Focus control device, focus control method, and program

Abstract

This invention provides a focus control device, a focus control method, and a program that enable suppression of image quality degradation due to focus drive when multiple images are taken in succession. [Solution] The focus control device of the present disclosure is a focus control device comprising a processor, wherein when a portion of the image sensor corresponding to a specific area in an captured image is exposed, the processor performs at least one of the following controls: a first control that sets the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less.

Description

Technical Field

[0001] The technology of the present disclosure relates to a focus control device, a focus control method, and a program.

Background Art

[0002] The focus control device described in Patent Document 1 sets a partial area in one imaging screen as a detection area, and performs detection only on the exposure period corresponding to the detection area from a CMOS sensor with exposure by a rolling shutter method to obtain an evaluation value, and moves a focus lens to the lens position for the next evaluation value sample acquisition. At this time, since the detection area is a partial area of one imaging screen, a long time can be ensured for the pause period between the corresponding detection periods every two horizontal synchronization periods. By setting the timing to move the focus lens during this pause period, it is possible to execute evaluation value acquisition and focus lens movement at the timing every one horizontal synchronization period.

[0003] The imaging system described in Patent Document 2 acquires an image sequence including at least two images, at least one of which is used as a measurement image and at least one of which is used as a final image, and determines an exposure time for the measurement image and an exposure time for the final image. The non-exposure time can be determined based on the exposure time for the measurement image and the exposure time for the final image. As a result, the imaging optical system can be adjusted during the non-exposure time.

[0004] The imaging device described in Patent Document 3 comprises: an imaging means having a focus lens with a variable focal length; an exposure control means for realizing multiple images with different sensitivities; a camera signal processing means for generating video signals and focus evaluation values ​​indicating the degree of focus; an image synthesis means for synthesizing and outputting multiple video signals with different sensitivities generated by the camera signal processing means; and a focus control means for controlling the focus lens of the imaging means and adjusting the focal length based on the focus evaluation values ​​output by the camera signal processing means. The camera signal processing means generates a focus evaluation value for each of the multiple image signals with different sensitivities output by the imaging means, and the focus control means controls the focus lens based on the corresponding focus evaluation values ​​for each of the multiple images with different sensitivities of the imaging means. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-243527 [Patent Document 2] Japanese Patent Publication No. 2009-516448 [Patent Document 3] Japanese Patent Publication No. 2013-106113 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technology disclosed herein provides a focus control device, a focus control method, and a program that enable suppression of image quality degradation due to focus drive when multiple images are taken in succession. [Means for solving the problem]

[0007] To achieve the above objective, the focus control device of this disclosure is a focus control device comprising a processor, wherein when a portion of the image sensor corresponding to a specific area in an captured image is exposed, the processor performs at least one of the following controls: a first control that sets the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less.

[0008] It is preferable that the image sensor uses a rolling shutter method for exposure.

[0009] It is preferable for the image sensor to perform multiple exposures in response to a single imaging instruction.

[0010] The processor preferably performs focus drive over a period of time during which multiple exposures are performed.

[0011] Preferably, the processor acquires the focus drive amount and executes a second control when the change in depth of field corresponding to the acquired focus drive amount is greater than a predetermined value.

[0012] The predetermined speed is preferably the focus drive speed when the focus drive is performed with a focus drive amount corresponding to a predetermined value.

[0013] Preferably, the image sensor includes multiple phase-difference detection pixels, and the processor calculates the focus drive amount based on the defocus amount determined based on the output values ​​of the multiple phase-difference detection pixels.

[0014] In addition to the first or second control, the processor preferably performs a third control, which drives the focus during the non-exposure period obtained by shifting the exposure timing.

[0015] In the third control, it is preferable for the processor to perform focus driving at a focus driving speed greater than a predetermined speed.

[0016] The specific area is preferably the area to be focused on.

[0017] The specific area may be an area including a specific subject.

[0018] The focus control method of the present disclosure includes executing at least one of a first control for making the focus driving speed constant and a second control for limiting the focus driving speed to a predetermined speed or less when the processor exposes a part of the imaging element corresponding to a specific area in the captured image.

