JP2003156679A - Focus detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique to easily bring a subject into focus by improving a probability that the subject is detected by efficient autofocusing control. SOLUTION: In the case of setting focusing evaluation areas R1 to R3 being an object whose evaluated value concerning the focusing state of a photographic lens is calculated at a position where contrast is hardly found on an image G10 stored in an image memory, the change of the evaluated value equal to or above a fixed value can not be detected in spite of performing general autofocusing operation and 1st low contrast scanning operation to detect the change of the evaluated value equal to or above the fixed value while driving the photographic lens by aiming all the focusing driving range, so that 2nd low contrast scanning operation to detect the change of the evaluated value equal to or above the fixed value while driving the photographic lens by aiming all the focusing driving range is performed concerning the image of the changed focusing evaluation areas R2, R4 and R5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera, and more particularly to automatic focusing (hereinafter
Also referred to as "autofocus" or "AF". ) Technology.

[0002]

2. Description of the Related Art Conventionally, as an autofocus technology for a digital camera, a contrast method (so-called hill climbing method) autofocus is known in which a position where the contrast of an image is maximized is obtained and the position is specified as an in-focus position. There is.

Generally, in the contrast type autofocus, the photographing lens is gradually stepped in a part of the drivable range (focusing driving range) of the photographing lens in the focusing operation of the photographing lens before performing the main photographing operation. While driving, an evaluation value (contrast value) regarding the focusing state of the taking lens is calculated for a specific evaluation area of the image acquired at each lens position, and the focusing operation of the taking lens is performed based on this evaluation value.

FIG. 11 is a schematic diagram showing a curve CL representing the relationship between the evaluation value and the position x of the taking lens in the optical axis direction.
As shown in FIG. 11, the evaluation value is the largest when the taking lens is in the in-focus position (x = xv). The contrast autofocus operation is performed by comparing the evaluation values of at least two captured images that are captured with different positions x in the optical axis direction of the taking lens. Specifically, the evaluation values of the two images are compared, and the taking lens is driven in the direction in which the evaluation value becomes larger. Then, by repeating such an operation to drive the taking lens, the taking lens can be driven to the in-focus position.

Further, in the above-described autofocus operation, since the taking lens is driven stepwise in a part of the focusing drive range, for example, as shown in FIG. 11, the taking lens is only in the range of positions xa to xb. When it is not driven, there is no peak above a certain level in the evaluation value. The amount of change in the evaluation value is small. The overall level of evaluation value is low. When any one of the above conditions is satisfied, the digital camera automatically determines that there is no contrast above a certain level in the specific evaluation area of the image. In this case,
Subsequent to the autofocus operation described above, the evaluation value relating to the focus state of the taking lens is calculated for the evaluation area of the image acquired at each lens position while driving the taking lens for the entire focusing drive range. By performing the operation (hereinafter, referred to as “low contrast scan operation”), the photographing lens can be driven to the in-focus position.

[0006]

However, when there is no subject having a certain contrast or more in the specific evaluation area of the acquired image, the photographing lens is in focus even if the low-con scan operation is performed. There is a problem that it cannot be driven to the position.

Further, although the subject in the image can be detected by increasing the size of the evaluation area for the acquired image from the beginning, the subject can be detected without increasing the size of the evaluation area. Even if it is possible, depending on this method, the evaluation area is large from the beginning, so that there is a problem that the time required to calculate the evaluation value becomes long.

The present invention has been made in view of the above problems, and provides a technique capable of easily focusing on a subject by improving the probability of detecting the subject by efficient autofocus control. With the goal.

[0009]

In order to solve the above-mentioned problems, the invention of claim 1 inputs an image composed of a plurality of pixels while driving the taking lens in the optical axis direction, and takes the taking lens. A focus detection device for detecting the in-focus position of
Calculating means for calculating an evaluation value relating to the in-focus state of the taking lens for a predetermined evaluation area set in the image; and focusing of the taking lens when the evaluation value does not satisfy a predetermined contrast condition. A first scanning means for calculating a first re-evaluation value for the evaluation area while driving the taking lens, targeting a range wider than the partial scan range when the evaluation value is obtained. An area changing means for changing the evaluation area when the first re-evaluation value does not satisfy the contrast condition, and a range wider than the partial scan range in the focusing drive range of the photographing lens. And a second scanning unit that calculates a second re-evaluation value for the changed evaluation region while driving the photographing lens. That.

The invention according to claim 2 is the focus detection device according to claim 1, wherein the driving directions of the photographing lenses in the first and second scanning means are opposite to each other. And

Further, the invention of claim 3 is the focus detecting apparatus according to claim 1 or 2, wherein the driving direction of the photographing lens is switched at the end of the focusing drive range. Characterize.

