Mask single pixel deletion

Questions and answers about processing in StarTools and how to accomplish certain tasks.

Mask single pixel deletion

Postby TinySpeck » Thu May 10, 2018 8:39 pm

I'm a new Star Tools user. When creating a mask using Auto / Stars, I sometimes end up with a large number of single pixel mask dots in order to capture the faintest stars in the mask. When I then do the shrink / grow trick to eliminate them, I lose some of my faintest stars too. My faintest stars are only a few pixels large. I've tried experimenting with the adjustable parameters in Auto and can't seem to get the faintest stars without the single-pixel noise.

So is there a way to make shrink/grow only delete single pixels? It seems to be just slightly too aggressive. Or any other way to scrub my mask clean of single pixels?

Thanks for any help!
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Re: Mask single pixel deletion

Postby almcl » Fri May 11, 2018 3:46 pm

Not sure if this directly answers your issue, but I don't find the Auto/stars function works very well on my images.

So instead, I do this: Select Auto but change Selection Mode to Highlights>Threshold (two clicks on the rh arrow button)
set the threshold to say, 60% then click on the do button.

If too few stars are selected go back to Auto and reduce the threshold, if too many, then increase it. It will be necessary (probably) to deselect any bits of nebula that get caught along the way, and to finally invert the mask, but this gives a better result in my noisy imges than the auto/ stars route.
Skywatcher 200P with an astro modded Canon 700d, cls ccd filter, field flattener, guided by QHY 5Lm, PHD2
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Re: Mask single pixel deletion

Postby happy-kat » Fri May 18, 2018 12:33 pm

I have found that is the image is noisy then lots of single none stars are found when doing a mask. If too many pixels are found I just use a shrink then grow to retain the real stars.
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