Optional Step to Remove Larger Stars (for Star De-Emphasis)

If the Main star mask characterizes all of the stars you want to De-emphasize- then this step isn't necessary. However, this technique will not really do much to the largest stars in the image and it is a challenge to create the perfect initial star mask with MLT with just the right-sized stars. So removing the largest stars is helpful and very easy to do. 

Take the copy of the Main_Mask you made and after naming it "Halos" create a copy of it. Then apply the Closing Morphological Transformation process to it with a structure element slightly smaller than a large star in the mask. Here I use a structure element of 15. Dilate the result by 3 or 5 pixels just to be certain you are going to completely encompass these stars. The image below is a zoomed out view of the image... showing only the very brightest stars in the mask. Name this image Big_Stars .

star_demph_big_stars
Figure 1-  These are the largest stars that remain after Closing. 

 

Now subtract Big_Stars from Halos to remove the largest stars that are unnecessary to adjust. 

star_demph_big_stars
Figure 2 - This Pixel Math expression will remove the large stars from the Halos mask