[0019] The program of the present disclosure causes the processor to execute a process including executing at least one of a first control for making the focus driving speed constant and a second control for limiting the focus driving speed to a predetermined speed or less when exposing a part of the imaging element corresponding to a specific area in the captured image.

Brief Description of the Drawings

[0020] [Figure 1] It is a diagram showing an example of the configuration of the imaging device. [Figure 2] It is a diagram showing an example of the light receiving surface of the imaging element. [Figure 3] It is a block diagram showing an example of the functional configuration of the processor. [Figure 4] It is a diagram conceptually showing an example of the distance measurement process by the distance measurement unit. [Figure 5] It is a flowchart showing an example of the flow of focus control. [Figure 6] It is a diagram showing an example of various timings related to focus control. [Figure 7] It is a flowchart showing an example of the flow of focus control according to the second embodiment. [Figure 8] It is a flowchart showing an example of the flow of the process for determining the limit speed. [Figure 9] It is a diagram showing an example of the amount of change in the depth of field of view when the subject distance is short. [Figure 10] It is a diagram showing an example of the amount of change in the depth of field of view when the subject distance is large. [Figure 11] This figure shows an example of various timings related to focus control according to the second embodiment. [Figure 12] This figure shows an example of various timings in the third control. [Modes for carrying out the invention]

[0021] An example of an embodiment relating to the technology of this disclosure will be described with reference to the attached drawings.

[0022] First, let's explain the terminology used in the following explanation.

[0023] In the following explanation, "AF" is an abbreviation for "Auto Focus". "MF" is an abbreviation for "Manual Focus". "IC" is an abbreviation for "Integrated Circuit". "CPU" is an abbreviation for "Central Processing Unit". "ROM" is an abbreviation for "Read Only Memory". "RAM" is an abbreviation for "Random Access Memory". "CMOS" is an abbreviation for "Complementary Metal Oxide Semiconductor". "OVF" is an abbreviation for "Optical View Finder". "EVF" is an abbreviation for "Electronic View Finder".

[0024] As one embodiment of the imaging device, the technology of this disclosure will be explained using a lens-interchangeable digital camera as an example. However, the technology of this disclosure is not limited to lens-interchangeable cameras, but can also be applied to lens-integrated digital cameras.

[0025] [First Embodiment] Figure 1 shows an example of the configuration of the imaging device 10. The imaging device 10 is a lens-interchangeable digital camera. The imaging device 10 consists of a main body 11 and an imaging lens 12 which is interchangeably attached to the main body 11 and includes a focus lens 31. The imaging lens 12 is attached to the front side of the main body 11 via a camera-side mount 11A and a lens-side mount 12A.

[0026] The main unit 11 is provided with an operating section 13, which includes a dial, a shutter release button, and the like. The operating modes of the shooting device 10 include, for example, still image shooting mode, continuous shooting mode, video shooting mode, and image display mode. The operating section 13 is operated by the user when setting the operating mode. The operating section 13 is also operated by the user when starting still image shooting, continuous shooting, or video shooting.

[0027] Furthermore, the control unit 13 is operated by the user when selecting a focus mode. There are two focus modes: AF mode and MF mode. AF mode is a mode in which the focus is automatically controlled for the focus target area (hereinafter referred to as the AF area) within the angle of view. The user can set the AF area within the angle of view using the control unit 13. MF mode is a mode in which the user manually controls the focus by operating the focus ring (not shown). The shooting device 10 may also be configured to allow the user to set the AF area via a display 15 with touch panel functionality or a viewfinder 14 with eye-tracking functionality.

[0028] Furthermore, the main body 11 is equipped with a viewfinder 14. Here, the viewfinder 14 is a hybrid viewfinder (registered trademark). A hybrid viewfinder refers to a viewfinder in which, for example, an optical viewfinder (hereinafter referred to as "OVF") and an electronic viewfinder (hereinafter referred to as "EVF") are selectively used. The user can observe the optical image or live view image of the subject projected by the viewfinder 14 through the viewfinder eyepiece (not shown).

[0029] Furthermore, a display 15 is provided on the back of the main unit 11. The display 15 shows images based on image data obtained through shooting, as well as various menu screens, etc. The user can also observe the live view image displayed on the display 15 instead of the viewfinder 14.

