How to place spreads on a specific color of an image

Hello to all!
I’m new to 4V and I’m trying to create a patch that replaces the color of an image with a pointcloud in 2d.
I made a this with the delaunay element and then I blended an image over it.
I would now like to know if it was possible to delimit a color area to generate my spreads (for exemple the generated points will be only in the brightness or the darkness of the picture) ?
And big thanks for this incredible software!!!

I think that Pipet is what are you looking for or at least is the only ready made way to get the rgba (or hsva) per pixel of an image