JPH0769513B2 - Focus control signal forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjustment signal forming device for forming a focus adjustment signal for a still video camera, a video camera or the like.

(Prior Art) A drawback of a conventional one-point autofocus device that measures only one position on a screen, that is, "in a scene in which two people are lined up or a scene in which the people are biased toward one end , The main subject (mainly a person) deviates from the distance measuring area on the screen, so that the main subject is out of focus and is focused at infinity. A so-called wide-field (multipoint) distance measuring method for measuring points has been proposed.

An example of a conventionally known automatic focusing device using such a wide-field distance measurement is as follows: (1) Of a plurality of distance measurement results, a system that focuses on the closest distance measurement result (for example, GENERAL & MECHANICAL 4582424, JP 61-88211
No. 6, JP-A-61-55618) (2) A plurality of distance measurement results indicate the focal length of the photographing lens,
If the depth of field is determined by the aperture, the average value is focused so that all subjects corresponding to a plurality of focus points are in focus (Japanese Patent Laid-Open No. 61-88).
(No. 211, JP-A-61-55619, JP-A-61-53614) (3) Whether it is outside or inside is determined by brightness information, and if it is outside, focus on the farthest one from a plurality of distance measurement results. For example, there is a method of focusing on the nearest thing in the door (JP-A-61-55619 and JP-A-61-53614).

(Problems to be Solved by the Invention) However, in the method of (1) described above, in many cases, a scene in which two people are lined up or a scene in which the people are biased to the edge, Although the subject is in focus, for example, when there are obstacles in the front or when there is a foreground, the obstacles are brought into focus and the person (main subject) is out of focus. There are difficulties.

With the method of (2) above, if all of the distance measurement results are within the depth of field, it is rare except when using a short focus lens or under high-luminance shooting conditions. However, when a long-focus lens is used or when shooting is performed in a low-luminance condition, there is a problem that the effects of camera shake appear on the image and that none of a plurality of distance measurement results are in focus.

Further, in the above-mentioned method (3), the background is focused outdoors, while the obstacles in front are focused indoors, for example, the person (main subject) is not focused. There is a problem that causes the problem.

As described above, in the conventional wide-field distance measuring type auto-focusing device according to the related art, in many cases, a person (main subject) is shot in a scene where two people are lined up or a scene in which the people are biased toward the edge.
However, on the other hand, the main subject becomes out of focus in a scene that was in focus with the conventional one-point distance measurement method (foreground and background are in focus). There is a problem that it causes another problem called ".

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a focus adjustment signal forming apparatus that focuses on a desired object at a high rate without requiring a complicated operation.

(Means for Solving the Problem) In order to achieve the above object, the present invention provides a signal related to the distance of each of a plurality of objects by receiving light from a plurality of objects scattered in the visual field direction. A light receiving means for forming and a judging means for judging whether or not the object located at the center of the visual field is the shortest distance based on the relative positional relationship of the plural objects in the visual field direction and the perspective relationship of the plural objects. And a signal forming means for forming a focus adjusting signal according to the judgment result of the judging means.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

Embodiment 1 FIG. 1 is a diagram showing the principle of distance measurement of an active system applicable to the present invention, which system uses a triangulation method used in, for example, a lens shutter camera.

In FIG. 1, the output light of the light projecting element 22 is converged by the light projecting lens 21 and is directed to the subject 25 as a thin beam, and the spot light reflected by the subject 25 is formed by the light receiving lens 23 on the surface of the light receiving element 24. I am trying to do it. The deviation d from the center position of the spot light shown in Fig. 1 is inversely proportional to the distance L to the subject, and the closer it is, the larger d becomes. This relationship is expressed as f / L = d / S (where f is the received light). Focal length of lens 23, S
Is the baseline length).

In the wide-field distance measuring method, the number of points on the screen to be measured is appropriately determined depending on the application, cost, etc. of the camera using the autofocus device. However, in the following embodiment, FIG. A case will be described as an example in which distance measurement is performed on three points in the screen shown in FIG.

