I did a quick screen recording of a ‘one color monochrome’ image. That image I did a few month ago from a JPG in GIMP 2.10, using layers, cutting a mask etc.
I wanted to try if one can do the same in darktable from the RAW image – and yes, it’s easy and fast.
The result is far from perfect. The image was rather poor to begin with. The sky is totally blown out. The camera was new and I am still earning. And one can only learn from mistakes. The image still has some color pixel errors. I leave it like that for now.
You can ask – why use a parametric mask and not just the lasso (drawn mask) in the first place? It’s correct, there is only one red element in the image, but imagine you have several, like blossoming flowers, than the parametric mask will be quite handy.