modulation mask modulation electrodes 58 each driver reads the bit it receives and either switches on or off when shut off the driver supplies a repelling voltage to its associated modulation electrodes 58 preventing current from passing through that particular mask slot 42 at appropriate times while the megacycle clock 70 cycles particular modulation electrodes 58 are switched on or off and the selected discharge multiplier 34d is fired for a fraction of the line time divided by 2 n which is approximately two microseconds for the embodiment described herein during this discharge multiplier pulse each of the 2100 modulation mask sensing pads 50 see fig3 for that line must charge negative from pad voltages approximately equal to 50 volts or integral fraction thereof back to approximately zero volts with charge passing through only those slots 42 which are addressed 34 on 34 if no current is to be wasted the sensing pad capacitances must be such as to allow an amount of charge to pass to the screen for the full pulse which is approximately 1 u00f7 n or 1 17th for this embodiment of what is needed to produce 100 ft lamberts at the screen the system as described so far involves addressing the 2100 modulation electrodes 58 on the modulation mask 36 with 2100 driver circuits 72 each of which is switched to either an 34 on 34 or an 34 off 34 voltage during appropriate times in the seventeen cycles within a sixty microsecond line time the discharge multiplier 34d see fig2 is fired once during each of these seventeen cycles causing the sensing pads 50 to discharge.