How to deselect areas of a star mask?

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How to deselect areas of a star mask?

Postby 404timc » Wed Feb 05, 2020 2:39 am

Hi - first post here. Let's say I create a star mask for my image but I only want to target stars in the edges and corners. After creating a star mask for the image (all stars), how can I easily de-select those stars in the center of the image so that I'm only targeting the stars in the edges/corners? I hope my question makes sense.

Thanks,

Tim
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Re: How to deselect areas of a star mask?

Postby happy-kat » Wed Feb 05, 2020 9:51 am

Hi
I would use the lasso tool, then you start drawing the lasso with your pointer on a selected star then continue around the area to unselect.
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Re: How to deselect areas of a star mask?

Postby 404timc » Wed Feb 05, 2020 1:35 pm

Well, I was trying to use the lasso to deselect but it would just wind up creating a solid mask in the center of the frame. I guess I could then lasso it again to deselect it but you’d have to trace the original route exactly or you’ll have remnants to deal with. I’m sure there is something I’m missing though. Is there a deselect lasso mode like PS where I can lasso a large area of a star mask to deselect all of the star masks in the area I draw the lasso around? Right now when I do that, it just fills in the entire area with a solid mask.

Tim

happy-kat wrote:Hi
I would use the lasso tool, then you start drawing the lasso with your pointer on a selected star then continue around the area to unselect.
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Re: How to deselect areas of a star mask?

Postby happy-kat » Wed Feb 05, 2020 4:25 pm

I use the lasso tool, then you start drawing the lasso with your pointer on a selected star (i'e green area) then continue around the area to unselect, everything previously selected is deselected.
Inversely, if when you start drawing the lasso with your pointer on a not selected area then continue around the area to lasso everything is then selected.

The reason it fills in the area solidly for you is you pick an area not already selected as you start to draw the lasso.
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Re: How to deselect areas of a star mask?

Postby almcl » Wed Feb 05, 2020 5:57 pm

Here's a method that works for me.

Select all the stars (auto, stars, do):
Select stars.jpg
Select stars.jpg (35.83 KiB) Viewed 1300 times


then lasso the area you want to deselect the stars in:
Lasso.jpg
Lasso.jpg (32.12 KiB) Viewed 1300 times


Now switch brush mode to something like 'flood fill lighter pixels' (other modes will also work) and then click inside the lassoed area:
reset brush mode.jpg
reset brush mode.jpg (32.7 KiB) Viewed 1300 times
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Re: How to deselect areas of a star mask?

Postby 404timc » Wed Feb 05, 2020 6:49 pm

Awesome- thank you both very much. As I figured, more than one way to get the job done.

Tim
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Re: How to deselect areas of a star mask?

Postby admin » Thu Feb 06, 2020 4:55 am

Hi Tim,

Here's another one;

Select all stars with your favorite method (for example, Mask->Auto->Stars). Then, still in the Mask editor, click Auto, for 'Selection mode' set 'Radius (use Threshold)', and set 'Old Mask' to 'Subtract New From Old'. The 'Threshold' parameter will function as the radius of a circle that needs to be erased. Try setting it to ~35% fo starters. Hit 'Do' to see the result. From the here Undo and Auto again to try a new parameter if needed.

What is happening here is that the Auto mask generator is generating a new mask, and is told subtract from the old mask ('Old Mask' is set to 'Subtract New From Old') what it just created. E.g. it generates a perfect circle, but subtracts that perfect circle from the old mask, setting anything that was 'on' inside the circle to 'off'.

Hope this helps!
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