Hi Jeff,
Glad to see you here! (Jeff and I often meet at dark sites around the area).
... ran successfully to make a subtle improvement on the dark areas of a nebula image (Rosette)
So you felt that the script didn't do much, correct? Do remember you can adjust the "amount" parameter as well as the number of iterations.
If you want an even more controlled application of this script, this is how I'd suggest using it:
1- Check "Extract mask"
2- Run the script
3- Un-do whatever the script did to the image
4- Apply the mask as a mask
5- Adjust the histogram/curves of the mask (the bright areas in the mask are the ones defining the dark areas in the image)
6- Adjust image histogram to perform the "darkening"...
One of the good things of doing it like this is that by using real-time previews, on step 6 you can get instant feedback of how much "darkening" you're applying, rather than running the script and wait to see whether you like the results or not. The other benefit I see is that on step 5 you can better control the areas that later will be darkened. What I would usually do at that step is to relax the areas that look brighter in the mask, that is, reduce a bit their brightness in the mask (to avoid darkening too much the areas that are already dark in the image) and maybe increase a bit the brightness in the other areas. This usually results in darkening the areas you really wanted a bit darker, not the ones that were already dark.
