JPH0481080A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To eliminate the unnecessary movement of a lens and to obtain a natural focusing operation by temporarily stopping the operation of the lens or outputting a signal for delaying the operational speed of the lens from a focusing control circuit when the amount of blurring is more than a prescribed value. CONSTITUTION:A blurring detector 10 detects the change of an angle (angular velocity) to be displaced per unit time and outputs an electric signal. When it is judged that the amount of blurring detected by the blurring detector 10 is larger than the prescribed value, namely, when an image pickup preparation step is judged, a focusing control circuit 11 controls a driving circuit 7 so as to temporarily stop the operation of a lens 1 concerning focusing or to delay the operational speed of a motor 6 to drive the lens 1. Thus, even when the electric signal is distorted by blurring in the image pickup preparation step, the unnecessary movement of the lens is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focusing device that automatically adjusts the focus of a video camera.

[Prior Art] Fig. 3 is a block diagram showing the operating principle of a conventional automatic focusing device disclosed in, for example, Japanese Patent Publication No. 39-5265. An image sensor that receives light and converts it into an electrical signal; 3 is a signal processing circuit that converts the output signal of the image sensor 2 into a video signal (luminance signal); 4 is a signal processing circuit that converts a portion of the video signal output from the signal processing circuit 3; A gate circuit for extraction, 5 is a control circuit that detects a signal indicating the degree of focus matching (focus evaluation value A) from the video signal output from the gate circuit 4, and controls the drive circuit 7 to maximize this signal. , 6 is a motor connected to the focus adjustment mechanism of the lens 1, and 7 is a drive circuit for driving the motor 6.

Next, the operation will be explained. The lens 1 generally has a low-pass characteristic with respect to spatial frequencies, and spatial frequency components finer than the resolution of the lens 1 do not pass through the lens, and when the lens system is not focused, this spatial frequency It is known that the passband for χ exhibits an even narrower low-pass characteristic.

First, light incident through the lens 1 is converted into an electrical signal by the image sensor 92, and further converted into a video signal (luminance signal) by the signal processing circuit 3. When the lens 1 is not focused on the image sensor 2, this video signal is also band limited and exhibits a low-pass characteristic corresponding to the low-pass characteristic of the lens 1 with respect to the spatial frequency. Therefore, the magnitude of the high frequency component in the video signal changes depending on the degree of focus of the lens l, and a large high frequency component indicates that the state is close to being in focus. Therefore, the magnitude of this high frequency component can be used as a value representing the degree of focus (focus evaluation value A).

The control circuit 5 controls the drive circuit 7 so that the focus evaluation value A becomes maximum, adjusts the lens 1, and brings the device into focus.

Next, this control operation will be explained in detail. Now, consider a case where the motor 6 rotates and moves the lens l in one direction. At this time, if the focus evaluation value A increases as the lens 1 moves, the lens 1 is getting close to being in focus, so the control circuit 5 drives the motor 6 in the same direction as the drive circuit 7. A control signal is output to continue rotating the lens 1 and driving the lens 1. On the other hand, if the focus evaluation value A decreases as the lens 1 moves, the lens 1 is moving away from focus, so the control circuit 5 reverses the direction 6 with respect to the drive circuit 7, and vice versa. A control signal is output to drive the lens 1 in the direction shown in FIG. In this way, the control circuit 5 operates to maximize the focus evaluation value A. At the maximum point of the focus evaluation value A, the lens l is in the focused state. Configure a focusing device.

Here, the operation of the gate circuit 4 in this conventional example will be explained in detail. In general, when shooting with a video camera, the angle of view (field of view) of the video often includes multiple subjects, near and far, at the same time (the automatic focusing device of the video camera selects one of these multiple subjects). However, in most cases, the main subject is often photographed in the center of the screen, so the gate circuit 4 in this conventional example By extracting a partial signal in the video signal corresponding to the central part of the screen, detecting the focus evaluation value A from this partial signal, and performing the above series of automatic focusing operations, multiple subjects near and far can be captured within the angle of view of the video. It is possible to automatically focus on the main subject located in the center of the field of view even when taking pictures that include.

