

Also my first thought. Maybe MT with some deconvolution tossed in just on the stars, just to keep them tight.

 

Thanks for the link. Available from mid July, so that would make it a nice summer-read.

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I really appreciate all your feedback thx a lot!

I just played around with the Starshrink plugin, it works like a dream. Just one thing that then really gets visible are the halo's around the stars. So you'll have a nice tight star sitting on a halo-disc (visible also in the first reply picture of pyrasanth), but maybe one can handle this in some way, i'll have to play around.

@alan4908 I was dabbling with this, but somehow never really got a working procedure. There are tutorials on how to remove stars in pixinsight but nothing really worked for me. When i'm doing narrowband i only do tone mapping now, and use a small software called straton to remove the stars (amazing tool btw). How do you go about separating the stars from the rest of the image to stretch separately?

My experiments with masked stretching also didn't go very well, either i had white halos or dark halos around the stars, to get it right just never worked nowhere close.

Maybe somebody can give me a push in the right direction. I'd prefer to do it 'right' during processing than using a method to reduce star size afterwards, as with my setup, i've got halos left right and center.

Kind regards, Graem

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Try the method I decribed, and practice it (practice makes perfect!). The key to getting it right is to open a new view of the image (in Ps), as this allows you to see the changes you are making in real time so it avoids dark/light halos. The best part about it (if you already have Ps) is that its free and gives you more control.

Its far better to do it mid-process using layer masks, rather than use a plugin as an after-thought. Just keep trying, no-one gets it right overnight (I wouldnt expect them to!)..... well.. not unless you've just attended one of my imaging workshops - where this is covered as a matter of routine. If you are getting dark halos, it means your mask it too strong so you need to apply some negative curves or some blurring to the part of the mask giving you the dark halo.

But, with whatever method you use there will always be some sort of artefact leftover, and there is nothing to be gained from trying to remove it. Besides, concentric halos can look quite nice!

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56 minutes ago, graemlourens said:

How do you go about separating the stars from the rest of the image to stretch separately?

Yes - I agree with Rob.  Before you start, you might want to refresh your knowledge about how PS layers interact with masks - this is the key to understanding how the technique works.   

Alan

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Hi Alan.

Thx will do. I have been in Pixinsight for around 1.5 years, and never touched photoshop much. Will give it a try tough to see if maybe me trying to stick to pixinsight for everything is a mistake.

Kind regards, Graem

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Eventually, you might realise that an image can go through three or four bits of software in order achieve your goal. Some of the best imagers I know use PI for initial processing (ie: DBE), before finishing off in Ps with its layer masking.

Remember: Layer masks are your friend! They can be used to restore burnt cores, combine data from different telescopes/cameras, reduce star sizes, and (with careful use) remove blotches or repair images. The only limit is your imagination ;)

 

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Yes, thats really currently maybe a very narrow-minded attitude of mine to not hop through software, i guess its a beginners approach though, to try and keep things rather simple in the jungle of AP possibilities :)

I'll definitively give this a try. This is my large problem still in processing that i have not mastered at all yet.

Kind regards, Graem

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