JP2015210286A - Imaging apparatus and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a focusing time by improving the probability of moving a focus lens to the direction of the presence of a subject, when focus adjustment is performed by a contrast detection system.SOLUTION: An imaging apparatus includes: an imaging element (107); driving means (114 and 125) for driving the focus lens included in an imaging optical system; a contrast signal processing circuit (124) for performing focus detection on the basis of the contrast of an image signal outputted from the imaging element, while changing the position of the focus lens; a direction determination part (142) for determining the movement direction of the focus lens; and a storage part (141) for storing information having the probability of the presence of the subject for each distance from the imaging apparatus and the relation between the distance and the focus lens position. The direction determination part determines the movement direction of the focus lens when the focus detection is started as the direction where the probability of the presence of the subject is high on the basis of the position of the focus lens and the information stored in the storage part.

Description

  The present invention relates to an imaging apparatus having an autofocus function and a control method thereof.

  Conventionally, there is a contrast detection method as one of the general methods used in an autofocus (hereinafter referred to as AF) method of an imaging apparatus. In the contrast detection method, focusing on the high-frequency component signal among the output signals from the image sensor, the position of the focus lens where the contrast evaluation value with the contrast of the subject as the index is the largest is set as the in-focus position. It is a method. However, as it is said to be a hill-climbing method, it is necessary to acquire a contrast evaluation value while moving the focus lens and search for a position where the contrast evaluation value is maximized. ing.

  One of the reasons why it is considered unsuitable is that the direction in which the contrast evaluation value is expected to be maximum, that is, the direction to be searched for, is not known at the time when the focus adjustment is started. On the other hand, Patent Document 1 describes a technique for determining a direction by a contrast detection method in recent years.

JP 2006-215546 A

  In the technique described in Patent Document 1, it is determined whether to move the moving direction to infinity or the closest direction based on the focus lens position before the AF start, and at a speed determined in the determined direction. The contrast evaluation value is acquired while moving the focus lens. Then, when the peak of the contrast evaluation value is detected, the movement of the focus lens is stopped and the focus position is determined by moving the focus lens in the reverse direction from the stopped position. Specifically, if the focus lens position is on the infinity side, the direction is infinity, and if the focus lens is on the close side, the close direction is set.After moving to the infinity end or the close end, the focus lens is moved in the direction opposite to the end. While moving, the contrast evaluation value is acquired and the in-focus position is searched.

  However, in Patent Document 1, since the movement direction is determined according to the focus lens position before the AF start without considering the subject position, if the focus lens is moved in a direction different from the subject position, the focusing time Will become longer.

  The present invention has been made in view of the above problems, and improves the probability of moving the focus lens in the direction in which the subject exists and shortens the focusing time when performing focus adjustment using the contrast detection method. Objective.

  In order to achieve the above object, an imaging apparatus of the present invention includes an imaging unit that photoelectrically converts a subject image formed by an imaging optical system and outputs an image signal; and a focus lens included in the imaging optical system. A driving means for driving; a focus detecting means for performing focus detection based on a contrast of an image signal output from the imaging means while changing a position of the focus lens; and a determining means for determining a moving direction of the focus lens And storage means for storing information having a probability that a subject exists for each distance from the imaging device and a relationship between the distance and the focus lens position, and the determination means detects the focus by the focus detection means. The moving direction of the focus lens when starting the operation is based on the position of the focus lens and the information stored in the storage means. The probability that Utsushitai exists is determined to a higher direction.

  According to the present invention, when focus adjustment is performed using a contrast detection method, it is possible to improve the probability of moving the focus lens in the direction in which the subject is present and to shorten the focusing time.

