JP2015055635A - Imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable detection of a true in-focus point as to a subject having a repeating pattern and having difficulty being focused on in imaging devices performing phase difference detection type focus adjustments.SOLUTION: An imaging device 100 comprises an imaging control circuit 112 that reads a focus detection image signal from an image pickup element 106, and calculates an amount of defocus. A lens drive circuit 201 drives a focus lens by a lens drive circuit in accordance with the amount of defocus. When it is detected that a subject has a periodic pattern, the imaging control circuit 112 calculates an amount of defocus to a plurality of in-focus point candidates, and calculates an evaluation value for detection of a true in-focus point from the plurality of candidates. The lens control circuit 201 controls the drive of the focus lens in accordance with each amount of defocus of the plurality of candidates, and the imaging control circuit 112 acquires the evaluation value of each candidate and selects a candidate having the highest evaluation value as the true in-focus point.

Description

  The present invention relates to an automatic focus adjustment technique using an imaging surface phase difference detection method.

  As a focus detection method for an image pickup apparatus, a method using a focus detection element (hereinafter referred to as a first method) and a method using an image sensor (hereinafter referred to as a second method) are known. In the first method, two types of waveforms for focus detection are acquired, and focus detection is performed by correlation calculation between waveforms. In the second method, so-called contrast AF (autofocus) is employed. Focus detection is performed based on the evaluation value using the contrast component of the image. The first method has a higher AF processing speed than the second method, but when using a phase difference focus detection element different from the image pickup element, there are disadvantages in terms of upsizing and cost of the image pickup apparatus. Further, a camera having a structure such as a mirror-up or a mirrorless camera cannot perform AF using a focus detection element. Therefore, in the imaging plane phase difference AF, a phase difference type focus detection is performed at the same time as imaging as a configuration in which light of a different pupil plane of the imaging lens is received by the pixels of the imaging element.

  Patent Document 1 describes focus detection for a subject such as a repetitive pattern using phase difference AF. It is disclosed that the priority of focus detection is lowered when a repetitive pattern of a subject is detected. Patent Document 2 discloses a means for limiting the shift amount when detecting that the pattern of the subject is periodic by phase difference AF and obtaining the correlation amount.

JP 2007-52205 A Japanese Unexamined Patent Publication No. 6-94987

In the phase difference AF control disclosed in Patent Document 1 and Patent Document 2, when it is detected that the subject has a repetitive pattern, the focus detection priority is lowered or the shift amount is limited. This is because in conventional phase difference AF, it is theoretically difficult to find a true in-focus position in a repetitive pattern, and there may be a case where it is finally out of focus. For example, in the imaging plane phase difference AF, when the focus detection calculation waveform obtained from the imaging sensor causes image collapse when the focus lens is not near the focal point, the correlation amount is calculated from the waveform. The reliability of the evaluation value for determining the focus may be reduced.
An object of the present invention is to detect a true in-focus point for an object that has a repetitive pattern and is difficult to detect a focus in an imaging apparatus that performs focus adjustment control using a phase difference detection method.

In order to solve the above problems, an apparatus according to a first aspect of the present invention is an imaging apparatus that performs focus adjustment of an imaging optical system by phase difference detection using a focus detection signal from an imaging element, When detecting the focus detection signal from the image sensor and calculating the defocus amount to the in-focus point of the focus adjustment lens constituting the image pickup optical system, and detecting a periodic pattern of the subject image A control unit that acquires defocus amounts of a plurality of in-focus candidates from the focus detection unit, calculates an evaluation value of the plurality of candidates, and selects one in-focus point from the plurality of candidates; and the control unit Lens driving means for driving the focus adjusting lens according to the defocus amount up to the in-focus point selected by (1). The control unit moves the focus adjustment lens to a position corresponding to the defocus amount of the plurality of candidates by a lens driving unit, calculates an evaluation value of each candidate, and most of the plurality of candidates Select a focal point with a high evaluation value.
An apparatus according to a second aspect of the present invention is an image pickup apparatus that performs focus adjustment of an image pickup optical system by phase difference detection using a focus detection signal from an image pickup element, and the focus detection signal from the image pickup element. And a focus detection means for calculating a defocus amount until the focal point of the focus adjustment lens constituting the imaging optical system, and a periodic pattern of the subject image are detected, a plurality of focal point candidates are detected. A defocus amount is acquired from the focus detection unit, an evaluation value of the plurality of candidates is calculated, a control unit that selects one in-focus point from the plurality of candidates, and the in-focus point selected by the control unit Lens driving means for driving the focus adjusting lens according to the defocus amount. The control means calculates the evaluation values of the first to third candidates by moving the focus adjustment lens to positions corresponding to the defocus amounts of the first to third candidates by the lens driving means. When the evaluation value of the second candidate is higher than the evaluation values of the adjacent first and third candidates, the second candidate is selected as the focal point.

