JP2003262788A - Autofocus device and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus device capable of realizing the speed-up of autofocus control operation without lowering focusing performance, and an imaging device. <P>SOLUTION: An autofocus control part 20 of a digital camera 1 is equipped with a luminance detection part 25 for detecting the luminance value Bv of an object and a frame rate setting part 26 changing the frame rate in reading a CCD imaging device 13 according to the detected luminance value Bv, and a control part performing the focus control of a focusing lens 12 on the basis of the contrast value C of an image constituted of image signals from the device 13. The setting part 26 changes the frame rate of the device 13 to any of a plurality of stages (for example, three stages) set in advance according to the luminance value Bv. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus control technique.

[0002]

2. Description of the Related Art Generally, in autofocus control in a digital camera, the contrast in the focus area of an image is detected based on an image signal obtained by photographing an object, and the image is photographed at a lens position where the contrast value shows a peak. A method of driving an image to bring an image into a focused state by driving a lens (a so-called hill climbing method) is used.

In this method, the contrast of the image of the main subject is low when the image of the main subject is out of focus, and the contrast gradually increases as the image of the main subject approaches the in-focus state. It is based on the principle of maximum contrast. In this autofocus control, the contrast is detected at each lens position while driving the shooting lens at a predetermined pitch, and the lens position where the contrast shows a peak is specified as the focus position of the shooting lens, and shooting is performed at that focus position. A control mode in which a lens (more precisely, a focusing lens) is moved is adopted.

[0004]

However, in the above autofocus control technique, the CCD is used.
The frame rate when reading a plurality of images for autofocus from the (imaging device) is constant. Therefore, CC
It takes a certain amount of time to acquire a plurality of images for autofocus from D (image sensor). For example,
At least (1/30) to obtain 10 autofocus images at a frame rate of 30 FPS
Seconds × 10 sheets = 1/3 (seconds) is required. In this case, the operation time of the autofocus control becomes a value that is at least longer than this required time. As described above, there is a problem that the speed at the time of autofocus is limited because the time for acquiring a plurality of autofocus images does not become shorter than a predetermined amount.

Further, it is not possible to obtain an image signal having a sufficient S / N ratio because the exposure time of the CCD is too short only by adopting a high value as the frame rate. This leads to a situation where the focusing performance is deteriorated.

Therefore, in view of the above problems, it is an object of the present invention to provide an autofocus device and an image pickup device capable of speeding up the autofocus control operation without deteriorating the focusing performance.

[0007]

In order to achieve the above object, the invention of claim 1 is an autofocus system for inputting an image signal from a photoelectric conversion means forming a plurality of pixels to control the focus of a photographing lens. The device is a device for detecting brightness of a subject, a frame rate setting unit for changing a frame rate of the photoelectric conversion unit according to the brightness of the subject, and a frame rate after the change for reading from the photoelectric conversion unit. Control means for performing focus control of the photographing lens based on the captured image.

According to a second aspect of the present invention, in the autofocus device according to the first aspect of the invention, the frame rate of the photoelectric conversion means is set to one of a plurality of preset levels according to the subject brightness. It is characterized by being done.

According to a third aspect of the invention, in the autofocus device according to the first aspect of the invention, the control means is the first
During the period, the focus control operation is performed based on the image read from the photoelectric conversion unit at the first frame rate, and during the second period after the first period, the second frame rate The focus control operation is performed on the basis of the image read out from the photoelectric conversion means, and the second frame rate is a value changed from the first frame rate according to the subject brightness. And

According to a fourth aspect of the present invention, in the autofocus device according to the third aspect of the invention, the control means may be arranged before the instruction input from the operator to start the focus control. Focus control is performed based on the image read from the photoelectric conversion unit at the first frame rate, and after the instruction input is received, the focus control is performed from the photoelectric conversion unit at the second frame rate. It is characterized in that the focus control is performed on the basis of the outputted image.

