DISPLAY TUBE WITH REDUCED SPOT-GROWTH

摘要

A method according to the invention reduces spot-growth towards the edges of a display screen (10) of a display tube (1). The number of electrons per second in a modulated electron beam is determined by a picture signal (Pi). A corrected modulated electron beam is obtained by reducing the number of electrons per second in the modulated electron beam from the center of the display screen (10) towards its edges. Consequently, a dimension of a spot caused by the corrected modulated electron beam on the display screen (10) increases to a smaller extent or does not increase at all towards the edges of the display screen (10). The number of electrons per second in the modulated electron beam can be decreased (2), for example by means of a contrast control which is adapted for this purpose. As a result of the decrease (2) of the number of electrons per second in the modulated electron beam, a decrease of light is obtained towards the edges of the display screen (10). In one embodiment of the invention, this decrease of light is corrected by causing the deflection rate to decrease (4, 5) from the center of the display screen (10) towards its edges. The influence of the deflection rate (4, 5) has the result that a picture signal (Pi) to be displayed on the display screen (10) will not occur at a correct position. This position error of the picture signal (Pi) can be corrected by shifting (3) the picture signal (Pi) in time.