JP2013254166A - Imaging device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device capable of performing focus detection at further high speed with high accuracy in performing hybrid focus detection by a phase difference AF detection method and a contrast AF detection method.SOLUTION: An imaging device includes third control means for switching between phase difference AF and contrast AF by using subject information extracted from a second pixel signal output from an imaging pixel for detecting a plurality of light beams passing through a pupil area of an imaging optical system having a focus lens.

Description

  The present invention relates to an imaging apparatus such as a digital still camera and a digital video camera, and a control method thereof. In particular, the present invention relates to an image pickup apparatus using a hybrid AF detection method using contrast AF and phase difference AF, and a control method thereof.

  As a general method of the focus detection adjustment method of the imaging apparatus, there are contrast AF and phase difference AF. Contrast AF is an AF method often used in video cameras and digital still cameras, and an image sensor is used as a focus detection sensor.

  Focusing on the output signal of the image sensor, particularly the contrast information of the high-frequency component, the AF method uses the position of the focus lens where the AF evaluation value is the largest as the in-focus position. However, as it is also called a hill-climbing method, it is necessary to obtain an evaluation value while moving the position of the focus lens in the optical axis direction by a small amount and move it until it is understood that the evaluation value is the maximum as a result. Therefore, it is not suitable for high-speed focus detection operation.

  On the other hand, focus detection by the phase difference AF detection method is frequently used in single-lens reflex cameras, and is a technology that contributes to the practical application of automatic focus detection (AutoFocus: AF) single-lens reflex cameras. For example, in a digital single-lens reflex camera, the phase difference AF detection method is performed by a focus detection unit including a secondary imaging optical system. The focus detection unit includes a pupil division unit that divides the light beam that has passed through the exit pupil of the photographing optical system into two regions, and the divided light beam is second-order through an optical path division unit disposed in the mirror box. An image is formed on a set of focus detection sensors by an imaging optical system.

  Then, by detecting the shift amount of the signal output according to the received light amount of the focus detection sensor, that is, the relative positional shift amount in the pupil division direction, the shift amount in the focus direction of the photographing optical system is directly obtained. . Therefore, once the accumulation operation is performed by the focus detection sensor, the amount and direction of the focus shift can be obtained at the same time, and a high-speed focus adjustment operation is possible. At the time of photographing after focus detection, the optical path dividing means is retracted out of the photographing light beam, and the image sensor is exposed to obtain a photographed image.

  Further, Patent Document 1 discloses a technique for providing a phase difference AF function to an image pickup device and realizing high-speed AF even in electronic viewfinder observation or moving image shooting in which an image is confirmed in real time by a display means such as a rear liquid crystal. Yes. For example, a technique for providing a pupil division function by decentering a sensitivity region of a light receiving unit with respect to an optical axis of an on-chip microlens in a part of light receiving pixels of an image sensor is disclosed.

  These pixels are used as focus detection pixels, and are arranged at predetermined intervals between the photographing pixel groups, thereby performing imaging surface phase difference AF detection. Here, the location where the focus detection pixels are arranged corresponds to a missing portion of the shooting pixels, and therefore, image information is generated by interpolation from surrounding shooting pixel information. According to this example, since imaging surface phase difference AF detection can be performed on the imaging surface, high-speed and high-precision focus detection can be performed even when observing an electronic finder or shooting a moving image.

  In recent years, hybrid AF has also been proposed as a method utilizing the mutual advantages of contrast AF and phase difference AF. In Patent Document 2, the focus lens is adjusted based on the focus detection result of the phase difference AF, and the focus detection is changed to the contrast AF near the in-focus position, thereby enabling high-speed and high-precision focus detection.

  Japanese Patent Application Laid-Open No. 2004-26883 utilizes the fact that the accuracy of the focus detection result changes according to the characteristics of the signal used for the focus detection of the phase difference AF. For example, when the phase difference AF provides a highly reliable focus detection result with high signal reliability, focus adjustment is performed using the focus detection result of the phase difference AF until it is closer to the in-focus position. I do. Thereby, further speedup can be realized.

JP 2009-003122 A JP 2010-256824 A

  However, in the conventional techniques disclosed in Patent Documents 1 and 2 described above, it is sometimes difficult to achieve both high speed and high accuracy. Patent Document 1 is configured to estimate the focus detection accuracy of the phase difference AF from the signal used for the focus detection of the phase difference AF. However, since the focus detection accuracy of the phase difference AF is affected by various factors, there is a possibility that the estimation accuracy of the focus detection accuracy is lowered only by a signal used for focus detection in the phase difference AF detection method.

  In Patent Document 2, the focus adjustment is performed with the focus detection result of contrast AF for the purpose of high-precision focus adjustment near the in-focus position. However, contrast AF may not have sufficient focus detection accuracy depending on the subject and the shooting environment.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging apparatus having a focus detection device that can perform high-speed and high-precision focus detection when performing hybrid focus detection of phase difference AF and contrast AF. is there.

