Head-up display with brightness control

A head-up display system for a vehicle, comprising:

• a projector part positioned outside a field of view of an observer;
• a partially reflecting combiner arranged in the field of view of the observer to provide for an image of the projector part to be combined with a view of outside environment thereby providing the observer with a view of the outside environment with symbols superimposed thereto;
• a light source for providing light of the projector part;
• an image generator display for modulating the light of the light source thereby creating an image to be combined with the view of the outside environment;
• and
• an image generator controller having a brightness control unit arranged to provide different brightness of different portions of the image;
• wherein the brightness control unit comprises a vehicle pitch and roll angle input unit including inputs for vehicle pitch angle and roll angle, and a virtual horizon position calculator unit configured to calculate, based on said pitch and roll angles, a position in the image of a virtual horizon line, corresponding to a real horizon line as perceived by the observer, and wherein the brightness control unit comprises an upper portion identifier unit configured to calculate which portions of the image that are above said virtual horizon line, and wherein the brightness control unit comprises a lower portion identifier unit configured to calculate which portions of the image are below the virtual horizon line, and wherein the brightness control unit comprises an upper portion symbol brightness control subunit configured to control the brightness of symbols above said virtual horizon line to be different from the brightness of symbols below the virtual horizon line, thereby increasing contrast between symbols above the virtual horizon line and below the virtual horizon line and the outside environment.