Imaging apparatus and control method thereof, program and storage medium

Abstract

To use an image stabilization mechanism to obtain appropriate low-pass filter characteristics.SOLUTION: An imaging apparatus comprises: an imaging element in which a plurality of pixels, including focus detection pixels that output signals so as to be able to acquire a pair of focus detection signals having parallax on the basis of light fluxes that have passed through mutually different pupil regions of an imaging optical system, are arranged; movement control means that moves incident positions of the light fluxes in the imaging element; and focus detection means that performs phase difference focus detection using the pair of focus detection signals. The movement control means periodically moves the incident positions a plurality of integer cycles during exposure time for acquiring the pair of focus detection signals, and a point spread function in a first direction for detecting a phase difference obtained by movement has three or more peaks or has a rectangular shape.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an imaging apparatus, a control method thereof, a program, and a storage medium, and more particularly to a vibration-type low-pass filter technique used in the imaging apparatus. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a technique for reducing aliasing distortion by disposing an optical low-pass filter on the incident surface side of an imaging element such as a CCD or CMOS has been known.

[0003] Fig. 10 is a diagram showing a typical spatial frequency and response characteristic of an image generally acquired by an image sensor when no optical low pass filter is arranged. In Fig. 10, the horizontal axis shows the spatial frequency (where the Nyquist frequency is 1), and the vertical axis shows the response. A solid line 901 shows the response characteristic of the image obtained. The response characteristic shown here takes into account the MTF characteristic as an optical characteristic of the photographic optical system for forming an image of the subject light on the image sensor, and therefore the response characteristic slopes downward toward 1, which is the sampling frequency. The MTF characteristic changes depending on various optical conditions, such as the focal state of the lens, the image height on the image sensor, the F-number, zoom, focus position, etc.

[0004] If no optical low-pass filter is used, only the pixel aperture and the imaging optical system have a low-pass filter effect. For example, H The response is also large for relatively high frequencies such as F H According to the sampling theorem, the response to L When calculating the phase difference for focus detection, this frequency F L If you are extracting a band such as HTherefore, conventionally, an optical low-pass filter made of a birefringent material is placed in front of the image sensor to reduce the response characteristics in frequencies higher than the Nyquist frequency, as shown by the dotted line 903, thereby reducing components above the Nyquist frequency that cause moire in the image and noise during focus detection.

[0005] Additionally, the minimum value at which the low-pass filter characteristics cut off frequency components to almost zero is called the trap point (Tp in Fig. 10). Because the low-pass filter characteristics of optical low-pass filters made of birefringent materials vary depending on the material and thickness of the birefringent material, they are generally designed to set the trap point at a position higher than the Nyquist frequency to prevent aliasing signals.

[0006] Meanwhile, many image stabilization techniques have been disclosed for image capture devices such as digital cameras, which correct the effects of shake on the device by moving an image sensor such as a CMOS sensor or some optical elements of the photographing optical system in a direction perpendicular to the optical axis.In addition, a technique has been disclosed for a vibration-type low-pass filter that utilizes a mechanism for image stabilization techniques to obtain an effect equivalent to that of an optical low-pass filter by performing a predetermined drive during image capture (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2021-071573 A Summary of the Invention [Problem to be solved by the invention]

[0008] To prevent aliasing signals, it is ideal to obtain low-pass filter characteristics that do not cut off signals below the Nyquist frequency in order to maintain resolution, but reduce frequency components higher than the Nyquist frequency to zero, as shown by dashed-dotted line 904 in Figure 10. However, conventional optical low-pass filters made of birefringent materials that have a trap point between spatial frequencies 1 and 2 end up with a response as shown by dotted line 903 described above, making it difficult to reduce frequency components higher than the Nyquist frequency to close to zero.

[0009] On the other hand, Patent Document 1 discloses drive control for obtaining the effect of a low-pass filter using a vibration type low-pass filter, but does not describe specific drive control for exerting the effect of a low-pass filter that can reduce frequency components higher than the Nyquist frequency.

[0010] The present invention has been made in consideration of the above problems, and has an object to make it possible to obtain appropriate low-pass filter characteristics by utilizing an image stabilization mechanism. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the imaging device of the present invention comprises an imaging element in which a plurality of pixels including a focus detection pixel that outputs a signal so as to obtain a pair of focus detection signals having parallax based on light beams that have passed through different pupil regions of an imaging optical system, a movement control means for moving the incident position of the light beam on the imaging element, and a focus detection means for performing phase difference focus detection using the pair of focus detection signals, wherein the movement control means periodically moves the incident position for an integer number of periods during the exposure time for obtaining the pair of focus detection signals, and a point spread function in a first direction for detecting the phase difference obtained by the movement has three or more peaks or is rectangular. Effect of the Invention

[0012] According to the present invention, it is possible to obtain appropriate low-pass filter characteristics by utilizing the image stabilization mechanism. [Brief description of the drawings]

[0013] [Figure 1] 1 is a central cross-sectional view and a block diagram showing a functional configuration of an imaging device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing an example of a pixel arrangement in the first embodiment. [Diagram 3] 1A and 1B are schematic diagrams illustrating the case where conventional control of the incident position of incident light using a vibration-type low-pass filter is applied to the present invention, and schematic diagrams for explaining the obtained low-pass filter characteristics and problems. [Figure 4] 3A and 3B are schematic diagrams for explaining a periodic locus of incident light and low-pass filter characteristics of the vibration type low-pass filter in the first embodiment. [Diagram 5] 3A and 3B are schematic diagrams for explaining a periodic locus of incident light by the vibration type low-pass filter and the obtained low-pass filter characteristics in the first embodiment. [Figure 6] FIG. 6 is a schematic diagram showing an example of a periodic locus obtained by driving the anti-vibration lens unit and the image sensor to obtain the periodic locus shown in FIG. 5. [Figure 7] 13A and 13B are schematic diagrams for explaining a periodic locus of incident light by a vibration type low-pass filter and the obtained low-pass filter characteristics in the second embodiment. [Figure 8] 8 is a schematic diagram showing an example of a periodic locus obtained by driving the anti-vibration lens unit and the image sensor to obtain the periodic locus shown in FIG. 7. [Figure 9] 13 is a schematic diagram showing a periodic locus of incident light caused by a vibration type low-pass filter in a modified example. [Figure 10] FIG. 1 is a schematic diagram showing response characteristics with respect to spatial frequency in a conventional optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0015] <First embodiment> FIG. 1 is a diagram showing a configuration of an imaging device 100 according to a first embodiment of the present invention, where FIG. 1(a) is a central cross-sectional view of the imaging device 100, and FIG. 1(b) is a block diagram showing a functional configuration.

