JPH03238978A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain the focal state quickly and accurately by driving a focusing lens up to the focal position in response to a focusing lens position signal, a focus evaluation signal and an object distance signal. CONSTITUTION:A CPU 18 compares a focal position of a focus lens 42 outputted from a ROM 24 at first with a position of a current focusing lens 42 inputted from a focusing lens position detector 30. When the difference is larger than a predetermined value, since the CPU 18 drives the focusing lens 42 up to the focal position outputted from the ROM 24, the moving direction and the moving distance of the focusing lens 42 are calculated and the signal is given to a focus motor driver 26. Thus, the movement of the focusing lens 42 to the focal position is implemented at once and the focusing lens 42 is quickly moved to the nearly focal position.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an imaging device such as a video camera, and in particular,
The present invention relates to an autofocus method for an imaging device.

[Prior Art] FIG. 3 is a block diagram of a video camera that employs autofocus using a conventional video processing method.

Referring to FIG. 3, a conventional video camera has an optical system 10 that has a predetermined optical axis and focuses incident light rays along the optical axis onto a predetermined image plane using a focusing lens 42. and a CCD (Charg) for converting the image of the subject formed by the optical system 10 into an electrical signal.
e-Coup ledDevice) 12 and CCD1
A video signal processing circuit 14 performs video signal processing on the electrical signal outputted by the video signal processing circuit 2 and outputs it as a video signal. Autofocus circuit 1 that outputs a focus evaluation value signal for automatic focusing
6, a focusing lens position detector 30 that detects the position of the focusing lens 42 and outputs a focusing lens position signal, and is connected to the autofocus circuit 16 and the focusing lens position detector 30, and responds to a focus evaluation value signal. CPU for calculating in which direction and how much to move the focusing lens.
18, a focus motor driver 26 connected to the CPU 18, and a focus motor 28 connected to the focus motor driver 26 for moving the focusing lens 42 in a predetermined direction by an amount calculated by the CPU 18.

The optical system 10 includes a front lens 36, a cam section 34 for performing a magnification change operation using a so-called zoom mechanism, an erector 38, a mask lens 40, and a focusing lens 42. A zoom motor 32 for driving a zoom mechanism is connected to the cam portion 34.

The cam section 34 includes a variator 44 that is a variable magnification lens, and a compensator 46 for compensating for a shift in focus due to variable magnification by the variator 44. Variator 44
and compensator 46 are movable back and forth along the optical axis.

The autofocus circuit 16 extracts a high frequency component from the luminance signal component of the video signal output from the video signal processing circuit 14 and outputs it as a focus evaluation value. In response to the focus evaluation value signal output from the autofocus circuit 16, the CPU 18 calculates the moving direction of the focusing lens 42 and its distance by so-called "mountain climbing control."

The operation of a conventional video camera will be explained with reference to FIGS. 3 and 4. The light rays from the subject are imaged by the optical system 10 onto the light receiving surface of the CCD 12 . The CCD 12 converts the formed image of the subject into an electrical signal. The electrical signal is input to the video signal processing circuit 14, subjected to video signal processing, and output as a video signal. The autofocus circuit 16 receives the luminance signal component of the video signal from the video signal processing circuit 14 . The autofocus circuit 16 extracts only a predetermined high frequency component from the manually input luminance signal component and outputs it to the CPU 18 as a focus evaluation value signal.

On the other hand, the focusing lens position detector 30 detects the position of the focusing lens 42 along the optical axis and sends a lens position signal indicating the position of the focusing lens 42 to the C
Output to PU18.

The CPU 18 calculates the moving direction and amount of movement of the focusing lens 42 in response to the focus evaluation value signal input from the autofocus circuit 16 and the lens position detection signal input from the focusing lens position detector 30. do.

The calculation method uses the hill-climbing method as described above.

Referring to FIG. 4, when the focusing lens 42 is close to being in focus, the high frequency component of the obtained video signal increases. When the image is in focus, the so-called edges are clear. Such signals contain many high frequency components. Therefore, by detecting the amount of high frequency components among the luminance signal components output from the video signal processing circuit 14, the focusing lens 42
The in-focus state of the image can be evaluated.

The CPU 18 constantly monitors the focus evaluation value manually input from the autofocus circuit 16. And CPU1
8 moves the focusing lens 42 in the direction in which the focus evaluation value signal always increases. Referring to FIG. 4, for example, if the focus evaluation value is at point Q, lens 42 is moved closer to point P. As a result, the focus evaluation value increases. On the other hand, it is assumed that the lens 42 has gone too far at point P and has reached point R. At this time, the focus evaluation value becomes maximum at point P, and becomes a value smaller than point P at point R. Therefore, the CPU 18 now reversely moves the lens from point R to point P.

Through the above-described hill-climbing control, the moving direction of the focusing lens 42 is determined so that the lens is always at point P, that is, the focusing lens 42 is in focus.

