GB1093806A - Improvements relating to pick-up tube arrangements - Google Patents

Abstract

1,093,806. Television; cathode-ray tube circuits. ELECTRIC & MUSICAL INDUSTRIES Ltd. Aug. 28, 1964 [Aug. 31, 1963], No. 34506/63. Headings H4F and H4T. The beam current in a camera tube 1 (e.g. an image orthicon or lead oxide, photoconductive type) which is employed for generating a high definition luminance signal Y is restricted so as to obtain the highest resolution or to limit noise. This introduces a disadvantage however in that the current is insufficient to discharge the target for high lights, particularly those in excess of the selected value for peak white for which the beam current is normally chosen to be just adequate. In accordance with the invention this disadvantage is overcome by controlling the beam current or its discharge effect in accordance with a low definition video signal derived from at least one further camera tube. In one way of carrying out the invention the beam current is controlled by a low definition signal derived from cameras 2, 3 and 4 (e.g. vidicon or lead oxide, photoconductive type) which produce colour signals R, G and B. The signals are combined in a resistor network 5, 6 and 7 and may be gamma corrected, reference being made to the production of an equi-energy brightness signal and luminance signals of the kind having individual and overall gamma correction. After amplification at 8 and levelling in a circuit 9 the signal is applied through a circuit 10 to control the beam current in tube 1. Circuit 10 is an amplitude discriminator and may be set to pass signals exceeding peak white or a selected value below this level. If desired, circuit 10 may be dispensed with and the signal from circuit 9 applied to control tube 1 continuously. Reference is made to the use of a signal store, e.g. a storage tube, to permit repeated control of tube 1 in successive fields from an excess signal derived in one field. As an alternative to controlling the beam current intensity in tube 1, the discharge effect may be controlled by controlling the potential of the target relative to the cathode. The signal from circuit 10 may also control the gain of an amplifier for the tube signal. In another way of carrying out the invention, Fig. 2 (not shown), the signal from the colour cameras are applied via a diode selector circuit which passes the maximum signal in excess of peak white at any instant. It is stated that the invention may be applied to a monochrome camera by the addition of a further low definition pick-up tube.