[0016] As shown in Fig. 1(a), an imaging device 100 of the present invention comprises a camera body 1 and a lens unit 2 that is detachable from the camera body 1. The lens unit 2 has a photographing optical system 3 consisting of a plurality of lenses including an anti-vibration lens unit 19. Note that a dotted line 4 indicates the optical axis of the photographing optical system 3. The camera body 1 also includes an image sensor 6 and an electronic viewfinder 10a, also called an EVF, that constitutes part of a display device 10. The camera body 1 and the lens unit 2 are connected to be able to communicate with each other via electrical contacts 14.

[0017] 1(b) is a block diagram showing a schematic configuration of the imaging device 100. The imaging device 100, which is made up of a camera body 1 and a lens unit 2, has three main components: an imaging system, an image processing system, a recording / playback system, and a control system. The imaging system includes a photographing optical system 3 and an image sensor 6, and the image processing system includes an image processing unit 7 and a focus detection unit 11. The recording / playback system includes a memory 8 and a display device 10, and the control system includes a camera system control unit 5, a camera operation unit 9, a focus detection unit 11, a lens system control unit 15, a lens shake correction unit 18, and a focus adjustment unit 22.

[0018] 1(a), the lens unit 2 further includes a lens system control unit 15, a lens shake correction unit 18 that drives an anti-shake lens unit 19 to correct image shake, and a lens shake detection unit 20. It also includes a focus adjustment unit 22 that drives a focus lens included in the photographing optical system 3.

[0019] In this embodiment, the lens shake detection unit 20 uses a vibration gyro using the Coriolis force and detects the rotational shake applied to the lens unit 2. The lens shake detection unit 20 detects the shake of the lens unit 2 (hereinafter referred to as "lens shake") caused by the user's hand shake or the like, and outputs a lens shake detection signal representing the lens shake to the lens system control unit 15. The lens system control unit 15 uses the lens shake detection signal to calculate a shift amount (correction amount) of the vibration-proof lens unit 19 for reducing (offsetting) the image shake caused by the lens shake, and outputs a vibration prevention instruction including the shift amount to the lens shake correction unit 18. The lens shake correction unit 18 controls the movement of the vibration-proof lens unit 19 based on the vibration prevention instruction from the lens system control unit 15. Specifically, the lens shake prevention is performed by controlling an actuator included in a shift mechanism in response to the vibration prevention instruction to drive the vibration-proof lens unit 19 by the calculated shift amount.

[0020] In addition to the above-mentioned vibration reduction control, the lens system control unit 15 can drive the focus lens included in the photographing optical system 3 via the focus adjustment unit 22, and drive and control the aperture mechanism and zoom lens (not shown). In addition to vibration reduction control, the lens shake correction unit 18 can drive and control the vibration reduction lens unit 19 based on the control of the lens system control unit 15 so as to reduce the influence of moire caused by aliasing of high spatial frequency components of the subject. This realizes the function as a vibration type low pass filter in this embodiment. Details of the periodic drive control in this embodiment will be described later.

[0021] 1(a), the camera body 1 further includes a camera system control unit 5, an image processing unit 7, a memory 8, a camera operation unit 9, a display unit 10, a focus detection unit 11, a camera shake correction unit 12, and a camera shake detection unit 13. In addition to the electronic viewfinder 10a, the display unit 10 includes a rear display unit (not shown) and a small display panel (not shown) provided on the top surface of the camera body 1 for displaying shooting information.

[0022] FIG. 2 is a diagram showing an example of a pixel array of the image sensor 6 in this embodiment, and shows the pixel array of a two-dimensional CMOS sensor used as the image sensor 6 in a range of 4 columns by 4 rows of imaging pixels.

[0023] In this embodiment, the pixel group 200 is composed of pixels arranged in 2 columns by 2 rows, and is covered with color filters in a Bayer array. In each pixel group 200, a pixel 200R having a spectral sensitivity of R (red) is arranged at the upper left position, a pixel 200G having a spectral sensitivity of G (green) is arranged at the upper right and lower left positions, and a pixel 200B having a spectral sensitivity of B (blue) is arranged at the lower right position. Furthermore, in the image sensor 6 of this embodiment, in order to perform focus detection using an image plane phase difference method, each pixel has multiple photodiodes (photoelectric conversion units) for one microlens 215. In this embodiment, each pixel is composed of two photodiodes 211, 212 arranged in 2 columns by 1 row. Hereinafter, a pixel having such a configuration will be called a "focus detection pixel."

[0024] The image sensor 6 is capable of acquiring an image signal and a focus detection signal by arranging a large number of pixel groups 200, each of which is made up of 2 columns x 2 rows of focus detection pixels (4 columns x 2 rows of photodiodes) as shown in FIG. 2, on the imaging surface.

[0025] In each focus detection pixel having such a configuration, light beams passing through different pupil regions are separated by the microlens 215 and imaged on the photodiodes 211, 212. A signal (signal A+B) obtained by adding the signals from the two photodiodes 211, 212 is used as an imaging signal, and two signals (signal A, signal B) read out from each of the photodiodes 211, 212 are used as a focus detection signal pair. Note that the imaging signal and the focus detection signal may be read out separately, but in consideration of the processing load, the following may also be used. That is, the imaging signal (signal A+B) and a focus detection signal (e.g., signal A) from either one of the photodiodes 211, 212 are read out, and the difference is taken to obtain the other focus detection signal (e.g., signal B) having parallax.

