A head-up display for a vehicle, the head-up display comprising: a driver monitoring system arranged to illuminate and monitor in use a driver, wherein the driver monitoring system comprises an infrared display channel comprising: an infrared light source arranged to emit in use infrared light; and a hologram arranged to receive the infrared light from the infrared light source and output in use spatially-modulated light in accordance with the hologram to form in use an infrared light pattern on a replay plane, wherein the head-up display further comprises: a picture generating unit arranged to display in use a picture on the replay plane, whereir the picture generating unit comprises a visible light display channel, wherein the visible light display channel comprises: a visible light source arranged to emit in use visible light; a spatial light modulator arranged to receive the visible light from the visible light source and output in use spatially-modulated light in accordance with a computer-generated hologram displayed on the spatial light modulator to form in use a visible light pattern on the replay plane; and a controller arranged to output in use a light-modulation distribution comprising the computer-generated hologram to the spatial light modulator, wherein the head-up display further comprises: an optical combiner and an optical system arranged to relay in use the infrared light pattern and the visible light pattern from the replay plane to the optical combiner, said optical combiner being arranged to direct in use the relayed light to an eye-box, wherein the optical system comprises: an input arranged to receive in use the infrared light pattern and the visible light pattern from the replay plane; an output arranged to output in use light of the infrared light pattern and light of the visible light pattern to the optical combiner; and at least one mirror arranged to guide light in use from the input to the output along an optical path. an infrared light source arranged to emit in use infrared light; and a hologram arranged to receive the infrared light from the infrared light source and output in use spatially-modulated light in accordance with the hologram to form in use an infrared light pattern on a replay plane, wherein the head-up display further comprises: a picture generating unit arranged to display in use a picture on the replay plane, whereir the picture generating unit comprises a visible light display channel, wherein the visible light display channel comprises: a visible light source arranged to emit in use visible light; a spatial light modulator arranged to receive the visible light from the visible light source and output in use spatially-modulated light in accordance with a computer-generated hologram displayed on the spatial light modulator to form in use a visible light pattern on the replay plane; and a controller arranged to output in use a light-modulation distribution comprising the computer-generated hologram to the spatial light modulator, wherein the head-up display further comprises: an optical combiner and an optical system arranged to relay in use the infrared light pattern and the visible light pattern from the replay plane to the optical combiner, said optical combiner being arranged to direct in use the relayed light to an eye-box, wherein the optical system comprises: an input arranged to receive in use the infrared light pattern and the visible light pattern from the replay plane; an output arranged to output in use light of the infrared light pattern and light of the visible light pattern to the optical combiner; and at least one mirror arranged to guide light in use from the input to the output along an optical path. a visible light source arranged to emit in use visible light; a spatial light modulator arranged to receive the visible light from the visible light source and output in use spatially-modulated light in accordance with a computer-generated hologram displayed on the spatial light modulator to form in use a visible light pattern on the replay plane; and a controller arranged to output in use a light-modulation distribution comprising the computer-generated hologram to the spatial light modulator, wherein the head-up display further comprises: an optical combiner and an optical system arranged to relay in use the infrared light pattern and the visible light pattern from the replay plane to the optical combiner, said optical combiner being arranged to direct in use the relayed light to an eye-box, wherein the optical system comprises: an input arranged to receive in use the infrared light pattern and the visible light pattern from the replay plane; an output arranged to output in use light of the infrared light pattern and light of the visible light pattern to the optical combiner; and at least one mirror arranged to guide light in use from the input to the output along an optical path. an input arranged to receive in use the infrared light pattern and the visible light pattern from the replay plane; an output arranged to output in use light of the infrared light pattern and light of the visible light pattern to the optical combiner; and at least one mirror arranged to guide light in use from the input to the output along an optical path.