Automatic video contrast control circuit

Claim 2

Apparatus for processing a video signal comprising peak detector means for detecting the peak white and peak black levels of said video signal and means coupled to said detector means for utilizing said detected peak white and peak black levels to provide the white and black levels in said processed video signal, and wherein each field of said processed video signal is displayed substantially one field in time subsequent to the field of the video signal field being sampled by said peak detector means.

Claim 5

An automatic contrast control circuit for processing an incoming analog type video signal comprising in combination: means for coupling said incoming video signal to first input terminals of a plurality of digital comparator circuits for converting said analog type video signal into a digital type video signal; first and second signal detecting means for detecting the peak white and peak black levels of said incoming video signal and providing a pair of output signals; means for coupling differentially said output signals of said first and second signal deteCting channels across a series resistance type potential divider circuit to divide said differential output into a plurality of step voltage level signals; means for coupling said plurality of step voltage level signals to second input terminals of individual ones of said digital comparator circuits thereby providing comparison levels for said digital comparator circuits; and means coupled to the output terminals of said digital comparator circuits for summing the output voltages of said digital comparator circuits to provide an analog type video output signal.

Claim 6

An automatic contrast control circuit for processing an incoming analog type video signal comprising in combination: means for coupling said incoming video signal to first input terminals of a plurality of digital comparator circuits for converting said analog type video signal into a digital type video signal; first and second signal detecting means for detecting the peak white and peak black levels of said incoming video signal and providing a pair of output signals; means for coupling differentially said output signals of said first and second signal deteCting channels across a series resistance type potential divider circuit to divide said differential output into a plurality of step voltage level signals; means for coupling said plurality of step voltage level signals to second input terminals of individual ones of said digital comparator circuits thereby providing comparison levels for said digital comparator circuits; and means coupled to the output terminals of said digital comparator circuits for summing the output voltages of said digital comparator circuits to provide an analog type video output signal.

Claim 7

In a copier system comprising a document reading device for generating an analog signal representative of the information content of the document; first means for detecting the peak white level amplitude of said analog signal; second means for detecting the peak black level amplitude of said analog signal; black level clamping circuit means adapted to receive said analog signal and further coupled to receive the black level signal detected by said second means; utilization means including a scanning device; a video automatic gain control circuit having an output terminal and responsive to the black clamped video signal from said black level clamping circuit means and the white level signal from said first means and providing a further analog signal at said output terminal; and means coupling said output terminal of said video automatic gain control circuit to said scanning device for providing a video enhanced image of the information content of the document.

Claim 8

In a copier system comprising a document reading device for generating an analog signal representative of the information content of the document; first means for detecting the peak white level amplitude of said analog signal; second means for detecting the peak black level amplitude of said analog signal; black level clamping circuit means adapted to receive said analog signal and further coupled to receive the black level signal detected by said second means; utilization means including a scanning device; a video automatic gain control circuit having an output terminal and responsive to the black clamped video signal from said black level clamping circuit means and the white level signal from said first means and providing a further analog signal at said output terminal; and means coupling said output terminal of said video automatic gain control circuit to said scanning device for providing a video enhanced image of the information content of the document.

Claim 9

In combination in a television camera system including a television camera; first means coupled to said television camera for detecting the peak black and white amplitude levels of the analog video signal generated by said television camera; video digitizer circuit means coupled to said first means for converting said analog video signal into a plurality of different amplitude level signal voltages; summing amplifier means coupled to said video digitizer circuit means for combining said different amplitude level signal voltages to provide a further analog type video information signal; and means for adding sync and blanking pulse signals developed by said television camera to said further analog type video information signal to provide a processed high contrast composite video signal.

Claim 10

In combination in a television camera system including a television camera; first means coupled to said television camera for detecting the peak black and white amplitude levels of the analog video signal generated by said television camera; video digitizer circuit means coupled to said first means for converting said analog video signal into a plurality of different amplitude level signal voltages; summing amplifier means coupled to said video digitizer circuit means for combining said different amplitude level signal voltages to provide a further analog type video information signal; and means for adding sync and blanking pulse signals developed by said television camera to said further analog type video information signal to provide a processed high contrast composite video signal.

Claim 11

The combination according to claim 5 further comprising means for simultaneously displaying said analog video signal and said processed high contrast video signal.

