Imaging device, its control method, and program

Abstract

The present invention provides an imaging device, a control method thereof, and a program that reduce the impact of vibrations caused by the focal-plane shutter on captured images and that can appropriately switch the shutter drive mode according to the subject's condition. [Solution] The system comprises a shooting optical system, an image sensor, a shutter speed selection means, a subject detection means, a shutter drive mode switching means for switching the shutter drive mode between a mechanical shutter mode and an electronic front curtain shutter mode, and a camera shake correction means. The shutter drive mode to be switched by the shutter drive mode switching means is determined according to the selection result of the shutter speed selection means and the detection result of the subject detection means in the shooting preparation state.

Description

Technical Field

[0005] ,

[0001] The present invention relates to an imaging device, a control method thereof, and a program, and particularly to an imaging device having a shake correction means during shooting, a control method thereof, and a program.

Background Art

[0002] In recent years, due to the high performance of imaging devices, many imaging devices and photographic lenses are equipped with a shake correction mechanism. With the shake correction mechanism, when a user takes a picture using an imaging device, it is possible to reduce the influence of shake on the captured image.

[0003] In an imaging device equipped with such a shake correction function, vibrations generated by the driving of a driving unit inside the imaging device such as a shutter may be transmitted to a shake detection means or a shake correction mechanism provided for detecting hand shake. In this case, a phenomenon called shutter shock occurs in which the shake correction mechanism operates regardless of hand shake and blur occurs in the captured image. The focal plane shutter that causes the vibration causing shutter shock has two shutter traveling curtains, which are divided into a mechanical front curtain shutter that is driven as the exposure of the imaging device starts and a mechanical rear curtain shutter that is driven at the end of exposure.

[0004] Many imaging devices are provided with a plurality of shutter drive modes. One of them is a mechanical shutter mode in which both the mechanical front curtain shutter and the mechanical rear curtain shutter are used for shutter drive. In addition, there are an electronic front curtain shutter mode in which the mechanical front curtain shutter is not used by electronically performing the readout start operation of the imaging element, and an electronic shutter mode in which neither the mechanical front curtain shutter nor the mechanical rear curtain shutter is used by electronically performing the exposure end operation of the imaging element.

[0005] Shutter shock is primarily caused by vibrations from the mechanical front curtain shutter's operation during image sensor exposure, which are transmitted to the blur detection and blur correction mechanisms. Therefore, shutter shock occurs frequently in mechanical shutter mode, is reduced in frequency in electronic front curtain shutter mode, and almost completely disappears in electronic shutter mode.

[0006] On the other hand, in electronic front curtain shutter mode, the image sensor, which acts as the electronic front curtain shutter, and the mechanical rear curtain shutter are separated in the optical axis direction. This can cause a phenomenon called "bokeh clipping," where the shape of bokeh in the captured image is distorted, especially at high shutter speeds. Therefore, it is generally preferred to drive the shutter in mechanical shutter mode at high shutter speeds.

[0007] This "bokeh defect" is a phenomenon where uneven exposure occurs within the bokeh because the mechanical rear curtain shutter of the focal-plane shutter and the image sensor (where the electronic front curtain shutter moves) are separated in the optical axis direction. This phenomenon is particularly noticeable at high shutter speeds. Therefore, although the electronic shutter mode has the advantage of suppressing shutter shock, it is generally preferred to drive the shutter in mechanical shutter mode at high shutter speeds.

[0008] Therefore, for example, in Patent Document 1, if the amount of blur detected by the blur detection means is above a certain level and the shutter speed is low, the effect of shutter shock becomes large, so the system is controlled to electronic front curtain shutter mode, and in other cases, it is controlled to mechanical shutter mode. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2007-193155 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the technology described in Patent Document 1 has the problem that, in a shooting mode where the imaging device automatically determines the exposure (shutter speed), the shutter speed changes with each shot, and consequently, the shutter drive mode also changes frequently.

[0011] Furthermore, imaging devices equipped with an image stabilization mechanism that drives the image sensor to correct for camera shake may also have an automatic horizontal correction function that rotates the image sensor relative to the optical axis of the imaging optical system to ensure that the captured image is horizontal. This function works by driving the image sensor in accordance with the tilt of the imaging device detected by the shake detection means, thereby correcting the slight tilt of the imaging device at the start of shooting during handheld shooting and maintaining the horizontality of the captured image.

[0012] When this automatic horizontal correction function is activated, using the technology disclosed in Patent Document 1 presents the problem that uneven exposure occurs each time the shutter mode is switched.

[0013] Therefore, the present invention aims to provide an imaging device, a control method therefor, and a program that can reduce the influence of vibrations caused by a focal-plane shutter on captured images and appropriately switch the shutter drive mode according to the conditions of the subject. [Means for solving the problem]

[0014] To solve the above problems, the imaging device according to claim 1 of the present invention is characterized by comprising: an imaging optical system; an image sensor; a shutter speed selection means for selecting a shutter speed; a detection means for detecting the state of a subject from a captured image; a focal plane shutter equipped with a mechanical front curtain shutter and a mechanical rear curtain shutter; an electronic front curtain shutter; a shutter drive mode switching means for switching the shutter drive mode during shooting operation to one of a first shutter drive mode using the mechanical front curtain shutter and the mechanical rear curtain shutter in the focal plane shutter, or a second shutter drive mode using the electronic front curtain shutter and the mechanical rear curtain shutter in the focal plane shutter; a blur correction means; and a determination means for determining the shutter drive mode to be switched by the shutter drive mode switching means according to the selection result of the shutter speed selection means and the detection result of the detection means in a shooting preparation state. [Effects of the Invention]

[0015] According to the present invention, the influence of vibrations caused by the focal-plane shutter on the captured image is reduced, and the shutter drive mode can be appropriately switched depending on the subject. [Brief explanation of the drawing]