A fifth aspect of the invention is an image pickup apparatus including the autofocus device according to any one of the first to fourth aspects of the invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION <A. First Embodiment><A1. Structure, etc.> FIG. 1 is a block diagram showing the structure of a digital camera 1 according to the present invention.

The digital camera 1 inputs a photographing function unit 10 for realizing a photographing function for photographing a subject and an image signal generated by the photographing function performed by the photographing function unit 10 to input the photographing lens 11 to the photographing lens 11. An autofocus control unit 20 that performs focus control, an overall control unit 50 that controls the overall operation of the digital camera 1 including the photographing function unit 10 and the autofocus control unit 20, and an operation unit that includes operation buttons such as a shutter button. 60, and a lens drive unit 70 that drives the taking lens 11 based on a control signal from the autofocus control unit 20.

The photographing function unit 10 photoelectrically converts a photographing lens 11 including a focusing lens 12 movable along the optical axis direction by driving the lens driving unit 70 and a subject image incident through the photographing lens 11 into an image. C for generating data (data consisting of an array of pixel data for each pixel)
Image memory 14 for temporarily storing the image data from the CD image pickup device 13 and the CCD image pickup device 13, and predetermined image processing such as color conversion processing and image compression processing on the image data obtained from the image memory 14. The image processing unit 15
A liquid crystal display unit 16 that displays a display image that has been subjected to image processing for image display in the image processing unit 15, and a recording medium that records a captured image that has been subjected to image processing for image recording in the image processing unit 15. 17 are provided.

Under the control of the overall control unit 50, the photographing function unit 10 displays the live view image before the main photographing on the liquid crystal display unit 1.
The live view image capturing operation for displaying the image on the display unit 6 and the main capturing operation for capturing the image for recording on the recording medium 17 when the shutter button is fully pressed are configured. In the live view image shooting operation, the image processing unit 15 performs relatively simple image processing as compared with the main shooting operation. Further, even if the liquid crystal display unit 16 is in the off state, the photographing operation by the CCD image pickup device 13 is performed at least during the autofocus control operation.

The autofocus control unit 20 extracts a focus evaluation area for extracting an image component of the focus evaluation area from the image memory 14 based on a preset focus evaluation area for evaluating the focus state of an image. The unit 21, the contrast calculation unit 22 for obtaining the contrast value C of the image based on the image component of the focus evaluation area, the in-focus state of the image is determined based on the contrast value C, and the in-focus position of the photographing lens 11 is determined. The focusing control unit 24 is provided for sending a control signal for driving the lens to the lens driving unit 70.

The autofocus control section 20 further includes a brightness detection section 25 and a frame rate setting section 26. The brightness detection unit 25 has a function of detecting the brightness of the subject of the image, and calculates the detection result as the brightness value Bv. Further, the frame rate setting unit 26 is configured to detect the subject brightness (brightness value B
Based on v), the frame rate setting for reading the image signal from the CCD image sensor 13 is changed.

The overall control unit 50 performs auto-focusing so that the image component of the focus evaluation area is in an appropriate focus state when, for example, the shutter button is half-pressed (hereinafter also referred to as "state S1"). The control unit 20 is caused to function so that the photographing function unit 10 performs the main photographing operation when the fully-pressed state (hereinafter, also referred to as “state S2”). Further, before the main shooting, the overall control unit 50 causes the shooting function unit 10 to sequentially perform image shooting as a live view image shooting operation, and causes the liquid crystal display unit 16 to display images that are sequentially updated, or the autofocus control unit 20. Control to give to.

The lens driving section 70 moves the focusing lens 12 from, for example, the far side to the near side based on a control signal provided from the focusing control section 24 of the autofocus control section 20. The drive pitch at this time is designated by the focus control unit 24. Then, the autofocus control unit 20 specifies the lens position (focus position) at which the image component in the focus evaluation area is in focus, and the lens drive unit 70 specifies the focus position by the focus control unit 24. In that case, the focusing lens 12 is moved to the designated lens position, and an image in which the image components in the focus evaluation area are in focus is formed on the CCD image pickup device 13.

