JP4640614B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus, and more particularly to a technique for detecting a flicker frequency of a light source.

  In recent years, with the advent of digital cameras, image pickup apparatuses adopting so-called contrast type (mountain climbing) AF control have become widespread. In general, it is known that AF control with contrast method (contrast AF control) has higher AF accuracy than AF control with phase difference method (phase difference AF control).

  However, under a light source such as a fluorescent lamp, fluctuations in the amount of light occur due to so-called flicker, so the peak shape of the evaluation value for evaluating the in-focus state collapses at the timing of acquiring an image in contrast AF control. Focusing accuracy decreases.

  To deal with such a problem, Patent Document 1 proposes a technique for improving AF accuracy in contrast AF control by performing sampling (image acquisition) at a cycle that is an integral multiple of the flicker cycle.

JP 2001-324670 A

  By the way, in order to use, for example, the technique disclosed in Patent Document 1, it is required to detect the flicker frequency of the light source. The flicker frequency of such a light source is preferably detected at high speed.

  Accordingly, an object of the present invention is to provide a technique capable of detecting a flicker frequency of a light source at high speed.

  In order to solve the above-described problem, the invention of claim 1 is an imaging apparatus, and includes two imaging sensors each capable of acquiring time-series image data, and acquisition of image data by the two imaging sensors. Setting means for setting each frame rate, and frequency detection means for detecting the flicker frequency of the light source based on a plurality of image data acquired in parallel by the two imaging sensors at different frame rates. It is characterized by that.

  The invention of claim 2 is the image pickup apparatus according to claim 1, further comprising image signal focusing means for performing a focusing operation based on the image data acquired by the two imaging sensors. Features.

  According to a third aspect of the present invention, in the imaging apparatus according to the second aspect of the present invention, the setting means determines the frame rate of the two imaging sensors when the flicker frequency is detected by the frequency detection means. A common frame rate determined according to a flicker frequency is set, and the image signal focusing means is configured to perform the focusing operation based on image data acquired by each of the two imaging sensors at the common frame rate. It is characterized by performing.

  According to a fourth aspect of the present invention, in the imaging apparatus according to the third aspect of the invention, the common frame rate (fps: number of frames per second) is n times the flicker frequency (Hz) (n is a natural number). ) Is set to the value obtained.

  According to a fifth aspect of the present invention, in the imaging apparatus according to any one of the second to fourth aspects, the two imaging sensors are respectively arranged at different positions on the optical path through which the subject image is guided. It is characterized by.

  The invention of claim 6 is the imaging apparatus according to any one of claims 2 to 5, further comprising a phase difference AF unit that detects a focus state on a reference plane by a phase difference method, The reference plane of the phase difference AF unit is disposed between the two imaging sensors on an optical path through which a subject image is guided.

  According to a seventh aspect of the present invention, in the imaging apparatus according to any one of the second to fifth aspects, the flicker frequency of the light source is detected when the imaging apparatus is activated. To do.

  According to an eighth aspect of the present invention, in the imaging apparatus according to any of the second to fifth aspects, the flicker frequency of the light source is detected when switching to the still image shooting mode is performed. It is characterized by.

  The invention of claim 9 is the imaging apparatus according to any one of claims 2 to 5, wherein the flicker frequency of the light source is detected when a change in proper exposure is detected. Features.

  According to a tenth aspect of the present invention, in the imaging apparatus according to any one of the second to fifth aspects, the flicker frequency of the light source is a white balance of the image data acquired by the two imaging sensors. It is detected when it is changed.

  The invention according to claim 11 is the imaging apparatus according to any one of claims 2 to 5, wherein the imaging apparatus is capable of detaching a photographing lens, and the flicker frequency of the light source is the photographing lens. It is characterized in that it is detected when the attachment of the is detected.

  According to the first to eleventh aspects of the present invention, image data is acquired in parallel at different frame rates using two imaging sensors, and a plurality of image data acquired by the two imaging sensors is obtained. Since the flicker frequency of the light source is detected based on this, it is possible to acquire image data used for detecting the flicker frequency at high speed, and to detect the flicker frequency of the light source at high speed.

  In particular, according to the second aspect of the present invention, the flicker frequency of the light source can be detected by using the two imaging sensors that are also used for the focusing operation by the image signal focusing means. Therefore, the flicker frequency of the light source can be detected without providing a new configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1. Configuration>
<1-1. Overview>
FIG. 1 is a diagram illustrating a schematic configuration of an imaging apparatus 1 according to an embodiment of the present invention. The imaging device 1 is configured as a lens interchangeable single-lens reflex digital camera.

  As shown in FIG. 1, the imaging apparatus 1 includes a camera main body (camera body) 2, and an interchangeable photographic lens unit 3 can be attached to and detached from the camera main body 2.

  The photographic lens unit 3 mainly includes a lens barrel 36, and a lens group 37 and a diaphragm 38 provided in the lens barrel 36. The lens group 37 includes a focus lens that changes the focal position by moving in the optical axis direction.

  The camera body 2 is provided with a mechanical shutter (hereinafter simply referred to as “shutter”) 4 and an image sensor (CCD sensor or CMOS sensor) 5. The camera body 2 further includes a main mirror 6, a sub mirror 7, a pentaprism 8, a lens unit 9, a finder 10, and an AF module 20. The finder 10 functions as a so-called optical finder.

  When acquiring a recording still image or the like related to the subject, the main mirror 6 and the sub mirror 7 are retracted upward so as not to block the light from the subject, and the light from the photographic lens unit 3 is opened to the shutter 4. To reach the image sensor 5. As described above, the light from the subject is guided to the image sensor 5 through the photographing lens unit 3, thereby obtaining a photographed image (photographed image data) relating to the subject. The image sensor 5 is also expressed as an image sensor for acquiring a recorded image.

  On the other hand, when the composition is determined using the optical viewfinder and when the AF operation is performed using the AF module 20, the main mirror 6 and the sub mirror 7 are lowered as necessary, and the subject from the photographing lens unit 3 is moved. It is arranged on the optical path of the image (see FIG. 1).

  At this time, the light from the photographic lens unit 3 is reflected by the main mirror 6 to change the course upward, further changes the course by the pentaprism 8, and then travels to the viewfinder 10 through the lens unit 9. The photographer can check the subject image by looking through the viewfinder 10.

  Further, the main mirror 6 can transmit a part of light, and the light transmitted through the main mirror 6 is reflected by the sub mirror 7, changes its path downward, and enters the AF module 20. The AF module 20 is a module for performing autofocus (AF) control (also referred to as “autofocus device”). The AF module 20 implements an AF operation using light that has entered through the main mirror 6 and the sub mirror 7. The AF module 20 will be described later.

  Next, an overview of functions of the imaging apparatus 1 will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the imaging apparatus 1.

  As shown in FIG. 2, the imaging apparatus 1 further includes an operation unit 80, a control unit 101, a focus control unit 121, a mirror control unit 122, a shutter control unit 123, a timing control circuit 124, a digital signal processing circuit 50, and the like. Prepare.

  The operation unit 80 includes various buttons and switches such as a shutter start button (shutter button) 11 (see FIG. 1) and an operation mode switching switch. In response to a user input operation on the operation unit 80, the control unit 101 realizes various operations. The shutter button is a two-stage detection button that can detect two states, a half-pressed state (S1 state) and a fully-pressed state (S2 state). When the imaging apparatus 1 is in the S1 state, a preparatory operation for the main photographing operation including AF control is performed, and in the S2 state, the main photographing operation (the recording still image photographing operation) is performed.

  The control unit 101 mainly includes a CPU, a memory, a ROM, and the like, and implements various functions by reading a program stored in the ROM and executing the program by the CPU. Specifically, the control unit 101 includes a contrast AF control unit 101a and a phase difference AF control unit 101b.

  The contrast AF control unit 101a recognizes the state of the light source (light source information) when performing contrast AF control. Specifically, it is determined whether or not the light source (light source light amount) is a light source (also referred to as a “flicker light source”) that causes fluctuation (flicker), and if the light source is a flicker light source, the flicker of the light source is determined. Detect frequency. Then, an accurate AF evaluation value is calculated by changing the acquisition timing of the image (image signal) acquired by the AF module 20 and the calculation method of the AF evaluation value (also referred to as “contrast value”) according to the state of the light source. To do. Further, the contrast AF control unit 101a outputs a control signal for controlling the focus lens to the focus control unit 121 based on the AF evaluation value. The image acquisition timing can be expressed by using an image acquisition interval (frame acquisition interval) or the number of frames (images) acquired per unit time (1 second) (frame rate).

  The phase difference AF control unit 101b detects a position (lens focusing position) where the in-focus state of the subject is realized based on a signal from the phase difference AF sensor 26. Then, the phase difference AF control unit 101b outputs a control signal for controlling the focus lens to the focus control unit 121 in accordance with the lens focusing position that is obtained as appropriate.