The focus motor driver 26 receives a signal indicating the moving direction of the focusing lens 42 from the CPU 18 and drives the focus motor 28 . The focus motor 28 moves the focus lens 42 in a direction specified by the CPU 18. Thereby, the image formed on the CCD 12 is always in focus.

[Problems to be Solved by the Invention] Conventional autofocus circuits have the advantage of being able to bring the focusing lens 42 into focus with a relatively simple structure.

However, conventional video cameras have the following problems. For example, assume that the focus lens 42 is located far from the focused state.

In this case, the distance that the focusing lens 42 moves before moving to the in-focus state is quite large. On the other hand, CPU18
The driving control of the focusing lens 42 is performed by repeatedly evaluating the focus evaluation value from the autofocus circuit 16. Through mountain climbing control by the CPU 18, the focusing lens 42 is moved little by little until it is in focus. Therefore, there is a problem in that it takes a long time for the focusing lens 42 to move to a completely in-focus position.

Furthermore, for example, for some reason (such as when horizontal stripes are applied to the subject), there may be a case where there is a maximum point in the middle of the graph drawn by the focus evaluation value. In this case, the focusing lens 42 may not be able to focus to the original focus position and may remain near the maximum value of the focus evaluation value. In such a case, the resulting video signal will be significantly out of focus.

Therefore, it is an object of the present invention to provide an imaging device that can quickly and accurately reach a focused state.

[Means for Solving the Problems] An imaging device according to the present invention has a focusing lens that is movable along a predetermined optical axis, and captures an image of a subject at an arbitrary position by adjusting the distance between the focusing lens and the subject. an optical system that forms an image on a predetermined imaging plane by moving the focusing lens to a determined focusing position; and a lens position detection means that detects the position of the focusing lens along the optical axis and outputs a focusing lens position signal. an imaging means provided on the imaging plane for converting the image of the subject into an electrical signal;
A video signal circuit that processes electrical signals and outputs them as video signals, and extracts a predetermined frequency band component whose magnitude changes depending on the focus state from the luminance signal component of the video signal and indicates the focus state. A focus evaluation means for outputting a video signal as a focus evaluation value signal, an object distance measuring means for measuring the distance between the optical system and the object and outputting an object distance signal, a focusing lens position signal, and a focus evaluation value signal. , and a focusing lens driving means for driving the focusing lens to the in-focus position in response to the subject distance signal.

[Operation] In the imaging apparatus having the above structure, the focusing lens driving means drives the focusing lens in response to the focus evaluation value signal and the subject distance signal. That is, when the focusing lens is far out of focus, the focusing lens is quickly moved to near the in-focus state in response to the subject distance signal. On the other hand, near the in-focus state, the lens is driven in response to the focus evaluation value signal.

[Embodiment] Referring to FIG. 1, the video camera according to the embodiment of the present invention is different from the conventional video camera shown in FIG.
A distance detection sensor 20 for detecting the distance from the subject to the optical system 10 and outputting it as a distance detection signal, and an A/D converter for A/D (analog/digital) conversion of the output of the distance detection sensor 20. 22 and A/D converter 2
2, and a ROM 24 for calculating and outputting the optimal position of the focusing lens 42 in response to the distance from the subject to the optical system 10. The output of the ROM 24 is connected to the CPU 18.

In the video camera shown in FIG. 1, parts that are the same as those shown in FIG. 3 are given the same reference numerals and names. Their functions are also the same.

Therefore, detailed explanations about them will not be repeated here.

The data stored in the ROM 24 is a table showing the correlation between the distance from the subject to the optical system 10 and the position of the focusing lens 42 for obtaining a focused state in that case.

As the distance detection sensor 20, for example, an ultrasonic sensor or an infrared sensor can be used.

The operation of a video camera according to an embodiment of the present invention will be explained with reference to FIG. An image of the subject is formed on the light receiving surface of the CCD 12 by the optical system 10 .

The CCD 12 converts the image of the subject into an electrical signal and outputs it to the video signal processing circuit 14. The video signal processing circuit 14 is
The output of the CCD 12 is subjected to video signal processing and output as a video signal, while its luminance signal component is output to the autofocus circuit 16.

The autofocus circuit 16 outputs a focus evaluation value signal indicating the magnitude of the high frequency component included in the luminance signal component to CP.
Output to U18. Focusing lens position detector 3
0 detects the current position of the focusing lens 42 and provides that information to the CPU 18.

The distance detection sensor 20 detects the distance between the subject and the optical system 10 and outputs it to the A/D converter 22 as an electrical signal.

The A/D converter 22 converts the electrical signal output from the distance detection sensor 20 into a digital signal. ROM24 is A
A focusing lens 42 corresponding to the distance between the subject and the optical system 10 uses the output of the /D converter 22 as an address.
The in-focus position is calculated from the table and provided to the CPU 18.