FIG. 2 is a diagram showing an example of the focus evaluation area FR1. In FIG. 2, an image G1 shows an image obtained by the photographing operation of the CCD image pickup device 13. In this embodiment, as shown in FIG. 2, the focus evaluation area FR1 is set in the substantially central portion of the image G1, and in the autofocus controller 20, the image is calculated based on the image components included in the focus evaluation area FR1. The contrast of is evaluated.
The focus evaluation area FR1 shown in FIG. 2 is an example, and other focus evaluation areas may be set when actually applied to the digital camera 1 or the like. Further, a plurality of focus evaluation areas may be set for the image G1.

In the autofocus control section 20,
First, the focus evaluation area extraction unit 21 extracts an image component corresponding to the focus evaluation area FR1 from the image stored in the image memory 14.

The CCD image pickup device 13 has a so-called Bayer array pixel arrangement structure.
When the image capturing operation is performed in, the pixel data of R (red), G (green), and B (blue) color components for the entire screen according to the Bayer array is stored in the image memory 14.

Therefore, when the focus evaluation area extraction unit 21 extracts the image component of the focus evaluation area FR1, the pixel data of each color component corresponding to the focus evaluation area FR1 is extracted.

The image components extracted by the focus evaluation area extraction unit 21 are given to the contrast calculation unit 22.

The contrast calculator 22 has a structure as shown in FIG. That is, the contrast calculation unit 22 calculates a difference absolute value between the pixel of interest and a pixel located in the vicinity of the pixel of interest and having a fixed positional relationship with the pixel of interest, and a difference calculation result thereof. And a cumulative addition unit 222 for cumulatively adding.
The difference calculation unit 221 performs calculation until all the pixels included in the focus evaluation region FR1 are selected as the target pixel, and the cumulative addition unit 222 selects each pixel included in the focus evaluation region FR1 as the target pixel. The absolute values of the differences that are sometimes obtained are sequentially cumulatively added, and finally the focus evaluation area FR is reached.
The contrast value C for 1 is obtained.

When obtaining the contrast value C in the contrast calculating section 22, the calculation may be performed based on the pixel data of each color component of R, G, B obtained from the image memory 14. Alternatively, the luminance data may be generated once from the pixel data of each color component of R, G, B, and the calculation may be performed based on the luminance data.

FIG. 4 is a diagram showing a change curve of the contrast value C.

As described above, the contrast value C has a maximum value in the vicinity of the focus position PA. Therefore, by obtaining the maximum value of the contrast, the lens position PA corresponding to the maximum value can be obtained as the in-focus position.

<A2. Regarding Frame Rate Change> In the first embodiment, the frame rate R when the autofocus image is acquired from the CCD image pickup device 13
The case where T is set to any one of a plurality of stages (here, three stages) predetermined according to the subject brightness will be exemplified.

More specifically, as shown in FIG. 5, the frame rate setting unit 26 sets the frame rate RT to the value RT3 = 120FPS (when the brightness value Bv as the detection result of the subject brightness is equal to or higher than a predetermined threshold value TH1. Frames Per S
econd). In addition, the frame rate setting unit 26
When the brightness value Bv is less than the predetermined threshold value TH1 and more than the predetermined threshold value TH2, the frame rate RT is set to the value RT2.
= 60 FPS and the brightness value Bv is a predetermined threshold value TH2.
If less than, the frame rate RT is set to the value RT1 = 30.
Set to FPS. The threshold TH2 is a value smaller than the threshold TH1.

For example, when the brightness Bv is equal to or higher than a predetermined threshold value TH1 (that is, when the subject is very bright),
By changing the setting of the frame rate, the frame rate RT becomes the value RT3 (= 120 FPS) and the shutter speed SS becomes 1/120 (second). At this time, since the subject has sufficient brightness, it is possible to acquire an image with a sufficient S / N ratio even with such a high frame rate.

