A method and apparatus are provided for controlling a digital display device to generate an image for display, wherein the display device is arranged to generate the image as an array of pixels each of a defined brightness achieved by emitting a respective combination of light pulses of durations defined according to a predetermined pulse width modulation (PWM) scheme. Whereas, under conventional PWM schemes, each light pulse would be emitted by the same pixel of a display device, in the present invention rate data from an associated tracker system and data defining predetermined characteristics of the display and operation thereof are used to calculate a pixel displacement in respect of each defined pulse of the PWM scheme. The pixel displacement is used to modify control data defining those pixels to be activated to emit the defined pulse such that a different pixel to that intended emits the pulse during relative movement of the direction of gaze of a user's eye and the display apparatus. This has the effect of reducing unwanted display artefacts during such relative movement which are prevalent in conventional digital display systems.