Claim 12

In a video contrast enhancement circuit for processing an analog signal representative of video information first means for coupling said analog signal to video clamping circuit means, said video clamping circuit means including a video switching amplifier circuit; a video driver circuit; a plurality of digital comparator circuits having first and second input terminals and an output terminal; second means for coupling said analog signal to said video driver circuit and the first input terminals of said plurality of digital comparator circuits; a further video switching amplifier circuit having an input terminal; third means for coupling said analog signal to the input terminal of said further video switching amplifier circuit; peak black level detector circuit means coupled to said video switching amplifier circuit, said black detector circuit means including a first holding capacitor connected across the output terminal thereof; peak white level detector circuit means, said white detector including a first holding capacitor connected across the output terminal thereof; further video clamp circuit means coupled between said video driver circuit and said peak white level detector circuit means; pulse generating circuit means for providing sample and dump control signal voltages; sample and hold circuit means coupled to said first and second holding capacitors; fourth means Including a transistor responsive to said dump signal for controlling switching means coupled across said first and second holding capacitors in circuit to ground; fifth means including a transistor for controlling further switching means coupled in series circuit in said sample and hold circuit means; first scaling circuit means coupled to said sample and hold circuit means for scaling the peak white signal output from said sample and hold circuit means; second scaling circuit means coupled to said sample and hold circuit means for scaling the peak black signal output from said sample and hold circuit means and double inverting said peak black signal; sixth means including voltage divider network means coupled to said second input terminals of said plurality of digital comparator circuits for biasing said plurality of digital comparator circuits; seventh means for coupling said plurality of output terminals of said digital comparator circuits to said further video switching amplifier, and video driver circuit means responsive to the output of said further video switching amplifier for providing an analog signal representative of video information having contrast enhanced characteristics.

Claim 13

In a video contrast enhancement circuit for processing an analog signal representative of video information first means for coupling said analog signal to video clamping circuit means, said video clamping circuit means including a video switching amplifier circuit; a video driver circuit; a plurality of digital comparator circuits having first and second input terminals and an output terminal; second means for coupling said analog signal to said video driver circuit and the first input terminals of said plurality of digital comparator circuits; a further video switching amplifier circuit having an input terminal; third means for coupling said analog signal to the input terminal of said further video switching amplifier circuit; peak black level detector circuit means coupled to said video switching amplifier circuit, said black detector circuit means including a first holding capacitor connected across the output terminal thereof; peak white level detector circuit means, said white detector including a first holding capacitor connected across the output terminal thereof; further video clamp circuit means coupled between said video driver circuit and said peak white level detector circuit means; pulse generating circuit means for providing sample and dump control signal voltages; sample and hold circuit means coupled to said first and second holding capacitors; fourth means Including a transistor responsive to said dump signal for controlling switching means coupled across said first and second holding capacitors in circuit to ground; fifth means including a transistor for controlling further switching means coupled in series circuit in said sample and hold circuit means; first scaling circuit means coupled to said sample and hold circuit means for scaling the peak white signal output from said sample and hold circuit means; second scaling circuit means coupled to said sample and hold circuit means for scaling the peak black signal output from said sample and hold circuit means and double inverting said peak black signal; sixth means including voltage divider network means coupled to said second input terminals of said plurality of digital comparator circuits for biasing said plurality of digital comparator circuits; seventh means for coupling said plurality of output terminals of said digital comparator circuits to said further video switching amplifier, and video driver circuit means responsive to the output of said further video switching amplifier for providing an analog signal representative of video information having contrast enhanced characteristics.

Claim 14

In a system for processing composite video signals including analog signals proportional to picture light values to develop window search control signals for processing the video within a window search area, vertical drive signals, and composite blanking signals; first means responsive to said composite blanking signals for providing a horizontal component of window search control signals; second means responsive to said vertical drive signals for providing a vertical component of window search control signals; third means for combining said horizontal and vertical components to provide said window search control signals, and fourth means including peak detector means responsive to said window search control signals for determining maximum and minimum amplitudes of said analog signals within the window area.

Claim 15

In a system for processing composite video signals including analog signals proportional to picture light values to develop window search control signals for processing the video within a window search area, vertical drive signals, and composite blanking signals; first means responsive to said composite blanking signals for providing a horizontal component of window search control signals; second means responsive to said vertical drive signals for providing a vertical component of window search control signals; third means for combining said horizontal and vertical components to provide said window search control signals, and fourth means including peak detector means responsive to said window search control signals for determining maximum and minimum amplitudes of said analog signals within the window area.

Claim 16

The system according to claim 8 wherein said window area is wholely within the visible area of said scanned video signals.