The invention according to claim 4 is the focus detecting apparatus according to any one of claims 1 to 3, wherein the area changing means changes the size of the predetermined evaluation area. Is characterized by.

According to a fifth aspect of the present invention, there is provided the focus detection apparatus according to any one of the first to third aspects, wherein the area changing means changes the position of the predetermined evaluation area. Characterize.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<Main Configuration of Digital Camera> FIG. 1 is a perspective view showing a digital camera 1 according to an embodiment of the present invention. 2 is a rear view of the digital camera 1.

As shown in FIG. 1, a taking lens 11 and a finder window 2 are provided on the front side of the digital camera 1. A CCD image pickup device 30 is provided inside the photographing lens 11 as an image generation unit for photoelectrically converting a subject image incident through the photographing lens 11 to generate an image signal (a signal including an array of pixel data for each pixel). It is provided.

The photographic lens 11 includes a lens system which can be driven along the optical axis direction, and by driving the lens system in the optical axis direction, a subject image formed on the CCD image pickup device 30 is formed. It is configured so that a focused state can be realized. Further, the drivable lens system of the photographing lens 11 has a drivable range (focusing driving range) of the photographing lens in a focusing operation, and here, a focusing state is realized for a subject in the closest view. The position of the lens system that can achieve this is referred to as the “near end”, and the position of the lens system that can achieve the in-focus state for the object in the farthest view (infinity) is referred to as the “infinite end”.

A shutter button 8, a zoom key 10, a camera status display section 13, and a photographing mode setting button 14 are arranged on the upper surface of the digital camera 1. The shutter button 8 is a button that the user presses to photograph the subject and gives a photographing instruction to the digital camera 1. Here, the shutter button 8 is half-pressed (S1) to perform an autofocus operation described later, and the fully-pressed state (S2) is to perform a main shooting described later. The zoom key 10 is pressed by the user to take the photographing lens 1.
1 is driven to perform zooming. Camera status display 1
Reference numeral 3 is composed of, for example, a segment display type liquid crystal monitor, and is provided to show the user the present setting contents and the like in the digital camera 1. The shooting mode setting button 14 is used to manually select and set one shooting mode corresponding to the subject from a plurality of shooting modes such as a portrait mode and a landscape mode when the digital camera 1 performs a shooting operation. It is a button to do.

A mounting portion 15 for mounting a memory card 9 for recording image data obtained by a main photographing operation in response to a user's operation of pressing the shutter button 8 is formed on a side surface portion of the digital camera 1. A removable memory card 9 can be attached. further,
A card take-out button 7 that is pressed when taking out the memory card 9 from the wearing section 15 is arranged.
The memory card 9 can be taken out from.

As shown in FIG. 2, the rear view of the digital camera 1 is provided with a liquid crystal display unit 16 for displaying live view images, photographed images, etc., and various setting states of the digital camera 1. An operation button 17 and a finder window 2 are provided.

<Functional Block of Digital Camera> FIG. 3 is a block diagram showing the internal structure of the digital camera 1.
As shown in FIG. 3, the digital camera 1 includes a photographing function unit 3 for processing an image signal, a focus detection unit 150 for realizing autofocus control, and a lens driving unit 11.
0, and a camera control unit 100 that integrally controls each unit provided in the digital camera 1.

CCD image pickup device 3 through the taking lens 11
The subject image formed at 0 is converted into an electric image having a plurality of pixels, that is, an image signal in the CCD image pickup device 30, and is guided to the A / D converter 40.

The A / D converter 40 converts the image signal output from the CCD image pickup device 30 into, for example, a digital signal of 10 bits per pixel. The image signal output from the A / D converter 40 is guided to the image processing unit 50.

The image processing section 50 performs image processing such as white balance adjustment, γ correction and color correction on the image signal. At the time of displaying the live view image, the image processing unit 50 outputs the image signal subjected to the image processing to the live view image creation unit 6
Give to 0. Further, when performing the autofocus control, the image processing unit 50 gives an image signal to the image memory 70. Further, during the shooting operation (main shooting) performed in response to the pressing operation of the shutter button 8, the image processing unit 50 gives an image signal subjected to image processing to the image compression unit 80.

When the live view image is displayed, the live view image forming section 60 generates an image signal suitable for the liquid crystal display section 16 and supplies it to the liquid crystal display section 16. Therefore, at the time of displaying the live view image, image display is performed on the liquid crystal display unit 16 based on the image signal obtained by successive photoelectric conversion in the CCD image pickup device 30.

