JPH0492578A - Automatic focus matching device for image pickup device - Google Patents

Abstract

PURPOSE:To exactly enable a focus matching operation at a close-up photographic area by switching an extraction range so that the range of a video signal larger than usual can be extracted at the time of detecting a state in which the matching position of the focus is at the close-up photographic position closer than a preliminarily set position. CONSTITUTION:When the matching position of the focus is at the close-up photographic area closer than preliminarily set constant position in a gate circuit 8, an evaluation value is extracted from the range where the video signal is large, rather than the range except for the close-up photographic area. A close-up photographic area discriminating signal N is can be obtained by a switch which is interlocked with the focus adjusting mechanism of a lens for example, and set in order to output the signal when the focus adjusting mechanism is at the position closer than the constant position. Thus, the evaluation value can be stably obtained even when a design without any signal component which indicates the focusing at the central part of a screen is photographed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic focusing device for an imaging device, and particularly for a video camera, which automatically adjusts the focus based on a signal indicating the degree of focus of an optical image in a photoelectric conversion section. The present invention relates to an automatic focusing device for an imaging device that adjusts the focus to an optimal position.

[Conventional technology]

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. In the figure, 1 is a lens, and 6 is a focus adjustment mechanism of the lens 1. The connected motor, 7 is a drive circuit that drives the motor 6, 2 is an image sensor that receives the light passing through the lens 1 and converts it into an electrical signal, and 3 is an image sensor that converts the output signal of the image sensor 2 into a video signal (luminance signal). 4 is a gate circuit for extracting a part of the video signal output from the signal processing circuit 3; 5 is a signal indicating the degree of focus matching from the video signal output from the gate circuit 4 (focus evaluation value); This is a control circuit that detects A) and controls the drive circuit 7 so that this becomes the maximum.

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 do not pass through the lens. Furthermore, it is known that when the lens system is out of focus, the pass band for this spatial frequency exhibits a reduced pass characteristic that is even narrower.

The light that has now entered through the lens 1 is converted into an electrical signal by the image sensor 2, and further converted into a video signal (luminance signal) by the signal processing circuit 3.

When the lens 1 is out of focus, 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 spatial frequencies. Therefore, the magnitude of the high frequency component in the video signal is determined by the degree of focus of the lens 1, and the larger the high frequency component is, the closer to the in-focus state it is, so the magnitude of this high frequency component represents the degree of focus. value (focus evaluation value A).

The control circuit 5 controls the drive circuit 7 so that this evaluation value A becomes maximum. The lens 1 is moved through the motor 6 to bring the device into focus.

Here, this control operation will be explained in detail.

Now, consider a case where the motor 6 rotates and moves the lens 1 in one direction. At this time, if the evaluation value A is increasing as the lens 1 moves, the lens 1 is approaching focus, so the control circuit 5 rotates the motor 6 in the same direction as the drive circuit 7 to move the lens 1. Outputs a control signal to continue driving. Conversely, if the evaluation value A decreases as the lens 1 moves, the lens 1 is moving away from focus, so the control circuit 5 reverses the motor 6 relative to the drive circuit 7 and moves the lens 1 in the opposite direction. Outputs a control signal to drive. In this way, the control circuit 5 operates to maximize the evaluation value A, and at the maximum point of the evaluation value A, the lens 1 is in focus.

Next, the operation of the gate circuit 4 will be explained in detail. In general, when shooting with a video camera, the angle of view of the image often includes multiple subjects, near and far, and the automatic focusing device of the video camera selects one of these multiple subjects to focus on. I have to do it, but
In many cases, the main subject is often photographed in the center of the screen, so the gate circuit 4 in the conventional example extracts the part of the video signal corresponding to the center of the screen based on the synchronization signal of the video signal. By detecting the evaluation value A from this signal and performing the series of automatic focusing operations described above, even when shooting including multiple subjects near and far within the angle of view of the image, the main subject in the center of the angle of view is automatically focused. I try to focus on the subject.

[Problem to be solved by the invention]

The automatic focusing device of a conventional imaging device is configured as described above, so when the main subject is located in the center of the shooting angle of view, accurate focusing is performed by the gate circuit. When the subject is not located in the center of the angle of view, the focusing operation is often incorrect.

In particular, when it comes to focus adjustment in close-up areas, the subject often appears large across the entire angle of view, or the composition is such that there is no signal component in the center of the screen that can detect focus. There is a problem in that the automatic focusing operation often malfunctions because the camera often takes pictures of

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic focusing device for an imaging device that can accurately perform a focusing operation even in a close-up area.

