JP3239413B2 - Camera autofocus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera autofocus apparatus, and more particularly to a camera autofocus apparatus for measuring a distance to a subject from a phase difference between two subject images.

[0002]

2. Description of the Related Art Conventionally, there has been known an autofocus device for a camera which measures a distance to a subject from a phase difference between two subject images formed on an image sensor such as a CCD through two optical systems.

In such a conventional autofocus apparatus, the correlation between the two images is calculated while scanning the two images on the image sensor in accordance with the distance, and the change in the correlation value is used to calculate the correlation between the two images. Find the peak with the best correlation,
This point is defined as the distance to the subject.

[0006] Whether this point is adopted or not is determined by providing a judgment value for the height of the peak of the correlation, the sharpness of the peak, and the like, which is used as the criterion.

[0005]

However, in the conventional auto-focusing device for a camera, if there are a plurality of subjects having similar shapes in a distance measurement field, such as a periodic pattern, the same is applied to different subjects. There is a case where the object is recognized as an object and the distance measurement value which is completely out of target is output (hereinafter, referred to as false focusing). In such a case, there is a problem that the focus is largely shifted.

[0006] This false focusing is particularly conspicuous when a subject that is originally at a long distance is erroneously focused on a very short distance side. The present invention has been made in order to solve such a conventional problem, and for a subject in which false focusing occurs,
An object of the present invention is to provide an automatic focusing device for a camera, which can surely prevent a large shift in focus.

[0007]

According to the first aspect of the present invention, an image is formed on an image pickup device through two different optical systems provided at positions for receiving a light beam other than a light beam transmitted through a photographing lens. The correlation between two subject images is detected, and the detected correlation value and the object detected by the correlation value are detected.
In an autofocus device for a camera that detects a subject distance, based on a determination value that is a value for determining whether or not to adopt a body distance, a determination unit that changes the determination value according to an image interval for calculating a correlation. It has.

According to a second aspect of the present invention, in the automatic focusing apparatus for a camera according to the first aspect, the determination value is determined based on the object distance.
Varies from 3 m to 7 m so as to be set gently at an image interval of 7 m . According to a third aspect of the present invention, in the camera autofocus device according to the first aspect, the determination value is gently corresponding to an image interval corresponding to a long distance side and corresponds to a short distance side .
It changes so that the image interval becomes strict.

[0009]

In the camera autofocus device of the present invention,
To determine whether to use the detected subject distance
Determination value is a value, is changed in accordance with the image interval for calculating the correlation. Then, the judgment value is changed from the object distance of 3 m to 7
By changing the image interval so as to be gradual at the image interval corresponding to m, the point at which the correlation between the two images at the common distance is the best matches is preferentially adopted. Further, by changing the image interval corresponding to the close distance side so that the setting becomes strict, there is a possibility that even a subject such as a periodic pattern that causes false focusing may be erroneously focused on the short distance side. Reduced.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a camera in which an embodiment of the autofocus device of the present invention is arranged.

In this camera, subject light that has passed through a taking lens 2 disposed in a camera body 1
Is imaged. An AF optical system 4 of a passive triangulation type is arranged on the upper part of the camera body 1, and the subject light passes through a pair of distance measurement lenses L1 and L2 and passes through mirrors 5 and 6.
Are reflected on the image sensors S1 and S2 and detected as two images.

The two subject images detected by the image sensors S1 and S2 are sent to a distance calculating device 7 constituted by a microprocessor or the like. In the distance measurement arithmetic unit 7, the distance to the subject is obtained from the detected distance between the subject images.

In accordance with the distance measurement result of the distance measurement arithmetic unit 7,
The photographing lens 2 is driven by the lens driving device 8 to focus on the subject. FIG. 2 shows the principle of distance measurement according to this embodiment.
Is imaged on the image sensors S1 and S2 through
The image sensors S1 and S2 output sensor outputs I1 and I2 corresponding to the intensity of the subject image.

[0014] Correlation windows W1 and W2 smaller than the widths of the image sensors S1 and S2 are virtually set, and the correlation between the sensor outputs I1 and I2 is calculated in the correlation windows W1 and W2.

