This is a technique
attributed to Russ
Croman, that I found documented on the
Shadows Remote Observatory. At the end of the procedure is a
link to download a PhotoShop Action. The file contains two actions...
one for an RGB image and the other for gray scale. I couldn't get one
action to work for both images. I guess I need to work on my PhotoShop development
1. Star Selection (from Russ Croman):
2. Make a grayscale copy of the image. I'll call this image #2.
3. High-pass filter image #2 with a radius of one pixel.
4. Apply a Gaussian blur to image #2 with a radius of one pixel.
5. Invoke Image->Adjust->Threshold.
6. Adjust the Threshold Level one click at a time until just the
stars are white and everything else is black.
7. In the original image, in the Channels Palette, create a new
channel. Name it "Stars." Choose "color indicates
8. Paste image #2 into this channel.
9. Make just the RGB channels visible (i.e. make the Stars
10. Discard image #2.
11. In the original image, invoke Select->Load Selection. Choose
the Stars channel you just created.
12. Invoke Select->Expand and expand the selection by a few
pixels (e.g., three).
here to download the PhotoShop action file. This has been tested with PhotoShop CS3
4, 5 & 6.