Abstract In the exposure of film with a CRT, for example, the resulting recorded information density on the film is not proportional to the amplitude of the video signal applied to the CRT. That is, if a linear ramp function is applied to a CRT for the purpose of exposing film, the resulting exposed density on the film will be an exponential function. This response is defined as the gamma of the film and produces an error in recording an image on film. The disclosed embodiment of this invention is a circuit for correcting the error which results during the exposure of a photographic film or in the transmission of light through a layer of phosphor, such as found on the face of a CRT, due to the gamma characteristic thereof. The circuit is formed of an amplifier having a resistance feedback and a second resistance connecting the video signal to an input of the amplifier. In one embodiment, the input resistance is formed of a F.E.T., and in a second embodiment the feedback resistance is formed of an F.E.T. The operating characteristics of the F.E.T. establish the amount of correction provided to the video signal by the circuit. The operating characteristics of the F.E.T. in both embodiments of the invention can be varied by applying the video signal to a gate electrode of that F.E.T.
A signal-correction circuit comprising a signal-input terminal and a signal-output terminal, an amplifier having at least one input and an output, a first variable impedance means connected between said input terminal and an input of said amplifier, a second variable impedance means connected from the output of said amplifier to an input of said amplifier, one of said first and second impedance means having a main conduction path and a control member, and means connected between said input terminal and said control member to modify the impedance of said main conduction path in response to variations in the amplitude of signals applied to said input terminal.
Claim 2
Dependent Claim
106 words
A signal-correction circuit comprising a signal-input terminal and a signal-output terminal, an amplifier having at least one input and an output, a first variable impedance means connected between said input terminal and an input of said amplifier, a second variable impedance means connected from the output of said amplifier to an input of said amplifier, one of said first and second impedance means having a main conduction path and a control member, and means connected between said input terminal and said control member to modify the impedance of said main conduction path in response to variations in the amplitude of signals applied to said input terminal.
Claim 3
Dependent Claim
43 words
The signal-correction circuit defined in claim 1 wherein said variable impedance means having the main conduction path and the control member comprises a means whose impedance varies nonlinearly with respect to the control voltage applied to the means connected to the control member.
Claim 4
Dependent Claim
25 words
The signal correction circuit defined in claim 2 wherein said variable impedance means having a main conduction path and a control member comprises a transistor.
Claim 5
Dependent Claim
29 words
The signal correction circuit defined in claim 3 wherein said means connected between said input terminal and said control member comprises a second amplifier having a second feedback path.
Claim 6
Dependent Claim
24 words
The signal-correction circuit defined in claim 1 wherein said first variable impedance comprises said impedance with the main conduction path and the control member.
Claim 7
Dependent Claim
24 words
The signal-correction circuit defined in claim 1 wherein said second variable impedance comprises said impedance with the main conduction path and the control member.