In this embodiment, each of the image sensors S1 and S2 has 20 pixels G, and each of the correlation windows W1 and W2 has a length corresponding to 10 pixels. The interval D between the correlation windows W1 and W2 (hereinafter referred to as the correlation window interval D) corresponds to the distance to the subject O, and is small on the long distance side and large on the short distance side.

Here, assuming that the focal lengths of the distance measuring lenses L1 and L2 are f and the interval is B, the distance measuring lens L
The relationship between the distance R to 1 and L2 and the correlation window interval D is as follows.

R = f · B / (DB) (1) FIG. 3 shows a change in the correlation value C when the correlation window interval D is changed when the subject O is at a specific distance. Is shown.

Here, the correlation value C is the correlation window W1, W2
Is the sum of the absolute values of the differences between the sensor outputs I1 and I2, and the minimum value is obtained at the position where the two values are the best.
In FIG. 3, the position is Dn, and the correlation value at this time is Cn
It is.

At this time, as shown in FIG. 3, the correlation value C is
It can be obtained discretely in pixel units of the image sensors S1 and S2, and can be obtained up to one pixel or less by performing an interpolation operation using several points before and after the minimum value of the correlation.

Whether or not to use the correlation valley CBn is determined by the sharpness of the correlation valley and the height of the minimum value of the valley. That is, when Cn-1 is larger than Cn + 1, the sharpness SL of the correlation valley is set as SL = Cn-1 -Cn (2), and the bottom CB of the correlation valley is set as CB = Cn- [ (Cn-1-Cn + 1) / 2] (3) In this embodiment, the sharpness S of the valley of these correlations is obtained.
L and the determination values HSL and H for the bottom CB of the valley of the correlation
The CB uses the judgment values as functions HSL (D) and HCB (D) of the correlation window interval D.
When the bottom CB of the valley of the correlation is larger than the determination value HSL (D),
When it is lower than the determination value HCB (D), it is determined that the subject O exists at this position.

FIG. 4 shows the judgment value functions HSL (D) and HCB (D). The functions of these judgment values are as follows.
It is set in advance. In this embodiment, the correlation valley sharpness SL
The judgment value HSL (D) becomes larger as the correlation window interval D becomes larger (subject O distance becomes shorter). On the short distance side, the existence of the subject O is not recognized unless the correlation valley is sharp. Also, the determination value HCB (D) of the bottom CB of the valley of the correlation
Decreases as the correlation window interval D increases (the subject O distance decreases), and on the short distance side, the existence of the subject O is not recognized unless the bottom of the correlation valley is low.

The function HSL (D) of the judgment value is set to be, for example, about two to three times longer on the short distance side than on the long distance side, and the function HCB (D) is set on the long distance side, for example. Is set to be about two to three times the short distance side.

FIG. 5 shows a state in which the distance to the subject O in which false focusing occurs is measured. In this embodiment, white and black patterns are formed at predetermined intervals in the subject O, and as the correlation windows W1 and W2 are moved, as shown in FIG. , Da and Db, the valleys of correlation CBa and CBb occur.

That is, the true object O position is the position of Da, and the detection distance at this time is Ra.
Since a black and white pattern is formed in the position Db, a correlation valley CBb also occurs at the position Db, and the detection distance at this time is Rb.

As shown in FIG. 6, the valley CBa of the correlation may be lower than the valley CBa of the correlation due to the unevenness in the sensitivity of the image sensors S1 and S2 and the unevenness in the reflection characteristics of the object O. In this case, if the determination value is kept constant, the valley of correlation CBb is adopted, the detection distance becomes Rb, and an erroneous detection distance is obtained.

Therefore, in this embodiment, as shown in FIG. 4, by changing the judgment value HSL (D) and the judgment value HCB (D), the adoption of the correlation valley CBb is prevented. .

The details of the automatic focusing apparatus of this embodiment will be described below with reference to the flowcharts shown in FIGS. FIG. 7 shows a main routine for distance measurement. In this example, correlation windows W1 and W2 for 10 pixels are provided to the image sensors S1 and S2 each having 20 pixels on the left and right sides.
The case where the distance measurement is performed imaginarily is shown.

First, the array variable I1 [0. . 19], I2
[0. . 19], 20 of the image sensors S1 and S2.
The pixel data is read (step S1). Next, the two correlation values C from the smallest interval between the correlation windows W1 and W2.
Is calculated using the function Corr (n) of the correlation operation shown in FIG.