[0030] The main unit 11 and the photographic lens 12 are electrically connected by contact between an electrical contact 11B provided on the camera-side mount 11A and an electrical contact 12B provided on the lens-side mount 12A.

[0031] The photographic lens 12 includes an objective lens 30, a focusing lens 31, a rear-end lens 32, and an aperture 33. Each component is arranged along the optical axis A of the photographic lens 12, from the objective side, in the order of objective lens 30, aperture 33, focusing lens 31, and rear-end lens 32. The objective lens 30, focusing lens 31, and rear-end lens 32 constitute an optical system. The type, number, and arrangement order of the lenses constituting the optical system are not limited to the example shown in Figure 1.

[0032] Furthermore, the photographic lens 12 has a lens drive unit 34. For example, the lens drive unit 34 includes a stepping motor that moves the focus lens 31 in the direction of the optical axis A, and a driver that supplies pulses to the stepping motor. The stepping motor moves the focus lens 31 in accordance with the pulses supplied from the driver.

[0033] The lens drive unit 34 is electrically connected to the processor 40 in the main body 11. The lens drive unit 34 drives the focus lens 31 based on control signals transmitted from the processor 40. The lens drive unit 34 drives the focus lens 31 based on focus control signals transmitted from the processor 40 to adjust the position of the focus lens 31.

[0034] Furthermore, the main unit 11 houses an image sensor 20, a processor 40, and a memory 42. The image sensor 20, memory 42, control unit 13, viewfinder 14, and display 15 are all controlled by the processor 40.

[0035] The processor 40 is composed of, for example, a CPU, RAM, ROM, etc. In this case, the processor 40 performs various processes based on a program 43 stored in memory 42. The processor 40 may also be composed of an assembly of multiple IC chips.

[0036] The image sensor 20 is, for example, a CMOS type image sensor. The image sensor 20 is arranged such that the optical axis A is perpendicular to the light-receiving surface 20A and the optical axis A is located at the center of the light-receiving surface 20A. Light that has passed through the imaging lens 12 is incident on the light-receiving surface 20A. Multiple pixels are formed on the light-receiving surface 20A, which generate an imaging signal by performing photoelectric conversion. The image sensor 20 generates and outputs image data PD (hereinafter simply referred to as image data PD) by performing photoelectric conversion on the light incident on each pixel.

[0037] Furthermore, a Bayer-type color filter array is arranged on the light-receiving surface 20A of the image sensor 20, with one of the R (red), G (green), or B (blue) color filters positioned opposite each pixel. Some of the multiple pixels arranged on the light-receiving surface of the image sensor 20 are phase-difference detection pixels that output a phase-difference detection signal.

[0038] Figure 2 shows an example of the light-receiving surface 20A of the image sensor 20. Multiple imaging pixels 21 and multiple phase-difference detection pixels 22 are arranged on the light-receiving surface 20A. The imaging pixels 21 are pixels on which the above-mentioned color filters are placed. The imaging pixels 21 receive the light beam that passes through the entire area of ​​the exit pupil of the imaging optical system. The phase-difference detection pixels 22 receive the light beam that passes through half the area of ​​the exit pupil of the imaging optical system. In the example shown in Figure 2, some of the G pixels arranged diagonally in the Bayer array are replaced with phase-difference detection pixels 22. The phase-difference detection pixels 22 are arranged at regular intervals in the vertical and horizontal directions on the light-receiving surface 20A. The phase-difference detection pixels 22 are divided into first phase-difference detection pixels that receive the light beam that passes through half the area of ​​the exit pupil and second phase-difference detection pixels that receive the light beam that passes through the other half of the area of ​​the exit pupil.

[0039] Multiple imaging pixels 21 output imaging signals to generate an image of the subject. Multiple phase difference detection pixels 22 output phase difference detection signals. The captured image PD output from the image sensor 20 includes the imaging signal and the phase difference detection signal. The phase difference detection signal corresponds to the "output value of the phase difference detection pixel" related to the technology of this disclosure.

