Hologram calculation for compact head-up display

Abstract

An optical system and a method of calculating a hologram of a virtual image (700) for the optical system is described. The optical system comprises a display device arranged to display the hologram and a waveguide arranged to replicate the hologram. The method comprises determining a sub-hologram (820, 920) of a virtual image point (701) within an area defined by straight line paths (711) from the virtual image point to the perimeter of an entrance pupil of a viewer (720). The area comprises at least part of a virtual replica of the display device formed by the waveguide.