This probably explains it: https://fstoppers.com/photoshop/selective-color-possibly-best-tool-photographers-7954
and there are a couple of videos about it too.
If you're interested in developing a new plugin for gimp 3, that would be a good candidate, because it's been hotly sought after from ex-photoshopers.
@eugenialoli
So, I guess I have still to watch some of the videos - anyway, I suppose you had tried Colors -> Channel Mixer
@gwidion It's not the same thing unfortunately. CM changes the whole image, the Selective one only changes only small parts of one color. So basically, if I have an ultramarine blue, and want to change it to cyan. And it would affect only that color in the image, not the whole image.
@eugenialoli so, this part of affecting just a color window is similar to the selection existing in the HSV mapping, also in the color menu?
@gwidion The easiest way to understand it, is to go to https://www.photopea.com and load a colorful picture in it. Then, use Layer - New Adjustment Layer - Selective Color. Then play with it. Photopea has cloned it from Photoshop, so even if you don't have photoshop, you can investigate it there. It's the best way than trying to understand it second-hand via articles or videos.
@eugenialoli Hi - I am late building a working GIMP 3 build environment on my computer - But I checked the functionality online -
Yes, it is a matter of building a GEGL plugin targeting the appropriate channels. Once one is more or less proficient in it, it should take a couple of hours (I am not, yet) ,I don't think layer effects in GIMP 3 can be individually masked, though - the workaround for that is having a layer copy, with a mask, and apply the effect on that.