On the other hand, when the brightness Bv is less than the predetermined threshold value TH2 (that is, when the subject is relatively dark), the frame rate R is changed by changing the above frame rate setting.
T becomes the value RT1 (= 30 FPS), and the shutter speed SS becomes 1/30 (second). At this time, by setting such a relatively low frame rate, a sufficient S / N ratio can be obtained even when the subject is relatively dark.
It is possible to obtain a ratio image.

When the brightness Bv is lower than the predetermined threshold TH1 and higher than the threshold TH2 (that is, when the subject is moderately bright), the frame rate RT is changed to the value RT2 (= 60FP
S) and shutter speed SS is 1/60 (second)
Becomes At this time, since the subject is relatively bright, S / S is sufficient even with such a relatively high frame rate.
It is possible to acquire N ratio images.

In this way, the frame rate at the time of reading the image signal from the CCD image pickup device 13 is changed according to the subject brightness. Thereby, an image signal having a sufficient S / N ratio can be acquired.

<A3. Operation> Here, in live view display, it is assumed that the image is read from the CCD image sensor 13 at the frame rate of the value RT1 (= 30 FPS), and then the shutter button is half-pressed (that is, the state S1). The automatic focus control operation starts when the The frame rate RT after the start of the autofocus control operation is, as described above,
The brightness value Bv of the subject is set by the frame rate setting unit 26.
It is set according to.

FIG. 6A shows that the shutter button is in the state S1.
FIG. 9 is a diagram showing an autofocus control operation in the case where the frame rate RT is changed to a relatively large value RT3 (= 120 FPS) after being set to. In addition, FIG.
(B) shows that the frame rate RT is not changed before and after the shutter button is set to the state S1, and the value RT is relatively low even after the shutter button is set to the state S1.
It is a figure which shows the timing chart at the time of performing autofocus control operation | movement by continuing using the frame rate RT of 1 (= 30 FPS).

As shown in FIG. 6A, when the shutter button is set to the state S1 at time TA, the frame rate setting unit 26 determines a new value of the frame rate RT. Specifically, the frame rate setting unit 26 changes the frame rate RT based on the latest brightness detection value Bv at that time. In FIG. 6A, time T
It is shown that the brightness value Bv of the image two frames before the image subjected to the exposure process in A is calculated just before the time TA. The frame rate setting unit 26 performs a frame rate changing process based on the brightness value Bv.

The image signal generated by photoelectric conversion after being exposed at a predetermined time is read from the CCD image pickup device 13 at the time corresponding to the next frame, and at the time corresponding to the next frame. Is calculated based on the brightness value Bv. Since each brightness value Bv is calculated two frames after the exposure processing time, at time TA, the brightness value Bv relating to the image that has been subjected to the exposure processing two frames before is used. Of.

Further, here, the brightness value Bv is the threshold value T
It has a value of H1 or more. When the frame rate setting unit 26 determines that the brightness value Bv is greater than or equal to the threshold value TH1, the frame rate setting unit 26 changes the setting of the frame rate RT to the value RT3.

Then, the autofocus control section 20
The autofocus control operation based on the changed frame rate RT (= RT3) is started from time T0. In this autofocus control operation, the focusing lens (photographing lens) 12 is driven at a predetermined pitch, the contrast is detected at each lens position, the lens position where the contrast shows a peak is specified as the in-focus position, and the in-focus position is determined. In addition, it has a control mode in which the focusing lens 12 is moved. In this autofocus control operation, the contrast of the image of the main subject is low when the image of the main subject is blurred, and the contrast gradually increases as the image of the main subject approaches the in-focus state. It is based on the principle of maximum contrast. Then, the lens position PA corresponding to the maximum value Cmax of the contrast as shown in FIG. 4 is determined as the in-focus position.

More specifically, as shown in FIG.
The exposure process EP1 of the first frame image for autofocus is performed from time T0 to time T1, the exposure process EP2 of the second frame image for autofocus is performed from time T1 to time T2, and time T2
From time T3 to time T3, the exposure process EP3 for the third frame image for autofocus is performed. Similarly, the exposure process EPi (i = 4, i = 4
5, ...) are sequentially performed.

