An image display apparatus has a control circuit that periodically varies a characteristic, such as an amplitude characteristic or timing characteristic, of the displayed image signal. Periodic variations may be produced by passing the image signal through a variable inductance element, for example, or by alternately selecting two amplifier circuits with different gain characteristics, or by periodically delaying the image signal. The periodic variations reduce peaks in the spectrum of unintended radiation emissions, and suppress undesired moire patterns in the displayed image.