The image memory 70 is for temporarily storing an image signal for performing autofocus control. In the image memory 70, the focus detection unit 150 drives the lens position of the taking lens 11 in a stepwise manner, and the image signal taken at each lens position of the taking lens 11 is stored under the control of the camera control unit 100.

The timing at which the image signal is stored in the image memory 70 from the image processor 50 is the timing at which the autofocus control is performed. For this reason, when it is desired to display a focused live view image on the liquid crystal display unit 16 during live view image display, an image signal may be stored in the image memory 70 during the live view image display. Good.

When the shutter button 8 is pressed, it is necessary to perform autofocus control before the shooting operation of the main shooting. Therefore, before performing the main photographing operation, the image signals photographed at the respective lens positions are stored in the image memory 70 while driving the lens positions of the photographing lens 11 in stages. The focus detection unit 150 is configured to acquire an image signal stored in the image memory 70 and perform a contrast autofocus operation. Then, after the autofocus control by the focus detection unit 150 is performed and the taking lens 11 is driven to the in-focus position, the shooting operation of the main shooting is performed, and the image signal obtained by the main shooting is given to the image compression unit 80. .

The image compression unit 80 is configured to perform an image compression process by a predetermined compression method on the image signal obtained by the actual photographing, and the image signal subjected to the image compression is output from the image compression unit 80. And is stored in the memory card 9.

The camera control unit 100 is realized by the CPU executing a predetermined program, and when the user operates various buttons including the photographing mode setting button 14, the shutter button 8, and the operation button 17, the operation contents thereof. Depending on the type, each part of the photographing function part 3 and the focus detection part 1
Is configured to control 50. In addition, the camera control unit 100 is connected to the focus detection unit 150, and when the focus detection unit 150 drives the lens position of the taking lens 11 stepwise during the autofocus control, C is set at each lens position.
The photographing operation of the CD image pickup device 30 is controlled, and the photographed image signal is stored in the image memory 70.

The lens driving section 110 is a driving means for driving the taking lens 11 along the optical axis in response to a command from the focus detecting section 150, and focuses a subject image formed on the CCD image pickup device 30. It changes the state.

<Regarding Focus Detection Unit 150> The focus detection unit 150 includes an image data acquisition unit, a region image extraction unit, a region setting unit, an evaluation value calculation unit, a contrast detection unit, a low contrast determination unit, a drive control unit, and a region change. And configured to obtain an image signal stored in the image memory 70,
Autofocus control by contrast method.
In other words, the photographing lens 11 operates so as to guide the subject image formed on the CCD image pickup device 30 to the in-focus position.

The image data acquisition unit acquires the image signal stored in the image memory 70, and the area image extraction unit extracts the image component included in the predetermined focus evaluation area from the image signal.

The focus evaluation area is a unit area for calculating an evaluation value serving as an index value of the focus state in the contrast method, and the focus evaluation area is an area for the image stored in the image memory 70. It is set by the setting unit. The focus evaluation area may be a fixed area with respect to the image stored in the image memory 70, or may be set at various positions according to various operations of the operation button 17 by the user before photographing. It can be anything.

The evaluation value calculation section drives the lens position of the photographing lens 11 in a predetermined partial scan range in a stepwise manner in the focus evaluation area, as is the case with a general autofocus operation. Meanwhile, the evaluation value regarding the in-focus state of the taking lens 11 at each lens position is calculated. This evaluation value is calculated as the sum of the contrast values for each pixel in the focus evaluation area.

The contrast detecting unit determines whether or not a predetermined contrast condition is satisfied for the evaluation value calculated by the evaluation value calculating unit while driving the lens position of the taking lens 11, and more specifically, it is set in advance. It is detected whether or not there is a change in the value above a certain level.

The low-contrast discriminating unit cannot detect a change in the evaluation value that is equal to or more than a certain value by the contrast detecting unit, that is, there is no peak in the evaluation value that is more than the certain value. The amount of change in the evaluation value is small. The overall level of evaluation value is low. If all three conditions are satisfied, it is determined that the contrast is low. As described above, when it is determined that the contrast is low in the general autofocus operation (hereinafter, referred to as “basic autofocus operation”), the first low-conscan operation (hereinafter, “first low-conscan operation”) is performed. (Referred to as “second low-conscan operation” hereinafter) is started when the contrast is low in the first low-con scan operation. The low contrast scan operation will be described later.

