Automatic focusing device capable of removing noise components from focusing contrast information

Claim 1

An automatic focusing device for focusing an image of an object incident on an image pick-up device via a lens, comprising: contrast information separating means for separating a contrast signal representative of a contrast from a luminance signal generated by said image pick-up device; extracting means for extracting a predetermined part of said contrast signal lying in a focus area which is defined in a picture represented by said contrast signal; removing means for removing noise components of a predetermined level from the extracted part of said contrast signal, said removing means comprising a reference voltage source for generating a reference voltage defining said predetermined level, first slicing means for slicing said extracted part of said contract signal by using said reference voltage, second slicing means for inverting said extracted part of said contrast signal and then slicing said inverted extracted part by using said reference voltage, and differential amplifying means for amplifying a difference between an output of said first slicing means and an output of said second slicing means which are respectively applied to a non-inverting input terminal and an inverting input terminal of said differential amplifying means; integrating means for integrating outputs of said differential amplifying means, from which the noise components of said predetermined level have been removed, to thereby calculate an evaluation value for focusing; deciding means for determining a focus condition on the basis of said evaluation value produced by said integrating means, and then selecting a direction in which said lens is to be removed; and driving means for driving said lens on the basis of a result of decision of said deciding means.