Hello afre,
You flatter me.
I tend to make my own newbie filters for personal use. They aren’t ready for release.
IMHO, you are underestimating your filters skills! 
Thanks a lot indeed for your suggestions.
My question was just out of sheer curiosity because I do think you are quite expert on the G’MIC stuff
In all truth, every day I took so many pictures at work of my samples that I have hardly any time left to improve them (e.g. via sharpening) later on. Luckilly my reflex is quite forgiving…
Best of luck with your father!