JP7130521B2 - IMAGING DEVICE, IMAGING DEVICE CONTROL METHOD AND PROGRAM - Google Patents

Description

The present invention relates to an imaging apparatus that performs focusing using two filters with different frequency components of signals extracted from an image, a control method for the imaging apparatus, and a program.

2. Description of the Related Art Conventionally, in an imaging device such as an electronic still camera, autofocus control, which automatically focuses using an imaging signal output from an imaging device, is used as control for moving a focus lens to focus on a subject. be done. A phase difference detection method and a contrast detection method are known as focusing methods in autofocus control. For example, in the phase difference detection method, light beams from a subject that pass through mutually different exit pupil areas of an imaging optical system are imaged on an imaging device, and a pair of parallax sensors obtained from distance measurement sensors arranged in the imaging device. A defocus amount is calculated based on the signal phase difference. Furthermore, by moving the focus lens by a movement amount corresponding to the calculated defocus amount, the in-focus state of the imaging optical system can be quickly obtained (see, for example, Patent Document 1).

By the way, when a plurality of objects are included in an image, the phase difference detection method uses a low-pass filter for extracting low-frequency component signals from the image and a high-pass filter for extracting high-frequency component signals from the image. A signal extracted using a low-pass filter contains signal components of a plurality of objects, and a signal extracted using a high-pass filter contains signal components of an object that is relatively in focus. Therefore, first, a defocus amount calculated using a low-pass filter (hereinafter referred to as a "low-pass defocus amount") is used to focus on an intermediate position of a plurality of subjects. After that, when the difference between the low-frequency defocus amount and the defocus amount calculated using the high-pass filter (hereinafter referred to as "high-frequency defocus amount") becomes equal to or less than a predetermined value, the high-frequency defocus amount is Focusing is performed on an object that is close to the in-focus state.

JP-A-09-54242

However, when the high-frequency defocus amount is used to focus on a subject that is close to being in focus, the difference between the low-frequency defocus amount and the high-frequency defocus amount (hereinafter referred to as "defocus amount difference"). ) can be large. When the defocus amount difference becomes larger than the predetermined value, focusing is performed again using the low-range defocus amount. As a result, focusing using the low-frequency defocus amount and focusing using the high-frequency defocus amount are repeated, and it may take time to focus.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an imaging device capable of focusing in a short time, a control method for the imaging device, and a program.

In order to achieve the above object, the image pickup apparatus of the present invention includes signal generation means for generating signals of two images respectively corresponding to a pair of light fluxes from a subject that have passed through mutually different pupil regions of a focus lens; A first filter for extracting a signal of a first frequency component from an image, and a second filter for extracting a signal of a second frequency component, which is a higher frequency component than the first frequency component, from the two images. and calculating a first defocus amount based on the phase difference between the signals extracted from the two images by the first filter, and extracting from the two images by the second filter defocus amount calculation means for calculating a second defocus amount based on the phase difference of the signals obtained; and the first defocus amount based on the difference between the first defocus amount and the second defocus amount. selecting means for selecting one of the focus amount and the second defocus amount as the defocus amount to be used for focusing; confirmation means for confirming the number of times of switching to the defocus amount or from the second defocus amount to the first defocus amount; The means is characterized by changing a method of selecting a defocus amount used for focusing.

According to the present invention, focusing can be performed in a short time.

1 is a diagram schematically showing the configuration of an electronic still camera as an imaging device according to a first embodiment of the present invention; FIG. 2 is a diagram showing the configuration of a pixel array in FIG. 1; FIG. 2 is a flowchart showing shooting processing executed by the electronic still camera of FIG. 1; FIG. 4 is a flowchart showing autofocus processing in S304 of FIG. 3; FIG. FIG. 5 is a flowchart showing focus detection processing in S401 of FIG. 4; FIG. FIG. 10 is a diagram for explaining general filtering; 7 is a graph for explaining normal focusing; 4 is a flow chart showing filter determination processing as a control method of the imaging apparatus according to the first embodiment of the present invention; FIG. 9 is a diagram showing the data structure of a selection history held in S803 of FIG. 8; FIG. 9 is a flowchart showing filter selection processing in S802 of FIG. 8. FIG. 10 is a flow chart showing filter determination processing as a control method of an imaging device according to a second embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the configurations described in the following embodiments are merely examples, and the scope of the present invention is not limited by the configurations described in the embodiments. First, a first embodiment of the present invention will be described.

FIG. 1 is a diagram schematically showing the configuration of an electronic still camera as an imaging device according to the first embodiment of the invention.

In FIG. 1, an electronic still camera 101 has a photographing lens 111 . The photographing lens 111 has a fixed lens 112 , a diaphragm 113 and a focus lens 114 . The focus lens 114 is a lens for focus adjustment and is normally composed of a plurality of lenses. Note that FIG. 1 schematically shows the focus lens 114 as a single lens.