FIG. 2 is a block diagram showing the configuration of the automatic focusing apparatus according to the first embodiment of the present invention. In this figure, 1a, 1b and 1c are used for performing distance measurement corresponding to three points in the screen. A block of a light projecting element and a light projecting lens is shown, and a light emission control circuit 2
The light emission is controlled by. Reference numeral 3 indicates a block of a light receiving element and a light receiving lens, and an output terminal from the light receiving element is connected to a distance measuring circuit 4 which calculates a distance to a subject. Reference numeral 5 denotes an interface circuit having an A / D conversion function, which connects between a microprocessor unit (hereinafter referred to as MPU) 6 and various circuits. Reference numeral 7 denotes a drive circuit for moving the taking lens unit 8 to the in-focus position based on the control signal from the MPU.

The operation of the autofocus device in this example configured as described above is performed by turning on the main switch (not shown).
Light emission control circuit 2 from U6 via interface circuit 5
A light emission start signal is given to. As a result, the light emission control circuit 2 sequentially lights the light projecting elements 1a, 1b, 1c at the timing given by various constants set in the circuit. The output light from the light projecting element is reflected by the subject to form a real image on the surface of the light receiving element 3, and the output from the light receiving element 3 receiving this reflected light is input to the distance measuring circuit 4 in FIG. The distance to the subject corresponding to each of the indicated distance measuring points is sequentially calculated.

The distance measurement information calculated by the distance measurement circuit 4 is read into the MPU 6 via the interface circuit 5 in synchronization with the lighting timing of the light projecting element, and the MPU 6 calculates the focus position as described below. Based on the result, the drive circuit 7 moves the taking lens unit 8 to a predetermined position.

The feature of the automatic focusing device of the first embodiment having the above-described configuration and operation is that the photographing lens unit 8 is moved based on the distance measurement result information (distance measurement value) from the distance measurement circuit 4 for the three points. The operation procedure of the MPU 6 for calculating, calculating and outputting the control signal is performed according to the flow chart shown in FIG.

The procedure will be described in detail below.

The operation procedure of the MPU 6 of this example is roughly composed of the following three stages. That is, the first is a step of detecting the closest point LN, the farthest point LF, and the midpoint LM based on the distance measurement information (hereinafter referred to as the first step). Second, by comparing these LNs, LMs, and LFs with each other or with other conditions, the focus position required for the scene currently being photographed differs from the focus position required for other scenes. This is the stage (hereinafter referred to as the second stage) in which the relevant scene is distinguished from the other scenes. Third
Is a step (hereinafter referred to as a third step) of calculating a focus position suitable for each scene divided in the above case by using a preset distance calculating unit.

First, regarding the above-mentioned first stage, in this stage, in the MPU 6 which has read the ranging information of the three points on the screen input from the ranging circuit 4, the closest point LN, the farthest point LF, and the intermediate point LM.
Is required.

Next, regarding the above-mentioned second step, in this step in this example, the case is divided into six cases for convenience, and the priority is the difference between the intermediate point LM and the closest point LN. Then, the difference (that is, | LN−LM |) is compared with a constant k corresponding to the depth of field determined by the focal length of the taking lens, the open F value, etc., and the distance measurement result for the closest point LN is obtained. Discrimination of whether or not (hereinafter referred to as discrimination (a))
Cases are classified according to. Here, invalid means that the data is unnecessary for detecting the focal position (the same applies below).

When the most recent point LN is considered to be valid or invalid in the above, the following determination is made for each.

That is, for the former (when the closest point is valid), the difference between the farthest point LF and the middle point LM (that is, | LF−LM |) is calculated,
This difference is compared with a constant k that corresponds to the depth of field determined by the focal length of the taking lens and the open F value, and the validity or invalidity of the distance measurement result for the farthest point LF is determined (hereinafter, determination ( Case classification according to b)) is performed. When the farthest point LF is valid as a result of the discrimination (that is, | LM-L
For F | ≦ k), it is further determined whether the closest point LN is the central distance measuring point on the screen or another distance measuring point (hereinafter referred to as “determination (C)”).

This determination (c) is one of the features of this embodiment, and this point will be described in detail below.

As described above, when the difference between the intermediate point LM and the closest point LN is smaller than k (that is, | LN-LM | ≦ k), three convenient cases are eventually made.

