JP7612334B2 - Control device, imaging device, control method, and program - Google Patents

Description

The present invention relates to an imaging device.

Phase-difference focus detection (Phase-difference AF) is known as an autofocus detection (AF) method for imaging devices. Phase-difference AF is a method often used in digital still cameras, and some imaging devices use an image sensor as a focus detection sensor. Patent Document 1 discloses an imaging device in which some pixels are used as focus detection pixels for performing focus detection using a pupil splitting method. In this type of focus detection method, the baseline length of a pair of pupil-split focus detection pixels affects the focus detection accuracy.

In addition, when performing focus detection, it is generally necessary to set the exposure conditions (target exposure value) to provide proper exposure. Therefore, if the exposure is not suitable for focus detection, the exposure conditions are set to proper exposure conditions by the photometry means and focus detection is performed. Patent Document 2 discloses an imaging device that changes the settings of exposure conditions and whether or not to perform photometry depending on the reliability of the focus detection result immediately before the release button is half-pressed, so that a quick transition to focus detection can be made when the release button is half-pressed to perform focus detection.

JP 2008-52009 A JP 2013-25132 A

The focus detection accuracy of phase difference AF is determined by various factors such as the baseline length, which is determined by the aperture diameter (F-number) of the imaging optical system, the contrast of the subject, or the amount of signal acquired by the exposure setting. The baseline length changes according to the aperture diameter (F-number) of the imaging optical system. Generally, the larger the F-number, the smaller the baseline length, and the lower the focus detection accuracy. However, in conventional technology, the presence or absence of photometry and the target exposure value do not take into account the baseline length, which affects the focus detection accuracy of phase difference AF, and the emphasis is on acquiring a certain amount of signal through photometry. For this reason, even in a situation where focus detection is possible if the baseline length is taken into account, it may not be possible to perform quick and highly accurate focus detection.

The present invention aims to provide a control device, an imaging device, a control method, and a program that enable quick and highly accurate focus detection.

A control device according to one aspect of the present invention is a control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, and includes an exposure control unit that performs exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value, and an exposure condition acquisition unit that acquires exposure conditions for the focus detection based on information based on a base line length, the information based on the base line length being information regarding the aperture value and an image height, and the exposure conditions being exposure conditions that become a first exposure target value in information based on a first base line length, and the information based on the line length is an exposure condition resulting in a second exposure target value different from the first exposure target value, the first exposure target value and the second exposure target value are each exposure target values for the focus detection, the exposure control unit performs the exposure control to achieve the exposure condition, the first base line length is shorter than the second base line length and the first exposure target value is higher than the second exposure target value, and in the information based on the first base line length , the first exposure target value is higher than a third exposure target value for acquiring an captured image based on the pixel signal.

A control device according to another aspect of the present invention is a control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, and includes an exposure control unit that performs exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value, a focus adjustment unit that performs focus adjustment control of the imaging optical system, and an exposure change determination unit that determines whether or not the exposure control needs to be performed based on at least current luminance information and information based on a base line length during the focus adjustment control by the focus adjustment unit, and the information based on the base line length is used to default an image shift amount. the information relating to a conversion coefficient for converting the amount of shavings into an amount of shavings, the exposure change determination unit having a first exposure determination condition for information based on a first baseline length and a second exposure determination condition different from the first exposure determination condition for information based on a second baseline length, the exposure control unit performing the exposure control when the exposure change determination unit determines to perform the exposure control, the first baseline length being shorter than the second baseline length, and the first exposure determination condition being a determination condition having a smaller tolerance for the difference between the current luminance information and an appropriate exposure for the focus detection than the second exposure determination condition.
A control device as another aspect of the present invention is a control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, and has an exposure control unit that performs exposure control based on exposure control values including exposure time, imaging sensitivity, and aperture value, a focus adjustment unit that performs focus adjustment control of the imaging optical system, and an exposure change determination unit that determines whether or not the exposure control needs to be performed based on at least current luminance information and a lens ID during the focus adjustment control by the focus adjustment unit, wherein the exposure change determination unit sets a larger allowable range for the difference between the current luminance information and the appropriate exposure in the case of a lens in which it is easy to obtain a baseline length than in the case of a lens in which it is difficult to obtain a baseline length, and the exposure control unit performs the exposure control when the exposure change determination unit determines that the exposure control should be performed.

Other objects and features of the present invention are described in the following embodiments.

The present invention provides a control device, an imaging device, a control method, and a program that enable quick and highly accurate focus detection.

FIG. 2 is a block diagram of an imaging device in each embodiment. FIG. 2 is a diagram showing a pixel arrangement in each embodiment. FIG. 2 is a diagram showing a pixel structure in each embodiment. 4A and 4B are explanatory diagrams of an image sensor and a pupil division function in each embodiment. 4A and 4B are explanatory diagrams of an image sensor and a pupil division function in each embodiment. 5 is a diagram showing the relationship between a defocus amount and an image shift amount in each embodiment. 5 is a flowchart showing a focus adjustment process according to the first embodiment. FIG. 4 is a diagram showing a target exposure value in the first embodiment. 10 is a flowchart showing a focus adjustment process according to a second embodiment. 13 is a timing chart according to the third embodiment.

The following describes in detail an embodiment of the present invention with reference to the drawings.