The electronic still camera 101 also includes an aperture control unit 115 , a focus control unit 116 and a lens control unit 117 . A diaphragm control unit 115 drives the diaphragm 113 to adjust the aperture diameter of the diaphragm 113 and adjust the amount of light during photographing. The focus control unit 116 determines the driving amount of the focus lens 114 based on the amount of deviation of the photographing lens 111 in the focus direction, and drives the focus lens 114 to adjust the focus. In particular, in the present embodiment, automatic focus adjustment is realized by movement control of focus lens 114 by focus control unit 116 . A diaphragm control unit 115 and a focus control unit 116 are controlled by a lens control unit 117 .

Further, the electronic still camera 101 includes a pixel array 200 , a timing generator 122 , a CDS/AGC/AD converter 123 , an imaging signal processing section 124 , a focus detection signal processing section 125 and a camera control section 141 . The electronic still camera 101 also includes a display control unit 132, a display unit 133, a recording medium control unit 134, a recording medium 135, an SDRAM 136, a ROM 137, a flash ROM 138, a first SW139 and a second SW140. In this embodiment, the camera control unit 141 corresponds to signal extraction means, defocus amount calculation means, selection means, confirmation means initialization means, change means, and the like.

In the electronic still camera 101, a luminous flux (incident light) incident through the photographing lens 111 forms an image on the light receiving surface of each imaging element (unit pixel) 121 of the pixel array 200, and is converted into an electric signal by the imaging element 121. be. The imaging element 121 (signal generating means) is a photoelectric conversion element that photoelectrically converts a subject image (optical image) into signal charges, and is configured by a CCD or CMOS sensor. The signal charges accumulated in each photoelectric conversion element are sequentially read out from the image sensor 121 as electric signals (imaging signal and focus detection signal) corresponding to the signal charges according to the drive pulse output by the timing generator 122 .

The CDS/AGC/AD converter 123 performs correlated double sampling for removing reset noise, sensor gain adjustment, and digitization processing on the imaging signal and focus detection signal read from the imaging device 121 . The CDS/AGC/AD converter 123 outputs the imaging signal to the imaging signal processing unit 124 and outputs the imaging plane phase difference method focus detection signal to the focus detection signal processing unit 125 . In this embodiment, a case of using an imaging plane phase difference method as a focus detection method will be described, but the focus detection method is not limited to this, and any phase difference method may be used.

The focus detection signal processing unit 125 sets the focus detection area within the imaging screen. Further, the focus detection signal processing unit 125 performs a correlation operation on the two image signals for focus detection output from the CDS/AGC/AD converter 123, and obtains image shift amount, reliability information (degree of coincidence between two images, image steepness) is evaluated, and the defocus amount and the reliability of the defocus amount are output. The imaging signal processing unit 124 stores the imaging signal output from the CDS/AGC/AD converter 123 in the SDRAM 136 via the bus 131 . The imaging signal stored in the SDRAM 136 is read by the display control section 132 via the bus 131 and displayed on the display section 133 . Also, in the operation mode for recording the imaging signal, the imaging signal stored in the SDRAM 136 is recorded in the recording medium 135 by the recording medium control unit 134 .

The ROM 137 stores control programs executed by the camera control unit 141 and various data necessary for control, and the flash ROM 138 stores various setting information related to the operation of the electronic still camera 101 such as user setting information. The first SW 139 is a switch for performing shooting standby operations such as AF and AE, and the second SW 140 is a shooting switch for shooting after the first SW 139 is operated.

The camera control unit 141 determines the lens drive amount based on the defocus amount output from the focus detection signal processing unit 125 and the reliability of the defocus amount. The determined lens drive amount is transmitted to the lens control unit 117 and further transmitted to the focus control unit 116, thereby realizing automatic focus adjustment. Also, the camera control unit 141 determines the accumulation time of the image sensor 121 based on an instruction from the operator or the magnitude of the imaging signal temporarily accumulated in the SDRAM 136 . Furthermore, the camera control unit 141 similarly determines the set value of the gain of the CDS/AGC/AD converter 123 and the set value of the timing generator 122 .

FIG. 2 is a diagram showing the configuration of the pixel array 200 in FIG. 1. As shown in FIG. In FIG. 2, the pixel array 200 has a plurality of imaging elements 121 arranged in rows and columns. Each imaging element 121 has two photodiodes (PDs) 202 a and 202 b as photoelectric conversion means, and the PDs 202 a and 202 b are covered with a single microlens 201 . A single microlens 201 passes incident light from the same object through different pupil regions and separates the light into two images having two different phase differences. Then, two images having different phase differences from the same subject which are spectroscopically separated are incident on the PDs 202a and 202b, respectively. Hereinafter, in the present embodiment, two images having different phase differences from the same object will be referred to as an A image and a B image, respectively. The PD 202a photoelectrically converts the A image to generate a signal, and the PD 202b photoelectrically converts the B image to generate a signal.