  According to the present invention, it is possible to detect a true in-focus point with respect to a subject that has a repetitive pattern and is difficult to detect a focus.

It is a figure which shows the structural example of the camera which concerns on embodiment of this invention. It is a figure which shows the pixel arrangement | sequence of the image pick-up element in embodiment of this invention. It is a block diagram which shows the structural example of the circuit part of the camera which concerns on embodiment of this invention. It is a figure explaining the focus detection in the conventional phase difference AF sensor. It is a figure explaining the focus detection in imaging surface phase difference AF. It is a figure explaining the focus detection algorithm at the time of the repeated pattern detection which concerns on 1st Embodiment of this invention. It is a flowchart explaining the example of imaging | photography process which concerns on embodiment of this invention. It is a flowchart explaining the example of a focus detection process which concerns on embodiment of this invention. It is a flowchart explaining the focus detection at the time of the repeated pattern detection which concerns on 1st Embodiment of this invention. It is a figure explaining the focus detection algorithm at the time of the repeating pattern detection which concerns on 2nd Embodiment of this invention. It is a flowchart explaining the focus detection at the time of the repeating pattern detection which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the evaluation value used by embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
[First Embodiment]
FIG. 1 is a configuration diagram showing an outline of an imaging system according to an embodiment of the present invention. First, the configuration of the camera body will be described.
The imaging apparatus 100 includes an erect image optical system 101 and an eyepiece lens 102 that constitute a finder optical system. A finder screen 103 and a first mirror 104 are provided. The first mirror 104 is a translucent optical element that deflects a part of the imaging light beam to the finder optical system. The imaging light flux that has passed through the first mirror 104 is deflected to the focus detection device 109 by being reflected by the second mirror 105.
The image sensor 106 is an image sensor that images a subject and outputs an electrical signal by photoelectric conversion. The image sensor 106 receives a light beam from a subject that has passed through the lens device 200 and outputs an electrical signal. The image sensor 106 has a focus detection function. The shutter device 107 blocks light to the image sensor 106. The built-in strobe 108 is a light emitting device housed in the imaging device 100 and includes a Fresnel lens 114.

  The focus detection device 109 includes a plurality of sensors including a plurality of light receiving units, and performs focus detection using a phase difference detection method. Specifically, the light beam that has passed through the exit pupil of the focus adjustment lens (focus lens) included in the lens apparatus 200 is divided into two, and a set of line sensors receives the two divided light beams. In the present embodiment, image signals obtained from the light beams divided into two are referred to as an image signal A and an image signal B, respectively. The defocus amount of the focus lens is calculated by detecting the shift amount of the signal output according to the amount of light received by each line sensor, that is, the relative positional shift amount in the beam splitting direction. Therefore, once the accumulation operation is performed by the line sensor of the focus detection device 109, the amount and direction in which the focus lens should be moved is obtained, and the lens is driven.

  As a second method related to focus detection, there is a mode (imaging surface phase difference detection method) in which focus detection pixels are arranged on an image sensor to acquire focus detection information. In this embodiment, a plurality of photoelectric conversion units are arranged for each microlens constituting the image sensor. A defocus amount is calculated by detecting an image shift amount from a plurality of light beams that have passed through different pupil regions of the imaging optical system.

  FIG. 2 shows a pixel array of the image sensor in the present embodiment. FIG. 2 shows a state in which a range of 6 rows in the vertical direction (Y direction) and 8 columns in the horizontal direction (X direction) of the two-dimensional CMOS (complementary metal oxide semiconductor) sensor is observed from the imaging optical system side. A Bayer array is applied to the color filters, and green and red color filters are alternately provided in order from the left in pixels in odd rows. Further, blue and green color filters are alternately provided in order from the left on the pixels in even rows. In the pixel 211, a plurality of rectangular frames arranged inside the on-chip microlens indicated by the circular frame 211i indicate the photoelectric conversion units 211a and 211b, respectively. Based on the photoelectrically converted pixel data, an image shift amount is calculated by correlation calculation of two image signals by pupil division, and converted to a defocus amount. Although FIG. 2 shows a form in which focus detection pixels are arranged over all the pixel portions, there is also a form in which focus detection pixels are arranged in a distributed manner.

