JP2016156931A - Imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction in picture definition by implementing a focus adjustment control dealing with a movement speed of a subject.SOLUTION: An imaging device capable of shooting a movie is configured to: implement focus detection using an output signal of a focus detection pixel of an image pick-up element 107; and control a focus adjustment operation by controlling a drive of a focus lens (105) in accordance with an amount of detection of a focus position. A CPU 121 is configured to set a time or the number of determinations for determination to be used in determining whether to reboot the focus lens from a point of time of stopping a drive of a focus lens when determining that a subject is focused to be smaller as an amount of change in an amount of detection (amount of defocus) per time is greater. The CPU 121 is configured to, when the time or the number of frequencies when the amount of detection has exceeded a threshold, control so as to reboot the drive of the focus lens.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for automatic focus adjustment (AF control) of an imaging apparatus.

  An imaging device such as a digital camera has an imaging surface phase difference type autofocus (hereinafter referred to as imaging surface phase difference AF) function that detects a focal position from a phase difference of an image obtained by performing pupil division on the imaging surface. There is an installed device. In the imaging surface phase difference method, focus detection with high accuracy and response can be performed by the phase difference AF method while performing an imaging operation of the image sensor, and therefore, the effect is particularly effective when shooting a moving image. In the AF operation for moving image shooting, the focus lens drive is temporarily stopped at the time of focusing on the main subject in order to avoid degradation of image quality due to the focus lens moving unnecessarily too much. Thereafter, when the main subject moves beyond the in-focus area, control for resuming driving of the focus lens is performed.

  Patent Document 1 includes a focus detection unit that detects a focus position of a subject image at a plurality of positions on an imaging plane, and predicts a focus position of the subject image at a predetermined time based on the stored output of the focus detection unit. Techniques to do this are disclosed. The apparatus disclosed in Patent Document 2 detects that the subject has moved with a component in the direction perpendicular to the optical axis based on an image signal obtained from the first focus detection that detects the focus based on the phase difference. After the in-focus state, whether or not to restart the automatic focus adjustment is determined based on the result of the first focus detection and the result of the second focus detection for detecting the focus using a signal from the image sensor.

JP 2012-189934 A JP 2012-128316 A

In the prior art, various parameters when the AF operation is restarted are changed according to the defocus amount obtained by focus detection, and the followability to a moving subject can be improved. However, since control according to the moving speed of the subject is not performed, there is a concern that the quality of the captured video may be lowered depending on the moving speed. For example, an AF operation is performed on a subject with a slow moving speed without making a large amount of video, but as the moving speed of the subject increases, the defocus amount increases and the video quality may decrease. is there.
An object of the present invention is to suppress a reduction in image quality by performing focus adjustment control corresponding to the moving speed of a subject.

An imaging apparatus according to the present invention performs focus detection using an imaging element having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of an imaging optical system, and output signals of the plurality of focus detection pixels. And a control unit that performs focus adjustment control by controlling driving of a lens that forms the imaging optical system using a detection amount detected by the focus detection unit.
In the imaging apparatus according to the first aspect of the present invention, when the control unit determines that the subject is in focus, the control unit determines whether to restart from the point of time when driving of the lens is stopped. The determination time or number to be used is set to be smaller as the temporal change in the detection amount detected by the focus detection means is larger, and the time or number of times that the detection amount exceeds the threshold is the determination time or When the number of times is exceeded, control to restart the driving of the lens is performed.
In the imaging apparatus according to the second aspect of the present invention, the control means integrates the detection amount detected by the focus detection means from the time when the driving of the lens is stopped when it is determined that the subject is in focus. Then, when the integrated value exceeds the threshold value, a control for restarting the driving of the lens is performed.

  According to the present invention, it is possible to suppress a reduction in image quality by performing focus adjustment control corresponding to the moving speed of a subject.

It is a schematic block diagram of the imaging device in the Example of this invention. It is the schematic of the pixel arrangement | sequence in the Example of this invention. It is the schematic plan view (A) and schematic sectional drawing (B) of the pixel in the Example of this invention. It is the schematic explaining the relationship between the pixel and pupil division in the Example of this invention. It is a schematic explanatory drawing (A) of an image sensor and pupil division in an embodiment of the present invention, and a schematic relation diagram (B) of defocus amounts and image shift amounts of a first focus detection signal and a second focus detection signal. It is a flowchart explaining the focus detection process in the Example of this invention. It is a schematic explanatory drawing of the shading by the pupil shift | offset | difference of the 1st focus detection signal and the 2nd focus detection signal in the Example of this invention. It is a graph which illustrates the filter frequency band in the example of the present invention. It is a figure which illustrates the change of a subject's motion and defocus amount in the example of the present invention. It is a flowchart explaining the process in Example 1 of this invention. It is a figure which shows the range of the reliability determination of the image surface moving speed in Example 1 of this invention. It is a flowchart explaining the process in Example 2 of this invention. It is a figure which illustrates the sum total of the moving speed of the to-be-photographed object and the defocus amount in Example 2 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each embodiment, description will be given mainly assuming a configuration of a single-lens reflex camera as an example of a means for realizing the present invention. However, the present invention is not limited to the form of a single-lens reflex camera, and can be applied to any imaging device capable of shooting a moving image, such as a video camera or a compact digital camera. In addition, the specifications of the apparatus should be appropriately modified or changed according to the configuration of the apparatus to which the present invention is applied and various conditions. The configuration and operation of an imaging apparatus common to the embodiments of the present invention will be described with reference to FIGS. 1 to 9, and then each embodiment will be described with reference to FIGS. 10 to 13. In the present embodiment, control related to focus detection and lens driving when shooting a moving image using imaging surface phase difference AF will be described.

  FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to the present embodiment. The first lens group 101 is disposed at the tip of the imaging optical system (imaging optical system), and is held by a lens barrel so as to be able to advance and retract in the optical axis direction. The aperture / shutter 102 adjusts the aperture diameter to adjust the amount of light during shooting, and also functions as an exposure time adjustment shutter when shooting a still image. The second lens group 103 moves forward and backward in the optical axis direction integrally with the diaphragm / shutter 102, and has a zoom function by zooming operation by interlocking with the forward / backward movement of the first lens group 101. The third lens group 105 is a focus lens that performs focus adjustment by advancing and retreating in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the captured image. The image pickup element 107 includes a two-dimensional CMOS (complementary metal oxide semiconductor) photosensor and a peripheral circuit, and is disposed on the imaging plane of the image pickup optical system.

  The zoom actuator 111 performs a zooming operation by moving the first lens group 101 and the second lens group 103 in the optical axis direction by rotating a cam cylinder (not shown). The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. The focus actuator 114 adjusts the focus by moving the third lens group 105 in the optical axis direction.

  The electronic flash 115 for illuminating the subject is used at the time of photographing, and a flash illumination device using a xenon tube or an illumination device including a continuous light emitting LED (light emitting diode) is used. The AF auxiliary light source 116 improves the focus detection capability for a low-luminance subject or a low-contrast subject. The AF auxiliary light source 116 projects a mask image having a predetermined aperture pattern onto the object field via the light projection lens.

  A CPU (Central Processing Unit) 121 that constitutes a control unit of the camera system has a control center function that controls various controls. The CPU 121 includes a calculation unit, ROM (read only memory), RAM (random access memory), A (analog) / D (digital) converter, D / A converter, communication interface circuit, and the like. The CPU 121 drives various circuits included in the camera according to a predetermined program stored in the ROM, and executes a series of operations such as AF control, photographing, image processing, and recording processing. The CPU 121 controls image processing.

  The electronic flash control circuit 122 controls lighting of the electronic flash 115 in synchronization with the photographing operation in accordance with a control command from the CPU 121. The auxiliary light driving circuit 123 controls lighting of the AF auxiliary light source 116 in synchronization with the focus detection operation according to the control command of the CPU 121. The image sensor driving circuit 124 controls the image capturing operation of the image sensor 107, A / D converts the acquired image signal, and transmits it to the CPU 121. The image processing circuit 125 performs processing such as γ (gamma) conversion, color interpolation, JPEG (Joint Photographic Experts Group) compression of an image acquired by the image sensor 107 in accordance with a control command of the CPU 121. The image processing circuit 125 has a processing function for still image data acquired during still image shooting and moving image data acquired during moving image shooting.

  The focus driving circuit 126 controls driving of the focus actuator 114 based on the focus detection information according to the control command of the CPU 121, and adjusts the focus by moving the third lens group 105 in the optical axis direction. The aperture shutter drive circuit 128 drives the aperture shutter actuator 112 in accordance with a control command from the CPU 121 to control the aperture diameter of the aperture / shutter 102. The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation instruction of the photographer according to the control command of the CPU 121. The shake detection unit 130 detects a shake of the apparatus by a gyro sensor, an acceleration sensor, or the like incorporated in the photographing lens device or the image pickup apparatus, and outputs a shake detection signal to the CPU 121.

  The display unit 131 has a display device such as an LCD (Liquid Crystal Display), and displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. To do. The operation unit 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like, and outputs an operation instruction signal to the CPU 121. The flash memory 133 is a recording medium that can be attached to and detached from the camera body, and records captured image data and the like.

Next, with reference to FIG. 2, the arrangement of the imaging pixels and focus detection pixels of the imaging device in the present embodiment will be described. FIG. 2 illustrates an imaging pixel array of a two-dimensional CMOS sensor in a range of 4 columns × 4 rows, and illustrates a focus detection pixel array in a range of 8 columns × 4 rows. The pixel group 200 of 2 columns × 2 rows includes a set of pixels 200R, 200G, and 200B described below.
Pixel 200R (see the upper left position): a pixel having a spectral sensitivity of R (red) color.
Pixel 200G (refer to the upper right and lower left positions): a pixel having G (green) spectral sensitivity.
Pixel 200B (refer to the lower right position): a pixel having a spectral sensitivity of B (blue) color.
Each pixel unit is composed of a first focus detection pixel 201 and a second focus detection pixel 202 arranged in 2 columns × 1 row. A large number of 4 columns × 4 rows of pixels (8 columns × 4 rows of focus detection pixels) shown in FIG. 2 are arranged in a grid pattern on the plane, so that captured image signals and focus detection signals can be acquired. . In the imaging device of the present embodiment, the pixel period P is 4 (μm), and the number N of pixels is 5575 columns × 3725 rows (= about 20.75 million pixels). Also in the column direction of the period _{P AF} focus detection pixels and 2 ([mu] m), the focus detection pixel number _{N AF} horizontal 11150 rows × vertical 3725 lines and (= approximately 41.5 million pixels).