[0016] [Figure 1A] This is a schematic cross-sectional view of the imaging device in the first embodiment of the present invention. [Figure 1B] This is a block diagram showing the hardware configuration of the imaging device. [Figure 2] This figure illustrates the principle of exposure unevenness generation in the first embodiment of the present invention. [Figure 3] This figure illustrates a method for determining the shutter drive mode when photographing a subject with significant brightness unevenness in the first embodiment of the present invention. [Figure 4] This figure illustrates a method for determining the shutter drive mode when photographing a subject with minimal brightness unevenness in the first embodiment of the present invention. [Figure 5]It is a flowchart of a shooting control process according to the first embodiment of the present invention. [Figure 6] It is a diagram for explaining a method for determining a shutter drive mode when shooting a subject located near the center of the screen in the second embodiment of the present invention. [Figure 7] It is a diagram for explaining a method for determining a shutter drive mode when shooting a subject with a high spatial frequency in the third embodiment of the present invention.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential for the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0018] (First Embodiment) Hereinafter, an imaging device (hereinafter, imaging device 100) according to the first embodiment of the present invention will be described with reference to FIGS. 1A, 1B, 2 to 5. FIG. 1A is a schematic cross-sectional view of the imaging device 100, and FIG. 1B is a block diagram showing the hardware configuration of the imaging device 100. Configurations denoted by the same reference numerals in FIGS. 1A and 1B represent the same configuration

[0019] In FIGS. 1A and 1B, the imaging device 100 includes a camera body 1, a lens barrel 2 attached to the camera body 1, and an electrical contact 11 for communicating between the camera body 1 and the lens barrel 2.

[0020] The lens barrel 2 includes a photographing optical system 3 composed of a plurality of lenses on the photographing optical axis 4 and a lens system control unit 12. The photographing optical system 3 includes a blur correction lens 3a for performing blur correction.

[0021] The camera body 1 comprises a camera system control unit 5, an image sensor 6, an image processing unit 7, a memory means 8, and a display means 9. The camera body 1 also includes an operation detection unit 10 that detects signals from an operation means, including a focal-plane shutter 17 located in front of the image sensor 6 and a shutter release button (not shown).

[0022] The camera system control unit 5 consists of a CPU, ROM, RAM, etc. The CPU reads a program from the ROM and loads it into the RAM, thereby executing the shooting control process (Figure 5) described later.

[0023] Furthermore, the lens barrel 2 includes a lens-side image stabilization means 13 (image stabilization means) that drives an image stabilization lens 3a for image stabilization in a plane perpendicular to the shooting optical axis 4, and a lens-side image stabilization detection means 16 that detects the amount of shake of the imaging device 100. Similarly, the camera body 1 includes a camera-side image stabilization means 14 (image stabilization means) that drives the image sensor 6 in a plane perpendicular to the shooting optical axis 4, and a camera-side image stabilization detection means 15 that detects the amount of shake of the imaging device 100.

[0024] The camera body 1 further includes a shutter drive mode switching means 18, a subject detection means 19, a shutter speed selection means 20, and a focus point selection means 21.

[0025] The shutter drive mode switching means 18 switches the shutter drive mode during shooting operation according to a command from the camera system control unit 5. In this embodiment, the shutter drive mode switching means 18 switches the shutter drive mode to either the mechanical shutter mode (first shutter drive mode) or the electronic front curtain shutter mode (second shutter drive mode). Here, the mechanical shutter mode is a mode in which the shutter is driven using the mechanical front curtain shutter and the mechanical rear curtain shutter of the focal plane shutter 17. The electronic front curtain shutter mode is a mode in which the shutter is driven using the electronic front curtain shutter using the image sensor 6 (described later) and the mechanical rear curtain shutter of the focal plane shutter 17.

[0026] The subject detection means 19 (detection means) primarily uses the captured image during the preparation stage to detect the state of the subject. The detected state of the subject includes the position of the subject within the captured image, as well as brightness unevenness and contrast differences within the captured image.

[0027] The shutter speed selection means 20 not only selects the shutter speed in response to user operation, but in program AE mode, it also determines the exposure based on the metering results obtained from a metering means (not shown) during the shooting preparation stage, and automatically selects the shutter speed.

[0028] The autofocus point selection means 21 may automatically select a point near the center of a subject to be focused on when the subject detection means 19 detects such a subject, or it may select an autofocus point in response to user operation.

[0029] In this embodiment, an imaging device 100 having two image stabilization means, a lens-side image stabilization means 13 and a camera-side image stabilization means 14, is described, but the imaging device according to the present invention is not limited to this. The present invention is effective for imaging devices having at least a camera-side image stabilization means 14.

[0030] The imaging device 100, consisting of a camera body 1 and a lens barrel 2, has imaging means, image processing means, recording and playback means, and control means.

[0031] The imaging means includes a photographic optical system 3 and an image sensor 6, the image processing means includes an image processing unit 7, and the recording and playback means includes a memory means 8 and a display means 9. The control means includes a camera system control unit 5, an operation detection unit 10, a camera-side shake detection means 15, a camera-side shake correction means 14, a lens system control unit 12, a lens-side shake detection means 16, and a lens-side shake correction means 13. In addition to the shake correction lens 3a, the lens system control unit 12 can also drive a focus lens (not shown) and an aperture, etc., using a drive means (not shown).

[0032] The camera-side shake detection means 15 and the lens-side shake detection means 16 are capable of detecting rotational shake applied to the imaging device 100 relative to the shooting optical axis 4, and this is achieved using, for example, a vibration gyroscope. Based on the amount of rotational shake detected by the camera-side shake detection means 15 and the lens-side shake detection means 16, the camera-side shake correction means 14 drives the image sensor 6 and the lens-side shake correction means 13 drives the shake correction lens 3a on a plane perpendicular to the shooting optical axis 4.

[0033] Furthermore, the camera-side shake detection means 15 is equipped with, for example, an acceleration sensor, and can detect translational shake applied to the imaging device 100. Therefore, the camera-side shake correction means 14 drives the image sensor 6 in a plane perpendicular to the optical axis 4 based on the rotational shake and translational shake detected by the camera-side shake detection means 15.

