JP2020003693A - Imaging device and control method for imaging device - Google Patents

Abstract

To provide an imaging device with which it is possible to reduce non-focusing and blurred focusing even in the case where an image includes a low-contrast subject.SOLUTION: The imaging device comprises: acquisition means for acquiring a first signal and a second signal that correspond to beams passing through mutually different pupil areas of an imaging optical system; calculation means for performing a plurality of filtering processes mutually differing in band on the first and second signals and calculating a plurality of defocus amounts and a plurality of degrees of reliability on the basis of the first and second signals after filtering processes; and determination means for determining a defocus amount used in focus adjustment from among the plurality of defocus amounts on the basis of a difference in the plurality of defocus amounts and at least one of the plurality of degrees of reliability. At least one or more of the plurality of defocus amounts respectively are assigned the priority of selection by the determination means.SELECTED DRAWING: Figure 13

Description

  The present invention relates to an imaging device and a control method of the imaging device, and particularly to a focus adjustment method used in the imaging device.

  2. Description of the Related Art Some imaging devices such as digital cameras perform a phase difference detection type autofocus that performs focus detection and focus adjustment by detecting a phase difference between a pair of parallax image signals. In particular, a focus detection method of a phase difference detection method using an output signal from an imaging element that captures a subject image is referred to as an imaging surface phase difference detection method. In the imaging surface phase difference detection method, after performing band-pass filter processing on two (one pair) image signals of each pixel of the imaging device, an image shift amount is calculated by performing a correlation operation of two images in a predetermined area. The defocus amount is calculated based on the image shift amount. The characteristics of the defocus amount differ depending on the frequency band of the band-pass filter applied to the image signal. For example, when the frequency band is a low band (low-band filter), the defocus amount can be detected even in a large blur state, but the accuracy of the defocus amount near the in-focus position decreases. On the other hand, when the frequency band is a high band (high band filter), the accuracy of the defocus amount near the in-focus position is high, but the defocus amount cannot be detected in a large blur state.

  In Patent Literature 1, a correlation operation is performed using bandpass filters of a plurality of frequency bands, and reliability is calculated from the degree of matching and contrast of the shape of the image signal of each pair of the correlation operations. Then, a technique is disclosed in which the comparison and selection (filter band inheritance) are performed in order from a low-frequency band to a high-frequency band to select a defocus amount to be used for focus adjustment, thereby enabling accurate and high-speed focus detection.

  Further, in Patent Document 2, in an automatic selection mode in which a focus detection area (focus detection frame) is automatically selected from a plurality of focus detection areas, reliability at the time of correlation calculation in each focus detection frame is calculated, and Calculate and compare the weighted reliability including the focus detection frame. Thus, a technique has been disclosed that allows more accurate focus detection frame selection, that is, subject selection.

JP 2018-036628A JP 2017-223760 A

  However, when the filter band is taken over or the focus detection frame is selected by comparing only the reliability, when the focus detection of an image including a low-contrast subject is performed, the reliability of the calculation result by the band-pass filter in the low-frequency band is reduced. It is easier to be selected to be better. Accordingly, out-of-focus or blur focus may occur due to improper handover of the filter band or selection of the focus detection frame. That is, for a subject having a low contrast, the reliability of the calculation result of the low-band filter becomes equal to or higher than the reliability of the high-band filter, and the defocus amount used for focus adjustment may be switched every several frames. In the vicinity of the in-focus position, the accuracy of the defocus amount of the low-band filter is low, so that a problem occurs in which the lens is repeatedly inverted and exceeds a predetermined number of times of inversion and becomes out of focus.

  Furthermore, in the automatic selection mode, when a low-contrast subject is included in the focus detection area, an erroneous frame selection may be performed because the reliability of the calculation result of the low-band filter in the focus detection frame is increased. There is. For this reason, a focus detection frame of a high-contrast subject that the photographer originally wants to perform the focus adjustment cannot be selected, and there is a problem that the image is out of focus.

  The present invention has been made in view of the above circumstances, and has as its object to provide an imaging apparatus capable of reducing out-of-focus or out-of-focus even when a low-contrast subject is included.

  In order to solve the above-described problems, an imaging apparatus according to the present invention includes: an acquisition unit configured to acquire a first signal and a second signal corresponding to a light beam passing through different pupil regions of an imaging optical system; Calculating means for performing a plurality of filtering processes having different bands on the second signal, and calculating a plurality of defocus amounts and a plurality of reliability based on the first signal and the second signal after the respective filtering processes; Determining means for determining a defocus amount used for focus adjustment from among the plurality of defocus amounts, based on a difference between the plurality of defocus amounts and at least one of the plurality of degrees of reliability, The determining means may add a selection priority to at least one of the plurality of defocus amounts.

  According to the present invention, even when a low-contrast subject is included, out-of-focus and blur focus can be reduced.

