JP2000298232A - Focus detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a focus detecting device which can improve focusing accu racy with a short time lag, even in a night view or in the case of photographing against the sun. SOLUTION: Electric charges generated by receiving and converting light are accumulated for an integrated time T and then read out as a sensor data output SDATA thereafter and while electric charges are accumulated for an integral time T' longer than the integral time T successively to the read, AF operation is carried out on the basis of the sensor data SDATA corresponding to the integral time T. Consequently, while the time lag is shortened, wrong distance measurement due to deficiency in the quantity of light from a main subject is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device, and more particularly, to a focus detection device that accumulates electric charges by a photoelectric conversion element and outputs a focus detection signal.

[0002]

2. Description of the Related Art In recent years, autofocus cameras have been improved in performance until the focus can be detected even when the subject is a backlight or a night scene. It is also known that focusing on the main subject may still be weak.

[0003] Regarding such a phenomenon, a case where a night scene is set as a subject will be described first.

FIG. 14A is a view showing a state of a photographing object observed through a finder.

[0005] The photographer is a person 8 standing in front of the road 85.
2 is placed in the approximate center of the screen and used as the main subject.
I am trying to shoot with 1 as the background.

A street lamp 86 in the background is located to the right of the person 82, and a neon 84 of a building 83 in the background is located to the left of the person 82.

In an AF target 87 indicating a distance measuring frame,
The person 82, the streetlight 86, and the neon 84 are located, and the surroundings are dark and have low brightness because they are night views.

The above-described scene is generally one of the typical scenes when shooting a night view. In other words, some light source is located in the distance measurement frame, and the light source is often the light of a window of a building in the background or a street lamp, and it is rather rare that the inside of the distance measurement frame is completely dark.

Even when there is no main subject in front of the subject, that is, for example, when photographing a night scene itself, it is considered that almost any light source is almost always located within the distance measurement frame. Can be

[0010] The light source in the night view photographing is different from the case where the whole scene is illuminated by daytime sunlight or the like, and is often a point light source such as a streetlight or a window light.

FIG. 14B shows sensor data when the scene shown in FIG. 14A is photoelectrically converted by a pair of left and right AF sensors.

The detection method of this AF sensor is a known passive phase difference detection method. The left side shows the output of the left sensor row, and the right side shows the output of the right sensor row.

The horizontal axis is, for example, the arrangement order of all the pixels composed of 64 elements (el), and the vertical axis is the sensor data output SDATA
Are shown, and lines drawn by connecting output levels of adjacent pixels are illustrated.

As can be seen from FIG. 14B, since the image of the street lamp 86 is a point light source and very bright, a thin and steep output can be obtained from the AF sensor. Is darker than the streetlight 86 and the neon 84, the resulting output is small and nearly flat.

That is, since there is a large difference in brightness between a bright point light source and a person who has not been subjected to special lighting or the like, an output is obtained in which the image of the person located at the center becomes a dark part and is crushed. I will.

When the main subject is in backlight, the same can be said for the night scene as described above. This will be described with reference to FIG.

FIG. 15A is a diagram showing a state of a photographing target observed through a finder.

A photographer is about to perform photographing with a person 82 standing in the foreground positioned substantially at the center of the screen as a main subject and against a back light 91 including the sun 99 as a background.

FIG. 15B shows sensor data obtained by imaging the scene of FIG. 15A with the AF sensor. FIG. 15 (B)
As can be seen, the backlight 9 against the sun 99
Since 1 is very bright, the edge (contour) of the face of the person 82 becomes a sharp image, but the image of the face of the person 82 itself is considerably darker than the background and the output is small.

That is, since there is a large difference in brightness between a bright background and a person whose back side is shaded on the opposite side, an output is obtained in which the image of the person located at the center is darkened and collapsed. Would be done.

When focus is calculated based on the sensor output having a large difference in brightness as shown in FIGS. 14 and 15, and photographing is performed, a photograph in which neither the background nor the person is in focus may be obtained. This is due to the following three problems that the passive phase difference detection method originally has in principle. (1) A backlit subject is hard to focus on the center image because the center image is destroyed. (2) If the focus calculation is performed based on a steep image (for example, a point light source image formed only in a few pixels), the calculation accuracy is reduced. (3) The peripheral portion of the AF target 87 has a larger aberration than the central portion.

As an example of means for solving such a problem, for example, Japanese Patent Application Laid-Open No.
A technique is described in which, when a backlight state is detected, the integration time of the AF sensor is extended and integration is performed again to output an image of a dark portion.

FIG. 14A and FIG.
FIGS. 14 (C) and 15 (C) show the states of output signals obtained when applied to the scene as shown in FIG. 5 (A).

When the technique described in JP-A-5-264887 is applied, the output level of a streetlight image in a night view or a background image in backlight, which is a high luminance portion, is saturated, but is located at the center. The output level of the image of the person is increased, the contrast becomes clear, and the person can be focused.

The output of the AF sensor is
The integration time required to increase the level as shown in FIG. 14 (C) or FIG. 15 (C) is several times longer than the integration time in the case shown in FIG. 14 (B) or FIG. 15 (B). It has become.