[0034] Furthermore, the camera-side image stabilization means 15 (automatic horizontal correction means) can detect how much the camera body 1 is tilted relative to the horizontal from the output of an acceleration sensor or vibration gyroscope. The camera-side image stabilization means 14 rotates the image sensor 6 relative to the shooting optical axis 4 according to the detected tilt from the horizontal, thereby correcting the slight tilt of the camera body 1 at the start of shooting during handheld shooting and realizing an automatic horizontal correction function that maintains the horizontal level of the captured image.

[0035] The imaging means described above is an optical processing system that focuses light from an object onto the imaging surface of the image sensor 6 via the imaging optical system 3. Since the focus evaluation amount / appropriate exposure amount is obtained from the image sensor 6, the imaging optical system 3 is appropriately adjusted based on this signal, so that the image sensor 6 is exposed to an appropriate amount of object light, and the subject image is formed near the image sensor 6.

[0036] The image processing unit 7 contains an A / D converter, a white balance adjustment circuit, a gamma correction circuit, an interpolation calculation circuit, etc., and can generate images for recording. Furthermore, the image processing unit 7 (color interpolation processing means) generates a color image by performing color interpolation (demosaiking) processing on the Bayer array signal. In addition, the image processing unit 7 compresses data such as images, videos, and audio using a predetermined method.

[0037] The memory means 8 includes a storage unit such as an HDD.

[0038] The camera system control unit 5 outputs the image for recording generated by the image processing unit 7 to the recording unit of the memory means 8, and also decompresses the image compressed by the image processing unit 7 and displays it on the display means 9 as an image to be presented to the user.

[0039] The camera system control unit 5 generates timing signals in response to external operations during image capture and controls the imaging system, image processing system, and recording / playback system based on the generated timing signals. For example, the camera system control unit 5 controls the driving of the image sensor 6, the operation of the image processing unit 7, and compression processing based on the timing signal generated when the operation detection unit 10 detects the pressing of a shutter release button (not shown). Furthermore, the camera system control unit 5 controls the state of each segment of the display means 9, which is an information display device that displays information. The display means 9 consists of a rear display device 9a and an EVF (electronic viewfinder) 9b, but the rear display device 9a, which is a touch panel, may also serve as both the display means 9 and the operation means.

[0040] The adjustment operation of the control system's optical system will now be explained. The camera system control unit 5 is connected to the image processing unit 7, and based on the signal from the image sensor 6 obtained via the image processing unit 7, it determines the appropriate focal position and aperture position. The camera system control unit 5 issues a command to the lens system control unit 12 via the electrical contact 11, and the lens system control unit 12 controls the focal lens driving means and aperture driving means (not shown) based on this command. Furthermore, in the mode for performing image stabilization, the camera system control unit 5 performs image stabilization by controlling the camera-side image stabilization means 14 to drive the image sensor 6 based on the signal obtained from the camera-side image stabilization means 15. Similarly, in the mode for performing image stabilization, the lens system control unit 12 performs image stabilization by controlling the lens-side image stabilization means 13 to drive the image stabilization lens 3a based on the signal obtained from the lens-side image stabilization means 16.

[0041] The basic control operation in the image stabilization mode of the imaging device 100 is as follows: First, the camera system control unit 5 and the lens system control unit 12 detect the camera shake signals (rotational shake and translational shake) detected by the camera-side shake detection means 15 and the lens-side shake detection means 16, respectively. Based on the detection results, the camera system control unit 5 and the lens system control unit 12 each calculate the amount of drive required for the image sensor 6 and the image stabilization lens 3a to correct the image shake. Subsequently, the calculated drive amount is sent as a command value to the camera-side image stabilization means 14 and the lens-side image stabilization means 13, which then drive the image sensor 6 and the image stabilization lens 3a, respectively.

[0042] Furthermore, as described above, the camera system control unit 5 and the lens system control unit 12 control the operation of various parts of the camera body 1 and lens barrel 2 in response to user operations on operating means (not shown) provided on the camera body 1 and lens barrel 2. This enables the capture of both still images and videos.

[0043] In this invention, the shutter drive mode switching means 18 switches the shutter drive mode by referring to the shutter speed selected by the shutter speed selection means 20 and the detection result by the subject detection means 19. As described above, in this embodiment, the shutter drive mode can be switched to either the electronic front curtain shutter mode or the mechanical shutter mode.

[0044] Furthermore, the camera may switch the shutter drive mode by referring to the tilt of the image sensor 6 around the optical axis relative to the camera body 1 before exposure begins (the rotation angle θ of the image sensor 6, which will be described later), obtained from the camera-side image stabilization means 14.

[0045] In this embodiment, by switching the shutter drive mode, the frequency of switching can be reduced compared to switching the shutter drive mode based solely on the shutter speed. Furthermore, in this embodiment, the shutter drive mode can be appropriately switched according to the state of the subject, making it possible to appropriately reduce the effect of vibrations caused by the focal plane shutter 17 on the captured image.

[0046] Next, using Figure 2, the principle of exposure unevenness in this embodiment will be explained.

[0047] Figure 2 schematically shows the image stabilization system and the mechanical rear curtain shutter 25 of the focal plane shutter 17 provided on the camera body 1. Figure 2(a) shows the state of the image sensor 6 before exposure for still image capture begins, and Figure 2(b) shows the state of the image sensor 6 at a certain point during exposure for still image capture after the shooting operation has been performed from the state in Figure 2(a).

[0048] In Figure 2(a), state 22 indicates that the image sensor 6 is not rotated around the optical axis, and state 23 indicates that the image sensor 6 is rotated around the optical axis. When the automatic horizontal correction function described above is activated, the image sensor 6 is rotated according to the tilt of the camera body 1 during the shooting preparation stage to maintain the horizontal alignment of the captured image. As a result, the image sensor 6 is rotated relative to the mechanical rear curtain shutter 25 in the direction shown in state 23.

[0049] Figure 2(a) shows the state of the image sensor 6 before exposure for still image capture begins, and the camera body 1 is in what is known as the live view display state. At this time, the focal plane shutter 17 is open, the image sensor 6 performs sequential exposure, and the acquired images are continuously displayed on the display means 9 such as the EVF 9b. In Figure 2(a), the state 23 of the rotating image sensor 6 is represented by a white rectangle, which indicates that the image sensor 6 is performing exposure for live view display.

