Author Topic: how to protect stars core when using Masked stretch?  (Read 2320 times)

Offline lucchett

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Hi,
using MS often ruins the star cores.
this happens as soon as only a few pixel of the star are saturated.

this usually impact only a small set of bright stars.

I tried the HSV repair script but couldn't really make it work.

How would you solve this?

Thanks a lot,
Andrea

Offline jkmorse

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Re: how to protect stars core when using Masked stretch?
« Reply #1 on: 2015 July 14 11:51:38 »
One way would be to stretch the image twice, once with MS and once with HistogramTransform for the stars.  Then, using a star mask, substitute the HT stars for those from the MS image.  Harry in t his Astroshed tutorials, has a tutorial on doing the opposite, subbing MS stars into an HT image, but you would just need to reverse the process.

Hope that helps,

Jim
Really, are clear skies, low wind and no moon that much to ask for? 

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Offline lucchett

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Re: how to protect stars core when using Masked stretch?
« Reply #2 on: 2015 July 14 13:15:21 »
Thank you Jim.
I know that process and actually applied to my current image.
Except few big stars, I prefer the MS results.

But I will think about this.

Thank you,
Andrea

Offline jkmorse

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Re: how to protect stars core when using Masked stretch?
« Reply #3 on: 2015 July 15 13:42:50 »
You can always use clonestamp to protect everything but those few stars but I recognize that is a slow process.
Really, are clear skies, low wind and no moon that much to ask for? 

New Mexico Skies Observatory
SBIG STXL 6303E w/AOX
Planewave CDK17 - Paramount MEII
Planewave IFR90 - Astrodon LRGB & NB filters
SkyX - MaximDL - ACP

http://www.jimmorse-astronomy.com
http://www.astrobin.com/users/JimMors

Offline lucchett

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Re: how to protect stars core when using Masked stretch?
« Reply #4 on: 2015 July 16 04:16:42 »
Jim, You mean masking the MS process?
I tried but it doesn't work (for now), it leaves a darker center.

What I have been able to do with some success is to create a star mask, erode the star profiles and apply convolution to the star's core.

Not very elegant, but does improve the problematic stars.


Andrea
 

Offline Warhen

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Re: how to protect stars core when using Masked stretch?
« Reply #5 on: 2015 July 18 13:13:05 »
Andrea, just so we're on the 'same page', I think the issue is that MS protects the cores too well- you therefore end up with a dot of intense color saturation. I agree with you, although the HSV script was encouraging- it often doesn't work well. I prefer the contrast of HT to the saturation protection of MS, so that's how I generally roll.
Best always, Warren

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Offline lucchett

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Re: how to protect stars core when using Masked stretch?
« Reply #6 on: 2015 July 18 14:38:45 »
Thanks Warren,
It is an interesting point of view, which I didn't consider .
In this case a very light mask on the star core should work or help.
Andrea

Offline jkmorse

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Re: how to protect stars core when using Masked stretch?
« Reply #7 on: 2015 July 20 12:48:03 »
Andrea,

Another thing to consider is using a star mask and then applying a convolution filter to soften the stars.  I often use that to get a nice even and smooth look to stars that may have gotten out of whack in the deconvolution or sharpening processes.

Best,

Jim
Really, are clear skies, low wind and no moon that much to ask for? 

New Mexico Skies Observatory
SBIG STXL 6303E w/AOX
Planewave CDK17 - Paramount MEII
Planewave IFR90 - Astrodon LRGB & NB filters
SkyX - MaximDL - ACP

http://www.jimmorse-astronomy.com
http://www.astrobin.com/users/JimMors