1 is a block diagram showing a schematic configuration of an imaging apparatus according to a first embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of an image sensor according to a first embodiment. The figure which shows an example of a to-be-photographed object existence probability and a focus lens movement amount. The figure which shows an example of the object presence probability for every position of a focus lens. 6 is a flowchart illustrating a procedure of focus adjustment processing in the first embodiment. 5 is a flowchart illustrating focus movement direction determination processing according to the first embodiment. The block diagram which shows schematic structure of the imaging device in 2nd Embodiment. The top view and sectional drawing of the normal pixel of the image sensor in 2nd Embodiment. The top view and sectional drawing of a focus detection pixel of an image sensor in a 2nd embodiment. Explanatory drawing of the vignetting of the focus detection pixel of the image pick-up element in 2nd Embodiment, and the gravity center space | interval of a focus detection light beam. 9 is a flowchart illustrating a procedure of focus adjustment processing in the second embodiment. 10 is a flowchart illustrating focus movement direction determination processing according to the second embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a schematic configuration of an electronic camera capable of recording a moving image and a still image as an example of an imaging apparatus according to the first embodiment of the present invention. In FIG. 1, the first lens group 101 is disposed at the tip of the imaging optical system and is held so as to be able to advance and retract in the optical axis direction. The aperture 102 (hereinafter referred to as “aperture”) adjusts the light amount at the time of shooting by adjusting the aperture diameter, and also has a function as an exposure time adjustment shutter at the time of still image shooting. The second lens group 103 moves forward and backward in the optical axis direction integrally with the stop 102, and can achieve a zooming function (zoom function) in conjunction with the forward and backward movement of the first lens group 101.

  The third lens group 105 (focus lens) 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 sensor 107 is composed of a CMOS sensor and its peripheral circuits, and is arranged on the image plane of the image pickup optical system. The image sensor 107 is a two-dimensional single-plate color sensor in which M pixels in the horizontal direction and N pixels in the vertical direction are squarely arranged and a Bayer array primary color mosaic filter is formed on-chip. The above-described first lens group 101, stop 102, second lens group 103, third lens group 105, and optical low-pass filter 106 constitute an imaging optical system.

  The zoom actuator 111 rotates a cam cylinder (not shown) manually or by an actuator to drive the first lens group 101 to the third lens group 103 back and forth in the optical axis direction, thereby performing a zooming operation. The aperture actuator 112 controls the aperture diameter of the aperture 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 driving the third lens group 105 back and forth in the optical axis direction.

  The CPU 121 performs various controls of the camera body, and includes a calculation unit, ROM, RAM, A / D converter, D / A converter, communication interface circuit, and the like. The CPU 121 drives various circuits of the camera based on a predetermined program stored in the ROM, and executes a series of operations such as focus adjustment (AF), shooting, image processing, and recording.

  The CPU 121 includes a storage unit 141 and a direction determination unit 142. The storage unit 141 stores the existence probability of the subject position created based on the past shooting data, and transmits it to the direction determination unit 142. The direction determination unit 142 sets the focus movement direction based on the existence probability of the subject acquired from the storage unit 141 and the focus lens position, and transmits the focus movement direction to the focus drive circuit 125.

  The image sensor driving circuit 122 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 123 performs processes such as γ conversion, color interpolation, and JPEG compression of the image acquired by the image sensor 107.

  The contrast signal processing circuit 124 generates a contrast evaluation value by extracting a high-frequency component by performing γ processing and various filter processing on the imaging signal from the imaging element 107.

  The focus drive circuit 125 controls the focus actuator 114 based on the focus detection result, and performs focus adjustment by driving the third lens group 105 back and forth in the optical axis direction. The aperture drive circuit 127 controls the aperture of the aperture 102 by drivingly controlling the aperture actuator 112. The zoom drive circuit 128 drives the zoom actuator 111 according to the zoom operation of the photographer.

  A display unit 131 such as an LCD displays information on the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, an index of a focus detection area at the time of focus detection, a focus state display image, and the like. 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. The detachable flash memory 133 records captured images.

  Next, the configuration of the image sensor 107 in the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a schematic configuration of the image sensor 107. Note that FIG. 2 shows a minimum configuration that can explain the reading operation, and a pixel reset signal and the like are omitted.

As shown in FIG. 2, m × n pixels 201 are two-dimensionally arranged, and each pixel 201 includes a photodiode, a pixel amplifier, a reset switch, and the like. The vertical scanning circuit 208 can sequentially turn on the selection switches 202 of the pixels 201 in units of rows by sequentially outputting signals V ₀ 0 to V _n−1 . Then, the output of the pixel 201 appears on the vertical output line 210 via the switch 202 that is turned on.

The signal PVST is a data input of the vertical scanning circuit 208, PV1 and PV2 are shift clock inputs, and data is set when PV1 = H level and data is latched when PV2 = H level. PV1, by inputting the shift clock PV2, by sequentially shifting the PVST, can be successively in H a V _n-1 from the signal V _0. The signal SKIP is used at the time of thinning-out reading, and the signal Vn can be skipped at a predetermined interval by setting the signal SKIP to H.

