1. A sensor unit ( 100 ) for sensing imaging properties of a display system ( 500 ) adapted for generating three dimensional images by combining at least first sub-images for a first eye and second sub-images for a second eye, the sensor unit ( 100 ) comprising a detector ( 102 ) and being adapted to detect a signal comprising information related to separate properties of the radiation used for the displaying of said first sub-images and/or separate properties of the radiation used for the displaying of said second sub-images individually.