[Means to solve the problem]

The automatic focus adjustment device for an imaging device according to the present invention causes the gate circuit to output a video signal that is higher than the range to be extracted in a normal case outside the close-up area when the focus alignment position is in a close-up area that is closer than a predetermined fixed position. The evaluation value is extracted from a larger range of .

[Effect]

In this invention, when the gate circuit is in a close-up area where the focus matching position is closer than a predetermined fixed position, the evaluation value is extracted from a larger range of the video signal than the range normally extracted outside the close-up area. Since the image is extracted, the evaluation value can be stably obtained even when photographing a pattern or the like in which there is no signal component indicating focus at all in the center of the screen.

〔Example〕

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

FIG. 1 shows a block configuration diagram of an automatic focusing device for an imaging device according to an embodiment of the present invention, where the same reference numerals as in FIG. A close-up area discrimination signal indicating that the focus is aligned at a close position, 8 is a gate circuit that extracts a part of the video signal output from the signal processing circuit 3, and inputs the close-up area discrimination signal N to perform the extraction. Switch the range of video signals to be used. Note that the close-up area discrimination signal N is, for example, the lens 1.
This can be obtained from a switch, etc., which is linked to the focus adjustment mechanism and is set to output a signal when the focus adjustment mechanism is closer than a certain position.

Next, the operation will be explained.

When the focal point matching position is farther than a predetermined constant position, the gate circuit 8 corresponds to the central part of the screen angle of view as shown in FIG. 2(a) based on a preset normal extraction range. Extract the range of the video signal. In this case, the control circuit 5 uses the evaluation value A indicating the degree of focus in the video signal in the range extracted by the gate circuit 8 to perform the same operation as in the conventional example to obtain focus alignment.

On the other hand, if the focus matching position is closer than a predetermined fixed position, the close-up area discrimination signal N is input to the gate circuit 8, and the gate circuit 8 Extract a large video signal range. In this case, the control circuit 5 receives the evaluation value A indicating the degree of focus in the video signal in the range extracted by the gate circuit 8, controls the evaluation value A to be the maximum, and as a result, the focus Get alignment.

Therefore, in the close-up area where the focus matching position is closer than a predetermined fixed position, the gate circuit 8 extracts the video signal from a larger angle of view and performs matching, so that the center of the screen is completely focused during close-up shooting. Even when there is no signal component that can be detected, focusing can be detected based on signals from the peripheral portion of the screen.

As described above, in this embodiment, when the focus alignment position is closer than a predetermined fixed position, the focus adjustment mechanism of the lens 1 is linked, and when the focus adjustment mechanism is closer than the fixed position, the signal is output. A close-up area discrimination signal N obtained from a switch set to output the image is input to the gate circuit 8, which extracts a video signal from a larger angle of view and extracts a video signal from a larger angle of view and extracts the image signal from the peripheral part of the angle of view. Since alignment is performed, it is possible to obtain an automatic focus alignment device that is less likely to malfunction even when photographing a composition in which there is no signal component in the center of the screen, which tends to occur during close-up photography.

〔Effect of the invention〕

As described above, according to the automatic focus matching device for an imaging device according to the present invention, when the focus matching position is in a close-up area that is closer than a predetermined fixed position, the focus matching evaluation value is set to a larger image. Since the configuration is configured to calculate the image signal based on the video signal from the corner, automatic focusing is possible with fewer malfunctions and smooth operation, even when capturing images of designs with no signal component in the center of the screen, which tends to occur during close-up photography. This has the advantage that a matching device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic focusing device for an imaging device according to an embodiment of the present invention, and FIG. 2 is a block diagram of an automatic focusing device for an imaging device according to an embodiment of the present invention. FIG. 3, which is a diagram showing an example of the screen angle of view, is a block configuration diagram of an automatic focusing device of a conventional imaging device. In the figure, 1 is a lens, 2 is an image sensor, 3 is a signal processing circuit, 8 is a gate circuit, A is an evaluation value, and 1 is a close-up area discrimination signal. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) In an automatic focusing device that detects a signal indicating the degree of focus matching from a video signal obtained from an image sensor and drives an optical focus adjustment mechanism to maximize the detected signal, the automatic focusing device performs focus matching. The present invention is characterized by comprising means for detecting a state in which the collation position is at a close-up position that is closer than a preset position, and in this case switching the extraction range so as to extract a larger range of video signals than usual. Automatic focusing device for imaging device.