  FIG. 3A shows a plan view of one pixel 200G in the image sensor shown in FIG. 2 viewed from the light receiving surface side (+ z side) of the image sensor. The z axis is set in a direction perpendicular to the paper surface of FIG. 3A, and the near side is defined as the positive direction of the z axis. Also, the y-axis is set in the vertical direction perpendicular to the z-axis, the upper direction is the positive direction of the y-axis, the x-axis is set in the horizontal direction perpendicular to the z-axis and the y-axis, and the right direction is the positive direction of the x-axis It is defined as FIG. 3B shows a cross-sectional view when seen from the −y direction along the line aa in FIG.

A pixel 200G illustrated in FIG. 3B includes a plurality of divided photoelectric conversion units in which a microlens 305 that collects incident light is formed on the light-receiving surface side (+ z direction) of each pixel. For example, the number of division in the x direction and N _H, the division number in y-direction and N _V. FIG. 3 illustrates an example in which the pupil region is divided into two in the x direction, that is, a case where N _H = 2 and N _V = 1, and a photoelectric conversion unit 301 and a photoelectric conversion unit 302 are formed as sub-pixels. ing. The photoelectric conversion unit 301 corresponds to the first focus detection pixel 201, and the photoelectric conversion unit 302 corresponds to the second focus detection pixel 202. The photoelectric conversion unit 301 and the photoelectric conversion unit 302 are formed as, for example, a pin structure photodiode in which an intrinsic layer is sandwiched between a p-type layer 300 and an n-type layer. Alternatively, if necessary, the intrinsic layer may be omitted and formed as a pn junction photodiode. In each pixel, a color filter 306 is formed between the microlens 305 and the photoelectric conversion unit 301 and the photoelectric conversion unit 302. If necessary, the spectral transmittance of the color filter 306 may be changed for each sub-pixel, or the color filter may be omitted.

  The light incident on the pixel 200G is collected by the microlens 305 and further dispersed by the color filter 306, and then received by the photoelectric conversion unit 301 and the photoelectric conversion unit 302. In the photoelectric conversion unit 301 and the photoelectric conversion unit 302, a pair of electrons and holes (holes) are generated according to the amount of received light, separated by a depletion layer, and then electrons having a negative charge are transferred to an n-type layer (not shown). Accumulated. On the other hand, the holes are discharged to the outside of the image sensor through a p-type layer connected to a constant voltage source (not shown). Electrons accumulated in the n-type layer (not shown) of the photoelectric conversion unit 301 and the photoelectric conversion unit 302 are transferred to the capacitance unit (FD) via the transfer gate and converted into a voltage signal.

  FIG. 4 is a schematic explanatory diagram showing the correspondence between the pixel structure and pupil division. 4A and 4B are a cross-sectional view of the cross section taken along the line aa of the pixel structure shown in FIG. 3A when viewed from the + y direction, and an exit pupil plane of the imaging optical system (see the exit pupil 400). ) Is viewed from the −z direction. In FIG. 4, in order to correspond to the coordinate axis of the exit pupil plane, the x axis and the y axis are shown reversed in the cross-sectional view from the state shown in FIG. The first pupil partial region 501 corresponding to the first focus detection pixel 201 is substantially conjugated by the microlens 305 with respect to the light receiving surface of the photoelectric conversion unit 301 whose center of gravity is biased in the −x direction. That is, the first pupil partial region 501 represents a pupil region that can be received by the first focus detection pixel 201, and the center of gravity is biased in the + x direction on the pupil plane. In addition, the second pupil partial region 502 corresponding to the second focus detection pixel 202 is substantially conjugated by the microlens 305 with respect to the light receiving surface of the photoelectric conversion unit 302 whose center of gravity is decentered in the + x direction. . The second pupil partial region 502 represents a pupil region that can be received by the second focus detection pixel 202, and the center of gravity is biased in the −x direction on the pupil plane.

A pupil region 500 illustrated in FIG. 4 is a pupil region that can receive light in the entire pixel 200G when the photoelectric conversion unit 301 and the photoelectric conversion unit 302 (the first focus detection pixel 201 and the second focus detection pixel 202) are combined. is there. The correspondence between the image sensor and pupil division is shown in the schematic diagram of FIG. The light beams that have passed through the different pupil partial areas of the first pupil partial area 501 and the second pupil partial area 502 are incident on each pixel of the image sensor at different angles. Incident light on the imaging surface 800 is received by the first focus detection pixel 201 and the second focus detection pixel 202 divided into N _H (= 2) × N _V (= 1). The photoelectric conversion unit 301 of the first focus detection pixel 201 and the photoelectric conversion unit 302 of the second focus detection pixel 202 convert light into an electrical signal. In the present embodiment, an example is shown in which the pupil region is divided into two pupils in the horizontal direction. If necessary, pupil division may be performed in the vertical direction.

  The image sensor 107 according to this embodiment includes a first focus detection pixel that receives a light beam passing through the first pupil partial region of the imaging optical system, and a second imaging optical system that is different from the first pupil partial region. A second focus detection pixel that receives a light beam passing through the pupil partial region is provided. A plurality of imaging pixels that receive a light beam passing through a pupil region that is a combination of the first pupil partial region and the second pupil partial region of the imaging optical system are arranged in a two-dimensional array. That is, each imaging pixel is composed of a first focus detection pixel and a second focus detection pixel. If necessary, the imaging pixels, the first focus detection pixels, and the second focus detection pixels have individual pixel configurations, and the first focus detection pixels and the second focus detection pixels are partially distributed in the imaging pixel array. A configuration may be adopted.

