This plugin calculates the saturation from a picture with four different saturation algorithms:
2. (max-min) / sum
3. like HSV: (max-min) / max
4. like HSL: (max-min) / (max+min)
Build and install it with:
$ gimptool-2.0 --install elsamuko-saturation.c
You'll find it then under Colors->Components->Calc Saturation.
The resulting b/w image can be used as layer mask to filter saturation. For example the script elsamuko-naturalize below uses this plugin to give oversaturated images a more natural impression:
(cc) by Edgar Chambon 94
If you like it, hug someone.
Update1: Fixed a check if used from script
Also: Added a sample script, which uses this plugin.
For all scripts together, go here: