CCD dark mean level correction circuit employing digital processing and analog subtraction requiring no advance knowledge of dark mean level

A digital black clamp circuit comprising:

• a source of successive lines of a video signal, each line having a first interval of black level pixels and a second interval of image pixels;
• a differential amplifier having first and second inputs and an output;
• wherein said source is coupled to one of said first and second inputs;
• an analog-to-digital converter (ADC) coupled to said output of said differential amplifier;
• a digital signal processor coupled to said ADC for accumulating and averaging digital black level pixels in said first interval to produce and average black level signal;
• a digital-to-analog converter (DAC) coupled to said digital signal processor for converting a digital signal to an analog signal;
• and
• a control for controlling said digital signal processor and said digital-to-analog converter to cause said digital signal processor to accumulate and average digital black level pixels in the first interval of line of the video signal and to load an average black value into said DAC during the first interval of a next line of video signal in order to eliminate signal errors due to pipeline delay and settling time of said DAC.