Next, shooting processing in the electronic still camera 101 will be described. FIG. 3 is a flow chart showing shooting processing executed by the electronic still camera 101 in FIG. The processing in FIG. 3 is executed by the lens control unit 117 and the camera control unit 141 according to a predetermined program stored in the ROM 137 or the like.

First, the state of the first SW 139 is determined (S301). If the first SW 139 is pressed (ON), the process proceeds to S302. If the first SW 139 is not pressed (OFF), the process returns to S301. Next, various parameters are initialized in preparation for filter determination processing in FIG. 8, which will be described later (S302). The details of the processing of S302 will be described later. After that, automatic exposure processing is performed based on the imaging signal output from the imaging signal processing unit 124 (S303). In automatic exposure processing in S303, the exposure conditions (shutter speed, aperture, sensitivity) for subsequent autofocus processing are determined.

Next, autofocus processing is performed (S304). The details of the processing of S304 will be described later. After that, the state of the second SW 140 is determined (S305). If the second SW 140 is pressed (ON), the process proceeds to S307. If the second SW 140 is not pressed (OFF), the process proceeds to S306. Next, in S306, the state of the first SW 139 is determined. If the first SW 139 is pressed (ON), the process returns to S305. If the first SW 139 is not pressed, the process returns to S301. After that, the exposure at the time of photographing is determined (S307), exposure control for the main exposure is performed (S308), then the photographing operation is performed (S309), and this processing ends.

FIG. 4 is a flowchart showing autofocus processing in S304 of FIG. In FIG. 4, focus detection processing is first performed (S401), the defocus amount is detected, and the reliability of the defocus amount is evaluated. Details of the focus detection process will be described later.

Next, it is determined whether or not the reliability of the defocus amount evaluated in the focus detection process is higher than a preset second reliability threshold (S402). If the reliability of the defocus amount is higher than the second reliability threshold, the process proceeds to S403, and if the reliability of the defocus amount is not higher than the second reliability threshold, the process proceeds to S409. Here, the case where the reliability of the defocus amount is not higher than the second reliability threshold means that the defocus amount is not reliable enough to be used for final focusing, but the focus position direction is It corresponds to the case where the defocus amount has sufficient reliability to be defined. Note that the focus position direction is the direction in which the lens should be driven for focusing.

Next, it is determined whether or not the defocus amount detected by the focus detection process is equal to or less than a preset second defocus amount threshold (S403). If the defocus amount is equal to or less than the second defocus amount threshold, the process proceeds to S404, and if the defocus amount is not equal to or less than the second defocus amount threshold, the process proceeds to S408. Here, when the defocus amount is equal to or less than the second defocus amount threshold, when the focus lens 114 is driven according to the defocus amount, the depth of focus can be reduced by driving within a predetermined number of times (for example, three times). This is the case where the focus lens 114 can be moved within. As the second defocus amount threshold, for example, a value five times the depth of focus is set.

Next, it is determined whether or not the reliability of the defocus amount evaluated in the focus detection process is higher than a preset first reliability threshold (S404). If the reliability of the defocus amount is higher than the first reliability threshold, the process proceeds to S405, and if the reliability of the defocus amount is not higher than the first reliability threshold, the process proceeds to S408. Here, the case where the reliability of the defocus amount is higher than the first reliability threshold corresponds to the case where the accuracy variation of the defocus amount is within a predetermined range (for example, within the depth of focus).

Next, it is determined whether or not the defocus amount detected by the focus detection process is equal to or less than a preset first defocus amount threshold (S405). If the defocus amount is equal to or less than the first defocus amount threshold, the process proceeds to S406, and if the defocus amount is not equal to or less than the first defocus amount threshold, the process proceeds to S407. Here, the case where the defocus amount is equal to or less than the first defocus amount threshold corresponds to the case where the focus lens 114 is positioned within the depth of focus. After that, in S406, it is determined that the subject is in focus, and the process ends.

In S407, the focus lens 114 is driven by a drive amount corresponding to the defocus amount detected in S401, and then the process returns to S401. In S408, the focus lens 114 is driven by a drive amount of a predetermined ratio to the defocus amount detected in S401, and then the process returns to S401. The predetermined ratio in S408 is a ratio (for example, 80%) at which the drive amount of the focus lens 114 is smaller than the defocus amount. Further, the driving speed of the focus lens 114 at this time is set lower than the moving speed corresponding to the distance that the focus lens 114 can move in the time corresponding to one frame, for example. As a result, for example, when the detected defocus amount is incorrect, it is possible to prevent the focus lens 114 from exceeding the in-focus position while the focus lens 114 is being driven.

In S409, it is determined whether or not the out-of-focus condition is satisfied. If the out-of-focus condition is satisfied, the process proceeds to S410, and if the out-of-focus condition is not satisfied, the process proceeds to S411. Here, the out-of-focus condition is a condition under which it is determined that there is no object to be focused. This corresponds to the case of returning to the initial position after detection. After that, in S410, it is determined that the subject is out of focus, and the process ends.