  In the present embodiment, the first focus detection signal is generated by collecting the light reception signals of the first focus detection pixels 201 of each pixel in the image sensor, and the light reception signals of the second focus detection pixels 202 of each pixel are collected to obtain the second focus. A detection signal is generated. In focus detection, a process of calculating an image shift amount from the first focus detection signal and the second focus detection signal is performed. Further, by adding the output signal of the first focus detection pixel 201 and the output signal of the second focus detection pixel 202 for each pixel of the image pickup device, an image pickup signal having a resolution of the effective pixel number N is generated. Thereby, captured image data can be acquired.

  Next, the relationship between the defocus amount and the image shift amount of the first focus detection signal and the second focus detection signal acquired by the image sensor 107 will be described. FIG. 5B is a relationship diagram schematically showing the defocus amounts of the first focus detection signal and the second focus detection signal and the image shift amount between the first focus detection signal and the second focus detection signal. is there. An imaging element (not shown) is arranged on the imaging surface 800, and the exit pupil of the imaging optical system is divided into the first pupil partial region 501 and the second pupil partial region as in the case of FIGS. 4 and 5A. Divided into 502.

  The size | d | of the defocus amount d represents the distance from the imaging position of the subject image to the imaging surface 800. The orientation is defined as a negative sign (d <0) in the front pin state where the imaging position of the subject image is closer to the subject side than the imaging surface 800, and a positive sign (d> 0) in the rear pin state opposite to this. To do. In an in-focus state where the image formation position of the subject image is on the imaging surface (in-focus position), d = 0. The position of the subject 801 shown in FIG. 5B indicates a position corresponding to the in-focus state (d = 0), and the position of the subject 802 exemplifies a position corresponding to the front pin state (d <0). . Hereinafter, the front pin state (d <0) and the rear pin state (d> 0) are collectively referred to as a defocus state (| d |> 0).

In the front pin state (d <0), the luminous flux that has passed through the first pupil partial area 501 (or the second pupil partial area 502) out of the luminous flux from the subject 802 is once condensed and then the gravity center position G1 of the luminous flux. (Or G2) is spread around the width Γ1 (or Γ2). In this case, the image is blurred on the imaging surface 800. The blurred image is received by the first focus detection pixel 201 (or the second focus detection pixel 202) constituting each pixel arranged in the image sensor, and a first focus detection signal (or a second focus detection signal) is generated. Is done. Therefore, the first focus detection signal (or the second focus detection signal) is detected as a subject image (blurred image) having a width Γ1 (or Γ2) at the gravity center position G1 (or G2) on the imaging surface 800. Is done. The width Γ1 (or Γ2) of the subject image increases approximately proportionally as the magnitude | d | of the defocus amount d increases. Similarly, when the image shift amount of the subject image between the first focus detection signal and the second focus detection signal is denoted by “p”, the magnitude | p | is the magnitude of the defocus amount d | d | It increases with the increase. For example, the image shift amount p is defined as a difference “G1−G2” in the center of gravity position of the light beam, and its magnitude | p | increases approximately proportionally as | d | increases. In the rear pin state (d> 0), the image shift direction of the subject image between the first focus detection signal and the second focus detection signal is opposite to the front pin state, but there is a similar tendency.
In the present embodiment, the first focus detection signal and the second focus detection signal, or the defocus amount of the imaging signal obtained by adding the first focus detection signal and the second focus detection signal increases as the first focus detection signal increases. The magnitude of the image shift amount between the focus detection signal and the second focus detection signal increases.

Next, phase difference type focus detection in this embodiment will be described.
In the phase difference type focus detection, the first focus detection signal and the second focus detection signal are relatively shifted to calculate the correlation amount indicating the degree of coincidence of the signals, and the shift that increases the correlation (signal coincidence). The image shift amount is detected from the amount. As the defocus amount of the imaging signal increases, the relationship that the amount of image shift between the first focus detection signal and the second focus detection signal increases is used. The detection amount of the focal position is obtained by converting the image shift amount into the defocus amount.

  FIG. 6 is a flowchart schematically showing the flow of focus detection processing in the present embodiment. This process is performed by a focus detection unit realized by controlling the image sensor 107 and the image processing circuit 125 according to a program executed by the CPU 121.

  In S110, processing for setting a focus detection region for performing focus adjustment within the effective pixel region of the image sensor 107 is performed. The focus detection unit generates a first focus detection signal from the light reception signal (A image signal) of the first focus detection pixel in the focus detection region, and generates a second signal from the light reception signal (B image signal) of the second focus detection pixel. A focus detection signal is generated. In S120, an addition process for three pixels in the column direction is performed on the first focus detection signal and the second focus detection signal in order to suppress the amount of signal data. Further, Bayer (RGB) addition processing is performed in order to convert the RGB signal into a luminance signal (Y signal). These two addition processes are collectively referred to as a pixel addition process. In S130, shading correction processing (optical correction processing) is performed on each of the first focus detection signal and the second focus detection signal.

  With reference to FIG. 7, the shading by the pupil shift | offset | difference of a 1st focus detection signal and a 2nd focus detection signal is demonstrated. FIG. 7 shows the relationship between the first pupil partial region 501 of the first focus detection pixel 201 and the second pupil partial region 502 of the second focus detection pixel 202 and the exit pupil 400 of the imaging optical system at the peripheral image height of the image sensor. Show the relationship.

