JPH041886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus control device, and more particularly to an automatic focus control device for a video camera.

In optical imaging devices such as photo cameras and video cameras, depending on the distance between the subject and the phototaking lens, the distance between the phototaking lens and the imaging plane (i.e., the photo film for photo cameras, the imaging plane for video cameras) It is necessary to adjust the relative distance to the surface of the tube or solid-state image sensor) to form a focused image on the imaging plane. As a means for automatically performing this focus adjustment operation (so-called focusing), there is an automatic focus control device called a contour detection method. An automatic focus control device using a conventional contour detection method will be described below.

FIG. 1 is a block diagram schematically showing the configuration of an automatic focus control device for a video camera using a conventional contour detection method. In FIG. 1, this device includes an image sensor 2 that converts light from a subject (not shown) focused by a photographic lens 1 into an electrical signal.
The output of the image sensor 2 is converted into a video signal 4 through a signal processing circuit 3. A portion of the video signal 4 passes through the high-pass filter 5, the integrator 6, the focal voltage detection circuit 7, and the A/D converter 9 in this order, and is input to the top detection means 55 and the fluctuation detection means 57. On the other hand, a lens position detection circuit 10 that detects the relative distance between the lens 1 and the imaging surface of the imaging element 2
As a result, an output signal proportional to this relative distance is generated, converted into a digital signal through the A/D converter 11, and input to the top drawing means 55. The output of the top pulling means 55 is input to the drive signal generating means 58, and the output of the fluctuation detecting means 57 is input to the top pulling means 55.
is input. Further, the lens 1 is movable in the direction of its optical axis, and in response to the output of the drive signal generation means 58, the drive means 54 is driven, for example, by a motor 1.
Move by 3.

Among these, the top pulling means 55, the fluctuation detecting means 57, and the drive signal generating means 58 can be configured using a microcomputer.

Next, the operation of the apparatus shown in FIG. 1 will be explained. The video signal 4 obtained by processing the output of the image sensor 2 with the signal processing circuit 3 is a signal obtained by scanning the optical image formed on the imaging surface of the image sensor 2. Reflects changes in shading on the imaging surface.
Generally, when a video camera is focused on the subject, the outline of the image formed on the imaging surface has precise changes in shading, whereas when the video camera is out of focus, the outline of the image formed on the imaging surface has unclear changes in shading. , resulting in a so-called blurred image. Therefore, the video signal 4 obtained by scanning the imaging surface contains a large amount of high frequency components when the image is in focus, and the high frequency component is reduced when it is out of focus. In other words, how close is the amount of high-frequency components of the video signal 4 to the in-focus state (hereinafter referred to as "focus degree")?
It is used as an indicator for judgment. Therefore, by sequentially passing a part of the video signal 4 through the high-pass filter 5 and the integrator 6, the high frequency part of the video signal 4 is integrated for one field period, and then the focal voltage detection circuit 7 integrates the high frequency part of the video signal 4 for one field period. If you output each field,
The output (hereinafter referred to as focus voltage 8) is a signal corresponding to the degree of focus. The relationship between the position of the lens 1 and this focal voltage 8 is shown in FIG. This relationship is such that the focal point F is the maximum and the focal voltage 8 decreases gently on both sides thereof. This output is A/
The D converter 9 converts the signal into a digital signal. on the other hand,
The lens position detection circuit 10 outputs a signal corresponding to the relative distance between the lens 1 and the surface of the image sensor 2, and this output is converted into a digital signal by the A/D converter 11. These two circuits are connected to the lens position detection means 5.
3. Therefore, the outputs of the two A/D converters 9 and 11 each include information on the degree of focus and the lens position. A motor 3 that moves the lens 1 based on these two signal information
Next, the process of providing the control output by the microcomputer will be explained with reference to the flowchart of FIG. First, when the user of the video camera turns on the start switch S, the top retracting means 55 detects this and outputs an output to move the lens 1 either toward the subject or away from the subject. , is generated by the drive signal generating means 58 and applied to the motor 13 ("Start" 14).
This direction is arbitrary and may be determined in advance. With this movement,
If the focal voltage 8 increases, the lens 1 continues to be driven in that direction, and if the focal voltage 8 decreases, the moving direction of the lens 1 is reversed ("Search" 1).
5). This operation is performed by the top pulling means 55 based on the output of the high frequency integrating means 52. By this,
The lens 1 approaches a focused state. lens 1
When passes through the focused state, the focus voltage 8 changes from increasing to decreasing. Since the point at which this increase changes to a decrease is the in-focus state, this position is stored by the top detection means 55 based on the input from the lens position detection means 53 ("top detection" 16). after that,
The lens 1 is returned to the memorized focal point position and stopped ("stop" 17). Even after this stop, the movement of the subject is monitored by the fluctuation detection means 57 based on the fluctuation of the focal voltage 8, and if necessary, such as when the focal voltage 8 fluctuates by more than a certain value, ” 14 (“Wait” 18). The movement of the focal voltage during this period is shown in FIG. 2, where once the focal voltage exceeds the maximum peak, it returns again and reaches the focal point F.

