Possible configurations in the marching 2 × 2 px square. Black dots represent pixels above a threshold, and open dots pixels below this threshold. The gray area is the body that is assumed to be present in the window. The positions of the corners located between pixel centers are interpolated based on the actual pixel values (Mantz et al. 2008). When diagonally opposite pixels are above the threshold, we make the arbitrary choice to view this as two disconnected triangles.