  FIG. 7A shows a case where the exit pupil distance Dl of the imaging optical system and the set pupil distance Ds of the image sensor are the same. In this case, the first pupil partial region 501 and the second pupil partial region 502 divide the exit pupil 400 of the imaging optical system substantially equally. On the other hand, FIG. 7B shows a case where the exit pupil distance Dl of the imaging optical system is shorter than the set pupil distance Ds of the image sensor. In this case, at the peripheral image height of the imaging element, a pupil shift occurs between the exit pupil of the imaging optical system and the entrance pupil of the imaging element, and the exit pupil 400 of the imaging optical system is non-uniformly divided into pupils. FIG. 7C shows a case where the exit pupil distance Dl of the imaging optical system is longer than the set pupil distance Ds of the image sensor. In this case, at the peripheral image height of the imaging element, a pupil shift occurs between the exit pupil of the imaging optical system and the entrance pupil of the imaging element, and the exit pupil 400 of the imaging optical system is non-uniformly divided into pupils. As pupil division becomes uneven at the peripheral image height, the intensity of the first focus detection signal and the second focus detection signal becomes uneven. As a result, shading occurs in which the intensity of one of the first focus detection signal and the second focus detection signal is relatively large and the other is small.

  In S130 of FIG. 6, the shading correction coefficient is determined according to the image height of the focus detection area, the F value of the imaging lens (imaging optical system), and the exit pupil distance. That is, a first shading correction coefficient for the first focus detection signal and a second shading correction coefficient for the second focus detection signal are generated. The first shading correction coefficient is multiplied by the first focus detection signal, the second shading correction coefficient is multiplied by the second focus detection signal, and shading correction processing is executed.

  In phase difference type focus detection, detection amount acquisition processing is performed based on the correlation (the degree of coincidence of signals) between the first focus detection signal and the second focus detection signal. When shading due to pupil shift occurs, the correlation between the first focus detection signal and the second focus detection signal may decrease. In the phase difference type focus detection, the correlation between the first focus detection signal and the second focus detection signal can be improved by the shading correction process, and the focus detection performance can be improved.

  In S140 of FIG. 6, filter processing is performed on the first focus detection signal and the second focus detection signal. The pass band of the filtering process is illustrated in the solid line graph ga of FIG. The horizontal axis represents the spatial frequency (line space / mm), and the vertical axis represents the gain with the maximum value being 1. In the present embodiment, since focus detection is performed with a large defocus amount by phase difference focus detection, the filter is configured so that the pass band in the filter processing includes a low frequency band. When performing focus adjustment from a large defocus amount to a small defocus amount as necessary, the passband in the filter processing at the time of focus detection according to the defocus state is shown in a dashed-dotted line graph gb in FIG. As shown, it may be adjusted to a higher frequency band.

Next, in S150 of FIG. 6, a shift process for relatively shifting the first focus detection signal and the second focus detection signal after the filter process in the pupil division direction is performed. By the shift process, a correlation amount representing the degree of coincidence between the first focus detection signal and the second focus detection signal is calculated. The kth first focus detection signal after the filtering process is A (k), and the kth second focus detection signal after the filtering process is B (k). The range of the number k corresponding to the focus detection area is set to W. The amount of correlation COR is calculated by equation (1), where s ₁ is the amount of shift by the shift process, and Γ1 is the range (shift range).

As a result of the shift process using the shift amount s ₁ , the k-th first focus detection signal A (k) and the “k-s ₁ ” -th second focus detection signal B (k-s ₁ ) are subtracted in correspondence with each other. As a result, a shift subtraction signal is generated. By calculating the absolute value of the generated shift subtraction signal and calculating the sum at number k within the range W corresponding to the focus detection area, the correlation amount COR (s ₁ ) can be calculated. If necessary, the correlation amount calculated for each row may be added over a plurality of rows for each shift amount.

  In S160, a process of calculating a real value shift amount at which the correlation amount is the minimum value is executed from the correlation amount obtained in S150 by subpixel calculation, and the image shift amount p1 is obtained. The detection amount is calculated by multiplying the image shift amount p1 by the image height of the focus detection area, the F value of the imaging lens (imaging optical system), and the first conversion coefficient K1 corresponding to the exit pupil distance. .

Next, an AF control algorithm executed at the time of moving image shooting using the above focus detection method will be described.
At the time of moving image shooting, high-quality AF control with respect to the driving of the focus lens is required instead of the AF control for quickly focusing on the subject as in the case of still image shooting. That is, in the case of moving image shooting, the appearance itself of the image by the focusing operation in the AF control is recorded. For this reason, rather than focusing quickly, the quality of the focusing operation is important. As one of the controls for improving the quality, the focus lens is not always driven, but the focus lens is stopped when the subject is in focus, and the focus lens is driven according to a predetermined condition judgment result thereafter. There is control to resume. The predetermined condition determination result is, for example, that the subject has changed or that the subject image has become blurred. In this control, for example, when the drive continues without stopping the focus lens, when carelessly performing focus detection on a subject with low focus detection accuracy such as a low-contrast part, or when other subjects are instantaneously Problems can arise when crossing. In such a case, if the focus lens is inadvertently driven, the image may be lost and the quality of the moving image may be lowered. Therefore, when it is determined that the subject is in focus at the time of moving image shooting, the imaging apparatus according to the present embodiment temporarily stops driving the focus lens and determines again whether or not the subject has changed. When it is determined that the subject has changed, control for restarting the driving of the focus lens is performed, so that the frequency of useless lens driving can be suppressed and the quality can be improved.

