Automatic white adjusting circuit for a television camera

Abstract

An automatic white adjusting circuit for a television camera having a color image pick-up tube comprises a first and second variable gain amplifiers for amplifying two predetermined primary color signals of the three primary color signals from an output signal of the image pick-up tube, a matrixing circuit for producing a luminance signal and two color difference signals, by being supplied with either said luminance signal from the output of the image pick-up tube or one remaining primary color signal of the three primary color signals, and outputs of the first and second variable gain amplifiers, an averaging circuit for producing a first and second white detection signals by substantially averaging all or a part of the respective video duration time of the output color difference signals from the matrixing circuit, reference level producing circuit in which a reference level equal to a DC current level of the two predetermined color difference signals of the output signal of the image pick-up tube upon image-picking up of a white object by the image pick-up tube is produce, first and second level comparators for respectively comparing the levels of the first and second white detection signals from the averaging circuit with the reference level from the reference level producing circuit,, and first and second control voltage producing circuit for producing a first and second control voltages according to the outputs of the first and second level comparators. The first and second control voltages are supplied respectively to the first and second variable gain amplifiers, and controlling their respective gains so that the two color difference signals from the matrixing circuit upon image-picking up of the white object by the image pick-up tube become to substantially zero.