Apparatus and method for controlling white balance of a cathode ray tube projector

Abstract

An input signal is input to a detector and a synchronizing frequency of the input signal is detected by a frequency detector. Then, the number of the horizontal lines per vertical period of the input signal is determined according to the synchronizing frequency by a calculator. A control signal for defocusing an electron beam with which a blue fluorescent substance emits light is generated from a defocus controller according to the number of the horizontal lines of the input signal. Here, a range of control signals is previously stored corresponding to a range of numbers of horizontal lines. A focus signal for exactly focusing the electron beam is added to the control signal output from the defocus controller by an adder. Then, the defocus signal is output tom the adder. The defocus signal is amplified by a focus adjusting amplifier 15. The diameter of the electron beam with which the blue fluorescent substance emits the light is controlled according to the amplified defocus signal by a focus adjusting coil.

Dependencies are inferred from the claim text.