CCD dark mean level correction circuit employing digital processing and analog subtraction requiring no advance knowledge of dark mean level
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United States of America Patent
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Aug 19, 1997
Grant Date -
N/A
app pub date -
Oct 31, 1994
filing date -
Oct 31, 1994
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A digital black clamp circuit for calibrating the black level of an image signal produced by an imaging device, such as a CCD sensor. The digital black clamp circuit comprises a source of a video signal 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 the source is coupled to one of the first and second inputs; an A/D converter coupled to the output of the differential amplifier; a digital signal processor coupled to the A/D for accumulating and averaging digital black level pixels; a D/A converter coupled to the digital signal processor; and a control for selectively uncoupling the D/A converter to the other of the first and second inputs of the differential amplifier during the first interval of the video signal; and for coupling the D/A converter to the other of the first and second inputs during the second interval of the video signal to clamp the image pixels to an average black level.
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