On the other hand, the difference between the closest point LN and the midpoint LM, that is, | LN−LM |
Is larger than the above constant k (| LN−LM | ≧ k)
In the present example, the determination by determining whether or not the following conditions are satisfied (hereinafter, determination (d),
(Referred to as (e)) is performed. This discrimination is one of the features in this example, and it is discriminated whether the subject at the closest point is the main subject or an obstacle.

The conditions used as the reference in the above judgments (d) and (e) are that the closest point LN may be an obstacle that is inferred from the shooting conditions such as the focal length and brightness information of the shooting lens. It is longer than a high distance r (for example, a distance of about 1 m in the case of a 38 mm lens).

Condition The distance measurement point of the closest point LN is the center.

According to the determinations (d) and (e), the case where at least one of these conditions is satisfied and the case where none of these conditions are satisfied are classified.
The latter case (when neither is satisfied) is further classified according to whether the distance measurement result for the farthest point LF is valid or invalid (hereinafter referred to as discrimination (f)).

Therefore, as described above, even in the case of the above | LN−LM | ≧ k, three cases are eventually divided.

Next, the calculation performed in the next stage (third stage) will be described according to the above case classification.

When the difference (| LN−LM |) between the closest point LN and the intermediate point LM is smaller than the above constant k by the above discrimination (a) (| LN
As described above, when −LM | ≦ k) is detected and selected, the distance measurement result for the closest point LN is regarded as valid information, as described above. )
The cases are classified according to (1) and (c), that is, the three scenes are classified into cases, and ones that match each of the following three modes A, B, and C are selected to calculate the focus position. Will be done.

I. (When | LM−LF | ≧ k) The focus position is calculated from the average value of LM and LN.

B. (When | LM-LF | ≦ k and the closest point LN is the distance measuring point at the center of the screen according to the determination (c)) The focus position is calculated by the three-point center-weighted average method.

C. (When | LM−LF | ≦ k and the closest point LN is a distance measuring point other than the center of the screen according to the determination (c)) The focus position is calculated by the simple averaging method of three points.

On the other hand, in the above, when the difference (| LN−LM |) between the closest point LN and the intermediate point LM is larger than the above constant k (| LN−LM | ≧ k) is detected and selected by the discrimination (a). As for the case, the ranging result for the nearest point LN is regarded as invalid information as described above. Further, in this case, three scenes for which different focus positions are to be determined are further divided into cases according to the discriminations (d) and (e), and one of the following three modes d, h, and f that are suitable for this is respectively adapted. Is selected and the focus position is calculated.

D. (When at least one of the above conditions is satisfied) Calculate the focus position from LN.

E. (Neither of the above conditions is satisfied and | LM-L
When F | ≧ k) The focus position is calculated from LM.

F. (Neither of the above conditions is satisfied and | LM-L
When F | ≦ k) The focus position is calculated from the average value of LM and LF.

In the above embodiment, the results of the determinations (a) to (c), which are the features of this embodiment described above, are selected as an operation that matches the operation modes of B and C among the cases divided above.

That is, in these cases of b and c, | LN−LM | ≦ k and | L
It can be said that the so-called three points where the condition of M−LF | ≦ k is satisfied are at similar (approximate) distances. Even in such a scene, for example, a close-up shot or a background is immediately after the main subject. As described above, in a certain scene, there is a problem that the focus position is drawn backward when the focus position is calculated based on a simple average value of three points. Therefore, in the autofocus device of this example, it is considered that it is normal for the main subject to be in the center in the above-mentioned close-up shot or a scene in which the background is immediately behind the main subject (assuming that),
First, when the most recent point is the center distance measuring point on the screen, the focus is calculated by averaging with emphasis on the center instead of the simple average, and in other cases, the simple average method is adopted.

That is, in short, if the three points are at similar (approximate) distances and the closest point is the center distance measuring point of the screen, it is regarded as a scene with emphasis on the closest point, and in other cases, the closest point is an obstacle. It can be said that it is a method that does not consider the scene to be the closest point in consideration of the possibility that it is.

The calculation of the focus position in the case of the center emphasis is performed by obtaining the focus position LP by the following formula in which the data of the closest point is weighted, for example.

However, a is a numerical value that is determined in consideration of the application of the camera, the focal length of the lens, and the like, and has a> 1, and a numerical value of approximately 2 to 3 is desirable. Further, LN, LM, LF, and LP in the above equation are all values converted into the amount of extension in lens control.

