JP2002244022A - Camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that separation between a background and a main subject becomes harder as a distance is longer and the distance can not be exactly detected because distance dependency is not improved in the conventional passive AF system. SOLUTION: This camera is equipped with a control part 1 switching a 1st mode in which a focusing position is decided by correcting range-finding output and a 2nd mode in which the focusing position is decided without correcting the range-finding output, so that a subject decided to exist within a specified distance range is brought into focus at a specified position uniformly. The camera performs focusing control to cover many subjects distributed at many distances according to the depth of field, and is preferentially focused on the subject in a scene where the specified subject forms clear contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a so-called passive AF camera which performs focusing control using a subject image.

[0002]

2. Description of the Related Art Generally, automatic focusing (AF) of a camera.
In addition to the passive AF method, there is an active AF method in which light for distance measurement is projected onto a main subject from the camera side and focusing is performed according to the reflected signal light. In the active AF method, the main subject is at a long distance,
When it is difficult to detect the reflected signal light, there is known a so-called infinity stage processing technique of performing focusing at a predetermined distance.

[0003] The present applicant also discloses, for example, Japanese Patent Application Laid-Open
Japanese Patent Laid-Open No. 59677 proposes an improvement of the technology of the infinite distance processing. As a passive type AF method,
There were no similar proposals.

[0004]

SUMMARY OF THE INVENTION
In the case of the F system, since the distance measurement accuracy changes depending on the S / N ratio of the light reflected by the subject, technical improvements have been made actively. On the other hand, in the passive AF method which basically has no distance dependency in the sense of a change in the S / N ratio, sufficient improvement has been made in the technology of improving the distance measurement accuracy corresponding to the change in the S / N ratio. Had not been done. However, in practice, for example, when a person is a main subject, it is clear that the longer the distance, the smaller the proportion of the main subject in the screen becomes. This makes it difficult to perform accurate distance detection. In addition, the focus position of a landscape or the like is far away, but the contrast tends to be low, and the focusing by the passive AF method tends to be difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a camera equipped with a passive AF type distance measuring device, which can accurately focus a main subject at a long distance.

[0006]

In order to achieve the above object, the present invention provides: (1) a distance measuring means for detecting a subject image and detecting a distance to the subject; and an output of the distance measuring means. A focus control switching means for switching between a first mode for determining a focus position with correction and a second mode for determining the focus position without correction; wherein the focus control switching means comprises: A camera that switches between the first mode and the second mode depending on the image state of the image and the background. The distance measuring means uses two images having parallax, and the focus control switching means detects the image state between the subject image and the background according to the contrast of the subject image or the degree of coincidence between the two images. The camera according to claim 1, wherein the operation is performed. The focus control switching means gives priority to the second mode when it is determined that the degree of coincidence and the contrast of the images are better than a predetermined value as a result of the image state detection between the subject image and the background.

(2) Distance measuring means for detecting a subject image and detecting the distance to the subject, and focusing control for determining the focusing distance by comparing the output of the distance measuring means with a predetermined value. A camera comprising: means, image state detecting means for detecting the state of the subject image, and switching means for switching the comparison operation with the predetermined value according to the state of the subject image.

The camera having the above-described configuration focuses on a subject determined to be within a predetermined distance range to a predetermined position, and covers many subjects distributed at many distances depending on the depth of field. Focus control is performed.
However, in a scene in which a specific subject forms a clear contrast, focusing is performed with priority given to the subject so that even if the photograph is enlarged, it can be endured. In other words, in a scene where the contrast is not clear, even if the photograph is stretched greatly, the focus position does not matter much, but if the subject with clear contrast is not perfectly focused, the user can easily do so. However, it is easy to notice dissatisfaction with the focus of the photographed image, but in the present invention, the focus control method has been changed in accordance with such a situation, so that a photograph can be taken without dissatisfaction.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of a block configuration related to distance measurement and focusing in a camera as a first embodiment of the camera of the present invention.
FIG. 2 shows an external configuration of the camera.

This configuration comprises a light receiving lens 2 (2a, 2b) used for distance measurement, and a pair of sensor arrays 3 (3a) which receive an object image guided by the light receiving lens 2 and generate electric signals by photoelectric conversion. 3a, 3b) and an A / D for converting an electric signal into a digital signal to generate a subject image signal
A conversion unit 4, a control unit (CPU) 1 composed of a one-chip microcomputer or the like and performing arithmetic processing for focusing based on a subject image signal, and an EEPROM for storing information necessary for focusing, for example, a correction amount of a photographic lens or the like A memory unit 5 composed of a non-volatile memory such as a flash memory, a strobe light emitting unit 13 for projecting distance measuring light for distance measurement, a release switch 15 for starting an exposure operation, and a photographing lens 11 driven. It is composed of a focusing unit 10 for performing focusing.

