Video projector with optical feedback

Abstract

Geometric distortion in a scanning beam video laser porjector, or the like, is corrected by comparing the time of arrival of the projection beam at a selected pixel on the projection screen with a predetermined time of arrival, and computing therefrom the changes in beam control required to remove the distortion. A peripheral portion of the projected video field is blank, being reserved for projection of bright beam alignment fiducials comprising selected pixels of the peripheral field portion. An optical fiber is placed on the screen periphery so as to receive one pixel of each projected fiducial, its output being applied (through a light sensitive diode) to a beam control processor or the like. Geometric distortion or a change in projector alignment shifts the beam time of arrival at the sensor. The processor compares the time of arrival of the projector beam at each sensor with a lock-up table and, from this comparison, determines the beam control corrections required to remove geometric distortion. Significantly, only one sensor is required in a given portion of the projected image to precisely measure any alignment shift of a projected beam fiducial, because such a shift changes the beam time of arrival at the sensor by an amount proportional to the magnitude of the alignment shift and by a direction in time (backward or forward in time) corresponding to the direction of the alignment shift.