Since the conventional automatic focus control device using the contour detection method is configured as described above, when there are multiple objects at different distances from the lens 1 of the video camera within the shooting range ("angle of view"), , which object among them is in focus is determined by the lens position at the "activation" step 14. Therefore, there is a drawback that an object that is contrary to the user's intention of the video camera is brought into focus, and the composition desired by the user may not be obtained.

The present invention was made in order to eliminate the drawbacks of the conventional device as described above.
To provide an automatic focus control device that can focus on an arbitrary object according to the selection of a video camera user even when there are a plurality of objects at different distances from the video camera (hereinafter referred to as "multi-subject state"). The purpose is to

To summarize, in the present invention, when in a multi-subject state, the lens 1 and the image sensor 2 have a focal voltage of 8.
In response to the fact that the dependence on the distance between Means is provided to provide an automatic focus control system that performs this forced movement and then automatically retracts to its desired maximum point based on a switch selection by the video camera user.

EMBODIMENT OF THE INVENTION Hereinafter, the structure and operation|movement of the Example of this invention are demonstrated based on drawing, and the details of this invention are clarified. FIG. 4 is a block diagram schematically showing the configuration of an embodiment of the present invention. Similar to the conventional automatic focus control device shown in FIG. 1, light from a subject (not shown) is focused by a photographing lens 1 to form an optical image on the surface of an image sensor 2. This image pickup device is an image pickup tube, a solid-state image pickup device, or the like. The output of the image sensor 2 is converted into a video signal 4 by a signal processing circuit 3. The imaging device 2 and the signal processing circuit 3 constitute an imaging means 51 for obtaining the video signal 4 from the optical signal. A part of this video signal 4 is passed through a high-pass filter 5,
The voltage passes sequentially through an integrator 6 and a focus detection circuit 7 to become a focus voltage 8, which is converted into a digital signal by an A/D converter 9. The high-pass filter 5, the integrator 6 and the focus detection circuit 7 form a high-pass integrating means 52. On the other hand, lens position detection means 5 detects the position of the lens 1 and generates an output signal according to the position.
3, a lens position detection circuit 10 is provided. Driving means 5 for moving the lens 1 in the optical axis direction
4, for example, a motor 13 is also provided in the same manner as in the prior art. In addition to the focus control start switch S, the switches include two changeover switches 19A and 19B.
will be established. Hereinafter, for convenience, the changeover switch 19A will be referred to as the "front" switch 19A, and the changeover switch 19B will be referred to as the "rear" switch 19B.
These two changeover switches 19A and 19B constitute a switching means 62. High frequency integration means 52
After passing through the A/D converter 9, the output is input to the top drawing means 55, the minimum passing means 56, and the fluctuation detecting means 57. The output of the lens position detection means 53 is input to the top pulling means 55 after passing through the A/D converter 11 . The focus control activation switch S is connected to the top pull-in means 55, and the switching means 62 is connected to the minimum passage means 56 through the switching change detection means 60, respectively. Fluctuation detection means 5
7 is input to the top pull-in means 55, and the outputs of the top pull-in means 55 and the minimum passage means 56 are input to the drive signal generation means 58, respectively. Also,
The minimum passage means 56 is also connected to the top retraction means 55. The output of the drive signal generating means 58 is the output of the drive means 5.
4 is input. Among these, the top retraction means 55,
Minimum passage means 56, fluctuation detection means 57, drive signal generation means 58, and switching change detection means 6
0 can be configured by a microcomputer.