It is a block diagram of an imaging device concerning a 1st embodiment. FIG. 3 is a diagram illustrating a pixel configuration example of a non-imaging plane phase difference method and an imaging plane phase difference method. 5 is a flowchart illustrating an operation of the imaging device according to the first embodiment. 5 is a flowchart illustrating an AF operation according to the first embodiment. 5 is a flowchart illustrating an AF operation according to the first embodiment. 5 is a flowchart illustrating a focus detection process according to the first embodiment. FIG. 3 is an explanatory diagram of a focus detection area according to the first embodiment. FIG. 3 is an explanatory diagram of an AF signal (a pair of image signals) according to the first embodiment. FIG. 4 is an explanatory diagram of a relationship between a shift amount of an AF signal and a correlation amount according to the first embodiment. FIG. 7 is an explanatory diagram of a relationship between a shift amount of an AF signal and a correlation change amount. 6 is a flowchart illustrating selection of a defocus amount according to the first embodiment. It is a flowchart which shows the handover determination from large Def to middle Def. It is a flowchart which shows the transfer determination from medium Def to small Def. It is a flow chart which shows AF processing at the time of automatic selection concerning a 2nd embodiment. FIG. 4 is a diagram illustrating an example of a focus detection area in a shooting range. It is a flowchart which shows the frame selection process concerning 2nd Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

(1st Embodiment)
First, the configuration of the imaging device according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram of an imaging device 10 (interchangeable lens camera system). The imaging device 10 includes a camera body 200 (imaging device body) and a lens device 100 (interchangeable lens) that is detachable from the camera body 200. The lens device 100 is detachably (exchangeably) attached to the camera body 200 via a mount (not shown) having an electric contact unit. Note that the present embodiment is also applicable to an imaging device in which a lens device and a camera body are integrally configured.

  The lens device 100 includes a photographing lens 101, an aperture and a shutter 102, a focus lens 103, a motor 104, and a lens controller 105. The taking lens 101 includes a zoom mechanism. The aperture and shutter 102 control the amount of light. The focus lens 103 is a lens for focusing on an image sensor 201 described later. The motor 104 drives the focus lens 103. The lens controller 105 controls the entire lens device 100 and connects to the camera body 200 via the communication bus 106.

  The camera body 200 includes an image sensor 201, an A / D converter 202, an image processor 203, an AF signal processor 204, and a format converter 205. The imaging element 201 functions as a light receiving unit (photoelectric conversion unit) that converts reflected light from a subject into an electric signal. The A / D converter 202 includes a CDS circuit for removing output noise of the image sensor 201 and a non-linear amplifier circuit for performing A / D conversion. In the present embodiment, the AF signal processing unit 204 has an acquisition unit 204a and a calculation unit 204b. The camera body 200 includes a high-speed internal memory (DRAM) 206 such as a random access memory (RAM), and is used as a high-speed buffer as a temporary image storage unit or as a work memory in image compression / decompression. .

  Further, the camera body 200 includes an image recording unit 207, a system control unit 209, a lens communication unit 210, an AE processing unit 211, an image display memory (VRAM) 212, and an image display unit 213. The image recording unit 207 includes a recording medium such as a memory card and an interface thereof. A system control unit 209 controls the system such as a shooting sequence. The lens communication unit 210 performs communication between the camera body 200 and the lens device 100 by being connected to the lens controller 105 via the communication bus 106. The image display unit 213 displays a shooting screen and a focus detection area at the time of shooting, in addition to displaying an image, a display for assisting operation, and displaying a camera state.

  Further, the camera body 200 includes an operation unit 214 for a user to operate the camera body 200, a menu switch for performing various settings such as a shooting function of the imaging apparatus 10 and settings for image playback, and a shooting mode and playback mode. It includes a mode operation mode changeover switch and the like. The shooting mode switch 215 is a switch for selecting a shooting mode such as a macro mode and a sports mode. The main switch 216 is a switch for turning on power to the system (imaging device 10). A switch (SW1) 217 is a switch for performing a shooting standby operation such as an automatic focus adjustment (AF) and an automatic exposure (AE), and a switch (SW2) 218 is a switch for performing a shooting after the switch SW1 is operated. It is.

  The imaging element 201 includes a CCD sensor, a CMOS sensor, and the like, and photoelectrically converts a subject image (optical image) formed via the imaging optical system of the lens device 100 to output a pixel signal (image data). That is, the light beam incident from the imaging optical system forms an image on the light receiving surface of the imaging element 201, and is converted into signal charges corresponding to the amount of incident light by pixels (photodiodes) arranged in the imaging element 201. The signal charges stored in each photodiode are sequentially read from the image sensor 201 as a voltage signal corresponding to the signal charges based on a drive pulse output from the timing generator 208 in accordance with a command from the system control unit 209.

  Each pixel of the image sensor 201 used in the present embodiment is provided for two (a pair) of photodiodes A and B and for the pair of photodiodes A and B (the photodiodes A and B are shared). It is configured to include one micro lens. That is, the imaging element 201 has a pair of photodiodes (a first photoelectric conversion unit and a second photoelectric conversion unit) for one microlens, and a plurality of microlenses are two-dimensionally arranged. Each pixel divides incident light with a microlens to form a pair of optical images on a pair of photodiodes A and B. The pair of photodiodes A and B form a pair of optical images used for AF signals described later. It outputs pixel signals (A image signal and B image signal). Further, by adding the outputs of the pair of photodiodes A and B, an imaging signal (A + B image signal) can be obtained.

  Then, by synthesizing a plurality of A image signals and a plurality of B image signals output from a plurality of pixels, respectively, an AF signal (AF for imaging plane phase difference AF) using the imaging plane phase difference detection method (imaging plane phase difference AF) is used. A pair of image signals as a focus detection signal) is obtained. An AF signal processing unit 204, which will be described later, performs a correlation operation on the pair of image signals to calculate a phase difference (image shift amount) which is a shift amount of the pair of image signals, and further calculates a data of the imaging optical system from the image shift amount. The focus amount (and the defocus direction) is calculated.

  As described above, the imaging element 201 photoelectrically converts an optical image formed by receiving a light beam that has passed through the imaging optical system of the lens device 100 into an electric signal, and outputs image data (image signal). The image sensor 201 according to the present embodiment is provided with two photodiodes for one microlens, and can generate an image signal used for focus detection by the imaging surface phase difference AF method. Note that the number of photodiodes sharing one microlens may be changed, such as providing four photodiodes for one microlens.

