AUTOMATIC CORRECTION OF MISCONVERGENCE OF IMAGE FOR A VIDEO PROJECTION SYSTEM

摘要

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. The comparison develops an error signal for each unit of each test pattern, enabling convergence correction signals to be fed to convergence control deflections coils (120, 122, 124) of each of the cathode ray tubes (50, 54, 58) so as to effectively shift each of two of the images to superposition with the third.