The photometric device 110 in FIG. 1 performs exposure measurement. The lens 111 is an optical element that forms an image of a light beam from the subject on the photometric device 110. The imaging control circuit 112 that controls the imaging apparatus 100 includes a microprocessor and performs focus adjustment control, exposure control, and the like.
The camera body is provided with an accessory shoe 113 for mounting an external strobe or the like. The viewfinder display unit 115 displays image information superimposed on the optical viewfinder. The external display unit 116 displays various types of information on the display screen of the outer casing unit of the imaging apparatus 100.

  Next, the configuration of the lens device 200 will be described. The lens device 200 is an interchangeable lens (so-called interchangeable lens) that constitutes an imaging optical system. The lens control circuit 201 includes a microprocessor and the like, and communicates with the imaging control circuit 112 of the imaging apparatus 100 through a communication unit. The imaging optical system 202 includes a plurality of lenses for imaging, but is simplified in FIG. The imaging optical system 202 includes a movable optical element such as a focus lens, and is provided with a lens driving mechanism and a driving circuit (not shown). The diaphragm device 203 adjusts the amount of light in accordance with a control command from the lens control circuit 201.

FIG. 3 is a block diagram illustrating a circuit configuration example of the imaging device 100 and the lens device 200 that configure the imaging system. First, the imaging apparatus 100 will be described.
The microprocessor 112 </ b> M constituting the imaging control circuit 112 is a central part that controls the imaging apparatus 100. The motor drive circuit 1 is a circuit for driving the movable member of the imaging apparatus 100. The photometric unit 2 measures the luminance of the subject (included in the photometric device 110 in FIG. 1). The focus detection unit 3 detects the focus state of the lens device 200. In the case of phase difference AF using the focus detection device 109 of FIG. 1, the focus detection unit 3 acquires a focus detection signal from the device and performs focus detection. In the case of the imaging plane phase difference AF, the focus detection unit 3 performs focus detection by acquiring a focus detection signal from the focus detection pixels of the image sensor 106. The shutter control circuit 4 controls the exposure amount of the imaging device 100 by driving control of the shutter device 107 in FIG. The diaphragm control circuit 5 controls the light flux taken into the imaging apparatus 100 by driving control of the diaphragm device 202 of FIG.

  The display device 6 displays the state of the imaging device 100, images, and the like, and includes the finder display unit 115 and the external display unit 116 of FIG. The strobe control circuit 7 controls the built-in strobe 108 in FIG. The storage device 8 includes a memory that stores data such as a setting state of the imaging device 100. The imaging circuit 9 performs an imaging process by the imaging element 106. The lens communication circuit 10 performs communication processing with the lens device 200 attached to the imaging device 100. The communication circuit 11 communicates with an external strobe (not shown). The first switch 12 (SW1) is an operation switch for instructing the start of the imaging preparation operation. The second switch 13 (SW2) is an operation switch for instructing the start of the imaging operation. SW1 is turned on by the first stroke (half press) operation of the release button, and SW2 is turned on by the second stroke (full press) operation. The built-in strobe 108 not only illuminates the subject at the time of imaging without an external strobe, but also has a function as auxiliary light that irradiates the subject at the time of focus detection.

  Next, the lens device 200 will be described. The microprocessor 201M constituting the lens control circuit 201 controls the lens apparatus 200. The lens driving circuit 21 drives the movable optical element in the lens device 200. The lens position detection circuit 22 detects the position of the lens device 200. The lens focal length detection circuit 23 detects the focal length of the lens device 200. The storage circuit 24 includes a memory that stores setting values, optical information, and the like of the lens device 200. The diaphragm drive circuit 25 is included in the diaphragm device 203 of FIG. 1 and drives the diaphragm. The lens communication circuit 26 communicates with the lens communication circuit 10 of the imaging device 100.