The drive control unit controls the drive of the lens position of the taking lens 11 by sending a signal to the lens drive unit 110. Before the low-conscan operation is started, the drive of the lens position of the photographing lens 11 in the basic auto-focus operation which is the general auto-focus operation described above is controlled, and after the low-con scan operation is started, the low-con scan operation is performed. The driving of the lens position of the taking lens 11 is controlled. The control of driving the lens position of the taking lens 11 after the start of the low contrast scan operation will be described later.

The area changing unit changes the focus evaluation area before the second low contrast scan operation is started. The change of the focus evaluation area will be described later in detail.

<Regarding Low Contrast Scan Operation> When the contrast discriminating unit discriminates that the contrast is low based on the evaluation value in the general autofocus operation, the lens position of the photographing lens 11 at the time of the discriminating is close to. The lens position is driven to the one of the end or the infinite end, whichever is closer. After that, the lens position of the photographing lens 11 is changed from one end of the focusing drive range to the other end (from the near end to the infinite end,
Alternatively, while driving in stages from the infinite end to the near end), the evaluation value regarding the focusing state of the photographing lens is calculated for the specific evaluation region of the image acquired at each lens position. In this low contrast scan operation, until the contrast detection unit detects a change in the evaluation value equal to or greater than a certain value, the photographing lens 11 is targeted for the entire range of the focusing drive range and the end of the focusing drive range. While driving in stages from the end to the end, the evaluation value regarding the in-focus state of the taking lens 11 is calculated for the in-focus evaluation area of the image acquired at each lens position.

However, here, in the middle of the low contrast scan operation, the evaluation value has a certain peak or more.
The amount of change in the evaluation value is large. The overall level of evaluation value is high. If the contrast detection unit can detect a lens position that satisfies even one of the three conditions described above, the lens position of the photographing lens 11 is not driven from one end to the other end of the focusing drive range, and after that, a general Similar to the automatic focusing operation, the photographing lens 11 operates so as to guide the subject image formed on the CCD image pickup device 30 to the in-focus position.

Further, in the above-described first low contrast scan operation, when the contrast detection unit cannot detect a change of the evaluation value calculated by the evaluation value calculation unit that is equal to or more than a certain value, the region change unit detects the change. After changing the focus evaluation area, the second low contrast scan operation is started. The second low contrast scan operation will be described below.

In the above-described first low-contrast scanning operation, since the lens position of the taking lens 11 is driven stepwise from the end of the focusing drive range, the second low-contrast scanning operation is started. At times, the lens position of the taking lens 11 is at the end (near end or infinite end) of the focusing drive range, and by switching the driving direction of the taking lens 11, the first low-conscan operation and the second low-conscan operation are performed. The driving direction of the taking lens 11 in the low contrast scan operation is the reverse direction. Regarding the second low contrast scan, the point that the above-mentioned evaluation area is changed and the taking lens 11
Since an operation similar to that of the first low-contrast scan is performed except that the driving direction is reversed, the description thereof will be omitted.

The autofocus operation here is as follows.
When the second low contrast scan operation is performed, it is composed of three operations, which are a general autofocus operation, a first low contrast scan operation, and a second low contrast scan operation.

In the first and second low-conscan operations, the lens position of the taking lens 11 is driven from one end to the other in the focusing drive range. Therefore, the taking lenses in the first and second low-con scan operations are performed. By setting the driving direction of the lens position of 11 as the opposite direction and switching the driving direction of the lens position of the taking lens 11 at the end of the focusing drive range of the taking lens 11, the first low contrast scan and the second low contrast scan Since a time loss is not generated between the first and second operations, the autofocus operation including the second low-conscan operation can be efficiently performed in a short time.

<Change of Focus Evaluation Area> FIG. 4 is a diagram showing an example of change of the focus evaluation area before the start of the second low-conscan operation. FIG. 4A shows the focus evaluation area before the change, and FIG. 4B shows the focus evaluation area after the change. As shown in FIG. 4, before the change, a plurality of focus evaluation areas R1 to R3 are set for the image G10 stored in the image memory 70, and after the change, the image G10 stored in the image memory 70. For this, a plurality of focus evaluation areas R2, R4, R5 are set. Here, the focus evaluation areas R1 to R3 and the focus evaluation areas R2, R4, and R5 are focus evaluation areas for extracting the contrast of the image G10 and calculating the focus evaluation value. That is,
Focus evaluation area R before and after changing the focus evaluation area
1, R3 are changed to the focus evaluation areas R4 and R5, and the position of the focus evaluation area is changed. It should be noted that, here, of the three focus evaluation areas, the focus of the shooting lens 11 is determined based on the evaluation value of the focus evaluation area that can bring the shooting lens 11 into the focus state for the object in the closest view. The focus operation is performed.

