Apparatus for creating an image indicating distances to objects in a scene, comprising: a modulated source of radiation (40), having a first modulation function (60), which directs radiation toward a scene; a detector (22), which detects radiation reflected from the scene, modulated by a second modulation function (62), and generates, responsive to said detected modulated radiation, signals responsive to the distance to regions of the scene; a processor (24), which receives signals from the detector and forms an image, based on the signals, having an intensity value distribution indicative of the distance of objects from the apparatus; and a controller (46), which varies at least one of the first and second modulation functions, responsive to the intensity value distribution of the image formed by the processor.