In S411, it is determined whether or not the focus lens 114 has reached the far side or near side lens end. If the focus lens 114 has reached the far side or near side lens end, the process proceeds to S412. On the other hand, if the focus lens 114 has not yet reached the far side or near side lens end, the process proceeds to S413. In S412, the driving direction of the focus lens 114 is reversed, and then the process returns to S401. In S413, the drive direction of the focus lens 114 is maintained, and then the process returns to S401. As the drive speed of the focus lens 114 at this time, for example, the upper limit of the drive speed of the focus lens 114 is set so that the focus lens 114 does not exceed the in-focus position when the defocus amount becomes detectable. .

FIG. 5 is a flowchart showing focus detection processing in S401 of FIG. In FIG. 5, first, an arbitrary range of focus detection areas is set in the pixel array 200 of the image pickup device 121 (S501), and a pair of image signals for focus detection from each of the image pickup devices 121 in the focus detection region is an A image signal. and B image signals (two-image signals) are acquired (S502).

Next, vertical row averaging processing is performed on each pair of acquired image signals (S503). By performing the row averaging process, the influence of noise on each image signal can be reduced. After that, filter processing is performed to extract components in a predetermined frequency band (hereinafter referred to as "frequency components") from the row-averaged signal (S504). In the present embodiment, in the filtering process of S504, a low-pass filter (first filter) for extracting a low-frequency component (first frequency component) and a high-frequency component (second frequency component) and a high-pass filter (second filter) that extracts . However, for convenience, any one of the three types of filters may be used by adding a mid-range filter for extracting a frequency component in the middle (middle range) between the low range and the high range.

Next, the amount of correlation is calculated from the signal acquired by the filtering process (S505), the amount of correlation change is calculated from the calculated amount of correlation (S506), and the amount of image shift is calculated from the calculated amount of correlation change. (S507). Thereafter, the defocus amount is calculated by multiplying the calculated image shift amount by the conversion coefficient (S508). The conversion coefficient is set in advance according to the position of the zoom lens, the aperture value, and the image height of the imaging plane, and is held by the electronic still camera 101 .

Next, the reliability indicating how reliable the calculated defocus amount is is evaluated (S509), and whether or not the reliability of the defocus amount is evaluated for all filters (low-pass filter and high-pass filter). is determined (S510). If the reliability of the defocus amount has been evaluated for all filters, the process advances to S512. If the reliability of the defocus amount has not been evaluated for all the filters, the process advances to S511. In S511, the filter used in the process is changed to a filter that has not been used in evaluating the reliability of the defocus amount (S511), and then the process returns to S504.

In S512, a filter for calculating the defocus amount used for conversion of the focus lens drive amount is determined from the filters used in S504. After that, this process is terminated.

By the way, as shown in FIG. 6A, for example, in a live view image 601 displayed on the display unit 133, when an image 603 of a flower and an image 604 of a dog, which are a plurality of subjects, exist within a focus detection area 602. think of. At this time, if the flower image 603 is closer to the focused state than the dog image 604, the image signal representing the horizontal component of any row in the focus detection area 602 is input as shown in FIG. A signal 611 is obtained. The left half of the input signal 611 corresponds to a flower image 603 that is close to being in focus, and a relatively finely fluctuating signal corresponding to the components of the detailed shape (for example, petals) of the flower image 603 appears. The right half of the input signal 611 corresponds to the far-out-of-focus dog image 604, and a relatively roughly fluctuating signal corresponding to the overall shape component of the dog image 604 appears.

When the input signal 611 is filtered using a low-pass filter, the component corresponding to the detailed shape of the flower image 603 close to the focused state is removed from the input signal 611, and the flower image 603 and the dog image 604 are removed. A low frequency component 612 that mainly contains the overall shape component is extracted. On the other hand, when the input signal 611 is filtered using a high-pass filter, components corresponding to the overall shapes of the flower image 603 and the dog image 604 are removed from the input signal 611 . As a result, a high-frequency component 613 that mainly includes the detailed shape component of the subject, particularly the detailed shape component of the flower image 603 in FIG. 6B, is extracted.

Therefore, the use of the low-pass filter makes it possible to roughly focus on the flower image 603 and the dog image 604, but it is difficult to precisely focus on any subject. On the other hand, if a high-pass filter is used, it is possible to precisely focus on any subject, especially the flower image 603 in FIG. 6B. Therefore, in the conventional focusing method, first, rough focusing is performed using the defocus amount of the low-pass component 612 extracted using the low-pass filter, and then the high-pass filter extracted using the high-pass filter. High-precision focusing is finally performed using the defocus amount of the area component 613 .

FIG. 7 is a graph for explaining normal focusing. In FIG. 7, the vertical axis indicates the defocus amount, and the horizontal axis indicates the position of the focus lens 114 (hereinafter simply referred to as "focus lens position").