With reference to FIG. 4, the characteristics of the repetitive pattern in the phase difference AF sensor will be described.
FIG. 4 is a graph illustrating the amount of correlation obtained from a subject such as a repetitive pattern in waveforms at three focus lens positions. The graph 3-1 illustrates the correlation waveform near the in-focus point in focus when the image blur is large, the graph 3-2 illustrates the image blur small, and the graph 3-3 illustrates the correlation waveform near the in-focus point in focus. Let A be the true focal point. The horizontal axis represents the shift amount Shift, and the vertical axis represents the correlation amount COR. The shift amount Shift indicates that the larger the value, the greater the shift in the waveform of the two images, and the greater the blur of the subject image. In addition, the smaller the value of the correlation amount COR, the better the degree of coincidence of the waveforms of the two images used for the focus detection calculation output from the AF sensor. At the time of focus detection, the shift amount that becomes the focal point is calculated from the portion where the correlation amount is minimized. If there are a plurality of positions where the minimum value exists, the correlation change amount indicating the steepness of the change in the correlation amount at that time, the contrast value indicating the magnitude of the contrast of the subject, and the degree of coincidence between the waveforms of the two images are calculated. An evaluation value such as the degree of coincidence of two images is used. The true focal point is detected from these values, and the shift amount can be calculated. The in-focus point corresponds to the focus lens position in the in-focus state. Originally, when a plurality of in-focus candidates illustrated in FIG. 4 are found, the true in-focus is detected using the above evaluation value. However, in the case of a subject having a repetitive pattern, the correlation amount is minimized. Will appear periodically. Further, there is no difference in the amount of correlation change in the portion that is the minimum value. In this case, since the waveform does not change regardless of the focus state where the degree of blur is different, it is difficult to detect the true focal point even if the focus lens is driven.

  Next, the characteristics of the repetitive pattern in the imaging plane phase difference AF will be described with reference to FIG. FIG. 5 is a graph illustrating the amount of correlation obtained from a subject such as a repetitive pattern in waveforms at three lens positions. A graph 4-1 illustrates the correlation waveform near the in-focus point where the focused image is large, a graph 4-2 illustrates the case where the image blur is small, and a graph 4-3 illustrates the correlation waveform near the in-focus point. Let B be the true focal point. The horizontal axis represents the shift amount Shift, and the vertical axis represents the correlation amount COR. The meaning of each amount is as described in FIG.

  In focus detection using the imaging surface phase difference AF, a portion where the correlation amount is minimal appears periodically in the waveform indicating the correlation amount of a subject having a repetitive pattern. The correlation waveform changes depending on the focus states shown in graphs 4-1 to 4-3, and the slope of the extreme value portion becomes steeper as it approaches the focal point. Accordingly, by actually driving the lens and changing the focus state, it can be determined that the time when the amount of correlation change is the highest is in the vicinity of the in-focus point, so that the true in-focus point can be detected.

With reference to FIG. 6, a first algorithm relating to in-focus selection at the time of repetitive pattern detection in the imaging plane phase difference AF according to the present embodiment will be described. The horizontal axis of each graph shown in FIG. 6 represents the shift amount Shift, and the vertical axis represents the correlation amount COR.
Graph 5-1 shows the correlation amount when the focus detection unit detects the repeated pattern. In this case, “a”, “b”, “c”, “d” and “e” indicate the positions of the minimum values, and five candidate in-focus points are found.
First, the shift amount of the focal point as a candidate S _a to S _e is calculated, converted process to the defocus amount is performed. This is because the lens can be driven based on the defocus amount. Each value after conversion to the defocus _amount, and D a to D _e.
Next, the control for driving the focus lens to the in-focus candidate a having the closest shift amount from the current lens position on the closest end side is executed. The waveform after this driving is shown in graph 5-2. At this time, an evaluation value FNC (a) for selecting the true in-focus point is calculated and stored in the memory. The method for obtaining the evaluation value will be described later.

Subsequently, the focus lens is driven to a position corresponding to the in-focus candidate b. The waveform after driving is shown in graph 5-3. At this time, an evaluation value FNC (b) for selecting the true in-focus point is calculated and stored in the memory. Similarly, in the case of the in-focus candidate c, a waveform after driving the lens is shown in a graph 5-4. Evaluation value FNC (c) is calculated and stored in the memory. Further, in the case of the in-focus candidate d, the waveform after driving is shown in a graph 5-5. Evaluation value FNC (d) is calculated and stored in the memory. Finally, the focus lens is driven to the in-focus candidate e, and the waveform after driving is shown in a graph 5-6. Evaluation value FNC (e) is calculated and stored in the memory.
When the result obtained above, that is, the position having the highest evaluation value is searched from among FNC (a) to FNC (e) and there is a difference equal to or greater than the threshold value, the determination process with the shift amount at that time as the focal point is performed. Executed. When such a focal point is not found on the close end side, the lens driving circuit 21 reverses the moving direction of the focus lens. A process of driving the focus lens to a candidate focal point at the infinity end side, detecting the focal point by the same method as described above, and calculating the shift amount is executed.