As an example of a technique for solving the problem described in the above (3), for example, Japanese Patent Publication No. 6-84
Japanese Patent Application Laid-Open No. 890 discloses a technique for correcting the aberration amount with respect to the center of the periphery of a focus detection optical system by software. This focuses on the fact that the result of distance measurement at the periphery is more easily adopted than at the center in backlight.

On the other hand, although it is not a technique for directly solving the above-described problem, Japanese Patent Publication No. 7-75402 discloses a technique for reducing the time lag at the time of photographing by starting the next integration during focus detection. Is described.

[0028]

However, in the technique described in the above-mentioned Japanese Patent Application Laid-Open No. H5-264887, since backlight under sunlight is to be detected, the technique shown in FIG. Such a sensor output is difficult to determine as backlight, and there is a problem that the process of extending the integration time is not performed. This is because backlight is determined only when the output obtained from the pixels on both sides of the AF sensor is larger than the output obtained from the pixels on the center.
Also, in order to re-integrate for the first time after it is determined to be backlight,
There is also a problem that the time lag is large.

In the technique described in Japanese Patent Publication No. Hei 6-84890, the amount of aberration often varies from camera to camera due to manufacturing variations (component variations and assembly variations). At times, adjustment is required as a value unique to the body, and software for correction is also a heavy burden, which increases the manufacturing cost.

On the other hand, in the technique described in Japanese Patent Publication No. 7-75402, since the same integral control is performed every time, there is a high possibility that the same image is always obtained.
There is a problem that it is not always possible to focus on the central person in a night view or under backlight.

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 detection device capable of improving focusing accuracy with a short time lag even in a night view or under backlight.

[0032]

In order to achieve the above object, a focus detection apparatus according to a first aspect of the present invention is a photoelectric conversion apparatus which receives light, converts the light into electric charges, accumulates the electric charges, and outputs it as a focus detection signal. An element, first integration control means for controlling the time during which charge is accumulated by the photoelectric conversion element to a first charge accumulation time, and a second charge accumulation time longer than the first charge accumulation time. After the operation of the photoelectric conversion element under the control of the first integration control means is completed, the charge accumulation of the photoelectric conversion element is controlled while controlling the time for accumulating the electric charge to be the second charge accumulation time. And second integration control means for starting the operation.

Further, the focus detecting device according to the second aspect of the present invention
The focus detection device according to the first aspect of the present invention further includes a backlight determination unit that determines whether the subject is in a backlight state. When the backlight determination unit determines that the subject is in a backlight state, The focus calculation is performed based on the focus detection signal output from the photoelectric conversion element controlled by the second integration control means.

Further, the focus detection apparatus according to the third invention is the focus detection apparatus according to the first or second invention, wherein it is determined whether or not there is a noise light source which may hinder accurate focus detection. Noise light source determining means for determining whether the noise light source exists is determined by the noise light source determining means.
The focus calculation is performed based on the focus detection signal output from the photoelectric conversion element controlled by the integration control means.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 12 show a first embodiment of the present invention, and FIG. 1 is a block diagram showing an outline of a focus detection device.

This focus detection device has a focus control unit 1 for controlling the automatic focus adjustment. The focus control unit 1 receives a subject image, performs photoelectric conversion, accumulates the electric charge, and stores the electric charge. A focus detection unit 2 serving as a focus detection unit including a photoelectric conversion element such as an AF sensor that outputs a focus detection signal, and a charge accumulation (integration) operation of the AF sensor of the focus detection unit 2 is controlled to provide an appropriate integration amount. An integration control unit 3 serving also as a first integration control unit and a second integration control unit; determining whether a focus detection signal includes noise light for AF such as a street lamp in a night view; A harmful scene determination unit 4 serving as a backlight determination unit and a noise light source determination unit for determining whether the object is in a state, and a focus calculation unit 5 for calculating a defocus amount of the taking lens based on an output of the focus detection unit 2 ,But It has been continued.

A specific configuration of a camera to which such a focus detection device is applied will be described with reference to FIG. FIG.
FIG. 2 is a block diagram showing an optical and electrical configuration of a camera to which the focus detection device is applied.

A photographing lens 1 for forming an image of a subject light beam
Reference numeral 0 denotes, for example, a five-group configuration, in which the first group lens 11,
Group lens 12, third group lens 13, fourth group lens 14,
And the lens group of the fifth group lens 15 and the stop 16.

The first group lens 11 and the second group lens 12
Is moved to perform focusing,
The third group lens 13 and the fourth group lens 14 are moved to perform a zoom operation. Further, by moving the first group lens 11 and the second group lens 12 at the same time as the zoom operation by the cam structure, the movement of the focus due to the zoom operation is corrected.

The light beam that has passed through the photographing lens 10 enters a main mirror 17 that can take an observation state inserted into the light path of the light beam and a photographing state retracted from the light path.

The main mirror 17 is configured as a half mirror, and in the above observation state, 70% of the incident light amount is reflected toward the finder optical system 20, and the remaining 30% of the incident light amount is used as the main mirror. After being transmitted through the mirror 17 and reflected by the sub-mirror 18, it is guided to the AF optical system 30.

The finder optical system 20 includes a screen 21 disposed at a position optically equivalent to the film surface,
It is configured to include a condenser lens 22, a prism 23, a mold roof mirror 24, and an eyepiece 25, so that a subject image passing through these can be observed by a photographer.

When the main mirror 17 and the sub-mirror 18 are in the photographing state, the position is as shown by the dotted line in the figure, and the light beam of the subject that has passed through the photographing lens 10 reaches the position of the shutter 19. Therefore, when the shutter 19 is open, the exposure to the film 40 is performed during that time.

The AF optical system 30 includes a field stop 31 and
An infrared cut filter 32, a condenser lens 33,
The optical system includes a mirror 34, a re-imaging stop 35, and a re-imaging lens 36, and guides a light beam for focus detection to an AF sensor 37 which is a photoelectric conversion element and is focus detection means. System.

Next, the electrical configuration of the camera will be described with reference to FIG.

The camera control section 50 controls the entire camera as a whole, and internally has a central processing unit (CP).
U) 51, an interface IC 52, and the like.

The CPU 51 includes first integration control means,
It also serves as second integration control means, backlight determination means, and noise light source determination means. A timer section 51a for measuring time is provided therein, and the charge accumulation time during the distance measurement operation is provided. (Integration time) and the like are measured.

The camera control unit 50 includes an exposure control unit 42 that controls the exposure of the film 40 by moving the main mirror 17 up and down and driving the shutter 19.
A film drive unit 41 for controlling the winding / rewinding of the film 40; and a photodiode array 37L and 37R, which are a pair of left and right photoelectric conversion element arrays, and focus on the outputs of the photodiode arrays 37L and 37R. An AF sensor 37 that outputs a detection signal to the camera control unit 50; an aperture drive unit 43 that drives the aperture 16 in the imaging lens 10 to an appropriate aperture value based on an instruction from the camera control unit 50; Encoder 44 for zoom position
b. a zoom control unit 44 that controls and drives the zoom lens group by a zoom motor 44a while detecting by b.
It has an AF lens control unit 45 that controls and drives the AF lens 45a while detecting the positions of the focus lens groups 11 and 12 by an encoder 45b, and a sensor such as a photodiode that generates an output according to the luminance of the subject. For example, a photometric unit 46 installed in the finder optical system 20, a strobe control unit 47 for controlling a strobe for illuminating a subject by flash light emission,
A switch group 48 including all switches operated by the photographer is connected.

The switches included in the switch group 48 include, for example, a main switch for turning on the power to the camera, a release switch including a two-stage switch for performing a release operation, a zoom switch for performing a zoom operation, and the like. And a photographing mode switch as a mode selecting means for setting a photographing mode of the camera.

The release switch is half-pressed.
Depending on the stroke, the first release switch (hereinafter,
1R switch) is turned on, and A
An operation such as F or lens driving is performed, and a second release switch (hereinafter abbreviated as 2R switch) is turned on by a second stroke of full depression, so that exposure to the film 40 is performed.

The photographing mode set by the photographing mode switch includes a landscape mode suitable for photographing a landscape, a portrait mode suitable for photographing a person, a sports mode for increasing the shutter speed, and the like. In addition, there is a night view mode suitable for shooting a night view.

When the night scene mode is set,
The camera is designed to enter an operation mode in which the exposure time is shifted to a longer time so that a portion having a low luminance in the screen is more clearly photographed.

FIG. 3 is a block diagram showing the internal configuration of the AF sensor 37.

The AF sensor 37 receives a pair of left and right light beams split by the AF optical system 30 and receives a pair of left and right photodiode arrays 37L and 37R for generating electric charges in accordance with the amounts of the light beams. A pixel amplifier circuit (EAC) 37a for independently amplifying the charges generated by the arrays 37L and 37R for each photodiode and generating a voltage signal for the generated charges;
A shift register (SR) for sequentially outputting the outputs of the pixel amplifier circuits (EAC) 37a corresponding to the respective photodiodes of the photodiode arrays 37L and 37R from the sensor data output terminals as sensor data output SDATA in response to the clock signal CLK from the first clock signal CLK ) 37b and the CPU 51
And a sensor control circuit (SCC) 37c for controlling the internal operation of the AF sensor 37 in accordance with each signal (CEN, RES, END, CLK).

The pixel amplifier circuit (EAC) 37a generates a monitor output MDATA in accordance with the maximum value of the charges generated by each photodiode, that is, the output of the pixel amplifier circuit corresponding to the photodiode having the largest incident light amount. ,
Output from the monitor output terminal. This monitor output MDAT
A represents the level of charge accumulation (integration), and indicates that the larger the output, the more the integration is advanced.

FIG. 4 is a timing chart showing the operation of the CPU 51 and the AF sensor 37.

The sensor control circuit (SCC) 37 c
Upon receiving the reset signal RES from the U51, each block in the AF sensor 37 is initialized, and the photodiode arrays 37L and 37R and the pixel amplifier circuit (E
AC) The charge accumulation operation by 37a is started.

During this charge accumulation operation, the pixel amplifier circuit (EAC) 37a outputs a monitor signal corresponding to the charge accumulation level as a monitor output MDATA.

The CPU 51 outputs the monitor output MDATA
Is monitored as needed by a built-in A / D converter, and when the level reaches an appropriate charge storage amount, an accumulation end signal END is output to the AF sensor 37 to terminate the integration operation.

Next, the CPU 51 sets the read clock C
LK is output to the AF sensor 37, and the shift register (S
R) 37b is a photodiode array 37
The output voltages of the pixel amplifier circuit (EAC) 37a corresponding to the accumulated charges of the photodiodes constituting L and 37R are sequentially output as sensor data output SDATA.

The CPU 51 outputs the sensor data output SD
The ATA is sequentially A / D-converted by a built-in A / D converter and stored in an internal RAM.

The operation of the latter half of FIG. 4 (that is, the operation after the start of the reintegration) will be described later.

FIG. 5 is a flowchart of a main routine showing the operation of the entire camera of the first embodiment.

First, when the main switch of the switch group 48 is turned on, the CPU 51 is power-on reset and starts operation, and initializes the I / O port and RAM.
Are initialized (step S1).

Next, it is determined whether or not the 1R switch, which is the first stage of the release switch, is on (step S2).
Move to 10.

On the other hand, when the 1R switch is on, the photometric unit 46 is operated to perform photometric measurement of the subject brightness, and the aperture value and the shutter speed value for proper exposure are calculated (step S3).

Then, a subroutine "AF" is executed to detect the focus of the object, and the first lens group 11 as a focus lens group is detected based on the focus detection result.
And the second group lens 12 are driven to the in-focus position, and the object is focused (step S4). The contents of the subroutine "AF" will be described later in detail.

Next, as a result of the execution of the AF operation, it is determined whether or not the subject is focused (step S5). Here, even when the subject has low contrast or the like and cannot perform AF, it is determined that the subject is out of focus.

If it is determined in step S5 that the image is out of focus, the process proceeds to step S9 to be described later, and after displaying, the process returns to step S2, and it is determined that the image is in focus. Until the operation, the operation cannot be shifted to the exposure operation on the film 40.

On the other hand, if the camera is in focus,
It is determined whether the R switch is turned on (step S6).

If the 2R switch is off, the process returns to step S2 to repeat the above-described operation and waits for the on-state. On the other hand, if the 2R switch is on, the process returns to step S3. Based on the result of the calculation, the aperture 16, the main mirror 17, and the shutter 19 are controlled to perform an exposure operation on the film 40 (step S7).

When the exposure operation is completed, the photographic frame of the film 40 is wound up by the film drive unit 41 and fed to the next frame position (step S8), and a series of photographic operations is completed. Then, after a display device (not shown) such as an LCD or an LED is controlled to perform display (step S9), the process returns to step S2 to wait for the next photographing operation to be performed.

If it is determined in step S2 that the 1R switch is off, the state of the other switches is set in response to the operation of any switch other than the 1R switch and the 2R switch. Is detected (step S10).

If no other switch is turned on, the process proceeds to step S9. If any switch is turned on, a process corresponding to the switch is executed (step S11). ), Step S
Move to 9.

FIG. 6 is a flowchart showing details of the subroutine "AF" in step S4.

When this operation is started, first, the recalculation flag is cleared to 0 as an initial value (step S2).
1).

Then, the integration of the AF sensor 37 is started in accordance with the timing chart described with reference to FIG. 4 (step S22), and the counting of the integration time is started using the timer section 51a built in the CPU 51. (Step S23).

Then, the value of the monitor output MDATA is changed to A /
D conversion is performed (step S24). This monitor output MDA
TA indicates the integral amount as described above, and it is determined whether or not this is an appropriate value (step S25). If the integrated value has reached the appropriate value, the process proceeds to step S27 to be described later. If not, it is determined whether the integration time has reached the limit value (for example, 200 ms) (step S26). If it has not reached, the process returns to step S24 to continue the integration. If it has reached the limit value, continuing the integration any longer increases the time lag, so the process moves to the next step S27.

Then, the integration is restarted (step S27). Here, this reintegration will be described with reference to FIG. FIG. 8 is a flowchart showing the processing content of the subroutine "reintegration start".

First, the count value of the timer section 51a when the integration is completed in step S25 is stored in the RAM as the integration time T, and the integration time T is read out first (step S51).

Then, a value obtained by multiplying the integration time T by N and extending it is set as an integration time T 'in the re-integration (step S52). Thereafter, integration of the AF sensor 37 is started in the same manner as in step S22 (step S22).
53), counting of the integration time is started in the same manner as in step S23 (step S54).

In this way, the timer 51 a
When the time T 'obtained in step 52 has come, the integration of the AF sensor 37 is stopped using the interrupt function of the CPU 51 (step S55).

The contents of the processing shown in FIG.
The timing chart of FIG. 4 shows the second half of FIG.

That is, the sensor data output SDATA is sequentially A / D-converted by the built-in A / D converter and stored in the internal RAM, and then the integration is restarted.
The integration control with the integration time extended and the AF calculation (correlation calculation and the like to be described later) are simultaneously and simultaneously processed.

Returning to the description of FIG. 6, next, sensor data of all pixels is read into the RAM of the CPU 51 (step S).
28), illuminance correction, which is a known technique for correcting a variation in sensor sensitivity and a decrease in peripheral light amount of the AF optical system, is performed (step S29).

Next, a correlation operation of the central block is performed (step S30). The central block refers to FIG.
Alternatively, FIG. 14 (B) and FIG. 15 (B) show the blocks at the center between the left and right sensors, respectively.

The center block will be described more specifically with reference to FIG. FIG. 7 is a diagram showing a state in the finder screen.

At the center of the entire area 60 in the viewfinder, an AF target 64 indicating a distance measurement range is located as shown in the figure, and the entire left and right widths of the AF target 64 are set to all pixels of the AF sensor 37 (described above). The image is taken with 64 pixels in the example).

The 64 pixels are divided into a central block 61, a left block 62, and a right block 63 as shown (see also FIGS. 14 (B) and 15 (B)), and A correlation operation is performed.

That is, the above-mentioned step S30 performs the correlation operation in the central block 61. Since this correlation operation is a known technique, its detailed description is omitted.

It is determined whether or not focus detection is impossible based on the result of the correlation calculation (step S3).
1). This is a process for determining whether or not focus detection cannot be performed, for example, because the subject has low contrast.

If the detection is not possible, a correlation operation in the right block 63 is performed (step S32), and it is determined based on the result of the correlation operation whether the focus detection is impossible (step S33). ). If focus detection is not possible, a correlation calculation in the left block 62 is further performed (step S34), and it is determined whether focus detection is impossible based on the result of the correlation calculation (step S35).
Here, if the focus cannot be detected, it means that the focus cannot be detected in all the blocks. Therefore, the process exits without performing anything.

On the other hand, steps S31, S33, S3
If it is determined that the focus can be detected in any one of Steps 5 and 5, it is determined whether or not the recalculation flag is set to 1 (Step S36). Shifts to step S39 described later.

If the re-calculation flag is not set, for example, in the initial state where the re-calculation flag is cleared in step S21, a point light source / backlight determination process is executed (step S37). ), The presence or absence of a point light source or backlight is determined based on the execution result (step S).
38).

Here, it is determined whether noise light that may hinder accurate focus detection when performing AF, for example, whether a background such as a main subject contains a point light source like a streetlight, For example, it is determined whether or not the main subject is backlit.

If the noise light for AF is included or the backlight condition is satisfied, the flow shifts to step S44, which will be described later. Otherwise, the defocus amount of the photographing lens 10 is calculated. (Step S3
9), correcting the aberration of the taking lens 10 (Step S)
40). This aberration correction corrects the difference in the detected defocus amount due to the difference in the focal length of the photographing lens 10.

Next, it is determined whether or not the detected defocus amount is within a predetermined allowable value.
0 is already in focus or not (step S)
41).

If the camera is already in focus, it is not necessary to drive the photographing lens 10 so that the process exits from this process. Is calculated (step S42).
The photographing lens 10 is driven to the in-focus position based on the calculation result (step S43), and the process ends when the in-focus is achieved.

Note that the above steps S39, S40, S4
The processing in S2 and S43 is the same as the processing conventionally performed as a known technique.

On the other hand, if it is determined in step S38 that noise light for AF such as a street lamp is included or backlight conditions are determined, accumulation of charge restarted (integration) in step S27 is performed. ) Is determined (step S44).

In this step S44, the process stands by until the integration is completed by the interruption.
In most cases, the integration is completed while the processing from step S44 to step S44 is performed.
At 44, there is a high possibility that the user will not wait at all.

Then, the recalculation flag is set to 1 (step S45), and the flow returns to step S28. As a result, since the recalculation flag is set, the processing in the next steps S37 and S38 is not executed.

With this configuration, the normal integration processing is performed for the first time, and the integration processing is performed by extending the integration time at the next time. Therefore, it is possible to always obtain both normal (non-saturated) sensor data and (saturated) sensor data when the integration time is extended without increasing the time lag.

With reference to FIG. 9 to FIG. 11, the processing of the point light source / backlight determination in step S37 will be described. FIG. 9 is a diagram showing an example of sensor output when AF is performed on a person who is a main subject with a night view as a background by ordinary integration processing. FIG. FIG. 11 is a diagram illustrating an example of a sensor output when AF detection is performed on a face of a person who is a main subject in a backlight, when AF detection is performed by the integration processing described above.

Note that the sensor data shown in FIG.
4 (B), the sensor data of FIG. 10 is the same as that of FIG. 14 (C), and the sensor data of FIG. 11 is the same as that of FIG. 15 (C).

First, FIG. 9 shows a case where the influence of a point light source on focus detection in a night scene is large.

As described above, the streetlight image is a point light source for the AF sensor and is very bright, resulting in a thin and steep image. However, the image of a person is darker than the background streetlight or neon light, and the output is low. Is small.

That is, since the difference in brightness between the streetlight and the person is large, the output of the image of the center, which is the image of the person, is crushed as a dark portion, and the pixel width A and the pixel width B shown in FIG. Although it is large, the pixel width C is smaller than these, and this pixel width C is, for example, about 3 pixels although it differs depending on the pixel pitch.

The output level a and the output level b shown in FIG. 9 are small, and the output level c is much higher than these. When detecting such sensor data, it is determined that a point light source exists.

FIG. 10 shows sensor data when the integration time is extended.

The pixel widths A ′, B ′, and C ′ shown in FIG.
Each pixel width is slightly larger than the pixel widths A, B, and C shown in FIG. 9, but does not change so much. On the other hand, the output levels a ′ and b ′ shown in FIG. 10 are much higher than the output levels a and b shown in FIG. The output level c 'is saturated as shown in the figure.

As described above, in the case of FIG. 10, although the image of the street lamp is steep and can still be noise light,
Since the human image and the neon image are clearly output as compared with the case of FIG. 9, the influence of noise light on focus detection is relatively small. In such a case, there is no noise light. You can judge it.

For an outline of such a judgment,
The details are also described in Japanese Patent Application No. 10-349576 filed by the present applicant.

A description will now be given, with reference to FIG. 11, of a point light source / backlight determination in the case of backlight.

In the case of backlight, it is determined whether or not the subject is backlit by detecting that the output in the central block where the main subject is located is small and the contrast in the central block is small. It has become.

FIG. 12 is a flowchart showing details of the subroutine "point light source / backlight determination" in step S37.

First, the maximum output value and the pixel are searched for among all the pixels, and the value is set as Max (step S).
61). This corresponds to the output value indicated by reference numeral c in FIG.

Then, it is determined whether or not this Max is larger than the first threshold value (step S62). If it is not larger, the point light source flag is cleared (step S71). The process moves to S72.
That is, when Max is not larger than a certain level, it is determined that the light source cannot be a point light source.

On the other hand, when it is determined that Max is larger than the first threshold value, the output of the pixel two pixels ahead of the pixel providing the maximum output is obtained, and the output is set as Maxp (step S63). Further, the output of a pixel two pixels before the pixel providing the maximum output is obtained, and the output is set as Maxm (step S64).

Then, it is determined whether or not Max-Maxp is larger than a second threshold value (step S6).
5) If not large, the process proceeds to step S71.

When Max-Maxp is larger than the second threshold value, Max-Maxm
Is determined to be greater than the second threshold value (step S66), and if not, the process also proceeds to step S71.

That is, it is detected whether or not the sensor data changes abruptly in the range of ± 2 pixels. If the sensor data does not change abruptly, it is determined that the light source is not a point light source.

In steps S65 and S66, M
If it is determined that ax-Maxp is larger than the second threshold value and Max-Maxm is also larger than the second threshold value, the maximum output pixel ± 2 pixels except for 5 pixels is obtained. The output value is searched, and the value is set as Max '(step S67).

Similarly, the minimum output value (the output level d in FIG. 9 and the output level d in FIG.
Corresponding to the output level d ′ of the
in '(step S68). These Max 'and M
The value of in ′ is, for example, as shown in FIG.

Then, it is determined whether or not Max'-Min 'is larger than the third threshold value (step S6).
9) If it is larger, the process proceeds to step S71.
That is, this is the same as determining the contrast of the output of the remaining pixels except for five pixels of the maximum output pixels ± 2 pixels, and the contrast of the output of the remaining pixels is high (Max ′).
If −Min ′ is large), the sensor data is as shown in FIG. 10, for example, and it is determined that the influence on the focus detection of the point light source is small.

On the other hand, when the contrast of the output of the remaining pixels is low (Max′−Min ′ is small), the sensor data is as shown in FIG. 9, for example, and the influence on the focus detection of the point light source is large. Is determined, the point light source flag is set (step S70), and the routine goes to the subsequent step S72.

After step S72, a backlight determination is performed.

That is, first, it is determined whether or not the maximum output Max obtained in step S61 exists in the central correlation block (step S72).

Here, if it is determined that the light is present in the central correlation block, it is not a backlight, so that
The backlight flag is cleared (step S78). On the other hand, when it is determined that the pixel does not exist in the central correlation block but exists in one of the left and right correlation blocks, the maximum output value Maxc in the central correlation block (see FIG. 11) (step S73) and a minimum output value Minc (FIG. 1).
1) (step S74).

First, it is determined whether or not the maximum output value Maxc is smaller than the fourth threshold value (step S).
75) If it is greater than or equal to the fourth threshold value, it is determined that the subject is not a backlight, and the process proceeds to step S78 to clear the backlight flag.

On the other hand, if it is determined in step S75 that the maximum output value Maxc is smaller than the fourth threshold value, then it is determined whether Maxc-Minc is larger than the fifth threshold value. A determination is made (step S76). That is, in step S76, it is determined whether or not the contrast of the output in the central correlation block is equal to or more than a predetermined value.

Here, when the contrast of the output in the central correlation block is larger than the fifth threshold value,
The process proceeds to step S78 because it is determined that the subject is not backlit. On the other hand, if it is smaller than the fifth threshold value, it is determined that the subject is backlit and a backlight flag is set (step S77).

Thus, when either step S77 or step S78 is completed, the routine returns.

In the above description, the next integration after the completion of the integration control controlled by the extended integration time is the normal integration control without extending the time, but the present invention is not limited to this. The integration control in which the integration time is further extended may be performed simultaneously with the AF calculation.

According to the first embodiment, since the reintegration with the integration time extended is performed, compared to the case of FIG. 9 in which the integration time is not extended, the first person is included. The image of the subject is output with contrast as shown in FIG. 10, and even if noise light such as a point light source or a backlight is detected, the distance to the person who is the main subject is reliably detected by the central block correlation calculation. do it,
Focusing becomes possible.

Further, since the AF calculation based on the sensor data obtained by the integration of the normal integration time is performed simultaneously with the integration with the integration time extended, the re-integration is performed. However, there is an advantage that the time lag is short.