Embodiment 2 The distance measuring device used in the present invention may be based on the principle shown in FIG. 5 in addition to the case shown in FIG.

The principle of this distance measuring method is that of a passive method called SST, and the distance measuring operation is basically based on the double matching method.

That is, the distance data is obtained by observing the positional correlation between the two images obtained by the two optical systems.

Fig. 5 schematically shows the principle, and
25 is a subject to be measured. The light receiving lens 26 and the mirrors 28, 29 aim the subject 25 on its optical axis a, and are referred to as a reference optical system. On the other hand, the light receiving lens 27 and the mirrors 30 and 31 are arranged with a reference length S from the reference side optical system, and are called the reference side optical system.

In the above structure, the image of the subject 25 captured by the light receiving lenses 26 and 27 is formed on the image sensor 32, the image based on the reference side optical system is on the reference visual field A, and the image based on the reference optical system. Are formed on the reference visual field B, respectively.

Assuming that the subject 25 is now at infinity, the subject 25 is the axis a of each of the reference side optical system and the reference side optical system,
In order to come to the upper side of b, the subject image by each optical system is formed as IMB on the standard visual field A and IMR1 on the reference visual field B, respectively. On the other hand, when the subject 25 approaches the axis a of the reference side optical system, the subject with respect to the reference optical system
The optical path from 25 is tilted. Therefore, the image of the subject 25 by the reference side optical system shifts on the reference side visual field B like IMR2. Therefore, by detecting at which position on the reference visual field B the same image as the image IMB on the standard visual field A is formed, the distance to the subject can be known.

FIG. 6 shows a block diagram of an automatic focusing device according to a second embodiment of the present invention using this distance measuring device.

In the figure, 9a, 9b and 9c are distance measuring devices composed of a lens, a mirror and an image sensor, 10a, 10b and 10c are distance measuring circuits for calculating the distance from the output of the image sensor, and 11 is an interface circuit.

The MPU 6 in this example also reads the distance measurement results at three points via the interface circuit 11 in the same manner as in the first embodiment, and the focus position is calculated according to the flowchart of FIG. 4 described in the first embodiment.

The control output to the drive circuit 7 that controls the taking lens unit 8 is given based on the above calculation result.

Embodiment 3 FIG. 7 is an optical layout diagram of an automatic focusing apparatus according to Embodiment 3 of the present invention, in which 41 is a lens element and 42 is for recombining images of the pupil plane of the lens element. It is a small lens group of, and generally consists of 20 or more.
Reference numerals 43 to 46 denote pixels of a light receiving element such as a CCD (charge coupled device) element. The pixels 43 and 44 correspond to the small lens 42a, and the pixels 45 and 46 correspond to the small lens 42b. Pixel 43 is aperture 48 through small lens 42a
The pixel 44 faces the aperture 47 through the small lens 42a. Similarly, pixel 45 is a small lens 42b
Through the aperture 48 part, the pixel 46 is a small lens 42
It faces the 47 part of the aperture through b.

If the small lens 42a is the nth lens and 42b is the (n-1) th small lens, the pixel facing the aperture 48 through the nth lens is An, the pixel facing the aperture 47 is Bn,
Pixels facing the aperture 48 through the (n-1) th lens
The pixel facing An-1 and the aperture 47 is Bn-1. Further, the F surface corresponds to the focal plane of the lens 41. Therefore lens 41
By changing the position in the left-right direction on the screen, the subject distance at which an image is correctly formed on the F plane differs. When capturing the image of an object at the in-focus distance as the output of the sensor, An = Bn,
An-1 = Bn-1, whereas An = Bm (where n ≠ m) when capturing an image of an object that is not at the in-focus distance.

FIG. 8 is a block diagram of an automatic focusing device according to the third embodiment of the present invention. In this figure, 12 is the seventh
A sensor unit consisting of the small lens group and the light receiving element array described in the figure, 13 is an A / D converter, 14 is a gate that divides the output of the A / D converter 13 into three memories, 15, 16 and 17 are memories,
18 Ha interface circuit.