  The focus control unit 121 moves the focus lens included in the lens group 37 of the photographing lens unit 3 by generating a control signal based on the signal input from the control unit 101 and driving the motor M1. Further, the position of the focus lens is detected by the lens position detection unit 39, and data indicating the position of the focus lens is sent to the control unit 101. As described above, the focus control unit 121, the control unit 101, and the like control the movement of the focus lens in the optical axis direction.

  The mirror control unit 122 controls state switching between a state in which the main mirror 6 is retracted from the optical path (mirror up state) and a state in which the main mirror 6 blocks the optical path (mirror down state). The mirror control unit 122 switches between the mirror-up state and the mirror-down state by generating a control signal based on the signal input from the control unit 101 and driving the motor M2.

  The shutter control unit 123 controls the opening and closing of the shutter 4 by generating a control signal based on the signal input from the control unit 101 and driving the motor M3.

  The timing control circuit 124 performs timing control of the image sensor 5 and the like in accordance with an instruction signal from the control unit 101.

  An imaging element (here, a CCD sensor (also simply referred to as a CCD)) 5 converts an optical image of a subject into an electrical signal by a photoelectric conversion action, and generates an image signal related to the captured image. In response to the drive control signal (accumulation start signal / accumulation end signal) input from the timing control circuit 124, the image sensor 5 performs exposure (charge accumulation by photoelectric conversion) of the subject image formed on the light receiving surface. Then, an image signal related to the subject image is generated. Further, the image sensor 5 outputs the image signal to the signal processing unit 51 in response to the read control signal input from the timing control circuit 124. The timing signal (synchronization signal) from the timing control circuit 124 is also input to the signal processing unit 51 and the A / D conversion circuit 52.

  The image sensor 5 is driven by the drive mechanism 5a and moves in a plane perpendicular to the optical axis of light from the subject. Optical camera shake correction can be performed by detecting the shake of the image pickup apparatus 1 by the gyro sensor 44 and driving the image pickup device 5 so as to correct the shake.

  The image signal acquired by the image sensor 5 is subjected to predetermined analog signal processing in the signal processing unit 51, and the image signal after the analog signal processing is converted into digital image data (image data) by the A / D conversion circuit 52. Is done. This image data is input to the digital signal processing circuit 50.

  The digital signal processing circuit 50 performs digital signal processing on the image data input from the A / D conversion circuit 52 to generate image data related to the captured image. The digital signal processing circuit 50 includes a black level correction circuit 53, a white balance (WB) circuit 54, a γ correction circuit 55, and an image memory 56.

  The black level correction circuit 53 corrects the black level of each pixel data constituting the image data output from the A / D conversion circuit 52 to a reference black level. The WB circuit 54 performs white balance adjustment of the image. The γ correction circuit 55 performs gradation conversion of the captured image. The image memory 56 is a high-speed accessible image memory for temporarily storing generated image data, and has a capacity capable of storing image data for a plurality of frames.

  At the time of actual photographing, the image data temporarily stored in the image memory 56 is appropriately subjected to image processing in the control unit 101 and stored in the memory card 90 via the card I / F 132.

  The image data temporarily stored in the image memory 56 is appropriately transferred to the VRAM 131 by the control unit 101, and an image based on the image data is displayed on the liquid crystal display unit (LCD) 12 disposed on the back surface of the camera body unit 2. The Thereby, confirmation display (after view) for confirming the captured image, reproduction display for reproducing the captured image, and the like are realized.

  Furthermore, the imaging apparatus 1 has a communication I / F 133 and can perform data communication with a device (for example, a personal computer) to which the interface 133 is connected.

  The imaging device 1 also includes a flash 41, a flash control circuit 42, and an AF auxiliary light emitting unit 43. The flash 41 is a light source used when the luminance of the subject is insufficient. Whether or not the flash is turned on, the lighting time, and the like are controlled by the flash control circuit 42, the control unit 101, and the like. The AF auxiliary light emitting unit 43 is an auxiliary light source for AF. The presence or absence of lighting of the AF auxiliary light emitting unit 43, the lighting time, and the like are controlled by the control unit 101 and the like.

<1-2. AF module 20>
FIG. 3 is a diagram showing the configuration of the AF module 20.

  As shown in FIG. 3, the AF module 20 includes a condenser lens 21 and a half mirror 22. The half mirror 22 and a later-described beam splitter 29 have a function of dividing an optical path through which a subject image is guided into three optical paths.

  The light that passes through the main mirror 6 (see FIG. 1), is reflected by the sub-mirror 7 and enters the AF module 20 from above the AF module 20 passes through the condenser lens 21 and reaches the half mirror 22.

  The half mirror 22 has a function of dividing an optical path through which a subject image is guided into two optical paths, specifically, an optical path of transmitted light of the half mirror 22 and an optical path of reflected light of the half mirror 22. .

  On the optical path of the transmitted light of the half mirror 22, a part of the AF module 20, specifically, an IR (infrared) cut filter 23, a diaphragm mask 24, a separator lens 25, a phase difference AF sensor 26, Is arranged.

  The light transmitted through the half mirror 22 reaches the phase difference AF sensor 26 through the IR (infrared) cut filter 23, the aperture mask 24, and the separator lens 25. A signal from the phase difference AF sensor 26 is transmitted to the control unit 101 and used for the phase difference AF.

  Thus, the IR (infrared) cut filter 23, the aperture mask 24, the separator lens 25, and the phase difference AF sensor 26 function as a phase difference AF unit. This phase difference AF unit detects the in-focus state on the reference plane P0 (see FIG. 3) of the phase difference AF sensor 26 by the phase difference method.

  Here, the phase difference AF sensor 26 (specifically, the reference plane of the phase difference AF sensor 26) is optically equivalent to the position of the imaging surface of the imaging element 5 in the optical axis direction of the photographing lens unit 3. It is assumed that they are arranged at various positions. According to this, the in-focus state on the reference plane P0 (see FIG. 3) of the phase difference AF sensor 26 and the in-focus state on the imaging surface P10 (see FIG. 1) of the image sensor 5 match. It will be.

  Further, another element group of the AF module 20, specifically, a relay optical system 27, an IR cut filter 28, a beam splitter 29, and sensors 31 and 32 are arranged on the optical path of the reflected light of the half mirror 22. ing.

  The light reflected by the half mirror 22 is guided to the beam splitter 29 through the relay optical system 27 and the IR cut filter 28 when its path is changed to the left side of the figure.

  The beam splitter 29 has a function of dividing the optical path of the reflected light from the half mirror 22 into two optical paths, specifically, an optical path of the transmitted light of the beam splitter 29 and an optical path of the reflected light of the beam splitter 29. is doing. A sensor 31 is disposed on the optical path of the reflected light of the beam splitter 29, and a sensor 32 is disposed on the optical path of the transmitted light of the beam splitter 29. Therefore, the reflected light (light that is split by the beam splitter 29 and travels downward) reaches the contrast detection sensor 31, and the transmitted light (light that is split by the beam splitter 29 and travels straight to the left in the figure) is for contrast detection. The sensor 32 is reached.

  The sensors 31 and 32 arranged at different positions on the optical path through which the subject image is guided in this way function as contrast detection sensors. Specifically, each of the sensors 31 and 32 is an imaging sensor configured by an imaging device or the like, and sequentially acquires images (image signals) related to the subject image at predetermined minute time intervals (frame acquisition intervals). be able to. That is, the sensors 31 and 32 can acquire time-series image data, respectively.

  Specifically, if the light source is a flicker light source, the frame acquisition interval is changed according to the flicker frequency of the light source. For example, when the flicker frequency of the light source is 100 Hz, an image signal is acquired at the first frame acquisition interval (here, 1/200 second), and when the flicker frequency of the light source is 120 Hz, An image signal is acquired at a frame acquisition interval of 2 (here, 1/240 seconds).

  Image signals from the sensors 31 and 32 are transmitted to the control unit 101 and used for calculation of an AF evaluation value for contrast AF and the like. By calculating the AF evaluation value (contrast value) of the image based on the images acquired by the sensors 31 and 32, the position where the AF evaluation value is maximized is detected. The AF evaluation value calculation method will be described later.

  As described above, the relay optical system 27, the IR cut filter 28, the beam splitter 29, and the two sensors 31, 32 function as a contrast AF unit. The element group including the sensor 31 is also expressed as a first contrast AF unit, and the element group including the sensor 32 is also expressed as a second contrast AF unit.

  Here, the sensors 31 and 32 are not disposed at optically equivalent positions (also referred to as optical equivalent positions) with respect to the position of the imaging element 5 in the optical axis direction of the photographing lens unit 3, respectively. It is arranged at a position shifted by a minute amount from the optical equivalent position. FIG. 4 is a diagram conceptually showing such an arrangement state. In FIG. 4, the optical positional relationship among the image pickup device 5, the sensor 31, and the sensor 32 is shown, and the change curves L1, L2 of the AF evaluation values Vn, Vf acquired by the sensors 31, 32, respectively. It is shown.

  More specifically, the imaging surface P1 of the sensor 31 is arranged with a small distance from an optically equivalent position (optical equivalent position) to the reference plane P0 of the sensor 26 for phase difference AF. Specifically, the imaging surface P1 of the sensor 31 is shifted by a predetermined amount Δx (here, about 30 μm) closer to the optical equivalent position with respect to the reference surface P0 of the phase difference AF sensor 26. Has been.