Here, each frame image is an image corresponding to a different lens position. Specifically, after the exposure process EP1 of the first frame image is completed, the focusing lens 12 is driven and the lens position moves by a predetermined amount. Then, the exposure process EP2 for the second frame image is started. Therefore, the lens positions of the first frame image and the second frame image are displaced from each other by a predetermined amount.

After the exposure process EP2 for the second frame image is completed, the focusing lens 12 is driven and the lens position is further moved by a predetermined amount. Then, the exposure process EP3 for the third frame image is started. Therefore, the lens positions of the second frame image and the third frame image are displaced from each other by a predetermined amount.

Similarly, after the exposure processing of a predetermined frame image is completed, the focusing lens 12 is moved by a predetermined amount.
After the move, the exposure process of the next frame image is started.

Each frame image is read from the CCD image pickup device 13 with a delay of one frame (time corresponding to the reciprocal of the frame rate) from the exposure time. More specifically, the reading process RD1 of the first frame image for autofocus is performed from time T1, the reading process RD2 of the second frame image for autofocus is performed from time T2, and from time T3. A reading process RD3 of the third frame image for autofocus is performed. Thereafter, similarly, the read processing RDi (i = 4, 5, ...) Of each frame image is sequentially performed.

Further, the contrast value C is obtained for each frame image read from the CCD image pickup device 13. More specifically, processing AF1 for obtaining the contrast value C of the first frame image is performed from time T2, processing AF2 for obtaining the contrast value C of the second frame image is performed from time T3, and from time T4. Third
Process A for obtaining the contrast value C of the th frame image
F3 is performed. Thereafter, similarly, the processing AFi (i = 4, 5, ...) Obtaining the contrast value C of each frame image is sequentially performed.

Then, the focusing control section 24 finds the maximum value from the plurality of contrast values C obtained by each processing AFi, and determines the lens position corresponding to the maximum value as the focusing position. . Specifically, as shown in FIG. 4, each frame image is acquired while moving the lens position from the position PB in a predetermined direction (for example, leftward in FIG. 4) by a predetermined pitch. Then, when the peak of the contrast change curve formed by the respective contrast values C of the plurality of frame images is specified, the lens position corresponding to the peak is determined as the focus position.

The focusing control section 24 drives the focusing lens 12 to move the focusing lens 12 to the determined focusing position. This completes the autofocus control operation. When the peak position cannot be determined because the frame image has a low contrast, the focusing lens 12 is moved to a predetermined specific position. Such a specific lens position may be, for example, the lens position before the start of the autofocus control operation, or the lens position on the farthest side assuming that the subject exists at infinity. However, in this embodiment, since the frame rate is appropriately set according to the brightness of the subject, it is possible to prevent the situation where the peak position cannot be specified due to low contrast due to the exposure time being too short.

After that, when the shutter button is further pressed to be in the fully pressed state S2, the main photographing operation is performed in the photographing function section 10 and an image having a large pixel size is acquired.

Here, as can be seen by comparing FIGS. 6A and 6B, the autofocus control operation as shown in FIG. 6A, that is, from the CCD image pickup device 13 to each autofocus is performed. According to the autofocus control operation that involves changing the frame rate RT to a larger value when reading a frame image, according to the autofocus control operation, the relatively low frame rate is used as it is without changing the frame rate. Compared with the case (FIG. 6B), the time required for the autofocus control operation can be shortened. When the frame rate RT is relatively high as shown in FIG.
This is because the time interval between the frame images is shortened as compared with the case where the frame rate RT is relatively low as in (b). Therefore, the same number of frame images can be acquired in a shorter period.

