Rca Inc.

Charles L Olson

Lucas J Bazin

Joseph F Hacke

John F Monahan

A gamma corrector for a video signal includes a first amplifier, a nonlinear signal translating stage and a second amplifier coupled in cascade in the order named. A feedback network coupled between the output of the second amplifier and a gain-control input of the first amplifier derives a gain-control signal indicative of the white level of the video signal produced at the output of the second amplifier. A gamma control signal is applied to a gain control input of the second amplifier in one embodiment and to a black level clamp associated with the first amplifier stage in another embodiment.

Adjustable gamma controller

A black-level clamp for a signal derived from a transducer such as a camera tube includes a controllable voltage offset generator such as a series capacitor or an amplifier. The television signal is sampled during the horizontal sync interval to produce a control signal indicative of the current black-level signal, and the control signal is applied to adjust the charge on the series capacitor to place one plate at a reference voltage or is compared with a reference level to produce a further control signal for adjusting the offset of the amplifier. In either case, drift of the reference voltage which may perturb the operation of the clamp is reduced by deriving the reference voltage from the television signal at times within the vertical blanking interval.

Black level clamp for television signals

A feedback amplifier is configured as a contrast compressor for video signals including a reference blanking level. A feedback resistance is divided into two resistors coupled at a juncture. Contrast compression is accomplished by a diode coupled to the juncture and to a voltage source which may be adjusted to vary the point of onset of compression. The diode current perturbs the operating point of the amplifier, thereby producing a condition in which the blanking level at the output is other than zero volts. This is undesirable as it may affect following circuits adversely or require further setup. A clamp is coupled to the inverting input terminal for offsetting the perturbation of the amplifier operating point caused by the diode current.

Adjustable contrast compressor

In a television camera having an electron scanning beam stabilizer circuit, a circuit for improved handling of highlights comprises means for forming an electrical signal corresponding to a pickup tube image highlight, limiting the magnitude of said signal to a predetermined level and utilizing that signal to form a highlight handling signal which causes the increase in beam scanning current necessary to discharge said highlight. In a color camera, the output from one pickup tube can be used to derive the signals necessary to control all three tubes simultaneously. A modified beam stabilizer circuit comprises means for allowing the beam current to increase without reduction by the beam stabilizer in order to discharge the highlight. A complementary signal derived from the highlight handling signal is applied to the modified beam stabilizer simultaneously with the highlight handling signal in order to neutralize the beam stabilizer.

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Oaklyn, NJ, United States of America

Charles L Olson