  Next, FIG. 2A schematically illustrates a configuration example of a pixel that does not support the imaging surface phase difference AF method, and FIG. 2B illustrates a configuration of a pixel that supports the imaging surface phase difference AF method. An example is shown schematically. In each of the pixel configurations of FIGS. 2A and 2B, a Bayer array is used, where R is a red color filter, B is a blue color filter, and Gr and Gb are green color filters. Is shown. In the pixel configuration of FIG. 2B corresponding to the imaging plane phase difference AF, one pixel (pixel indicated by a solid line) in the pixel configuration that is not compatible with the imaging plane phase difference AF method illustrated in FIG. , Two photodiodes A and B divided in the horizontal direction in FIG. 2B are provided. The photodiodes A and B (the first photoelectric conversion unit and the second photoelectric conversion unit) receive light beams that have passed through mutually different pupil regions of the imaging optical system.

  As described above, since the photodiodes A and B receive light beams that have passed through different areas of the exit pupil of the imaging optical system, the B image signal has parallax with the A image signal. In addition, one of the image signal (A + B image signal) and one of the pair of parallax image signals has a parallax. Note that the pixel dividing method illustrated in FIG. 2B is an example, and the pixel is divided in the vertical direction in FIG. 2B, or divided into two in the horizontal and vertical directions (total of four). Other configurations may be adopted. In addition, a plurality of types of pixels divided by different division methods may be included in the same image sensor.

  Note that, in the present embodiment, a configuration in which a plurality of photoelectric conversion units are arranged for one microlens and a pupil-divided light beam is incident on each photoelectric conversion unit has been described, but the present invention is not limited to this. Not something. For example, the focus detection pixel may have a configuration in which one photodiode is provided below the microlens and pupil division is performed by shielding the light from left and right or up and down by a light shielding layer. Alternatively, a configuration may be adopted in which a pair of focus detection pixels are discretely arranged in an array of a plurality of imaging pixels, and a pair of image signals are acquired from the pair of focus detection pixels.

  The imaging signal and the AF signal read from the imaging element 201 are input to the A / D converter 202. The A / D converter 202 performs correlated double sampling, gain adjustment, and digitization of the imaging signal and the AF signal to remove reset noise. The A / D converter 202 outputs the imaging signal to the image processing unit 203 and outputs the AF signal to the AF signal processing unit 204.

  The AF signal processing unit 204 (the acquisition unit 204a) outputs the AF signal (a first signal (A image signal) and a second signal (B image signal) as a pair of image signals) output from the A / D conversion unit 202. To get. Further, the AF signal processing unit 204 (calculating unit 204b) calculates an image shift amount by performing a correlation operation based on the AF signal, and calculates a defocus amount based on the image shift amount. The AF signal processing unit 204 (calculation unit 204b) ranks the reliability based on the reliability information of the AF signal (the coincidence of two images, the steepness of two images, contrast information, saturation information, and flaw information). Attach it. The defocus amount and the reliability information (reliability) calculated by the AF signal processing unit 204 are output to the system control unit 209. The details of the correlation calculation by the AF signal processing unit 204 will be described later.

  Next, an operation of the imaging device 10 according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart illustrating the operation of the imaging device 10. Each step in FIG. 3 is mainly executed by each unit based on a command from the system control unit 209.

  First, in step S301, the system control unit 209 controls the AE processing unit 211 to perform AE processing on an output signal of the image processing unit 203. Next, in step S302, the system control unit 209 determines whether the switch 217 (SW1) is on. If the switch 217 (SW1) is on (Yes), the process proceeds to step S303. On the other hand, if the switch 217 (SW1) is off (No), the process returns to step S301.

  Next, in step S303, the system control unit 209 performs an AF operation. The details of the AF operation will be described later. Next, in step S304, the system control unit 209 determines whether the switch 217 (SW1) is on. If the switch 217 (SW1) is on (Yes), the process proceeds to step S305. On the other hand, if the switch 217 (SW1) is off (No), the process returns to step S301.

  Next, in step S305, the system control unit 209 determines whether the switch 218 (SW2) is on. If the switch 218 (SW2) is off (No), the process returns to step S304. On the other hand, if the switch 218 (SW2) is on (Yes), the process proceeds to step S306. In step S306, the system control unit 209 performs a shooting operation. Then, the process returns to step S301.

  Next, the AF operation (step S303 in FIG. 3) in the present embodiment will be described in detail with reference to FIGS. 4 and 5 are flowcharts showing the AF operation. 4 and 5 are mainly executed by the AF signal processing unit 204 and the system control unit 209.

  First, in step S401, the system control unit 209 controls the AE processing unit 211 to perform AE processing on an output signal of the image processing unit 203. Next, in step S402, the AF signal processing unit 204 performs focus detection processing using the pair of image signals, and calculates the defocus amount and the reliability. The details of the focus detection processing will be described later.

  Next, in step S403, the system control unit 209 determines whether or not the reliability calculated in step S402 (the reliability of the focus detection result) is higher than a preset second reliability threshold. . When the reliability is higher than the second reliability threshold (Yes), the process proceeds to step S404. On the other hand, if the reliability is less than the second reliability threshold (No), the process proceeds to step S413. If the reliability is less than the second reliability threshold, the accuracy of the defocus amount cannot be guaranteed, but the direction of the in-focus position of the subject can be guaranteed if the reliability is lower than the second reliability threshold.