[0040] The image sensor 20 has an electronic shutter function and performs exposure using a rolling shutter method. In the rolling shutter method, pixels arranged in a matrix as shown in Figure 2 are scanned line by line. For example, one horizontal line is selected, and the pixel values ​​are read out sequentially from this horizontal line. The pixels whose values ​​have been read are reset, and exposure is resumed. Subsequently, the next horizontal line adjacent to the above horizontal line is selected, and the pixel values ​​are read out and reset in the same manner. In other words, the rolling shutter method is a "line exposure sequential readout method" in which exposure is performed for each horizontal line. In the rolling shutter method, the exposure period is the time from when the reset is performed for each horizontal line until the pixel value is read out, and the exposure period is shifted by one horizontal line at a time.

[0041] Figure 3 shows an example of the functional configuration of the processor 40. The processor 40 implements various functional units by executing processing according to the program 43 stored in the memory 42. As shown in Figure 3, for example, the processor 40 implements a main control unit 50, an imaging control unit 51, an image processing unit 52, a display control unit 53, an image recording unit 54, and a distance measuring unit 55. The distance measuring unit 55 operates when the AF mode is set.

[0042] The main control unit 50 comprehensively controls the operation of the imaging device 10 based on instruction signals input from the operation unit 13. The imaging control unit 51 controls the image sensor 20 to perform an imaging process that causes the image sensor 20 to generate an image PD. The imaging control unit 51 drives the image sensor 20 in still image shooting mode, continuous shooting mode, or video shooting mode. The image sensor 20 outputs the image PD generated by imaging through the imaging lens 12. The image PD output from the image sensor 20 is supplied to the image processing unit 52 and the distance measuring unit 55.

[0043] The image processing unit 52 acquires the captured image PD output from the image sensor 20 and performs image processing on the captured image PD, including white balance adjustment and gamma correction.

[0044] The display control unit 53 displays the captured image PD, which has been processed by the image processing unit 52, as a live view image on the display 15. When the release button is fully pressed, the image recording unit 54 records the captured image PD, which has been processed by the image processing unit 52, as a recorded image PR in the memory 42.

[0045] The distance measuring unit 55 determines the distance from the image sensor 20 to the subject within the AF area and outputs a distance measurement value. Specifically, the distance measuring unit 55 acquires multiple phase difference detection signals from the AF area of ​​the captured image PD output from the image sensor 20, and outputs the distance determined based on the acquired multiple phase difference detection signals as a distance measurement value. The distance measurement value corresponds to the defocus amount, which represents the amount of deviation from the focus position of the focus lens 31.

[0046] Furthermore, if a subject detection function is provided, the distance measuring unit 55 may define the area containing a specific subject detected by subject detection as the AF area, calculate the distance to the subject included in the AF area, and output a distance measurement value. The type of subject detected by subject detection is, for example, a human face.

[0047] The main control unit 50 moves the focus lens 31 via the lens drive unit 34 based on the distance measurement value output from the distance measurement unit 55, thereby bringing the subject included in the AF area into focus. In this embodiment, the main control unit 50 performs focus control using a phase difference detection method. The main control unit 50 is an example of a "focus control device" according to the technology of this disclosure. Hereinafter, moving the focus lens 31 will be referred to as "focus driving".

[0048] Figure 4 conceptually shows an example of distance measurement processing by the distance measuring unit 55. In Figure 4, reference numeral 60 denotes the AF area. For example, the AF area 60 is rectangular in shape. The distance measuring unit 55 acquires multiple phase difference detection signals from the AF area 60 to determine the distance value, and then outputs the distance value. The AF area 60 is an example of a "specific area" related to the technology of this disclosure.

[0049] When multiple images are captured consecutively, such as in continuous shooting or video recording, focus drive may occur during the exposure of the image sensor 20. As mentioned above, in the rolling shutter method, the exposure period differs for each horizontal line, so if focus drive occurs during exposure, the focus position will differ for each horizontal line. This degrades image quality.

[0050] To suppress this image quality degradation, it is conceivable to perform focus drive during the non-exposure period between the end of one exposure and the start of the next. However, in high-frame-rate continuous shooting or video recording, a non-exposure period may not be available, in which case focus drive cannot be performed, and focus tracking of the AF target subject cannot be performed. The technology of this disclosure performs focus drive while minimizing image quality degradation caused by focus drive when multiple images are taken in succession.

[0051] Figure 5 shows an example of the focus control flow by the main control unit 50. Figure 5 shows the case when the AF mode is set in continuous shooting mode or video shooting mode.