Note that each embodiment has a specific and specific configuration to facilitate understanding and explanation of the invention, but the present invention is not limited to such specific configurations. For example, the following describes an embodiment in which the present invention is applied to a single-lens reflex digital camera with interchangeable lenses, but the present invention is also applicable to digital cameras and video cameras that do not have interchangeable lenses. The present invention can also be implemented in any electronic device equipped with a camera, such as a mobile phone, a personal computer (such as a laptop, tablet, or desktop type), or a game console.

First Embodiment
First, a schematic configuration of an image capture device according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a block diagram of an image capture device 100 according to this embodiment. The image capture device 100 is a digital camera system equipped with a camera body and an interchangeable lens (image capture optical system or image forming optical system) that is detachable from the camera body. However, this embodiment is not limited to this, and can also be applied to an image capture device in which the camera body and the lens are integrally configured.

The first lens group 101 is arranged at the front (on the subject side) of the multiple lens groups that make up the photographing lens (image pickup optical system), and is held in the lens barrel in a state in which it can be advanced and retreated in the direction of the optical axis OA (optical axis direction). The aperture/shutter (aperture) 102 adjusts its aperture diameter to adjust the amount of light during shooting, and also functions as a shutter for adjusting exposure time during still image shooting. The second lens group 103 advances and retreats in the optical axis direction together with the aperture/shutter 102, and has a zoom function that performs a magnification change operation in conjunction with the advance and retreat movement of the first lens group 101. The third lens group 105 is a focus lens group that performs focus adjustment (focus operation) by advancing and retreating in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the photographed image.

The image sensor 107 performs photoelectric conversion of the subject image (optical image) via the imaging optical system, and is composed of a two-dimensional photosensor such as a CMOS sensor or CCD sensor and its peripheral circuits, and is arranged on the imaging plane of the imaging optical system. For example, the image sensor 107 may be a two-dimensional single-chip color sensor in which a primary color mosaic filter in a Bayer array is formed on-chip on a light-receiving pixel having m pixels in the horizontal direction and n pixels in the vertical direction.

The zoom actuator 111 rotates (drives) a cam barrel (not shown) to move the first lens group 101 to the second lens group 103 along the optical axis, thereby performing a magnification change operation. The aperture/shutter actuator 112 controls the aperture/shutter 102 opening diameter to adjust the amount of light (amount of light for shooting) and also controls the exposure time when shooting still images. The focus actuator 114 moves the third lens group 105 along the optical axis to perform focus adjustment.

The electronic flash 115 is an illumination device used to illuminate a subject. The electronic flash 115 may be a flashlight illumination device equipped with a xenon tube or an illumination device equipped with a continuous-light emitting LED (light-emitting diode). The AF auxiliary light means 116 projects an image of a mask having a predetermined aperture pattern onto the subject via a projection lens. This can improve focus detection capabilities for dark subjects or low-contrast subjects.

The CPU 121 is a control device (control means) that controls various aspects of the imaging device 100. The CPU 121 has an arithmetic unit, ROM, RAM, an A/D converter, a D/A converter, and a communication interface circuit. The CPU 121 reads out and executes a specific program stored in the ROM to drive various circuits of the imaging device 100 and control a series of operations such as focus detection (AF), shooting, image processing, and recording. The communication interface circuit is capable of communication using not only cables such as USB and wired LAN, but also wireless technologies such as wireless LAN.

The CPU 121 is a control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of the imaging optical system. The CPU 121 has an exposure control unit 121a, an exposure condition acquisition unit 121b, a focus adjustment unit 121c, and an exposure change determination unit 121d. The exposure control unit 121a performs exposure control based on exposure control values including exposure time, imaging sensitivity, and aperture value. The exposure condition acquisition unit 121b acquires exposure conditions for focus detection based on information based on the baseline length. The focus adjustment unit 121c controls the focus drive circuit 126 to perform focus adjustment (focus control) of the imaging optical system.

The CPU 121 stores in its internal memory coefficients (correction value calculation coefficients) for calculating the correction value Kgain required to calculate the defocus amount. For example, a plurality of correction value calculation coefficients are prepared for each focus state corresponding to the position of the third lens group 105, zoom state corresponding to the positions of the first lens group 101 to the second lens group 103, F-number of the imaging optical system, set pupil distance of the imaging element, and pixel size. When performing focus adjustment, the CPU 121 selects an optimal correction value calculation coefficient according to the combination of the focus adjustment state (focus state, zoom state) of the imaging optical system, the aperture value (F-number), the set pupil distance of the imaging element, and the pixel size. The CPU 121 then calculates the correction value based on the selected correction value calculation coefficient and the image height of the imaging element.

In this embodiment, the correction value calculation coefficients are stored in the internal memory of the CPU 121, but this is not limiting. The correction value calculation coefficients may be stored in a memory provided outside the CPU 121. Also, in an interchangeable lens type imaging device, an interchangeable lens having an imaging optical system may have a non-volatile memory, and the correction value calculation coefficients may be stored in that memory. In this case, the correction value calculation coefficients may be transmitted to the imaging device according to the focus adjustment state of the imaging optical system.

The electronic flash control circuit 122 controls the lighting of the electronic flash 115 in synchronization with the shooting operation. The assist light driving circuit 123 controls the lighting of the AF assist light means 116 in synchronization with the focus detection operation. The image sensor driving circuit 124 controls the imaging operation such as vertical and horizontal scanning of the image sensor 107, and also A/D converts the acquired image signal and transmits it to the CPU 121. The A/D conversion circuit may be provided within the image sensor 107. The image processing circuit 125 performs processes such as γ (gamma) conversion, color interpolation, and JPEG (Joint Photographic Experts Group) compression of the image data output from the image sensor 107.