[0050] In Figure 2(b), the shaded area 24 schematically represents the electronic front curtain shutter, showing how the electronic front curtain shutter is driven in the direction of the arrow 30 on the tilted image sensor 6 as in state 23. Therefore, on the image sensor 6, the pixels corresponding to the shaded area 24, which is the electronic front curtain shutter, have not yet been exposed.

[0051] The mechanical rear curtain shutter 25, schematically shown by hatching, represents in Figure 2(b) that the mechanical rear curtain shutter 25 has descended to the middle of the image sensor 6 in state 23, in the direction of arrow 29. Therefore, of the image sensor 6 in state 23, the pixels that overlap with the mechanical rear curtain shutter 25 shown by hatching have already completed exposure.

[0052] When the image sensor 6 is rotated for automatic horizontal correction and is in state 23, the electronic front curtain shutter drives at an angle along the image sensor 6, while the mechanical rear curtain shutter 25 drives perpendicular to the camera body 1. As a result, a difference in exposure time is created on the left and right sides of the image sensor 6, which is determined by the slit width produced by both shutters.

[0053] When the image sensor 6 is not tilted relative to the camera body 1 due to automatic horizontal correction or the like, the slit width 27 (Figure 2(b)) will be the same regardless of whether it is located on the left or right side of the image sensor 6, and will correspond to the exposure time determined by the set shutter speed.

[0054] On the other hand, when the image sensor 6 is rotating (tilted relative to the camera body 1) as shown in state 23 of Figure 2, the slit width 26 for pixels on the left side of the page becomes narrower than the slit width 27. In other words, the actual exposure time for pixels on the left side of the page is shorter than the set shutter speed. Conversely, the slit width 28 for pixels on the right side of the page becomes wider than the slit width 27. In other words, the actual exposure time for pixels on the right side of the page is longer than the set shutter speed. Thus, pixels on the right side of the page are exposed for a longer time than pixels on the left side. This difference in exposure time causes uneven exposure on the left and right sides of the image sensor 6.

[0055] In other words, if the image sensor 6 is tilted relative to the camera body 1 at the start of exposure for a still image due to automatic horizontal correction or other reasons, uneven exposure will occur on the left and right sides of the screen.

[0056] The degree to which this uneven exposure occurs is determined by the drive speed of the electronic front curtain shutter and the mechanical rear curtain shutter 25, the set shutter speed, and the degree of rotational drive of the image sensor 6, and can be calculated before shooting begins.

[0057] Here, the drive speed of the mechanical rear curtain shutter 25 and the drive speed of the electronic front curtain shutter are the same, v [m / s], and the exposure time of the image sensor 6 determined by the shutter speed selected by the shutter speed selection means 20 is t [s]. In this case, when the image sensor 6 is not rotating, the slit width, which is represented by the distance between the electronic front curtain shutter and the mechanical rear curtain shutter 25, is expressed as 1000vt [mm]. That is, the slit width 27, which is represented by the arrow in the center of the screen in Figure 2(b), is expressed as 1000vt [mm].

[0058] On the other hand, when the image sensor 6 is rotated and arranged as in state 23 in Figure 2, the exposure widths on the left and right sides in state 23 differ as described above. For pixels on the left side of the page, the slit width 26 is shorter than the slit width 27, and its length is 1000vt-18sinθ. Here, the rotation angle θ is the angle at which the image sensor 6 rotates around the optical axis of the imaging optical system 3 from state 22 due to the automatic horizontal correction function, as in state 23, that is, the tilt of the image sensor 6 with respect to the camera body 1. Therefore, the slit width 26 is the amount obtained by subtracting the length obtained by multiplying half of the length of the long side of the image sensor 6, which is 36mm, by the sine of the rotation angle θ from the slit width 27 (=1000vt[mm]). Similarly, for pixels on the right side of the page, the slit width 28 is longer than the slit width 27, and its length is 1000vt+18sinθ.

[0059] In this invention, when the image sensor 6 is rotated as in state 23, it is determined whether the ratio K of the left and right slit widths (in this embodiment, (1000vt-18sinθ) / (1000vt+18sinθ)) has a significant effect on the brightness distribution of the captured image. Based on this, it is then decided whether or not to change the shutter drive mode.

[0060] The slit width ratio K is close to 1 when the image sensor 6 is not rotating, and in this case, the difference in slit width between the left and right sides of the image sensor 6 is small. On the other hand, when the slit width ratio K is small, the difference in slit width between the left and right sides of the image sensor 6 is large. Therefore, when the image sensor 6 is rotating significantly, exposure in electronic front curtain shutter mode may result in a difference in exposure time between the left and right sides, potentially causing uneven exposure. This uneven exposure due to the difference in exposure time between the left and right sides becomes particularly noticeable when the brightness of the image is nearly uniform depending on the subject.

[0061] When the subject is affected by uneven exposure, it is preferable to shoot in mechanical shutter mode rather than electronic front curtain shutter mode. On the other hand, when the subject is affected by uneven exposure, it is preferable to shoot in electronic front curtain shutter mode to reduce image degradation caused by so-called shutter shock, which occurs due to vibrations generated by the operation of the mechanical front curtain shutter in mechanical shutter mode.

[0062] For example, when photographing the sky, the brightness is often uniform across the entire screen at a high value, so the maximum and minimum brightness values ​​within the screen are close together. Therefore, when the image sensor 6 rotates significantly as in state 23, and the slit width ratio K decreases, pixels on the side of the slit width 26, which has been shortened by this rotation, experience a decrease in brightness due to the reduction in exposure time. As a result, there is a possibility that pixels with lower brightness than the minimum brightness value obtained during live view shooting before exposure will occur. The difference in exposure unevenness within the screen caused by this decrease in the slit width ratio K due to rotation will be referred to as exposure unevenness step below. Therefore, in this embodiment, when the brightness unevenness of the subject being photographed is small (for example, an image in which the exposure difference of less than 1 / 3 stop occurs within the screen), shooting is performed in mechanical shutter mode rather than electronic front curtain shutter mode.

