![]() ![]() ![]() ![]() One precondition for correct colour-video reproduction is that monochrome pictures are reproduced with neutral colours. It is based on a colour tube in a colour television set, and on projection tubes for displaying video signals. The invention relates to cutoff and gain control for a device for displaying video signals. ![]() Circuit arrangement which processes video signals, having a video processor (2), and amplifiers (3) which are arranged between this video processor (2) and a colour tube (1) or projection tubes, and having devices for controlling the cutoff point and the gain by means of reference cathode currents (IK1, IK2) which correspond to different brightness levels and are caused by measurement pulses (MIK1, MIK2), in that measurement signal voltages (u1, u2) are injected into the drive signals of the colour tubes (1) or projection tubes, by means of a measurement line generator circuit (25) (arranged in the video signal processor (2)) during a vertical blanking period, and the video signal processor (2) has control devices which control both the amplitudes and the DC voltage offset (u0) of the measurement pulses (MIK1, MIK2) in such a manner that the reference cathode current (IK1, IK2) are produced for the colour tube (1) or for 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): EMI27.1 and corresponding operating parameter values (n, v1) for the value of the exponent ( gamma ) are used in the control algorithm, characterized in that means for determining and setting these operating parameter values (n, v1) are provided in the video processor (2). Method according to Claim 1, characterized in that the operating parameter values (n, v1) are determined from signal voltages (V1, V2) after correction to the reference cathode currents (IK1, IK2), which signal voltages (V1, V2) are derived from the cathode control voltages (VK1, VK2) which are set during the correction to the reference cathode currents (IK1, IK2).ĥ. Method according to Claim 1, characterized in that the operating parameter values (n, v1) are defined in the appliance production sequence by circuitry of the video processor (2), on the basis of the tube type used.Ĥ. Method according to Claim 1, characterized in that the operating parameter values (n, v1) are set in the appliance production sequence on the basis of the tube type used, and are stored at a suitable paint.ģ. Method for controlling the cutoff point and the gain in a video reproduction arrangement having a colour tube (1) or projection tubes, by means of reference cathode currents (IK1, IK2), which correspond to different brightness levels, caused by measurement pulses (MIK1, MIK2), in that, during a vertical frame blanking period, measurement signal voltages (u1, u2) are injected into the drive signals for the colour tube (1) or projection tubes by means of a measurement line generator circuit (25) arranged in a video signal processor (2), and the video signal processor (2) has control devices which control both the amplitudes and the 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 (1) 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): : EMI26.1 and corresponding operating parameter values (n, v1) for the value of the exponent ( gamma ) are used in the control algorithm, characterized in that these operating parameter values (n, v1) are adjustable.Ģ. The aim in this case is to reduce a gamma -dependent DC voltage offset u0f to zero.ġ. Thus, according to the invention, the exponent gamma is defined as a function of the colour tube 1. However, it has been found that, if a fixed value is assumed for the exponent gamma or for the ratio of the two cathode currents IK1 and IK2, it is not possible to achieve an optimum result for displaying monochrome pictures. Owing to the physically dependent exponential beam current characteristic profile as a function of the cathode control voltage VK, the exponent gamma of the characteristic profile and the ratio of two cathode components IK1 and IK2 are in this case used to form control reference values for cutoff and drive control, this process being started in each case from a fixed value of the exponent gamma or of the ratio of the two cathode currents IK1 and IK2. Recent circuit concepts inject measurement lines, for cutoff and drive control of the cathode current, into each colour channel during the vertical frame blanking period. ![]()
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