  Next, an evaluation value for detecting a true in-focus point will be described with reference to FIG. FIG. 12A is a graph illustrating the contrast value when driving the lens from the state where the degree of blurring is large to the vicinity of the focal point in the imaging plane phase difference AF. The horizontal axis represents the degree of blur of the subject, and the vertical axis represents the contrast value SQRCNT. Each position indicated by 5-2 to 5-6 in the drawing corresponds to each of the graphs 5-2 to 5-6 in FIG. The focus detection unit 3 calculates the contrast value at each position from the waveforms of the two images for focus detection. In FIG. 12 (A), it can be seen that the contrast value SQRCNT increases as approaching the focal point. Candidate c corresponding to graph 5-4 in FIG. 6 is detected as the true focal point.

  FIG. 12B is a graph illustrating the amount of change in correlation when the focus lens is driven from a state where the degree of blur is large to the vicinity of the focal point in the imaging plane phase difference AF. The horizontal axis represents the degree of blurring of the subject, and the vertical axis represents the correlation change amount MAXDER. Each position indicated by 5-2 to 5-6 in the drawing corresponds to each of the graphs 5-2 to 5-6 in FIG. The correlation change amount MAXDER can be calculated by the following equation (1).

上式中のｋは位置を特定するための整数の変数である。
図１２（Ｂ）に示すように、撮像面位相差ＡＦでは暈けの度合が大きい状態から合焦点での状態に近づくにつれて、相関変化量の値が大きくなることが分かる。図６のグラフ５−４に対応する候補ｃが、真の合焦点として検出される。
以上のように、撮像面位相差ＡＦでは、コントラスト値や相関変化量を評価値として使用し、評価値が最も高くなる合焦点を真の合焦点として検出することができる。

K in the above equation is an integer variable for specifying the position.
As shown in FIG. 12B, it can be seen that in the imaging plane phase difference AF, the value of the correlation change amount increases as the degree of blurring approaches from the in-focus state. Candidate c corresponding to graph 5-4 in FIG. 6 is detected as the true focal point.
As described above, in the imaging surface phase difference AF, the contrast value or the correlation change amount is used as the evaluation value, and the focal point with the highest evaluation value can be detected as the true focal point.

Next, imaging processing according to the present embodiment will be described with reference to the flowchart of FIG. This processing is realized by the microprocessor 112M (hereinafter referred to as MPU) reading out and executing a control program from the memory and controlling each unit in FIG.
First, in S601, the MPU determines whether or not the first switch 12 (SW1) of the imaging apparatus 100 is in an on state. If SW1 is in the on state, the process proceeds to S602. If SW1 is in the off state, the determination process in S601 is repeated in the wait state. In step S602, the focus detection unit 3 performs focus detection processing. Details of the focus detection process will be described later.
In S603, the MPU acquires focus detection information from the focus detection unit 3, and determines whether or not the focus detection result calculated in S602 is within the in-focus range. If the focus detection result is within the focus range, the process proceeds to S605. If the focus detection result is outside the focus range, the process proceeds to S604. In step S <b> 604, the MPU transmits a focus lens driving command from the lens communication circuit 10 through the lens communication circuit 26 of the lens device 200. Accordingly, the lens control circuit 201 performs drive control of the focus lens based on the focus detection result calculated in S602 according to the drive command.

  In S605, the MPU determines whether or not the second switch 13 (SW2) is on. If SW2 is in the on state, the process proceeds to S606, and if SW2 is in the off state, the process proceeds to S607. In step S606, the MPU performs a shooting preparation process. In step S608, the MPU performs a recording process of image data captured by the imaging circuit 9, and then ends the shooting process. In S607, the MPU determines whether or not the first switch 12 (SW1) is on. If SW1 is on, the process returns to S605, and if SW1 is off, the process ends.