The focus drive circuit 126 drives the focus actuator 114 based on the focus detection result, and adjusts the focus by moving the third lens group 105 along the optical axis direction. The aperture shutter drive circuit 128 drives the aperture shutter actuator 112 to control the aperture diameter of the aperture/shutter 102. The zoom drive circuit 129 drives the zoom actuator 111 in response to the zoom operation of the photographer.

The display 131 is configured to include, for example, an LCD (liquid crystal display device). The display 131 displays information about the shooting mode of the imaging device 100, a preview image before shooting, a confirmation image after shooting, or an in-focus state display image at the time of focus detection. The operation unit (operation switch group) 132 is configured to include a power switch, a release (shooting trigger) switch, a zoom operation switch, and a shooting mode selection switch. The release switch has two switch stages: a half-pressed state (SW1 is ON) and a fully pressed state (SW2 is ON). The recording medium 133 is, for example, a flash memory that is detachable from the imaging device 100, and records the captured image (image data). The operation unit 132 may also include a touch panel or the like, allowing operation using the touch panel.

Next, the pixel array and pixel structure of the image sensor 107 in this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a diagram showing the pixel array of the image sensor 107. Figure 3 is a diagram showing the pixel structure of the image sensor 107, with Figure 3(a) showing a plan view of pixel 200G of the image sensor 107 (as viewed from the +z direction) and Figure 3(b) showing a cross-sectional view of line a-a in Figure 3(a) (as viewed from the -y direction).

Figure 2 shows the pixel array (array of imaging pixels) of the image sensor (two-dimensional CMOS sensor) 107 in an area of 4 columns x 4 rows. In this embodiment, each imaging pixel (pixels 200R, 200G, 200B) is composed of two sub-pixels 201, 202 (two focus detection pixels). For this reason, the sub-pixel array is shown in an area of 8 columns x 4 rows in Figure 2.

2, in the pixel group 200 of 2 columns x 2 rows, the pixels 200R, 200G, and 200B are arranged in a Bayer array. That is, in the pixel group 200, the pixel 200R having the spectral sensitivity of R (red) is arranged at the upper left, the pixel 200G having the spectral sensitivity of G (green) is arranged at the upper right and lower left, and the pixel 200B having the spectral sensitivity of B (blue) is arranged at the lower right. Each pixel 200R, 200G, and 200B (each imaging pixel) is composed of sub-pixels 201 (first focus detection pixel) and sub-pixels 202 (second focus detection pixel) arranged in 2 columns x 1 row. The sub-pixel 201 is a pixel that receives a light beam that has passed through a first pupil partial region of the imaging optical system. The sub-pixel 202 is a pixel that receives a light beam that has passed through a second pupil partial region of the imaging optical system. The sub-pixels 201 constitute a first pixel group, and the sub-pixels 202 constitute a second pixel group. The image sensor 107 is configured with a large number of 4 columns x 4 rows of image pixels (8 columns x 4 rows of sub-pixels) arranged on its surface, and outputs an image signal (sub-pixel signal or focus detection signal).

As shown in FIG. 3B, the pixel 200G of this embodiment is provided with a microlens 305 for concentrating incident light on the light receiving surface side of the pixel. A plurality of microlenses 305 are arranged two-dimensionally, and are arranged at a position a predetermined distance away from the light receiving surface in the z-axis direction (direction of the optical axis OA). The pixel 200G also has a photoelectric conversion unit 301 and a photoelectric conversion unit 302 that are N _H- divided (two-divided) in the x-direction and N _V -divided (one-divided) in the y-direction. The photoelectric conversion unit 301 and the photoelectric conversion unit 302 correspond to the sub-pixels 201 and 202, respectively. In this way, the image sensor 107 has a plurality of photoelectric conversion units for one microlens, and the microlenses are arranged two-dimensionally. The photoelectric conversion unit 301 and the photoelectric conversion unit 302 are each configured as a photodiode with a pin structure in which an intrinsic layer is sandwiched between a p-type layer and an n-type layer. If necessary, the intrinsic layer may be omitted and a pn junction photodiode may be formed.

In pixel 200G (each pixel), a G (green) color filter 306 is provided between the microlens 305 and the photoelectric conversion unit 301 and the photoelectric conversion unit 302. Similarly, in pixels 200R and 200B (each pixel), an R (red) color filter 306 and a B (blue) color filter 306 are provided between the microlens 305 and the photoelectric conversion unit 301 and the photoelectric conversion unit 302, respectively. If necessary, the spectral transmittance of the color filter 306 can be changed for each subpixel, or the color filter may be omitted.

As shown in FIG. 3, the light incident on pixel 200G (200R, 200B) is collected by microlens 305, dispersed by G color filter 306 (R, B color filter 306), and then received by photoelectric conversion unit 301 and photoelectric conversion unit 302. In photoelectric conversion unit 301 and photoelectric conversion unit 302, pairs of electrons and holes are generated according to the amount of received light, and after they are separated by a depletion layer, negatively charged electrons are accumulated in the n-type layer. Meanwhile, holes are discharged to the outside of image sensor 107 through a p-type layer connected to a constant voltage source (not shown). Electrons accumulated in the n-type layers of photoelectric conversion unit 301 and photoelectric conversion unit 302 are transferred to a capacitance unit (FD) through a transfer gate based on scanning control by image sensor drive circuit 124, and converted into a voltage signal.

