Abstract: A video projection system employs a reflective light valve (10) that is optically addressed by an image from a cathode ray tube (12) and provides an output image for projection by means of a high intensity reading light directed to the output face of the liquid crystal light valve. Improved reading illumination is provided by scanning the face of the liquid crystal light valve (10) with a narrow beam of light (80) that moves across the liquid crystal in synchronism with the scanning image from the writing CRT (12). The scanned narrow band (80) of illumination is provided by a circular sequence of three quasi cylindrical lens (56, 58, 60) or mirrors (56a, 58a, 60a) mounted on a rotating wheel (52) and which may be made of sequentially different colors to provide a color display. Rotation of the lens or mirror bearing wheel (52) is synchronized with the vertical sync of the CRT scan, as are the index positions of each of the three lens or mirror segments on the wheel.

Abstract: A color video projection system (10) in which images of three separate colors (22,24,26) are separately projected to converge on a common region of the screen (20) is provided with automatic convergence control to ensure that three images are precisely superimposed upon each other. A test pattern of a number of pattern units (36,38) of an intensity (42,44,48) that varies over each unit in a similar manner is imaged on a two dimensional matrix array of charged coupled devices (CCD) (32). The test pattern is projected in sequence by each of the three CRT projectors (50,54,58,14,16,18) of the system, and during the projection of the test pattern, the position of the centroid (40) of each unit of the test pattern is determined from the light intensity pattern received by the CCD matrix array, and stored (112). The centroid positions of each unit of a test pattern of two of the projectors are compared with positions of the centroids of each unit of the test pattern projected by a third one of projectors.