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Help processing luminance in PixInsight


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Can someone please give me some guidance on processing a luminance stack in PixInsight. I've looked at a number of web resources and Keller's book but I'm still a bit confused about what I might expect to achieve - what should the end result look like.

Apologies for this being M101 again and the quality of the image but it was high in the sky and convenient for a short night with non-optimal seeing.

The image comprises 19x300s subs (you know I don't know why I didn't take 20 with my OCD and all that) which I've calibrated with 50 each dark, bias and flats, registered and stacked in PixInsight. I've used STF to pull the image from the background and then saved as a jpg so you can view the image. It's taken with an Atik428ex mono on a SW80ED DS-Pro + NEQ6-Pro using SGP and PHD - focussed as best I could recognising the seeing conditions.

M101-Luminance.thumb.jpg.e33d98f42fc3adafe2f5353558b2f5ad.jpg

I think I am getting the hang of processing osc rgb images in PI but I'm not sure of the best approach with a luminance image and what I might expect to achieve.

I've included the fit and xsif file if somone wouldn't mind having a go and showing me what is achievable and what I should typically aim for - and how!

I am keen to try to get to grips with the mechanics before those long dark nights set in - whenever that might be!

As ever many thanks in anticipation of any help/guidance/advice.

Adrian

P.S. ImageAnalysis gives me the following stats on the image:

595f9d351d293_Screenshot2017-07-0715_36_42.png.d3ee385da292ac3997a2dd764bc5c49e.png

Is this good, bad or indifferent? What is 'good' and what is 'bad' or 'in need of improvement'?

Thank you :)

M101-luminance.fit

M101-Luminance.xisf

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Forget the numbers, look at the stars.

As for what to do with luminance: make a stunning b/w image: contrast, sharpness, small stars, low noise, etc.

I'll have a look at your image.

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Looks about right. DynamicPSF confirms the FWHM values for the stars. Which, btw, look nice round, but maybe a little 'fat'. With your focal length (600 mm) and pixel size (4.54 um), you are imaging at 1.56 "/pixel, wich makes the fwhm of your stars 2.8 x 1.56 = 4.4 ". My guess is that either your seeing was bad, or your guiding not optimised.

Unfortunately, this also affects the details you capture in the galaxy. Deconvolution can restore some of the detail, but it's no miracle cure. The lack of astro darkness shows in the noise in your image. To get this down, you would need to shoot a lot more subs.

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Thank you Wim.

The seeing was not good - although it was better than it has been for some time.

The guiding seems good to me from what I can see from the PHD graph, with Total RMS error of 0.81".

I stopped taking subs because it was starting to get light again, in fact I should probably be more ruthless in excluding some taken at the beginning and end of the session.

I wasn't expecting to get a great image; I am just keen to know if I should be doing something over and above what I am trying now.

I appreciate your help and comments.

Adrian

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For this target, I would wait for better conditions. Galaxies are at their best when they show detail. This is better achieved during dark nights with good seeing. Galaxies also benefit from smaller pixel scales (either smaller pixels or a larger focal length).

 

Good luck,

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2 hours ago, ollypenrice said:

It looks pretty good. I do this stuff in Photoshop so I'm not well up on PI but couldn't you use the masked stretch function to hold down the stars while stretching the galaxy?

Olly

Yes, if the background is well behaved. It's easy to stretch noise and 'mottle' with masked stretch. And you run the risk of creating halos around the stars. TANSTAAFL.

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Just now, wimvb said:

Yes, if the background is well behaved. It's easy to stretch noise and 'mottle' with masked stretch. And you run the risk of creating halos around the stars. TANSTAAFL.

So much easier to use Photoshop...

:evil4:lly

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On 7/7/2017 at 16:41, Adreneline said:

Can someone please give me some guidance on processing a luminance stack in PixInsight. I've looked at a number of web resources and Keller's book but I'm still a bit confused about what I might expect to achieve - what should the end result look like.

Apologies for this being M101 again and the quality of the image but it was high in the sky and convenient for a short night with non-optimal seeing.

The image comprises 19x300s subs (you know I don't know why I didn't take 20 with my OCD and all that) which I've calibrated with 50 each dark, bias and flats, registered and stacked in PixInsight. I've used STF to pull the image from the background and then saved as a jpg so you can view the image. It's taken with an Atik428ex mono on a SW80ED DS-Pro + NEQ6-Pro using SGP and PHD - focussed as best I could recognising the seeing conditions.

