The last month I have been fortunate enough to get out to shoot the aurora a few times. On March 18th the moon was almost in new moon phase so the stars were very prominent in the sky. I headed out North and West of Calgary to find some darker skies and was able to get some pretty cool photos of the Northern Lights show that night. However, when I was editing my pictures I did not think my stars stood out enough. I tried to find some tutorials/explanations on editing stars, but most I found were about the milky way specifically and a lot of the time required that you download someone else's actions. So I came up with a way to do it myself. Any comments or suggestions are always appreciated if someone has an easier/better way of doing this. This is just a basic tutorial outlining what I have done and I assume you know some of the basics about Photoshop, such as duplicating layers and using adjustment layers.
Here is my starting image. I have already applied all my edits except for what I will do with the stars.
Make two copies of your background image. Then select the first copy. Go to Filter > Noise > Dust and Scratches.
Set the radius so that you can no longer see the stars in the preview. This seems to generally be a low value. Then adjust your threshold. I've made copy #2 invisible so you can see what happens to the photo after you've made your adjustments.
Next select copy #2 (make sure it's visible) and go to Image > Apply Image. Select copy #1 in the Layer option. Set blending mode to Subtract, Scale to 1. The image below shows what you get after Apply Image.
Next open a Levels adjustment layer and move the sliders over to the left. You will see the stars stand out more. The tree and bushes that were backlit by the green of the aurora are also affected but this will be dealt with in another step.
I wanted to remove the blue color in some of my stars. So I opened a Hue/Saturation adjustment layer and desaturated my stars completely as this is what I wanted for my image.
Select copy #2, Levels and Hue/Saturation adjustment layers and create a group. Make this group a mask. Delete copy #1 as you do not need it any more.
I made the blending mode of my group Screen. This where I can make adjustments and fix the edges of the trees and bush. I paint out the parts of the image that I don't want my star adjustment group affecting using the black brush. Make sure you have selected the layer mask of the group before you start brushing.
I thought the Levels adjustment was just a bit much so I changed the opacity of just that layer.
For the finished image and more of my aurora photos check out the album here.