[0063] On the other hand, for example, if there are subjects with varying brightness levels scattered within the screen, and the overall brightness variation is large, the maximum and minimum brightness values ​​within the screen will be far apart. Therefore, even if the image sensor 6 rotates significantly as in state 23, and the slit width ratio K becomes small, the decrease in brightness of pixels on the slit width 26 side due to this rotation may not have a significant impact on the captured image. In other words, if the brightness variation of the subject is greater than the resulting exposure unevenness, the impact of exposure unevenness will be less. Therefore, in this embodiment, if the brightness variation of the subject being photographed is large (for example, an image in which an exposure difference of 1 / 3 stop or more occurs within the screen), the image is captured in electronic front curtain shutter mode instead of mechanical shutter mode.

[0064] In this embodiment, the formula shown is for the case of a so-called full-frame sensor, but the present invention is effective regardless of the size of the image sensor. That is, if the image sensor size is different, the same effect can be obtained by using the formula appropriate for that size to calculate the slit width.

[0065] Next, using Figure 3, we will explain how to determine the shutter drive mode when photographing a subject with significant brightness unevenness in this embodiment.

[0066] Figure 3 illustrates a scene with significant brightness unevenness within the screen as an example of photographing a cake with lit candles. Image 31 shown in Figure 3(a) represents the image captured by the image sensor 6 in live view mode before the image sensor 6 performs exposure for still images. The brightness graph 33 shown in Figure 3(b) represents the brightness value of each pixel in the row of the dashed line 32 (Figure 3(a)) on the image sensor 6, and the double arrow shown in Figure 3(b) represents the difference 34 between the maximum brightness value and the minimum brightness value on the brightness graph 33.

[0067] In scenes with large brightness variations, as illustrated in Figure 3(a), the difference 34 between the maximum and minimum brightness values ​​of each pixel in the row indicated by the dashed line 32 becomes relatively large, as shown in Figure 3(b). In such scenes, even if the image sensor 6 rotates as shown in Figure 2 and exposure unevenness steps occur in the image sensor 6, the difference 34 is larger than the exposure unevenness step, so the effect of exposure unevenness becomes relatively small. For example, if multiplying the maximum brightness value in the brightness graph 33 by the slit width ratio K results in a brighter image than the pixel with the minimum brightness value in the brightness graph 33, then the effect of exposure unevenness on the row indicated by the dashed line 32 in the image sensor 6 is small. In other words, if the brightness variation within the image is larger than the exposure unevenness step that occurs, the effect of exposure unevenness will be small.

[0068] Therefore, if the image to be captured is an image with large brightness unevenness between the left and right sides of the screen, as shown in Figure 3 (for example, an image in which a brightness difference of 1 / 3 stop or more occurs within the screen), even if exposure unevenness occurs during shooting, the effect of that exposure unevenness on the captured image will be small. For this reason, in this embodiment, if the difference 34 between the maximum brightness value and the minimum brightness value of the row of the dashed line 32 (Figure 3(a)) in the image sensor 6 is greater than a predetermined brightness unevenness, the shutter drive mode when shooting is determined to be the electronic front curtain shutter mode. Here, the predetermined brightness unevenness may be set to the exposure unevenness step calculated above, or it may be set to 1 / 3 stop, which reduces the effect of exposure unevenness, as described above.

[0069] Next, using Figure 4, we will explain how to determine the shutter drive mode when photographing a subject with minimal brightness unevenness in this embodiment.

[0070] Figure 4 illustrates a scene with minimal brightness unevenness within the screen, such as a scene of photographing the sky. Image 41 in Figure 4(a) represents the image captured by the image sensor 6 in live view mode before the image sensor 6 performs exposure for still images. The brightness graph 43 in Figure 4(b) represents the brightness value of each pixel in the row of the dashed line 42 (Figure 4(a)) on the image sensor 6, and the double arrow in Figure 4(b) represents the difference 44 between the maximum brightness value and the minimum brightness value in the brightness graph 43.

[0071] In scenes with small brightness variations, as illustrated in Figure 4(a), the difference 44 between the maximum and minimum brightness values ​​of each pixel in the row indicated by the dashed line 32 is also relatively small, as shown in Figure 4(b). In such scenes, as shown in Figure 2, the image sensor 6 rotates, and if exposure unevenness steps occur in the image sensor 6, the effect of exposure unevenness becomes relatively larger because the exposure unevenness step is smaller than the difference 44. For example, if multiplying the maximum brightness value in the brightness graph 43 by the slit width ratio K results in a darker pixel than the pixel with the minimum brightness value in the brightness graph 43, then the effect of exposure unevenness is significant in the row indicated by the dashed line 32 in the image sensor 6. In other words, if the brightness variation within the image is smaller than the exposure unevenness step that occurs, the effect of exposure unevenness becomes larger.

[0072] Therefore, if the image to be captured is an image with small brightness unevenness between the left and right sides of the screen, as shown in Figure 4 (for example, an image where the brightness difference within the screen is less than 1 / 3 stop), then if exposure unevenness occurs during shooting, that exposure unevenness will have a significant impact on the captured image. For this reason, in this embodiment, if the difference 44 between the maximum brightness value and the minimum brightness value of the row of dashed line 42 (Figure 4(a)) in the image sensor 6 is less than the predetermined brightness unevenness described above, the shutter drive mode when shooting is determined to be the mechanical shutter mode.

[0073] In Figures 3 and 4, the explanation described how the shutter drive mode is changed based on the brightness values ​​of each pixel in a specific row of the image sensor 6 (brightness data for one row), represented by dashed lines 32 and 42, respectively. However, the present invention is not limited to this. For example, the shutter drive mode may be changed according to the comparison result with exposure unevenness that occurs based on the brightness data of each row, or the shutter drive mode may be changed according to the comparison result using the average of the brightness data of each row. In other words, it is sufficient to change the shutter drive mode according to the comparison result between brightness unevenness occurring in the shooting screen and exposure unevenness that occurs during exposure, using brightness data acquired from the image sensor 6.

