JP3977406B2 - Autofocus device, autofocus method, imaging device, program, storage medium - Google Patents

Description

The present invention relates to an autofocus device, an autofocus method , an imaging device , a program, and a storage medium , and particularly relates to a reduction in time required for autofocus.

  In a digital camera or the like, an autofocus (hereinafter referred to as AF) (refer to Patent Document 1 below) method called a TV-AF method is often adopted. In this method, the subject position is calculated from the value of the AF evaluation signal at each point by moving the focus position within a certain range. The AF evaluation signal is calculated using a BPF (band pass filter) or the like so that the signal becomes larger as the focus is achieved.

  For example, when the range is from infinity to 50 cm, as shown in FIG. 6, an AF evaluation signal at a focus position focusing on infinity is acquired, and AF evaluation signals at each distance are sequentially obtained while approaching the focus position to 50 cm. get. Control is performed by a method of comparing the AF evaluation signals of the respective distances and bringing the focus position to the distance A determined to be most focused. Note that the horizontal axis in FIG. 6 indicates the subject distance at which the focus lens is focused.

In addition, since it is usually difficult to continuously acquire the AF evaluation signal while moving the focus position, for example, the AF evaluation signal is often acquired by thinning out at every distance interval corresponding to the depth of field.
Japanese Patent Laid-Open No. 2000-152064

  However, in the case of a camera having an optical system with a shallow depth of field or a camera with a wide distance measuring range, the total number of data to be acquired is not limited even if the AF evaluation signal is acquired by thinning as described above. The problem arises that the distance measurement time increases and the distance measurement time increases.

The present invention has been made under such circumstances, and provides an autofocus device, an autofocus method , an imaging device , a program, and a storage medium that can shorten the AF time without reducing AF accuracy. It is for the purpose.

In order to achieve the above object, in the present invention, an autofocus device, an autofocus method, an imaging device, a program, and a storage medium are configured as follows.
(1) first detection means for detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to the first drive range;
Second detection means for detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to a second drive range;
The first detection unit divides the first drive range into a plurality of parts, and detects the AF evaluation value when it is determined that the focus is in one of the divided drive ranges. And when it is determined that one of the divided drive ranges is out of focus, the AF evaluation value is detected in the other divided drive range,
The second detection means detects the AF evaluation value in the second drive range narrower than the first drive range including the focus position of the focus lens detected at the time of previous imaging,
Further, when the current shooting parameter is changed from the previous shooting parameter, the first detection means detects the AF evaluation value, and when there is no change, the second detection means detects the AF evaluation value. Detecting an autofocus device.
(2) The autofocus device according to (1),
The shooting parameters include at least one of a zoom lens position, shooting time, shooting mode, AF frame setting, subject brightness, AF evaluation value, white balance control value, and vertical / horizontal position of the autofocus device. An autofocus device characterized by that.
(3) An imaging device comprising the optical system having the autofocus device and the focus lens according to (1) or (2).
(4) a first detection step of detecting an AF evaluation value indicating an in-focus state by driving the focus lens with respect to the first drive range;
A second detection step of detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to a second drive range;
In the first detection step, the first drive range is divided into a plurality of parts, and the AF evaluation value is detected when it is determined that the focus is in one of the divided drive ranges. When the operation is terminated and it is determined that one of the divided drive ranges is out of focus, the AF evaluation value is detected for the other divided drive range,
In the second detection step, the AF evaluation value is detected with respect to the second drive range narrower than the first drive range including the focus position of the focus lens detected at the previous imaging. ,
Furthermore, by executing the first detecting step when the current imaging parameters was a change as seen from the previous imaging parameters, if the change was not a feature to perform the second detection step Autofocus method to use.
(5) A program for causing a computer to execute the autofocus method according to (4).
(6) A storage medium storing the program according to (5) so as to be readable by a computer.

  As described above, according to the present invention, the AF time can be shortened without reducing the AF accuracy even when the total number of AF evaluation signals to be acquired is large.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to digital camera examples. The present invention is not limited to the form of the apparatus, and can be implemented in the form of a method supported by the description of the embodiments.

Example 1
FIG. 1 is a diagram illustrating a schematic configuration of a “digital camera” as an imaging apparatus having an autofocus device according to a first embodiment.

  This digital camera includes a CDS circuit that photoelectrically converts light imaged by an optical system 01 having a zoom lens and a focus lens 02 by an imaging device 03 and removes output noise, and a non-linear amplification circuit that is performed before A / D conversion. The signal digitized through the preprocessing circuit 04 and the A / D converter 05 is stored in the memory 07 via the memory controller 06, converted into an image by a signal processing circuit (not shown), and then stored in the recording medium 08. Record an image.