In this way, the focus detection device has a short time lag and does not lower the focusing accuracy even in a night scene where the focusing accuracy is reduced or under backlight.

FIG. 13 shows a second embodiment of the present invention, and is a flowchart showing the processing contents of the subroutine "reintegration start".

The contents of the processing other than the configuration of the second embodiment and the subroutine "reintegration start" are substantially the same as those of the first embodiment described above, and a description thereof will be omitted.
In addition, among the processing illustrated in FIG. 13, steps that are the same as the processing in FIG. 8 of the above-described first embodiment are denoted by the same reference numerals, and description thereof is omitted.

When the reintegration start process is performed, first, after reading the integration time T in step S51, it is determined whether or not the night view mode has been selected by the shooting mode switch of the switch group 48. It is determined based on whether or not it has been performed (step S56).

If the night view mode has been selected, the process proceeds to step S52, where the integral time T is multiplied by N to obtain an extended integration time T '. On the other hand, if the night view mode has not been selected. In step S57, a value obtained by multiplying the integration time T by N 'is set as an extended integration time T' (step S57).

These steps S56 or S5
7, when the extended integration time T 'is set by any one of the steps 7, the process proceeds to step S53 to start integration.

That is, in the second embodiment, the extension coefficient (N or N ') by which the integration time T is multiplied is
It can be changed depending on whether the shooting mode is set to the night scene mode.

This is because the luminance of the dark portion (here, for example, the luminance of the face of the person who is the main subject) is darker in the night scene than in the backlit subject, so that it is better to make the extension time longer. That is, in the above-mentioned coefficient, N
It is preferable to set the relationship such that> N ′.

According to the second embodiment, substantially the same effects as those of the first embodiment can be obtained, and in the night view mode, it is possible to output a dark portion with a clearer contrast. .

In each of the above embodiments, an example is described in which one sensor data is divided into three distance measurement frames. However, the present invention is not limited to this, and for example, a plurality of AF sensors are provided. It is also possible to apply to so-called multi AF.

In each of the above embodiments, the point light source / backlight determination is performed based on the output of the AF sensor. However, the present invention is not limited to this. For example, the determination may be performed based on the output of the photometry unit 46. Absent.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications and applications are possible without departing from the gist of the invention.

[Appendix] According to the above-described embodiment of the present invention, the following configuration can be obtained.

(1) A photoelectric conversion element which receives light, converts it into electric charge, accumulates the electric charge and outputs it as a focus detection signal, and a time for accumulating electric charge by the photoelectric conversion element is a first electric charge accumulation time. And the second charge accumulation time longer than the first charge accumulation time is set, and the operation of the photoelectric conversion element under the control of the first integration control means ends. And a second integration control means for starting the charge storage operation of the photoelectric conversion element while controlling the time for storing the charge to be the second charge storage time. Focus detection device.

(2) The apparatus further comprises a backlight determining means for determining whether or not the subject is in a backlight state. When the backlight determining means determines that the subject is in a backlight state, the second integration is performed. The focus detection device according to (1), wherein focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by a control unit.

(3) The apparatus further comprises a noise light source determining means for determining whether or not there is a noise light source which may hinder accurate focus detection. When it is determined that there is a focus operation, focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by the second integration control means (1). Or the focus detection device according to supplementary note (2).

(4) A photoelectric conversion element which receives light, converts it into electric charge, accumulates the electric charge, and outputs it as a focus detection signal, and causes the photoelectric conversion element to perform a charge accumulation operation for a first predetermined time. And after the operation of the photoelectric conversion element under the control of the first integration control means is completed, the charge accumulation operation of the photoelectric conversion element is performed for a time longer than the first predetermined time. A second integration control means for controlling the first integration to be performed only for a second predetermined time, wherein the first integration is performed in parallel with the operation of the photoelectric conversion element under the control of the second integration control means. A focus detection device for performing a focus calculation based on a focus detection signal output from the photoelectric conversion element controlled by a control means.

(5) The apparatus further comprises a backlight determining means for determining whether or not the subject is in a backlight state. When the backlight determining means determines that the subject is not in the backlight state, the first integration is performed. A focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by the control means. If the subject is determined to be in a backlight state by the backlight determination means, the second integration control is performed. The focus detection device according to (1) or (4), wherein the focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by the means.

(6) The apparatus further comprises a noise light source determining means for determining whether or not there is a noise light source which may hinder accurate focus detection, and the noise light source is present by the noise light source determining means. If it is determined that there is no noise light source, the focus calculation is performed based on the focus detection signal output from the photoelectric conversion element controlled by the first integration control means, and the noise light source is determined by the noise light source determination means. When it is determined that the focus operation is performed, the focus calculation is performed based on the focus detection signal output from the photoelectric conversion element controlled by the second integration control means. (1) The focus detection device according to (4) or (5).

(7) The photoelectric conversion element has a plurality of pixels, and the backlight determining means performs backlight determination based on signals output from the pixels constituting the photoelectric conversion element. The focus detection device according to supplementary note (2) or supplementary note (5), wherein:

(8) Mode selection means for setting a night scene mode suitable for photographing a night scene is further provided.
The focus detection device according to claim 1, wherein the length of the second charge accumulation time is changed depending on whether the night view mode is set.