[0052] The main control unit 50 acquires the distance measurement value generated when the distance measuring unit 55 measures the distance based on the captured image PD output from the image sensor 20, which is captured by the image sensor 20 (step S10). Specifically, the main control unit 50 acquires the distance measurement value output from the distance measuring unit 55 at each vertical synchronization period (1V).

[0053] Next, the main control unit 50 obtains the focus drive amount by predicting the distance of the subject after a predetermined time based on a plurality of distance measurement values ​​acquired in the past (step S11). The focus drive amount is the amount of movement of the focus lens 31 from its current position required to focus on the subject to be AF after a predetermined time.

[0054] Next, the main control unit 50 starts the focus drive (step S12). Specifically, the main control unit 50 moves the focus lens 31 in the direction in which the subject to AF is in focus, at a focus drive speed corresponding to the amount of focus drive. The focus drive speed is the speed at which the focus lens 31 moves when it is driven.

[0055] Next, the main control unit 50 determines whether or not a portion of the image sensor 20 corresponding to the AF area 60, which is an example of the specific region described above (see Figure 6), is currently being exposed (step S13). Specifically, the portion of the SR is the region within the light-receiving surface 20A that corresponds to the AF area 60 (specific region).

[0056] If the partial SR of the image sensor 20 is not being exposed (step S13: NO), the main control unit 50 proceeds to step S15. On the other hand, if the partial SR of the image sensor 20 is being exposed (step S13: YES), the main control unit 50 sets the focus drive speed to a constant value (step S14). Setting the focus drive speed to a constant value means keeping the rate of change of the movement speed of the focus lens 31 within a certain range. Thus, the control that sets the focus drive speed to a constant value when exposing a partial SR of the image sensor 20 corresponding to a specific area in the captured image PD corresponds to the "first control" in the technology of this disclosure.

[0057] Next, the main control unit 50 determines whether the amount of movement of the focus lens 31 has reached the focus drive amount acquired in step S11 (step S15). If the amount of movement has not reached the focus drive amount (step S15: NO), the main control unit 50 returns to step S13 and continues the focus drive. On the other hand, if the amount of movement has reached the focus drive amount (step S15: YES), the main control unit 50 terminates the focus drive (step S16).

[0058] Next, the main control unit 50 determines whether or not the termination condition is met (step S17). For example, the termination condition is that the mode has been switched, and if the mode has been switched, the termination condition is met. If the termination condition is not met (step S17: NO), the main control unit 50 returns to step S10. On the other hand, if the termination condition is met (step S17: YES), the main control unit 50 terminates the process.

[0059] Figure 6 shows an example of various timings related to focus control. As shown in Figure 6, in this embodiment, the image sensor 20 performs multiple exposures in response to a single imaging instruction, and the main control unit 50 performs focus driving over the period during which multiple exposures are performed.

[0060] As shown in Figure 6, the exposure timing shifts by one horizontal line. Exposure is performed every vertical sync period (1V). The predicted timing is the timing at which the focus drive amount is obtained by predicting the distance of the subject after a predetermined time. In the example shown in Figure 6, the distance of the subject after three vertical sync periods (3V) is predicted.

[0061] In the example shown in Figure 6, the main control unit 50 keeps the focus drive speed constant during the period Ts in which a portion of the image sensor 20 corresponding to a specific area is exposed, from the start time t1 to the end time t2 of focus driving, and changes the focus drive speed during the other periods. Note that the main control unit 50 only needs to keep the focus drive speed constant during at least the period Ts, and may keep the focus drive speed constant during the other periods as well.

[0062] Furthermore, in the example shown in Figure 6, the timing and length of period Ts are constant, but the timing or length of period Ts may change. For example, if the position or size of the AF area 60 is changed, the position or size of the partial SR of the image sensor 20 corresponding to a specific area changes, and the timing or length of period Ts changes accordingly.

[0063] As described above, in this embodiment, when exposing a partial SR of the image sensor 20 corresponding to a specific area within the captured image PD, a first control is performed to keep the focus drive speed constant, thereby suppressing image quality degradation of specific areas of high importance within the captured image PD. As a result, image quality degradation of the captured image PD is kept to a minimum. In other words, according to this embodiment, when multiple images are taken in succession, focus driving can be performed while minimizing image quality degradation due to focus driving.