FIG. 7 shows a relationship 701 between the defocus amount calculated using the low-pass filter and the focus lens position, and a relationship 702 between the defocus amount calculated using the high-pass filter and the focus lens position.

As mentioned above, the low pass filter allows the flower image 603 and the dog image 604 to be roughly focused. Therefore, in the relationship 701, the focus lens position 704 at which the defocus amount calculated using the low-pass filter (hereinafter referred to as "low-pass defocus amount") (first defocus amount) is "0" is , the center between the flower image 603 and the dog image 604 is the in-focus position.

Also, by using a high-pass filter, each subject can be focused with high accuracy. Therefore, in the relationship 702, the focus lens position 703 at which the defocus amount calculated using the high-pass filter (hereinafter referred to as "high-frequency defocus amount") (second defocus amount) is "0" is This is the position where the flower image 603 is in focus. In the relationship 702, another focus lens position 705 at which the high-frequency defocus amount is "0" is a position where the dog image 604 is in focus. Note that the relationship 702 also becomes “0” at the focus lens position 704 .

In the conventional focusing method, as described above, first, rough focusing is performed using the defocus amount of the low-pass component 612 extracted using the low-pass filter, and then extraction is performed using the high-pass filter. High-precision focusing is finally performed using the defocus amount of the high-frequency component 613 thus obtained.

Next, referring to FIG. 7, the case where the conventional focusing method is used and the focus detection processing of S401 is first performed at the focus lens position 710 will be described. In the focus detection process, as described above, the low-pass defocus amount is calculated using the low-pass filter, and the high-pass defocus amount is calculated using the high-pass filter. Here, the low-frequency defocus amount at the focus lens position 710 (point 706 in the relationship 701) is def1, and the high-frequency defocus amount at the focus lens position 710 (point 709 in the relationship 702) is def3.

In the conventional focusing method, when the difference (def1-def3) between the low-frequency defocus amount and the high-frequency defocus amount is larger than a predetermined value, first, rough focusing is performed using the low-frequency defocus amount. Specifically, the focus lens 114 is driven so that the low-frequency defocus amount becomes small.

After that, when the focus lens 114 is driven to the focus lens position 711 (the point 707 in the relationship 701 and the point 708 in the relationship 702), the low-frequency defocus amount changes to def2, and the high-frequency defocus amount changes to def4. . Here, when the difference between the low-frequency defocus amount and the high-frequency defocus amount (def2-def4) is equal to or less than a predetermined value, the conventional focusing method can then perform rough alignment using the high-frequency defocus amount. do the charcoal. Specifically, the focus lens 114 is driven so that the high-frequency defocus amount becomes small. When driving the focus lens 114 so as to reduce the high-frequency defocus amount, in FIG. 7, the focus lens 114 is driven either toward the focus lens position 704 or toward the focus lens position 703. can be considered. However, as described above, since the focus lens position 704 is a position where the center between the flower image 603 and the dog image 604 is in focus, the focus lens 114 is driven toward the focus lens position 703 .

After that, when the focus lens 114 is driven to the focus lens position 710 (the point 706 in the relationship 701 and the point 709 in the relationship 702), the difference (def1-def3) between the low-frequency defocus amount and the high-frequency defocus amount becomes a predetermined value. be larger than In that case, the conventional focusing method performs rough focusing again using the low-frequency defocus amount.

That is, in the conventional focusing method, when a photographed image includes a plurality of subjects and one of the subjects is closer to being in focus (when so-called "far and near competition" occurs), low-frequency defocusing is performed during focusing. Focusing using the focus amount and focusing using the high-frequency defocus amount are repeated. As a result, the final focused state is not achieved, and the focus lens 114 continues to be driven until the position of any subject changes, making it impossible to focus for a short period of time. In this embodiment, in response to this, repetition of focusing using the low-frequency defocus amount and focusing using the high-frequency defocus amount is suppressed.

FIG. 8 is a flow chart showing filter determination processing as a control method for the imaging apparatus according to the present embodiment. The processing in FIG. 8 is executed in S512 of the focus detection processing in FIG. 5, as described above.

In FIG. 8, first, it is determined whether the flag ENKIN_FLAG is TRUE or FALSE (S801). The flag ENKIN_FLAG is a flag indicating whether or not a near-far conflict has occurred. If it is TRUE, it indicates that a near-far conflict has occurred. If it is FALSE, it indicates that a near-far conflict has not occurred. . If it is determined that the flag ENKIN_FLAG is FALSE, the process proceeds to S802.

Next, in S802, filter selection processing for selecting whether to use the low-frequency defocus amount or the high-frequency defocus amount for focusing is performed. Details of the filter selection process will be described later. After that, in the filter selection process, the selection history (history information) of which filter was selected to calculate the defocus amount used for focusing is held in the SDRAM 136 (holding means) (S803). ).