  When the driving of the lens is restarted from the stopped state of the focus lens, it is necessary to determine whether or not the focus surface of the subject has changed in order to prevent inadvertent lens driving. When it can be determined with certainty that the focus plane of the subject has changed, control for restarting the drive of the focus lens is executed. For example, when the defocus amount is within a predetermined threshold value, the restart is not performed, and the restart is performed when a defocus amount equal to or greater than the predetermined threshold value is detected for a certain period of time (reference time for determination). Done. According to such control, a high-quality image that does not move unnecessarily when the subject is not moving can be obtained. However, when the subject starts to move, when the predetermined time for determination (or detection time) is provided, the focus lens is driven after the subject has moved a distance corresponding to the passage of the time. That is, when the determination time length is a fixed value, a delay of a certain time occurs at the start of tracking of the subject. For this reason, there is a concern that some blur will occur in the image. The amount of blurring of the image is negligible when the movement speed of the subject is slow, but increases as the movement speed of the subject increases. As the amount of movement of the subject within the predetermined time increases, the amount of blurring of the image increases. Therefore, depending on the movement speed of the subject, the quality of the image may be reduced.

FIG. 9 is a graph showing a change in the defocus amount when the moving subject is imaged by the imaging device. The horizontal axis in FIG. 9 indicates time (seconds), and the vertical axis indicates the defocus amount ([Fδ]). This defocus amount is a value obtained by dividing the defocus amount calculated in units of mm by the F value that is the aperture value and the allowable confusion circle diameter δ, and thereby a value proportional to the amount of gain. It can be handled. For example, when the F value is 2.0 and δ is 0.02 mm, when the defocus amount is 1 mm, the blur amount can be quantitatively expressed as 25 [Fδ].
FIG. 9A shows a case where the subject is moving at a speed of 1 m / s. FIG. 9B shows a case where the subject is moving at a speed of 2 m / s. At the position of the inflection point in each graph, the drive of the focus lens is restarted and the tracking of the subject starts, so the absolute value of the defocus amount decreases again. In FIG. 9A and FIG. 9B, the determination time is set to the same value. Therefore, in the case of FIG. 9B, the absolute value of the maximum defocus amount at the time of starting movement at the restart is larger than that in the case of FIG. 9A. That is, it can be seen that the quality of the video is lowered.
Therefore, in the following embodiment, lens drive control corresponding to the movement speed of the subject is realized by controlling the time or number of determinations as a variable value according to the movement speed of the subject.

[Example 1]
An imaging apparatus as Example 1 will be described with reference to FIGS. 10 and 11 according to the first embodiment of the present invention.

  FIG. 10 is a flowchart for explaining a main part of the AF control. The following processing is performed by a focus adjustment control unit realized by controlling the image sensor 107, the image processing circuit 125, and the focus driving circuit 126 according to a program executed by the CPU 121.

  The process starts in S1101 of FIG. 10 and proceeds to S1102. When calculating the image plane moving speed at a certain time t in S1102, the CPU 121 traces the time t and the previous n times (t−1, t−2,..., T−n) from the time t. ) To obtain the defocus amount. Data on the past defocus amount history is stored in the memory. In the next S1103, linear approximation (linear approximation processing) is performed based on the current and past n defocus amounts acquired in S1102, and the inclination is calculated to obtain the image plane moving speed V (Fδ / s). Is acquired. In this case, the defocus amount acquisition count n is set to a fixed value or a variable value within a range of 2 or more. In the case of a variable value, the setting is changed as needed by increasing or decreasing the number of acquisitions n according to the required accuracy. In the case of linear approximation, the calculation accuracy can be improved by using the least square method.

  In step S1104, it is determined whether the value of the image plane moving speed V is reliable. In this determination, the value of the image plane moving speed V obtained in S1103 is compared with a predetermined value Vmin (lower limit value) and a predetermined value Vmax (upper limit value). Is determined. FIG. 11 is a diagram showing the range of reliability determination of the image plane moving speed. The horizontal axis in FIG. 11 indicates time, and the vertical axis indicates the defocus amount. The slope of the straight line rising to the right represents the image plane moving speed V. When the image plane moving speed V is less than the predetermined value Vmin, the possibility that the subject is moving is low. For example, if the subject is slightly shaken (for example, if the subject moves back and forth due to breathing, or if it is shaken by the wind), restarting the focus lens drive may cause the quality of the image to deteriorate. There is. Even when the image plane moving speed V exceeds the predetermined value Vmax, the possibility that the subject is moving may be low. As such a case, there are a case where the subject is out of the focus detection frame, or a case where it is erroneously detected that the subject has moved suddenly because another object has suddenly crossed in front of the subject. When the driving of the focus lens is restarted immediately in response to such a situation, there is a possibility that the quality of the image is lowered. In the present embodiment, a determination process is performed regarding a condition that the image plane moving speed V is equal to or higher than the first threshold (Vmin or higher) and equal to or lower than the second threshold (Vmax or lower). As a result of the determination, if the condition is satisfied, the process proceeds to S1105 in FIG. 10, and if the condition is not satisfied, the process returns to S1102.

  In step S1105, the CPU 121 executes determination processing for panning detection. When the photographer performs a panning operation of the imaging apparatus, the value of the image plane moving speed V may change abruptly even if the subject does not move. For this reason, if the V value at that time is used for the determination for restarting the focus lens drive, there is a concern that erroneous lens drive may occur. Therefore, in S1105, the CPU 121 acquires a shake detection signal from the shake detection unit 130 (see FIG. 1), and determines whether a panning operation has been performed. If it is determined that the panning operation has not been performed, the process proceeds to S1106. If it is determined that the panning operation has been performed, restart of the focus lens drive using the image plane moving speed V is prohibited, and the process returns to S1102 to acquire the defocus amount again. Although the panning operation is exemplified as the photographing direction changing operation, the determination of the tilting operation is similarly performed. When it is determined that the tilting operation has been performed, restart of the focus lens drive using the image plane moving speed V is prohibited.

