Because of some very local details I went for a drawn mask.
First a rough contour and then local fine tuning including changes of feather radius. However, trying to edit in restricted edit mode, adding and deleting nodes, (cnrtl-)clicking and moving individual (feather) nodes was very, very cumbersome. Sometimes it worked, most of the times nothing happened. What was supposed to be a quick local edit became an hour at least (and lots of crtl z’s).
I think darktable isn’t made for the kind of very precise localised work you seem to need here.
That kind of very precise masking is more the domain of Gimp, Krita and similar bitmap-oriented programs, where you can create masks with pixel precision. It’s also the kind of work where a graphics tablet is very helpful.
I never said it wasn’t possible. Just that it’s not what dt is designed to do, and so might not be the best tool for the job if you need very precise masking.
After all, you can drive a screw with a hammer, but I find a screwdriver easier for that job. Otoh, I wouldn’t want to drive a nail with a screwdriver…
Trying to stay in one environment has also its advantages. I cannot recall GIMP having the same feather options - especially useful for the feathers on breast and head. For the eye feather is not needed and relatively few pixels are involved (Fuzzy Select works fine enough).
If it’s just about those results you demonstrated in jpeg, that can be done in less than a minute using the drawn and parametric mask. Provide your raw file and I’ll demonstrate it to you as a video.
Usually I think for fine detail you will get the best results starting with some version of a parametric mask and then just enclose the area in a rougher drawn mask…here I just did a vary quick parametric mask with a rough circling of the area and about three or four turns of the mouse scroll in the Tone EQ…reduced the opacity…obviously just working from this jpg download and no real effort on the mask or TE settings…total time maybe 60 seconds…
I have not looked into darktable’s source code. But when you use OpenGL for example and you want to pick (select) a point on the screen you do not want to select one single pixel - you want to select the neighborhood and get a hit. But if there is some relative, or absolute, margin this would make life (picking) easier.