For example, when the autofocus control operation is realized by using three frame images, the frame rate RT is changed from the value RT1 (= 30 FPS) to the value R.
By speeding up to T3 (= 120 FPS), 3
The time required to acquire one frame image is about 1 /
From 10 (= 3/30) seconds to about 1/40 (= 3/120)
Shortened to seconds. Further, when the autofocus control operation is realized by using 10 frame images, the time required to acquire the frame images is approximately 1/3 (= 10/30) by the similar speedup. About 1 / second
It is shortened to 12 (= 10/120) seconds. However, for simplification of the description, the fact that the reading from the CCD image pickup device 13 is delayed by one frame is not taken into consideration. However, even if such a delay is taken into consideration, the speed of the autofocus control operation is still increased. Is realized.

Further, as described above, in the first embodiment, the frame rate RT in the autofocus control operation is set according to the detected value Bv of the subject brightness.

Specifically, when the brightness Bv is equal to or higher than a predetermined threshold value TH1 (that is, when the subject is very bright),
The frame rate RT is set to the value RT3 (= 120 FPS). Thus, when the subject has sufficient brightness, the frame rate RT is set to a relatively high value RT3.
Even when set to, it is possible to acquire an image with a sufficient S / N ratio. Therefore, it is possible to speed up the autofocus control operation while suppressing deterioration of the focusing performance.

On the other hand, when the brightness Bv is less than the predetermined threshold value TH2 (that is, when the subject is relatively dark), the frame rate RT is set to the value RT1 (= 30 FPS). If the subject is relatively dark, the frame rate R
By setting T to a relatively low value, it is possible to acquire a frame image for autofocus with a higher S / N ratio. Therefore, it is possible to suppress deterioration of the focusing performance when the subject is dark.

When the brightness Bv is less than the predetermined threshold value TH1 and more than the threshold value TH2 (in short, when the subject is moderately bright), the frame rate RT is the value R.
It is set to a value RT2 (= 60 FPS) between T1 and RT3. At this time, it is possible to speed up the autofocus control operation while suppressing deterioration of the focusing performance.

As described above, since the frame rate of reading from the CCD image pickup device 13 is changed to a higher value as the detected value Bv of the subject brightness increases, the autofocus control operation is speeded up. It is possible. Further, as the detected value Bv of the subject brightness becomes smaller, the frame rate of reading from the CCD image pickup device 13 is changed to a slower value, so it is possible to suppress deterioration of the focusing performance. In this way, the frame rate of the photoelectric conversion means can be appropriately set according to the subject brightness.

Further, the frame rate of the CCD image pickup device 13 is set in a plurality of preset stages (here, three stages of RT1, RT2 and RT3) according to the brightness of the subject.
Since it is changed to any one of the above, the control is easier than the case where the frame rate is changed to an arbitrary value. Therefore, the software and hardware for realizing the above control can be more easily configured.

In the above embodiment, the driving of the focusing lens 12 is described as temporarily stopped for each exposure process of each frame image, but the driving is not limited to this. For example, a driving operation may be adopted in which the focusing lens 12 is continuously moved even during the exposure period of each frame image. In this case, the lens position corresponding to each frame image is obtained as a virtual center position in the exposure period of each frame image.
For example, when the moving speed of the focusing lens 12 is constant, this center position is obtained as the center position between the lens position at the start of exposure and the lens position at the end of exposure. When adopting such a driving operation, the lens driving speed may be changed according to the frame rate RT. More specifically, the frame rate RT
Is relatively large, the focusing lens 12
Is driven at a relatively high speed, and when the frame rate RT has a relatively small value, the focusing lens 12 may be driven at a relatively low speed.

<B. Second Embodiment> Next, a second embodiment will be described. The digital camera according to the second embodiment has the same configuration as the digital camera according to the first embodiment. Below, it demonstrates centering around difference.

In the second embodiment, the above-mentioned first embodiment is used.
Similar to the embodiment, the frame rate of the CCD image pickup device 13 is changed according to the brightness, and the focus control of the focusing lens 12 is performed based on the contrast value of each frame image.

