Image sensor and rangefinder device with background subtraction using

Abstract

A rangefinder device includes means for projecting a beam of light to illuminate a spot on an object in a scene, an image sensor having an array of photosensors for sensing an image of the scene, and signal processing means responsive to the photosignals from the photosensors for determining the relative location of the illuminated spot in the scene. The device includes an improved image sensor comprising an array of N photosensors for sensing the image of the scene and generating N photosignals in response thereto, and an analog shift register having 2N cells for receiving the photosignals, in parallel, into N alternate cells. The sensor is operated once with the light beam off and the photosignals generated thereby, representing the background illumination, are entered into the N alternate cells of the shift register. Then the contents of the shift register are shifted by one cell. Next, the sensor is operated with the beam on and the N photosignals, representing the background plus the light beam illumination, are entered into the shift register, with the result that the background signals are interlaced with the background plus light beam signals in the shift register. The photosignals are read out of the shift register serially, and the pairs of signals originating from each respective photosensor are differenced to yield a series of N photosignals free from background scene information. The difference signals are supplied serially to a peak detector to determine the location of the illuminated spot.