Television camera gain control circuit with compressed wide contrast range response

Claim 2

A gain control circuit for extending the contrast range response capability of a television camera, said circuit comprising: first circuit means responsive to the video signal produced by said camera for splitting said signal into high and low amplitude portions about a predetermined first amplitude level; second circuit means coupled to said first circuit means for controllably compressing the high amplitude portion of said video signal when the maximum amplitude of said high amplitude portion exceeds a predetermined second amplitude level, said second amplitude level being greater than said first amplitude level; and algebraic adder means responsive to said video signal produced by said camera and coupled to said first and second circuit means, said algebraic adder means subtracting the high amplitude portion of said video signal from the sum of said signal plus the compressed high amplitude portion of said video signal so as to produce a composite signal comprising the sum of the low amplitude and compressed high amplitude portions of said video signal.

Claim 3

The apparatus of claim 1 including level detector means coupled to said second circuit means, said level detector means sensing the maximum amplitude of the high amplitude portion of said video signal and controlling the amount by which said second circuit means compresses the high amplitude portion of said video signal whenever the maximum amplitude of said high amplitude portion exceeds said second amplitude level.

Claim 4

The apparatus of claim 1 including level detector means coupled to said second circuit means and producing an output signal varying in accordance with the maximum amplitude of the high amplitude portion of said video signal above said second amplitude level, and integrating means coupling the output of said level detector means to said second circuit means, said integrating means delaying the effect of application of said output signal from said level detector means on said second circuit means, said second circuit means compressing the high amplitude portion of said video signal in response to the level detector output signal received for an extended duration from said integrating means.

Claim 5

The apparatus of claim 3 including video signal amplitude limiting means coupled to the input of said first circuit means and limiting the maximum amplitude of said video signal furnished to said first circuit means to a predetermined third amplitude level, said third amplitude level being greateR than said second amplitude level.

Claim 6

The apparatus of claim 3 wherein said second circuit means includes fixed signal attenuating means coupling said first circuit means to said level detector means, and third circuit means coupled to said fixed signal attenuating means for controllably adding attenuation to said fixed signal attenuating means in response to output signal amplitude of said integrating means.

Claim 7

The apparatus of claim 5 including video signal amplitude limiting means coupled to the input of said first circuit means and limiting the maximum amplitude of said video signal furnished to said first circuit means to a predetermined third amplitude level, said third amplitude level being greater than said second amplitude level.

Claim 8

A television camera gain control circuit with extended contrast range response comprising: means for clipping a video signal at a predetermined first amplitude level; controlled voltage attenuation circuitry coupled to said clipping means and preset to attenuate a video signal of amplitude above said first amplitude level whenever said video signal exceeds a predetermined second amplitude level, said second amplitude level being greater than said first amplitude level; and algebraic adder means coupled jointly to the input and output of said means for clipping the video signal and to the output of said controlled voltage attenuation circuitry for subtracting the portion of video signal above said first amplitude level from the sum of said video signal plus the output signal of said controlled voltage attenuation circuitry so as to produce an amplitude limited video signal which retains detail in the signal representative of the dark portion of a scene being viewed by said camera while preserving most of the detail in the signal representative of the light portion of said scene.

Claim 9

A television camera gain control circuit with extended contrast range response comprising: means for clipping a video signal at a predetermined first amplitude level; controlled voltage attenuation circuitry coupled to said clipping means and preset to attenuate a video signal of amplitude above said first amplitude level whenever said video signal exceeds a predetermined second amplitude level, said second amplitude level being greater than said first amplitude level; and algebraic adder means coupled jointly to the input and output of said means for clipping the video signal and to the output of said controlled voltage attenuation circuitry for subtracting the portion of video signal above said first amplitude level from the sum of said video signal plus the output signal of said controlled voltage attenuation circuitry so as to produce an amplitude limited video signal which retains detail in the signal representative of the dark portion of a scene being viewed by said camera while preserving most of the detail in the signal representative of the light portion of said scene.

Claim 10

The apparatus of claim 7 including additional clipping means coupled to the input of said means for clipping the video signal at a third amplitude level, said additional clipping means clipping said video signal at a third amplitude level above said second amplitude level.

Claim 11

The apparatus of claim 7 including level detector means coupled to said controlled voltage attenuation circuitry and responsive to the portion of video signal above said second amplitude level, and integrating means responsive to said level detector means, said integrating means being coupled to said signal attenuating means for controlling the amount of attenuation of said portion of video signal above said first amplitude level in accordance with the amplitude by which said portion of video signal above said first amplitude level exceeds said second amplitude level.

Claim 12

The apparatus of claim 8 including level detector means coupled to said controlled voltage attenuation circuitry and responsive to the portion of video signal above said second amplitude level, and integrating means responsive to said level detector means, said integrating means being coupled to said signal attenuating means for controlling the amount of attenuation of said portion of video signal above said first amplitude level in accordance with the amplitude by which said portion of video signal above said first amplitude level exceeds said second amplitude level up to a maximum of said third amplitude level.

Claim 13

The apparatus of claim 9 wherein said controlled voltage attenuation circuitry includes fixed signal attenuating means coupling said clipping means to said level detector means, and circuit means coupled to said fixed signal attenuating means for controllably adding attenuation to said fixed signal attenuating means in response to said integrating means.

Claim 14

The apparatus of claim 11 wherein said fixed signal attenuating means comprises resistance means, and said circuit means comprises transistor means connected to said resistance means to provide an additional signal path from said resistance means, said signal path being of conductivity depending upon amplitude of ouTput signal from said integrating means.

Claim 15

A gain control circuit for extending the contrast range response capability of a television camera, said circuit comprising: first circuit means responsive to the video signal produced by said camera for splitting said signal into high and low amplitude portions about a predetermined first amplitude level; second circuit means coupled to said first circuit means for controllably compressing the high amplitude portion of said video signal when the maximum amplitude of said high amplitude portion exceeds a predetermined second amplitude level, said second amplitude level being greater than said first amplitude level; and signal combining means coupled to said first and second circuit means, said signal combining means serving to add the compressed high amplitude portion of said video signal to the low amplitude portion of said video signal so as to produce a composite signal comprising the sum of the low amplitude and compressed high amplitude portions of said video signal.

Claim 16

A gain control circuit for extending the contrast range response capability of a television camera, said circuit comprising: first circuit means responsive to the video signal produced by said camera for splitting said signal into high and low amplitude portions about a predetermined first amplitude level; second circuit means coupled to said first circuit means for controllably compressing the high amplitude portion of said video signal when the maximum amplitude of said high amplitude portion exceeds a predetermined second amplitude level, said second amplitude level being greater than said first amplitude level; and signal combining means coupled to said first and second circuit means, said signal combining means serving to add the compressed high amplitude portion of said video signal to the low amplitude portion of said video signal so as to produce a composite signal comprising the sum of the low amplitude and compressed high amplitude portions of said video signal.

Claim 17

The apparatus of claim 13 including level detector means coupled to said second circuit means and producing an output signal varying in accordance with the maximum amplitude of the high amplitude portion of said video signal above said second amplitude level, and integrating means coupling the output of said level detector means to said second circuit means, said integrating means delaying the effect of application of said output signal from said level detector means on said second circuit means, said second circuit means compressing the high amplitude portion of said video signal in response to the level detector output signal received for an extended duration from said integrating means.