m17 - starmask difficulty

[mmnb]

Lately I've found it pretty easy to create starmasks with MLT (I used to have a really hard time with the star mask tool, trying to get the noise threshold just right). My typical workflow has been to create a small star mask with MLT, a big star mask with range selection, take the max of those to make a final star mask.  I then take the lightness channel, lo pass filter it, stretch, paint out rings from bright stars and then subtract the star mask to make the nebulosity mask.  In some nebulas I will use the red channel instead of lightness to get a better nebula "shape".

This linear M17 image (Hyperstar C14, EOS 60Da ~20 exposures) has been processed up to PCC. I am having a lot of trouble getting a good starmask....making the threshold low picks up nebulosity (there are some really bright regions in there....I am honestly not sure if they are poorly resolved stars?).  Is the right solution to clone paint that stuff away?  Or am I just not making star masks competently? 


https://drive.google.com/open?id=1vtFBJJ8RWCDvykjMt3kClM6vfWTrzp5a

[pfile]

you might try using the StarNet module to make star masks. pretty foolproof if you can get it installed.

rob

[mmnb]

I installed Starnet a few months ago, I haven't had great success with it in my hands.

I extracted the L channel, stretched and then did an MLT-based star mask and a Starnet++ one (binarizing both representatively).  I miss some stars in both, but Starnet++ misses more and gives some weird looking artifacts.

I am always surprised that more people don't have trouble with star masks, makes me wonder if it is just me.

[pfile]

well you can of course add together the two masks you've generated if there are some stars that StarNet picked up but MLT didn't.

i think generally when you have stars that are buried in nebulosity it's a tall order to dig out the stars. it can be done, but it may require tweaking a copy of the original image to first produce more contrast between the stars and nebula.

rob

[mmnb]

ok, I feel better knowing that pulling out some of those stars does indeed take a bit more effort.
stretching and getting rid of the last dregs of nebulosity with clone painting seem to do the job for me mostly.

[hvb356]

You may try MaskGen.js

[Herbert_W]

Hi,

yes, GAME MaskGen is the solution.
Set the parameters carefully and you have a perfect star mask :-)





Best regards!
Herbert, Austria

[hvb356]

Dear Herbert, did you say GAME?
Hartmut

[Herbert_W]

Hello Hartmut!
Sorry ... my mistake.
GAME ist another great Script from HvB ... 

[freed]

Maskgen is a really cool script. In particular, you can pick which stars to mask by magnitude which can be vey useful.

[mmnb]

Very very nice.  I thought the offset was due to my collimation error...but it really looks offset after blinking the mask...
Hmmmm wonder why the astrometric solution seem to be off slightly (I used PCC to get the astrometric solution...having trouble grabbing coordinates from my original images for some reason).

[hvb356]

Please check imagesolver distortion correction and solve with higher magnitudes (16..17)

[mmnb]

That fixed it.

Easy to manually fix...but I am ignorant about why there seem to be a few reasonably bright stars missing from the mask?
Just not in the catalog for some reason?

[hvb356]

Dear friend,
that's good. The "bright star" at pixel coordinates 329, 141 is probably an infrared object named WISEA J182007.42-161830.6 .  Candidates for IrS are in general the Sun and the planets, certain stars, nebulae, and galaxies.
Thank you.

[mmnb]

Thank you for doing this for me, I just presumed that IR objects wouldn't show up.
Thanks for all the great advice, perhaps I can stop complaining about star masks now