The CPU 1g first determines the in-focus position of the focus lens 42 output from the ROM 24 and the current focus position of the focus lens 42 manually input from the focusing lens position detector 30.
Compare with the position of If the difference is larger than a predetermined value, the CPU 18 drives the focusing lens 42 to the in-focus position output from the ROM 24.
The moving direction and moving distance of the focusing lens 42 are calculated and the signals thereof are given to the focus motor driver 26. The focus motor driver 26 drives the focus motor 28 and controls the focusing lens 42 from the CPU.
18 in the direction specified and by the specified distance.

As the focusing lens 42 moves, the lens position signal output from the focusing lens position detector 30 almost matches the signal output from the ROM 24 indicating the focused position of the focusing lens. In this case, the focusing lens 42 can be moved all at once to the in-focus position. Therefore, the focusing lens 42 can be quickly moved almost to the in-focus position.

When the focusing lens 42 almost reaches the in-focus position, the signal output from the focusing lens position detector 30 and the signal output from the ROM 24 almost match.

When the CPU 18 detects this coincidence, it stops moving the focusing lens 42 based on the output of the ROM 24 and starts mountain climbing control based on the output of the autofocus circuit 16.

Even if the focus evaluation value output by the autofocus circuit 16 has a maximum value at a position other than the focus position, the movement of the focusing lens 42 to the focus position is
Since the focusing is performed all at once based on the output from the ROM 24, there is no possibility that the focusing lens 42 will stop erroneously near such a maximum value. Therefore, the focusing lens 4 is always near the maximum focus evaluation value.
2, the CPU 18 moves the focus motor 2 so that
8 can be controlled.

FIG. 2 is a flowchart showing an outline of a program executed by the CPU 18. Referring to FIG. 2, in step S1, the distance detection sensor 20, the A/D converter 2
2. The subject distance information obtained by the ROM24 is
Manpower will be provided by PU18.

In step S2, zoom position information is manually input from, for example, a zoom position detection device (not shown) provided in the cam section 34, taking into account the influence of the zoom position on the focal length of the optical system 10.

In step S3, the focusing lens position signal output from the focusing lens position detector 30 is input.

In step S4, position calculations such as the moving direction and amount of movement of the focusing lens 42 are performed based on the in-focus position of the focusing lens 42 output from the ROM 24 and the current lens position output from the focusing lens position detector 30. .

In step S5, the CPU 18 provides information for driving the focus motor 28 to the focus motor driver 26. As a result, the focus motor 28 and therefore the focusing lens 42 are moved by a predetermined amount in a predetermined direction.

Subsequently, in step S6, the autofocus circuit 1
Based on the focus evaluation value signal outputted by the focus lens 6 and the lens position signal outputted from the focusing lens position detector 30, the autofocus operation is performed using the above-mentioned hill climbing control. That is, in step S6, the focusing lens 42 is moved to an accurate focusing position.

In step S7, the focusing lens 42 is stopped and the program ends.

[Effects of the Invention] As described above, according to the present invention, the focusing lens driving means drives the focusing lens in response to the focus evaluation value signal and the subject distance signal. From a state far out of focus position to near the focus position, the lens is moved at high speed based on the subject distance signal. On the other hand, in the vicinity of the focused state, focusing is performed precisely based on the focus evaluation value. Therefore, it is possible to obtain a focusing state that is more accurate than a focusing operation based only on the distance to the subject, faster than when no action is performed based only on the focus evaluation value, and with fewer errors.

That is, it is possible to provide an imaging device that can quickly and accurately reach a focused state.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video camera according to an embodiment of the present invention, FIG. 2 is a flowchart of a program executed by the CPU of a video camera according to an embodiment of the present invention, and FIG. 3 is a block diagram of a conventional video camera. FIG. 4 is a block diagram of a video camera, and FIG. 4 is a graph showing mountain climbing control. In the figure, 10 is an optical system, 12 is a CCD, 14 is a video signal processing circuit, 16 is an autofocus circuit, 18 is a CPU,
20 is a distance detection sensor, 24 is a ROM, 30 is a focusing lens position detector, and 42 is a focusing lens. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) It has a focusing lens that is movable along a predetermined optical axis, and the image of a subject at an arbitrary position is fixed by moving the focusing lens to a focus position determined according to the distance from the subject. an optical system for forming an image on an image forming surface of the object; a lens position detection means for detecting a position of the focusing lens along the optical axis and outputting a focusing lens position signal; an image pickup means for converting the image of the image into an electric signal; a video signal circuit for processing the electric signal and outputting it as a video signal; a video signal focus evaluation means that extracts a changing predetermined frequency band component and outputs it as a focus evaluation value signal indicating a focus state; and a video signal focus evaluation means that measures a distance between the optical system and the object and outputs an object distance signal. the focusing lens position signal;
An imaging device comprising: a focusing lens driving means for driving the focusing lens to the in-focus position in response to the focus evaluation value signal and the object distance signal.