  Further, the image pickup surface P2 of the sensor 32 is arranged with a minute distance from a position (optical equivalent position) optically equivalent to the reference plane P0 of the sensor 26 for phase difference AF. Specifically, the image pickup surface P2 of the sensor 32 is arranged so as to be shifted by a predetermined amount Δx (about 30 μm in this case) to the far side with respect to the optical equivalent position of the reference surface P0 of the sensor 26 for phase difference AF. Yes.

  As shown in FIG. 4, the sensor 31 (also referred to as a near-side sensor) is arranged with a minute amount Δx shifted to the near side with respect to the sensor 26, so that the change curve L1 of the AF evaluation value Vn related to the sensor 31 When the focus lens is present at a position shifted by a minute amount Δx closer to the original in-focus position, it has a peak.

  Further, since the sensor 32 (also referred to as a far-side sensor) is arranged with a slight amount Δx shifted to the far side with respect to the sensor 26, the change curve L2 of the AF evaluation value Vf related to the sensor 32 is the original value of the focus lens. It has a peak when it exists at a position shifted by a minute amount Δx on the far side from the in-focus position.

<1-3. AF Principle Using AF Module 20>
Next, the principle of AF control using the AF module 20 will be described with reference to FIGS. FIG. 5 is a timing chart showing the distance measuring operation and the lens driving operation in the phase difference AF. FIG. 6 is a conceptual diagram showing a case where the focus lens is driven in the far direction, and FIG. 7 is a conceptual diagram showing a case where the focus lens is driven in the near direction. Further, FIGS. 8 to 10 are conceptual diagrams showing focusing operations when the lens positions PA, PB, and PC are stopped in the phase difference AF, respectively.

  Basically, the controller 101 first performs an automatic focusing operation by phase difference AF. Specifically, as shown in FIG. 5, a distance measuring operation using the phase difference AF is performed using an output signal from the phase difference AF sensor 26, and a lens driving operation is performed as necessary. In FIG. 5, lens driving toward the in-focus position is started in accordance with the distance measuring operation, and then the focus lens is moved toward the in-focus position by phase difference AF while gradually reducing the lens driving speed. The focus lens drive is stopped at time t10. As a result, the focus lens is positioned near the original focus position.

  However, in the AF operation using only the phase difference AF, the focus lens is present at a position deviated from the vicinity of the original focus position, and may not be focused with sufficient accuracy.

  Therefore, in this embodiment, contrast AF is used together to further improve AF accuracy.

  Specifically, focusing operation with higher accuracy is realized in consideration of AF evaluation values (contrast values) Vn and Vf acquired by the sensors 31 and 32, respectively. More specifically, the increase / decrease change directions of the AF evaluation values Vn and Vf in the sensors 31 and 32 are used. Here, as shown in FIG. 5, the AF evaluation values Vn and Vf by the sensors 31 and 32 are acquired during the movement of the focus lens for automatic focusing by the phase difference AF, and the increase / decrease change direction is determined. An example of performing more detailed in-focus determination will be described.

  As described above, the sensors 31 and 32 of the AF module 20 are arranged at positions shifted by a minute amount Δx from a position optically equivalent to the position of the imaging element 5 in the optical axis direction of the photographing lens unit 3. (See FIG. 4). Therefore, the peak positions of the AF evaluation values Vn and Vf acquired by the sensors 31 and 32 are shifted by Δx from the original focus position. Here, focusing determination or the like is performed using a shift in the peak positions of the two AF evaluation values Vn and Vf.

  As shown in FIG. 4, here, a deviation range within ± Δx with respect to the original in-focus position is set as a final in-focus range RB. Further, both the near-side range RB and the far-side range RC from the in-focus range RB are set as the out-of-focus range.

  In other words, the in-focus state is determined according to whether the stop position of the focus lens is in the range RA, RB, or RC. When the focus lens is in the range RB (for example, the position PB (FIG. 7)), it is determined that the focus lens is in focus. When the focus lens is in the range RA or the range RC, it is determined that the focus lens is out of focus. judge.

  For example, as shown in FIG. 6, it is assumed that the focus lens is moved from the near side to the far side in the phase difference AF (when moving in the far direction). In this case, the position of the focus lens can be distinguished into the following three ((1) to (3)) according to the increase / decrease change direction of the AF evaluation values Vn and Vf.

  (1) If the AF evaluation values Vn and Vf continue to increase immediately before the lens drive is stopped, neither of the AF evaluation values Vn and Vf has yet exceeded the peak, and the focus lens is still out of focus. It is determined that it is located within the range RA and has not reached the in-focus range RB.

  (2) Immediately before the lens drive is stopped, when the AF evaluation value Vn changes from increasing to decreasing after exceeding the peak, and the AF evaluation value Vf is still increasing, the focus lens exists at a position within the focusing range RB. It is determined that it is to be performed, and it is determined that the focus state is final. In other words, when the increase / decrease change direction (here, the decrease direction) of the AF evaluation value Vn is opposite to the increase / decrease change direction (here, the increase direction) of the AF evaluation value Vf, the final focus state is determined. To do.

  (3) When the AF evaluation values Vn and Vf both change from increasing to decreasing immediately after stopping lens driving, the focus lens is positioned in the out-of-focus range RC beyond the focusing range RB. It is determined to do.

  Conversely, as shown in FIG. 7, a case is assumed in which the focus lens is moved from the far side to the near side in the phase difference AF (when the focus lens is moved in the near direction). In this case, the position of the focus lens can be distinguished into the following three ((4) to (6)) according to the increase / decrease change direction of the AF evaluation values Vn and Vf.

  (4) If the AF evaluation values Vn and Vf continue to increase immediately before the lens drive is stopped, neither of the AF evaluation values Vn and Vf has yet exceeded the peak, and the focus lens is still out of focus. It is determined that it is located within the range RC and has not reached the in-focus range RB.

  (5) Immediately before the stop of lens driving, when the AF evaluation value Vf changes from an increase to a decrease beyond the peak and the AF evaluation value Vn continues to increase, the focus lens exists at a position within the focusing range RB. It is determined that it is to be performed, and it is determined that the focus state is final. In other words, when the increase / decrease change direction of the AF evaluation value Vf (here, the decrease direction) is opposite to the increase / decrease change direction of the AF evaluation value Vn (here, the increase direction), it is determined that the focus state is finally in focus. To do.

  (6) When the AF evaluation values Vn and Vf both change from increasing to decreasing immediately after stopping lens driving, the focus lens is positioned within the out-of-focus range RA beyond the focusing range RB. It is determined to do.

  As described above, when the increase / decrease change direction of the AF evaluation value Vn and the increase / decrease change direction of the AF evaluation value Vf are opposite, it is determined that the focus state is finally reached, and the increase / decrease change direction of the AF evaluation value Vn and the AF When the increase / decrease change direction of the evaluation value Vf is the same, it is determined that the state is out of focus.

  Among the above, when it is determined that the focus state is final ((2), (5)), the AF operation is terminated without further driving the focus lens. For example, as shown in FIG. 9, when it is determined that the focus lens position PB after the lens movement due to the phase difference AF is within the range RB, the AF operation ends without performing additional driving. Thereby, a highly accurate AF operation is realized such that the focus lens after the AF operation exists at a position within the range RB (that is, a position within ± Δx from the original in-focus position).

  On the other hand, when it is determined that the focus state is not yet final ((1), (3), (4), (6)), the focus lens is additionally finely driven.

  For example, as shown in FIG. 8, when the focus lens moves in the far direction due to phase difference AF, it is determined that the position of the focus lens is still within the out-of-focus range RA (for example, position PA) ( In (1) above, the focus lens is additionally driven by a minute amount Δx in the same direction (far direction).

  Then, the AF evaluation values Vn and Vf are compared before and after the additional driving. When it is determined that the AF evaluation value Vn exceeds the peak and then increases to decreases (Vn1> Vn2) and the AF evaluation value Vf continues to increase (Vf1 <Vf2), the focus lens is within the in-focus range RB. It is determined that it exists at the position of, and it is determined that it is the final focused state. In other words, when the increase / decrease change direction (here, the decrease direction) of the AF evaluation value Vn is opposite to the increase / decrease change direction (here, the increase direction) of the AF evaluation value Vf, the final focus state is determined. To do. Here, the values Vn1 and Vn2 represent the AF evaluation values Vn before and after the additional drive, and the values Vf1 and Vf2 represent the AF evaluation values Vf before and after the additional drive, respectively.

  When it is determined that the focus state is final, the AF operation ends. On the other hand, if it is determined that the focus state is not yet final, the same additional driving is further repeated. For example, when the stop position after the phase difference AF is the position PA0 (FIG. 8) closer to the position PA, the final focusing is performed after additional driving in the far direction several times. The state will be realized.

  Further, as shown in FIG. 10, when the focus lens moves in the far direction by the phase difference AF, when it is determined that the position of the focus lens is within the out-of-focus range RC (for example, the position PC) (described above) In (3)), the focus lens is additionally driven by a minute amount Δx in the reverse direction (near direction).

