Abstract: A time-varying control signal is developed by a current sensor connecting the imaging screen and a closely proximate screen grid of a cathode ray tube as an imaging electron beam is operatively swept across the screen to produce images thereon. The control signal is processed and then applied to at least one of the tube operating elements--such as the horizontal and vertical deflection coils, the focusing lens, the electron beam generator and, in a plural beam tube, the convergence assembly--which controls a characteristic affecting the quality of an image. Specific arrangements for using the time-varying control signal to compensate for geometric image distortions affecting horizontal linearity and to increase the imaging resolution of the tube are disclosed.