  Next, in step S404, the system control unit 209 determines whether or not the defocus amount (the detected defocus amount) calculated in step S402 is equal to or less than a preset second Def amount threshold. If the detected defocus amount is equal to or smaller than the second Def amount threshold (Yes), the process proceeds to step S405. On the other hand, if the detected defocus amount is larger than the second Def amount threshold (No), the process proceeds to step S412. The second Def amount threshold is controlled such that when the defocus amount is equal to or less than the second Def amount threshold, the focus lens 103 is moved within the depth of focus within a predetermined number of times (for example, three times) by the defocus amount. It is set to a possible value (e.g., five times the depth of focus).

  Next, in step S405, the system control unit 209 determines whether the focus lens 103 is in a stopped state (during stop). If the focus lens 103 is stopped (Yes), the process proceeds to step S406. On the other hand, if the focus lens 103 is not stopped (No), the process proceeds to step S410.

  Next, in step S406, the system control unit 209 determines whether or not the reliability calculated in step S402 (the reliability of the focus detection result) is higher than a preset first reliability threshold. . If the reliability is higher than the first reliability threshold (Yes), the process proceeds to step S407. On the other hand, if the reliability is less than the first reliability threshold (No), the process proceeds to step S410. The first reliability threshold is set such that the accuracy variation of the defocus amount is within a predetermined range (for example, within the depth of focus) when the reliability is equal to or more than the first reliability threshold.

  Next, in step S407, the system control unit 209 determines whether the defocus amount calculated in step S402 (the detected defocus amount) is equal to or less than a preset first Def amount threshold. If the detected defocus amount is equal to or smaller than the first Def amount threshold (Yes), the process proceeds to step S408. On the other hand, if the detected defocus amount is larger than the first Def amount threshold (No), the process proceeds to step S409. Note that the first Def amount threshold is set so that the focus lens 103 is controlled within the depth of focus if the detected defocus amount is equal to or less than the first Def amount threshold.

  Next, in step S408, the system control unit 209 determines that the focus state is the in-focus state, and ends this flow. On the other hand, in step S409, the system control unit 209 drives the focus lens 103 by the defocus amount calculated in step S402 (detected defocus amount), and then returns to step S402. By performing the series of operations in steps S405 to S409 again, if the reliability calculated in step S402 is higher than the first reliability threshold, the system control unit 209 again stops the focus lens 103 and stops decoding. The focus amount can be calculated.

  Next, in step S410, the system control unit 209 drives the focus lens 103 by a predetermined ratio with respect to the defocus amount detected in step S402. Next, in step S411, the system control unit 209 instructs the focus lens 103 to stop, and returns to step S402. Next, in step S412, the system control unit 209 drives the focus lens 103 for the defocus amount detected in step S402, and returns to step S402.

  Next, in step S413, the system control unit 209 determines whether the out-of-focus condition is satisfied. If the out-of-focus condition is satisfied (Yes), the process proceeds to step S414. On the other hand, if the out-of-focus condition is not satisfied (No), the process proceeds to step S415. Here, the out-of-focus condition is a condition that the system control unit 209 determines that there is no subject to be focused. As an out-of-focus condition, for example, a case where lens driving is completed in the entire movable range of the focus lens 103, that is, a case where the focus lens 103 detects both the far-side and near-side lens ends and returns to the initial position. The conditions are set.

  Next, in step S414, the system control unit 209 determines that the focus state is out of focus, and ends this flow. On the other hand, in step S415, the system control unit 209 determines whether the focus lens 103 has reached the far or near lens end. If the focus lens 103 has reached the lens end (Yes), the process proceeds to step S416, while if the focus lens 103 has not reached the lens end (No), the process proceeds to step S417.

  Next, in step S416, the system control unit 209 reverses the driving direction (lens driving direction) of the focus lens 103, and returns to step S402. Next, in step S417, the system control unit 209 drives the focus lens 103 in a predetermined direction, and returns to step S402. The drive speed (focus lens speed) of the focus lens 103 is set to, for example, the fastest speed within a range of lens speeds that does not pass the focus position when the defocus amount can be detected.

  Next, the focus detection process (step S402 in FIG. 4) will be described in detail with reference to FIG. FIG. 6 is a flowchart showing the focus detection processing. Each step in FIG. 6 is mainly executed by the system control unit 209 or the AF signal processing unit 204 based on a command from the system control unit 209.

  First, in step S501, the AF signal processing unit 204 (system control unit 209) sets a focus detection area in an arbitrary range in the image sensor 201. Next, in step S502, the AF signal processing unit 204 acquires a pair of image signals for focus detection (A image signal and B image signal) from the image sensor 201 for the focus detection area set in step S501. Next, in step S503, the AF signal processing unit 204 performs row averaging processing on the pair of image signals acquired in step S502 in the vertical direction. The row averaging process can reduce the influence of noise in the image signal. Next, in step S504, the AF signal processing unit 204 performs a filter process of extracting a signal component in a predetermined frequency band from the pair of image signals on which the row averaging process has been performed in step S503.

  Next, in step S505, the AF signal processing unit 204 calculates a correlation amount based on the pair of image signals after the filtering process in step S504. Next, in step S506, the AF signal processing unit 204 calculates a correlation change amount based on the correlation amount calculated in step S505. Next, in step S507, the AF signal processing unit 204 calculates an image shift amount based on the correlation change amount calculated in step S505. Next, in step S508, the AF signal processing unit 204 calculates the reliability of the image shift amount calculated in step S507. Next, in step S509, the AF signal processing unit 204 converts the image shift amount into a defocus amount.

