Auto focus circuit for video camera
First Claim
1. An autofocus circuit for a video camera including a focusing motor for focusing, comprising:
- .[.a.]. high-pass filter .[.circuit.]. .Iadd.means .Iaddend.to which a luminance signal of a video signal is applied .[.so that.]. .Iadd.for extracting .Iaddend.a high frequency component higher than a predetermined frequency .[.is extracted.]. from said applied luminance signal,.[.an absolute value calculating circuit connected to said high-pass filter circuit for obtaining an absolute value of the output of said high-pass filter circuit,.]..[.an.]. A-D converting .[.circuit.]. .Iadd.means operatively .Iaddend.connected to said .[.absolute value calculating circuit.]. .Iadd.high-pass filter means .Iaddend.for converting an analog .[.absolute value.]. output signal .[.provided.]. .Iadd.derived .Iaddend.from said .[.absolute value calculating circuit to.]. .Iadd.high-pass filter means into .Iaddend.a digital signal,.[.a.]. calculating .[.circuit.]. .Iadd.means .Iaddend.connected to said A-D converting .[.circuit.]. .Iadd.means .Iaddend.for adding the converted digital signal with a predetermined period cycle,.[.a.]. comparing .[.circuit.]. .Iadd.means .Iaddend.connected to said calculating .[.circuit.]. .Iadd.means .Iaddend.for comparing the output of calculation in one predetermined period and the output of calculation in .[.the predetermined period coming one.]. .Iadd.another .Iaddend.predetermined period .[.ahead of said predetermined period.]., and.[.a.]. focusing motor control .[.circuit.]. .Iadd.means .Iaddend.connected to said comparing .[.circuit.]. .Iadd.means .Iaddend.for providing a signal for controlling the rotation of the focusing motor included in said video camera in the clockwise direction or in the counter-clockwise direction based on the output of said comparing .[.circuit.]. .Iadd.means.Iaddend..
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Abstract
An auto focus circuit for a video camera comprises an A-D converting circuit (7) for converting to a digital amount a high frequency component absolute value output of a luminance signal in a sampling area for focusing. The A-D converting circuit (7) is connected so that the high frequency component absolute value output of a luminance signal is directly converted to a digital amount. Then, the signal converted to a digital amount is added in an integrating circuit (12) for each field and the signal amount in one field and the signal amount in the coming one field ahead of it or behind it are compared in a comparing circuit (10) so that the output of comparison serves for control of focusing. Thus, addition processing of the high frequency component of the luminance signal, that is, averaging processing is performed digitally in the integrating circuit (12). Accordingly, as compared with the case of analog averaging processing of a signal, the processing operation is stable and as a result the focusing precision is improved.
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Citations
9 Claims
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1. An autofocus circuit for a video camera including a focusing motor for focusing, comprising:
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.[.a.]. high-pass filter .[.circuit.]. .Iadd.means .Iaddend.to which a luminance signal of a video signal is applied .[.so that.]. .Iadd.for extracting .Iaddend.a high frequency component higher than a predetermined frequency .[.is extracted.]. from said applied luminance signal, .[.an absolute value calculating circuit connected to said high-pass filter circuit for obtaining an absolute value of the output of said high-pass filter circuit,.]. .[.an.]. A-D converting .[.circuit.]. .Iadd.means operatively .Iaddend.connected to said .[.absolute value calculating circuit.]. .Iadd.high-pass filter means .Iaddend.for converting an analog .[.absolute value.]. output signal .[.provided.]. .Iadd.derived .Iaddend.from said .[.absolute value calculating circuit to.]. .Iadd.high-pass filter means into .Iaddend.a digital signal, .[.a.]. calculating .[.circuit.]. .Iadd.means .Iaddend.connected to said A-D converting .[.circuit.]. .Iadd.means .Iaddend.for adding the converted digital signal with a predetermined period cycle, .[.a.]. comparing .[.circuit.]. .Iadd.means .Iaddend.connected to said calculating .[.circuit.]. .Iadd.means .Iaddend.for comparing the output of calculation in one predetermined period and the output of calculation in .[.the predetermined period coming one.]. .Iadd.another .Iaddend.predetermined period .[.ahead of said predetermined period.]., and .[.a.]. focusing motor control .[.circuit.]. .Iadd.means .Iaddend.connected to said comparing .[.circuit.]. .Iadd.means .Iaddend.for providing a signal for controlling the rotation of the focusing motor included in said video camera in the clockwise direction or in the counter-clockwise direction based on the output of said comparing .[.circuit.]. .Iadd.means.Iaddend.. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification