| 摘要 |
PURPOSE:To set a clamp potential so as to have the maximum number of picture elements of the luminance in the vicinity of an intermediate luminance automatically and to eliminate the burden of an operator by providing a clamp potential automatic control circuit in an infrared image pickup device of direct current reproducing system for impressing the clamp potential in common. CONSTITUTION:From the output of an A/D converter 9, the number of the picture elements every frame situated within a prescribed luminance level range is selected within an upper limit of 60% luminance and a lower limit of 40% luminance by amplitude comparators 21, 22 and the sum of the number of the picture elements every frame in the selected result is stored in a picture element number memory 23. When the storing is completed in both the picture element number memories 23, 24, the difference between both the number of the picture elements is calculated by a subtracter 25, only when the result is directed to the reduction, an up/down change over controller 26 is driven and the count direction of an up/down counter 27 is changed over. The counted number is converted by a D/A converter 28, the obtain clamp potential is impressed to a clamp circuit 6 to automatically set the sum of the picture elements every frame constantly situated within the the prescribed brightness level range to the maximum value.
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