  In step S <b> 1106, the CPU 121 determines the determination time using the obtained image plane moving speed V (Fδ / s). Specifically, in the case of the present embodiment, the defocus amount is acquired at discrete timing for each frame rate of the imaging apparatus, that is, for each signal readout cycle. Therefore, the determination time can be defined by the number of detections of the defocus amount. In this case, the determination time is proportional to the number of times the defocus amount is detected. Therefore, the CPU 121 determines the detection count k according to the image plane moving speed V. With reference to Table 1 below, the number of detections k corresponding to the image plane moving speed V is determined.

表１にて、「ｋ４＞ｋ３＞ｋ２＞ｋ１」の関係であり、像面移動速度Ｖが大きいほど、検出回数ｋは小さく設定される。像面移動速度Ｖが小さい場合には、検出回数ｋの値が大きいので、ゆっくりした被写体の動きに対し、滑らかで信頼性の高いレンズ駆動を実現することができる。また、像面移動速度Ｖが大きい場合には、検出回数ｋの値が小さいので、速い被写体の動きに少しでも早く追いつくために素早くレンズ駆動を再起動させることができる。

In Table 1, the relationship is “k4>k3>k2> k1”, and the larger the image plane moving speed V, the smaller the detection number k is set. When the image plane moving speed V is low, the value of the number of times of detection k is large, so that smooth and highly reliable lens driving can be realized with respect to slow movement of the subject. Further, when the image plane moving speed V is high, the value of the number of detections k is small, so that the lens drive can be restarted quickly in order to catch up with a fast subject movement as soon as possible.

  In step S1107, the CPU 121 executes a defocus amount detection process, and then advances the process to step S1108. In step S1108, the CPU 121 counts the number of times that the defocus amount exceeds a predetermined threshold, and determines whether the number of times exceeds the number of detections k determined in step S1106. If the measured number exceeds the detection number k, the process proceeds to S1109. If the measured number is equal to or less than the detection number k, the process returns to S1107 to continue the defocus amount detection process. In step S1109, the CPU 121 restarts driving of the focus lens, and then proceeds to a return process in step S1110.

  As described above, the determination time or number of times used to determine whether to restart the focus lens when it is determined that the subject is in focus and the focus lens driving is stopped depends on the temporal change in the defocus amount. Changed. The temporal change of the defocus amount is a change amount of the defocus amount per unit time, and corresponds to the image plane moving speed V. The determination time or number of times is set to a smaller value as the defocus amount change amount is larger.

  In the present embodiment, by using the above-described algorithm, AF control can be stably performed according to the image plane moving speed V, and the focus lens driving can be restarted that can quickly follow the movement of the subject. According to the present embodiment, by performing focus adjustment control corresponding to the moving speed of a moving object (subject), a moving image with less blur can be obtained, so that deterioration in video quality can be suppressed.

[Example 2]
Next, an imaging apparatus as Example 2 will be described with reference to FIGS. 12 and 13 according to the second embodiment of the present invention. In the first embodiment, the example in which the defocus amount detection count k is variably controlled according to the image plane moving speed V has been described. However, the stable restart determination is similarly performed using an index other than the image plane moving speed V. Can be done. In the present embodiment, the integrated value of the defocus amount acquired at every predetermined time interval is compared with a threshold value, and when the integrated value of the defocus amount exceeds the threshold value, the driving of the focus lens is restarted. In addition, about the same component as the case of 1st Embodiment in this embodiment, those detailed description is abbreviate | omitted by using the code | symbol already used, and it demonstrates centering on difference with 1st Embodiment. Hereinafter, the algorithm of this embodiment will be described with reference to FIG.

  Processing starts in S1201 of FIG. 12, and in the next S1202, the CPU 121 controls the focus detection operation and acquires the defocus amount (Def). In step S1203, the CPU 121 compares the defocus amount acquired in step S1202 with a predetermined threshold value, and determines whether the defocus amount is equal to or greater than the predetermined threshold value. This is a process for preventing detection values affected by noise or fluctuations in the subject image from being used for determination. If it is determined in S1203 that the defocus amount is greater than or equal to the predetermined threshold, the process advances to S1204. If it is determined that the defocus amount is less than the predetermined threshold, the process returns to S1202.

  In step S1204, the CPU 121 performs defocus amount addition (integration) processing. In this embodiment, the sum of the defocus amounts is denoted as “sum”, and its initial value is set to zero. In S1204, a process of adding the defocus amount acquired in S1202 to the sum sum added up to the present time is executed, and the process proceeds to S1205. In step S1205, the CPU 121 determines whether the value of the sum of defocus amounts calculated in step S1204 exceeds a predetermined value (threshold value). If the value of the sum sum does not exceed the predetermined value, the process returns to S1202 again to continue acquiring the defocus amount. If the sum sum exceeds a predetermined value, the process advances to step S1206. In step S1206, the CPU 121 restarts the driving of the focus lens, and then proceeds to a return process in step S1207.

