Apparatus for marking a bitmap image on tape includes a scanning mirror which is incorporated in a micro-electro-mechanical system (MEMS). The MEMS is torsionally resonant at two frequencies one being about three time the other. The MEMS is excited to resonance by applying an AC signal to the actuators, causing the mirror to oscillate. The AC signal has components at the two frequencies. The magnitude and phase-relationship of the components can be selected such that the mirror oscillates in an approximation of a triangle-wave.