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Video Threshold Circuit with Low Contrast Clamp and Absolute Black Clamp

IP.com Disclosure Number: IPCOM000052690D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11

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Gillingham, RD [+details]


Shown above is a threshold circuit for digitizing analog video into black and white data. Threshold V(T) is generated by voltage divider action between resistors 10 and 12. Resistor 10 is connected to voltage V(W), which is a white follower voltage. Voltage V(W) follows the white peaks in the analog video. Resistor 12 is connected to black following voltage V(B). Voltage V(B) follows the black peaks in the analog video signal. If resistors 10 and 12 are equal, the threshold V(T) will be half way between V(W) and V(B). This is, in effect, a contrast threshold that is dependent upon the dynamically varying white and black peaks in the analog signal.