[0064] [Second Embodiment] Next, a second embodiment of the present disclosure will be described. This embodiment differs from the first embodiment only in the focus control by the main control unit 50.

[0065] Figure 7 shows an example of the focus control flow by the main control unit 50 according to the second embodiment. Figure 7 shows the case when the AF mode is set in continuous shooting mode or video shooting mode.

[0066] The focus control according to this embodiment is the same as that of the first embodiment, except that step S20 is added between step S11 and step S12, and the processing content of step S14 is different.

[0067] In this embodiment, the main control unit 50 acquires the focus drive amount in step S11 and then determines the limit speed based on the acquired focus drive amount (step S20). In this embodiment, the main control unit 50 sets the focus drive speed to a limit speed or less in step S14. That is, in this embodiment, the main control unit 50 performs a second control that limits the focus drive speed to a predetermined speed or less, instead of the first control described in the first embodiment. The predetermined speed corresponds to the limit speed determined in step S20.

[0068] Even if the focus drive amount is the same, the amount of change in depth of field differs depending on the current subject distance. Subject distance refers to the distance from the image sensor 20 to the subject targeted by AF. Depth of field has the characteristic that it increases as the subject distance increases and the rate of change decreases. Since a large change in depth of field during focus drive leads to significant image quality degradation, in this embodiment, the focus drive speed is limited based on the amount of change in depth of field estimated by the focus drive.

[0069] Figure 8 shows an example of the process for determining the speed limit (step S20). The main control unit 50 calculates the change in depth of field D corresponding to the focus drive amount acquired in step S11 (step S21). For example, the main control unit 50 calculates the change in depth of field D corresponding to the focus drive amount (corresponding to the change in subject distance M shown in Figures 9 and 10) based on data representing the relationship between depth of field and subject distance (see Figures 9 and 10) that is pre-stored in the memory 42.

[0070] Next, the main control unit 50 determines whether the change amount D calculated in step S21 is greater than a predetermined value Di (step S22). For example, the predetermined value Di is the amount of change in depth of field that is allowed during the focus drive period (the period from t1 to t2). Specifically, the predetermined value Di is a value that represents how many times the current depth of field can be allowed.

[0071] If the change amount D is less than or equal to a predetermined value Di (step S22: NO), the main control unit 50 proceeds to step S24. On the other hand, if the change amount D is greater than the predetermined value Di (step S22: YES), the focus drive amount is recalculated based on the predetermined value Di (step S23). Specifically, the main control unit 50 calculates the focus drive amount corresponding to the change in subject distance Mi (see Figure 9) such that the change in depth of field from the current point in time becomes the predetermined value Di.

[0072] Next, the main control unit 50 calculates the speed limit corresponding to the focus drive amount (or the recalculated focus drive amount if it was recalculated in step S23) (step S24). The speed limit is the focus speed when focusing is performed using the focus drive amount, and it is higher the larger the focus drive amount.

[0073] Figure 9 shows an example of the change in depth of field D when the subject distance is close. In the example shown in Figure 9, D > Di, so the focus drive amount is recalculated based on the change in subject distance Mi corresponding to a predetermined value Di.

[0074] FIG. 10 shows an example of the change amount D of the depth of field when the subject distance is large. In the example shown in FIG. 10, since D < Di, the recalculation of the focus drive amount is not performed. The focus drive amount is a value corresponding to the change amount M of the subject distance.

[0075] FIG. 11 shows an example of various timings related to focus control according to the second embodiment. In this embodiment, during the period Ts in which the partial region SR of the image sensor 20 corresponding to the specific region is exposed, the focus drive speed is limited to a speed not higher than the limit speed. VL1 and VL2 are examples of the limit speed respectively. For example, VL1 is the limit speed when D > Di, and VL2 is the limit speed when D < Di.

[0076] Note that the main control unit 50 only needs to limit the focus drive speed to a speed not higher than the limit speed at least during the period Ts, and may make the focus drive speed higher than the limit speed during other periods.