FIG. 8 is a flowchart illustrating an example of focus detection processing according to the present embodiment. This process is a predefined process corresponding to S602 in FIG. 7, and is performed by the focus detection unit 3.
In S701, the focus detection calculation calculates the correlation amount from the two types of waveforms read from the sensor, and calculates the shift amount from the correlation waveform. In step S702, a repeated pattern detection process is performed. Regarding the detection result of the focus state calculated in S701, the reliability is determined in S702 because the reliability of the subject having a repetitive pattern is low. If the reliability is equal to or lower than the threshold value, that is, if the reliability of the focus detection result is not sufficient, the process proceeds to S704, and if the reliability is high, the process proceeds to S703.

In S704, when it is detected that the subject has a repetitive pattern, processing for calculating a true in-focus point is executed. The focus detection calculation that could not be calculated in S701 is performed again. This repeated pattern countermeasure process will be described later with reference to FIG.
In S703, conversion processing from the focus detection result calculated in S701 or S704 to the defocus amount is performed. Drive control of the focus lens is performed based on the conversion result from the image shift amount to the defocus amount. In the next S705, the reliability is determined for the defocus amount calculated in S703. The reliability is calculated by a known method, and a determination process is performed by comparison with a threshold value. Depending on the determination result, the lens driving control method in S604 of FIG. 7 is switched. The focus detection process ends, and a defocus amount necessary for driving the focus lens is obtained.

FIG. 9 is a flowchart illustrating an example of the repeated pattern countermeasure process. This process is a predefined process corresponding to S704 in FIG. 8, and is performed by the focus detection unit 3.
First, in S801, candidates for in-focus are represented by _{0 to n} , and shift amounts S0 to Sn are calculated. “0 to n” is a numerical value for specifying n + 1 candidates corresponding to a to e described in FIG. Subsequently in S802, the shift amount _S 0 to S _n calculated in S801, the process of converting the defocus amount is _performed, D 0 to D _n is calculated. The focus lens can be driven based on the defocus amount.

In S803, the value of the count variable i is first set to zero, and the focus lens is driven by a distance corresponding to the defocus amount D _i calculated in S802. In step S804, processing for calculating an evaluation value used when selecting a focal point is executed. 9 "evaluation value _{(D i)"} indicates that the evaluation value is a function of _{D i (FNC (D i)} ). The value of the count variable i is incremented by 1 (i = i + 1), and the processes of S803 and S804 are repeatedly executed as D ₁ , D ₂ ,..., And the same process is performed until D _n is reached. Is called.
In S805, it is determined whether or not the focus lens has been moved a distance corresponding to the defocus amount for all in-focus candidates 0 to n. _{If the} focus lens is driven to a distance corresponding to Dn, the process proceeds to S806. If not, the process returns to S803. Lens driving and evaluation value calculation processing are performed on the in-focus candidates whose evaluation values have not yet been calculated.
In S806, a process of selecting the candidate having the highest evaluation value among the evaluation values calculated in S804 as a true in-focus point is performed, and information on the defocus amount is output as a focus detection result.

  In the first embodiment, when a subject having a repetitive pattern is detected, the focus lens is driven according to each defocus amount for the candidate in-focus, and the true in-focus is obtained using the evaluation value obtained at that time. Can be detected. Therefore, it is possible to detect the focus of the imaging optical system for a subject having a repetitive pattern.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and detailed description thereof will be omitted. Differences will be mainly described.
With reference to FIG. 10, the second algorithm of the repeated pattern countermeasure process in the second embodiment will be described.
A graph 9-1 shows the correlation amount when a subject having a repetitive pattern is detected. The horizontal axis represents the shift amount Shift, and the vertical axis represents the correlation amount COR. Five in-focus points that are candidates for a, b, c, d, and e are detected.
First, to calculate the shift amount S _a to S _e of each focusing point as a candidate, the process of converting the defocus amount is performed. The focus lens can be driven based on the defocus amount. Each value after conversion to the defocus _amount, and D a to D _e.

