PURPOSE: To obtain an autofocus device which performs excellent hill-climing operation without reference to the number of longitudinal contour components of a photographed image, by preventing the saturation of the output voltage of a detector.
CONSTITUTION: A video signal outputted by a camera circuit 2 is inputted to a low-pass filter 11 and then led to a differentiating circuit 12 to obtain a signal which corresponds to a contour part of an image. The output signal of the circuit 12, after a threshold smplifier 13 removes contour components with lower contract than a predetermined threshold level, is counted by a counter 14. A gate signal generating circuit 15 holds an electronic switch 10 closed when the input counted value is less than a preset value, or turns on and off the switch 10 at every other horizontal scanning line on a screen while referring to a horizontal and a vertical synchronizing signal outputted from a synchronous separating circuit 16 to reduce input signals to a detector 5, thus preventing saturation.
MURAKAMI TOSHIO
TODAKA YOSHIHIRO
| JPS4812615A |