Note that the top pulling means 55 works as first and second top pulling means. The first top pulling means moves the lens 1 in a direction in which the integral value increases in response to the output of the high frequency integrating means 52 and the output of the lens position detecting means 53, and moves the lens 1 to a position where the integral value becomes maximum. A signal is output to retract the lens 1 up to the point. The second top drawing means detects that the lens 1 has passed through the position where the integral value is the minimum.
6, it outputs a signal to further move the lens 1 in the predetermined direction and retract the lens 1 to the position where the integral value is maximum.

Next, the operation of this embodiment will be explained. Light from a subject (not shown) is transmitted through a lens 1 to an image sensor 2.
The image sensor 2 and signal processing circuit 3 convert the light into a video signal 4, and the high-pass filter 5, integrator 6, and focal voltage detection circuit 7 convert it into a focal voltage 8. This operation is similar to the device shown in FIG. Here, the dependence of the focal voltage 8 on the distance between the lens 1 and the subject is a curve with a single maximum value, as shown in Figure 2, when there is only one subject within the angle of view. However, in relation to the purpose of the present invention, when a plurality of objects, such as object A and object B, exist within the angle of view and the distances between them and the lens 1 are different (FIG. 5a) think of. At this time, the dependence of the focal voltage 8 on the position of the lens 1 becomes a curve with two maxima, as shown in FIG. 5b. In FIG. 5a, x _A and x _B are the distances between object A and object B and the lens 1, respectively. In FIG. 5b, P _A and P _B are the positions of the lenses that focus on object A and object B, respectively, and P _C is the position of the lens that gives the minimum value of this curve. The focal voltage 8 having such characteristics is converted into a digital signal through an A/D converter 9. Further, a lens position detection circuit detects the position of the lens and generates a voltage proportional to the position of the lens, which is converted into a digital signal by the A/D converter 11. This operation is also similar to the conventional device. The automatic focusing operation performed by this device will be explained with reference to FIG. 6, which is a flowchart of this embodiment. First, focus control start switch S
Turn on. Then, the top retracting means 55 detects this, and causes the drive signal generating means 58 to generate a signal for driving the lens 1 in a certain direction, and outputting it to the motor 13 (Start 14). This direction is arbitrary, as described in connection with the conventional device of FIG. Thereafter, the top detection means 55 detects the change in the focal voltage 8 caused by this drive, moves the lens 1 in the direction in which the focal voltage 8 increases ("search" 15), and locates the maximum position. Detection and storage ("top detection" 16), returning the lens 1 to this maximum point, and stopping ("stop" 17) are also similar to conventional devices. If the initial position of the lens 1 is P ₀ in FIG. 5, this operation moves the lens position to P _A. By the way, the maximum point P _A that has moved in this way
is a state in which object A is in focus, and because P ₀ happens to exist between O and P _C in Figure 5b, the direction toward P _A is in the direction of increasing focal voltage 8. It's just a summer. If P ₀ is between P _C and ∞, lens 1 will be drawn into P _B. The object drawn into focus is substance A, and the object the user wants to focus on is object B.
, the user presses the "previous" switch 19A.
Turn on. This switching change is detected by the switching change detection means 60. Based on this detection output, the minimum passing means 56 causes the drive signal generating means 58 to output a signal for moving the lens 1 in the direction of ∞ in FIG.
A), the motor 13 is driven. By this,
The lens 1 moves in the direction toward ∞ until it passes the minimum point P _C ("Search" 30A). minimum point
When the vehicle passes P _C , the minimum detection means 56 detects this and switches from this drive to the drive/peak detection by the top detection means 55 ("Top Detection" 16).
Thereafter, the operation of retracting the lens 1 to the maximum point P _B ("stop" 17) is similar to the operation described above.
If the user desires to focus on object A when object B is in focus during the first retraction, the "rear" switch 13B is turned on. Then, in a completely symmetrical operation to the above-mentioned operation, the lens 1 is moved in the direction _O in FIG. In this way, after the user's desired subject is in focus,
The fluctuation detecting means 57 monitors the fluctuation of the focus voltage 8 ("standby"18'), and when a fluctuation of more than a certain value occurs, the operation returns to "start" 14 again and the focus is pulled in. When there is no variation in focal voltage 8,
"Front" switch 19A and "rear" switch 19
Return to B's monitoring of switching.