Next, the pupil division function of the image sensor 107 will be described with reference to FIG. 4. FIG. 4 is an explanatory diagram of the pupil division function of the image sensor 107, showing the pupil division in one pixel section. FIG. 4 shows a cross-sectional view of the a-a cross section of the pixel structure shown in FIG. 3(a) as viewed from the +y side, and the exit pupil plane of the imaging optical system. In FIG. 4, the x-axis and y-axis of the cross-sectional view are inverted with respect to the x-axis and y-axis of FIG. 3, respectively, to correspond to the coordinate axes of the exit pupil plane.

In FIG. 4, the pupil partial region (first pupil partial region) 501 of the sub-pixel (first focus detection pixel) 201 is in an approximately conjugate relationship with the light receiving surface of the photoelectric conversion unit 301, whose center of gravity is eccentric in the -x direction, via the microlens 305. Therefore, the pupil partial region 501 represents the pupil region that can receive light at the sub-pixel 201. The center of gravity of the pupil partial region 501 of the sub-pixel 201 is eccentric on the +X side on the pupil plane. Moreover, the pupil partial region (second pupil partial region) 502 of the sub-pixel (second focus detection pixel) 202 is in an approximately conjugate relationship with the light receiving surface of the photoelectric conversion unit 302, whose center of gravity is eccentric in the +x direction, via the microlens 305. Therefore, the pupil partial region 502 represents the pupil region that can receive light at the sub-pixel 202. The center of gravity of the pupil partial region 502 of the sub-pixel 202 is eccentric on the -X side on the pupil plane. The pupil region 500 is the pupil region that can receive light in the entire pixel 200G when all the photoelectric conversion units 301, 302 (sub-pixels 201, 202) are combined.

The difference between the center of gravity of the pupil partial region 501 of the subpixel 201 and the center of gravity of the pupil partial region 502 of the subpixel 202 corresponds to the baseline length. The longer the baseline length, the higher the separation performance of the pair of signals. Here, the larger the aperture diameter, the longer the baseline length, and therefore the smaller the F-number, the higher the focus detection accuracy. On the other hand, the smaller the aperture diameter, the shorter the baseline length, and therefore the larger the F-number, the lower the focus detection accuracy.

Next, the correspondence between the image sensor 107 and pupil division will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram of the image sensor 107 and the pupil division function. Light beams that have passed through different pupil partial regions 501 and 502 of the pupil region of the imaging optical system are incident on the imaging surface 800 of the image sensor 107 at different angles to each pixel of the image sensor 107, and are received by the sub-pixels 201 and 202 divided into 2×1. In this embodiment, an example is described in which the pupil region is pupil-divided into two in the horizontal direction, but this is not limited thereto, and pupil division may be performed in the vertical direction as necessary.

In this embodiment, the image sensor 107 has a first focus detection pixel that receives a light beam passing through a first pupil partial region of the image sensor (photographing lens). The image sensor 107 also has a second focus detection pixel that receives a light beam passing through a second pupil partial region different from the first pupil partial region of the image sensor. The image sensor 107 also has a plurality of imaging pixels arranged to receive a light beam passing through a pupil region that is a combination of the first and second pupil partial regions of the image sensor. In this embodiment, each imaging pixel (pixel 200) is composed of a first focus detection pixel (sub-pixel 201) and a second focus detection pixel (sub-pixel 202). If necessary, the imaging pixel, the first focus detection pixel, and the second focus detection pixel may each be composed of different pixels. In this case, the first focus detection pixel and the second focus detection pixel are arranged partially (discretely) in a part of the imaging pixel array.

In this embodiment, the imaging device 100 performs focus detection by collecting light receiving signals from the first focus detection pixel (sub-pixel 201) of each pixel of the image sensor 107 to generate a first focus detection signal, and collecting light receiving signals from the second focus detection pixel (sub-pixel 202) of each pixel to generate a second focus detection signal. The imaging device 100 also adds (sums up) the signals from the first and second focus detection pixels for each pixel of the image sensor 107 to generate an imaging signal (captured image) with a resolution of the effective pixel number N.

Next, the relationship between the defocus amount and the image shift amount of the first focus detection signal acquired from the sub-pixel 201 of the image sensor 107 and the second focus detection signal acquired from the sub-pixel 202 will be described with reference to FIG. 6. FIG. 6 is a relationship diagram between the defocus amount and the image shift amount. In FIG. 6, the image sensor 107 is disposed on the image sensor surface 800, and similarly to FIGS. 4 and 5, the exit pupil of the image sensor optical system is shown divided into two pupil partial regions 501 and 502.

The defocus amount d is defined as the distance from the subject's imaging position to the imaging plane 800, |d|, a front-focus state where the imaging position is closer to the subject than the imaging plane 800, with a negative sign (d<0), and a back-focus state where the imaging position is on the opposite side of the subject than the imaging plane 800, with a positive sign (d>0). In a focused state where the subject's imaging position is on the imaging plane 800 (focused position), the defocus amount d=0 is established. In FIG. 6, a subject 801 in a focused state (d=0) and a subject 802 in a front-focus state (d<0) are shown. The front-focus state (d<0) and the back-focus state (d>0) are collectively referred to as a defocus state (|d|>0).