However, in the above first embodiment,
The case where the autofocus control operation starts after the shutter button is in the half-pressed state S1 has been described. However, in the second embodiment, the autofocus control operation is performed even before the shutter button is in the half-pressed state S1. A case will be described.

FIG. 7 is a timing chart showing the autofocus control operation according to the second embodiment.

As shown in FIG. 7, before the shutter button is half pressed S1, the CCD image pickup device 13
Value RT1 (= 3) for which the frame rate is relatively low in
0 FPS). Then, when it is detected that the shutter button is in the state S1, in response to this detection signal, the frame rate of the CCD image pickup device 13 is changed according to the brightness value Bv in the period TM2 after the predetermined time T0. Be changed. In FIG. 7, it is assumed that it is determined that the brightness value Bv is greater than or equal to the threshold value TH1, and the value RT
A case where the value is changed to a value RT3 (= 120 FPS) faster than 1 is shown.

Here, in the autofocus control operation (FIG. 7) of the second embodiment, as can be seen by comparing with FIG. 6A, the autofocus control operation is performed also in the period TM1 before the period TM2. This is different from the autofocus control operation of the first embodiment in that

Specifically, during the period TM1, CC
A value RT in which the frame rate of the D image sensor 13 is relatively low
It is set to 1 (= 30 FPS). Then, the autofocus control unit 20 reads a plurality of frame images at time intervals corresponding to the frame rate RT1 while shifting the lens position of the focusing lens 12 at a predetermined pitch. Then, the autofocus control unit 20 performs the autofocus control operation based on the read contrast value of each frame image.

As described above, since the autofocus control operation is always performed during this period TM1, the subject is relatively in focus or in focus even before the shutter button is half pressed S1. It is close.

After that, the operator appropriately determines the arrangement of the subject in the screen and the like, and then half-presses the shutter button. In other words, the operator gives the digital camera 1 an explicit instruction input that the final stage autofocus control operation should be started in preparation for shooting.

On the other hand, the autofocus control unit 20 of the digital camera 1 performs the same autofocus control operation as that of the first embodiment in the period TM2 after the shutter button is half-pressed. Run.
Specifically, the brightness value B detected by the brightness detection unit 25
A new value of the frame rate RT is determined according to v.

Then, the autofocus control section 20
While shifting the lens position of the focusing lens 12 at a predetermined pitch, the changed frame rate (here, RT
A plurality of frame images are read at time intervals corresponding to 3), and the autofocus control operation is performed based on the read contrast value of each frame image.

Here, since the autofocus control operation has already been executed in the period TM1 prior to the same autofocus control operation as in the first embodiment, the lens position is changed when the shutter button is set to the state S1. There is a high probability that it already exists near the in-focus position. Therefore, by performing the autofocus control operation in the period TM1, it is possible to complete the autofocus control operation in the period TM2 in a shorter period than in the case without the autofocus control operation in the period TM1.
That is, it is possible to speed up the autofocus operation in the period TM2.

In particular, in the second embodiment, the autofocus control operation is already performed in the period TM1 prior to the time point when the instruction input from the operator is received, so that the autofocus in the period TM2 after the instruction input is performed. The control operation can be completed in a short time. Therefore, it is possible to further reduce the time (period) from the time when the instruction input from the operator is received to the time when the subject is in focus.

In the second embodiment, a relatively low frame rate RT1 is used in the operation of acquiring the frame image for autofocus during the period TM1. This is because the requirement for high speed is low in the period TM1 as compared with after the shutter button is in the state S1. By using a lower frame rate than the period TM2 in the period TM1, an increase in power consumption can be suppressed.

However, the present invention is not limited to this, and during the period TM1, the frame image may be acquired using the frame rate corresponding to the luminance value and the autofocus control operation may be performed. For example, even in the period TM1, when it is determined that the subject brightness is high, a high frame rate may be set. According to this, it is possible to realize a high-speed autofocus control operation even before the photographer sets the shutter button to the state S1.

<C. Others> Although the embodiments of the present invention have been described above, the present invention is not limited to the contents described above.