In the flowchart of FIG. 6, a change in the "front" switch 19A is detected first, and then a change in the "rear" switch 19B is detected, but it goes without saying that this order may be reversed. ,Also,
It is also possible to configure the system to detect changes at the same time under the condition that the "front" switch 19A and the "rear" switch 19B are not turned on at the same time. Furthermore, this configuration can be used not only when there are two subjects to be focused on, but also when there are a large number of subjects. That is, when the characteristic curve of the focal voltage 8 in FIG. 5b has three or more maximums, the "front" switch 19A or the "rear"
By turning on the switch 19B a required number of times, the lens 1 can be moved between adjacent maximum points each time to a desired maximum point. In this example, the target was a video camera, but when used in a photo camera,
The light condensed by the lens 1 may be separated by, for example, a half mirror, one of which may be imaged on a film, and the other light may be guided to the image pickup device 2. Furthermore, not only the contour detection method for image/video signals, but also the general case where the position of a member is controlled based on the amount of high frequency components of the input signal, the lens 1 and the imaging means 51 can be connected to other members, input It is applicable in a configuration in which the means are replaced.

As described above, according to the present invention, even when a camera is in a multi-subject state, it is possible to automatically focus on any subject by a simple switching operation by the camera user, which improves ease of use and , it is possible to obtain an automatic focus control device having a high composition creation function.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing the configuration of a conventional automatic focus control device. FIG. 2 is a diagram showing the lens position dependence of the focal voltage when there is one object within the angle of view. FIG. 3 is a flowchart of a conventional automatic focus control device. Fourth
The figure is a block diagram schematically showing the configuration of an embodiment of the present invention. FIGS. 5a and 5b are diagrams showing the mutual relationship between the lens and the object and the lens position dependence of the focal voltage, respectively, when two objects at different distances from the lens exist within the angle of view. FIG. 6 is a flowchart for an embodiment of the invention. In the figure, 1 is the lens, 2 is the image sensor,
3 is a signal processing circuit, 4 is a video signal, 5 is a high-pass filter, 6 is an integrator, 7 is a focal voltage detection circuit, 8 is a focal voltage, 9 and 11 are A/D converters. , 10 is a lens position detection circuit, 12 and 12' are microcomputers, 13 is a motor, 14 is a "start" process, and 15 is a "search"
16 is the "top detection" process, 17 is the "stop" process, 18 is the "focal voltage fluctuation detection" process, 19A and 19B are the "front" switch and "back" switch, respectively. camera, 22
and 23 respectively represent object A and object B,
28A and 28B carry out processing for detecting changes in the "front" switch and "back" switch, respectively;
29A and 29B are "activation" processes based on changes in the "front" switch and "rear" switch, respectively, and 30A and 30B are "search" processes based on changes in the "front" switch and "rear" switch, respectively. , 51 is an imaging means, 52 is a high-frequency integration means, 53 is a lens position detection means, 5
4 is a driving means, 55 is a top pulling means, 56 is a minimum passing means, 57 is a fluctuation detecting means, 58 is a driving signal generating means, 60 is a switching change detecting means, 62 is a changeover switching means, S indicates a focus control activation switch, respectively.

Claims (1)

[Scope of Claims] 1. A lens, a moving means for moving the lens in the optical axis direction, an imaging means for converting the light collected by the lens into an image signal, and an integrated high-frequency component of the output signal of the imaging means. death,
a high-frequency integrating means that outputs a signal according to the integral value; a lens position detecting means that detects the relative position of the lens and the imaging means and generates a signal according to the detected value; In response to the output and the output of the lens position detecting means, a signal is sent to the moving means to move the lens in a direction in which the integral value increases and to pull the lens to a position where the integral value becomes maximum. a first top pulling means for outputting an output; a switching means for selecting a focal point pulling position; in response to switching of the switching means, the lens is moved in a predetermined manner until the lens passes through a position where the integral value becomes minimum; a minimum passing means for outputting a signal for moving the lens in the predetermined direction to the moving means, and further moving the lens in the predetermined direction after the lens passes a position where the integral value is minimum. . An automatic focus control device comprising: second top retracting means for outputting a signal for retracting the lens to a position where the integral value is maximum to the moving means.