(9) The second charge accumulation time is set longer when the night scene mode is set than when the night scene mode is not set. Focus detection device.

(10) The apparatus further comprises mode selection means capable of setting a night scene mode suitable for photographing a night scene, and according to whether the night scene mode is set or not.
The focus detection device according to claim 4, wherein the length of the second predetermined time is changed.

(11) The second predetermined time is set longer when the night scene mode is set than when the night scene mode is not set. Focus detection device.

(12) Focus detection means for outputting a focus detection signal by using a photoelectric conversion element, first integration control means for controlling the charge accumulation time of the photoelectric conversion element, and a longer charge accumulation time. A second integration control means for setting a charge accumulation time, and after the operation of the first integration control means, starting the charge accumulation operation of the photoelectric conversion element so that the integration is completed in the extended charge accumulation time; And a focus detection device.

(13) The apparatus further comprises a backlight determining means for determining whether or not the subject is in a backlight state. When the backlight determining means determines that the subject is in a backlight state, the second integration is performed. The focus detection apparatus according to (12), wherein the focus is calculated based on the focus detection signal integrated by the control means.

(14) The apparatus further comprises a noise light source determining means for determining whether a noise light source harmful to the focus detection is present, and the noise light source determining means determines that the noise light source is present. In this case, the focus calculation is performed based on the focus detection signal integrated by the second integration control means.

(15) Focus detection means for outputting a focus detection signal using the photoelectric conversion element, and first integration control means for controlling the charge accumulation operation of the photoelectric conversion element to be performed for a first predetermined time. A second integration control means for controlling the charge accumulation operation of the photoelectric conversion element to be performed for a second predetermined time longer than the first predetermined time after the operation of the first integration control means is completed; After the operation of the first integration control means is completed, the focus calculation based on the focus detection signal integrated by the first integration control means is started in parallel with the operation of the second integration control means. A focus detection device characterized by the above-mentioned.

[0165]

As described above, according to the focus detection device of the present invention, the focusing accuracy can be improved with a short time lag even in a night view or under backlight.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a focus detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an optical and electrical configuration of a camera to which the focus detection device according to the first embodiment is applied.

FIG. 3 is a block diagram showing an internal configuration of the AF sensor according to the first embodiment.

FIG. 4 is a timing chart showing operations of a CPU and an AF sensor according to the first embodiment.

FIG. 5 is a flowchart of a main routine showing an operation of the entire camera according to the first embodiment.

FIG. 6 shows a subroutine “A” in the first embodiment.
The flowchart which shows the detail of "F".

FIG. 7 is a view showing a state in a finder screen of the camera according to the first embodiment.

FIG. 8 is a flowchart showing a processing content of a subroutine “reintegration start” in the first embodiment.

FIG. 9 is a diagram illustrating an example of a sensor output when a person who is a main subject with a night view as a background is detected by AF in a normal integration process in the first embodiment.

FIG. 10 is a diagram showing an example of a sensor output when AF detection is performed on a person who is a main subject with a night view as a background by integration processing in which time is extended in the first embodiment.

FIG. 11 is a diagram illustrating an example of a sensor output when the face of a person who is a main subject in backlight is detected by AF in the first embodiment.

FIG. 12 is a flowchart showing details of a subroutine “determination of point light source / backlight” in the first embodiment.

FIG. 13 is a flowchart showing processing contents of a subroutine “start reintegration” in the second embodiment of the present invention.

FIG. 14 is a diagram showing an example of a sensor output when a main subject having a night view as a background is integrated at different charge accumulation times according to the above embodiments and the conventional example.

FIG. 15 is a diagram illustrating an example of a sensor output when a main subject in backlight is integrated with different charge accumulation times according to the above embodiments and a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 focus control unit 2 focus detection unit (photoelectric conversion element, focus detection unit) 3 integration control unit (first integration control unit, second integration control unit) 4 harmful scene determination unit (backlight determination unit, Noise light source determination means 5 Focus control unit 37 AF sensor (photoelectric conversion element, focus detection means) 48 Switch group (including mode selection means) 51 CPU (first integration control means, second integration control) Means, backlight determination means, noise light source determination means)

Claims (3)

[Claims] 1. A photoelectric conversion element which receives light, converts it into electric charge, accumulates the electric charge, and outputs the electric charge as a focus detection signal, and a time for accumulating electric charge by the photoelectric conversion element is a first electric charge accumulation time. A first integration control means for controlling, and a second charge accumulation time longer than the first charge accumulation time are set, and the operation of the photoelectric conversion element under the control of the first integration control means is completed. And a second integration control means for starting the charge storage operation of the photoelectric conversion element while controlling the time for charge storage to be the second charge storage time. Focus detection device. 2. The image forming apparatus according to claim 1, further comprising: a backlight determining unit configured to determine whether the subject is in a backlight state. When the backlight determining unit determines that the subject is in a backlight state, the second integration control is performed. 2. The focus detection device according to claim 1, wherein a focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by the means. 3. A noise light source determining means for determining whether or not there is a noise light source which may hinder accurate focus detection, wherein the noise light source is present by the noise light source determining means. Wherein the focus calculation is performed based on a focus detection signal output from the photoelectric conversion element controlled by the second integration control means. Item 3. The focus detection device according to Item 2.