two problems creating masks

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

two problems creating masks

Postby micheleorsini » Tue Feb 27, 2018 7:48 am

Hi,
I was processing my latest image when I realized that after deconvolution some star profiles looked weird, so I looked at the star mask that should protect them and I found a couple of problems:

1. when you select "stars", fat stars are not selected, I had to edit the mask covering al big stars by hand. I always thought that "stars" imply fat ones but this is not the case. The best option I have is to make two different masks and the blend them outside startools (not to interrupt the processing) with an external tool
2. a considerable high number of normal stars where included selected in the mask, see the attached image, all those not masked stars will have an horrible profile after deconvolution (white irregular spots are my attempt to correct the mask, but at the end I gave up masking and deconvolving because it was an endless work to cover all remaining stars)

mask.PNG
mask blended with image
mask.PNG (443.66 KiB) Viewed 987 times


maybe this case is only an incorrect usage of the deconvolution module: field resolution is 2.5 arc/px so there should be (hopefully) nothing hidden by the seeing to be revealed, so maybe, the mask limit is caused by the resolution being too low

any comment?
micheleorsini
 
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Re: two problems creating masks

Postby Rkonrad » Tue Feb 27, 2018 2:44 pm

Hi Michele,

When you deconvolute you are given the option of startools auto creating a mask. From my experience, this is 99% the best option. You may or may not prefer to lower the mask fuzz but I find it also accurate.

This way you don't have to fiddle with creating your own mask. If you want to also mask the stretched stars (as opposed to linear which is "fat stars", you can, after auto creating, click cancel during the deconvoluting process (it will retain the mask) and then mask normal stars and select "add to old". Just make sure they are equally "grown" so they match the linear stars.

Hope this is clear.

Richard
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Re: two problems creating masks

Postby micheleorsini » Fri Mar 02, 2018 7:38 am

Hi Richard!
I used automask only for a long time, then I realized that sometimes it is better to make a few tricks as recommended by Ivo himself (e.g. create mask, then shrink and grow twice). My problem was that I wasn't aware of the option of adding to masks, now that I know I can have the best of two worlds

thank you!

Michele
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Re: two problems creating masks

Postby Rkonrad » Fri Mar 02, 2018 6:50 pm

Hi Michele,

From my experience, the shrink and grow twice routine usually has to do with stopping the mask from grabbing noise (which I do quite a lot) but if linear (fat stars) are selected for deconvolution will be no noise at all. Good luck.

Richard
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Re: two problems creating masks

Postby micheleorsini » Fri Mar 02, 2018 7:53 pm

Exactly!!

The point is that I wasn't aware you can add the to two masks, so until now (thank you again!) my procedure was

1. use "stars" and the trick for rejecting noise
2. fat stars are left out: add them manually

but yes, I agree with you, most of the times I use the auto creation

M.
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