Automatic aperture control of a television camera

摘要

R, G and B outputs from the corresponding preamplifiers of a television camera are supplied to a non-additive mixer (NAM) circuit for continuous selection of the greatest of the three outputs and the selected output is continuously supplied to a set of 9 electronic switches each selecting out a subdivision of the picture field (a, b . . . i). The switched outputs for each of the subfields are then provided to respective subfield measurement detectors which each produce an average value output and a peak value output. These are stored into subfield buffer units and then read out through a multiplexer and an analog to digital converter to a microprocessor. The various values are compared with corresponding past values for selecting between various measurement schemes for obtaining a camera diaphragm control signal, namely spot measurement, center-emphasized integral measurement and selective field measurement. Except when a decision for no setting change is made, the selected scheme of measurement is used to obtain a control signal from the average and dynamic range values of the several subfield video signals.