ｋは合焦点を特定するための位置に相当する整数の変数である。ＦＮＣ（ｋ−２）は第１の候補の評価値、ＦＮＣ（ｋ−１）は第２の候補の評価値、ＦＮＣ（ｋ）は第３の候補の評価値である。つまり、第１ないし第３の候補の評価値が必要であるが、この時点では、ＦＮＣ（ｋ）と比較する評価値（ｋ−２及びｋ−１における評価値）が不足しているため、次へ進んでさらに評価値の取得処理を続行する。 Next, the candidate a most shift amount is close to the current position, the lens drive circuit 21 drives the focus lens by a distance corresponding to D _a. The waveform after driving is shown in graph 9-2. Here, the focus detection unit 3 calculates an evaluation value FNC (a) for selecting the true in-focus point, and stores it in the memory. In the second algorithm, as shown in the following conditional expression (2), the true focal point is detected from the evaluation values of three adjacent candidates.

k is an integer variable corresponding to the position for specifying the focal point. FNC (k-2) is an evaluation value of the first candidate, FNC (k-1) is an evaluation value of the second candidate, and FNC (k) is an evaluation value of the third candidate. That is, the evaluation values of the first to third candidates are necessary, but at this point, the evaluation values to be compared with FNC (k) (evaluation values at k-2 and k-1) are insufficient. Proceed to the next step to continue the evaluation value acquisition process.

Next, the candidate shift amount is close b, the lens drive circuit 21 drives the focus lens by a distance corresponding to D _b. The waveform after driving is shown in graph 9-3. Here, the evaluation value FNC (b) is calculated and stored in the memory. Since evaluation values to be compared are still insufficient at this point, the evaluation value acquisition process is continued.
Next, the candidate shift amount near c, the lens drive circuit 21 drives the focus lens by a distance corresponding to D _c. The waveform after driving is shown in graph 9-4. Here, the evaluation value FNC (c) is calculated and stored in the memory. At this time, since three evaluation values FNC (a), FNC (b), and FNC (c) are prepared, the true focal point is determined using the conditional expression (2). However, the processing is continued on the assumption that the conditional expression (2) is not satisfied.
Shift amount for closer candidate d Then, the lens drive circuit 21 drives the focus lens by a distance corresponding to D _d. The waveform after driving is shown in graph 9-5. Here, the evaluation value FNC (d) is calculated and stored in the memory. Since three evaluation values are prepared at this time, the true focal point is determined by the conditional expression (2). From conditional expression (2),
FNC (c)> FNC (b) and FNC (c)> FNC (d)
Shall be satisfied. Since the first candidate b, the second candidate c, and the third candidate d are three adjacent candidates, and the evaluation value of the candidate c is higher than the evaluation values of the candidates b and d, the candidate c is true. Is determined to be the in-focus point.

As described above, the focus detection unit 3 detects the true focal point using the correlation change amount and the contrast evaluation value when detecting the repeated pattern. The difference between the first embodiment and the second embodiment is that, in the second embodiment, the process is terminated when a true in-focus point where the evaluation value is an extreme value is found. For Graph 9-5 in the example of FIG. 10, the movement of the focus lens of the distance corresponding to D _e it is not required. Therefore, the true focal point can be detected without comparing all the focal points, and the processing time is shortened.

FIG. 11 is a flowchart for explaining a repetitive pattern countermeasure processing example in the present embodiment. The focus detection unit 3 performs this process.
First, in S1001, the in-focus candidates are identified as _{0 to m} in order from the closest focus lens position, and the process of calculating the shift amounts S _{0 to} S _m is executed. In the next S1002, the processing for converting the calculated shift amount _S 0 to S _m, each defocus amount in step S1001 is executed. The defocus amount after _conversion, and D 0 to D _m.
In S1003, the value of the count variable i is set to zero, and the focus lens is driven at a distance corresponding to the defocus amount D _i calculated in S1002. In S1004, an evaluation value used when selecting a focal point is calculated. 11 "evaluation value _{(D i)"} indicates that the evaluation value is a function of _{D i (FNC (D i)} ). S1005 is a process for determining whether or not the conditional expression (2) is satisfied. If the conditional expression (2) is satisfied in S1005, the process proceeds to S1006. If the conditional expression (2) is not satisfied, the process proceeds to S1003, and after the count variable i is incremented, the evaluation value calculation process is continued. In S1006, the candidate indicated by the i value when the conditional expression (2) is satisfied in S1005 is determined as the true in-focus point, and information on the defocus amount D _i corresponding to the shift amount S _i is obtained as the focus detection result. It is done.