M101-Luminance.thumb.jpg.e33d98f42fc3adafe2f5353558b2f5ad.jpg

I think I am getting the hang of processing osc rgb images in PI but I'm not sure of the best approach with a luminance image and what I might expect to achieve.

I've included the fit and xsif file if somone wouldn't mind having a go and showing me what is achievable and what I should typically aim for - and how!

I am keen to try to get to grips with the mechanics before those long dark nights set in - whenever that might be!

As ever many thanks in anticipation of any help/guidance/advice.

Adrian

P.S. ImageAnalysis gives me the following stats on the image:

595f9d351d293_Screenshot2017-07-0715_36_42.png.d3ee385da292ac3997a2dd764bc5c49e.png

Is this good, bad or indifferent? What is 'good' and what is 'bad' or 'in need of improvement'?

Thank you :)

M101-luminance.fit

M101-Luminance.xisf

Is this is really taken with Skywatcher 80 ED? How much did you crop? Great looking by the way! 

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14 hours ago, Firas said:

Is this is really taken with Skywatcher 80 ED? How much did you crop? Great looking by the way! 

Thank you Firas. Yes, it is really was taken with a Skywatcher 80 ED DS-Pro and an Atik 428ex mono. I carried out a minimal crop in PI just to get rid of the stacking artefacts around the edges.

I've been using a 414ex and have attempted to image M101 many times over the last 10 months. I decided to liquidate some assests from a previous, long, long ago hobby and treated myself to a 428ex mono. I've only bought a luminance filter so far; I wanted to get some practice using the 428ex just to obtain luminance images.

I know essentially what I am trying to achieve in processing luminance it's just I'm not sure what I am doing currently is best practice - if such a thing exists.

On 7/8/2017 at 16:54, ollypenrice said:

It looks pretty good. I do this stuff in Photoshop so I'm not well up on PI but couldn't you use the masked stretch function to hold down the stars while stretching the galaxy?

Olly

Thank you for the comment Olly - I have tried processing in PS as well and created a mask so I could selectively stretch the galaxy.

With regard to processing is it fair to say I can allow the background sky to be 'blacker' than I might wish to achieve with rgb? When using the image for a luminance layer is contrast the overarching requirement? Does it matter if the background is clipped if it is going to be used as a luminance layer?

Thnak you again for your comments and advice.

Adrian

 

 

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8 hours ago, Adreneline said:

Thank you Firas. Yes, it is really was taken with a Skywatcher 80 ED DS-Pro and an Atik 428ex mono. I carried out a minimal crop in PI just to get rid of the stacking artefacts around the edges.

I've been using a 414ex and have attempted to image M101 many times over the last 10 months. I decided to liquidate some assests from a previous, long, long ago hobby and treated myself to a 428ex mono. I've only bought a luminance filter so far; I wanted to get some practice using the 428ex just to obtain luminance images.

I know essentially what I am trying to achieve in processing luminance it's just I'm not sure what I am doing currently is best practice - if such a thing exists.

Thank you for the comment Olly - I have tried processing in PS as well and created a mask so I could selectively stretch the galaxy.

With regard to processing is it fair to say I can allow the background sky to be 'blacker' than I might wish to achieve with rgb? When using the image for a luminance layer is contrast the overarching requirement? Does it matter if the background is clipped if it is going to be used as a luminance layer?

Thnak you again for your comments and advice.

Adrian

 

 

The luminance layer determines all the final brightnesses. That, by definition, is its role. If it's clipped the final image will be clipped, so avoid this at all costs in the L. I always keep my background above 26 while processing in Ps, knowing that it will easily be nibbled down to 23 where I usually want it to be at the end.

Olly

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12 hours ago, Adreneline said:

 

Thank you for the comment Olly - I have tried processing in PS as well and created a mask so I could selectively stretch the galaxy.

With regard to processing is it fair to say I can allow the background sky to be 'blacker' than I might wish to achieve with rgb? When using the image for a luminance layer is contrast the overarching requirement? Does it matter if the background is clipped if it is going to be used as a luminance layer?

Thnak you again for your comments and advice.