FIG. 9 is a diagram showing the data structure of the selection history held in S803 of FIG. In this embodiment, either the data structure 901 shown in FIG. 9A or the data structure 902 shown in FIG. 9B may be used. In the data structure 901, when the filter selection process has been executed N times in the past, the filter selected in the filter selection process is held as history data each time the filter selection process is executed. Note that in data structure 901, the high pass filter is indicated by "HIGH_FILTER" and the low pass filter is indicated by "LOW_FILTER".

Also, in the data structure 902, when the filter selection process has been executed about N times in the past, whether or not the filter selected in the current filter selection process is the same as the filter selected in the previous filter selection process is stored in the history. Retained as data. In the data structure 902, "SAME_FILTER" indicates that the filter is the same as the filter selected in the previous filter selection process, and "SWITCH_FILTER" indicates that it is different from the filter selected in the previous filter selection process. .

In this embodiment, the case where the data structure 901 is used will be described below. Note that in the data structures 901 and 902, when the number of history data to be held exceeds N, the latest history data is held as the N-th history data, and the order of the other history data is decremented by one. , re-delete past historical data.

Returning to FIG. 8, it is determined whether or not the number of pieces of history data held by the data structure 901 is N (N is a natural number) or more (S804). If the number of pieces of history data to be held is less than N, it is determined that there is not enough information for determining whether or not a near-far conflict has occurred, and the filter determination process ends. If the number of history data to be held is N or more, the process advances to S805 to confirm filter switching. Specifically, the data structure 901 is referenced to check whether the filter selected in one filter selection process is changed in the subsequent filter selection process. For example, the K−1th history data and the Kth history data in the data structure 901 are compared. Note that 2≦K≦N. As a result, the number of times the filter has been switched in the filter selection process for the past N times is counted.

Next, in S806, it is determined whether or not the counted number of times of filter switching is equal to or greater than a predetermined value. If the counted number of filter switching times is equal to or greater than a predetermined value, it is determined that a near-far conflict is occurring, and the flag ENKIN_FLAG is set to TRUE (S807). On the other hand, if the counted number of filter switching times is less than the predetermined value, it is determined that near-far conflict has not occurred, and the filter determination process is terminated.

If it is determined in S801 that the flag ENKIN_FLAG is TRUE and near-far conflict is occurring, the process proceeds to S808. In S808, the reliability of the high-pass filter is determined. Specifically, it is determined whether the reliability of the high-frequency defocus amount is equal to or greater than a predetermined value and whether the high-frequency defocus amount is equal to or less than a predetermined value.

When the reliability of the high-frequency defocus amount is equal to or higher than a predetermined value and the high-frequency defocus amount is equal to or lower than the predetermined value, it is determined that the high-pass filter is reliable and used for final focusing. A high-frequency defocus amount is selected as the defocus amount (S809). After that, the filter determination process is terminated. On the other hand, if the reliability of the high-frequency defocus amount is less than the predetermined value, or if the high-frequency defocus amount is greater than the predetermined value, it is determined that the high-pass filter is unreliable, and final focusing is performed. A low-frequency defocus amount is selected as the defocus amount used for (S810). After that, the filter determination process is terminated.

Note that in the initialization of various parameters in S302 described above, the flag ENKIN_FLAG is initialized to set FALSE, and the data structure 901 is also initialized.

FIG. 10 is a flowchart showing filter selection processing in S802 of FIG. In FIG. 10, first, the difference between the low-frequency defocus amount and the high-frequency defocus amount (hereinafter referred to as "defocus amount difference") is calculated, and it is determined whether or not the difference is equal to or less than a threshold value (S1001). If the defocus amount difference is equal to or less than the threshold, the reliability of the high-frequency defocus amount is determined (S1002).

Specifically, in S1002, it is determined whether or not the reliability of the high-frequency defocus amount is higher than or equal to the reliability of the low-frequency defocus amount and the reliability of the high-frequency defocus amount is not at the impossible level. If the reliability of the high-range defocus amount is greater than or equal to the reliability of the low-range defocus amount, and the reliability of the high-range defocus amount is not at the impossible level, the high-range defocus amount is used for focusing. Quantity is selected (S1003). On the other hand, if the reliability of the high-frequency defocus amount is less than the same as the reliability of the low-frequency defocus amount, or if the reliability of the high-frequency defocus amount is at an impossible level, the defocus used for focusing A low-frequency defocus amount is selected as the focus amount (S1004). After that, the filter selection process ends.

