how to protect stars core when using Masked stretch?

[lucchett]

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

[jkmorse]

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

[lucchett]

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

[jkmorse]

You can always use clonestamp to protect everything but those few stars but I recognize that is a slow process.

[lucchett]

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
 

[Warhen]

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.

[lucchett]

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

[jkmorse]

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