The Box Size register defines the size of overlying box, where N represents NxN size of box. It is NxN for progressive video and Nx2N for interlaced video. The size of the box has to be set smaller than the frame size that is set in the Active Height and Active Width register. This register relies on value of foreground pattern (0x0020). If foreground pattern register is 1, the box is enabled; otherwise the box is disabled.