[0074] Furthermore, while Figures 3 and 4 illustrate a method for changing the shutter drive mode using luminance data acquired from the image sensor 6, the data used may also be the contrast information within the image. In the case of an image where the contrast difference within the image is greater than a predetermined contrast difference (for example, when the contrast difference is greater than 20%), such as image 31 shown in Figure 3(a), exposure unevenness is less likely to be noticeable. Therefore, in such cases, the shutter drive mode is switched to the electronic front curtain shutter mode, which uses the focal plane shutter 17 to minimize vibration. On the other hand, in the case of an image where the contrast difference within the image is small, such as image 41 shown in Figure 4(a), which is less than or equal to a predetermined contrast difference, exposure unevenness is more likely to be noticeable. Therefore, in such cases, the shutter drive mode is switched to the mechanical shutter mode.

[0075] In this embodiment, the shutter drive mode is switched according to the shutter speed and the condition of the subject.

[0076] Next, the shooting control process according to this embodiment will be explained using the flowchart in Figure 5.

[0077] In this embodiment, the shutter drive mode of the imaging device 100 is set to a mode that automatically switches between mechanical shutter mode and electronic front curtain shutter mode (hereinafter referred to as auto mode), and this process starts when the power of the imaging device 100 is turned on. However, the shutter drive mode of the imaging device 100 may be user-selectable from auto mode, mechanical shutter mode, or electronic front curtain shutter mode. In this case, this process starts when auto mode is selected by the user as the shutter drive mode of the imaging device 100.

[0078] First, in step S5001, the camera system control unit 5 determines whether or not the camera is in a shooting preparation state. If it is in a shooting preparation state (YES in step S5001), the process proceeds to step S5002; otherwise (NO in step S5001), the process proceeds to step S5007. In this context, the shooting preparation state means that the user is in a so-called live view state, viewing the subject, changing the shooting angle of view, etc., and then half-pressing the shutter release button.

[0079] In step S5002, the camera system control unit 5 controls the shutter speed selection means 20 and determines the shutter speed based on the selection result. Specifically, the shutter speed determined in step S5002 is the shutter speed selected by the shutter speed selection means 20 based on the metering result obtained from a metering means (not shown). The process then proceeds to step S5003. The metering result is obtained according to the metering mode set by the user.

[0080] In step S5003, the camera system control unit 5 acquires information such as the position of the subject detected by the subject detection means 19 and brightness unevenness within the captured image (captured screen information), and then proceeds to step S5004.

[0081] In step S5004, the camera system control unit 5 (determination means) determines the shutter drive mode based on the shutter speed determined in step S5001, the shooting screen information obtained in step S5003, etc. Then, the process proceeds to step S5005. At this time, the shutter drive mode is determined based on the tilt (rotation angle θ) of the image sensor 6 relative to the camera body 1 after it has been rotated by the automatic horizontal correction function of the camera-side image stabilization means 14. If the user has specified the shutter speed depending on the shooting mode, the shutter drive mode may be switched according to the detection result of the subject detection means 19.

[0082] In step S5005, the camera system control unit 5 determines whether or not the camera is in the shooting start state. If it is in the shooting start state (YES in step S5005), the process proceeds to step S5006; otherwise (NO in step S5005), the process returns to step S5002. The shooting start state here refers to the state in which the user has fully pressed the shutter release button to start the exposure of a still image.

[0083] In step S5006, the camera system control unit 5 instructs the shutter drive mode switching means 18 to switch the shutter drive mode to the mode determined in step S5004, and performs a shooting operation at the shutter speed determined in step S5001. After that, the process proceeds to step S5007. Note that the shutter speed determined in step S5001 may be set to a high speed, and the shutter drive mode determined in step S5004 may be the electronic front curtain shutter mode. In this case, a message warning that there is a high risk of "blurring" may be displayed on the screen of the display means 9 during shooting.

[0084] In step S5007, the camera system control unit 5 determines whether or not the shooting has ended. If the shooting has ended (YES in step S5007), this process is terminated; otherwise (NO in step S5007), the process returns to step S5000 and is repeated from the beginning. The shooting has ended state here means that the user has turned off the power.

[0085] As described above, in this embodiment, the shutter drive mode is switched by referring to the shutter speed, shooting screen information, and rotation angle θ. This reduces the influence of vibrations caused by the focal plane shutter 17 on the captured image and allows the shutter drive mode to be switched appropriately according to the subject's condition.

[0086] (Second example) The imaging device according to the second embodiment of the present invention will now be described with reference to Figure 6. The second embodiment differs from the first embodiment in that it switches the shutter drive mode according to the position of the subject or the distance measurement point, rather than using the brightness information of the subject (within the shooting screen) as described using Figures 3 and 4.

[0087] In this description, hardware configurations identical to those in the first embodiment will be given the same numbering, and redundant explanations will be omitted.

[0088] Figure 6 illustrates the method for determining the shutter drive mode when photographing a subject located near the center of the screen in this embodiment. In Figure 6, Image 61 is an image captured by the image sensor 6 in live view mode before the image sensor 6 performs exposure for a still image, and Subject 62 is the main subject in this photograph, located near the center of the screen in Image 61. The metering point 63 is an area where distance measurement is performed in order to measure the focus state when using the autofocus function, and is selected automatically or by user operation by the metering point selection means 21.

[0089] When the main subject is positioned near the center of the screen, as in the subject 62 in Figure 6, the slit width 27 remains almost unchanged before and after the rotation, even when the image sensor 6 is rotated as in state 23 of Figure 2. In other words, in state 23 of the image sensor 6, exposure unevenness occurs on the left and right sides of the image sensor 6, but the effect on the subject 62 positioned near the center of the screen is minimal.

[0090] Similarly, as shown in Figure 6, when the distance measurement point selected by the distance measurement point selection means 21 is near the center, the effect of exposure unevenness caused by the rotational drive of the image sensor 6 is also small.