FIG. 5 is a schematic diagram showing an example in which the subject can be detected by the second low contrast scan operation when the position of the focus evaluation area is changed as shown in FIG. FIG. 5A shows the focus evaluation area before change, and FIG. 5B shows the focus evaluation area after change. Here, for convenience of description, the image stored in the image memory 70 and the frame indicating the focus evaluation area are shown together for convenience of description. However, the frame of the focus evaluation area is actually included in the image. It is not something that can be done. As shown in FIG. 5, the focus evaluation areas R1 to R3 are located in a portion where there is almost no contrast before the focus evaluation area is changed. Therefore, depending on the basic autofocus operation and the first low-contrast operation, the subject may be scanned. Although it cannot be detected, after the focus evaluation area is changed, the focus evaluation area (focus evaluation areas R2, R
Since a subject having a high contrast enters at (4, R5), the subject can be detected by the second low contrast scan operation.

<Operation of Digital Camera 1> Next, the operation of the digital camera 1 will be described. 6 and 7 are flowcharts showing the focusing operation in the digital camera 1, and show an example in which the autofocus control is performed when the user presses the shutter button 8. The operation of the digital camera 1 under this autofocus control is the basic autofocus operation,
It is composed of four operations: a first low contrast scan operation, a second low contrast scan operation, and a focusing operation of the taking lens 11. These operations will be described below with reference to the flowcharts shown in FIGS.

<Basic Auto Focus Operation> First, referring to FIG.
As shown in, when the digital camera 1 enters the shooting standby state, the process proceeds to step S1.

In step S1, the camera control unit 100 of the digital camera 1 determines whether the user has pressed the shutter button 8 halfway (S1) to input an instruction to start the autofocus operation. Then, when the user inputs an instruction for an autofocus operation, autofocus control for bringing the subject image formed on the CCD image pickup device 30 into the in-focus state in the digital camera 1 is started, and step S2 Proceed to.

In step S2, the area setting section
The focus evaluation area is set for the image stored in the image memory 70, and the process proceeds to step S3. Here, for example,
A focus evaluation area including the focus evaluation areas R1 to R3 shown in FIG. 4 is set.

In step S3, the lens position of the taking lens 11 is gradually changed near the lens position of the taking lens 11 at the time when the user presses the shutter button 8 to input an instruction to start the autofocus operation. While driving, the image data acquisition unit acquires the image signal stored in the image memory 70 at each lens position, and the area image extraction unit extracts the image component included in the focus evaluation area from the image signal. Then, in the evaluation value calculation unit,
An evaluation value regarding the focus state of the taking lens 11 is calculated for the image included in the extracted focus evaluation region, and then,
Go to step S4.

In step S4, the contrast detection unit determines, for the evaluation value calculated by the evaluation value calculation unit,
If there is a change of a predetermined value or more, the change is detected, and in response to the result, the low contrast determination unit determines whether the contrast is low. If it is determined that the contrast is low, the process proceeds to step S5, If it is determined that the contrast is not low, the process proceeds to step S13. Specifically, as shown in the schematic diagram of the image stored in the image memory 70 shown in FIG. 8, when a high-contrast subject exists in the focus evaluation area, as shown in FIG. If the range in which the lens position is driven stepwise is the position x = xa to xb, it is determined that the contrast is low. In addition, the in-focus position (x = x
When the lens position of the taking lens 11 is driven stepwise near v), it is determined that the contrast is not low.

In steps S5 to S10, the first low contrast scan operation is performed. The first low contrast scan operation will be described below.

<First Low-Contrast Scan Operation> In step S5, when it is determined that the contrast is low in step S4, whether the near end of the lens position is closer than the infinite end from the lens position of the taking lens 11 or not. Is determined by the drive control unit, and if the near end is closer, the process proceeds to step S6, and if the near end is farther, the process proceeds to step S7.

In step S6, the lens position of the taking lens 11 is driven to the near end under the control of the drive control unit,
Go to step S8.

In step S7, the lens position of the taking lens 11 is driven to the infinite end under the control of the drive controller, and the process proceeds to step S8.

In steps S5 to S7, the preparation for the first low contrast scan operation is performed.
At 8, the main operation of the first low contrast scan operation is started. Specifically, under the control of the drive control unit, the lens position of the photographing lens 11 is stepwise from one end to the other end (near end to infinite end, or infinite end to near end) of the focusing drive range. While driving the camera, the evaluation value calculation unit calculates an evaluation value regarding the in-focus state of the photographing lens for the focus evaluation region of the image acquired at each lens position by the image acquisition unit and the image extraction unit, and the process proceeds to step S9. . The focus evaluation area here is the same as that set in step S2.