The line memory 203 temporarily stores the output of the pixels 201 for one row selected by the vertical scanning circuit 208, and normally a capacitor is used. The switch 204 is connected to the horizontal output line 211 and resets the horizontal output line 211 to a predetermined potential VHRST, and is controlled by a signal HRST. Switch 205 is for sequentially outputting the output of the pixel 201 which is stored in the line memory 203 to the horizontal output line 211, is on / off controlled by H _m-1 from the signal H ₀ by the horizontal scanning circuit 206 .

The horizontal scanning circuit 206 sequentially outputs the outputs of the pixels 201 stored in the line memory 203 to the horizontal output line 211 by sequentially setting the signals H ₀ to H _m−1 to H. The signal PHST is a data input of the horizontal scanning circuit 206, PH1 and PH2 are shift clock inputs, and data is set when PH1 = H, and data is latched at PH2. PH1, by inputting the shift clock PH2, can be by sequentially shifting the PHST, sequentially in H a H _m-1 from the signal H _0. The signal SKIP is used at the time of thinning-out reading, and the signal Hm can be skipped at a predetermined interval by setting the signal SKIP to the H level.

  Next, the contrast detection method will be described. The contrast signal processing circuit 124 extracts a high frequency component by applying a filter to the image signal in the focus detection region, and generates a contrast evaluation value. The contrast signal processing circuit 124 according to the first embodiment includes a filter having a plurality of frequency characteristics or a filter capable of changing the frequency characteristics. In the contrast detection method, filter processing is performed on the imaging signal to generate contrast information, so that it is not necessary to store a large amount of the imaging signal and the calculation load is light. Therefore, it is possible to simultaneously perform signal processing on a plurality of focus detection areas without depending on the focus detection range.

  The contrast evaluation value generated by the contrast signal processing circuit 124 is a value representing the sharpness (contrast magnitude) of the image generated based on the output signal from the image sensor 107. The sharpness is high in an in-focus image and low in a blurred image, and can be used as a value representing the focus state of the imaging optical system. However, since the defocus amount cannot be obtained unlike the phase difference detection method, it is necessary to search for a focus lens position where the contrast evaluation value becomes a peak value.

  In the focusing operation using the contrast detection method, an image signal is acquired (scanned) from the image sensor 107 while driving the focus lens in a certain direction, a contrast evaluation value is obtained from the acquired image signal, and the contrast evaluation value increases. Explore. Then, the peak of the contrast evaluation value is acquired by moving the focus lens in that direction, and then the contrast evaluation value is acquired until it starts to decrease. Focus determination uses the top three or four points with the largest contrast evaluation values, calculates the in-focus position by performing interpolation calculation from the corresponding focus lens positions, and focuses on the calculated in-focus position. Move the lens.

  In the first embodiment, when the focus detection is started, the search direction when searching for the in-focus position is determined by the existence probability of the subject and the movement amount of the focus lens, so that the focus lens is moved in the direction in which the subject exists. Improve the probability of moving.

  FIG. 3 is a diagram illustrating the relationship between the subject position, the subject existence probability, and the movement amount of the focus lens with an arbitrary lens. The horizontal axis indicates the subject position at each distance, and the vertical axis indicates the subject existence probability and the focus lens movement amount from infinity. The solid line indicates the subject existence probability, and the dotted line indicates the focus lens movement amount. The relationship between the position of the subject and the subject existence probability is based on a database called a photo space. According to the photo space, the distribution of the position of the subject varies depending on the focal length, brightness, and the like. In the first embodiment, only one example is handled. In this arbitrary lens, based on the above-described relationship, there is a high probability that the subject exists in the range of 1 m to 6 m. The relationship between the subject position and the amount of movement of the focus lens is obtained from the optical design data of the lens. The amount of movement of the focus lens tends to increase rapidly as it comes closer.