In the front focus state (d<0), the light beam from the subject 802 that passes through the pupil partial region 501 (or pupil partial region 502) is once focused. After that, the light beam spreads to a width Γ1 (Γ2) centered on the center of gravity position G1 (G2) of the light beam, and becomes a blurred image on the imaging surface 800. The blurred image is received by the sub-pixels 201 (sub-pixels 202) that constitute each pixel arranged on the imaging element 107, and a first focus detection signal (second focus detection signal) is generated. Therefore, the first focus detection signal (second focus detection signal) is recorded at the center of gravity position G1 (G2) on the imaging surface 800 as a subject image in which the subject 802 is blurred to a width Γ1 (Γ2). The blur width Γ1 (Γ2) of the subject image increases approximately in proportion to the increase in the magnitude |d| of the defocus amount d. Similarly, the magnitude |p| of the image shift amount p (= the difference G1-G2 in the center of gravity position of the light beam) of the subject image between the first focus detection signal and the second focus detection signal also increases roughly in proportion to the increase in the magnitude |d| of the defocus amount d. The same is true for the back focus state (d>0), but the direction of the image shift of the subject image between the first focus detection signal and the second focus detection signal is opposite to that of the front focus state.

Therefore, in this embodiment, it is possible to calculate the defocus amount d based on the conversion coefficient K for converting the image shift amount p, which is obtained in advance, into the defocus amount d, and the image shift amount p of the subject image between the first focus detection signal and the second focus detection signal. Then, when the defocus amount d = 0, the focus is achieved.

The conversion coefficient K is proportional to the inverse of the baseline length, so it is information based on the baseline length. When calculating the image shift amount p, it is affected by the variation error due to the S/N of the acquired signal. If the variation error of the image shift amount p is constant, the smaller the conversion coefficient K, the smaller the variation. In other words, under conditions where the F-number is small and the baseline length is long, the focus detection variation is smaller and the focusing accuracy is high. However, the focus detection accuracy of phase difference AF is not determined only by the baseline length, but is also affected by the contrast of the subject and the amount of signal acquired by the exposure setting. In particular, if the S/N of the signal is increased by acquiring a large signal, the variation error when calculating the image shift amount p is reduced. Therefore, it is acceptable for the signal amount to be small under conditions where the F-number is small and the baseline length is long, but it is preferable for the signal amount to be large under conditions where the F-number is large and the baseline length is short. Such a tendency is more noticeable for low-contrast subjects, which are difficult to improve focus detection accuracy.

Next, the flow of focus adjustment processing during live view in this embodiment will be described with reference to FIG. 7. FIG. 7 is a flowchart showing the focus adjustment processing in this embodiment. Each step in FIG. 7 is mainly executed by the CPU 121.

The focus adjustment process begins when the release button is half-pressed during live view. First, in step S701, the CPU 121 acquires the focus detection result. If the CPU 121 acquires the focus detection result during standby, the result immediately before the release button was half-pressed may be used. Note that the focus adjustment process is not limited to being started in response to the release button being half-pressed, and may also be started by pressing a button to which an AF function is assigned.

Next, in step S702, the CPU 121 determines whether or not the focus detection result acquired in step S701 is reliable (whether or not it is reliable). If it is determined that the focus detection result is reliable, the process proceeds to step S707. In step S707, the CPU 121 performs lens drive (focus control) based on the focus detection result. On the other hand, if it is determined in step S702 that the focus detection result is unreliable, the process proceeds to step S703. In step S703, the CPU 121 acquires luminance information by photometry.

Next, in step S704, the CPU 121 (exposure condition acquisition unit 121a) acquires the AF exposure conditions (exposure conditions suitable for AF). As described above, the focus detection accuracy of phase difference AF depends on the baseline length. For this reason, the imaging device 100 of this embodiment has a condition setting table that sets the exposure conditions (exposure target value) suitable for AF according to the F-number, as shown in FIG. 8. FIG. 8 is a diagram in which general exposure conditions (exposure target value) are standardized as suitable exposure (image), and exposure conditions suitable for AF are shown as suitable exposure (AF). In FIG. 8, the horizontal axis indicates the F-number, and the vertical axis indicates the exposure ratio. In this embodiment, the S/N ratio of the signal is increased by taking a larger signal than in the past in a range darker than F2.8, which is the F-number at which it is difficult to obtain a baseline length.

Next, in step S705, the CPU 121 (exposure control unit 121a) sets the AF exposure conditions (exposure conditions that realize an exposure target value suitable for AF). In this embodiment, the exposure conditions are exposure time, imaging sensitivity, and aperture value (F value), but are not limited to these. The CPU 121 determines the exposure conditions using a program diagram prepared in advance based on the brightness information acquired in step S703 and the AF exposure conditions acquired in step S704. Table 1 shows, as an example, a comparison of a conventional suitable exposure (image) with an exposure time of 1/350, imaging sensitivity of 100, and aperture value of F5.6 for a lens with an open F5.6. As shown in FIG. 8, the AF exposure conditions (AF exposure target value) in this embodiment are 1.4 times the suitable exposure (image) at F5.6, so the suitable exposure (AF) condition is a state in which the exposure time is 1.4 times longer. Note that in Table 1, adjustment is made using the exposure conditions, but adjustment may also be made using the imaging sensitivity.

Next, in step S706, the CPU 121 acquires a focus detection result based on the AF exposure conditions (AF exposure target value) set in step S705. If a reliable focus detection result is obtained, then in step S707 the CPU 121 performs lens drive (focus control) based on the focus detection result acquired in step S706. On the other hand, if a reliable focus detection result is not obtained, then in step S707 the CPU 121 performs lens drive as a search.

