A mirror driven by a resonant mechanical oscillator is used to scan a modulated laser beam across a rotating dielectric drum. The incident laser beam line scans the drum to form a charge image thereon which is toned as the drum rotates through a toner bath. The toned image is then transferred to paper by rolling contact. The laser beam scan velocity across the drum varies sinusoidally because of the resonant nature of the drive system. The data flow which modulates the laser beam is rate-controlled by a variable clock to accommodate the periodic variations in scanning velocity. The modulation rate -- the data flow rate -- is varied periodically to match the periodically varying scan rate to produce a uniform image element density or spacing across the scan lines of the dielectric surface. The variable clock is also applied to the laser beam modulator to compensate for the periodic variations in the charge density of the image caused by the nonlinear scan velocity.