The purpose of Layer Masking is to try to separate some parts of a photograph from others, so as to be able to work on them independently. In astrophotography usually stars from background or background from nebulosity. You can leave it as it is or work on it with Levels to accentuate the black or white areas to gain more or less effect. The general practice is to use Layers to darken the black and lighten the white to a reasonably far extend to ensure the black as fully as possible protects and the .

Back to Processing with Photoshop. Unsharp Masking and High Pass. The more commonly used is Unsharp Masking. Easy enough to use, but it has drawbacks as you take it to extremes.

This method, in Photoshop, is called the J GaBany method. What Saturation does, but without inducing noise or other artefacts. Make three copies of the frame, these will lie above each other in the layers list. With the top one active, make the blending mode Luminosity. The second one, Soft Light.

Open the dialogue panel, and click the Channel button which should have RGB on it. It will open alternatives of Red, Green and Blue. Click your choice and the dialogue square and diagonal line will change to that colour. Dragging the line upwards will increase the intensity of that colour. All other facets of the dialogue box will perform as it does for RGB.

This is a way to make a large number of field stars smaller, it uses the Minimum filter in Photoshop. This will hide the Marching Ants so you can see the next actions without the Ants spoiling things. Clicking on Control-H again will bring them back.