[0026] Then, by collecting a plurality of A signals and a plurality of B signals output from a plurality of pixels, a pair of image signals (A image signal, B image signal) used for AF by the imaging surface phase difference detection method is obtained. Then, the pair of image signals are superimposed while shifting the relative positions, and a correlation calculation is performed to obtain, for example, the area amount of the difference part of the waveform (correlation amount) at each shift position. The shift position where this correlation amount is the smallest, that is, the phase difference which is the shift amount with the highest correlation (hereinafter referred to as "image shift amount") is obtained, and further the defocus amount and defocus direction of the photographing optical system are calculated from the calculated image shift amount.

[0027] By using an image sensor 6 having such a structure, it is possible to perform live view shooting in which the image sensor 6 receives light in real time and the subject image can be observed, and it is also possible to perform phase difference focus detection without a mechanism for splitting the subject light beam.

[0028] In this embodiment, it is assumed that all pixels of the image sensor 6 are focus detection pixels, and that the photodiode 212 receives light from approximately the left half of the exit pupil, and the photodiode 211 receives light from approximately the right half of the exit pupil. In this case, the distance between the photodiodes 211 and the photodiodes 212 adjacent to each other in the division direction is equal to the distance between adjacent focus detection pixels.

[0029] The imaging element 6 having the above configuration converts light from a subject incident via the photographing optical system 3 into an electrical signal by photoelectric conversion processing, and outputs the electrical signal, which is input to the image processing unit 7.

[0030] The image processing unit 7 has an internal A / D converter, a white balance adjustment circuit, a gamma correction circuit, an interpolation calculation circuit, etc., and can generate images for recording. The image processing unit 7 also has a color interpolation processing circuit, which performs color interpolation (demosaicing) processing on the Bayer array signal to generate a color image. The image processing unit 7 also compresses images, videos, audio, etc. using a predetermined method. In addition to such processing for imaging, the image processing unit 7 also works with the focus detection unit 11 to process pixel signals from focus detection pixels, performing so-called focus detection processing between captures.

[0031] The focus detection unit 11 cooperates with the image processing unit 7 to detect the amount of image shift of the optical image based on the output from the focus detection pixels included in the image sensor 6, and converts it into a defocus amount by a known method. The camera system control unit 5 transmits focus adjustment information to the lens system control unit 15 based on the defocus amount output from the focus detection unit 11, and the lens system control unit 15 drives the focus lens in the direction of the optical axis 4 via the focus adjustment unit 22.

[0032] In addition, the camera system control unit 5 performs a predetermined calculation process using the image data obtained by the image processing unit 7 to obtain an appropriate exposure amount, and based on this, controls the aperture included in the shooting optical system 3 and the exposure time of the image sensor 6. In this way, by appropriately adjusting the photographing optical system 3, the image sensor 6 is exposed to an appropriate amount of subject light, and a subject image is formed in the vicinity of the image sensor 6.

[0033] In this embodiment, the camera shake detection unit 13 uses a vibration gyro using the Coriolis force, and detects rotational shake applied to the camera body 1. The camera shake detection unit 13 detects shake of the camera body 1 caused by a user's hand shake or the like (hereinafter referred to as "camera shake"), and outputs a camera shake detection signal representing the camera shake to the camera system control unit 5. The camera system control unit 5 calculates a shift amount (correction amount) of the image sensor 6 for reducing (offsetting) image shake caused by the camera shake from the camera shake detection signal, and outputs an anti-shake instruction including the shift amount to the camera shake correction unit 12. The camera shake correction unit 12 controls an actuator included in a shift mechanism in response to the anti-shake instruction from the camera system control unit 5, thereby shifting the image sensor 6 by the shift amount within a plane perpendicular to the optical axis 4. This performs sensor anti-shake.

[0034] In addition to vibration reduction control, the camera shake correction unit 12 can also drive and control the image sensor 6 under the control of the camera system control unit 5 so as to reduce the effect of moire caused by aliasing of high spatial frequency components of the subject. This realizes the function of a vibration type low pass filter in this embodiment. The details of the drive control in this embodiment will be described later.

[0035] Here, we will explain the effects and problems of a low-pass filter obtained by applying the periodic drive control of the conventional vibration-type low-pass filter described in Patent Document 1. The vibration-type low-pass filter can be realized by moving at least one of the image sensor 6 and the vibration-proof lens unit 19 in a direction perpendicular to the optical axis by the camera shake correction unit 12 and / or the lens shake correction unit 18, thereby shifting the position of light incident on the image sensor 6. Therefore, in the following explanation, the image sensor 6, the vibration-proof lens unit 19, and the combination of the image sensor 6 and the vibration-proof lens unit 19 are collectively referred to as the "shake correction member."

[0036] Fig. 3(a) is a schematic diagram showing the periodic locus of incident light using a shake correction member. The upper part of Fig. 3(a) shows a part of the R (red) and G (green) rows in a Bayer array of pixels constituting the image sensor 6. The region corresponding to the photodiode on the left side of the pixel is conveniently referred to as region A, and the region corresponding to the photodiode on the right side of the pixel is conveniently referred to as region B, with the A regions of the R and G pixels shown as RA and GA, respectively, and the B regions of the R and G pixels shown as RB and GB, respectively.

[0037] The lower part of Fig. 3(a) shows the time change of the position (incident position) of the incident light on the GA pixel indicated by ▼ at the time of t = 0. The vertical axis indicates the downward time course, and the horizontal axis indicates the horizontal position. The time T for two memories indicated by the dotted line in the time direction AF indicates the vertical synchronization period, that is, the exposure time during focus detection or the exposure time during shooting. AF The focus detection pixel interval d is the interval between the focus detection pixels. AF That is, the amplitude of the periodic locus of the incident light shown in FIG. 3(a) is expressed as the interval d AF The periodic locus of the incident light shown in Fig. 3(a) can be realized by periodically driving and controlling the image stabilization member in the horizontal direction.

