Cathode for display device

A display device comprises field emission cathode means for emitting electrons. A plurality of electron beams are formed from the field emission cathode means. A screen, which has a phosphor coating facing the cathode receives the plurality of electron beams. The phosphor coating comprises a plurality of pixels each corresponding to a different one of said plurality of electron beams. A grid electrode means is disposed between the cathode means and the screen for controlling the flow of electrons from the cathode means. The field emission cathode means comprises extractor grid means, having a plurality of separately addressable portions associated with each of said plurality of pixels. A gamma transfer function between input data value and beam current is provided in order to emulate a conventional CRT. This can be achieved by use of a lookup table.