If the subject brightness changes during lens driving in step S707, the CPU 121 (exposure control unit 121a) may perform exposure control using photometry during focus adjustment processing. In this case, it is preferable to perform exposure control suitable for AF.

As described above, in this embodiment, the exposure condition acquisition unit 121b acquires the exposure conditions for focus detection based on information based on the baseline length. The exposure conditions are exposure conditions that result in a first exposure target value when the information is based on the first baseline length, and exposure conditions that result in a second exposure target value that is different from the first exposure target value when the information is based on the second baseline length. The exposure control unit 121a then performs exposure control so as to achieve the exposure conditions acquired by the exposure condition acquisition unit 121b.

Preferably, the first baseline length is shorter than the second baseline length, and the first exposure target value is higher than the second exposure target value (i.e., the more difficult it is to obtain a baseline length based on information based on the baseline length, the higher the exposure of the exposure conditions suitable for focus detection). Also preferably, the exposure condition acquisition unit 121b acquires exposure conditions based on information based on the contrast of the subject. Also preferably, the exposure control unit 121a performs exposure control based on changes in subject brightness while the focus adjustment unit 121c is performing focus adjustment. Also preferably, the information based on the baseline length is a value proportional to the baseline length or a value proportional to the reciprocal of the baseline length. Also preferably, the information based on the baseline length is an aperture value (F value), an image height, or a lens ID.

According to this embodiment, highly accurate focus detection can be performed by setting exposure conditions (exposure target value) using information based on the baseline length. In this embodiment, since there is a correlation between the baseline length and Fno (aperture value), focusing accuracy can be improved by changing the exposure conditions according to Fno as information based on the baseline length. The focusing accuracy of phase difference AF also depends on the contrast of the subject. For this reason, for example, when contrast is high, conventional suitable exposure (image) conditions may be used, and when contrast is low, suitable exposure conditions for AF may be used. Note that the contrast of a subject can be calculated by looking at the luminance change in the imaging signal or the spatial frequency components of the subject.

Second Embodiment
Next, a second embodiment of the present invention will be described. In an imaging device equipped with an electronic display device such as a rear liquid crystal display or an electronic viewfinder, an electric signal received by an imaging element is displayed on the electronic display device. The electric signal may also serve as a signal for image plane phase difference AF. For this reason, if the exposure setting is changed when the focus adjustment process is started by half-pressing the release button, the electronic display device may become brighter or darker, impairing visibility. In this embodiment, the condition (exposure judgment condition) for judging whether or not exposure control needs to be performed is changed based on the value of the conversion coefficient K as information based on the base line length, thereby realizing highly accurate phase difference AF with good visibility.

The issue of visibility caused by changing the exposure setting when the focus adjustment process starts can be improved by reducing the frequency of exposure changes. For example, even if the exposure immediately before the start of the focus adjustment process is two stops lower than optimal, if distance measurement is possible, the exposure change can be omitted and the focus adjustment process can be started, thereby avoiding a decrease in visibility.

As mentioned above, the baseline length has a large effect on the distance measurement performance of phase difference AF. If the baseline length is long, distance measurement is possible even with low exposure. On the other hand, if the baseline length is not long, distance measurement may not be possible if the exposure remains low.

Therefore, in this embodiment, the conditions (exposure determination conditions) for determining whether exposure control should be performed are changed based on the value of the conversion coefficient K as information based on the baseline length, thereby achieving highly accurate AF with good visibility. More specifically, the smaller the value of the conversion coefficient K, the more accurate phase difference AF with good visibility is achieved by allowing distance measurement at exposure lower than the optimum.

The flow of focus adjustment processing during live view in this embodiment will be described with reference to FIG. 9. FIG. 9 is a flowchart showing the focus adjustment processing in this embodiment. Each step in FIG. 9 is mainly executed by the CPU 121.

The focus adjustment process begins when the release button is half-pressed during live view. First, in step S901, the CPU 121 acquires the focus detection result. If the CPU 121 acquires the focus detection result during standby, the result immediately before the release button was half-pressed may be used. Note that the focus adjustment process is not limited to being started in response to the release button being half-pressed, and may also be started by pressing a button to which an AF function is assigned.

Next, in step S902, the CPU 121 determines whether or not the focus detection result acquired in step S901 is reliable (whether or not it is reliable). If it is determined that the focus detection result is reliable, the process proceeds to step S907. In step S907, the CPU 121 performs lens drive (focus control) based on the focus detection result. On the other hand, if it is determined in step S902 that the focus detection result is unreliable, the process proceeds to step S903. In step S903, the CPU 121 acquires luminance information by photometry.

Next, in step S904, the CPU 121 acquires the exposure control judgment conditions (judgment conditions for whether or not to change the exposure). In this embodiment, the exposure control judgment conditions are changed based on the conversion coefficient K. The CPU 121 acquires the conditions shown in Table 2, for example, and acquires the conditions for whether or not to change the exposure based on the relationship between the conversion coefficient K and the threshold value Thr0. When the conversion coefficient K is small (K<Thr0), the condition is that the baseline length is long, so even if the difference between the current brightness information and the optimal exposure (AF) is large, it is tolerated. On the other hand, when the conversion coefficient K is large (K≧Thr0), the condition is that the baseline length is not long, so the allowable range for the difference between the current brightness information and the optimal exposure (AF) is narrowed.