In this embodiment, when a subject having a repetitive pattern is detected, the true focus point can be detected by driving the focus lens and comparing adjacent evaluation values obtained at that time, thereby reducing the time required for detection. Is done.
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

3 Focus Detection Unit 21 Lens Drive Circuit 106 Image Sensor 112M, 201M Microprocessor

Claims (7)

An imaging apparatus that performs focus adjustment of an imaging optical system by phase difference detection using a focus detection signal from an imaging element,
Focus detection means for acquiring the focus detection signal from the image sensor and calculating a defocus amount to a focal point of a focus adjustment lens constituting the image pickup optical system;
When a periodic pattern of the subject image is detected, the defocus amounts of a plurality of in-focus candidates are acquired from the focus detection unit, and the evaluation values of the plurality of candidates are calculated to obtain a single focus from the plurality of candidates. A control means for selecting a focus;
Lens driving means for driving the focus adjustment lens according to the defocus amount to the in-focus point selected by the control means;
The control unit moves the focus adjustment lens to a position corresponding to the defocus amount of the plurality of candidates by a lens driving unit, calculates an evaluation value of each candidate, and most of the plurality of candidates An imaging apparatus characterized by selecting a focal point having a high evaluation value. An imaging apparatus that performs focus adjustment of an imaging optical system by phase difference detection using a focus detection signal from an imaging element,
Focus detection means for acquiring the focus detection signal from the image sensor and calculating a defocus amount to a focal point of a focus adjustment lens constituting the image pickup optical system;
When a periodic pattern of the subject image is detected, the defocus amounts of a plurality of in-focus candidates are acquired from the focus detection unit, and the evaluation values of the plurality of candidates are calculated to obtain a single focus from the plurality of candidates. A control means for selecting a focus;
Lens driving means for driving the focus adjustment lens according to the defocus amount to the in-focus point selected by the control means;
The control means calculates the evaluation values of the first to third candidates by moving the focus adjustment lens to positions corresponding to the defocus amounts of the first to third candidates by the lens driving means. An imaging apparatus, wherein when the evaluation value of the second candidate is higher than the evaluation values of the adjacent first and third candidates, the second candidate is selected as a focal point.   3. The imaging apparatus according to claim 1, wherein the control unit detects that the subject image has a periodic pattern when the focus detection signal has a periodic extreme value. 4. .   The lens driving means drives the focus adjustment lens in the direction of the infinity end after driving the focus adjustment lens in the direction of the infinity end when the control means detects a periodic pattern of the subject image. The imaging apparatus according to claim 3.   5. The imaging according to claim 1, wherein the control unit calculates the evaluation value from a change in a correlation amount between two images used for focus detection calculation or a contrast of a subject. apparatus. A control method executed by an imaging apparatus that performs focus adjustment of an imaging optical system by phase difference detection using a focus detection signal from an imaging element,
A focus detection step of obtaining the focus detection signal from the image sensor and calculating a defocus amount to a focal point of a focus adjustment lens constituting the image pickup optical system;
Control for acquiring defocus amounts of a plurality of in-focus candidates when a periodic pattern of a subject image is detected, calculating an evaluation value of the plurality of candidates, and selecting one in-focus from the plurality of candidates Steps,
A lens driving step of driving the focus adjustment lens according to a defocus amount to the in-focus point selected in the control step;
In the control step, the focus adjustment lens is moved to a position corresponding to the defocus amount of the plurality of candidates to calculate an evaluation value of each candidate, and the highest evaluation value among the plurality of candidates is calculated. A method for controlling an imaging apparatus, characterized by selecting a focal point. A control method executed by an imaging apparatus that performs focus adjustment of an imaging optical system by phase difference detection using a focus detection signal from an imaging element,
A focus detection step of obtaining the focus detection signal from the image sensor and calculating a defocus amount to a focal point of a focus adjustment lens constituting the image pickup optical system;
Control for acquiring defocus amounts of a plurality of in-focus candidates when a periodic pattern of a subject image is detected, calculating an evaluation value of the plurality of candidates, and selecting one in-focus from the plurality of candidates Steps,
A lens driving step of driving the focus adjustment lens according to a defocus amount to the in-focus point selected in the control step;
In the control step, the focus adjustment lens is moved to positions corresponding to the defocus amounts of the first to third candidates, the evaluation values of the first to third candidates are calculated, and the second A method for controlling an imaging apparatus, wherein when a candidate evaluation value is higher than the evaluation values of adjacent first and third candidates, the second candidate is selected as a focal point.

Images