The CPU 1 includes an image state detector 6 for determining the contrast of the subject image signal output from the A / D converter 4 and a predetermined value for comparison with the distance output or a focus position after comparison. A predetermined value storage unit 7 for storing a predetermined value;
A correlation calculator 8 for calculating an image shift amount x and a distance L from a subject image signal; an image state detector 6; a predetermined value storage 7; Focus position determination unit 9 that determines the focus position
It is composed of

A description will now be given of the distance measuring and focusing operations of the camera having the above-described configuration. First, the two light receiving lenses 2 are arranged with a parallax B to measure the distance of the subject 20 based on the principle of triangulation, and are guided by these light receiving lenses 2 onto the sensor arrays 3a and 3b. Each of the subject images is formed. These sensor arrays 3 are converted into electric signals based on the light and darkness of an image, and are further converted into digital signals by an A / D converter 4 to generate a subject image signal. The subject image signal is processed by the control unit 1 as described later. As shown in FIG. 1, the parallax B, the light receiving lens 2 and the sensor array 3
Has a phase shift amount x with respect to the subject distance L according to the distance f between them. That is, the subject image of the subject 20 at the distance L is formed at a position on the light receiving surface of the sensor array 3b which is separated from the optical axis of the light receiving lens by x = (B · f) / L. The CPU 1 calculates the relative image position difference x on these sensors.
Is obtained by comparing the two image signals, the focusing distance L is obtained. This is the principle of passive distance measurement.

FIG. 2 shows the appearance of a camera 12 equipped with such a passive type distance measuring device. On the front surface of the camera, the above-described two light receiving lenses 2a and 2b are arranged in addition to the photographing lens 11 and the strobe light emitting unit 13. A release switch 15 is provided on the upper surface of the camera. When the user presses the release switch 15, autofocus shooting is started.

In describing the distance measuring and focusing operations of the present embodiment, it will be described that as the distance increases as described in the subject, it becomes more difficult to separate the image of the background and the person, and accurate distance detection becomes impossible. . In a camera that focuses on the principle of the passive method, the main subject (person) 20 in the sensor array 3 depends on whether the main subject exists at a position near or far from the camera.
Changes the proportion occupied by the image. Here, the sensor array 3a will be described as an example.

[0015] As shown in FIG.
If 0 is present, the image signal output from the sensor array 3a clearly forms a person image in a predetermined pixel as shown in FIG. 3B. However, as shown in FIG.
When the person 20 exists on the far side, the width of the image formed on the sensor array 3a becomes narrow because the width and the distance f of the person 20 do not change. That is, as shown in FIG. 3D, the ratio (width) of the person 20 as the main subject in the image signal output from the sensor array 3a becomes small.

When comparing these two image signals,
Since accurate position comparison (detection of the relative image position difference x) cannot be performed unless image signals of a predetermined number of sensors (pixels) or more are used, as shown in FIG. If the proportion of the person becomes small, accurate focusing becomes difficult. In addition, a minute shadow of the image of the person 20 as shown in FIG. 3B is buried due to the pixel pitch and the limit of its resolution.
This may cause the accuracy of the image comparison to deteriorate. That is, if the subject is located at a long distance even in the passive system, accurate focusing cannot be performed.

Referring to FIG. 4, the reason why it is difficult to focus when the main subject is at a long distance and a method for coping with the difficulty will be described. When comparing the compositions (scenes) shown in FIGS. 4A and 4B, the composition of FIG. 4B shows that the person 20b exists at a longer distance, but as described above, the number of pixels for comparison (the distance measurement) If the area) is constant, the case where only the person 20a shown in FIG.
As shown in FIG. 4B, it is needless to say that the distance measurement becomes more difficult when the person 20b and the background subject 21b are mixed in the area. In this case, since the distance measurement data on the far side than the distance to be actually focused is output, it is more beautiful to set the focus position on the near side than the distance measurement result.

As another example, as shown in FIG. 4C, in the case of a landscape photograph for photographing a mountain or sky, the obtained subject image signal is an image signal without any contrast. The accuracy of distance measurement deteriorates. That is, a closer distance may be output even though the subject is at infinity. In such a composition, it is not the best to focus using the distance measurement result as it is. If the distance is longer than a predetermined distance, it is better to focus closer to the far side. Do.