In the present embodiment, when a photographed image includes a plurality of subjects, focusing is performed while driving the focus lens 114. In this focusing, for example, each time the focus lens 114 moves by a predetermined amount, 4 autofocus processing is executed. Each time the autofocus process of FIG. 4 is executed, the filter determination process of FIG. 8 is executed, and if the number of filter switching times is less than the threshold, the defocus amount used for focusing is changed according to the defocus amount difference. be. On the other hand, even if the defocus amount difference changes from less than the threshold to more than the threshold after the number of times of filter switching becomes equal to or more than the threshold, or changes from more than the threshold to less than the threshold, the filter selection process of S802 is not executed. The defocus amount used for focus is not changed. That is, the method of selecting the defocus amount used for focusing is changed, and the repetition of focusing using the low-range defocus amount and focusing using the high-range defocus amount, indicated by points 706 to 709 in FIG. does not occur. This prevents the focus lens 114 from being continuously driven, and allows focusing in a short period of time.

Note that the threshold for the number of filter switching times used in S<b>806 may be changed according to the imaging state of the electronic still camera 101 . For example, when the threshold value is small, the number of filter switching times decreases. is likely to occur. Therefore, when it is difficult for the electronic still camera 101 to obtain an in-focus state, the camera control unit 141 increases the threshold for the number of filter switching times to prevent the number of filter switching times from becoming smaller than necessary. For example, when the brightness of the subject image is less than or equal to a predetermined value, when the contrast of the subject image is less than or equal to a predetermined value, or when the aperture value when the imaging device 121 generates a pair of image signals is smaller than a predetermined value. , the camera control unit 141 increases the threshold for the number of filter switching times. Also, for example, when the focus detection area in the captured image is away from the center of the optical axis by a predetermined amount or more, or when the subject is a moving object, the camera control unit 141 increases the threshold for the number of filter switching times.

Next, a second embodiment of the invention will be described. The second embodiment is basically the same as the above-described first embodiment in terms of its configuration and action, so the duplicated configuration and action will be omitted, and the different configuration and action will be described below. Give an explanation. In the second embodiment, the threshold value of the defocus amount difference is changed depending on whether or not the near-far conflict occurs, and even if the number of filter switching times exceeds the threshold value, the filter selection process is not skipped. It differs from the first embodiment in that respect.

FIG. 11 is a flow chart showing filter determination processing as a control method of the imaging apparatus according to the present embodiment. The process of FIG. 11 is also executed in S512 of the focus detection process of FIG. 5, like the process of FIG.

In FIG. 11, first, it is determined whether the flag ENKIN_FLAG is TRUE or FALSE (S801). If it is determined that the flag ENKIN_FLAG is FALSE, the threshold (reference) of the defocus amount difference is set to TH1, and the process proceeds to S802 (S1101). On the other hand, if it is determined that the flag ENKIN_FLAG is TRUE, the threshold (reference) of the defocus amount difference is set to TH2, and the process proceeds to S802 (S1102). In the present embodiment, a relationship of threshold TH1<threshold TH2 is set. That is, when a near-far conflict occurs, the high-frequency defocus amount is preferentially used in focusing. Thereby, focusing can be performed with high precision. Further, when a near-far conflict occurs, switching from the high-pass filter to the low-pass filter is suppressed. As a result, continuous driving of the focus lens 114 is suppressed, and focusing can be performed in a short time. can be done.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist thereof. For example, the present invention supplies a program that implements one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and one or more processors of a computer of the system or device executes the program. It is also possible to implement the process of reading and executing the The invention can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

101 Electronic still camera 117 Lens control unit 121 Image sensor 141 Camera control units 202a, 202b Photodiodes 901, 902 Data structure

Claims (16)

