Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1985-10-04
1987-09-22
Adams, Russell E.
Facsimile and static presentation processing
Facsimile
Recording apparatus
354403, H04N 5232, G03B 300
Patent
active
046958932
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an automatic focusing apparatus suitable for video cameras and television cameras with a zoom lens in which an accurate focused state for those objects from a very close distance up to more than 10 m is desired.
BACKGROUND ART
In prior art automatic focusing apparatuses for video cameras, appropriate sharpness signals are detected from the high frequency components of brightness signals which are contained in the video signals, and movement of a focusing lens is controlled so that those brightness signals become a maximum. In others, the distance to an object is measured by performing projection-reception operations of infrared light or transmission-receiving operations of supersonic signals to the object, and on the basis of those measured results the movement of a focusing lens is controlled.
The former approach to obtain the focused state by detecting the sharpness signal is based on a principle widely known from disclosures such as NHK Research Laboratory Report, Showa 40, Vol. 17, No. 1, pages 21 to 37. As discussed therein, as the lens approaches a focused state, high frequency components in the video signals increase and peak at the focused state. This approach has advantages in comparison with other approaches such as, for example, the supersonic focusing method or the light projection-reception method. Namely, in those apparatuses, sensors are necessary as a distance measuring means. Sensors such as a supersonic transmitter/receiver element or a projection-reception element are used, and since ordinarily a tele-zoom lens is attached to video cameras or other cameras for use as the above-mentioned sensors, it is required that they are highly accurate even for distances greater than several meters. Thus, the cost becomes very expensive, and an accurate distance measurement for greater than 10 m, for example, becomes difficult. By contrast, measuring the focused state using the sharpness signal does not require any sensor as a particular distance measurement means, thereby making it possible to obtain an automatic focusing apparatus which is low-cost, small-sized, and capable of discriminating the focused state regardless of distance. However, such a device has difficulties of two kinds, as will be described below.
In the system in which appropriate sharpness signals corresponding to the sharpness of picture images are detected from high frequency components of the video signal and the movement of a focus adjustment lens is controlled, when an object moves from an arbitrary focused state to another focused state, the variations of the above-mentioned sharpness signals are used to control the movement of the lens. Namely, since the sharpness signals are at a peak when in a focused state, when the sharpness signal in an arbitrary focused state changes, it is judged that the lens goes from a focused position to an out of focused position, and the movement of the lens is started. However, it is known that the high-frequency components in the video signals vary when the contrast of the object, i.e., the brightness distribution state varies Therefore, for example, when in a state wherein an arbitrary focused state is obtained, such as when an object moves simply left or right without changing the distance to the automatic focusing apparatus, it is considered that the contrast of the object is easily changed.
In the case that the contrast of the object varies as described above, notwithstanding that the distance to the object does not change, the movement of the focusing lens is started. Thus, even though contrast variation takes place, the lens position at which the peak of the sharpness signals is obtained does not change its distance and remains at the same position as before the movement. The lens returns to the original position instantly and stops there, hence it is needless to describe in detail that the moving distance and the moving time are very small amounts. However, even though the moving distance and the moving time of the lens are slight, t
REFERENCES:
patent: 4550995 (1985-11-01), Toyama et al.
patent: 4581653 (1986-04-01), Kaneda
patent: 4591919 (1986-05-01), Kaneda et al.
patent: 4592638 (1986-06-01), Kaneda et al.
Kihara Tadaharu
Makino Hiroshi
Takashima Akira
Yoshino Tsunemi
Adams Russell E.
West Electric Company Ltd.
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