Why is the mask not sharp?

[flora1947]

I created the following object using the cylinder primitive. I have smooth shading turned off . But I am unable to have the mask stay cleanly within the edges of the face.

This is what it looks like currently:

I want to paint masks that look like this:

Hope that makes sense. Thank you.

[Holger_Schoenischka]

Not possible. The mask works exactly like the Vertex color it bleeds at the edges.
But if you want to extract exact areas, you can still do this.
This helps to understand:

Nomad sculpting (vertex painting vs texture painting)