Threshold for the amount of change in frame differencing

Hi , im doing a simple frame differencing using .absDiff method , then im drawing the frame differenciated image that draws white pixels where there have been a change from the previous frame.

The problem with this approach is that even if i dont move my hand in front of the kinect, it still drawing white pixels, because its almost imposible that my hand stays really quiet ( theres always a movement) .

I was wondering, how can i solve this problem?
How can i add a threshold that only draws points if there is a significant change from the previous frame?

any idea?