[0] and C [1] are stored (step S2, step S3).

The operation of the correlation operation function Corr (n) is as follows.
As shown in steps S81 to S85 in FIG. 8, the correlation windows W1 and W2 for 10 pixels out of 20 pixels are set by the argument n, and the sum of the absolute values of the differences is calculated.

Here, when the argument n is 0, the correlation window W
The interval between W1 and W2 is reduced, and each time the interval increases by 1, the correlation window W1 in the left image sensor S1 shown in FIG.
The pixel moves to the left by one pixel, and in the right image sensor S2, the correlation window W2 moves to the right by one pixel.

In order to further improve the accuracy, the movement of the correlation windows W1 and W2 may be performed one pixel at a time alternately on the left and right, or only one of the correlation windows W1 and W2 may be moved. .

Next, n is set to 1 as the initial position of the correlation windows W1, W2 (step S4). Thereafter, the newly calculated correlation value is stored in the array variable C [n + 1] (step S5).

Next, the array variable C [n] is changed to C [n-1].
And C [n + 1] is determined (step S6). When small, the correlation valley sharpness SL
Is calculated (step S7).

Next, the sharpness SL of the valley of the correlation is compared with the function HSL (n) of the determination value shown in FIG. 9 to determine whether or not to use this position (step S8). In this embodiment, as shown in FIG. 9, the function HSL (n) of the determination value is
The coefficients k1 and k2 are set to optimal values in advance according to the distance measuring optical system to be implemented.

The sharpness SL of the valley of the correlation is a function HS of the judgment value.
If it is larger than L (n), the value of DL used for the interpolation operation is obtained (step S9). This value of DL is a value corresponding to the second term of the above-described equation (3).

Next, the base CB of the valley of the correlation is calculated from DL (step S10). After this, the bottom CB of the valley of correlation is
It is compared with the function HCB (n) of the determination value shown in FIG. 10 to determine whether or not to use this position (step S1).
1).

In this embodiment, as shown in FIG. 10, the function HCB (n) of the judgment value is a linear expression, similarly to HSL (n), and the coefficients k3 and k4 are the distance measuring optical system to be implemented. Is set in advance to an optimum value.

The value of the bottom CB of the valley of the correlation is the function HCB
If it is larger than (n), the value of n for setting the positions of the correlation windows W1 and W2 is increased by 1 (step S12). Thereafter, when the correlation window W1, W2, it is determined whether the end position (step S13), and not the end position, step S5
Return to

When the correlation windows W1 and W2 are at the end positions, a definitive correlation cannot be obtained at any distance, such as when the object O has no clear pattern. In this case, 0 is stored as the subject distance R (step S14), and the routine ends.

On the other hand, in step S11, CB becomes H
When the distance is smaller than CB (n), it is determined that n at this time is the position where the object O exists. Therefore, the object distance R is set to 1 by interpolation using n, SL, and DL.
The number of pixels is calculated to be equal to or less than the number of pixels (step S15), and the routine ends.

Here, f is a distance measuring lens L1, L
2, B is the distance between the distance measuring lenses L1 and L2, D0
Is the initial value of the interval between the correlation windows W1 and W2, and p is the interval between the pixels of the image sensors S1 and S2.

In the camera auto-focusing device having the above-described structure, since the function HCB (D) of the correlation window interval D is used as the determination value, as shown in FIG. The position becomes lower than the determination value HCB (D), and CBb becomes a position higher than the determination value HCB (D). As a result, CBa satisfies the determination value. Since the Da corresponding to the position of the subject O is employed, it is possible to reliably prevent the focus from being greatly shifted with respect to the subject O in which false focusing occurs.

In this embodiment, the judgment value HCB
Since the bottom CB of the correlation valley is determined by (D) and the sharpness SL of the correlation valley is also determined by the determination value HSL (D), the object O in which false focusing occurs is determined. In addition, it is possible to more reliably prevent the focus from being largely shifted.

Further, in this embodiment, as shown in FIG. 4, the functions HCB (D) and HSL (D) of the judgment values are linear expressions, and the judgment is made strictly on the short distance side. It is possible to reliably prevent an erroneous focusing on an extremely short distance side even if the subject O causes false focusing.