[0077] [Third Embodiment] Next, the second embodiment of the present disclosure will be described. In this embodiment, the main control unit 50 executes a third control for performing focus drive during a non-exposure period obtained by shifting the exposure timing, in addition to the first control described in the first embodiment or the second control described in the second embodiment, which is different from the first embodiment or the second embodiment.

[0078] FIG. 12 shows an example of various timings in the third control. Basically, the image sensor 20 performs exposure in a so-called "back-loading" manner with the exposure period on the end side of one vertical synchronization period (1V). As shown in FIG. 12, in the third control, the main control unit 50 makes a part of the exposure period on the start side of one vertical synchronization period (1V), that is, a so-called "front-loading", to ensure a non-exposure period Tn in which no horizontal line of the image sensor 20 is exposed, and performs focus drive during the non-exposure period Tn. At this time, the main control unit 50 performs focus drive at a high speed without limiting the focus drive speed. Here, the high speed means a speed higher than the above-described limit speed.

[0079] In this embodiment, the main control unit 50 executes a third control in addition to the first or second control when the acquired focus drive amount is large. This allows focus driving to be performed in a short time even when the focus drive amount is large, further suppressing image quality degradation.

[0080] [Other variations] Furthermore, in each of the above embodiments, the AF area 60 is designated as a specific region, but the specific region may be a region other than the AF area 60. For example, the specific region may be a region that includes a specific subject detected by subject detection.

[0081] In each of the above embodiments, the main control unit 50 in the main body 11 performs focus control, but the lens drive unit 34 in the photographic lens 12 may also perform focus control. In other words, the focus control device according to the technology of this disclosure may be provided in either the main body 11 or the photographic lens 12.

[0082] Furthermore, the technology disclosed herein is not limited to digital cameras, but can also be applied to electronic devices such as smartphones and tablet devices that have a camera function.

[0083] In each of the above embodiments, each process is executed on any computer. Furthermore, any computer may execute these processes using a processor as hardware, a program as software, or a combination thereof. In this case, the processor is configured to work in cooperation with the program to execute the various processes in each of the above embodiments, and can function as a unit or means in each of the above embodiments. Also, the execution order of the processes by the processor is not limited to the order described and may be changed as appropriate. Any computer may be a general-purpose computer, a computer designed for a specific purpose, a workstation, or any other system capable of executing each process.

[0084] A processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a programmable logic device such as an FPGA (Field Programmable Gate Array), a dedicated circuit for executing a specific process such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the type of hardware may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a given processor, these components may reside in physically separate devices or in the same device. Also, in any embodiment, the order of each process performed by the processor is not limited to the order described above and may be changed as appropriate. Hardware is composed of electrical circuits (circuitry) that combine circuit elements such as semiconductor elements.

[0085] Furthermore, the program may be firmware or software such as microcode. Alternatively, the program may be, for example, a set of program modules, each function of which may be implemented by a processor configured to perform its respective function. The program may be program code or multiple code segments stored on one or more non-temporary computer-readable media (e.g., storage media or other storage). The program may be divided and stored on multiple non-temporary computer-readable media located on physically separate devices. Program code or code segments may represent any combination of procedures, functions, subprograms, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program statements. Program code or code segments may be connected to other code segments or hardware circuits by sending and receiving information, data, arguments, parameters, or memory contents.

[0086] Furthermore, although the above embodiments describe a configuration in which the program 43 is pre-stored (installed) in the memory 42, the invention is not limited to this configuration. The program 43 may be provided in the form of a recording medium such as a CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory), or USB (Universal Serial Bus) memory. Alternatively, the program 43 may be provided in the form of a download from an external device via a network.

[0087] The technology disclosed herein extends to all program products. A program product includes all forms of products for providing programs. For example, a program product includes programs provided via a network such as the Internet, and non-temporary computer-readable recording media such as CD-ROMs, DVDs, and USB memory sticks on which programs are stored.

