i've recently started playing with Android's camera api. And i'm using face detection and it's callback
(-1000, -1000) represents the top-left of the camera field of view, and (1000, 1000) represents the bottom-right of the field of view.
So to put in to screen coords (pseudocode):
screenX = (coord.x +1000) * screen.width / 2000 screenY = (coord.y +1000) * screen.height / 2000