[0038] In recent years, the frame rate during image capture and focus detection has increased significantly, and the exposure time T AF On the other hand, in order to obtain a low-pass filter characteristic capable of reducing frequency components above the trap point by periodically driving the image stabilization member, the exposure time T AF During the exposure time, it is desirable to shift the position of the incident light by one period or more (an integer period), as shown in FIG. 3(a). Conversely, if the exposure time is long, there is no need to increase the drive frequency of the shake correction member in order to reduce power consumption. Therefore, the exposure time T AF During this, the driving frequency of the shake correction member may be changed in accordance with the exposure time so that the position of the incident light is shifted by one period or more.

[0039] FIG. 3(b) is a one-dimensional graph showing only the direction of movement of the periodic locus on the image plane of the image sensor 6, showing the point spread function (hereafter referred to as "PSF") when a light beam from a point light source is focused on the image plane of the image sensor 6 and the image stabilization member is driven so as to draw a periodic locus as shown in FIG. 3(a). The horizontal axis represents the direction of movement of the incident position, and the vertical axis represents the light intensity. As shown in FIG. 3(a), the distance d AF When the vibration compensation member is driven to have a periodic locus with an amplitude of 1 / 2 of the vibration, the center of the periodic locus is set to 0, and the extreme value of the periodic locus is ±d AF The light intensity is greater at the position of / 2. In other words, the point spread function has two peak light intensities.

[0040] FIG. 3(c) is a diagram showing a schematic diagram of the modulation transfer function (hereinafter referred to as the "MTF characteristic") obtained by Fourier transforming the PSF shown in FIG. 3(b), which is obtained from a periodic locus such as that in FIG. 3(a). The horizontal axis represents spatial frequency, and the vertical axis represents the response. In other words, FIG. 3(c) shows the response characteristic (low-pass filter characteristic) as a vibratory low-pass filter when the shake correction member is driven so as to have the periodic locus of incident light shown in FIG. 3(a). In FIG. 3(a), the periodic locus of incident light has an amplitude (d AF Since the image stabilization member is driven to have a trap point (Tp1) at a frequency slightly higher than the Nyquist frequency (F / 2), the low-pass filter characteristic that is actually obtained has a trap point (Tp1) at a frequency slightly higher than the Nyquist frequency, as shown in FIG. 3(c). As described with reference to FIG. 10, the detection frequency during focus detection is the frequency F L Therefore, the frequency F H Therefore, the low-pass filter characteristic shown in FIG 3C cannot reduce the aliasing noise during focus detection.

[0041] Next, another periodic movement control of the incident position of incident light performed by driving the shake correction member and the resulting low-pass filter characteristics will be described with reference to FIG.

[0042] FIG. 4(a) shows waveforms of two types of amplitude when the incident position of the incident light is moved in one direction (here, the division direction of the focus detection pixels, i.e., the phase difference detection direction) in a plane perpendicular to the optical axis 4 so as to form a linear periodic locus. In FIG. 4(a), the amplitude (d AF / 2) is a periodic locus with an amplitude a larger than AF A periodic locus having an amplitude b smaller than d / 2 is shown by a dashed line 402. The amplitude a of the periodic locus 401 is determined by the interval d between focus detection pixels. AF d AF Less than.

[0043] Fig. 4(b) shows the PSF of light that forms an image on the image plane of the image sensor 6 when the shake correction member is driven so that a light beam from a point light source traces the periodic locus shown in Fig. 4(a) on the image sensor 6. A solid line 411 in Fig. 4(b) shows the PSF corresponding to the periodic locus 401 in Fig. 4(a), and a dashed line 412 shows the PSF corresponding to the periodic locus 402 in Fig. 4(a). In this case, as in Fig. 3(b), the light intensity becomes large at the extreme values ​​of the periodic loci 411 and 412 (±a for PSF 411 and ±b for PSF 412).

[0044] Fig. 4(c) shows the MTF characteristics. The low-pass filter characteristics obtained by driving the shake correction member so as to form the periodic locus 401 shown in Fig. 4(a) are as shown by the solid line 421 in Fig. 4(c). Moreover, the low-pass filter characteristics obtained by driving the shake correction member so as to form the periodic locus 402 shown in Fig. 4(a) are as shown by the dashed line 422 in Fig. 4(c).

[0045] Generally, the larger the amplitude, the greater the effect of the obtained low-pass filter, so the trap point is formed on the low-frequency side. Since the amplitude a of the periodic locus 401 shown in Fig. 4(a) is larger than the amplitude of the periodic locus shown in Fig. 3(a), the result is the low-pass filter characteristic 421 shown in Fig. 4(c). In addition, the amplitude a of the periodic locus 401 shown in Fig. 4(a) is determined so that the trap point (Tp2) of the low-pass filter characteristic 421 coincides with the Nyquist frequency.

[0046] On the other hand, since the amplitude b of the periodic locus 402 shown in FIG. 4(a) is smaller than the amplitude a of the periodic locus 401, the result is a low-pass filter characteristic 422 shown in FIG. 4(c), and a trap point (Tp3) is formed at a frequency higher than the Nyquist frequency. As can be seen from FIG. 4(c), the low-pass filter characteristic 422 is more effective at reducing the frequency F than the low-pass filter characteristic 421. H Therefore, the absolute amount of aliasing noise can be reduced. In this way, the low-pass filter characteristics of the periodic locus obtained by driving the shake correction member can be arbitrarily controlled by changing the amplitude.