In step S9, as in step S4, the contrast detection section detects, if there is a change of a predetermined value or more, with respect to the evaluation value calculated by the evaluation value calculation section, and receives the result. The low contrast determination unit determines whether or not the contrast is low. If it is determined that the contrast is low, the process proceeds to step S10. If it is determined that the contrast is not low, the process proceeds to step S13.

In step S10, the drive control section determines whether or not the taking lens 11 has been driven from one end to the other end of the focusing drive range in the first low contrast scan operation. That is, it is determined whether or not the lens position of the taking lens 11 is at the end of the focusing drive range. As a result, if the lens position is at the end, the process proceeds to step S11, and if the lens position is not at the end, the process returns to step S9. Here, if the lens position is not at the end, step S
Returning to 9 means that the photographing lens 11 is stepped from the end of the focusing drive range to the entire range of the focusing drive range of the taking lens 11 until a change in the evaluation value of a certain value or more is detected. The characteristics of the low contrast scan operation for calculating the evaluation value regarding the focus state of the taking lens 11 with respect to the focus evaluation area of the image acquired at each lens position while being driven dynamically are shown. The drive range of the taking lens 11 at this time is preferably the entire range of the focusing drive range as described above, but more generally, it is more than the partial scan range of the taking lens 11 in the basic autofocus operation. Is also set as a wide range. The same applies to the second low contrast scan operation described later.

In step S11, when the lens position of the taking lens 11 is at the end, the first low contrast scan operation is stopped under the control of the drive control section,
Proceed to 12.

In step S12, the focus changing area is changed by the area changing section, and the process proceeds to step S21. Explaining a specific example, the focus evaluation area shown in FIG. 4A set in step S2 is changed to the focus evaluation area shown in FIG. 4B in step S12. Changes are made.

Before describing step S13, step S2 in FIG.
1 and subsequent will be described first. After step S21, the second low contrast scan operation is performed. Less than,
The second low contrast scan operation will be described.

<Second Low-Contrast Scan Operation> In step S21, the drive control section determines the driving direction of the photographing lens 11 in the first low-contrast scan operation.
The driving direction of the taking lens 11 is switched to the opposite direction, and the process proceeds to step S22. That is, here, the drive direction of the taking lens 11 is switched at the end of the focusing drive range of the taking lens 11.

In step S22, the second low contrast scan operation is started. Specifically, as in step S8, the lens position of the photographing lens 11 is changed from one end to the other end (near end to infinite end or infinite end to near end) of the focusing drive range under the control of the drive control unit. ) In a stepwise manner, the evaluation value calculation unit calculates the evaluation value regarding the focus state of the photographing lens 11 for the focus evaluation region of the image acquired at each lens position by the image acquisition unit and the image extraction unit. Calculate and proceed to step S23. The focus evaluation area here is changed in step S12.

In step S23, as in step S9, the contrast detection unit detects any change in the evaluation value calculated by the evaluation value calculation unit that is equal to or greater than a predetermined value and receives the result. The low contrast determination unit determines whether or not the contrast is low. When it is determined that the contrast is low, the process proceeds to step S24, and when it is determined that the contrast is not low, the process proceeds to step S13.

In step S24, as in step S10, the drive control section determines whether or not the taking lens 11 has been driven from one end to the other end of the focusing drive range in the second low contrast scan operation. That is, it is determined whether or not the lens position of the taking lens 11 is at the end of the focusing drive range. As a result, if the lens position is at the end, the process proceeds to step S25, and if the lens position is not at the end, the process returns to step S23.

In step S25, the liquid crystal display 16 displays a warning message saying "imaging is not possible (low contrast)", and the lens position of the taking lens 11 is returned to the initial position before the autofocus operation is started. Locon processing is performed. That is, in step S25, the focus detection unit 15 cannot detect a change in the evaluation value equal to or more than a certain value even if the second low contrast scan operation is performed.
In the case of 0, the subject to be focused cannot be found, and under the control of the camera control unit 100, the autofocus operation is ended, the photographing is stopped, and the user is warned by displaying the fact. Then, after that, the process returns to step S1.

Next, in step S4, step S9, and step S23, when it is determined that the contrast is not low, the process proceeds to step S13, that is, the focusing operation of the taking lens 11 will be described below.