  Next, in step S510, the system control unit 209 determines whether or not the filter processing performed in step S504 has been calculated by the number of filter types. If the calculation of the filter processing has been completed for the number of filter types (Yes), the process proceeds to step S511. On the other hand, if the calculation of the filter processing has not been completed for the number of filter types (No), the process returns to step S504. In the present embodiment, in the filter processing in step S504, for example, band-pass filters of three different frequency bands (low, middle, and high) with respect to a pair of image signals on which row averaging processing has been performed. (Filtering) is performed in the horizontal direction. However, the low-pass filter, the middle-pass filter, and the high-pass filter indicate relative heights of frequency components extracted by the respective filters, and do not indicate absolute heights. In step S510, the system control unit 209 determines whether the series of processes in steps S504 to S509 has been performed for all three frequency bands.

  Next, in step S511, the system control unit 209 selects a defocus amount calculated using a filter that performs focus determination. That is, the system control unit 209 (decision unit) determines which combination of the defocus amount and the reliability among the three combinations of the defocus amount and the reliability calculated by the series of processes of steps S504 to S509. Select (determine) whether to use. In the present embodiment, the defocus amount calculated using the low-pass filter is large Def, the defocus amount calculated using the middle-pass filter is medium Def, and the defocus amount calculated using the high-pass filter is Expressed as a small Def. The selection of the defocus amount will be described later.

  Next, the focus detection area (AF area) set in step S501 in FIG. 6 will be described in detail with reference to FIG. FIG. 7 is an explanatory diagram of the focus detection area 602 on the pixel array 601 of the image sensor 201. The shift areas 603 on both sides of the focus detection area 602 are areas necessary for the correlation calculation. Therefore, an area 604 obtained by combining the focus detection area 602 and the shift area 603 is a pixel area necessary for the correlation calculation. 7, p, q, s, and t are coordinates in the horizontal direction (x-axis direction), respectively, where p and q are the x coordinates of the start point and end point of the area 604 (pixel area), respectively, and s and t are The x-coordinates of the start point and the end point of the focus detection area 602 are respectively shown.

  FIG. 8 is an explanatory diagram of AF signals (a pair of image signals) acquired from a plurality of pixels included in the focus detection area 602 in FIG. 8, a solid line 701 is one of the pair of image signals (A image signal), and a broken line 702 is the other of the pair of image signals (B image signal). FIG. 8A shows the A image signal and the B image signal before the shift, and FIGS. 8B and 8C show the A image signal and the B image signal, respectively, from the state of FIG. This shows a state shifted in the minus direction. When calculating the amount of correlation between a pair of image signals (A image signal indicated by a solid line 701 and B image signal indicated by a broken line 702), both the A image signal and the B image signal are bit-by-bit in the direction of the arrow. shift.

Next, a method of calculating the correlation amount will be described. First, as shown in FIGS. 8B and 8C, the A image signal and the B image signal are each shifted by one bit, and the sum of the absolute values of the differences between the A image signal and the B image signal is calculated. I do. The correlation amount COR [i] can be calculated using the following equation (1).

  In equation (1), i is the shift amount, ps is the maximum shift amount in the minus direction, qt is the maximum shift amount in the plus direction, x is the start coordinate of the focus detection area 602, and y is the coordinate of the focus detection area 602. End coordinates.

  Here, the relationship between the shift amount and the correlation amount COR will be described with reference to FIG. FIGS. 9A and 9B are diagrams illustrating the relationship between the shift amount and the correlation amount COR. FIG. 9B is an enlarged view of a region 802 in FIG. In FIG. 9A, the horizontal axis represents the shift amount, and the vertical axis represents the correlation amount COR. Of the regions 802 and 803 near the extreme value in the correlation amount 801 that changes with the shift amount, the degree of coincidence between the pair of image signals (A image signal and B image signal) is the highest in the shift amount corresponding to the smaller correlation amount. .

Next, a method of calculating the correlation change amount will be described. In the present embodiment, the difference between the correlation amounts at every other shift in the waveform of the correlation amount 801 shown in FIG. 9A is calculated as the correlation change amount. The correlation change amount ΔCOR [i] can be calculated using the following equation (2).

  Here, the relationship between the shift amount and the correlation change amount ΔCOR will be described with reference to FIG. FIGS. 10A and 10B are diagrams illustrating the relationship between the shift amount and the correlation change amount ΔCOR. FIG. 10B is an enlarged view of a region 902 in FIG. In FIG. 10A, the horizontal axis represents the shift amount, and the vertical axis represents the correlation change amount ΔCOR. The correlation change amount 901 that changes with the shift amount changes from plus to minus in the regions 902 and 903. The state where the correlation change amount is 0 is called zero cross, and the degree of coincidence between a pair of image signals (A image signal and B image signal) is the highest. Therefore, the shift amount giving the zero cross is the image shift amount.

ここで、整数部分βは、図１０（Ｂ）より、以下の式（４）を用いて算出することができる。

In FIG. 10B, reference numeral 904 denotes a part of the correlation change amount 901. A method for calculating the image shift amount PRD will be described with reference to FIG. The shift amount (k−1 + α) that gives a zero cross is divided into an integer part β (= k−1) and a decimal part α. The decimal part α can be calculated from the similarity between the triangle ABC and the triangle ADE in FIG. 10B by using the following equation (3).

Here, the integer part β can be calculated from FIG. 10B using the following equation (4).