  FIG. 4A shows an AF start position obtained by converting the current position of the focus lens before AF into the distance focus distance to the focal point based on the relationship between the subject position and the movement amount of the focus lens in FIG. It is shown on the horizontal axis. In addition, the bar graph indicates the probability that the subject exists in the infinity direction and the close direction with respect to the AF start position. The white bar graph indicates the probability that the subject exists in the infinity direction with respect to the AF start position, and the black bar graph indicates the probability that the subject exists in the closest direction to the AF start position. In the example shown in FIG. 4A, when the AF start position is about 4m to 5m, and the AF start position is on the infinity side, there is a high probability that the subject exists in the close direction. Has a high probability of an object in the direction of infinity. When the AF start position is larger than 4 m to 5 m, the focus lens is moved in the closest direction, and when the AF start position is smaller than 4 m to 5 m, the subject is present by moving the focus lens in the infinity direction. The probability of being able to search in the direction to go is high.

  However, when the AF start position is in the vicinity of 4 m to 5 m, the existence probability of the subject in the infinity direction and the close direction is both 40% or more (predetermined probability or more), so there is a possibility that the search direction is wrong. In addition, it is estimated that the AF start position is close to the subject position. Therefore, in the first embodiment, the predetermined focus lens moving range is set in the infinity direction and the close direction from such an AF start position, and the existence probability of the subject is recalculated within the range.

  FIG. 4B shows the result of obtaining the AF start position and the subject existence probability by the above method. FIG. 4B shows the result of obtaining the existence probability of the subject within the predetermined focus lens movement range when the AF start position where the existence probability of the subject is substantially equal in the infinity direction and the close direction is 4 m to 5 m. For this reason, an area where the moving amount of the focus lens is large from the AF start position is not included as an area for calculating the existence probability of the subject. The reason for limiting to the predetermined focus lens movement range is that it is determined that there is a high possibility that the AF start position is near the in-focus when the object existence probability is not different between the infinity direction and the close direction. is there.

  Although an example is shown in FIG. 4, the distribution of the existence probability of the subject and the moving amount of the focus lens differ depending on the focal length of the lens, the optical system, and the like. Therefore, a plurality of object existence probabilities corresponding to the focal length of the lens and the luminance at the time of shooting may be held as a database. Further, in order to grasp the tendency of the subject distance taken by the photographer, data obtained by converting the AF start position and the in-focus position into a distance is saved as a history, and the data in the storage unit 141 for storing the existence probability of the subject is updated. Also good.

  As described above, the existence probability of the subject can be obtained according to the AF start position and the search direction can be determined, so that the probability of starting the search in the direction in which the subject exists can be improved.

  Next, the focus adjustment processing procedure in the first embodiment will be described with reference to the flowchart of FIG. First, in S101, it is determined whether or not the photographer has pressed the release switch included in the operation unit 132 halfway (SW1 ON). If SW1 is turned on, the process proceeds to S102, and if it is turned off, the determination of S101 is repeated. In S102, the current focus lens position information is acquired, and the process proceeds to S103. In S103, a focus movement direction determination process is performed, and the process proceeds to S104. Details of the processing in S103 will be described later.

  In S104, the focus lens starts to move in the search direction set in S103, and the process proceeds to S105. In S105, a contrast AF scanning operation is performed to acquire a position where the contrast evaluation value reaches a peak, and the process proceeds to S106. In S106, the calculation of the in-focus position is performed based on the search result in S105, and the focus lens is moved to the in-focus position in S107, and the process is terminated.

  Next, the focus movement direction determination process performed in S103 will be described with reference to the flowchart of FIG. In S201, using the information such as the photo space and the shooting history, the object existence probabilities in the infinity direction and the close direction with respect to the current focus lens position are calculated as described with reference to FIG. The process proceeds to S202. In S202, it is determined whether the subject existence probabilities in the infinity direction and the close direction are both greater than or equal to a predetermined value. If it is equal to or larger than the predetermined value, the process proceeds to S203, and if it is equal to or smaller than the predetermined value, the process proceeds to S204. In S203, the object existence probabilities in the infinity direction and the closest direction are recalculated with the focus movement amount within a predetermined range from the current focus lens position, and the process proceeds to S204. In S204, it is determined whether or not the direction in which the subject existence probability is high is the infinity direction. If the direction is the infinity direction, the focus movement direction is set to the infinity direction in S205. The direction is set to the closest direction, and the process returns to the process of FIG.