The focusing operation of the present embodiment, including such operations, will be described in detail with reference to the flowchart shown in FIG. In the present embodiment, the contrast value is treated as a quantity indicating the image state, and focus control is performed. First, the outputs from the two sensor arrays 3 are A / D
The object image signal is detected by being digitized by the conversion unit 4 (step S1). Next, the image shift amount x of the two obtained images is obtained (step S2). Based on the image shift amount x, distance calculation is performed according to the above-described principle of triangulation to calculate a distance result L (step S3). The above-described contrast determination is performed to obtain a contrast value C (step S4).

Next, the contrast value C is compared with a predetermined amount C0 (step S5). In this comparison, when the distance is larger than the predetermined amount C0, it is determined that the reliability of the distance measurement is high, and the focus is corrected. However, when the contrast value C is equal to or less than the predetermined amount C0 (N
O), the composition is considered to be the composition shown in FIG. 4B or FIG. 4C, and the focus position correction described later is performed (step S6). This focus position correction is performed in consideration of the depth of focus and the degree of blur unique to the photographing lens of the camera.
The correction amounts H1 and H2 shown in (a) and (b) are stored in the memory unit 5 in advance. It is desirable that this setting be designed so that it can be easily changed in consideration of manufacturing variations of the camera.

In this focus position correction, when the distance measurement result L is 20
If it is longer than m (NO), the focus position of the taking lens is adjusted to 40 m, assuming that the composition is the same as the composition shown in FIG. 4C (step S7). On the other hand, if the distance measurement result L is closer than 20 m (NO), it is further determined whether or not the distance measurement result L is more than 10 m (step S8). In this determination, if the distance measurement result L is not less than 10 m (YES), that is, assuming that a main subject exists at a position farther than 10 m and closer than 20 m, focusing is performed at 9 m (step S9). In this case, it is considered that the scene to be photographed is equivalent to the composition shown in FIG. 4B, and the focus is slightly shifted toward the near side to perform control, assuming that the scene is affected by the background. This operation focuses on a position different from the distance L obtained from the distance measuring device. However, the distance L is covered by the depth of field, and the photograph is sufficiently focused. That is, the scene from step S6 to step S7 is shown in FIG.
It is considered that the composition is equivalent to that shown in FIG.
Even if the focus position is set to 40 m using the resolving power distribution of 1 or the infinity position (∞) of the landscape,
It is covered with a resolution that seems to be well focused. The scene from step S8 to step S9 is considered to have the same composition as that shown in FIG.
There is a focus peak at 9 m, but 10 m
m is also set to be covered by a high resolution. This is the composition shown in FIG. 4 (b). Even if a result of 10 m is output as a result of being farther than the distance of the person due to the contrast of the background, even if there is a person in the vicinity of 8 m before that, the focus is maintained. Looks like it fits. In addition, even if a person is actually at a position of 10 m, the user is not dissatisfied because the photographing is performed with high resolution in consideration of the depth of field. As described above, by correcting the photographing distance back and forth, it is possible to provide an AF camera that can accurately focus on a scene in which perspective is mixed or a low-contrast landscape.

However, when such a camera shoots a scene having a large contrast as shown in FIG.
Even if the building is more than 100m away, the focus is adjusted to 40m, so the picture will be a little sweet, and there is a side effect that the contrast of the subject is originally clear, so if you focus a little on the subject, you will be worried. Was. As shown in FIG. 4 (b), in a scene where subjects with various spatial frequencies are mixed as a whole, or in a scene having a low contrast as shown in FIG. 4 (c), a portion that is not particularly noticeable becomes clear here. .

An object having such a high contrast is
It is considered that the contrast of the sensor data obtained at the time of distance measurement is also high. For example, while the sensor data obtained from the landscape as shown in FIG. 3C is smooth as shown in FIG. In a scene as shown in FIG. 4D, sensor data in which brightness changes clearly as shown in FIG. 6B. Here, the data obtained by the two sensor arrays are shown by a solid line and a dotted line, respectively, but the shift amount x between the two image data is used at the time of the above-described triangulation. Further, the magnitude of the change in the brightness of the data is shown as a contrast amount C. In other words, when the contrast amount C is large, the reliability of the distance measurement is high, and it can be considered that the out-of-focus state can be easily determined when a photograph is taken.

Next, with reference to a flowchart shown in FIG. 8, distance measurement and focusing in a camera will be described as a second embodiment of the camera of the present invention. In the above-described embodiment, the contrast is used as the image state determination. However, the present embodiment is an example in which the image state is determined using the coincidence (reliability) of two images.