signal generating means for generating signals of two images respectively corresponding to a pair of light beams from a subject that have passed through mutually different pupil regions of a focus lens;
A first filter for extracting a signal of a first frequency component from the two images, and a second filter for extracting a signal of a second frequency component, which is a higher frequency component than the first frequency component, from the two images. a signal extraction means having a filter of
A first defocus amount is calculated based on the phase difference between the signals extracted from the two images by the first filter, and based on the phase difference between the signals extracted from the two images by the second filter. defocus amount calculation means for calculating a second defocus amount by
Either the first defocus amount or the second defocus amount is selected as a defocus amount to be used for focusing based on a difference between the first defocus amount and the second defocus amount. a selection means;
Checking the number of times the defocus amount used for focusing is switched from the first defocus amount to the second defocus amount or from the second defocus amount to the first defocus amount. and a confirmation means for
The image pickup apparatus, wherein the selection means changes a selection method of the defocus amount used for the focusing when the number of times of switching is equal to or greater than a predetermined threshold. When the reliability of the second defocus amount is equal to or higher than the reliability of the first defocus amount, and the difference between the first defocus amount and the second defocus amount is equal to or less than a predetermined value. 2. The imaging apparatus according to claim 1, wherein said selection means selects said second defocus amount as the defocus amount used for said focusing. When the number of times of switching is equal to or greater than a predetermined threshold, the reliability of the second defocus amount is equal to or greater than a predetermined value, and the second defocus amount is equal to or less than a predetermined value, the selecting means 3. The imaging apparatus according to claim 1, wherein the second defocus amount is selected as the defocus amount used for the focusing. If the number of times of switching is equal to or greater than a predetermined threshold and the reliability of the second defocus amount is less than a predetermined value, or if the second defocus amount is greater than a predetermined value, the selecting means 4. The imaging apparatus according to any one of claims 1 to 3, wherein said first defocus amount is selected as a defocus amount used for said focusing. 5. The imaging apparatus according to any one of claims 1 to 4, further comprising initialization means for initializing history information regarding selection of a defocus amount used for said focusing before focusing. . Determining whether to switch the defocus amount used for focusing from the first defocus amount to the second defocus amount or from the second defocus amount to the first defocus amount Further comprising holding means for holding the number of times the
6. The imaging apparatus according to any one of claims 1 to 5, characterized in that, when the number of said determinations held by said holding means is equal to or greater than a predetermined value, said confirmation means confirms said number of times of switching. . The holding means holds the first filter and the second defocus amount based on whether the defocus amount used for the focusing is the first defocus amount or the second defocus amount. 7. The image pickup apparatus according to claim 6, wherein a history of whether any one of the filters of 1 is used for said focusing is held. 8. The imaging apparatus according to claim 7, wherein said holding means holds a history indicating whether or not the filter used for previous focusing is the same as the filter used for focusing this time. Further comprising changing means for changing the predetermined threshold,
9. The imaging apparatus according to any one of claims 1 to 8, wherein when the brightness of the image of the subject is equal to or less than a predetermined value, the changing unit increases the predetermined threshold value. Further comprising changing means for changing the predetermined threshold,
10. The imaging apparatus according to any one of claims 1 to 9, wherein when the contrast of the image of the subject is equal to or less than a predetermined value, the changing means increases the predetermined threshold value. Further comprising changing means for changing the predetermined threshold,
11. The changing unit increases the predetermined threshold value when the aperture value at which the signal generation unit generates the signals of the two images is smaller than a predetermined value. 10. The image pickup device according to claim 1. Further comprising changing means for changing the predetermined threshold,
12. The imaging according to any one of claims 1 to 11, wherein when the focus detection areas in the two images are separated from the center of the optical axis by a predetermined amount or more, the changing means increases the predetermined threshold value. Device. Further comprising changing means for changing the predetermined threshold,
13. The imaging apparatus according to any one of claims 1 to 12, wherein when the subject is a moving body, the changing unit increases the predetermined threshold. When the number of times of switching is equal to or greater than a predetermined threshold, the selection means
A difference between the first defocus amount and the second defocus amount, which is a reference for selecting which one of the first defocus amount and the second defocus amount is used for focusing. 14. The image pickup apparatus according to any one of claims 1 to 13, wherein the image pickup apparatus is changed. a signal generating step of generating signals of two images respectively corresponding to a pair of light beams from a subject that have passed through mutually different pupil regions of a focus lens;
A first filter for extracting a signal of a first frequency component from the two images, and a second filter for extracting a signal of a second frequency component, which is a higher frequency component than the first frequency component, from the two images. a signal extraction step of extracting signals from said two images by means of a filter of 2;
A first defocus amount is calculated based on the phase difference between the signals extracted from the two images by the first filter, and based on the phase difference between the signals extracted from the two images by the second filter. a defocus amount calculation step of calculating a second defocus amount with
Either the first defocus amount or the second defocus amount is selected as a defocus amount to be used for focusing based on a difference between the first defocus amount and the second defocus amount. a selection step;
Checking the number of times the defocus amount used for focusing is switched from the first defocus amount to the second defocus amount or from the second defocus amount to the first defocus amount. and a confirmation step to
A control method for an imaging device, wherein when the number of times of switching is equal to or greater than a predetermined threshold, in the selecting step, a method of selecting a defocus amount used for focusing is changed. A program for causing a computer to execute a control method for an imaging device,
The control method of the imaging device includes:
a signal generating step of generating signals of two images respectively corresponding to a pair of light beams from a subject that have passed through mutually different pupil regions of a focus lens;
A first filter for extracting a signal of a first frequency component from the two images, and a second filter for extracting a signal of a second frequency component, which is a higher frequency component than the first frequency component, from the two images. a signal extraction step of extracting signals from said two images by means of a filter of 2;
A first defocus amount is calculated based on the phase difference between the signals extracted from the two images by the first filter, and based on the phase difference between the signals extracted from the two images by the second filter. a defocus amount calculation step of calculating a second defocus amount with
Either the first defocus amount or the second defocus amount is selected as a defocus amount to be used for focusing based on a difference between the first defocus amount and the second defocus amount. a selection step;
Checking the number of times the defocus amount used for focusing is switched from the first defocus amount to the second defocus amount or from the second defocus amount to the first defocus amount. and a confirmation step to
A program characterized in that, in the selecting step, a method of selecting a defocus amount used for focusing is changed when the number of times of switching is equal to or greater than a predetermined threshold.

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