Starmask: either creates large fluffy stars or small almost square stars

[Nocturnal]

Hi,

I'm trying to use the starmask module to create, well, a star mask. The problem I'm having is that the mask looks nothing like the stars in my image. My stars aren't *that* small but they're not in need of masks as generous as SM creates them. When I decrease the smoothness parameter I eventually get smaller stars but they're more square than round. I probably don't understand what this tool is for. To be honest I've never had it create a mask that looks remotely like the stars I want to protect. Shouldn't it create stars with comparable FWHM values as the stars it's protecting?

[Harry page]

Hi Sander

Star masks are fun  8)

If you just looking for a very sharp mask the size of your stars , just alter the mode to structure detection  . If you are looking for something not too fluffy you can reduce the smoothness a bit and reduce the growth to zero   ( this is in Star mask mode )

See how you get on

Harry

[Nocturnal]

Hi Harry,

I saw that option but didn't want to detect the whispy nebulosity I want to process (ie. not mask) so I didn't try it. Now I will

Thanks for reading and commenting!

[Juan Conejero]

Sander,

If you upload the image I'll try to give it a crank as well.

That image seems a relatively easy target for StarMask. I'm sure we can find an intermediate step between fluffy and square 

[Nocturnal]

Hi Juan,

I'll upload an image tonight.

[Nocturnal]

Here is the image Juan: http://www.tungstentech.com/files/SH2_240_preview05.tif

I tried structure detection and that works a little better but now it's a binary mask (which I realize I can soften) and there are still squares in it here and there. Strange.

[Harry page]

Hi Sander

Here is my go



Harry

[Juan Conejero]

And this is mine:

http://forum-images.pixinsight.com/legacy/SM/20100114/StarMask-1.jpg

If you want a really exhaustive star mask, try applying an aggressive HDRWT before SM:

http://forum-images.pixinsight.com/legacy/SM/20100114/StarMask-2.jpg

HDRWT used in this way will "flatten" the image throughout a wide range of scales, which facilitates StarMask's work. With this technique, we've been able to generate star masks of the M42 region, including all stars down to the Trapezium.

[Silvercup]

Hi Sander:

You can fine adjust the starmask shape to the stars shape with some MorfologicalTransformation->Erosion. You can realtime preview the efect by activating the mask in the main image and applying erosion to the starmask.

Silvercup

[Nocturnal]

Thanks everyone, I think my mask is better now. Still curious who'd want such a big blurry mask. Maybe the defaults need to be adapted? You know follow POLS (principle of least surprise) like Ruby does

http://en.wikipedia.org/wiki/Ruby_%28programming_language%29