Video processing amplifier providing black level correction

In a video processing amplifier having means for receiving a composite video signal input having predetermined video signal characteristics including black level composite sync and composite blanking signals, and means for correcting for any black level distortion present in said composite video signal input for restoring said black level to a substantially undistorted video signal black level, said composite sync signals comprising horizontal and vertical sync and said composite blanking signal comprising horizontal and vertical blanking signals;

• wherein the improvement comprises means operatively connected between said composite video input signal receiving means and said black level restoration means for removing said sync and blanking signals from said composite video signal input prior to said black level distortion correction and restoration;
• and said black level distortion correction and restoration means comprises means for providing a window signal positionable in a central area of the associated video picture produceable from said composite video signal input, said window signal having an associated width greater than an associated width of said vertical blanking signal and an associated width of said horizontal blanking signal by a predetermined amount, said predetermined amount providing a guard band about said window signal for preventing said video processing amplifier from black level sampling of any portion of said composite blanking signal, said window signal comprising a window pulse having an associated positive polarity, and keyed clamp DC restoration means operatively connected to said window signal providing means for receiving said window pulse positive polarity and for keying said keyed clamp DC restoration means on during said central area of said associated video picture information while said positive polarity of said window pulse is present for sampling said composite video signal input and clamping the blackest negative excursions of said composite video signal input to a predetermined positve voltage level, whereby said processing amplifier provides an output composite video signal having said black level restoration.