The display device (1) comprises picture elements (5) arranged in substantially parallel lines (6) on a display panel (2), and selection means (3) for controlling the decoupling of light from an optical waveguide plate at the picture elements. The selection means (3) are arranged for multiline addressing of the picture elements (5). For displaying gray scales, image information (4) is decomposed into a number of subfields (13) which are displayed. The time efficiency of the addressing of picture elements (5) in lines (16) in the subfields (13) is increased, enabling the display device (1) to display a relative large number of gray method of operating a display device (1) is carried out when the device is in operation.