Next, in step S905, the CPU 121 (exposure change determination unit 121d) determines whether or not to change the exposure. That is, the CPU 121 determines whether or not to change the exposure based on the luminance information acquired in step S903 and the conversion coefficient K and exposure control determination conditions acquired in step S904. If the CPU 121 determines that the exposure is not to be changed, the process proceeds to step S907, where the lens is driven (search driven) while maintaining the exposure. On the other hand, if the CPU 121 determines that the exposure is to be changed, the process proceeds to step S906. In step S906, the CPU 121 controls the exposure to change the exposure to an appropriate exposure (AF). Then, in step S907, the CPU 121 drives the lens.

As described above, the exposure change determination unit 121d determines whether or not exposure control should be performed when focus adjustment is performed by the focus adjustment unit 121c, based on at least the current brightness information and the information based on the baseline length. The exposure change determination unit 121d also has a first exposure determination condition for the information based on the first baseline length, and a second exposure determination condition different from the first exposure determination condition for the information based on the second baseline length. Then, when the exposure change determination unit 121d determines that exposure control should be performed, the exposure control unit 121a performs exposure control. Preferably, the first baseline length is shorter than the second baseline length, and the first exposure determination condition is a determination condition for matching the exposure condition to a condition more suitable for focus detection than the second exposure determination condition.

According to this embodiment, by performing the focus detection process as described above, unnecessary exposure changes can be reduced, and highly accurate phase difference AF with good visibility can be realized. In addition, considering that the depth of field changes depending on the aperture value, the threshold value Thr0 may be changed based on the aperture value. In addition, the exposure conditions include exposure time (tv), imaging sensitivity (ISO), and aperture value (Fno), and even if each exposure condition is changed, the exposure is maintained if the exposure is not changed. For example, Tv=1/240, ISO=100, Fno=2.0 and Tv=1/60, ISO=100, Fno=4.0 have the same exposure target value.

The imaging device 100 of this embodiment uses information based on the baseline length to set the presence or absence of photometry and the exposure conditions (exposure target value), enabling quick and highly accurate focus detection. Note that the information based on the baseline length is Fno in the first embodiment and conversion coefficient K in this embodiment, but is not limited to these, and for example, the determination may be made based on the baseline length itself. In addition, image height and lens ID can also be used as information based on the baseline length. The baseline length is determined by the relationship between the imaging optical system and the imaging element, but the higher the image height is due to the influence of pupil shift, the more difficult it is to obtain a baseline length, so the presence or absence of photometry and the exposure condition settings may be changed depending on the image height. In addition, in the case of an interchangeable lens system, since some lenses have a baseline length that is easy to obtain and others that are difficult to obtain, the presence or absence of photometry and the exposure condition settings may be changed using the lens ID as information based on the baseline length.

Third Embodiment
Next, a third embodiment of the present invention will be described. In the first and second embodiments, a so-called one-shot mode in which the user half-presses the release button or the like to perform focus detection has been described. However, the present invention is not limited to one-shot, and realizes quick and highly accurate AF by considering the base line length in exposure control during AF. The present invention is also applicable to each mode provided in the imaging device during continuous shooting, video standby, video recording, etc. In this embodiment, an example of applying the present invention during continuous shooting will be described.

Figure 10 is an example of a timing chart during continuous shooting. In Figure 10, a high-resolution first image is used to record a still image. A second image, which has a lower resolution than the first image, is displayed on an electronic display device such as a rear LCD or electronic viewfinder, and is used as a focus detection image for focus detection (focus adjustment processing).

The first image used for recording is preferably exposed at an appropriate exposure (image), and the second image used for focus detection is preferably exposed at an appropriate exposure (AF). In this embodiment, as in the first embodiment, AF is performed at the target exposure value shown in FIG. 5 using Fno as information based on the baseline length. Therefore, when continuous shooting is performed under conditions brighter than F2.8, the target exposure values of the first and second images are the same. On the other hand, when stopping down beyond F2.8, the exposure of the second image is higher than that of the first image.

As shown in FIG. 10, when the accumulation of a second image for focus detection is sandwiched between first images used for recording, highly accurate focus detection is possible even during continuous shooting by setting the second image to an appropriate exposure (AF). Note that, depending on the mode, the first image may serve as both a still image for recording and an image for focus detection. In this case, it is preferable to give priority to the exposure of the image for recording and expose it at an appropriate exposure (image). In addition, with regard to video, frequent exposure changes during video recording can degrade the quality, so one method is to set the exposure to an appropriate exposure (AF) when the video is on standby and to an appropriate exposure (image) when the video is being recorded.

The imaging device 100 of each embodiment uses information based on the baseline length to set whether or not to perform metering and the target exposure value, enabling quick and highly accurate focus detection. The present invention is applicable to all products capable of performing phase difference AF, and can also be applied to distance measurement sensors that use a phase difference structure other than imaging devices.

Other Embodiments
The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

According to each embodiment, the presence or absence of metering and the target exposure value can be set using information based on the baseline length. Therefore, according to each embodiment, it is possible to provide a control device, an imaging device, a control method, and a program that are capable of quick and highly accurate focus detection.

The above describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the gist of the invention.