In this embodiment, two images (main objects)
The above-described correlation operation is executed to check the degree of deviation. As shown in FIG. 8, a predetermined sensor of the sensor array is used as a start sensor, and image signals corresponding to a specific number of pixels (windows) are added from the sensor to two sensor arrays with a difference therebetween. While the area of one sensor array is fixed and the other area is shifted, the sum Sn of the differences between the pixel outputs is calculated.

Specifically, the correlation function S1 and the shift amount n
Is initialized (step S11). Next, a difference for each pixel is obtained for the two image signals (step S12), and the sum is calculated (step S13). This processing is performed up to a certain number of pixels (windows), that is, it is determined whether or not the number of the specified number of pixels has been completed (step S14). The sensor is shifted (step S15), and the process returns to step S12.
On the other hand, if the processing is completed (YES), the mode is switched to the L side (step S16). This means that if the two images match, any pixel matches and the difference S becomes 0, and the sum Sn also becomes 0, so that it can be determined that the correlation is the best. However, since this matching state depends on the distance of the main subject,
One image (called the R-side image) is fixed, and the other image (L-side image) is fixed.
Side image).

Then, it is determined whether or not the switching has been completed (step S17). If not completed (NO), the correlation function S1 is set to 0, the shift amount n is incremented (step S18), and the process returns to step S12. On the other hand, if the switching is completed (YES), the smallest correlation function (minimum value Smin) is calculated from S1 to Sn calculated so far (step S19). this is,
One image (the image on the R side) is fixed, and the other image (the image on the L side) is shifted. A predetermined shift is performed, and the correlation function (the minimum value of the Sn ) Smin
Ask for.

Then, the image shift amount is calculated from the L-side shift amount at that time (step S20). That is, the minimum value Sm
In is 0 when the correlation is the best, but in practice, it rarely coincides with 0 due to the relationship between pixel resolution and image position. Therefore, the minimum value Smin is equal to the predetermined value S.
When it is smaller than 0, it is determined that the correlation is good (high reliability), and when the minimum value Smin is larger than the predetermined value S0, it is determined that the correlation is bad (low reliability).

For example, in the scene as shown in FIG. 4B, as shown in FIG. 9, the image of the person and the background at different distances are mixed in the ranging area (window), so that the reliability is low. Become. That is, although the image shift amount of the image of the person is x1, the shift amount of the background image is x2, and when the image is shifted by x1 or x2, they do not exactly match. Therefore, the reliability is reduced. In such a state, since neither the person nor the background is in focus, when the reliability is poor, the focus is corrected slightly to the front to make it easier for the person to focus.

Next, with reference to a flowchart shown in FIG. 10, an example of distance determination using reliability judgment in the above-described second embodiment will be described. In this case, the contrast determination method described with reference to FIG. 5 may be used together, and the above-described reliability determination based on the image coincidence (reliability) and the contrast is performed by the same determination. First, distance measurement is performed to calculate a distance L to a subject that is considered to be a main subject (step S21). Then, the minimum value S of the correlation function obtained earlier
min is compared with a predetermined value S0 to determine whether the minimum value Smin is smaller than the predetermined value S0 (step S2).
2). If the minimum value Smin is smaller than the predetermined value S0 in this determination (YES), it is determined whether or not the contrast amount C is larger than the predetermined contrast amount C0 in consideration of the contrast of the image obtained at this time ( Step S2
3). If the contrast amount C is smaller (NO) in this determination, it is determined that the degree of coincidence (reliability) of the image is high but the contrast is low, and for example, FIG. 4C or FIG.
Assuming that the scene may be as shown in (a), it is determined whether or not the previously obtained distance L is longer than 20 m (step S25). If it is determined that the distance L is longer than 20 m (YES), the distance L is increased to make the scenery clearer.
For example, focus on 40m (step S26),
To return. This is due to the low contrast
This takes into account the possibility that there is an error in the distance measurement result.

On the other hand, in step S23, the contrast amount C
Is larger (YES) or the distance L in step S25.
Is less than 20 m (NO), the reliability is high and the contrast is high, for example, as shown in FIG.
Assuming that the scene is as shown in (d), focusing is performed on the distance L (step S24), and the process returns.

In the case where the minimum value Smin is larger than the predetermined value S0 in the judgment of the step S22, (N
O), it is determined whether or not the contrast amount C of the image obtained at this time is larger than a predetermined contrast amount C0 (step S27). If the contrast amount C is larger in this determination (YES), it is determined that the contrast is high, and it is determined whether the previously obtained distance L is longer than 20 m (step S28). This is effective only over a long distance only when the reliability is low but the contrast is high. If the distance L is longer than 20 m (YES), the focus is adjusted to 15 m (step S29), and the routine returns. On the other hand, if the distance L is equal to or less than 20 m in step S28 (NO),
The flow shifts to 24, where focusing is performed on the distance L, and the flow returns.