[0047] Taking the above-mentioned characteristics into consideration, a method for obtaining more effective low-pass filter characteristics will be described. 5A is a schematic diagram showing a periodic locus of incident light by the vibration type low-pass filter in this embodiment. This periodic locus is a periodic locus in which the incident position of the incident light moves along a periodic locus 401 of amplitude a and a periodic locus 402 of amplitude b shown in FIG. 4A for one period each for an exposure time T AF 4 shows the periodic locus when

[0048] FIG. 5(b) shows the PSF obtained when the shake correction member is driven to form the periodic locus shown in FIG. 5(a). The PSF in FIG. 5(b) is a combination of PSF411 and PSF412 in FIG. 4(b), and the light intensity is high at the extreme values ​​-a, a, -b, and b of the periodic locus shown in FIG. 5(a). In other words, this indicates that the PSF has four peak light intensities. Furthermore, in FIG. 5(a), -a, a, -b, and b are distributed over GA, GB, and RA. In other words, light emitted from the same point passes through the photographing optical system 3 and enters multiple different pixels of the image sensor 6.

[0049] The MTF characteristic obtained from the PSF shown in Fig. 5(b) is as shown in Fig. 5(c). The low-pass filter characteristic shown in Fig. 5(c) is a product of the low-pass filter characteristic 421 and the low-pass filter characteristic 422 in Fig. 4(c). Therefore, the frequency F is more effectively suppressed than the low-pass filter characteristic 421 shown in Fig. 4(c) that is obtained when the shake correction member is driven to have a periodic locus of a single amplitude. H In addition, the absolute amount of aliasing noise at frequency F during focus detection can be reduced. H In addition to the aliasing noise, signals exceeding the Nyquist frequency that generate moire signals in an image can also be more effectively suppressed.

[0050] In the example shown in FIG. 5, the image stabilization member is driven so that the amplitude of the periodic locus of the incident light has two types, amplitude a and amplitude b. However, the present invention is not limited to this. AF It is sufficient to control the shake correction member so that a periodic locus having at least two types of amplitude is inserted between the vibration source and the vibration source, one period for each of which is multiple periods. Three or more types of amplitude may be used.

[0051] In addition, by setting the smallest amplitude as the first amplitude and making the other amplitudes not integer multiples of the first amplitude, it is possible to prevent overlapping of trap points. This makes it possible to more effectively cut off high frequencies higher than the Nyquist frequency. For example, when the exposure time TAF When the incident position of the incident light is moved so as to have a periodic locus with three or more periods between the first amplitude and the second amplitude, it is possible to set a first amplitude and a second amplitude different from the first amplitude, and gradually change the amplitude from the first amplitude to the second amplitude.

[0052] Also, aliasing noise can be more effectively suppressed by combining the periodic trajectories of incident light of various amplitudes. However, it is generally better not to reduce the positive signal (the signal with a frequency equal to or lower than the Nyquist frequency) too much in order to maintain the sense of resolution of the image and to retain the focus detection signal.

[0053] During focus detection, the detection frequency F L However, when recording an image, the entire positive signal (signal below the Nyquist frequency) is required for the sense of resolution of the image. Therefore, the amplitude of the periodic locus of the incident light may be controlled so that different low-pass filter characteristics are obtained during focus detection and image recording.

[0054] As described above, the periodic locus shown in FIG. 5(a) can be obtained by driving at least one of the anti-vibration lens unit 19 and the image sensor 6. Below, we will explain a driving method when driving both the anti-vibration lens unit 19 and the image sensor 6.

[0055] 6 is a diagram showing the periodic locus when lens shake correction section 18 and camera shake correction section 12 drive anti-shake lens unit 19 and image sensor 6, respectively, to periodically move the incident position of incident light in the phase difference detection direction, and a composite waveform of these two periodic loci. The horizontal axis indicates time, and the vertical axis indicates position in the phase difference detection direction.

[0056] In the example shown in Fig. 6, the anti-vibration lens unit 19 and the image sensor 6 are driven so that the periodic locus of the incident light from each becomes a sine wave waveform having a mutually different amplitude and frequency in the phase difference detection direction. The dashed line 601 in Fig. 6 indicates the periodic locus obtained by driving the image sensor 6 by the camera shake correction unit 12, and the dashed-dotted line 602 indicates the periodic locus obtained by driving the anti-vibration lens unit 19 by the lens shake correction unit 18. In addition, the solid line 603 is a composite periodic locus of the two periodic loci 601 and 602.

[0057] In this way, by driving the vibration-proof lens unit 19 and the image sensor 6, it is possible to create a composite periodic locus that repeatedly changes the periodic locus of different amplitudes every period. This composite periodic locus is the same periodic locus as the time change in the incident position of the incident light on the image sensor 6 shown in FIG. 5(a).

[0058] Note that, although Fig. 6 shows an example in which the anti-vibration lens unit 19 and the image sensor 6 are driven on sinusoidal periodic loci with different amplitudes and frequencies, the present invention is not limited to the periodic locus shown in Fig. 6. It is sufficient that the periodic locus can obtain the desired low-pass filter effect by synthesizing two periodic loci obtained by driving the anti-vibration lens unit 19 and the image sensor 6 to obtain periodic loci with different amplitudes and frequencies.

[0059] As described above, according to the first embodiment, by driving the shake correction member so that the periodic locus of incident light has a plurality of different amplitudes during the exposure time, it is possible to obtain more effective low-pass filter characteristics.

[0060] <Second embodiment> Next, a second embodiment of the present invention will be described. In the second embodiment, another example of periodic movement control of incident light by a vibration type low-pass filter will be described. Note that the imaging device in the second embodiment is similar to that described in the first embodiment with reference to Figs. 1 and 2, and therefore the description will be omitted.

[0061] FIG. 7(a) is a schematic diagram showing the periodic locus of incident light in the second embodiment, which shows the time change in the phase difference detection direction of the position where the incident light is incident on the image sensor 6, and can be realized by driving the shake correction member in one direction in a plane perpendicular to the optical axis 4. In the example of FIG. 7(a), the periodic locus is a triangular wave, and the exposure time T AF The vibration correction member is driven so that it goes inside for one period.

