Television – Camera – system and detail – Optics
Reexamination Certificate
1999-05-20
2003-10-21
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Optics
C345S215000, C348S363000, C348S364000
Reexamination Certificate
active
06636262
ABSTRACT:
TECHNICAL FIELD
The present invention relates to autofocus apparatuses and more particularly, to an autofocus apparatus for use in a video camera or the like.
BACKGROUND ART
In an autofocus apparatus used in a video camera or the like, the high frequency component of a luminance signal is used as a focusing evaluation value and a focus is supposed to be obtained when the evaluation value is largest. There is a system such as an iris for adjusting the brightness of the entire picture plane according to the brightness of the picture plane to avoid saturation of the brightness. If therefore the entire picture plane is bright, the luminance difference between a high luminance object present in the picture plane and the picture plane is not large, and therefore the brightness of the high luminance object is adjusted to avoid saturation, so that an out-of-focus, unclear image will not be saturated in the white direction, and the evaluation value in focus is largest.
According to conventional art, when the entire picture plane is bright, the brightness and evaluation value of the entire picture plane are adjusted to avoid saturation using an iris or the like and a focus is obtained in the presence of a high luminance object, but when the entire picture plane is dark, the iris is considerably opened if there is a partly high luminance object. This is because if the iris is stopped down for a partly high luminance object, the entire picture plane also becomes very dark and the resultant image would appear quite disagreeable when compared to the object actually observed by a person. Then, the high luminance part being greatly different from the entire picture plane in luminance is saturated in the direction of white, and therefore the saturated region will be large when it is out of focus, and the contour will be large, which increases the high frequency component and the evaluation value. In that state, the autofocus apparatus often stops operating as if a focus is obtained.
It is therefore a main object of the present invention to provide an autofocus apparatus which removes a high frequency component from the evaluation value of an image having a high luminance part, by excluding integration of the high frequency component in an area having a luminance level equal to or higher than a prescribed value when the entire picture plane is dark and the iris is considerably opened.
DISCLOSURE OF INVENTION
The present invention is directed to an autofocus apparatus to adjust an image input to an imaging device into focus by controlling a lens unit, and includes a focus evaluation value detecting circuit for integrating the high frequency component of a video signal for each of a plurality of regions formed by dividing a picture plane to output the result as a focus evaluation value, a focus control circuit for performing a focusing operation by displacing the relative position of the lens to the imaging device such that the focus evaluation value is maximized, a luminance level detecting circuit for detecting the luminance level of each region of the picture plane, an iris detecting circuit for detecting the aperture degree of an iris, an excluding circuit for selectively excluding integration of the high frequency component of a region by the focus evaluation value detecting circuit in response to the detected luminance level of the region being equal to or higher than a prescribe threshold level, and a control circuit for controlling the excluding circuit to exclude integration of a high frequency component in a region having a luminance level detected by the focus evaluation detecting circuit higher than a prescribed value when the detected iris degree indicates an aperture degree equal to or higher than a prescribed value.
Therefore, according to the present invention, in response to a detected iris degree indicating a value equal to or higher than a prescribed value, integration of the high frequency component of a region having a luminance level equal to or higher than a prescribed value is excluded, so that a focus can be promptly obtained in response to a high luminance part such as a spot light in a dark background where the iris is extremely stopped down, so the picture plane is very much dark but still appears agreeable.
More preferably, in response to the aperture degree of the iris, the threshold value of the luminance level to determine a region which is excluded from integration is changed.
According to a more preferable embodiment, if the detected aperture area of the iris is not less than a prescribed value, the prescribed value is used as the threshold value, and if the aperture area of the iris is not more than the prescribed value, the threshold value is set based on the aperture area of the iris.
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European Search Report dated Feb. 13, 2002.
Okajima Tadashi
Tsujino Kazuhiro
Ho Tuan
Sanyo Electric Co,. Ltd.
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