  As described above, according to the first embodiment, the focus lens search direction in the contrast AF is determined based on the existence probability of the subject and the position of the focus lens, thereby focusing in the direction in which the subject is likely to exist. The lens can be moved.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. FIG. 7 is a block diagram illustrating a schematic configuration of the imaging apparatus according to the second embodiment. The image pickup apparatus described in the first embodiment shown in FIG. 1 includes a phase difference calculation processing circuit 226, a point that the image pickup element 227 has a focus detection pixel that enables focus detection by a phase difference detection method, The determination method by the direction determination unit 242 is different. The other configurations are the same as the configuration shown in FIG. 1, and thus the description thereof will be omitted.

  In the image sensor 227 according to the second embodiment, some of the pixels arranged as shown in FIG. 2 are composed of focus detection pixels. The configuration of the focus detection pixel will be described later with reference to FIGS.

  The phase difference calculation processing circuit 226 acquires the A image signal for AF and the B image signal for AF by separately acquiring the signals obtained from the photoelectric conversion regions of the focus detection pixels of the image sensor 227, and the A image and the A image The image shift amount of the B image is obtained by correlation calculation, and the defocus amount is calculated.

  The direction determination unit 242 sets the focus movement direction based on the subject existence probability acquired from the storage unit 141, the focus lens position, and the defocus amount calculated by the phase difference calculation processing circuit 226, and transmits the focus movement direction to the focus drive circuit 125. To do.

  8 and 9 are diagrams illustrating the structure of the normal pixel and the focus detection pixel. In the second embodiment, out of 4 pixels of 2 rows × 2 columns, pixels having G (green) spectral sensitivity are arranged in the diagonal 2 pixels, and R (red) and B ( A Bayer arrangement in which one pixel each having a spectral sensitivity of (blue) is arranged is employed. In addition, focus detection pixels having a structure to be described later are distributed and arranged in a predetermined rule between the Bayer arrays.

  FIG. 8A is a plan view of normal pixels of 2 rows × 2 columns. This 2-row × 2-column structure is repeatedly arranged.

FIG.8 (b) is sectional drawing which shows the cross section AA of Fig.8 (a). ML denotes an on-chip microlens arranged in front of each pixel, CF _R is a color filter, CF _G of R (red), a G (green) color filter. PD (Photo Diode) schematically shows a photoelectric conversion element of the image sensor 227. CL (Contact Layer) is a wiring layer for forming signal lines for transmitting various signals in the image sensor 227. TL (Taking Lens) schematically shows the imaging optical system.

  The on-chip microlens ML of the normal pixel and the photoelectric conversion element PD are configured to capture the light beam that has passed through the imaging optical system TL as effectively as possible. In other words, the exit pupil EP (Exit Pupil) of the imaging optical system TL and the photoelectric conversion element PD are designed to have a conjugate relationship by the microlens ML, and the effective area of the photoelectric conversion element PD is designed to be a large area. In FIG. 8B, the incident light beam of the R pixel has been described, but the G pixel and the B (blue) pixel have the same structure. Thus, the exit pupil EP corresponding to each RGB pixel for imaging has a large diameter, and the S / N of the image signal is improved by efficiently capturing the light flux from the subject.

FIG. 9 shows a plan view and a cross-sectional view of a focus detection pixel for performing pupil division in the horizontal direction (lateral direction) of the imaging optical system TL. Here, the horizontal direction (lateral direction) refers to a direction along a straight line that is orthogonal to the optical axis and extends in the horizontal direction when the camera is held so that the optical axis of the imaging optical system TL is horizontal. FIG. 9A is a plan view of pixels of 2 rows × 2 columns including focus detection pixels. When obtaining an image signal for recording or viewing, the main component of luminance information is acquired by G pixels. This is because human image recognition characteristics are sensitive to luminance information, and if G pixels are lost, image quality degradation is easily recognized. On the other hand, the R pixel or the B pixel is a pixel that acquires color information (color difference information). However, since human visual characteristics are insensitive to color information, the pixel that acquires color information has some defects. However, image quality degradation is difficult to recognize. Therefore, in the second embodiment, among the pixels of 2 rows × 2 columns, the G pixel is left as a normal pixel, and the R pixel and the B pixel are replaced with focus detection pixels at a certain ratio. This focus detection pixel pair is denoted as S _HA and S _HB in FIG.

  FIG.9 (b) is sectional drawing which shows the cross section AA in Fig.9 (a). The microlens ML and the photoelectric conversion element PD have the same structure as that of the normal pixel shown in FIG.