本実施形態では、相関変化量のゼロクロスが複数存在する場合、その急峻性に基づいて第１のゼロクロスを決定し、第１のゼロクロスを与えるシフト量を像ずれ量とする。 That is, the image shift amount PRD can be calculated from the sum of the decimal part α and the integer part β. As shown in FIG. 10A, when there are a plurality of zero crosses of the correlation change amount ΔCOR, the one where the steepness of the change of the correlation change amount ΔCOR in the vicinity is larger is defined as the first zero cross. This steepness is an index indicating the ease of performing AF, and indicates that the larger the value, the easier it is to perform high-precision AF. The steepness maxder can be calculated using the following equation (5).

In the present embodiment, when there are a plurality of zero crosses of the correlation change amount, the first zero cross is determined based on the steepness, and the shift amount that gives the first zero cross is defined as the image shift amount.

Next, a method for calculating reliability information (reliability) of the image shift amount will be described. The reliability of the image shift amount can be defined by the coincidence degree (coincidence degree of two images) fnclvl of the pair of image signals (A image signal and B image signal) and the steepness of the correlation change amount ΔCOR described above. , The reliability may be obtained from any value. The coincidence between two images is an index indicating the accuracy of the amount of image shift. Here, a smaller value means higher accuracy. In FIG. 9B, reference numeral 804 denotes a part of the correlation amount 801. The coincidence fnclvl of the two images can be calculated using the following equation (6).

  Next, the selection of the defocus amount (step S511 in FIG. 6) will be described with reference to FIG. FIG. 11 is a flowchart showing the selection of the defocus amount. Each step in FIG. 11 is mainly executed by the system control unit 209.

  First, in step S1001, the system control unit 209 determines whether to switch from a large Def (first defocus amount) to a medium Def (second defocus amount) described later. Next, in step S1002, the system control unit 209 determines whether the handover from the large Def to the middle Def has been performed. If the transfer from the large Def to the middle Def has been performed (Yes), the process proceeds to step S1003. On the other hand, if the takeover from the large Def to the middle Def cannot be performed (No), the process proceeds to step S1007.

  Next, in step S1003, the system control unit 209 performs a transition determination from a below-described middle def (second defocus amount) to a small def (third defocus amount). Next, in step S1004, the system control unit 209 determines whether the takeover from the middle Def to the small Def has been performed. If the transfer from the middle Def to the small Def has been performed (Yes), the process proceeds to step S1005. On the other hand, if the transfer from the middle Def to the small Def cannot be performed (No), the process proceeds to step S1006.

  In step S1005, the system control unit 209 selects small def as the defocus amount used for driving the focus lens 103 (focus control), and ends this flow. Also, in step S1006, the system control unit 209 selects medium Def as the defocus amount used for focus control, and ends this flow. In step S1007, the system control unit 209 selects the large Def as the defocus amount used for the focus control, and ends the present flow.

  Next, with reference to FIG. 12, a description will be given of the determination of the transition from the large Def to the middle Def (Step S1001 in FIG. 11). Each step in FIG. 12 is mainly executed by the system control unit 209.

  First, in step S1101, the system control unit 209 determines whether the difference between the defocus amounts of the large Def and the middle Def is equal to or less than a preset first depth threshold (first threshold). When the difference between the defocus amounts of the large Def and the middle Def is equal to or smaller than the first depth threshold (Yes), the process proceeds to step S1102. On the other hand, if the difference is larger than the first depth threshold (No), the process proceeds to step S1104. Note that the first depth threshold is set to, for example, nine times the depth of focus so that the large Def can be appropriately taken over from the middle Def. Also, by setting the first depth threshold based on the depth of focus (making it larger than the depth of focus), a uniform threshold can be set even if the F value or the focus detection area changes.

  Next, in step S1102, the system control unit 209 determines that the reliability of the middle Def (second reliability) is equal to or greater than the reliability of the large Def (first reliability) and that the reliability of the middle Def is the second reliability. It is determined whether it is higher than a threshold value (threshold value used in the determination in step S403 in FIG. 4). If both of these conditions are satisfied (Yes), the process proceeds to step S1103. On the other hand, if at least one of the conditions is not satisfied (No), the process proceeds to step S1104.

  In step S1103, the system control unit 209 determines that the takeover from the large Def to the middle Def can be performed, and ends the flow. On the other hand, in step S1104, the system control unit 209 determines that the takeover from the large Def to the middle Def cannot be performed, and ends the flow. Thereby, in the process of moving the focus lens 103 from the large blur state to the small blur state, the transition from the large Def to the middle Def is performed based on the difference between the defocus amounts of the large Def and the middle Def and the respective reliability. It can be determined whether or not it is possible to do so.

  Next, with reference to FIG. 13, a description will be given of the determination of the transition from the middle Def to the small Def (Step S1003 in FIG. 11). Each step in FIG. 13 is mainly executed by the system control unit 209. First, in step S1201, the system control unit 209 determines whether the middle Def is larger than a preset first defocus amount threshold. If the middle Def is large (Yes), the process proceeds to step S1202. On the other hand, if the middle Def is small (No), the process proceeds to step S1203.

  Note that the first defocus amount threshold is set to, for example, the depth of focus so that a large deviation (incorrect distance measurement) of the middle Def can be detected. This makes it possible to detect a case where the accuracy of the middle Def is low especially near the in-focus position. In addition, by setting the first defocus amount threshold with reference to the depth of focus, a uniform threshold can be set even when the F value or the focus detection area changes.

  Next, in step S1202, the system control unit 209 performs a process of lowering the reliability of the middle Def by one rank, and proceeds to step S1203. As a result, the condition for taking over from the medium Def to the small Def, which is determined in step S1204 to be described later, is easily satisfied, and the takeover to the small Def becomes easy. That is, by adding the process of lowering the reliability of the middle Def (S1202), priority is added to the selection of the middle Def and the small Def, and it is possible to make it difficult to select the middle Def with low accuracy near the focus position. .