FIG. 11 shows a decision value HCB (D) and a decision value HSL (D) set in another embodiment of the present invention.
In this embodiment, the determination value HCB (D)
Is a quadratic function of k1n ² + k2n + k3, and the judgment value HSL (D) is a quadratic function of k4n ² + k5n + k6.

Then, for example, at a distance of, for example, 3 to 7 m, which is commonly used in portrait photography, the determination value is set to be a gentle value. By setting the determination value in this way, for example, in portrait photography, it is possible to reliably prevent an erroneous focusing on an extremely short distance side.

In the above-described embodiment, an example in which the judgment value is set by a primary expression or a quadratic expression has been described. However, the present invention is not limited to such an embodiment.
Needless to say, it may be set by a third-order or higher order equation, or may be set in a step-like manner.

Also, in the above-described embodiment, an example has been described in which the function of the determination value is set to a predetermined function in advance.
The present invention is not limited to such an embodiment. For example, in a camera that can select a mode such as portrait photography or landscape photography, the function of the determination value can be changed by selecting these modes. Of course, it may be possible.

[0049]

[0050]

As described above, the camera autofocus apparatus of the present invention employs the detected subject distance.
Since the judgment value, which is a value for judging whether or not to perform, is changed in accordance with the image interval for calculating the correlation, the focus is greatly shifted with respect to the subject in which the false focusing occurs. Can be reliably prevented.

Then, the judgment value is determined when the object distance is 3 m.
By changing the image interval to be gradual at the image interval equivalent to 7 m, the focus position at the normal distance is preferentially adopted, and it is possible to reliably prevent a large shift in focus at the normal distance.

Further, by changing the setting such that the setting becomes strict on the short distance side, the possibility of erroneously focusing on the short distance side is reduced even for a subject such as a periodic pattern which may cause false focusing. You.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a camera provided with an embodiment of an autofocus device of the present invention.

FIG. 2 is an explanatory diagram illustrating a principle of distance measurement of the autofocus device in FIG. 1;

FIG. 3 is an explanatory diagram showing a relationship between a correlation value and a correlation window interval.

FIG. 4 is an explanatory diagram showing a determination value of a sharpness of a correlation valley and a determination value of a bottom of a correlation valley.

FIG. 5 is an explanatory diagram showing a case where false focusing occurs.

FIG. 6 is an explanatory diagram illustrating a relationship between a correlation value and a correlation window interval in FIG. 5;

FIG. 7 is a flowchart of the autofocus apparatus of FIG. 1;

FIG. 8 is a flowchart showing an operation for calculating a value of a function Coor (n).

FIG. 9 is a flowchart showing an operation for calculating a value of a function HSL (n).

FIG. 10 is a flowchart showing an operation for calculating a value of a function HCB (n).

FIG. 11 is an explanatory diagram showing a determination value of a correlation valley sharpness and a determination value of a correlation valley bottom according to another embodiment of the autofocus apparatus of the present invention.

[Explanation of symbols]

 O Object L1, L2 Distance measuring lens S1, S2 Image sensor W1, W2 Correlation window

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-15222 (JP, A) JP-A-2-15220 (JP, A) JP-A-1-172810 (JP, A) JP-A-58-58 59412 (JP, A) JP-A-4-145776 (JP, A) JP-A-62-14127 (JP, A) JP-A-63-252214 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B ^7/ 28-7/40

Claims (3)

(57) [Claims] 1. A correlation between two object images formed on an image sensor through two different optical systems provided at positions for receiving a light beam other than a light beam transmitted through a photographing lens, and the detected correlation value is detected. And the subject distance detected by the correlation value
In an autofocus device for a camera that detects a subject distance based on a determination value that is a value for determining whether or not to employ, a determination unit that changes the determination value according to an image interval for calculating a correlation is provided. An autofocus device for a camera, comprising: 2. The method according to claim 1, wherein the determination value is a value indicating whether the subject distance is 3 m.
2. The camera auto-focusing device according to claim 1, wherein the setting is changed so as to be set gently at an image interval equivalent to 7 m . 3. The method according to claim 1, wherein the determination value is a distance between images corresponding to a long distance side.
2. The camera auto-focusing device according to claim 1, wherein the setting changes gently at an interval and becomes strict at an image interval corresponding to a short distance side.