To suppress the noise in astro images I successfully use the freeware demo version of NeatImage
My practise is to use NeatImage as one of the last post-processing steps, after which I might - if necessary - do some final histogram adjustments In Photoshop.

The top part of this image (please click to enlarge) is before applying NeatImage, the middle part is after applying NeatImage [I used the default noise filter settings] and the bottom part is after final histogram adjustments in Photoshop.
Please note the noise reduction.

As NeatImage has an extensive functionality I hereby give a shortcut: the Quick User Guide (based on NeatImage version 4.5).

  1. Open image
  2. Tab: Device Noise Profile
  3. Draw a large enough rectangle in a noisy area with as few stars as possible
  4. Press the Blue ruler button
  5. Press the Green auto fine tune button
  6. Select tab Output Image
  7. Click on the Apply button
  8. NeatImage now recalculates the noise suppressed image
  9. Use the NeatImage Flower button (top right) to blink compare the difference
  10. You might use the 'Noise Filter Settings' tab to play with the filter settings and see the results thereof
    Via Tools you can even activate Advanced mode for advanced filter settings
  11. Save the image (via Options|Job Default you can specify what filename suffix to use, e.g. _neatimage)
    Note: the Demo version of NeatImage only saves as .jpg