Television – Camera – system and detail – Optics
Patent
1997-03-19
2000-03-07
Ho, Tuan
Television
Camera, system and detail
Optics
348354, 348351, H04N 5232
Patent
active
060347279
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a focus control method of focusing a lens on an object upon an image pickup thereof and a video camera apparatus for focusing its lens on the object by using the focus control method.
BACKGROUND ART
A consumer video camera has employed an autofocus method of automatically focusing a lens on an object.
It is well known that, in order to discriminate whether or not a lens is in focus or out of focus, it is sufficient to discriminate whether contrast of a video signal obtained by an image pickup is high or low. In other words, if the contrast is high, then the lens is in focus. If on the other hand the contrast is low, then the lens is out of focus. A high-frequency component is extracted from the video signal obtained by an image pickup, and a data obtained by integrating the high-frequency component in a predetermined set area is generated. It is possible to discriminate whether the contrast is high or low, by using the integrated data. The integrated data is indicative of how much there is the high-frequency component in the predetermined area. In general, this data is called an estimation value. Accordingly, it is possible to realize the autofocus method by driving a focus lens so that the estimation value should be maximum (i.e., the contrast should be maximum).
The estimation value extracted by the above method inevitably includes a plurality of factors in response to a state of an object upon the image pickup thereof. Hence, it is impossible to precisely determine a focus deviation amount based on the estimation value. Such estimation value inevitably includes a noise corresponding to an image pickup condition as an element thereof, and hence it is difficult to precisely extract a focus deviation, which is fundamentally necessary, amount from such estimation value. Therefore, since it is impossible for a conventional focus controlling apparatus and a conventional video camera to obtain a precise estimation value, it takes a considerable time for the conventional focus controlling apparatus and the conventional video camera to search for a maximum point of an estimation value. As a result, a camera man must continue taking a blurred picture while the above conventional focus controlling apparatus or the above conventional video camera is carrying out a focusing operation.
For example, it is sometimes observed that an image picked up by a video camera apparatus for use in a broadcasting station or for professional use is transmitted on the air as a live relay broadcast. If it is sometimes observed that in such live relay broadcast the satisfactory accuracy of the estimation value is not achieved and hence it takes a considerable time to carry out the autofocus operation, a video signal indicative of a blurred picture is transmitted on air. Therefore, a simplified, inexpensive and small autofocus apparatus such as that used in a consumer video camera is not necessary for the video camera for use in the broadcasting station or for professional use, but a high-accuracy focus control and a high-speed focus control are required therefor.
It is an object of the present invention to make it possible to generate an estimation value corresponding to an image pickup condition and to detect a focus position at high speed.
DISCLOSURE OF THE INVENTION
According to the present invention, a focus control method includes an estimation-value generating means for generating an estimation value by extracting a high-frequency component in a predetermined range of a video signal output from an imaging means while a focus lens is being moved, and a change detecting means for detecting change of the estimation value from the estimation-value generating means to thereby determine a maximum point of the estimation value. The maximum point is determined as a focus position when an estimation value is continuously decreased from a focus lens position determined as the maximum point by the change detecting means to a position whose distance therefrom is as long as a predetermi
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Ikeyama Chiaki
Inomata Naoki
Ito Yujiro
Kurita Susumu
Frommer William S.
Ho Tuan
Sony Corporation
Wilson Jacqueline
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