[0091] Therefore, in this embodiment, when the subject or autofocus point is located near the center of the screen in live view mode, shooting is performed in electronic front curtain shutter mode to minimize the effect of vibrations from the focal plane shutter 17 on the captured image.

[0092] Next, the shooting control process according to this embodiment, which is executed by the camera system control unit 5, will be described.

[0093] The flowchart for this process is basically the same as the flowchart in Figure 5 described in the first embodiment. However, in step S5002 of Figure 5, when acquiring shooting screen information, the camera system control unit 5 acquires the position of the subject or distance measurement point within the screen, and uses this information when determining the shutter drive mode in step S5004.

[0094] As described above, in this embodiment, the shutter drive mode is switched by referring to the shutter speed, the position of the subject or autofocus point in the frame, and the rotation angle θ. This reduces the influence of vibrations from the focal plane shutter 17 on the captured image and allows the shutter drive mode to be switched appropriately according to the subject's condition.

[0095] (Third embodiment) The imaging device according to the third embodiment of the present invention will now be described with reference to Figure 7. The third embodiment differs from the first embodiment in that it switches the shutter drive mode according to the spatial frequency of the subject, rather than the brightness information of the subject (within the shooting screen) as described using Figures 3 and 4.

[0096] In this description, hardware configurations identical to those in the first embodiment will be given the same numbering, and redundant explanations will be omitted.

[0097] Figure 7 illustrates the method for determining the shutter drive mode when photographing a subject with a high spatial frequency in this embodiment. In Figure 7, Image 71 is an image taken by the image sensor 6 in live view mode before exposure for a still image, and Subject 72 is a bird, the main subject of this photograph. Generally, bird feathers have fine patterns, so Subject 72 is a subject with a high spatial frequency. In this embodiment, the case where Subject 72 is a bird as an example of a subject with a high spatial frequency is illustrated, but the present invention is not limited to this, and any subject with a high spatial frequency and fine patterns can be considered Subject 72. For example, subjects with a spatial frequency exceeding 30 [lines / mm] or subjects with a spatial frequency exceeding 1 / 2 of the Nyquist frequency obtained from the pixel pitch of the image sensor 6 can be said to be subjects with a high spatial frequency. Specifically, other examples of subjects with a high spatial frequency include fabric products such as finely woven fabrics and dresses with fine embroidery, hair, and animal fur.

[0098] As shown in Figure 7, when the spatial frequency of the subject is high, even minute vibrations such as those of the mechanical front curtain shutter can cause the image sensor 6 to move, resulting in a loss of resolution in the captured image.

[0099] Therefore, in this embodiment, if the spatial frequency of the subject is higher than a predetermined spatial frequency, shooting is performed in electronic front curtain shutter mode in order to reduce the influence of vibrations by the focal plane shutter 17 on the captured image. Here, the pre-set spatial frequencies include a spatial frequency of 30 [lines / mm], or a spatial frequency of half the Nyquist frequency obtained from the pixel pitch of the image sensor 6.

[0100] In this embodiment, the spatial frequency of the subject is calculated by the subject detection means 19 performing an FFT analysis using the image in the live view state. However, any method that can calculate the spatial frequency of the subject is acceptable, and the method is not limited to this one.

[0101] Next, the shooting control process according to this embodiment, which is executed by the camera system control unit 5, will be described.

[0102] The flowchart for this process is basically the same as the flowchart in Figure 5 described in the first embodiment. However, in step S5002 of Figure 5, when acquiring the shooting screen information, the camera system control unit 5 acquires the spatial frequency information of the subject, and uses that information when determining the shutter drive mode in step S5004.

[0103] As described above, in this embodiment, the shutter drive mode is switched by referring to the shutter speed, the spatial frequency information of the subject, and the rotation angle θ. This reduces the influence of vibrations caused by the focal plane shutter 17 on the captured image and allows the shutter drive mode to be switched appropriately according to the condition of the subject.

[0104] (Other embodiments) In the above embodiments, the imaging device according to the present invention was described as a personal digital camera, but it is not limited to this. That is, as long as it is equipped with imaging and image synthesis functions and has a user interface for setting the exposure time, the imaging device according to the present invention may be a portable device, a smartphone, or a network camera connected to a server. In addition, some of the processing described above may be performed by a portable device, a smartphone, or a network camera connected to a server.

[0105] The present invention can also be realized by supplying a program that implements one or more of the functions of this embodiment to a system or device via a network or recording medium, and by having one or more processors in the computer of that system or device read and operate the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0106] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention.

[0107] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist.

