γ matching of a video processor by means of three measured currents

Method for controlling the cutoff point and the gain in a video reproduction arrangement having a colour tube or projection tubes, by means of reference cathode currents (IK1, IK2), which correspond to different brightness levels, caused by measurement pulses (MIK1, MIK2), comprising the steps of:

• injecting, during a vertical frame blanking period, measurement signal voltages (u1, u2) into the drive signals for the colour tube or projection tubes by means of a measurement line generator circuit arranged in a video signal processor;
• controlling, using control devices in the video signal processor, both an amplitudes and a DC voltage offset (u0) of the measurement pulses (MIK1, MIK2) in such a manner that the reference cathode currents (IK1, IK2) are produced in the colour tube or in the projection tubes, in which case the following relationship applies on the basis of an existing mathematical relationship between a cathode control voltage (VK) and a cathode current (IK):
• I K2 I K1 = ( V K2 V K1 ) γ
• and using corresponding operating parameter values (n, v1) for the value of the exponent (γ) in a control algorithm, wherein the operating parameter values (n, v1) are adjustable and are defined in an appliance production sequence by circuitry of the video signal processor, on the basis of the tube type used.