Abstract: In a patterned screen color cathode ray tube (CRT) display, for example, a shadow-mask type color CRT, particularly for use under a wide range of ambient light conditions, such as an aircraft cockpit, incompatibilities between the screen pattern character, the type of writing (such as stroke and raster), and the display linewidth, may result in stroke written lines which appear as a twisted fiber rope and in raster written areas which appear wavy or watery; that is, a moire appearance. Both of these effects vary in accordance with the required display brightness over the ambient light range due to variations in beam or linewidth with corresponding variations in the required cathode drive voltages.

Abstract: An apparatus for providing precise convergence compensation in a shadow mask type color CRT display. Coarse compensation is provided by the coefficients of primary terms x.sup.2, y.sup.2 of the beam's longitudinal and vertical position polynomial in an analog format, and fine compensation is provided by digital programmable read-only-memories. The fine compensation is representative of the precise values of the coefficients of the remaining terms in these polynomials, and a digital-to-analog converter converts the fine compensation to an analog format. The coarse and fine data are summed together and applied to the convergence correction coils of the CRT.