[0062] In the example shown in FIG. 7(a), the exposure time T AF In the example shown in FIG. 7A, the amplitude of the periodic locus between the focus detection pixels d is one period, but the present invention is not limited to this. The image stabilizer may be driven so that the period is an integer number of periods equal to or greater than one period. AF In FIG. 7A, the extreme values ​​of the periodic locus of the triangular wave are expressed as -c and c for the amplitude c, and c is the interval d between the focus detection pixels. AF is the same length as

[0063] FIG. 7(b) shows the PSF obtained when the shake correction member is driven to follow the periodic locus shown in FIG. 7(a). The PSF in FIG. 7(b) has a constant light intensity between the extreme values ​​-c and c in FIG. 7(a). In other words, the PSF is a rectangular function. Furthermore, in FIG. 7(a), -c and c are distributed over the two GAs, GB, RA, and RB. In other words, light emitted from the same point passes through the photographing optical system 3 and enters multiple different pixels of the image sensor 6.

[0064] The MTF characteristic obtained from this PSF is as shown in FIG. 7(c). The amplitude of the periodic locus of the triangular wave shown in FIG. 7(a) is calculated by dividing the periodic locus by the interval d of the focus detection pixels. AF 4(c) , the trap point (Tp4 in FIG. 7(c)) can be made to coincide with the Nyquist frequency. The low-pass filter characteristic obtained by this is more effective at reducing the frequency F than the low-pass filter characteristic 421 shown in FIG. H In addition, the absolute amount of aliasing noise at frequency F during focus detection can be reduced. HIn addition to the aliasing noise, signals above the Nyquist frequency that generate moire signals in an image can also be more effectively suppressed.

[0065] In addition, the periodic locus in Fig. 5(a) is AF In contrast, the periodic trajectory in Fig. 7(a) requires multiple amplitudes during the exposure time T AF Therefore, the periodic locus of FIG. 7(a) can lower the drive frequency of the shake correction member compared to the periodic locus of FIG. 5(a), so that the exposure time T AF In this manner, in the present embodiment, by driving the shake correction member so as to have a periodic locus of a triangular wave, it is possible to obtain more effective low-pass filter characteristics.

[0066] As described above, the periodic locus shown in FIG. 7(a) can be obtained by driving at least one of the anti-vibration lens unit 19 and the image sensor 6. Below, a driving method for driving both the anti-vibration lens unit 19 and the image sensor 6 will be described.

[0067] 8 is a diagram showing the periodic locus when lens shake correction section 18 and camera shake correction section 12 drive anti-shake lens unit 19 and image sensor 6, respectively, to periodically move the incident position of incident light in the phase difference detection direction, and a composite waveform of these two periodic loci. The horizontal axis indicates time, and the vertical axis indicates position in the phase difference detection direction.

[0068] In the example shown in Fig. 8, the anti-vibration lens unit 19 and the image sensor 6 are driven so that the periodic locus of the incident light from each becomes a sine wave waveform having a mutually different amplitude and frequency in the phase difference detection direction. The dashed line 801 in Fig. 8(a) indicates the periodic locus obtained by driving the image sensor 6 by the camera shake correction unit 12, and the dashed-dotted line 802 indicates the periodic locus obtained by driving the anti-vibration lens unit 19 by the lens shake correction unit 18. Moreover, the solid line 803 in Fig. 8(b) is a composite periodic locus of the two periodic loci 801 and 802.

[0069] The periodic locus obtained by driving the image sensor 6 has one-ninth the amplitude and three times the frequency of the periodic locus obtained by driving the vibration-proof lens unit 19. In this way, a composite periodic locus with a waveform of an approximately triangular wave can be obtained. This composite periodic locus has a waveform of a periodic locus close to the time change in the position where the subject light beam enters the image sensor 6 as shown in FIG. 7(a).

[0070] In this embodiment, it is desirable to obtain a periodic locus as shown in FIG. 7(a) by driving either the vibration-proof lens unit 19 or the image sensor 6. However, when the exposure time T AF As the period becomes shorter, it is necessary to set the drive frequency of the image stabilization member higher, which causes the response of the image stabilization member to the drive to become poor, and the triangular drive waveform becomes closer to a sine wave. In such a case, it is effective to obtain a composite periodic locus with a waveform close to a triangular wave by driving the image stabilization lens unit 19 and the image sensor 6 separately so as to obtain a periodic locus as shown in Figure 8(a).

[0071] The PSF and MTF characteristics due to the composite periodic locus shown in Fig. 8(b) are close to those in Fig. 7(b) and Fig. 7(c). Therefore, as shown in Fig. 8(a), by driving the anti-vibration lens unit 19 and the image sensor 6 so as to obtain a composite periodic locus whose waveform is close to the periodic locus of a triangular wave, it is possible to obtain more effective low-pass filter characteristics.

[0072] Note that the periodic locus for driving the anti-vibration lens unit 19 and the image sensor 6 to obtain a periodic locus close to a triangular wave is not limited to the periodic locus shown in Fig. 8(a). It is sufficient to drive the anti-vibration lens unit 19 and the image sensor 6 so as to obtain a periodic locus close to a triangular wave by combining two periodic loci obtained by driving the anti-vibration lens unit 19 and the image sensor 6 so as to obtain periodic loci with different amplitudes and frequencies.

[0073] As described above, according to the second embodiment, by driving the shake correction member so that the periodic locus of incident light during the exposure time has a triangular waveform, it is possible to obtain more effective low-pass filter characteristics.

[0074] <Third embodiment> Next, a third embodiment of the present invention will be described. Note that the imaging device in the third embodiment is similar to that described in the first embodiment with reference to Figs. 1 and 2, and therefore the description will be omitted.

[0075] In the above-described first and second embodiments, a method of driving the shake correction member so as to draw a linear periodic locus in the horizontal direction (focus detection direction) has been described. However, the image sensor 6 is also connected in the horizontal and vertical directions. Therefore, in the third embodiment, a case will be described in which the shake correction member is driven so as to draw a periodic locus in the vertical direction as well.

