Automatic contrast controller of a video camera

An automatic contrast controlled of a video camera having an image information processing system for processing supplied image information, comprising:

• pedestal level sample-and-hold means for detecting a pedestal level from an output signal of a clamping circuit clamping an input video signal, according to a clamp pulse;
• average image signal detecting means for detecting an average image signal from the output signal of said clamping circuit according to an input composite blanking signal;
• signal below reference level detecting means for detecting signals below a reference level from said input video signal amplified and standardized by said clamping circuit and an amplifier;
• lowest value detecting means for providing said reference level and for providing an output signal in response to vertical drive signals and a signal output from said signal below reference level detecting means;
• comparing means coupled to receive said output signal from said lowest value detecting means for comparison to said pedestal level combined with said average image signal provided from said pedestal level sample-and-hold means and said average image signal detecting means, respectively;
• variable gain amplifying means for adjusting and amplifying a gain of said signal output from the signal below reference level detecting means, according to a signal provided from said comparing means.

An automatic contrast controller, comprising:

• sample-and-hold means for providing, in response to reception of a video input signal, a video signal clamped at a pedestal level;
• average signal detecting means for providing an output integrated signal based upon said video input signal and a composite blanking signal;
• second detecting means for receiving said video input signal and said composite blanking signal, for detecting components of said video input signal having amplitudes below a reference level, and for providing a detected output signal;
• third detecting means for establishing said reference level and for providing a second output signal in response to the detected output signal having signals blanked therefrom in response to said composite blanking signal;
• means for providing a variable amplification control signal output by comparing the second output signal to the integrated signal combined with the video signal clamped at the pedestal level;
• and
• amplifying means of variable gain for providing a compensated output signal by varying the gain of said detected output signal from said signal below reference level detecting means in response to said variable amplification control signal.

An automatic contrast controller comprising:

• means for providing first intermediate signals indicative of amplitudes of input video signals below a reference level;
• means for providing pedestal level intermediate signals by maintaining said input video signals at a pedestal level;
• means for providing averaged intermediate signals representative of averages of said amplitudes of said input video signals below said reference level;
• and
• means for providing control signals varying in dependence upon said pedestal level intermediate signals and said averaged intermediate signals.

A process for automatically controlling contrast, comprising:

• providing first intermediate signals indicative of amplitudes of input video signals below a reference level;
• providing pedestal level intermediate signals by maintaining said input signals at a pedestal level;
• providing averaged intermediate signals representative of averages of said amplitudes of said input video signal;
• generating second intermediate signals characteristc of lowest amplitudes of said first intermediate signals;
• and
• providing control signals varying in dependance upon said pedestal level intermediate signals and said averaged intermediate signals by comparing said second intermediate signals with said pedestal level intermediate signals and said averaged intermediate signals.