In the second embodiment, since the signal of the focus detection pixel is not used for image generation, a transparent film CF _W (white) is disposed instead of the color separation color filter. Further, since pupil division is performed by the image sensor 107, the opening of the wiring layer CL is offset in the horizontal direction with respect to the center line of the microlens ML. Specifically, since the opening OP _HA of the pixel S _HA is decentered by 41 _{HA in the} right direction with respect to the center line of the microlens ML, it passes through the left exit pupil region EP _HA of the imaging optical system TL. A light beam 40 _HA is received. Similarly, since the opening OP _HB of the pixel S _HB is decentered by 41 _HB leftward with respect to the center line of the microlens ML, the light beam 40 that has passed through the right exit pupil region EP _HB of the imaging optical system TL. _HB is received.

The pixels _SHA having the above-described configuration are regularly arranged in the horizontal direction, and a subject image acquired from these pixel groups is defined as an A image. The pixels _SHB are also regularly arranged in the horizontal direction, and the subject image acquired from these pixel groups is defined as a B image. Then, by detecting the relative positions of the acquired A and B images, it is possible to detect the image shift amount of the subject image having a luminance distribution in the horizontal direction.

  Next, a method for obtaining a conversion coefficient for calculating the defocus amount from the image shift amount will be described. The conversion coefficient is calculated based on the aperture information of the imaging optical system and the sensitivity distribution of the focus detection pixels. The image sensor 227 receives a light beam limited by some constituent members such as the lens holding frame of the image pickup optical system TL and the diaphragm 102. FIG. 10 is a diagram illustrating a state in which the focus detection light beam is limited by the vignetting of the imaging optical system. FIG. 10 shows a state in which the light beam is restricted by the stop 102 of the imaging optical system at the position of the exit pupil plane 501 with respect to the pixels near the center of the image sensor.

  In FIG. 10A, the image sensor 227 at the planned image plane position is indicated by a solid line, and the image sensor 227 at the rear pin position is indicated by a broken line. The position of the optical axis 505 in the image sensor 227 at the planned imaging plane position is indicated by 506. The light condensed at the position 506 when it is limited by the diaphragm 102 (when the diaphragm 102 is narrowed) is represented by light beams 507 and 508. Further, light that is collected at the position 506 when it is not limited by the diaphragm 102 (when the diaphragm 102 is opened) is represented by light beams 509 and 510. Reference numerals 511 and 512 denote focus detection light beams corresponding to the light beams 507 and 508, respectively. Reference numerals 515 and 516 denote barycentric positions of the focus detection light beams 511 and 512, respectively. Similarly, 513 and 514 are focus detection light beams corresponding to the light beams 509 and 510, respectively. Reference numerals 517 and 518 denote the gravity center positions of the focus detection light beams 513 and 514, respectively. Reference numeral 530 denotes a lens holding frame on the side closest to the image sensor, and 531 denotes a lens holding frame on the side closest to the subject.

FIG. 10B is a diagram for explaining the change in the position of the center of gravity due to vignetting on the exit pupil plane 501 of the focus detection pixels arranged in the central portion of the image sensor 227. In FIG. 10B, the pupil region 523 indicates the pupil region when the aperture is limited and the pupil region 524 indicates the pupil region when the aperture is not limited with respect to the central pixel of the image sensor 227. Incident angle characteristics 525 and 526 indicate the incident angle characteristics of the focus detection pixels S _HA and S _HB , respectively. Light beams that have passed through the inside of the pupil regions 523 and 524 are incident on the focus detection pixels S _HA and S _HB with a sensitivity distribution indicated by incident angle characteristics 525 and 526. For this reason, it is limited when the focus detection light beam is limited (in a state where the aperture is stopped) by obtaining the distribution centroid of the focus detection light beam that has passed through the inside of the pupil regions 523 and 524, respectively. It is possible to calculate the center-of-gravity interval when there is no aperture (open aperture state). And each base line length can be calculated | required from these center-of-gravity intervals. By obtaining the sensitivity distribution information of the focus detection pixel and the aperture information of the imaging optical system from measurement and calculation and storing them in advance, a conversion coefficient for calculating the defocus amount from the image shift amount can be obtained.