  Next, in step S1203, the system control unit 209 determines whether the difference between the defocus amounts of the middle Def and the small Def is equal to or less than a preset second depth threshold (second threshold). If the difference between the defocus amounts of the middle Def and the small Def is equal to or smaller than the second depth threshold (Yes), the process proceeds to step S1204. On the other hand, if the difference is larger than the second depth threshold (No), the process proceeds to step S1206.

  The second depth threshold is set to, for example, three times the depth of focus so that the medium Def can be appropriately taken over from the small Def. Also, by setting the second depth threshold based on the depth of focus (making it larger than the depth of focus), a uniform threshold can be set even if the F-number or the focus detection area changes. Further, the second depth threshold is set to a value smaller than the first depth threshold used in the determination in step S1101 of FIG. This is because the variation in the detection of the defocus amount increases as the change from small Def to middle Def to large Def occurs, so that the difference between the middle Def and the large Def becomes larger than the difference between the small Def and the middle Def. is there.

  Next, in step S1204, the system control unit 209 determines that the reliability of the small Def is greater than or equal to the reliability of the middle Def, and that both the reliability of the small Def and the reliability of the middle Def are greater than the second reliability threshold. Is also high. If all of these conditions are satisfied (Yes), the process proceeds to step S1205. On the other hand, if at least one condition is not satisfied (No), the process proceeds to step S1206.

  Next, in step S1205, the system control unit 209 determines that the takeover from the middle Def to the small Def can be performed, and ends the flow. On the other hand, in step S1206, the system control unit 209 determines that it is not possible to take over from the middle Def to the small Def, and ends this flow. Thereby, in the process of moving the focus lens 103 from the small blur state to the in-focus position, the transition from the middle Def to the small Def is performed based on the difference between the defocus amounts of the middle Def and the small Def and the respective reliability. It can be determined whether it is possible to do so.

  In the present embodiment, the case where the low-pass filter, the middle-pass filter, and the high-pass filter are used has been described, but the type and number of the filters are not limited. In addition, the priority is added to the selection when the medium Def and the small Def are determined to be taken over, but the priority may be added to other selections when determining the takeover. Further, the priority is added by lowering the reliability of the middle Def. However, the priority may be added by giving hysteresis to the threshold for taking over the middle Def and the small Def.

  As described above, according to the present embodiment, when the reliability is calculated to be equal to or more than the small Def reliability even though the middle Def is erroneously measured, the priority of lowering the middle Def reliability by one rank Is added, the selection can be made difficult, and a stable handover determination can be made. In other words, even if the reliability of the calculation result of the low-band filter is equal to or higher than the reliability of the high-band filter in a subject having a low contrast, by adding the priority according to the band at the time of determining the handover, It can be taken over by a high-band filter stably. In addition, the inversion of the lens can be suppressed, and the focusing rate can be improved.

(2nd Embodiment)
Next, an AF operation at the time of automatic selection according to the present embodiment will be described with reference to FIG. FIG. 14 is a flowchart illustrating a focus detection process when the imaging apparatus is automatically selected. A control program relating to this operation is executed by the AF signal processing unit 204. When the AF operation is started, first, in step S1301, the AF signal processing unit 204 sets a focus detection area 141 for performing focus adjustment on a subject. In the process of step S1301, as shown in FIG. 15, a total of 49 focus detection frames 142 (vertical and horizontal 7 × 7) are set.

  Next, in step S1302, an AF signal necessary for focus detection is acquired in each focus detection frame. Specifically, after exposure is performed by the image sensor 201, an image signal of a focus detection pixel in the area of the focus detection frame 142 for the imaging surface phase difference AF is acquired. Next, in step S1303, a defocus amount is calculated from a shift amount of the obtained pair of image signals for each focus detection frame for the imaging surface phase difference AF. In the present embodiment, the reliability of the calculated defocus amount is also determined. The defocus amount and the reliability can be calculated in the same manner as in the first embodiment. That is, the defocus amount is obtained by performing the focus detection processing of FIG. 6, and the reliability is determined by the reliability information of the AF signal (the coincidence of two images, the steepness of two images, contrast information, saturation information, And flaw information).

  In the present embodiment, a case where a low-pass filter and a high-pass filter are used will be described. Hereinafter, the focus detection frame inherited up to the defocus amount calculated using the low-pass filter is expressed as a low-pass filter frame, and the focus detection frame inherited up to the defocus amount calculated using the high-pass filter is expressed as a high-pass filter frame. I do. Further, when the calculated defocus amount has a predetermined reliability, it is expressed as “the defocus amount has been calculated”, and the defocus amount cannot be calculated for some reason, or the calculated defocus amount is not reliable. When the degree is low, it is expressed as “the defocus amount cannot be calculated”.

  Next, in step S1304, frame selection processing is performed to select a subject to which the photographer wants to focus most from among the plurality of focus detection frames 142 set in step S1301. Basically, a focus detection frame with a defocus amount indicating the closest object is selected. However, in general, an object which a photographer wants to focus on is often present on the closest side. Details of this frame selection processing will be described later. Next, in step S1305, the focus lens 103 is driven based on the defocus amount calculated by the selected focus detection frame 142 (focus control).

  Next, in step S1306, a focus display is performed on the display unit 213 for the focus detection frame for which the defocus amount used for driving the lens has been calculated, and the focus detection processing ends. In the focus display processing, only the selected frame may be displayed, or all or a part of the focus detection frames whose difference between the selected focus detection frame and the defocus amount is within a predetermined range may be displayed. Good.