<Focusing Operation of Photographic Lens 11> Step S
In 13, the evaluation value calculation unit compares the evaluation values of at least two captured images captured at different positions of the taking lens 11 in the optical axis direction, and the drive control unit sets the evaluation value in a larger direction. The photographing lens 11 is driven. Then, the photographing lens 11 is driven by repeating such an operation to drive the photographing lens 11 to the in-focus position. Here, an evaluation value is calculated for each of the three focus evaluation areas R1 to R3 or the focus evaluation areas R2, R4, and R5 shown in FIG. 4, and based on the evaluation values, the object in the closest view is calculated. The lens position that brings the taking lens 11 into focus is calculated, and the process proceeds to step S14.

In step S14, the photographing lens 11 is driven under the control of the drive control unit so that the photographing lens 11 is brought into the in-focus state with respect to the subject, and the process proceeds to step S15.

In step S15, the shutter button 8
When is pressed, the camera control unit 1 determines whether or not the full-pressed state (S2) is given and an instruction to perform the main photographing is given.
00 judges. Here, if there is an instruction to perform the main photographing, the process proceeds to step S16, and if there is no instruction to perform the main photographing, the determination in step S15 is repeated. Although illustration is omitted here, if there is no instruction to carry out the main photographing for a certain period of time, the process returns to step S1.

In step S16, the main photographing is performed, the image signal is transmitted from the image processing unit 50 to the image compressing unit 80, and the image compressing unit 80 applies a predetermined compression method to the image obtained by the main photographing. Image compression processing is performed, and the image signal subjected to the image compression is output from the image compression unit 80 and stored in the memory card 9. Then, it returns to step S1.

As described above, with respect to the image of the predetermined focus evaluation area, the first low contrast for detecting the change of the evaluation value above a certain value while driving the photographing lens 11 over the entire focus driving range. When it is not possible to detect a change in the evaluation value above a certain level by performing the scanning operation, while driving the taking lens 11 for the entire focus driving range as to the image of the changed focus evaluation area, By performing the second low contrast scan operation that detects a change in the evaluation value that is equal to or greater than a certain value, the probability of detecting the subject can be improved without increasing the size of the focus evaluation area from the beginning. The subject can be easily and efficiently focused without increasing the calculation time required for the autofocus control.

<Modification> The embodiment of the present invention has been described above, but the present invention is not limited to the above-described contents.

For example, in the above-described autofocus control, the function of the focus detection unit 150 described above is
Can be realized by executing predetermined software, so that it is not always necessary that the respective units in the focus detection unit 150 be configured separately.

In the above embodiment, the second
Although the position of the focus evaluation area is changed before the start of the low-contrast scan, the present invention is not limited to this, and the size of the focus evaluation area may be changed. Figure 9
It is a figure showing the example which changes the size of a focus evaluation field. 9A shows the focus evaluation area before the change, and FIG.
(B) shows the focus evaluation area after the change, the focus evaluation area R6 is set for the image G10 stored in the image memory 70 before the change, and the image memory 7 after the change.
The focus evaluation area R7 is set for the image G10 stored in 0. Here, the focus evaluation areas R6 and R7 are focus evaluation areas for extracting the contrast of the image G10 and calculating the focus evaluation value. That is, the focus evaluation area R6 is changed before and after the focus evaluation area is changed.
The focus evaluation area R7, which is a larger area, is changed to
The size of the focus evaluation area is changed.

FIG. 10 is a diagram showing an example in which an object can be detected by the second low contrast scan when the size of the entire focus evaluation area is changed as shown in FIG. FIG. 10A shows the focus evaluation area before the change, and FIG. 10B shows the focus evaluation area after the change. Here, as in FIG. 5, for convenience of explanation, the image stored in the image memory 70 and the frame indicating the focus evaluation area are also shown together for the sake of convenience. The frame of is not included in the image. Figure 1
As shown in 0, since the focus evaluation area is located in a portion having almost no contrast before the focus evaluation area is changed,
Although the subject cannot be detected by the basic autofocus operation and the first low-contrast operation,
After the focus evaluation area is changed, a subject having a high contrast enters the focus evaluation area, and the subject can be detected by the second low-conscan operation, so that the taking lens 11 is brought into the focus state with respect to the subject. be able to. Therefore, even if the size of the focus evaluation area is changed, the probability of detecting a subject that can be focused can be improved, so that the subject can be easily focused.

