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THRESHOLD CIRCUIT FOR CONVERTING A VIDEO SIGNAL TO A BINARY VIDEO SIGNAL

  • US 3,763,357 A
  • Filed: 12/22/1971
  • Issued: 10/02/1973
  • Est. Priority Date: 12/22/1971
  • Status: Expired due to Term
First Claim
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1. In a particulate measuring system wherein a video signal having sloping transitions is generated by scanning a represented sample with a television camera, a threshold circuit for converting said video signal to a binary video signal having sharply defined transitions corresponding substantially with the particle boundaries of the represented sample being scanned, comprising:

  • a. adjustable threshold control circuit means for generating a first image intensity reference level signal;

    b. an automatic threshold network for generating a second image intensity reference level signal;

    c. first comparator circuit means connected to receive said video signal and said first and second image intensity reference level signals for comparing said video signal with either of said first or second image intensity reference level signals and including means for generating a first output signal whenever said video signal exceeds whichever one of said image intensity reference level signals with which it has been compared and a second output signal whenever said video signal does not, said first or second output signals being fed back to said automatic threshold network;

    d. first circuit means responsive to said video signal and said output signals of said first comparator circuit means for determining and storing the maximum value reached by said video signal between transitions of said otuput signals of said first comparator circuit means;

    e. second circuit means responsive to said video signal and said output signals of said first comparator circuit means for determining and storing the minimum value reached by said video signal between transitions of said output signals of said first comparator circuit means;

    f. signal summing network means connected to said first and second circuit means and responsive thereto for determining a predetermined weighted average of said maximum and minimum values of said video signal reached between transitions of said output signals of said first comparator circuit means;

    g. signal delay means receiving said video signal for delaying said video signal for a period of time equal to the time required by said first and second circuit means and said summing network to determine in concert the weighted average of said maximum and minimum values reached by said video signal between transitions of said output signals of said first comparator circuit means;

    h. second comparator circuit means connected to receive said delayed video signal, said first image intensity reference level signal and said weighted average signal for comparing said delayed video signal with said first image intensity reference level signal or said weighted average signal and including means for generating a binary video signal having a first state whenever said delayed video signal exceeds the signal with which it has been compared and a second state whenever said delayed video signal does not; and

    i. switching means for connecting said adjustable threshold control circuit means or said automatic threshold network to said first comparator circuit means and including means for connecting said adjustable threshold control circuit means or said signal summing network means to said second comparator circuit means.

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