  Then, the AF evaluation values Vn and Vf are compared before and after the additional driving. When it is determined that the AF evaluation value Vn increases (Vn3 <Vn4) and the AF evaluation value Vf decreases (Vf3> Vf4), it is determined that the focus lens exists at a position within the in-focus range RB. Is determined to be in a focused state. In other words, when the AF evaluation value Vn increase / decrease change direction (in this case, the increase direction) and the AF evaluation value Vf increase / decrease change direction (here, the decrease direction) are opposite, the final focus state is determined. To do. Here, the values Vn3 and Vn4 represent the AF evaluation values Vn before and after the additional drive, and the values Vf3 and Vf4 represent the AF evaluation values Vf before and after the additional drive, respectively.

  When it is determined that the focus state is final, the AF operation ends. On the other hand, if it is determined that the focus state is not yet final, the same additional driving is further repeated. For example, when the stop position after the phase difference AF is a position PC0 (FIG. 10) further away from the position PC, the final focusing is performed after several additional drives in the near direction. The state will be realized.

  Further, when the focus lens is moved in the near direction by the phase difference AF (see FIG. 7), the same is true when it is determined that the focus state is not yet final (above (4), (6)). .

  Specifically, when it is determined that the position of the focus lens is still within the out-of-focus range RC ((4) above), the focus lens is additionally driven by a minute amount Δx in the same direction (near direction). When the most recent AF evaluation value Vn increase / decrease change direction is opposite to the AF evaluation value Vf increase / decrease change direction, it is determined that the focus state is final. By repeating such additional driving as necessary, a final in-focus state is realized.

  Similarly, when it is determined that the position of the focus lens is within the out-of-focus range RA ((6) above), the focus lens is additionally driven by a minute amount Δx in the reverse direction (far direction). When the most recent AF evaluation value Vn increase / decrease change direction is opposite to the AF evaluation value Vf increase / decrease change direction, it is determined that the focus state is final. By repeating such additional driving as necessary, a final in-focus state is realized.

  As described above, the AF operation is realized such that the position of the focus lens after the AF operation is within the focusing range RB. In other words, it is possible to realize a highly accurate AF operation such that the position of the focus lens after the AF operation is within ± Δx from the original focus position.

<1-4. About shift amount Δx>
By the way, it is preferable that the shift amount Δx is determined so as to satisfy a condition such as the expression (1).

  Here, F is the minimum value (that is, the minimum F number) of the aperture values (F numbers) that can be set in the imaging apparatus 1, and δ is a value that is twice the pixel pitch in the image sensor 5.

  For example, when F = 1.4 and δ = 6 (μm) × 2 = 12 (μm), Δx <33.6 (μm) is obtained from the equation (1).

  The value (2 × F × δ) on the right side of the expression (1) is recognized as an image in a clear in-focus state without confirming a so-called out-of-focus state when the image is confirmed on a display such as a personal computer. This is the required depth of focus (one side). If the shift amount Δx is determined so as to satisfy Expression (1), the image can be visually recognized in a sufficiently focused state when the image is confirmed on a display such as a personal computer. In addition, the degree of focus required when confirming an image on a display such as a personal computer is higher than the degree of focus required when the image is printed on a photographic paper and viewed, and is required in a normal usage mode. The highest degree of focus. Therefore, a captured image obtained by focusing with a deviation amount within the minute amount Δx satisfying the expression (1) is recognized as an image having a sufficient degree of focusing in a very wide variety of scenes.

<1-5. About Flicker>
Next, light source flicker will be described.

  FIG. 11 is a diagram illustrating the relationship between the image acquisition timing and the flicker light source. In FIG. 11, from the top, the image acquisition timing (here, the frame rate of 200 fps) in the sensor 31 (or sensor 32), the temporal change in the light source light amount of the 50 Hz fluorescent lamp (flicker frequency 100 Hz), and 60 Hz fluorescence. The time variation of the light source light quantity of the lamp (flicker frequency 120 Hz) is shown. FIG. 12 is a diagram showing how the peak shape of the AF evaluation value changes due to a change in the AF evaluation value calculation method in contrast AF control. Black circles in FIG. 12 indicate AF evaluation values respectively calculated from a plurality of image signals sequentially acquired at a frame rate of 200 frames / second (fps) when the flicker frequency of the light source is 100 Hz. . The vertical axis represents the AF evaluation value, and the horizontal axis represents the lens position of the focus lens.

  Since a fluorescent lamp flickers in a short cycle according to the frequency (50 Hz or 60 Hz) of a commercial power supply, fluctuation (hereinafter also referred to as “flicker”) exists in the amount of light (light quantity) emitted from the fluorescent lamp.

  Specifically, as shown in FIG. 11, a fluorescent lamp with a commercial power supply of 50 Hz has a flicker with a 1/100 second period (flicker frequency 100 Hz), and a fluorescent lamp with a commercial power supply of 60 Hz has a 1/120 second period. Flicker (flicker frequency 120 Hz).

  Here, in contrast AF control, in each image acquired at a predetermined timing as described above, the sum of pixel value differences between adjacent pixels is calculated as an AF evaluation value, and focusing is performed using the AF evaluation value. The action is executed.

  For this reason, under a shooting environment using a fluorescent lamp as a light source, the exposure amount at each predetermined timing varies due to the influence of flicker, and thus an accurate AF evaluation value cannot be calculated. Specifically, as shown in FIG. 12, the AF evaluation values (black circles in FIG. 12) of images sequentially acquired at a frame rate of 200 fps are unclear in the vicinity of the maximum value (near the peak). As a result, an accurate AF evaluation value peak cannot be detected.

  Therefore, in the present embodiment, in a shooting environment using a flicker light source such as a fluorescent lamp as a light source, the sum of differences in pixel values between adjacent pixels is calculated for each sequentially acquired image, and this is calculated as an AF evaluation value. The AF evaluation value is calculated using a method different from the method (normal evaluation value calculation method).

  Specifically, for images acquired sequentially at a frame rate of 200 fps, the total sum of pixel value differences between adjacent pixels is calculated as a preliminary evaluation value, and two preliminary evaluation values calculated continuously in time A method (a flicker countermeasure evaluation value calculation method) is used in which an average value (X mark in FIG. 12) is used as one AF evaluation value. According to this, the AF evaluation value does not undulate greatly, and the peak shape of the AF evaluation value becomes clear (broken line in FIG. 12).

  Here, the principle that the peak shape of the AF evaluation value becomes clear when the flicker countermeasure evaluation value calculation method is adopted in the flicker light source will be described in detail. 13 and 14 are timing charts showing the principle of the flicker countermeasure evaluation value calculation method. In FIGS. 13 and 14, the image acquisition timing (the frame rate of 200 fps in FIG. 13, the frame rate of 240 fps in FIG. 14) and the 50 Hz fluorescent lamp (flicker frequency) in order from the top, respectively. The time variation of the light source light amount of 100 Hz) and the time variation of the light source light amount of the 60 Hz fluorescent lamp (flicker frequency 120 Hz) are shown. Note that the exposure time when the image is acquired by the sensor 31 (or sensor 32) is constant.

  As shown in FIG. 13, when images are sequentially acquired at a frame rate of 200 fps when the flicker frequency of the light source is 100 Hz, the frame acquisition interval becomes 1/2 of the fluctuation period of the light source light quantity and is continuous in time ( The sum of exposure amounts at two adjacent image acquisition timings is always constant. For this reason, if an average value of preliminary evaluation values (that is, two preliminary evaluation values) calculated based on images acquired at two consecutive (adjacent) image acquisition timings is used as an AF evaluation value. Regardless of the influence of flicker, the peak shapes of a plurality of AF evaluation values become clear.

  As described above, when the flicker frequency of the light source is 100 Hz, when images are sequentially acquired at a frame rate of 200 fps and the AF evaluation value is calculated using the flicker countermeasure evaluation value calculation method, the contrast AF that is not affected by flicker. Control becomes possible.

  However, as shown in FIG. 13, when the flicker frequency of the light source is 120 Hz, the fluctuation period of the light source light quantity is not twice the frame acquisition interval, and the sum of the exposure amounts at the two image acquisition timings is It is not constant. Therefore, when the flicker frequency is 120 Hz and the frame rate is 200 fps, the preliminary evaluation values calculated respectively based on the image data acquired at two image acquisition timings that are temporally continuous (adjacent) are obtained. Even if the average value is used as the AF evaluation value, the AF evaluation value is greatly undulated, and a clear peak shape of the AF evaluation value cannot be obtained.

  Therefore, when the flicker frequency is 120 Hz, the frame rate is set to 120 Hz when the flicker frequency is 120 Hz so that the frame acquisition interval is ½ of the fluctuation period of the light source light amount, as in the case where the flicker frequency is 100 Hz. What is necessary is just 240 fps. According to this, as shown in FIG. 14, the sum of the exposure amounts at two image acquisition timings that are temporally continuous (adjacent) is always constant. As a result, an average value of preliminary evaluation values (that is, two preliminary evaluation values) calculated based on image data acquired at two consecutive (adjacent) image acquisition timings is used as an AF evaluation value. For example, the peak shapes of a plurality of AF evaluation values are clarified regardless of the influence of flicker.