Adrian

 

 

Fyi, masked stretch is a process in PixInsight. So no need for masks. You can safely experiment with settings, especially clipping fraction (try 1-2 %, which isn't as bad as it sounds) and background target level. But as I noted before, it's easy to stretch noise with this tool. PixInsight is a powertool: easily overdone. For darkening the final background, I use the black point slider in histogram transformation, or curvetransformation. Both can give you excellent control.

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Thank you Wim.

Well I have had a go and this is the end result - or maybe not depending on the feedback I get :)

M101_Luminance_integration_ABE-stretched.thumb.jpg.a9dbe128da8ef68efad1a586e6769cf8.jpg

In the end I used PI and PS to set a black point - I went for 20 - hopefully I've not overdone it.

Thanks again in anticipation of your comments.

Adrian

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11 hours ago, Adreneline said:

Thank you Wim.

Well I have had a go and this is the end result - or maybe not depending on the feedback I get :)

M101_Luminance_integration_ABE-stretched.thumb.jpg.a9dbe128da8ef68efad1a586e6769cf8.jpg

In the end I used PI and PS to set a black point - I went for 20 - hopefully I've not overdone it.

Thanks again in anticipation of your comments.

Adrian

Good! Have you tried LHE (in PI) for emphasizing contrast within the galaxy? Doubtless to the rage of PI purists I always export an LHE-modded image into Ps to use as a layer. I rarely want to keep all of it across the entire image.

Olly

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23 hours ago, wimvb said:

Fyi, masked stretch is a process in PixInsight. So no need for masks. You can safely experiment with settings, especially clipping fraction (try 1-2 %, which isn't as bad as it sounds) and background target level. But as I noted before, it's easy to stretch noise with this tool. PixInsight is a powertool: easily overdone. For darkening the final background, I use the black point slider in histogram transformation, or curvetransformation. Both can give you excellent control.

I tried the masked stretch but not sure the end result is as good as repeated HT stretches - unless I'm doing something wrong.

5964a1a51f462_M101_L_int_ABE-MSPS.thumb.jpg.b87efb7dfeb57b1a1576b80911ea86d9.jpg

 

On 7/10/2017 at 08:17, ollypenrice said:

The luminance layer determines all the final brightnesses. That, by definition, is its role. If it's clipped the final image will be clipped, so avoid this at all costs in the L. I always keep my background above 26 while processing in Ps, knowing that it will easily be nibbled down to 23 where I usually want it to be at the end.

Olly

Thanks Olly. In both cases I set the background at 20 in PS in an attempt to improve the contrast.

Thanks again for all your advice.

Adrian

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6 minutes ago, ollypenrice said:

Good! Have you tried LHE (in PI) for emphasizing contrast within the galaxy? Doubtless to the rage of PI purists I always export an LHE-modded image into Ps to use as a layer. I rarely want to keep all of it across the entire image.

Olly

Hi Olly,

I think our post crossed in system. No I've not tried LHE - thank you - something else to try. One thing I am discovering is I need a much more disciplined approach to saving and naming files. Never mind being "Lost in Space", I'm getting lost in my own subdirectories.

Thanks again.

Adrian

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6 minutes ago, Adreneline said:

Hi Olly,

I think our post crossed in system. No I've not tried LHE - thank you - something else to try. One thing I am discovering is I need a much more disciplined approach to saving and naming files. Never mind being "Lost in Space", I'm getting lost in my own subdirectories.

Thanks again.

Adrian

I just do regular 'Save As' followed by P1 (Processing 1), P2, etc. This is a masterpiece of self dicipline ending with an image called Object X FINISHED.

Erm, then come things like Object x FINISHED V7d small stars background red+ core contrast down...

The best laid plans...

:icon_mrgreen:lly

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On 7/11/2017 at 10:57, ollypenrice said:

Good! Have you tried LHE (in PI) for emphasizing contrast within the galaxy? Doubtless to the rage of PI purists I always export an LHE-modded image into Ps to use as a layer. I rarely want to keep all of it across the entire image.

Olly

I used LHE (carefully) and combined the result with an image of M101 from earlier in the year. A bit more tweaking in PI and this is the end result:

59663db02a989_M101-LumRGB-cropped.thumb.jpg.d56cd21f3d73d76fbbe80864570d19e2.jpg
Compared with the original without added luminance:

59663dd70bf39_M101-withflat.thumb.jpg.9e27ed6d6d459949ff2c0cc9da221848.jpg

Well I don't think it is any worse but I'm not sure it is a lot better! Learnt lots though!

Many thanks.

Adrian

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