In FIG. 10A, the defocus amount 519 is DEF, and the distance 520 from the image sensor 227 to the exit pupil plane 501 is L. Further, the base line lengths (center-of-gravity distances) when the focus detection light beam is restricted and not restricted are respectively G1 (distance between centroid positions 515 and 516) and G2 (distance between centroid positions 517 and 518). ). Also, conversion coefficients for converting the image shift amounts 521 and 522 into PRED1 and PRED2 and the image shift amounts 521 and 522 into the defocus amount DEF are K1 and K2, respectively. At this time, the defocus amount DEF can be obtained by the following equation (1).
DEF = K1 × PRED1 = K2 × PRED2 (1)

Also, conversion coefficients K1 and K2 for converting the image shift amounts 521 and 522 into the defocus amount DEF are obtained by the following equations (2) and (3), respectively.
K1 = L / G1 (2)
K2 = L / G2 (3)
Here, K1 <K2. For this reason, comparing the case where the aperture is opened and the case where the aperture is stopped, if an error equivalent to the image shift amount occurs when calculating the image shift amount, However, an error of K2 / K1 times occurs as the defocus amount.
FIGS. 10C and 10D are diagrams showing the sensitivity distribution of the cross section AA in FIG. FIG. 10C shows the sensitivity distribution 530 of the A image pixel, the sensitivity distribution 531 of the B image pixel, and the sensitivity distribution 532 of the normal pixel when the aperture is opened, and FIG. Is shown. 10 (c) and 10 (d), the horizontal axis represents the light incident angle, and the vertical axis represents the sensitivity distribution. Comparing the two figures, the base length is longer in the fully open state, and the incident angle width with sensitivity is wider. Since the base line length is proportional to the image shift amounts of the A and B images with respect to defocus, the sensitivity of the image shift amount with respect to defocus increases as the base line length increases. As the incident angle width with sensitivity increases, the amount of blur and image vignetting of the A and B images with respect to defocusing increase. In general, as an image signal from a focus detection pixel, an image signal having a high sensitivity of an image shift amount with respect to defocus and a small amount of blur and image vignetting is desired.

  Next, the focus adjustment processing procedure in the second embodiment will be described with reference to the flowchart of FIG. First, in S301, it is determined whether or not the photographer has pressed the release switch included in the operation unit 132 halfway (SW1 ON). If SW1 is turned on, the process proceeds to S302. If it is turned off, the determination in S301 is repeated. In S302, the phase difference calculation processing circuit 226 performs the above-described phase difference focus detection using the signal output from the focus detection pixel, and the process proceeds to S303. In S303, it is determined whether the in-focus position has been detected by the focus detection in S302. If the in-focus position can be detected, the process proceeds to S309. If the in-focus position cannot be detected, the process proceeds to S304. In S304, the current focus lens position information is acquired, and the process proceeds to S305. In S305, focus movement direction determination processing is performed, and the process proceeds to S306. Details of the processing in S305 will be described later.

  In S306, the focus lens starts to move in the search direction set in S305, and the process proceeds to S307. In step S307, a contrast AF scan operation is performed to acquire a position where the contrast evaluation value reaches a peak, and the process proceeds to step S308. In S308, the calculation of the in-focus position is performed based on the result searched in S307, and in S309, the focus lens is moved to the in-focus position obtained in S302 or S308, and the process ends.

  Next, the focus movement direction determination process performed in S305 will be described with reference to the flowchart of FIG. In S401, it is determined whether the direction can be detected from the focus detection result in S302. If it is possible, the process proceeds to S402, and if not, the process proceeds to S403.

  In S402, a predetermined direction is set based on the direction detection result, and the process proceeds to S407 and is completed. In S403, using the information such as the photo space and the shooting history, the object existence probabilities in the infinity direction and the close direction with respect to the current focus lens position are calculated only in the range outside the focus detection range, and the process proceeds to S404. . The range in which the focus position can be detected with high accuracy by the phase difference detection method is often within a predetermined range from the current focus lens position. Therefore, if the focus position cannot be detected in S302 of FIG. 11, it is highly likely that the focus position is far from the current focus lens position. Therefore, from the current focus lens position, the subject existence probability is calculated by setting a region where the movement amount of the focus lens is equal to or greater than a predetermined amount outside the focus detection possible range. In S404, it is determined whether or not the direction in which the subject existence probability is high is the infinity direction. If the direction is the infinity direction, the focus movement direction is set to the infinity direction in S405, and if the direction is the closest direction, the focus movement is performed in S406. The direction is set to the closest direction, and the process returns to the process of FIG.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  Note that the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  101: First lens group, 102: Aperture, 103: Second lens group, 105: Third lens group, 106: Optical low-pass filter, 107, 227: Image sensor, 114: Focus actuator, 124: Contrast signal processing Circuit: 127: Focus drive circuit, 141: Storage unit, 142, 242: Direction determination unit, 226: Phase difference calculation processing circuit

