Star Size
adapted from Photoshop Astronomy by R.Scott Ireland

Stars can never be small enough to suit us--Pinpoint stars are what almost everyone wants to see. Unfortunately they're usually larger than that in our images. Here's one way to deal with them:

  1. Open your image
  2. Duplicate it by dragging it to the duplicating mini-icon.
  3. With the duplicate layer active, use Select > Color Range to select one of the brightest stars with the normal eyedropper.
  4. Use the + eyedropper to click on one of the medium brightness stars and then adjust the Fuzziness slider until the stars that you want to shrink are selected. Be careful not to select the faint stars because those are already small enough. Click OK to continue
  5. We want to extend the selections to beyond the saturated star centers so that color information is included in the selection area, so use Select > Modify > Expand with a value of 1 to 10 pixels depending on your image.
  6. Create a layer mask by clicking on the Add Layer Mask mini-icon. Notice how the selection is automatically transferred to the mask.
  7. Make the mask visible by Alt-clicking it
  8. Check the mask for any of your target object. Use a soft black paintbrush to mask out any areas you don't want to have changed by further processing.
  9. Give the mask a medium Gaussian blur using Filter > Blur > Gaussian Blur... Adjust the radius so that the star edges are soft, typically from 2 to 5 pixels.
  10. Click the copy layer's image thumbnail
  11. Apply a minimum filter using Filter > Other > Minimum... with a radius of 2. This may make your stars a bit diamond shaped rather than round, but that's okay.
  12. Adjust the opacity of the copy layer downward to make the stars more natural looking. The value that works best for you will depend on your taste in stars and your image. Something in the range of 50 to 75% will probably be fine.
  13. At this point if you're not happy with the overall star brightness, you can apply a curve.
  14. If you're happy, merge all the layers and save.
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