For example, the above-mentioned autofocus control unit 20 also functions as an autofocus device for performing autofocus control, and if it is applied to a photographing device such as a camera, the frame rate of the photoelectric conversion means will depend on the brightness of the subject. By properly setting, it becomes possible to perform the autofocus control operation at a higher speed while suppressing the deterioration of the focusing performance. Therefore, the autofocus control unit 20 described above can be applied to devices other than the digital camera 1.

Further, in the second embodiment, the frame rate is switched before and after the shutter button is set to the state S1, but the invention is not limited to this. For example, after the shutter button enters the state S1, first, the autofocus control operation is performed while sequentially acquiring the frame images for autofocus at the first frame rate, and after the predetermined period has elapsed, the brightness value Bv is set. A similar autofocus control operation may be performed by switching to another frame rate (second frame rate) depending on the situation.

[0077]

As described above, the claims 1 to 5 are as follows.
According to the invention described in (1), since the frame rate of the photoelectric conversion unit can be appropriately set according to the subject brightness, it is possible to perform the autofocus control operation at a higher speed while suppressing the deterioration of the focusing performance. Is.

Particularly, according to the second aspect of the present invention, the frame rate of the photoelectric conversion means is
Since it is changed to any one of a plurality of preset stages, the control is easier than when the frame rate is changed to an arbitrary value.

According to the third aspect of the invention, since the autofocus control operation has already been performed in the first period, the second focus changed according to the subject brightness.
It is possible to shorten the operation time of the autofocus control operation in the second period based on the image read at the frame rate of.

Further, according to the invention of claim 4,
Since the autofocus control operation has already been performed in the first period before the time point when the instruction input to start the autofocus control from the operator is received, the autofocus control operation in the second period thereafter. Can be completed in a short time. Therefore, it is possible to further shorten the time from the instruction input by the operator to the in-focus state of the subject.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital camera.

FIG. 2 is a diagram showing an example of a focus evaluation area.

FIG. 3 is a block diagram showing a detailed configuration of a contrast calculation unit.

FIG. 4 is a diagram showing an example of changes in a contrast value.

FIG. 5 is a diagram showing a relationship between a brightness value Bv and a frame rate RT to be set.

FIG. 6 is a timing chart showing the operation of the first embodiment.

FIG. 7 is a timing chart showing the operation of the second embodiment.

[Explanation of symbols]

1 digital camera 10 Shooting function section 11 Shooting lens 12 Focusing lens 20 Autofocus control unit C contrast value FR1 Focus evaluation area G1 image PA lens position RT frame rate S1, S2 (shutter button) status TH1, TH2 threshold

Claims (5)

[Claims] 1. An autofocus device for inputting an image signal from a photoelectric conversion means comprising a plurality of pixels to control focus of a photographing lens, the brightness detection means for detecting a brightness of a subject, and the brightness of the subject. Frame rate setting means for changing the frame rate of the photoelectric conversion means according to the above, and control means for performing focus control of the taking lens based on the image read from the photoelectric conversion means at the changed frame rate. An autofocus device comprising: 2. The autofocus device according to claim 1, wherein the frame rate of the photoelectric conversion means is set to one of a plurality of preset levels according to the subject brightness. Auto focus device. 3. The autofocus device according to claim 1, wherein the control unit performs a focus control operation based on an image read from the photoelectric conversion unit at a first frame rate in a first period. In the second period after the first period, the focus control operation is performed based on the image read from the photoelectric conversion unit at the second frame rate, and the second frame rate is The autofocus device is a value changed from the first frame rate according to the subject brightness. 4. The autofocus device according to claim 3, wherein the control unit is configured to perform the first frame rate even before a time point when an instruction input from the operator to start the focus control is received. Focus control is performed on the basis of the image read from the photoelectric conversion means, and after the instruction input is received, the second control is performed.
The focus control is performed based on the image read out from the photoelectric conversion unit at the frame rate. 5. An image pickup apparatus comprising the autofocus device according to claim 1.