  Hereinafter, details of the frame selection process performed in step S1304 will be described with reference to FIG. First, in step S1501, it is determined whether or not there is a frame in which the reliability of the high-pass filter frame is equal to or greater than a third reliability threshold set in advance among the focus detection frames for which the defocus amount has been calculated. If it exists (Yes), a focus detection frame whose reliability is equal to or higher than the third reliability threshold is set as a candidate frame, and the process proceeds to step S1503. On the other hand, if it does not exist (No), the process proceeds to step S1502.

  Next, in step S1502, it is determined whether or not there is a frame in which the reliability of the low-pass filter frame is equal to or greater than a predetermined third reliability threshold among the focus detection frames for which the defocus amount has been calculated. If it exists (Yes), a focus detection frame whose reliability is equal to or higher than the third reliability threshold is set as a candidate frame, and the process proceeds to step S1503. On the other hand, if it does not exist (No), the process proceeds to step S1505, it is determined that the selection frame is "none", and the present flow ends.

  As described above, first, the reliability is determined in the high-pass filter frame, and if the condition is not satisfied, the reliability of the low-pass filter frame is determined. Thereby, priority is added to the selection of the high-pass filter frame and the low-pass filter frame, and it is possible to make it difficult to select a defocus amount calculated using a low-accuracy low-band filter near the focus position.

  Next, in step S1503, among the frames set as the candidate frames in steps S1501 to S1502, the closest frame is set as the selection frame, and this flow ends.

  When the selection frame is set to “none”, in step S1305 in FIG. 14, it is determined that the focus lens 103 is not in focus without driving, and the process of displaying out of focus on the display unit 213 is performed. May go. Further, a search drive in which the focus lens 103 is driven in a predetermined direction until a highly reliable frame is selected may be performed.

  In the present embodiment, the case where the low-pass filter and the high-pass filter are used has been described, but the type and number of the filters are not limited. In addition, since an effect is obtained by making it harder to select a lower band filter, a priority may be added to all filters, or a priority may be added to at least one filter.

  As described above, according to the present embodiment, even when there is a focus detection frame that satisfies the condition selected as the selection frame in both the high-band filter frame and the low-band filter frame, priority is given by performing the determination from the high-band filter frame. Add degrees. Then, the defocus amount calculated using the higher-precision high-band filter can be selected. That is, in the automatic selection mode, even when a low-contrast subject is included in the focus detection area 141, the priority is added according to the band when the frame is selected. This makes it possible to more accurately select a focus detection frame of a high-contrast subject that the photographer wants to perform focus adjustment, thereby suppressing blurring.

  As described above, in the above-described embodiment, when the filter band is taken over or the focus detection frame is selected, the priority is given according to the frequency band of the band-pass filter, thereby improving the focusing rate in a case where a low-contrast subject is included. it can. From this, it is possible to provide an imaging device that can reduce out-of-focus or blur focus even when a low-contrast subject is included in focus detection.

  Although the preferred embodiments of the present invention have been described, the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

Reference Signs List 10 photographing device 204a acquisition unit 204b calculation unit 204 AF signal processing unit 209 system control unit

Claims (8)

Acquiring means for acquiring a first signal and a second signal corresponding to a light beam passing through different pupil regions of the imaging optical system;
A plurality of filter processes having different bands are performed on the first signal and the second signal, and a plurality of defocus amounts and a plurality of reliability are determined based on the first signal and the second signal after the respective filter processes. Calculating means for calculating;
A determination unit that determines a defocus amount used for focus adjustment from among the plurality of defocus amounts, based on at least one of the difference between the plurality of defocus amounts and the plurality of degrees of reliability,
The image capturing apparatus according to claim 1, wherein the determining unit adds a priority of determining the defocus amount to at least one of the plurality of defocus amounts. 2. The method according to claim 1, wherein the determining unit sets a lower priority for determining a defocus amount calculated using a filter having a relatively low band among the plurality of defocus amounts. 3. Shooting equipment. 3. The method according to claim 1, wherein the determining unit sets low reliability of the defocus amount calculated using a filter having a relatively lowest band among the plurality of defocus amounts. 4. Shooting equipment. 4. The method according to claim 1, wherein the determining unit adds the priority when determining a defocus amount calculated using a filter that performs focus determination among the plurality of defocus amounts. 5. The imaging device according to any one of the above. The determining means sets a threshold value, which is a condition for determining the plurality of defocus amounts, to have a hysteresis, so that the defocus amount used for the focus adjustment is calculated using a filter having a relatively low band. The imaging apparatus according to any one of claims 1 to 4, wherein the amount is switched to a defocus amount calculated using a filter having a relatively high band from the amount. The determining means may determine a defocus amount calculated using a filter of a relatively low band among the plurality of defocus amounts relatively later as a defocus amount used for the focus adjustment. The photographing apparatus according to claim 1, wherein: The determining means determines, after the other filters, a defocus amount calculated using a filter having a relatively lowest band among the plurality of defocus amounts as a defocus amount used for the focus adjustment. The photographing apparatus according to claim 1, wherein: An acquisition step of acquiring a first signal and a second signal corresponding to a light beam passing through different pupil regions of the imaging optical system;
A plurality of filter processes having different bands are performed on the first signal and the second signal, and a plurality of defocus amounts and a plurality of reliability are determined based on the first signal and the second signal after the respective filter processes. A calculating step of calculating;
Determining a defocus amount used for focus adjustment from among the plurality of defocus amounts, based on a difference between the plurality of defocus amounts and at least one of the plurality of degrees of reliability,
In the determining step, a priority of selection is added to at least one or more of the plurality of defocus amounts, respectively.

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