[0088] The following technologies can be understood from the above explanation. [Additional note 1] A focus control device comprising a processor, The aforementioned processor, When exposing a portion of the image sensor corresponding to a specific area within the captured image, at least one of the following controls is executed: a first control that keeps the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less. Focus control device. [Additional note 2] The aforementioned image sensor performs exposure using a rolling shutter method. The focus control device described in Appendix 1. [Additional note 3] The image sensor performs the exposure multiple times in response to a single imaging instruction. The focus control device described in Appendix 2. [Additional note 4] The aforementioned processor, Focus drive is performed over a period of time during which the aforementioned exposure is performed multiple times. The focus control device described in Appendix 3. [Additional note 5] The aforementioned processor, Obtain the focus drive amount, The second control is executed when the change in depth of field corresponding to the acquired focus drive amount is greater than a predetermined value. A focus control device as described in any one of the appendices 1 to 4. [Additional note 6] The predetermined speed is the focus drive speed when performing focus drive with a focus drive amount corresponding to the predetermined value. The focus control device described in Appendix 5. [Additional note 7] The image sensor includes a plurality of phase difference detection pixels, The processor calculates the focus drive amount based on the defocus amount determined based on the output values ​​of the plurality of phase difference detection pixels. The focus control device described in Appendix 5 or Appendix 6. [Additional note 8] The aforementioned processor, In addition to the first or second control, a third control is performed to drive the focus during the non-exposure period obtained by shifting the exposure timing. A focus control device as described in any one of the appendices 1 through 7. [Additional note 9] The aforementioned processor, In the third control, focus driving is performed at a focus driving speed greater than the predetermined speed. The focus control device described in Appendix 8. [Additional Note 10] The aforementioned specific region is the focus area. A focus control device as described in any one of the appendices 1 through 9. [Additional Note 11] The aforementioned specific region is a region that includes a specific subject. A focus control device as described in any one of the appendices 1 through 9. [Explanation of Symbols]

[0089] 10 Imaging device 11 Main unit 11A Camera-side mount 11B Electrical Contact 12 Shooting Lenses 12A lens-side mount 12B Electrical Contact 13 Control section 14 Finder 15 displays 20 Image sensors 20A light receiving surface 21 pixels for imaging 22 Pixels for phase difference detection 30 objective lenses 31 Focus Lens 32 Rear lens 33 aperture 34 Lens drive unit 40 processors 42 memory 43 Programs 50 Main control unit 51 Imaging control unit 52 Image Processing Unit 53 Display Control Unit 54 Image Recording Unit 55 Ranging section 60 AF area A optical axis PD imaging PR Record Images

Claims

1. A focus control device comprising a processor, The aforementioned processor, When exposing a portion of the image sensor corresponding to a specific area within the captured image, at least one of the following controls is executed: a first control that keeps the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less. Focus control device.

2. The aforementioned image sensor performs exposure using a rolling shutter method. The focus control device according to claim 1.

3. The image sensor performs the exposure multiple times in response to a single imaging instruction. The focus control device according to claim 2.

4. The aforementioned processor, Focus drive is performed over a period of time during which the aforementioned exposure is performed multiple times. The focus control device according to claim 3.

5. The aforementioned processor, Obtain the focus drive amount, The second control is executed when the change in depth of field corresponding to the acquired focus drive amount is greater than a predetermined value. A focus control device according to any one of claims 1 to 4.

6. The predetermined speed is the focus drive speed when performing focus drive with a focus drive amount corresponding to the predetermined value. The focus control device according to claim 5.

7. The image sensor includes a plurality of phase difference detection pixels, The processor calculates the focus drive amount based on the defocus amount determined based on the output values ​​of the plurality of phase difference detection pixels. The focus control device according to claim 5.

8. The aforementioned processor, In addition to the first or second control, a third control is performed to drive the focus during the non-exposure period obtained by shifting the exposure timing. The focus control device according to claim 1.

9. The aforementioned processor, In the third control, focus driving is performed at a focus driving speed greater than the predetermined speed. The focus control device according to claim 8.

10. The aforementioned specific region is the focus area. The focus control device according to claim 1.

11. The aforementioned specific region is a region that includes a specific subject. The focus control device according to claim 1.

12. The processor, When exposing a portion of the image sensor corresponding to a specific area within the captured image, at least one of the following controls is performed: a first control that keeps the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less. A focus control method including the following.

13. When exposing a portion of the image sensor corresponding to a specific area within the captured image, at least one of the following controls is performed: a first control that keeps the focus drive speed constant, and a second control that limits the focus drive speed to a predetermined speed or less. A program that causes the processor to execute a process that includes [a specific element / task].

Images