In the above configuration, the signal obtained from the sensor unit 12 is converted into a digital signal by the A / D converter 13, and the pixel is distributed to the three memories by the gate 14. This makes it possible to measure three points, and the MPU 6 reads the contents of these three memories and sets the focus position in the same manner as in the first and second embodiments described above according to the flowchart described in FIG. The drive circuit 7 controls the lens unit 8 based on the calculated value.

The present invention is not limited to the above embodiments,
It goes without saying that it can be realized as various modified embodiments. For example, the discriminating means for other case classification combined with the discriminations (a) to (c), and the arithmetic means prepared so as to fit each case are not limited to those in the above-mentioned embodiment. The known technical means can be appropriately selected and used according to the performance required for the camera to be designed.

As described above, the number of distance measuring points on the screen may be three or more. When the number of distance measuring points is four or more, the intermediate point, the farthest point, and the closest point can be determined by, for example, the distance measuring points. In the case of 4 points as shown in Fig. 9, the average value of the distance measurement results of the two points in the central part or the distance measurement result of the near side of the two points is set as the distance measurement result of the central part. Department,
The midpoint, the farthest point, and the closest point may be determined from the three distance measurement results in the central portion.

If there are five distance measuring points as shown in Fig. 10,
As shown in the four points in the figure, the average value of the distance measurement results of the three points in the center or the distance measurement result of the three points closest to the center is used as the distance measurement result of the center. The midpoint, the farthest point, and the closest point may be determined from two distance measurement results. Of the five distance measurement results, the closest one is the closest point, the third one is the intermediate point, and the fifth one. May be the farthest point.

In the above embodiment, the light receiving element 3, the distance measuring circuit 4 or the light receiving elements 9a to 9c, the distance measuring circuits 10a to 10c or the sensor unit, A /
The D converter corresponds to the light receiving means of the present invention, and also includes the first and the first MPU6.
The second step corresponds to the measuring means of the present invention, and the third step of the MPU 6 corresponds to the signal forming means of the present invention.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a focus adjustment signal forming apparatus that can focus on a desired object at a high rate without requiring a complicated operation.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of distance measurement used in the automatic focusing device according to the first embodiment of the present invention, and FIG. 2 is a block diagram showing the schematic configuration of the automatic focusing device according to the first embodiment. Three
FIG. 4 is a diagram showing an example of a light projecting device used in the first embodiment, FIG. 4 is a flow chart illustrating a procedure for focus detection performed in the microcomputer of the first embodiment, and FIG. FIG. 6 is a diagram for explaining the principle of distance measurement used in the automatic focusing device, FIG. 6 is a block diagram showing the schematic configuration of the automatic focusing device of the second embodiment, and FIG. 7 is used in the automatic focusing device of the third embodiment. Figure explaining the ranging principle,
FIG. 8 is a block diagram showing the outline of the configuration of the automatic focusing device according to the third embodiment. FIG. 9 and FIG. 10 are diagrams for explaining the case where the distance measuring points on the screen are four and five. 1a, 1b, 1c: Emitter element, 2: Light emission control circuit 3: Light detector element, 4: Distance measuring circuit 5: Interface circuit 6: Microprocessor unit (MPU) 7: Driving circuit, 8: Photographic lens unit 9a , 9b, 9c: Light receiving element, 10a, 10b, 10c: Distance measuring circuit 11: Interface circuit 12: Sensor unit, 13: A / D converter 14: Gate, 15, 16, 17: Memory 18: Interface circuit 21: Light emitting lens, 22: Light emitting element 23: Light receiving lens, 24: Light receiving element 25: Subject, 26: Light emitting lens 27: Light receiving lens, 28, 29: Mirror 30, 31: Mirror, 32: Image sensor 41: Lens Element, 42: Small lens group 42a, 42b: Small lens, 43, 44, 45, 46: Pixel 47, 48: Aperture

Claims (1)

[Claims] 1. Light receiving means for receiving light from a plurality of objects scattered in the visual field direction to form signals related to respective distances of the plurality of objects, and visual field directions of the plurality of objects. Determination means for determining whether or not the object located in the center of the visual field is the shortest distance based on the relative positional relationship and the perspective relationship of the plurality of objects, and a focus adjustment signal according to the determination result of the determination means. A focus adjustment signal forming device, comprising: a signal forming means for forming.