[0079]

As described above, according to the first aspect of the invention, the photographing lens is driven in the partial scan range of the focusing drive range while the photographing lens is focused on the image in the predetermined evaluation area. Calculate the evaluation value related to the state,
When the evaluation value does not satisfy the predetermined contrast condition, the photographing lens is driven while targeting a range wider than the partial scan range in the focusing drive range, and the image in the predetermined evaluation region is evaluated. A first low contrast scan operation for calculating a value is performed. As a result, when the predetermined contrast condition is not satisfied, the evaluation value is changed for the image in the changed evaluation area while driving the photographing lens, targeting a range wider than the partial scan range in the focusing drive range. By performing the second low-conscan operation for calculating, the probability of detecting the subject can be improved without extending the calculation time required for the autofocus control, and thus the subject can be easily and efficiently focused. can do.

Further, according to the invention of claim 2, the driving directions of the photographing lens in the first and second low-contrast scanning operations are made opposite to each other, so that the photographing lens is moved in the first low-contrast scanning operation. After being driven in one direction, the photographing lens can be subsequently driven in the opposite direction in the second low-conscan operation, so that the second low-con scan operation is completed after the first low-con scan operation is completed. The time loss before the start of is reduced, and the low contrast scan operation can be efficiently performed twice in a short time.

According to the third aspect of the invention, in the first low contrast scan operation, the photographing lens is driven to one end of the focusing drive range, and subsequently, from the one end of the focusing drive range to the second low drive range. Since the driving of the taking lens in the conscan operation can be started, the time loss from the end of the first low-con scan operation to the start of the second low-con scan operation is reduced, and the time can be shortened. The low contrast scan operation can be efficiently performed twice.

According to the invention of claim 4, the size of the evaluation area for calculating the evaluation value relating to the in-focus state of the photographing lens is changed before the second low contrast scan operation is started. The probability of detecting the subject can be improved.

According to the fifth aspect of the present invention, by changing the position of the evaluation area for calculating the evaluation value regarding the in-focus state of the taking lens before the second low contrast scan operation is started, The probability of detecting a subject can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a digital camera according to an embodiment of the present invention.

FIG. 2 is a rear view of the digital camera shown in FIG.

FIG. 3 is a block diagram showing an internal configuration of a digital camera.

FIG. 4 is a diagram showing an example of changing a focus evaluation area.

FIG. 5 is a schematic diagram showing an example of detecting a subject after changing a focus evaluation area.

FIG. 6 is a flowchart showing a focusing operation in the digital camera.

FIG. 7 is a flowchart showing a focusing operation in the digital camera.

FIG. 8 is a schematic diagram showing an example in which focusing can be performed by a general autofocus operation.

FIG. 9 is a diagram showing an example in which the size of a focus evaluation area is changed.

FIG. 10 is a schematic diagram showing an example of detecting a subject after changing the size of a focus evaluation area.

FIG. 11 is a schematic diagram showing the relationship between the evaluation value and the position of the taking lens in the optical axis direction.

[Explanation of symbols]

1 digital camera 8 shutter button 11 Shooting lens 30 CCD image sensor 70 image memory 100 camera controller 110 lens drive 150 Focus detection device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Kitamura             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. (72) Inventor Motohiro Nakanishi             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. F-term (reference) 2H011 AA03 BA31 BB03 BB04 CA21                 2H051 AA00 BA47 BA66 CE14 DA03                       DA10 DA19 DC15 EA08 FA47                       FA48                 5C022 AA13 AB22 AB28 AC42 AC54                       AC69 AC74

Claims (5)

[Claims] 1. A focus detection device for detecting an in-focus position of a photographing lens by inputting an image composed of a plurality of pixels while driving the photographing lens in the optical axis direction, the focus detecting device being set in the image. Calculating means for calculating an evaluation value relating to the in-focus state of the taking lens with respect to a predetermined evaluation region; and the evaluation of the focusing drive range of the taking lens when the evaluation value does not satisfy a predetermined contrast condition. A first scanning unit that calculates a first re-evaluation value for the evaluation area while driving the taking lens, targeting a range wider than the partial scan range when the value is obtained; A region changing unit that changes the evaluation region when the evaluation value does not satisfy the contrast condition, and is wider than the partial scan range in the focusing drive range of the photographing lens. Targeting the circumference, the focus detection apparatus characterized by comprising a second scanning means for calculating a second re-evaluation value for the changed evaluation area while driving the photographing lens. 2. The focus detection device according to claim 1, wherein the driving directions of the photographing lenses in the first and second scanning means are opposite to each other. 3. The focus detection device according to claim 1, wherein the drive direction of the taking lens is switched at an end of the focus drive range. 4. The focus detection device according to claim 1, wherein the area changing unit changes the size of the predetermined evaluation area. . 5. The focus detection device according to claim 1, wherein the area changing unit changes a position of the predetermined evaluation area.