Automatic digital iris correction

Claim 1

Automatic digital aperture control apparatus for a television camera having at least one video output signal and comprising; peak detection means responsive to said at least one video output signal for providing a peak signal having a value which varies with the intensity of said video output signal; count control means for producing a first command signal when said peak signal rises above a first upper limit, and a second command signal when said peak signal falls below a first lower limit; a source of first clock pulses having a first pulse repetition rate; bidirectional digital counting means for counting clock pulses in a first or second direction in response to said first and second command signals, said counting means providing a digital output signal having a value in dependence upon the pulse count difference between the number of clock pulses counted in said first direction and those counted in said second direction; digital to analog converting means for converting said digital output signal to a corresponding analog signal having a value in accordance with said pulse count difference; aperture control means for controlling the amount of light admitted to said television camera in response to said analog signal; a source of second clock pulse having a second pulse repetition rate greater than said first pulse repetition rate; gating means responsive to a third command signal for gating said second clock pulses to said counting means and for otherwise gating said first clock pulses to said counting means; and, means for providing said third command signal when said peak signal rises above a second upper limit greater than said first upper limit or falls below a second lower limit smaller than said first lower limit.