Star masks

[tooth_dr]

Would anyone be able to point me in the right direction of a star mark tutorial, and when to use it.  If I open an image in PS and then start stretching, when do I need to start masking?

(Photoshop and APP used)

 

Thanks in advance

Adam.

[AKB]

I could do with a better understanding of this too, but I have to say that I’ve all but given up on star masks since I started using Starnet++ to separate stars from background.

Tony

[tooth_dr]

4 minutes ago, AKB said:

I could do with a better understanding of this too, but I have to say that I’ve all but given up on star masks since I started using Starnet++ to separate stars from background.

Tony

Hi Tony.

Starnet is really brilliant.  Do you do like a a very light stretch of the original image in a separate later and add to the stretched starless version? At what stage do you remove the stars using Starnet?

[AKB]

I do find that it works better (for me) with a light stretch to begin with (typically so that I can start to see the nebula.). I then process separately, often adding a slight reverse stretch to diminish the stars before combining in a non linear fashion...

 

[wimvb]

Blair McDonald of the Canadian RASC wrote (a long time ago) an article about masked stretch in PS. I can't find it atm, but maybe there's more info here.

http://www.astronomersdoitinthedark.com/dslr_llrgb_tutorial.php

[wimvb]

Found a reference from 2014

https://astrodoc.ca/wp-content/uploads/2014/11/Brecher_JRASC_Dec2014.pdf
unfortunately only a reference in the contents, but there is/used to be an archive

Blair MacDonald, imager’s corner: masked stretch

Edited December 4, 2020 by wimvb

[Jm1973]

Not sure if this is what you mean exactly, but in PS you can do Select>Colour Range then choose Highlights to select the brightest points only, which is usually the stars (unless you have already blown out the white point).

Demonstrated in this video (start at 15:18) 

 

[tooth_dr]

56 minutes ago, Jm1973 said:

Not sure if this is what you mean exactly, but in PS you can do Select>Colour Range then choose Highlights to select the brightest points only, which is usually the stars (unless you have already blown out the white point).

Demonstrated in this video (start at 15:18) 

 

Thanks for the link 👍🏻
A useful tool indeed
 

 

[Scooot]

Here’s a guide Adam,

https://www.lightvortexastronomy.com/tutorial-producing-masks.html#Section3

[tooth_dr]

Thanks Richard - that will be useful for me as I'm just starting out with PI.  I got my download book today, so am reading through it now.

[ollypenrice]

Steve Richards outlines the star masking method I use in Ps in his book Dark Art...

But I rather agree with AKB that Starnet offers a better solution than masking, which I no longer use. When I did use masks I used them on the linear image and very gingerly for a soft initial stretch or two. After that I discarded them.

I outline my Starnet method here if it's of interest: 

 

Field stars (as opposed to stars placed over nebulosity) can be controlled using two stretches, a hard one for the galaxies and a soft one for the stars. If you get the background sky to exactly the same brightness in both stretches (this is vital) it is a simple matter to place the soft 'star' stretch over the hard 'galaxy' stretch and erase the top layer wherever it covers a galaxy or faint fuzzy. This, I think, gives the best result by far but only on images with few stars placed over nebulosity. Here are two examples of this method.

https://www.astrobin.com/335042/?image_list_page=2&nc=&nce=

https://www.astrobin.com/419975/?nc=user

Olly