  The operation of AF will be described. The AF operation is controlled by the control unit 11. First, when SW1 · 09 is pressed, the focus lens driving circuit 17 drives the focus lens 02 so as to scan the range selected by the imaging condition analysis unit 12 and the range setting unit 13, and from the imaging device 03, Obtain the output image signal. At each drive position of the focus lens 02, the acquired image signal is converted into an AF evaluation value indicating the degree of focusing by extracting the mid-high range signal component using the BPF by the AF evaluation value calculation circuit 14. The value focus position determination unit 15 with the highest AF evaluation value sets the position where the highest AF evaluation value is obtained as the focus position (A in FIG. 5), and the control unit 11 drives the focus lens. The focus lens 02 is driven to the in-focus position with respect to the circuit 17. When the drive of the focus lens 02 is completed and the SW2 · 10 is pressed by the user, photographing is performed. Further, the in-focus position and the shooting conditions at the time of shooting are stored in the shooting condition storage unit 16.

  The AF operation will be described in more detail with reference to the flow of FIG.

  In step 1 (denoted as S1 in the figure, the same applies hereinafter), the photographing conditions are analyzed. If it is the first scan of the focus lens 02, the process proceeds to the next step 2, where the focus lens 02 has a relatively wide scanning range (for example, the focus lens 02) so that an AF evaluation value can be obtained in a wide range. Is set to scan the entire scanable range. When the focus lens 02 is scanned for the second and subsequent times after the digital camera is turned on, it is determined whether or not the conditions of the previous shooting and the current shooting are almost the same. 2, the scanning range of the focus lens 02 is set so as to be narrower than the predetermined range and include the in-focus position at the time of the previous photographing. If not, the predetermined range is set to the focus lens 02 in step 2. Is set to scan.

  Comparison between the previous shooting parameter and the current shooting parameter, for example, when all of the following conditions are satisfied (corresponding to “when satisfying predetermined requirements” in the claims), shooting under almost the same conditions Is determined.

The zoom lens position at the time of shooting is exactly the same or almost the same at the time of previous shooting and this time.
There is not much time difference between the last shooting time and the current shooting time.
The setting of the macro mode for capturing a close subject / non-macro mode for capturing a normal subject is not changed.
The number of AF frames as the area of the image signal detected for obtaining the AF evaluation value is not changed.
The brightness when shooting is almost the same.
AF evaluation values are almost the same.

  In addition, a condition that “focusing was possible at the time of previous shooting” may be added. The AF evaluation value is calculated as follows using a known method, for example. While the BPF is applied to the photographed signal and the middle and high frequency components are extracted, the maximum amplitude value in the AF frame may be used as the evaluation value, or in a predetermined direction in which the BPF extracts in the AF frame. Accordingly, the maximum value may be extracted and the maximum value integrated in the direction perpendicular to the BPF direction may be used as the AF evaluation value. However, the method for calculating the AF evaluation value is not a point of the present invention, and therefore will be described. Is omitted.

As a comparison method, for example, the previous shooting information and the current shooting information may be stored in the storage unit 16 as shown in FIG.
[Previous shooting zoom position] = [Current shooting zoom position]
And [current shooting time]-[previous shooting time] <(10 seconds)
And [Previous Macro Setting] = [Current Macro Setting]
And [previous AF frame setting] = [current AF frame setting]
And | [Brightness this time]-[Brightness last time] | <1 (Ev)
And [[current AF evaluation value] − [previous AF evaluation value] | <300
If the condition is satisfied, it is considered that the image is taken under similar imaging conditions.

  In addition, the difference in other white balance results may be used as “substantially the same condition”, and in the case of a camera that can determine the vertical position and the horizontal position, it may be used for the determination as to whether or not the shooting position has been changed. In the case of a camera capable of moving the AF frame, whether or not the frame position has been moved may be used for the determination. In addition, one that can specify whether or not the shooting conditions are substantially the same may be used.

  The focus lens 02 is driven in step 3 within the scanning range determined in step 2 above, and an AF evaluation signal is obtained.

  Next, in step 4, the in-focus position is determined. The in-focus position is determined by performing an interpolation operation based on the AF evaluation value obtained by scanning to obtain a value between the AF evaluation values obtained in step 3, and the point where the AF evaluation value is maximized is determined as the in-focus position. And

  In step 5, the current photographing condition and the in-focus position obtained in step 4 are stored.

In step 6, an image signal is obtained from the image sensor 03 for recording on the recording medium 08, and the focus lens is driven to the in-focus position.
Thus, the AF operation is completed.

  By performing the processing as described above, when the scene is almost the same, the entire scanning range of the focus lens 02 is not scanned, and the focus lens 02 is scanned over a narrow range in the vicinity of the subject to perform AF evaluation. Since the signal is obtained, the focusing operation can be completed quickly without reducing accuracy.

  In the embodiment, the above-described conditions are all satisfied, but one or more conditions may be satisfied.

  As described above, according to the present embodiment, the AF time can be shortened without reducing the AF accuracy even when the total number of AF evaluation signals to be acquired is large.

(Example 2)
In the “digital camera” of the present embodiment, the scanning range of the focus lens 02 in the first embodiment is divided in advance, and the divided range is sequentially scanned (hereinafter referred to as divided scanning) so as to obtain an AF evaluation value. It is an example. Since other parts are common, description is omitted.