  However, as shown in FIG. 14, when the flicker frequency is 100 Hz, when sequentially acquiring images at a frame rate of 240 fps, the light source light quantity fluctuation period is not twice the frame acquisition interval. The sum of the exposure amounts at the image acquisition timing is not constant. Accordingly, when the flicker frequency is 100 Hz and the frame rate is 240 fps, the preliminary evaluation values calculated respectively based on the image data acquired at two consecutive image acquisition timings (adjacent) are obtained. Even if the average value is used as the AF evaluation value, the AF evaluation value is greatly undulated, and a clear peak shape of the AF evaluation value cannot be obtained.

  Therefore, the imaging apparatus 1 detects the state of the light source (the presence / absence of flicker and the flicker frequency) by the method described below, changes the image acquisition timing for calculating the AF evaluation value according to the state of the light source, and sets the AF evaluation value. Control to change the calculation method.

  Hereinafter, the light source state identification method will be described. FIGS. 15 and 16 are timing charts for explaining a method for identifying a flicker frequency, and FIGS. 17 to 20 are diagrams for explaining a method for identifying a flicker frequency. 15 and 16, in order from the top, the image acquisition timing (the frame rate of 100 fps in FIG. 15, the frame rate of 120 fps in FIG. 16) in the sensor 31 (or sensor 32), and the light source when the flicker frequency is 100 Hz. A time change of the light amount and a time change of the light source light amount when the flicker frequency is 120 Hz are shown.

  As shown in FIG. 15, when the frame rate is 100 fps and the flicker frequency is 100 Hz, the frame acquisition interval coincides with the fluctuation period of the light source light quantity. The pixel value (luminance) does not fluctuate between each image. On the other hand, when the frame rate is 100 fps and the flicker frequency is 120 Hz, the frame acquisition interval does not coincide with the fluctuation period of the light source amount of light, and therefore each acquired by the sensor 31 (or sensor 32). The pixel value (luminance) varies between images.

  On the other hand, as shown in FIG. 16, when the frame rate is 120 fps and the flicker frequency is 120 Hz, the frame acquisition interval and the fluctuation period of the light source light quantity coincide with each other, and therefore the sensor 31 (or sensor 32). The pixel value (brightness) does not fluctuate between the images acquired in (1). On the other hand, when the frame rate is 120 fps and the flicker frequency is 100 Hz, the frame acquisition interval does not coincide with the fluctuation period of the light source light amount. The pixel value (luminance) varies between images.

  In FIG. 17, when the frame rate is 120 fps and the flicker frequency is 120 Hz, the average value of pixels (average value of luminance) in each image (each frame) acquired by the sensor 31 (or sensor 32). Specific examples are shown. In FIG. 18, when the frame rate is 100 fps and the flicker frequency is 120 Hz, the average value of pixel values (average value of luminance) in each image (each frame) acquired by the sensor 31 (or sensor 32). ) Is shown.

  As shown in FIG. 17, when the frame rate is 120 fps and the flicker frequency is 120 Hz, there is almost no variation in the average value of luminance (luminance average value) between the frames.

  On the other hand, as shown in FIG. 18, when the frame rate is 100 fps and the flicker frequency is 120 Hz, the luminance average value fluctuates between the frames, and the luminance is in a cycle of 5 frames. The average value repeats increasing and decreasing.

  FIG. 19 shows a specific example of the fluctuation cycle of the luminance average value of the image data when the frame rate is 100 fps and the flicker frequency is 120 Hz. FIG. 20 shows the frame rate of 120 fps and the flicker. A specific example of the fluctuation cycle of the luminance average value of the image data when the frequency is 120 Hz is shown. In FIG.19 and FIG.20, the vertical axis | shaft has shown the number of frames between the minimum values of each period, and the horizontal axis has shown period No (number). Here, in principle, the range between adjacent local minimum values is defined as one cycle. However, when there is no minimum value in a predetermined range (for example, 10 frames), the predetermined range is regarded as one cycle, and the number of frames in the cycle corresponding to the predetermined range is expressed as 0 (zero). is doing. Here, the number of frames between the minimum values is used to represent the fluctuation cycle of the luminance average value. However, the number of frames between the maximum values may be used without being limited to this.

  As shown in FIG. 19, when the frame rate is 100 fps and the flicker frequency is 120 Hz, the luminance average value fluctuates in approximately 5 frame periods. Thus, for example, when the frame rate is set to 100 fps, the luminance average value fluctuates in 5 frame periods for 8 periods or more out of 10 periods (substantially equivalent to the section KB1 in FIG. 19) (situation 1 ), It can be determined that the flicker frequency of the light source is 120 Hz.

  Although not shown, when the frame rate is 120 fps and the flicker frequency is 100 Hz, the average luminance value fluctuates in almost 6 frame periods. Therefore, for example, in a situation (situation 2) where the luminance average value fluctuates in 6 frame periods for 8 periods or more of 10 periods when the frame rate is set to 120 fps, the flicker frequency of the light source is 100 Hz. Can be determined.

  On the other hand, as shown in FIG. 20, when the frame rate is 120 fps and the flicker frequency is 120 Hz, the luminance average value does not vary. Therefore, for example, when the frame rate is set to 120 fps and the luminance average value does not change in 6 frame periods for 8 or more of 10 periods (situation 3), the flicker frequency of the light source is not 100 Hz. Can be determined. Therefore, if the flicker frequency of the light source is either 100 Hz or 120 Hz, it can be determined that the flicker frequency of the light source is 120 Hz.

  Further, when the frame rate is 100 fps and the flicker frequency is 100 Hz, the luminance average value does not vary. Therefore, for example, when the frame rate is set to 100 fps and the luminance average value does not fluctuate in 5 frame periods for 8 or more of 10 periods (situation 4), the flicker frequency of the light source is not 120 Hz. Can be determined. Therefore, if the flicker frequency of the light source is either 100 Hz or 120 Hz, it can be determined that the flicker frequency of the light source is 100 Hz.

  Further, in the above determination, the case where data for 10 cycles when the range between adjacent local minimum values is (in principle) one cycle is illustrated, but the present invention is not limited to this. For example, in situation 1 and situation 4, it is possible to use data for 10 periods (that is, image data for 50 frames) assuming that 5 frames are one period. It is possible to use data for 10 periods (that is, image data for 60 frames) assuming that 1 period is 1 period. In the following, it is assumed that the above determination is made based on such data.

Using the above principle, the contrast AF control unit 101a of the imaging apparatus 1
i) When situation 1 is established in 50 frames acquired at a frame rate of 100 fps and situation 3 is established in 60 frames obtained at a frame rate of 120 fps, it is determined that the flicker frequency of the light source is 120 Hz. To do.

  On the other hand, if situation 4 is established in 50 frames acquired at a frame rate of 100 fps and situation 2 is established in 60 frames acquired at a frame rate of 120 fps, the flicker frequency of the light source is 100 Hz. Is determined.

  In cases other than i) and ii), it is determined that the light source is not a flicker light source, that is, a non-flicker light source.

  Note that it is possible to recognize whether the flicker frequency of the light source is 100 Hz or 120 Hz only by detecting the situation 1 or the situation 2, but here, the situation 3 or the situation 4 is also detected. Is illustrated. According to this, it is possible to more accurately recognize the flicker frequency.

<2. Operation>
<2-1. Shooting action>
Next, the shooting operation of the imaging apparatus 1 will be described. FIG. 21 is a flowchart showing a shooting operation in the imaging apparatus 1. This operation flow is realized by the control of the control unit 101. The imaging device 1 is in the mirror-up state at the time of shooting (step SP119), but is in the mirror-down state at other times (steps SP100 to SP118, SP120, SP122, etc.).

  In the imaging apparatus 1, first, when the operation mode switching switch included in the operation unit 80 is appropriately operated, the operation mode of the imaging apparatus 1 is set to a mode for capturing a still image (still image capturing mode). The process proceeds to step SP100 of 21.

  In step SP100, power is turned on to the two sensors 31, 32 functioning as a contrast AF unit, and driving of the sensors 31, 32 is started.

  In step SP101, the frame rate of the near sensor 31 of the two sensors 31, 32 is set to 100 fps. Specifically, in response to a signal from the control unit 101, the near-side sensor 31 starts reading an image signal at a frame rate of 100 fps.

  In step SP102, the frame rate of the far side sensor 32 of the two sensors 31, 32 is set to 120 fps. Specifically, in response to a signal from the control unit 101, the far-side sensor 32 starts reading an image signal of 120 fps.

  In step SP103, the image data for 50 frames is read at 100 fps using the sensor 31 on the near side, and the luminance average value (luminance average value of 100 fps) is calculated for each of the image data for 50 frames. Is done. The 50 luminance average values are temporarily stored in the memory in the control unit 101.

  In step SP104, image data for 60 frames is read at 120 fps using the far-side sensor 32, and a luminance average value (luminance average value of 120 fps) is calculated for each of the 60 frames of image data. Is done. The 60 luminance average values are temporarily stored in the memory in the control unit 101.

  Here, the operation of step SP104 is executed in parallel (in parallel) with the operation of step SP103. Therefore, the processing at step SP103 and the operation at step SP104 can be performed at a higher speed than when the operation is performed sequentially (in series).

  In step SP105, it is determined whether the luminance average value of 100 fps calculated in step SP102 has a periodic variation. Specifically, the situation (situation 1) in which the luminance average value fluctuates in 5 frame periods for 8 periods or more out of 10 periods when 5 frames are 1 period in the image data for 50 frames is recognized. Then, it is determined that there is a periodic variation in the luminance average value of 100 fps. If it is determined in step SP105 that there is a periodic variation, the process proceeds to step SP106, and if it is determined that there is no periodic variation, the process proceeds to step SP111.

  In step SP106, it is determined whether or not the 120 fps luminance average value calculated in step SP104 has no periodic variation. Specifically, the situation (situation 2) in which the luminance average value fluctuates in 6 frame periods of 8 periods or more out of 10 periods when 6 frames are defined as 1 period in 60 frames of image data is recognized. Otherwise, it is determined that the luminance average value of 120 fps has no periodic fluctuation. If it is determined in step SP106 that there is a periodic variation, the process proceeds to step SP107, and if it is determined that there is no periodic variation, the process proceeds to step SP109.

  In step SP107, the light source is recognized as a non-flicker light source. Specifically, since periodic fluctuations were observed in both luminance average values according to 100 fps and 120 fps, the light source flicker frequency cannot be determined to be 100 Hz or 120 Hz, and thus the light source is recognized as a non-flicker light source. .

  In step SP108, in accordance with the non-flicker light source recognized in step SP107, the frame rates of the two sensors 31 and 32 during the contrast AF operation are each set to 200 fps.

  In step SP109, the light source is recognized as a 60 Hz fluorescent lamp.

In step SP110, the frame rates of the two sensors 31 and 32 during the contrast AF operation are set to 240 fps in accordance with the light source (60 Hz) recognized in step SP109.
On the other hand, in step SP111, it is determined whether or not the 120 fps luminance average value calculated in step SP104 has a periodic variation. Specifically, the situation (situation 2) in which the luminance average value fluctuates in 6 frame periods of 8 periods or more out of 10 periods when 6 frames are defined as 1 period in 60 frames of image data is recognized. Then, it is determined that the brightness average value of 120 fps has a periodic variation. If it is determined in step SP111 that there is a periodic variation, the process proceeds to step SP112. If it is determined that there is no periodic variation, the process proceeds to step SP114.

  In step SP112, it is recognized that the light source is a 50 Hz fluorescent lamp.

In step SP113, the frame rates of the two sensors 31 and 32 during the contrast AF operation are set to 200 fps in accordance with the light source (50 Hz) recognized in step SP112.
In step SP114, the light source is recognized as a non-flicker light source. Specifically, since no periodic fluctuation was observed in both the luminance average values according to 100 fps and 120 fps, the light source is recognized as a non-flicker light source.

  In step SP115, in accordance with the non-flicker light source recognized in step SP114, the frame rates of the two sensors 31 and 32 during the contrast AF operation are each set to 200 fps.

  In step SP116, it is determined whether or not the S1 state of the shutter button 11 has been detected. Here, the determination in step SP116 is repeated until the S1 state is detected, and when the S1 state is detected, the process proceeds to step SP117.

  In step SP117, an automatic focusing operation (AF operation) is executed. Specifically, phase difference AF control and contrast AF control are executed as described later.

  In contrast AF control, images are acquired from the two sensors 31, 32 at a common frame rate (200 fps or 240 fps) set in the frame rate setting step (steps SP108, SP110, SP113, SP115), and based on the images. Then, the operation for calculating the AF evaluation value is executed.

  As described above, when the flicker frequency is detected, the imaging apparatus 1 determines the frame rate of the two sensors 31 and 32 in contrast AF according to the flicker frequency, and the two sensors 31 and 32 share a common rate. An AF evaluation value is acquired based on the image acquired at the frame rate, and a contrast AF operation is executed.

  In the next step SP118, it is determined whether or not the S2 state of the shutter button 11 has been detected. If the S2 state is detected, the process proceeds to step SP119, and if the S2 state is not detected, the process proceeds to step SP120.

  In step SP120, it is determined whether or not the state is the S1 state. If the state is the S1 state, the process proceeds to step SP118. If the state is not the S1 state, the process proceeds to step SP116.

  On the other hand, in step SP119, shooting is performed. In other words, a main photographing operation including an exposure operation for acquiring a recording still image is performed. During the main photographing operation, the image pickup apparatus 1 has a mirror-up state, and the subject image that has reached the image pickup device 5 is acquired as image data for recording. When this main photographing operation is completed, the imaging device 1 returns to the mirror-down state again.

  When shooting is completed, the process proceeds to step SP121, where it is determined whether or not the shooting mode is continued. If the shooting mode is continued, the processing from step SP116 to step SP120 is repeatedly executed, and if the shooting mode is released, the shooting operation is terminated.

  As described above, in the imaging device 1 according to the embodiment of the present invention, the flicker frequency of the light source is detected by the two sensors 31 and 32 based on a plurality of images acquired in parallel at different frame rates. Therefore, an image used for detecting the flicker frequency can be acquired at high speed, and the flicker frequency of the light source can be detected at high speed.

  In addition, since the imaging apparatus 1 can detect the flicker frequency of the light source using the two sensors 31 and 32 functioning as a contrast AF unit, the flicker of the light source can be provided without providing a new configuration for detecting the flicker frequency. The frequency can be detected.

  When the flicker frequency of the light source is detected, the frame rate at the time of image acquisition is set to twice the flicker frequency (200 fps or 240 fps), and two pieces of image data acquired continuously in time are set. A single AF evaluation value is used to calculate a plurality of AF evaluation values. Then, contrast AF control is executed based on the plurality of AF evaluation values. According to this, it is possible to reduce the influence of fluctuations in the amount of light from the subject due to the flicker of the light source, and to realize highly accurate focusing control.

  In addition, since the imaging apparatus 1 detects the flicker frequency of the light source when the still image shooting mode is selected, the light source information can be acquired before performing AF control (before the S1 state is detected), and the AF instruction After (S1 state detection), the focusing operation can be executed immediately.

<2-2. AF operation>
Next, the AF operation (step SP117) of the imaging apparatus 1 will be described in detail with reference to FIGS. 22 to 26 are flowcharts showing a subroutine process related to the AF operation of the imaging apparatus 1.

  When the shutter button 11 is in the S1 state (half-pressed state) (step SP116), an AF operation as shown in FIG. 22 is started.

  First, the phase difference AF sensor 26 is activated (step SP1). Thereafter, a distance measuring operation by phase difference AF is performed (step SP2). This distance measuring operation is realized by a phase difference AF unit including a separator lens 25, a sensor 26, and the like. At this time, the focus lens is not driven yet.

  In step SP3, the result of the distance measuring operation in the phase difference AF is determined. When it is determined that the subject is in focus, the process proceeds to step SP21 (FIG. 23), and when it is determined that the subject is not in focus, the process proceeds to step SP41 (FIG. 24).

  First, step SP41 and subsequent steps will be described. When it is determined in the phase difference AF that the focus lens is out of focus, the focus lens is driven by the control unit 101, the focus lens control unit 121, etc., and moved to a position determined to be in focus by the phase difference AF. (Steps SP41 and SP43). During the movement of the focus lens, an image is acquired at the common frame rate (200 fps or 240 fps) set in the frame rate setting step (steps SP108, SP110, SP113, SP115), and AF is performed based on the image. Evaluation values Vn and Vf are sequentially obtained (step SP42). The acquired time series data of each AF evaluation value Vn, Vf is stored in a memory or the like in the control unit 101. As described above, the AF evaluation values (contrast values) Vn and Vf are acquired while the movement operation of the focus lens is performed as the focusing operation of the phase difference method using the phase difference AF unit. As described above, the phase difference AF operation is completed.

  In calculating the AF evaluation value, the calculation method is changed according to the state of the light source. Specifically, when the light source is a non-flicker light source, a normal evaluation value calculation method is used, and when the light source is a flicker light source, a flicker countermeasure evaluation value calculation method is used.

  In steps SP44 to SP53, the determination operation in the contrast AF operation as described above is performed.

  Specifically, when the increase / decrease change direction of the AF evaluation value Vn is opposite to the increase / decrease change direction of the AF evaluation value Vf, it is determined that the in-focus state is reached.

  Specifically, when the AF evaluation value Vf does not exceed the peak and is still increasing, the AF evaluation value Vn exceeds the peak and is decreasing (steps SP44 and SP45) (see FIG. 7). Is determined to be in focus (step SP51). However, here, in order to prevent erroneous determination, it is further determined whether or not the driving direction by the phase difference AF is the far direction (step SP46). When the driving direction by the phase difference AF is not the far direction, it is determined that the in-focus state is exceptional (step SP49).

  Also, when the AF evaluation value Vf exceeds the peak and tends to decrease, the AF evaluation value Vn does not exceed the peak and still tends to increase (steps SP44 and SP47) (see FIG. 6). In principle, it is determined that the in-focus state is reached (step SP52). However, here, in order to prevent erroneous determination, it is further determined whether or not the driving direction by the phase difference AF is the near direction (step SP48). When the driving direction by the phase difference AF is not the near direction, it is determined as an exceptionally out-of-focus state (step SP53).

  As described above, when it is determined in step SP51 or step SP52 that the in-focus state is in effect, this AF operation ends.

  On the other hand, when the increase / decrease change direction of the AF evaluation value Vn and the increase / decrease change direction of the AF evaluation value Vf are the same, the AF evaluation value Vn is determined to be out of focus.

  Specifically, the AF evaluation value Vf does not exceed the peak and is still increasing, and the AF evaluation value Vn is not exceeding the peak and is still increasing (steps SP44 and SP45) (FIG. 6, FIG. 6). In FIG. 7, it is determined that the in-focus state is present (step SP49). Also, the AF evaluation value Vf tends to decrease beyond the peak, and the AF evaluation value Vn also tends to decrease beyond the peak (steps SP44 and SP47) (see FIGS. 6 and 7). The in-focus state is determined (step SP53).

  If it is determined that the in-focus state is present, a contrast AF operation accompanied by fine driving of the focus lens is further performed.

  Specifically, if it is determined in step SP49 that the lens is out of focus, the process proceeds to step SP61 (FIG. 25).

  In step SP61, the focus lens is driven by a minute amount (Δx here) in the same direction as the driving direction by the phase difference AF.

  When the driving direction by the phase difference AF is the far direction, the minute driving operations in steps SP61 to SP63 and the like are repeated until it is determined that the condition C1 (described below) is satisfied (step SP63). Here, the condition C1 is that the AF evaluation value Vn decreases and the AF evaluation value Vf increases. When the condition C1 is satisfied, it is determined that the in-focus state is achieved (step SP64), and this AF operation is terminated.

  When the driving direction by the phase difference AF is the near direction, the minute driving operations in steps SP61 to SP63 and the like are repeated until it is determined that the condition C3 (described below) is satisfied (step SP63). Here, the condition C3 is that the AF evaluation value Vn increases and the AF evaluation value Vf decreases. When the condition C3 is satisfied, it is determined that the in-focus state is achieved (step SP64), and this AF operation is terminated.

  When it is determined that the sum of the minute driving amounts (ΣΔx in this case) is greater than or equal to the threshold value TH1 during the repetition of the minute driving operation (step SP62), the in-focus determination (step SP65) is determined that automatic focusing is impossible. And the AF operation is terminated.

  If it is determined in step SP53 that the lens is out of focus, the process proceeds to step SP71 (FIG. 26).

  In step SP71, the focus lens is driven by a minute amount Δx in the direction opposite to the driving direction by the phase difference AF.

  When the reverse drive direction (in other words, the new drive direction) is the near direction, the minute drive operation of steps SP71 to SP73 is performed until it is determined that the condition C3 (described above) is satisfied (step SP73). Repeated. When the condition C3 is satisfied, it is determined that the in-focus state is achieved (step SP74), and this AF operation is terminated.

  When the reverse drive direction (in other words, a new drive direction) is the far direction, the minute drive operation of steps SP71 to SP73 is performed until it is determined that the condition C1 (described above) is satisfied (step SP73). Repeated. When the condition C1 is satisfied, it is determined that the in-focus state is achieved (step SP74), and this AF operation is terminated.

  If it is determined that the sum of the minute drive amounts is greater than or equal to the threshold value TH1 during repetition of the minute drive operation (step SP72), an out-of-focus determination is made (step SP75) and automatic focusing is not possible. finish.

  Next, a case where it is determined in step SP3 (see FIG. 22) that the in-focus state is achieved will be described. That is, an operation in a case where it is determined that the in-focus state is achieved by the phase difference type focusing determination using the phase difference AF unit, and the lens driving as the focusing operation by the phase difference method is not performed will be described. In this case, the process proceeds to step SP21 (FIG. 23).

  Since it is determined that the in-focus state is obtained in the phase difference AF, it exists in the vicinity of the original in-focus position, but contrast AF is also used in order to focus with higher accuracy. In the following, the AF operation is basically performed by applying the above-described concept. However, at this time, the distance measuring operation by the phase difference AF has already been performed, but the driving operation by the phase difference AF has not been performed yet, so that the increasing tendency of the AF evaluation values Vn and Vf by the sensors 31 and 32 is grasped. I can't. Therefore, here, the focus lens is first driven by a minute amount to perform an operation of grasping the increasing tendency of the AF evaluation values Vn and Vf.

  Therefore, first, in step SP21, the AF evaluation values Vn and Vf at the current position at the undriven time are acquired. Then, the moving direction of the lens is determined based on the magnitude relationship (step SP22). Specifically, when the AF evaluation value Vn is larger than the AF evaluation value Vf (Vn> Vf), it is assumed that the focus lens is relatively close to the camera, and is driven minutely in the far direction (step SP23). On the other hand, if the AF evaluation value Vn is smaller than the AF evaluation value Vf (Vn <Vf), it is assumed that the focus lens exists relatively far and the lens is driven minutely in the near direction (step SP28).

  When the driving direction is the far direction, the minute driving operation or the like (steps SP23 to SP25) is repeated until it is determined that the condition C1 (described above) is satisfied (step SP25). When the condition C1 is satisfied, it is determined that the in-focus state is achieved (step SP26), and this AF operation is terminated.

  When the driving direction is the near direction, the minute driving operation or the like (steps SP28, SP29, SP31) is repeated until it is determined that the condition C3 (described above) is satisfied (step SP31). When the condition C3 is satisfied, it is determined that the in-focus state is achieved (step SP33), and this AF operation is terminated.

  When it is determined that the sum of the minute driving amounts is equal to or greater than the threshold value TH1 during the repetition of the minute driving operation (steps SP24 and SP29), an out-of-focus determination (steps SP27 and SP32) is performed assuming that automatic focusing is impossible. At the same time, the AF operation is terminated.

  According to the AF operation as described above, since the focusing operation by the phase difference AF unit is performed and the focusing operation by the first contrast AF unit and the second contrast AF unit is performed, a high-speed and high-precision focusing operation is performed. be able to. Further, the imaging plane P1 of the first contrast AF unit is arranged to be shifted closer to the optical equivalent position of the reference plane P0 of the phase difference AF unit, and the imaging plane P2 of the second contrast AF unit is phase difference AF. The unit is arranged shifted to the far side with respect to the optical equivalent position of the reference plane P0 of the unit. Therefore, using the peak positions of the two evaluation values (AF evaluation values) Vn and Vf acquired by the imaging surfaces P1 and P2, a range very close to the original focus position (here, ± Δx). It is possible to move the focus lens inward and to focus with high accuracy.

  Further, since the evaluation values Vn and Vf for AF are acquired while the focus lens is moved for the focusing operation by the phase difference AF unit, the focus for the focusing operation by the phase difference AF unit is acquired. Compared with the case where the acquisition of the AF evaluation value is started after the lens movement is completed, the speed can be increased.

  Further, when it is determined that the in-focus state is obtained based on the evaluation values Vn and Vf acquired based on the image signals on the imaging surfaces P1 and P2, it is not always necessary to further drive the lens. That is, it is not always necessary to further perform the lens driving operation for contrast AF after the phase difference AF. As described above, by using the first and second evaluation values Vn and Vf acquired based on the image signals on the imaging surfaces P1 and P2 of the first and second contrast AF units, useless lens driving operation is reduced. And can be focused accurately.

<3. Modification>
In the above embodiment, it is determined whether or not the final focus state is obtained by using the increase / decrease change directions of the two evaluation values Vn and Vf, but the present invention is not limited to this. For example, the final focus state may be determined based on the magnitude relationship between the difference between the two evaluation values Vn and Vf and the threshold value. More specifically, the evaluation value Vn is determined when the in-focus state is determined by the in-focus determination of the phase difference method using the phase difference AF unit and the lens driving is not performed as the in-focus operation by the phase difference method. , Vf may be determined as being in focus when the difference between the threshold values TH2 is smaller than the threshold value TH2, and may be determined as being out of focus when the difference between the evaluation values Vn and Vf is greater than the threshold value TH2.

  FIG. 27 is a flowchart showing an operation according to such a modification, and FIG. 28 is a conceptual diagram for explaining the principle of focus determination.