[0076] FIG. 9(a) is a schematic diagram of a periodic locus of incident light obtained by driving the shake correction member in the third embodiment. In the example of FIG. 9(a), the shake correction member is driven in a plane perpendicular to the optical axis 4 so as to obtain an Arabic numeral eight shape. Furthermore, the shake correction member is driven so that the direction in which the two circles that form the figure eight of the periodic locus join together coincides with the phase difference detection direction. In addition, if the period until the figure eight is drawn is considered as one period of the figure eight-shaped periodic locus in FIG. 9(a), the exposure time T AF In the example shown in FIG. 9A, the length of both ends of the horizontal periodic locus of the figure eight is equal to or greater than the interval d between focus detection pixels. AF The vibration correction member is driven so that the vibration is twice as large as the vibration.

[0077] Fig. 9(b) shows the PSF obtained when the shake correction member is driven to form the periodic locus shown in Fig. 9(a). The horizontal axis is the horizontal direction of the image sensor 6 in Fig. 9(a), i.e., the direction in which the phase difference is detected by focus detection, and shows the PSF at the vertical center position of the figure-8-shaped periodic locus (L1 in Fig. 9(a)). In the example shown in Fig. 9(b), the horizontal center position of the figure-8-shaped periodic locus is expressed as 0, the left end as -c, and the right end as c, but c is d. AF This PSF has three peak light intensities, with the highest light intensity at the horizontal center position 0 of the figure-8 shaped periodic locus, followed by -c and c. Furthermore, as shown in FIG. 9(a), -c is distributed in BA, 0 in GA, and c in another BA. In other words, light emitted from the same point passes through the photographing optical system 3 and is incident on multiple different pixels of the image sensor 6.

[0078] The low-pass filter characteristic obtained from the PSF shown in Fig. 9(b) is as shown by a solid line 901 in Fig. 9(c). A dashed line 902 in Fig. 9(c) is the low-pass filter characteristic 421 corresponding to the periodic locus shown in Fig. 4(c). As shown in Fig. 9(a), the length of both ends of the figure-of-eight periodic locus in the horizontal direction is set to the interval d of the focus detection pixels. AF By setting it to twice the Nyquist frequency, one of the trap points (Tp5) can be made to coincide with the Nyquist frequency.

[0079] The low-pass filter characteristic 901 obtained by this is compared with the low-pass filter characteristic 902 at a frequency F H Although it cannot be said that the absolute amount of aliasing noise in the image is effectively reduced, aliasing of signals exceeding the Nyquist frequency 1, which generates moire signals in the image, can be more effectively suppressed. In this way, by driving the image stabilization member so as to form a figure-of-eight periodic locus, more effective low-pass filter characteristics can be obtained.

[0080] As described above, according to the third embodiment, by driving the shake correction member so that the periodic locus of incident light during the exposure time forms an eight-shape, it is possible to obtain more effective low-pass filter characteristics.

[0081] <Modification> Although aliasing noise can be suppressed more effectively by the above-mentioned various periodic locus drive control, it is generally better not to reduce the positive signal (signal below the Nyquist frequency) too much in order to maintain the resolution of the image and to leave the focus detection signal. Therefore, in the first to third embodiments, the trap points (Tp2, Tp4, Tp5) in the MTF characteristics are described as being equal to the Nyquist frequency, but this is not limited thereto, and the trap points may be equal to or higher than the Nyquist frequency. In other words, the trap points may be smaller than the amplitude of the periodic locus specified in the first and second embodiments, or the length of both ends of the figure-of-eight periodic locus in the horizontal direction specified in the third embodiment.

[0082] During focus detection, the detection frequency F L However, during image recording, the entire positive signal (signal below the Nyquist frequency) is necessary for the sense of resolution of the image, so the method of drive control of the periodic locus may be changed between focus detection and image recording.

[0083] 2, the photodiodes 211, 212 in the focus detection pixel are arranged in the row direction (horizontal direction), but they may be arranged in the column direction (vertical direction). In that case, the direction in which the periodic drive control is performed should be the column direction. In addition, if four photodiodes are arranged in a cross-shaped configuration in the focus detection pixel, the periodic drive control should be performed in the division direction of the exit pupil that corresponds to the combination of signals output from the photodiodes used for focus detection.

[0084] In the above-mentioned embodiment, the focus detection direction based on the phase difference is one direction, but the present invention can be applied to the case where the phase difference detection direction is two directions. That is, the periodic locus obtained by driving the shake correction member only in one direction in the first and second embodiments is obtained by driving the shake correction member in the other phase difference detection direction in the same manner. When the same periodic locus is driven in the same phase in two directions, it becomes a linear periodic locus in a plane perpendicular to the optical axis 4, which is a realizable periodic locus, but this is not limited. As a result, the low-pass filter characteristics obtained are the same as those described in the first and second embodiments.

[0085] In the above embodiment, all the photoelectric conversion units of the imaging pixels are focus detection pixels, but the present invention is not limited to this and the focus detection pixels may be arranged discretely. In this case, the above-mentioned periodic drive control may be performed when acquiring a signal for focus detection.

[0086] In the above embodiment, the explanation is given using a digital camera with interchangeable lenses (a so-called single-lens camera), but the present invention is not limited to this and may be a digital camera with fixed lenses (a so-called compact digital camera). Also, although there is no particular mention of whether the focus detection operation is for still images or videos, the present invention is not limited by this.

[0087] <Other embodiments> The present invention may be applied to a system made up of a plurality of devices, or to an apparatus made up of a single device.

[0088] The present invention can also be realized by supplying a program for implementing one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0089] <Summary> The disclosure of this embodiment includes the following configuration.