[Problem to be solved by the invention]

Since the conventional automatic focusing device is configured as described above, when there is a camera shake, the electric signal is naturally disturbed and the output of the signal processing circuit 3 also changes.

Therefore, if the subject in the screen area extracted by the gate circuit 4 changes, the focus evaluation value A will change, and even if the distance to the subject does not change much, the lens will move unnecessarily, resulting in natural focusing. There was a problem in that it was difficult to obtain movement.

This invention was made to solve the above-mentioned problems, and even if there is a disturbance in the electrical signal due to camera shake during the imaging preparation stage, unnecessary lens movement can be avoided by detecting the camera shake. The objective is to obtain an automatic focusing device that suppresses

[Means to solve the problem]

The automatic focusing device according to the present invention includes a gate circuit that detects and outputs a focus evaluation value indicating the degree of alignment of lens focus from a video signal, and a gate circuit that detects random change information of the video signal and changes in angular velocity of the device. a camera shake detection device that outputs an electric signal, and if the amount of camera shake output from the camera shake detection device is larger than a predetermined value, the operation of the lens is temporarily stopped.

Alternatively, a focusing control circuit that outputs a signal that delays the operating speed of the lens is provided.

[Operation] The camera shake detection device according to the present invention causes the focusing control circuit to temporarily stop the movement of the lens when random change information of the video signal or camera shake occurs, but outputs a control signal that delays the movement speed of the lens. Therefore, even if the focus evaluation value changes, unnecessary movements of the lens are suppressed.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the same parts as in FIG. 3 are indicated by the same reference numerals. In FIG. This is a focusing control circuit that captures information.

Next, the operation will be explained. First, the camera shake detection device 10
detects changes in the angle of displacement (angular velocity) per unit time and outputs an electrical signal.

When it is determined that the amount of camera shake detected by the camera shake detection device 10 is smaller than a predetermined value, the focusing operation of the lens 1 is performed in the same manner as in the conventional case. Further, when it is determined that the amount of camera shake detected by the camera shake detection device 10 is larger than a predetermined value, that is, when it is determined that the image capture preparation stage is reached, the focusing operation of the lens 1 is temporarily stopped, or the lens The focus control circuit 11 controls the drive circuit 7 to slow down the operating speed of the motor 6 that drives the focus control circuit 11.

In the above embodiment, for example, an image stabilization detection device using an angular velocity sensor is used to suppress the focusing operation of the lens during the imaging preparation stage. However, as another embodiment, as shown in FIG. 2, the image stabilization detection device 10 may detect random change information of the video signal and detect the ridges in this state as being affected by camera shake. , the same effect as the above embodiment is achieved.

[Effect of the Invention 1 As described above, according to the present invention, random change information of a video signal and changes in angular velocity of an automatic focusing device are captured by a camera shake detection device and an electric signal is output as the amount of camera shake,
When the amount of camera shake exceeds a predetermined value, the focus control circuit outputs a signal that temporarily stops lens operation or delays the lens operation speed, so even if the focus evaluation value changes, This also eliminates unnecessary lens movement, resulting in a more natural focusing operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an automatic focusing device according to an embodiment of the invention, FIG. 2 is a block diagram showing the configuration of an automatic focusing device according to another embodiment of the invention, and FIG.
The figure is a block diagram of a conventional automatic focusing device. In the figure, 1 is a lens, 4 is a gate circuit, 5 is a control circuit, 7 is a drive circuit, 10 is a camera shake detection device, and 11 is a focusing control circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A gate circuit that detects and outputs a focus evaluation value indicating the degree of alignment of lens focus from a video signal, and a control circuit that receives the focus evaluation value and controls a drive circuit to derive a maximum condition for the evaluation value. In an automatic focusing device having
a camera shake detection device that captures random change information of the video signal and changes in angular velocity of the device and outputs an electrical signal;
In place of the control circuit, a focus control circuit outputs a signal that temporarily stops the operation of the lens or delays the operation speed of the lens when the amount of camera shake output from the camera shake detection device is larger than a predetermined value. An automatic focusing device comprising: