A sheet separator includes an advancing roller driven to rotate to move a sheet forwards along a sheet path, and a reversing roller driven to rotate to move a sheet backwards along the path. A system can include a processor, a user interface, a display, and a camera. A shared source line is associated with a first pair of adjacent columns, the shared source line being maintained at a predetermined level, wherein source terminals of storage cells in the adjacent columns are electrically coupled to the shared source line. A threshold signal voltage of the first sub-pixel is lower than that of the second sub-pixel.