  The division scanning will be described. In this embodiment, the scanning range of the focus lens is divided as shown in FIG. 4, for example. In FIG. 4, the horizontal axis indicates the position where the focus lens is driven, and the object distance corresponding to the position where the focus lens is in focus is shown for convenience.

A method of scanning the area divided in this way will be described according to the flow of FIG.
In step 11, a zone n indicating a divided range to be scanned first is determined. In this embodiment, n = 1 is set, and scanning is performed in order from a range focusing on a far subject (zone 1) to a zone focusing on a near subject.

In step 12, the nth region of the zone that is in focus is scanned near the zone scanned last time in the divided range.
In step 13, in-focus determination is performed in each zone, and if in-focus is possible, the process ends. If focusing is impossible, the area is updated in step 14 and the process returns to step 12.

  That is, in this embodiment, in Step 1 of FIG. 2 in Embodiment 1, the divided scanning is used when it is determined that the conditions of the previous shooting and the current shooting are not substantially the same. Each zone is a range wider than the range set when it is determined that the conditions of shooting at this time and shooting conditions at this time are almost the same.

  As described above, in the first embodiment, it is determined whether the previous shooting condition and the current shooting condition are substantially the same, and if it cannot be determined that they are substantially the same, the entire range of the scanning area is scanned in step 2. However, in this embodiment, the predetermined distance measurement area is divided into three, the divided areas are sequentially scanned, and scanning is terminated in a focusable zone. Time can be shortened.

  In the case of divided scanning, it is possible to focus quickly when the subject is in the first scanned range, but it takes time to focus when the subject is in the later scanned range. . Accordingly, the distance may be measured in the vicinity of the previous in-focus position only when the in-focus position at the time of the previous shooting is in a zone scanned later. Further, the zone itself including the previous in-focus position may be scanned.

  In the second embodiment, the entire scanning range is set to be scanned at the time of the first scanning, but division scanning may be performed instead.

  It should be noted that a software program for realizing the functions of the above-described embodiment for an apparatus connected to the various devices or a computer in the system so as to operate various devices to realize the functions of the above-described embodiments. What was implemented by supplying the code and operating the various devices in accordance with a program stored in a computer (CPU or MPU) of the system or apparatus is also included in the scope of the present invention.

  In this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code constitutes the present invention. Further, means for supplying the program code to the computer, for example, a storage medium storing the program code constitutes the present invention. As a storage medium for storing the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) or other application software in which the program code is running on the computer, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.

  Further, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the CPU provided in the function expansion board or function expansion unit based on the instruction of the program code Needless to say, the present invention includes a case where the functions of the above-described embodiment are realized by performing part or all of the actual processing.

Block diagram showing the configuration of the first embodiment Flow chart showing processing during AF operation The figure which shows the memory example of the memory | storage part 16 FIG. 10 is a diagram illustrating an example of dividing the scanning range of the focus lens in the second embodiment. Flowchart showing processing during AF operation in Embodiment 2 The figure which shows the example of the relationship between the to-be-photographed object distance corresponding to a focus position, and AF evaluation value

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Control part 12 Imaging condition analysis part 13 Range setting part 14 AF evaluation value calculating circuit 15 Focus position determination part 16 Imaging condition memory | storage part 17 Focus lens drive circuit

Claims (6)

First detection means for detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to the first drive range;
Second detection means for detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to a second drive range;
The first detection unit divides the first drive range into a plurality of parts, and detects the AF evaluation value when it is determined that the focus is in one of the divided drive ranges. And when it is determined that one of the divided drive ranges is out of focus, the AF evaluation value is detected in the other divided drive range,
The second detection means detects the AF evaluation value in the second drive range narrower than the first drive range including the focus position of the focus lens detected at the time of previous imaging,
Further, when the current shooting parameter is changed from the previous shooting parameter, the first detection means detects the AF evaluation value, and when there is no change, the second detection means detects the AF evaluation value. Detecting an autofocus device. The autofocus device according to claim 1,
The shooting parameters include at least one of a zoom lens position, shooting time, shooting mode, AF frame setting, subject brightness, AF evaluation value, white balance control value, and vertical / horizontal position of the autofocus device. An autofocus device characterized by that.   An image pickup apparatus comprising the optical system having the autofocus device according to claim 1 and a focus lens. A first detection step of detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to the first drive range;
A second detection step of detecting an AF evaluation value indicating a focused state by driving the focus lens with respect to a second drive range;
In the first detection step, the first drive range is divided into a plurality of parts, and the AF evaluation value is detected when it is determined that the focus is in one of the divided drive ranges. When the operation is terminated and it is determined that one of the divided drive ranges is out of focus, the AF evaluation value is detected for the other divided drive range,
In the second detection step, the AF evaluation value is detected with respect to the second drive range narrower than the first drive range including the focus position of the focus lens detected at the previous imaging. ,
Furthermore, by executing the first detecting step when the current imaging parameters was a change as seen from the previous imaging parameters, if the change was not a feature to perform the second detection step Autofocus method to use.   A program causing a computer to execute the autofocus method according to claim 4.   A storage medium in which the program according to claim 5 is stored in a computer-readable manner.

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