Claims (12)

Imaging means for photoelectrically converting a subject image formed by the imaging optical system and outputting an image signal;
Driving means for driving a focus lens included in the imaging optical system;
A focus detection unit that performs focus detection based on the contrast of the image signal output from the imaging unit while changing the position of the focus lens;
Determining means for determining a moving direction of the focus lens;
Storage means for storing information including the probability that a subject exists for each distance from the imaging device and the relationship between the distance and the focus lens position;
The determination means includes the subject in the direction of movement of the focus lens when the focus detection means starts focus detection based on the position of the focus lens and information stored in the storage means. An imaging apparatus characterized by determining in a direction with a high probability.   The determination unit compares the probability that the subject exists in the closest direction and the probability that the subject exists in the infinity direction, rather than the focusing distance at the position of the focus lens, based on the information stored in the storage unit. The imaging apparatus according to claim 1, wherein a direction having a high probability is determined as the moving direction when the focus detection unit starts focus detection.   The determining means determines the focus lens when the probability that the subject is in the closest direction and the probability that the subject is in the infinity direction are both greater than or equal to a predetermined probability with respect to the in-focus distance at the position of the focus lens. The probability that the subject is in the close direction and the probability that the subject is in the infinity direction is calculated within a range of distances from the position to a predetermined amount of movement in the near direction and infinity direction, and the focus is calculated based on the calculated probability The imaging apparatus according to claim 1, wherein a moving direction of the lens is determined. The imaging means includes a plurality of focus detection pixels that respectively receive light beams that have passed through different exit pupil regions of the imaging optical system,
Detection means for detecting a focus position based on the phase difference of the image signal output from the focus detection pixel;
The imaging apparatus according to claim 1, wherein focus detection by the focus detection unit is not performed when a focus position can be detected by the detection unit.   The imaging apparatus according to claim 4, wherein the driving unit drives the focus lens based on the obtained in-focus state when the in-focus position can be detected by the detecting unit.   The determination means determines whether or not it is possible to detect the moving direction of the focus lens based on the detection result of the focus position when the detection position cannot be detected by the detection means. In addition, based on the in-focus position, the focus detection unit detects a moving direction of the focus lens when focus detection is started, and if not possible, the focus lens position and the storage unit are stored. 6. The imaging apparatus according to claim 5, wherein a moving direction of the focus lens is determined based on the information.   The storage means updates the information stored in the storage means with information obtained by converting the position of the focus lens when the focus detection means starts focus detection and the in-focus position into distance at the time of shooting. The imaging device according to any one of claims 1 to 6, wherein   The imaging apparatus according to claim 1, wherein the storage unit stores a plurality of pieces of information corresponding to at least one of a plurality of focal lengths and a plurality of luminances. . An imaging apparatus control method comprising: an imaging unit that photoelectrically converts an object image formed by an imaging optical system and outputs an image signal; and a driving unit that drives a focus lens included in the imaging optical system. ,
A focus detection step in which focus detection means performs focus detection based on the contrast of the image signal output from the imaging means while changing the position of the focus lens;
An acquisition step in which an acquisition unit acquires information having a probability that a subject exists for each distance from the imaging device and a relationship between the distance and the focus lens position, which is stored in the storage unit;
The determination means determines the moving direction of the focus lens when starting focus detection in the focus detection step based on the position of the focus lens and the information acquired in the acquisition step. And a determining step for determining in a higher direction. The imaging means includes a plurality of focus detection pixels that respectively receive light beams that have passed through different exit pupil regions of the imaging optical system,
A detecting step for detecting a focus position based on a phase difference of an image signal output from the focus detection pixel;
The control method according to claim 9, further comprising: a control unit that performs control so that the focus detection step is not performed when the in-focus position can be detected in the detection step.   The program for making a computer perform each process of the control method of Claim 9 or 10.   A computer-readable storage medium storing the program according to claim 11.

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