If it is determined in step S27 that the contrast amount C is equal to or less than the predetermined contrast amount C0 (N
O), the contrast is low, and the short distance is prioritized, for example, to cope with the mixed perspective state as shown in FIG. Therefore, it is determined whether or not the previously obtained distance L is longer than 10 m (step S30). This is considered to be a case where the reliability is low and the contrast is low, and is to cope with a mixed perspective state as shown in FIG. If it is determined that the distance L is longer than 10 m (YES), the focus is adjusted to 9 m (step S31), and the process returns. This is to correct this because focusing is performed at a distance farther than the person by mixing the background image. On the other hand, step S3
If the distance L is 0 and the distance L is 10 m or less (NO), the process shifts to step S24 to focus on the distance L and returns.

As described above, according to the present embodiment,
Since the state of the image signal for distance measurement is judged based on the degree of coincidence (reliability) and contrast of the image and the focus position correction at the time of focusing is switched, it can be properly performed even for long-distance subjects that were difficult to do conventionally. A focused photograph can be taken.

[0035]

As described above, according to the present invention, in a camera equipped with a passive AF type distance measuring device,
It is possible to provide a camera that can accurately focus on a main subject at a long distance.

[Brief description of the drawings]

FIG. 1 shows a camera according to a first embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a block configuration related to ranging and focusing in a camera.

FIG. 2 is a diagram showing an external configuration of a camera equipped with a passive type distance measuring device.

FIG. 3 is a diagram for explaining a subject distance and a sensor output.

FIG. 4 is a diagram for describing focusing on a position where a main subject exists.

FIG. 5 is a flowchart for explaining a focusing operation in the first embodiment.

FIG. 6 is a diagram illustrating an example of sensor data obtained from a composition to be photographed.

FIG. 7 is a diagram illustrating a correction amount stored in a memory unit for performing focus position correction.

FIG. 8 is a flowchart for explaining a focusing operation in the second embodiment.

FIG. 9 is a diagram showing an example of sensor data obtained from a composition in which a person and a background image having different distances are mixed in a distance measurement area (window).

FIG. 10 is a flowchart illustrating an example of distance determination using reliability determination according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Control part (CPU) 2, 2a, 2b ... Light receiving lens 3, 3a, 3b ... Sensor array 4 ... A / D conversion part 5 ... Memory part 6 ... Image state detection part 7 ... Predetermined value storage part 8 ... Correlation calculation Unit 9: Focus position determining unit 10: Focusing unit 11: Photographing lens 12: Camera 13: Strobe light emitting unit 15: Release switch 20: Subject

Continued on the front page F term (reference) 2F065 AA06 DD10 FF09 JJ02 JJ05 JJ09 JJ25 QQ03 QQ23 QQ25 QQ36 RR06 UU05 2F112 AC03 BA03 BA07 CA02 FA03 FA07 FA12 FA21 FA36 FA45 GA10 2H011 AA01 BA05 BB03 DA01 DA01 DAB DA31 DA38 DB01 DD09 DD10

Claims (4)

[Claims] 1. A distance measuring means for detecting a subject image and detecting a distance to the subject, a first mode for correcting an output of the distance measuring means to determine a focus position, and Focus control switching means for switching between a second mode for determining a focus position and a second mode for determining the focus position, wherein the focus control switching means is configured to switch the first mode or the second mode depending on the image state of the subject image and the background. 2. A camera characterized by switching between modes 2. 2. The method according to claim 1, wherein the distance measuring means uses two images having parallax, and the focus control switching means detects an image state between the subject image and the background by comparing the contrast of the subject image or the two images. The camera according to claim 1, wherein the determination is performed according to the degree of coincidence. 3. The focus control switching means according to claim 2, wherein when the image state of the subject image and the background is detected, it is determined that the degree of coincidence and the contrast of the images are better than predetermined values. 3. The camera according to claim 2, wherein said mode is prioritized. 4. A distance measuring means for detecting a subject image and detecting a distance to the object, and a focusing control means for comparing an output of the distance measuring means with a predetermined value to determine a focusing distance. A camera comprising: an image state detecting unit that detects a state of the subject image; and a switching unit that switches an operation of comparing the predetermined value with the predetermined value according to the state of the subject image.