8. A variant: active imaging

If performance at low light levels is not sufficient, one solution is to illuminate the scene (a technique known as "active imaging"). Time-division functions can be implemented to produce either images of ultrafast phenomena, or distance-resolved images by exploiting the speed of light. The principle is based on managing the synchronization of pulsed laser emission with that of the opening of a fast shutter (by controlling the polarization of the photocathode for an IL tube, for example) as a function of the distance from the observed scene, taking into account the time-of-flight of light propagation. The benefit of a very high-sensitivity, low-noise sensor will be to limit the need for illumination energy. All these illumination, detection and active image processing techniques could be the subject of a full article on their own.