121 CPU (control device)
121a Exposure control unit 121b Exposure condition acquisition unit

Claims (11)

A control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system,
an exposure control unit that performs exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
an exposure condition acquisition unit that acquires an exposure condition for the focus detection based on information based on a base line length,
the information based on the base line length is information regarding the aperture value and the image height,
the exposure condition is an exposure condition that results in a first exposure target value when based on information based on a first base line length, and is an exposure condition that results in a second exposure target value that is different from the first exposure target value when based on information based on a second base line length,
the first exposure target value and the second exposure target value are exposure target values for the focus detection,
the exposure control unit performs the exposure control so as to satisfy the exposure condition;
the first base length is shorter than the second base length;
the first exposure target value is higher than the second exposure target value;
The control device, characterized in that, in the information based on the first baseline length , the first exposure target value is higher than a third exposure target value for acquiring a captured image based on the pixel signal. The control device according to claim 1, characterized in that the exposure condition acquisition unit acquires the exposure conditions based on information based on the contrast of the subject. The imaging optical system further includes a focus adjustment unit that performs focus adjustment control of the imaging optical system,
3. The control device according to claim 1, wherein the exposure control section performs the exposure control based on a change in subject luminance while the focus adjustment section is performing the focus adjustment control. A control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system,
an exposure control unit that performs exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
a focus adjustment unit that performs focus adjustment control of the imaging optical system;
and an exposure change determination unit that determines whether or not the exposure control needs to be performed based on at least current luminance information and information based on a base line length when the focus adjustment unit performs the focus adjustment control,
the information based on the base line length is information regarding a conversion coefficient for converting an image shift amount into a defocus amount,
the exposure change determination unit has a first exposure determination condition in information based on a first base line length, and a second exposure determination condition different from the first exposure determination condition in information based on a second base line length;
the exposure control unit performs the exposure control when the exposure change determination unit determines that the exposure control is to be performed;
the first base length is shorter than the second base length;
A control device according to claim 1, wherein the first exposure determination condition is a determination condition having a smaller allowable range for the difference between the current brightness information and the optimum exposure for focus detection than the second exposure determination condition. The control device according to any one of claims 1 to 4, characterized in that the information based on the baseline length is a value proportional to the baseline length or a value proportional to the inverse of the baseline length. A control device that performs focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system,
an exposure control unit that performs exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
a focus adjustment unit that performs focus adjustment control of the imaging optical system;
and an exposure change determination unit that determines whether or not the exposure control needs to be performed based on at least current luminance information and a lens ID during the focus adjustment control by the focus adjustment unit,
the exposure change determination unit sets a larger allowable range for a difference between the current luminance information and an appropriate exposure in the case of a lens for which a baseline length is easily obtained than in the case of a lens for which a baseline length is difficult to obtain;
The control device, wherein the exposure control unit performs the exposure control when the exposure change determination unit determines that the exposure control is to be performed. an image sensor that performs photoelectric conversion on light passing through different pupil regions of an image pickup optical system and outputs pixel signals;
7. An imaging apparatus comprising: the control device according to claim 1, which performs focus detection based on the pixel signal. A control method for performing focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, comprising:
an exposure control step of performing exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
and acquiring an exposure condition for the focus detection based on information on a base line length,
the information based on the base line length is information regarding the aperture value and the image height,
the exposure condition is an exposure condition that results in a first exposure target value when based on information on a first base line length, and is an exposure condition that results in a second exposure target value that is different from the first exposure target value when based on information on a second base line length,
the first exposure target value and the second exposure target value are exposure target values for the focus detection,
In the exposure control step, the exposure control is performed so as to satisfy the exposure condition.
the first base length is shorter than the second base length;
the first exposure target value is higher than the second exposure target value;
A control method according to claim 1, wherein, in the information based on the first baseline length , the first exposure target value is higher than a third exposure target value for acquiring an image based on the pixel signal. A control method for performing focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, comprising:
an exposure control step of performing exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
a focus adjustment step of performing focus adjustment control of the imaging optical system;
and a determination step of determining whether or not the exposure control needs to be performed based on at least current luminance information and information based on a baseline length during the focus adjustment control,
the information based on the base line length is information regarding a conversion coefficient for converting an image shift amount into a defocus amount,
In the determination step, the necessity of implementation is determined according to a first exposure determination condition for the information based on a first base line length, and the necessity of implementation is determined according to a second exposure determination condition different from the first exposure determination condition for the information based on a second base line length;
When it is determined in the determination step that the exposure control is to be performed, the exposure control is performed in the exposure control step;
the first base length is shorter than the second base length;
A control method according to claim 1, wherein the first exposure determination condition is a determination condition having a smaller tolerance for the difference between the current brightness information and the optimum exposure for focus detection than the second exposure determination condition. A control method for performing focus detection based on pixel signals obtained by photoelectrically converting light passing through different pupil regions of an imaging optical system, comprising:
an exposure control step of performing exposure control based on exposure control values including an exposure time, an imaging sensitivity, and an aperture value;
a focus adjustment step of performing focus adjustment control of the imaging optical system;
and an exposure change determination step of determining whether or not the exposure control needs to be performed based on at least current luminance information and a lens ID during the focus adjustment control by the focus adjustment step,
In the exposure change determination step, a width for allowing a difference between the current luminance information and the appropriate exposure is set larger in the case of a lens for which a baseline length is easily obtained than in the case of a lens for which a baseline length is difficult to obtain;
a step of controlling the exposure when it is determined in the step of determining whether the exposure change is to be performed, and then the step of controlling the exposure performs the exposure control. A program for causing a computer to execute the control method according to any one of claims 8 to 10 .