Color projection television system with apparatus for correcting

Abstract

A projection television convergence method and apparatus allow rapid and simple correction of low-order misconvergence and misgeometry problems. A hybrid system employs digital programmable attenuators and a digital control system, making it possible to eliminate misconvergence and misgeometry using simple local adjustment on a limited number (e.g., 9) of locations in the picture. The values of the coefficients in the correction waveforms, which are represented by the settings on a number of programmable attenuators, are determined by simultaneously solving the convergence governing equations, and are stored in memory. Thus, the prior art tedious individual adjustment of typically more than 30 potentiometers, each with global effects, by a factory worker, service-engineer or the consumer is obviated. An alternate embodiment includes a simple black and white camera to eliminate the human adjuster. The system detects areas of misconvergence or misgeometry in the composite image by measuring the luminace reflected from the screen during the projection of complementary test patterns of equal luminance in the separate image sources. The system treats areas of luminace discrepancy as misconverged areas, and causes an appropriate level of correction signals to be fed to the misconverged CRTs.