Make camera view dark and outline special objects

Currently, I achieve outline special objects with post process materials. But camera still can seen other scene objects that NO what i want.
When I override global scene color tint with black, make scene entity dark but the outline materials no working anymore.
So, I’m looking a way to make scene see from the special camera, and the camera view darkness but can only seen the special outline objects.
Or any way to achieve effects:
Make the player focus on the special objects, and fadeout other scene objects;