Ink jet printing method, in which the jet is broken up in small and large drops at a fixed point, and the drops are charged according to the length of the break segment, in other words according to their diameter. The diameter reduction structure is positioned in proximity to a first seal and includes a plurality of stand off members movable between a first position, a second position, and a third position. The pattern encoding unit encodes a binary pattern of the image element and the shape of the image element is related to the binary pattern of the image element. A demagnetization circuit demagnetizes the shaft via the detecting coil.