[0108] This embodiment includes the following configurations, methods, and programs. (Configuration 1) An imaging device comprising: an imaging optical system; an image sensor; a shutter speed selection means for selecting a shutter speed; a detection means for detecting the state of a subject from a captured image; a focal-plane shutter equipped with a mechanical front curtain shutter and a mechanical rear curtain shutter; an electronic front curtain shutter; a shutter drive mode switching means for switching the shutter drive mode during shooting operation to one of a first shutter drive mode using the mechanical front curtain shutter and the mechanical rear curtain shutter in the focal-plane shutter, or a second shutter drive mode using the electronic front curtain shutter and the mechanical rear curtain shutter in the focal-plane shutter; a blur correction means; and a determination means for determining the shutter drive mode to be switched by the shutter drive mode switching means according to the selection result of the shutter speed selection means and the detection result of the detection means in a shooting preparation state. (Configuration 2) The imaging device according to Configuration 1, characterized in that the detection means detects brightness unevenness within the screen of the captured image, and when the detection means detects that the brightness unevenness within the screen of the captured image is greater than a predetermined brightness unevenness, the determination means determines the switchable shutter drive mode to the second shutter drive mode. (Configuration 3) The imaging device according to Configuration 2, further comprising an automatic horizontal correction means that rotates the image sensor relative to the camera body around the optical axis of the imaging optical system in accordance with the tilt of the camera body relative to the horizontal, wherein the predetermined brightness unevenness is an exposure unevenness step in the screen that occurs in the second shutter drive mode, calculated according to the tilt of the image sensor relative to the camera body after it has been rotated by the automatic horizontal correction means in the shooting preparation state and the exposure time corresponding to the selected shutter speed. (Configuration 4) The imaging device according to Configuration 1, characterized in that the detection means detects the position of a subject within the screen of the captured image, and if the position of the detected subject is near the center of the screen of the captured image, the determination means determines the switchable shutter drive mode to the second shutter drive mode. (Configuration 5) The imaging apparatus according to Configuration 1, further comprising a distance measuring point selection means, wherein if the position of the distance measuring point selected by the distance measuring point selection means is near the center of the screen of the captured image, the determination means determines the switchable shutter drive mode to the second shutter drive mode. (Configuration 6) The imaging apparatus according to Configuration 1, characterized in that the detection means detects the contrast difference within the screen of the captured image, and when the detection means detects that the contrast difference within the screen of the captured image is greater than a predetermined contrast difference, the determination means determines the switchable shutter drive mode to the second shutter drive mode. (Configuration 7) The imaging apparatus according to Configuration 1, characterized in that the detection means calculates the spatial frequency of the subject, and if the calculated spatial frequency is higher than a predetermined spatial frequency, the determination means determines the switchable shutter drive mode to the second shutter drive mode. (Method 1) A control method for an imaging device comprising: an imaging optical system; an image sensor; a shutter speed selection means for selecting a shutter speed; a detection means for detecting the state of a subject from a captured image; a focal-plane shutter equipped with a mechanical front curtain shutter and a mechanical rear curtain shutter; an electronic front curtain shutter; a shutter drive mode switching means for switching the shutter drive mode during shooting operation to one of a first shutter drive mode using the mechanical front curtain shutter and the mechanical rear curtain shutter in the focal-plane shutter, or a second shutter drive mode using the electronic front curtain shutter and the mechanical rear curtain shutter in the focal-plane shutter; and a blur correction means, the control method characterized by having a determination step in which, in a shooting preparation state, the shutter drive mode to be switched by the shutter drive mode switching means is determined according to the selection result of the shutter speed selection means and the detection result of the detection means. (Program 1) A program for causing a computer to function as one of the means of an imaging device described in any one of configurations 1 to 7. [Explanation of Symbols]

[0109] 3. Imaging optical system 5. Camera System Control Unit 6 Image sensor 12 Lens System Control Unit 13 Lens-side image stabilization means 14. Camera-side image stabilization means 15 Camera-side shake detection means 16 Lens-side shake detection means 17. Focal-plane shutter 18. Shutter drive mode switching means 19. Subject detection means 20. Shutter speed selection method

Claims

1. The imaging optical system, Image sensor and A shutter speed selection method for selecting the shutter speed, A detection means for detecting the state of the subject from a captured image, A focal-plane shutter equipped with a mechanical front curtain shutter and a mechanical rear curtain shutter, Electronic front curtain shutter, A shutter drive mode switching means for switching the shutter drive mode during shooting operation between a first shutter drive mode using the mechanical front curtain shutter and the mechanical rear curtain shutter of the focal plane shutter, and a second shutter drive mode using the electronic front curtain shutter and the mechanical rear curtain shutter of the focal plane shutter, Image stabilization means, An imaging device comprising: a determination means for determining the shutter drive mode to be switched by the shutter drive mode switching means, in accordance with the selection result of the shutter speed selection means and the detection result of the detection means in the shooting preparation state.

2. The detection means detects brightness unevenness within the screen of the captured image, The imaging apparatus according to claim 1, characterized in that, when the detection means determines that the brightness unevenness within the screen of the captured image is greater than a predetermined brightness unevenness, the determination means determines the switchable shutter drive mode to the second shutter drive mode.

3. The system further includes an automatic horizontal correction means that rotates the image sensor relative to the camera body around the optical axis of the imaging optical system in accordance with the tilt of the camera body relative to the horizontal, thereby maintaining the horizontality of the captured image. The imaging apparatus according to claim 2, characterized in that the predetermined brightness unevenness is an exposure unevenness step in the image that occurs in the second shutter drive mode, calculated according to the tilt of the image sensor relative to the camera body after it has been rotated by the automatic horizontal correction means in the shooting preparation state, and the exposure time corresponding to the selected shutter speed.

4. The detection means detects the position of the subject within the image of the captured image, The imaging apparatus according to claim 1, characterized in that, if the position of the detected subject is near the center of the screen of the captured image, the determination means determines the switchable shutter drive mode to the second shutter drive mode.

5. Further equipped with a means for selecting distance measurement points, The imaging apparatus according to claim 1, characterized in that, if the position of the distance measuring point selected by the distance measuring point selection means is near the center of the screen of the captured image, the determination means determines the switchable shutter drive mode to the second shutter drive mode.

6. The detection means detects the contrast difference within the screen of the captured image, The imaging apparatus according to claim 1, characterized in that, when the detection means determines that the contrast difference within the screen of the captured image is greater than a predetermined contrast difference, the determination means determines the switchable shutter drive mode to the second shutter drive mode.

7. The detection means calculates the spatial frequency of the subject, The imaging apparatus according to claim 1, characterized in that, when the calculated spatial frequency is higher than a predetermined spatial frequency, the determination means determines the switchable shutter drive mode to the second shutter drive mode.

8. The imaging optical system, Image sensor and A shutter speed selection method for selecting the shutter speed, A detection means for detecting the state of the subject from a captured image, A focal-plane shutter equipped with a mechanical front curtain shutter and a mechanical rear curtain shutter, Electronic front curtain shutter, A shutter drive mode switching means for switching the shutter drive mode during shooting operation between a first shutter drive mode using the mechanical front curtain shutter and the mechanical rear curtain shutter of the focal plane shutter, and a second shutter drive mode using the electronic front curtain shutter and the mechanical rear curtain shutter of the focal plane shutter, Image stabilization means, A control method for an imaging device comprising: A control method characterized by having a determination step in which the shutter drive mode to be switched by the shutter drive mode switching means is determined according to the selection result of the shutter speed selection means and the detection result of the detection means in the shooting preparation state.

9. A program for causing a computer to function as each of the means of the imaging apparatus described in claim 1.

Images