The process will be described with reference to FIG. FIG. 13 is a graph illustrating the temporal change in the detected defocus amount when the moving speed of the subject is 1 m / s and 2 m / s. The horizontal axis indicates the elapsed time (seconds), and the vertical axis indicates the total defocus amount ([Fδ]) (see D1 to D3). In this example, the acquisition timing of the defocus amount is shown from T1 to T4. Here, it is assumed that the predetermined value (threshold value) used in S1205 in FIG. 12 is set to D2. As shown by the graph line g2 in FIG. 13, when the subject is moving at a speed of 2 m / s, it takes time T2 until the sum of the defocus amounts sum exceeds D2. On the other hand, as shown by the graph line g1 in FIG. 13, when the subject is moving at a speed of 1 m / s, the time T4 (>) until the sum sum of defocus amounts exceeds D2. T2) is required. Therefore, for the subject moving at a speed of 2 m / s, the driving of the focus lens is restarted after the elapse of time T2, and for the subject moving at a speed of 1 m / s, the focus lens is moved after the elapse of time T4. The drive restarts. Thereby, it is possible to realize the focus lens driving according to the movement of the subject.
By performing the restart determination process and the focus lens drive according to the present embodiment, it is possible to obtain a moving image with stable quality.

[Other examples]
The said Example is an example on implementation of this invention, Comprising: This invention is not limited to the said Example. For example, in the above-described embodiment, in order to calculate the image plane moving speed, a linear approximation is performed by storing a plurality of past defocus amounts. For example, when it is detected that the subject is accelerating, the image plane movement speed prediction process may be performed using a polynomial approximation line instead of a linear approximation. In the above-described embodiment, the description has been made mainly on the algorithm within one focus detection frame arbitrarily selected by the photographer. The present invention can also be applied to an automatic selection mode using a plurality of focus detection frames, and can be used in combination with a subject tracking function.

105 Third lens group 107 Image sensor
121 CPU
124 Image sensor drive circuit 125 Image processing circuit 126 Focus drive circuit 130 Shake detection unit 201, 202 Focus detection pixel

Claims (11)

An imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the imaging optical system;
Focus detection means for performing focus detection using output signals of the plurality of focus detection pixels;
Control means for performing focus adjustment control by controlling the driving of the lens constituting the imaging optical system using the detection amount detected by the focus detection means,
The control means determines the time or number of times used for determination when determining whether or not to restart from the time when driving of the lens is stopped when it is determined that the subject is in focus. The smaller the change in the detection amount detected by the step, the smaller the setting, and when the time or number of times the detection amount exceeds the threshold exceeds the determination time or number of times, the lens drive is restarted. An imaging apparatus characterized by performing control to be performed.   The control unit calculates the image plane moving speed of the subject from the temporal change in the detection amount detected by the focus detecting unit, and sets the determination time or number to be smaller as the image plane moving speed increases. The imaging apparatus according to claim 1.   The control means compares the image plane moving speed with a lower limit value and an upper limit value, and when the image plane moving speed is equal to or higher than the lower limit value and equal to or lower than the upper limit value, the time for determination is determined. The imaging device according to claim 2, wherein the number of times is changed.   When the control means acquires a shake detection signal of the imaging apparatus and detects an operation for changing the shooting direction, the operation for changing the shooting direction is not detected without changing the time or number of times for the determination. The imaging apparatus according to claim 2, wherein the determination time or the number of times is changed. An imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the imaging optical system;
Focus detection means for performing focus detection using output signals of the plurality of focus detection pixels;
Control means for performing focus adjustment control by controlling the driving of the lens constituting the imaging optical system using the detection amount detected by the focus detection means,
The control means integrates the detection amount detected by the focus detection means from the time when driving of the lens is stopped when it is determined that the subject is in focus, and when the integrated value exceeds a threshold, the lens An image pickup apparatus that performs control to restart the driving of the image pickup apparatus.   The imaging apparatus according to claim 5, wherein the control unit compares the detection amount detected by the focus detection unit with a threshold value, and performs integration when the detection amount is equal to or greater than the threshold value.   7. The detection amount according to claim 1, wherein the detection amount is a defocus amount normalized using an aperture value and an allowable confusion circle diameter of the imaging optical system at the time of photographing. Imaging device. The pixel portion of the image sensor is
A microlens that collects incident light;
A first focus detection pixel that receives a light beam passing through a first pupil partial region of the imaging optical system;
A second focus detection pixel that receives a light flux that passes through the second pupil partial region of the imaging optical system, different from the first pupil partial region;
The imaging device according to claim 1, further comprising: an imaging pixel that receives a light beam passing through a pupil region including the first pupil partial region and the second pupil partial region. .   The image pickup apparatus according to claim 1, further comprising an image processing unit that acquires an output signal of the image pickup element and processes moving image data. An imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the imaging optical system;
Focus detection means for performing focus detection using output signals of the plurality of focus detection pixels;
A control method executed by an imaging apparatus, comprising: a control unit that performs focus adjustment control by controlling driving of a lens constituting the imaging optical system using a detection amount detected by the focus detection unit. Because
The control means is
Detection by which the focus detection means detects the time or number of times used for determining whether to restart after the lens driving is stopped when it is determined that the subject is in focus A step of setting a smaller value as the temporal change of the amount is larger;
A control method for an imaging apparatus, comprising: a step of performing control to restart driving of the lens when the time or number of times that the detection amount exceeds a threshold exceeds the time or number of times for determination . An imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the imaging optical system;
Focus detection means for performing focus detection using output signals of the plurality of focus detection pixels;
A control method executed by an imaging apparatus, comprising: a control unit that performs focus adjustment control by controlling driving of a lens constituting the imaging optical system using a detection amount detected by the focus detection unit. Because
From the time when the driving of the lens is stopped when the control means determines that the subject is in focus,
Integrating the detection amount detected by the focus detection means;
A control method for an imaging apparatus, comprising: a step of performing control to restart driving of the lens when an integrated value of the detection amount exceeds a threshold value.

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