  As shown in FIG. 28, in the vicinity of the original in-focus position, the difference (absolute value) between the two evaluation values (AF evaluation values) Vn and Vf becomes a relatively small value. Utilizing such a property, here, when the difference between the two evaluation values (AF evaluation values) Vn and Vf, that is, | Vn−Vf | is smaller than a predetermined threshold value TH2 (| Vn−Vf | <TH2 ) Is determined to be the final in-focus state. Conversely, when the difference | Vn−Vf | is larger than a predetermined threshold value TH2 (| Vn−Vf | <TH>), it is determined that the final in-focus state is not yet achieved. As described above, by using the difference between the two evaluation values Vn and Vf, it is possible to realize a focus determination operation with higher accuracy. Note that an appropriate value may be set as the threshold TH2. If the threshold value TH2 is set to a relatively small value, the focusing range RD becomes a relatively narrow range as shown in FIG.

  In FIG. 27, the process performed instead of each process of FIG. 23 in the said embodiment is shown. Specifically, if it is determined in step SP3 (see FIG. 22) that the in-focus state is obtained, the process proceeds to step SP21 in FIG. In step SP21, AF evaluation values Vn and Vf at the current time (undriven time) are acquired.

  Next, proceeding to step SP36, it is determined whether or not the difference between the two evaluation values (AF evaluation values) Vn and Vf is smaller than a predetermined threshold value TH2 (| Vn−Vf | <TH2).

  When the inequality, | Vn−Vf | <TH2, is satisfied, it is determined that the focus state is finally reached (step SP37).

  On the other hand, when the inequality, | Vn−Vf | <TH2, is not satisfied, it is determined that the focus state is not final, and the process proceeds to step SP22. Note that when the equal sign is established (| Vn−Vf | = TH2), it may be determined that the final in-focus state is reached.

  After step SP22, the same operation as described above (see FIG. 23) is performed. That is, micro-driving by contrast AF is performed.

  Also by the operation as described above, a high-speed and high-precision focusing operation can be performed. In particular, when | Vn−Vf | is smaller than a predetermined threshold value TH2 (| Vn−Vf | <TH2), it is confirmed that the final focused state is achieved without driving the lens.

  In the above embodiment, the shift amount of both imaging surfaces P1 and P2 with respect to the optical equivalent position of the reference surface P0 of the phase difference AF unit, specifically, the shift amount of the imaging surface P1 of the sensor 31 and the sensor 32 The shift amount of the imaging surface P2 is Δx, which is substantially the same. In other words, the case where the image pickup surface P1 of the sensor 31 and the image pickup surface P2 of the sensor 32 are present at substantially the same distance from the optical equivalent position of the reference surface P0 of the phase difference AF unit is illustrated. However, the present invention is not limited to this, and the shift amounts of the imaging surfaces P1 and P2 with respect to the optical equivalent position of the reference surface P0 of the phase difference AF unit may be different from each other.

  In the above embodiment, in contrast AF control, the frame rate is set to twice the flicker frequency, and one AF evaluation value is calculated using two pieces of image data acquired continuously in time. It is not limited to this. For example, when the frame rate is set to 3 times the flicker frequency, the fluctuation period of the light source light quantity is 3 times the frame acquisition interval, and therefore the sensor 31 (or sensor 32) continuously acquires in time. One AF evaluation value may be calculated from the three image data.

  Furthermore, when the frame rate (the number of frames per second: fps) is set to n times the flicker frequency (Hz) (n is a natural number), the fluctuation period of the light source quantity and the n times the frame acquisition interval are Match. For this reason, for example, one AF evaluation value may be calculated using n images acquired continuously in time by the sensor 31. According to this, it is possible to reduce the influence of fluctuations in the amount of light from the subject due to the flicker of the light source, and to realize highly accurate focusing control.

  In the above embodiment, the flicker frequency of the light source is detected when the still image shooting mode is selected. However, the present invention is not limited to this.

  Specifically, the flicker frequency of the light source may be detected when the imaging device 1 is activated. “When the imaging device is activated”, for example, (a) when the imaging device 1 is powered on (ON), (b) a predetermined button from a power saving mode such as automatic power off (auto power off) This includes the case of returning by operation. Alternatively, the flicker frequency of the light source may be detected when a change in proper exposure is detected in the shooting mode. Alternatively, the flicker frequency of the light source may be detected when the white balance of the image acquired by the two sensors 31 and 32 is changed. Alternatively, the flicker frequency of the light source may be detected when the photographic lens unit 3 is exchanged in the power-on state and the installation of a new photographic lens unit 3 is detected.

  In the above embodiment, the fluctuation of the amount of light (light quantity) emitted from the light source due to the flickering of the fluorescent lamp is referred to as “flicker”, and the frequency of the fluctuation is referred to as “flicker frequency”. For example, the fluctuation of the amount of light (light quantity) emitted from a light source other than the fluorescent lamp may be generally referred to as “flicker”, and the frequency of the fluctuation may be referred to as “flicker frequency”.

It is the schematic which shows the imaging device which concerns on embodiment. It is a block diagram which shows the function structure of an imaging device. It is a figure which shows the structure of AF module. It is a figure which shows the optical positional relationship of an imaging device and two sensors for contrast detection. It is a timing chart which shows the ranging operation and lens drive operation in phase difference AF. It is a conceptual diagram which shows the case where a focus lens is driven to a far direction. It is a conceptual diagram which shows the case where a focus lens is driven to a near direction. It is a conceptual diagram which shows a focusing operation | movement when stopping to the lens position in the near-in-focus range by phase difference AF. It is a conceptual diagram which shows a focusing operation | movement when it stops at the lens position in a focusing range by phase difference AF. It is a conceptual diagram which shows a focusing operation | movement when it stops in the lens position in the far-in-focus range by phase difference AF. It is a figure which shows the relationship between an image acquisition timing and a flicker light source. It is a figure which shows the change of the peak shape of AF evaluation value based on the change of the calculation method of AF evaluation value. It is a timing chart which shows the principle of the flicker countermeasure evaluation value calculation method. It is a timing chart which shows the principle of the flicker countermeasure evaluation value calculation method. It is a timing chart explaining the identification method of a flicker frequency. It is a timing chart explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. 3 is a flowchart illustrating a shooting operation in the imaging apparatus 1. It is a flowchart which shows AF operation | movement of an imaging device. It is a flowchart which shows AF operation | movement of an imaging device. It is a flowchart which shows AF operation | movement of an imaging device. It is a flowchart which shows AF operation | movement of an imaging device. It is a flowchart which shows AF operation | movement of an imaging device. It is a flowchart which shows the operation | movement which concerns on a modification. It is a conceptual diagram explaining the principle of the focus determination which concerns on a modification. It is a conceptual diagram explaining the principle of the focus determination which concerns on a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up device 2 Camera main-body part 3 Shooting lens unit 5 Image pick-up element 20 AF module 22 Half mirror 23,28 IR cut filter 25 Separator lens 26 Phase difference AF sensor 27 Relay optical system 29 Beam splitter 31, 32 (For contrast AF) Image sensor Δx Shift amount P0 Reference plane P1 (for phase difference AF sensor 26) Image plane P2 (for image sensor 31) Image plane P2 (for image sensor 32) Image plane Vn, Vf Evaluation value

Claims (11)

An imaging device,
Two imaging sensors each capable of acquiring time-series image data,
Setting means for setting a frame rate at the time of image data acquisition by the two image sensors;
Frequency detection means for detecting a flicker frequency of a light source based on a plurality of image data acquired in parallel by the two imaging sensors at different frame rates;
An imaging apparatus comprising: The imaging device according to claim 1,
Image signal focusing means for performing a focusing operation based on image data acquired by the two imaging sensors;
An image pickup apparatus further comprising: The imaging device according to claim 2,
The setting means sets a frame rate of the two imaging sensors to a common frame rate determined according to the flicker frequency when a flicker frequency is detected by the frequency detection means,
The imaging apparatus, wherein the image signal focusing means performs the focusing operation based on image data acquired by each of the two imaging sensors at the common frame rate. The imaging device according to claim 3.
The common frame rate (fps: number of frames per second) is set to a value obtained by multiplying the flicker frequency (Hz) by n (n is a natural number). The imaging apparatus according to any one of claims 2 to 4,
The two imaging sensors are respectively arranged at different positions on an optical path through which a subject image is guided. In the imaging device in any one of Claims 2-5,
A phase difference AF unit that detects the in-focus state on the reference surface by a phase difference method;
Further comprising
The imaging apparatus, wherein the reference plane of the phase difference AF unit is disposed between the two imaging sensors on an optical path through which a subject image is guided. In the imaging device in any one of Claims 2-5,
The image pickup apparatus, wherein the flicker frequency of the light source is detected when the image pickup apparatus is activated. In the imaging device in any one of Claims 2-5,
The flicker frequency of the light source is detected when switching to a still image shooting mode is performed. In the imaging device in any one of Claims 2-5,
The imaging apparatus according to claim 1, wherein the flicker frequency of the light source is detected when a change in proper exposure is detected. In the imaging device in any one of Claims 2-5,
The flicker frequency of the light source is detected when a white balance of the image data acquired by the two image sensors is changed. In the imaging device in any one of Claims 2-5,
The imaging device is detachable from a photographic lens,
The imaging apparatus according to claim 1, wherein the flicker frequency of the light source is detected when attachment of the photographing lens is detected.

Images