[0090] (Item 1) an image sensor in which a plurality of pixels are arranged, including focus detection pixels that output signals so that a pair of focus detection signals having parallax can be obtained based on light beams that have passed through different pupil regions of an image capturing optical system; a movement control means for moving an incident position of the light beam on the imaging element; a focus detection unit that performs focus detection by a phase difference method using the pair of focus detection signals, the movement control means periodically moves the incident position an integer number of times during an exposure time for acquiring the pair of focus detection signals, and a point spread function in a first direction for detecting a phase difference obtained by the movement has three or more peaks or is rectangular. (Item 2) 2. The imaging device according to item 1, wherein the movement control means moves the incident position in the first direction. (Item 3) The imaging device described in item 2, characterized in that the periodic movement of the incident position includes a movement of a first amplitude determined based on the interval between the focus detection pixels and a movement of a second amplitude different from the first amplitude. (Item 4) 4. The imaging device according to item 3, wherein the first amplitude is greater than 1 / 2 the spacing between the focus detection pixels and smaller than the spacing between the focus detection pixels. (Item 5) 3. The imaging device according to item 2, wherein the movement control means moves so that a locus of the incident position with respect to time forms a triangular wave. (Item 6) 6. The imaging device according to item 5, wherein the amplitude of the triangular wave is the interval between the focus detection pixels. (Item 7) The imaging device described in item 1, characterized in that the movement control means moves the incident position so as to form a trajectory of two connected circles in the first direction during the exposure time for acquiring the pair of focus detection signals. (Item 8) The length of the two circles in the first direction is twice the interval between the focus detection pixels. 8. The imaging device according to item 7, characterized in that (Item 9) The imaging device according to any one of items 1 to 8, characterized in that the movement control means moves at least one of the image sensor and an anti-vibration lens included in the imaging optical system on a plane perpendicular to the optical axis of the imaging optical system. (Item 10) The imaging device described in item 9, characterized in that the movement control means moves the image sensor and the vibration-proof lens included in the imaging optical system on a plane perpendicular to the optical axis of the imaging optical system, thereby moving the incident position of the light beam with amplitudes and periods different from each other. (Item 11) A control method for an imaging device having an image sensor in which a plurality of pixels including focus detection pixels that output signals capable of acquiring a pair of focus detection signals having parallax for performing focus detection by a phase difference method based on light beams that have passed through different pupil regions of an imaging optical system, and a movement control means that moves an incident position of the light beams on the image sensor, the control method comprising: the movement control means includes a step of periodically moving the incident position for an integer number of periods during an exposure time for acquiring the pair of focus detection signals, A control method, characterized in that a point spread function in a first direction for detecting a phase difference obtained by the movement has three or more peaks or is rectangular. (Item 12) A program for causing a computer to execute each step of the control method described in item 11. (Item 13) Item 13. A computer-readable storage medium storing the program according to item 12. [Explanation of symbols]

[0091] 1: camera body, 2: lens unit, 3: photographing optical system, 5: camera system control unit, 7: image processing unit, 11: focus detection unit, 12: camera shake correction unit, 15: lens system control unit, 18: lens shake correction unit, 19: vibration-proof lens unit, 22: focus adjustment unit, 100: imaging device

Claims

1. An image sensor having multiple pixels arranged in a plurality of pixels, including focus detection pixels that output signals in a manner that allows acquisition of a pair of focus detection signals having parallax based on light beams passing through different pupil regions of the imaging optical system, Movement control means for moving the incident position of the light beam in the image sensor, The system includes a focus detection means that performs phase difference type focus detection using the pair of focus detection signals, The imaging apparatus is characterized in that the movement control means performs periodic movement of the incident position for an integer number of periods during the exposure time for acquiring the pair of focus detection signals, and the point image distribution function in the first direction for detecting the phase difference obtained by the movement has three or more peaks or is rectangular.

2. The imaging apparatus according to claim 1, characterized in that the movement control means moves the incident position in the first direction.

3. The imaging apparatus according to claim 2, characterized in that the periodic movement of the incident position includes a movement of a first amplitude determined based on the interval of the focus detection pixels and a movement of a second amplitude different from the first amplitude.

4. The imaging apparatus according to claim 3, characterized in that the first amplitude is greater than half the spacing between the focus detection pixels and less than the spacing between the focus detection pixels.

5. The imaging apparatus according to claim 2, characterized in that the movement control means moves such that the trajectory of the incident position with respect to time is a triangular wave.

6. The imaging apparatus according to claim 5, characterized in that the amplitude of the triangular wave is the interval between the focus detection pixels.

7. The imaging apparatus according to claim 1, characterized in that the movement control means moves the incident position during the exposure time for acquiring the pair of focus detection signals such that the trajectory consists of two interconnected circles in the first direction.

8. The length of the two circles in the first direction is twice the distance between the focus detection pixels. The imaging apparatus according to claim 7, characterized by the following:

9. The imaging apparatus according to any one of claims 1 to 8, characterized in that the movement control means moves at least one of the image sensor and the vibration-damping lens included in the imaging optical system on a plane perpendicular to the optical axis of the imaging optical system.

10. The imaging apparatus according to claim 9, characterized in that the movement control means moves the image sensor and the vibration-damping lens included in the imaging optical system on a plane perpendicular to the optical axis of the imaging optical system, thereby moving the incident position of the light beam with different amplitudes and periods from each other.

11. The imaging apparatus according to claim 2, characterized in that the point image distribution function in the first direction for detecting the phase difference obtained by the movement has three or more peaks.

12. A control method for an imaging device comprising: an image sensor having a plurality of pixels arranged such that each pixel includes a focus detection pixel that outputs a pair of focus detection signals having parallax for performing phase-difference focus detection based on light beams passing through different pupil regions of the imaging optical system; and a movement control means for moving the incident position of the light beam in the image sensor, The movement control means includes a step of performing a periodic movement of the incident position for an integer number of periods during the exposure time for acquiring the pair of focus detection signals. A control method characterized in that the point image distribution function in the first direction for detecting the phase difference obtained by the aforementioned movement has three or more peaks or is rectangular.

13. A program for causing a computer to perform each step of the control method described in claim 12.

14. A computer-readable storage medium storing the program described in claim 13.

Images