How to make big/fat/white stars appear tighter
Posted: Mon Nov 12, 2012 2:35 am
This question comes up a lot, so here is a quick guide on how to take care of stars that seem 'washed out' or have large halos.
To make big/fat/white stars appear tighter, there is a special 'tighten' setting in the Magic module. This module allows you to change general star appearance.
What you will want to do, is have Startools create a mask for you that has those big/fat/white stars in them. This is very easy - in the mask editor, click 'Auto', 'Stars'. This preset will usually do a decent job at grabbing all the stars. However, this time, we're only interested in the big/fat/white stars. To grab only those, change the the 'Selection Mode' into 'Highlights>Threshold'. This does exactly what it says on the tin - it grabs only very bright pixels that are bigger than the 'Threshold' parameter (which by default sits at 100%). All you need to do then, is set 'Threshold' to something smaller than 100% (let's say 90%). Now 'click' Do.
If all is well, you should notice that the cores of the big/fat/white stars are now 'green' in the mask editor (meaning they are now part of the mask). You might want to click 'Grow' once or twice to select neighbouring pixels that are also quite white.
Congratulations - you're now working with 'advanced masking techniques'!
Now click 'Keep' to keep your mask and to start using it in the module of your choice (the Magic module in this instance).
If you launch the Magic module with the mask we just created, you'll see it subtly shrinks the big/fat/white stars by default. Very useful for busy star fields that detract from a DSO. But it's not what you're after right now. To accomplish what you are after in this case, select the 'Tighten' setting for the 'Mode' parameter. What you'll notice now is that it gets rid of the halo around big/fat/white stars. It will only get rid of any pixels of halos that are part of your mask. Just so you don't have to go back to the mask editor to 'grow' your mask, for your convenience there is a 'Mask Grow' parameter that temporarily grows the mask, including more of those pesky halo pixels as you increase the setting.
Finally, the 'Iterations' parameter affects the 'strength' of the effect.