In order to achieve the above object, in the present invention, a plurality of shooting pixels for capturing a subject image formed by a shooting optical system having a focus lens, and focus detection that is discretely arranged in the plurality of shooting pixels. A phase difference AF based on a first pixel signal output from an imaging element having a pixel for detection and a focus detection pixel for detecting a plurality of light beams passing through different pupil regions of the imaging optical system. Control means; second control means for performing contrast AF based on a second pixel signal output from the imaging pixel that detects a plurality of light fluxes passing through a pupil region of the imaging optical system; and Subject information extraction means for extracting subject information from the image signal of
It has a third control means for switching between the phase difference AF and the contrast AF using subject information extracted from the second image signal.

  According to the present invention, it is possible to provide an imaging apparatus having a focus detection apparatus that can perform focus detection with higher speed and higher accuracy when performing a hybrid AF detection method of phase difference AF and contrast AF. .

It is a flowchart for demonstrating the focus detection process of a present Example. It is a block diagram of the digital camera of a present Example. It is a figure explaining the drive of the focus lens in the imaging surface phase difference AF of FIG. It is the figure which showed a mode that the one part optical image on an image pick-up element was formed. It is the figure which showed the output signal obtained by the optical image shown in FIG. It is a figure explaining the setting of the step width of the lens drive amount at the time of TVAF control. It is the figure which showed the flow of the focus adjustment process subroutine by TVAF control. It is a figure explaining TVAF control. It is the figure which showed the flow of the focus adjustment process subroutine by an imaging surface phase difference AF control.

Example 1
Hereinafter, in Embodiment 1 of the present invention, an example in which the imaging apparatus of the present invention is applied to a single-lens reflex digital camera capable of exchanging lenses will be described.

  FIG. 2 is a block diagram of the digital camera of this embodiment. The digital camera of this embodiment is an interchangeable lens type single-lens reflex camera, and includes a lens unit 100 and a camera body 120. The lens unit 100 is connected to the camera body 120 via a mount M indicated by a dotted line in the center of the drawing.

  The lens unit 100 includes a first lens group 101, a diaphragm shutter 102, a second lens group 103, a focus lens group (hereinafter simply referred to as “focus lens”) 104, and control means described later. As described above, the lens unit 100 includes the focus lens 104 and includes a photographing optical system that forms an image of a subject.

  The first lens group 101 is disposed at the tip of the lens unit 100 and is held so as to be able to advance and retreat in the optical axis direction OA. 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 diaphragm / shutter 102 and the second lens group 103 integrally move forward / backward in the optical axis direction OA, and realize a zoom function in conjunction with the forward / backward movement of the first lens group 101. The focus lens 104 performs focus adjustment by moving back and forth in the optical axis direction.

  The control means includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, an aperture shutter drive circuit 115, a focus drive circuit 116, a lens MPU 117, and a lens memory 118.

  The zoom actuator 111 performs a zoom operation by driving the first lens group 101 and the third lens group 103 forward and backward in the optical axis direction OA. 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 113 drives the focus lens 104 back and forth in the optical axis direction OA to perform focus adjustment. The focus actuator 113 has a function as a position detection unit that detects the current position of the focus lens 104.

  The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the photographer. The shutter drive circuit 115 controls the aperture of the diaphragm shutter 102 by drivingly controlling the diaphragm shutter actuator 112.

  The focus drive circuit 116 drives and controls the focus actuator 113 based on the focus detection result, and performs focus adjustment by driving the focus lens 104 forward and backward in the optical axis direction OA.

  The lens MPU 117 performs all calculations and control related to the photographing optical system that forms a subject image on the image sensor 122, and controls the zoom drive circuit 114, the shutter drive circuit 115, the focus drive circuit 116, and the lens memory 118. The lens MPU 117 detects the current lens position, and notifies the lens position information in response to a request from the camera MPU 125. The lens memory 118 stores optical information necessary for automatic focus adjustment.

  The camera body 120 includes an optical low-pass filter 121, an image sensor 122, and a control unit described later.

  The optical low-pass filter 121 reduces false colors and moire in the captured image.

  The image sensor 122 is composed of a C-MOS sensor and its peripheral circuit, and one photoelectric conversion element is arranged on light receiving pixels of m pixels in the horizontal direction and n pixels in the vertical direction. The image sensor 122 is configured to be able to output all pixels independently. Some pixels are focus detection pixels, and focus detection (imaging surface phase difference AF) using the phase difference AF detection method is possible on the imaging surface.

  The focus detection pixels are discretely arranged in the plurality of imaging pixels (FIG. 4).

  More specifically, the image sensor 122 has a plurality of shooting pixels that each receive a light beam that passes through the entire exit pupil of an imaging optical system that forms an image of the subject and generates an image of the subject. The image sensor 122 further includes a plurality of focus detection pixels that each receive a light beam that passes through different exit pupil regions of the imaging optical system. The plurality of focus detection pixels as a whole can receive a light beam passing through the entire exit pupil of the photographing optical system. For example, the imaging element 122 leaves a pair of G pixels arranged diagonally out of 2 × 2 pixels as imaging pixels, and replaces R and B pixels with focus detection pixels.

  The driving means includes an image sensor driving circuit 123, an image processing circuit 124, a first control means, a second control means, a camera MPU 125 having functions of a third control means, a display 126, an operation switch group 127, a memory. 128, an imaging surface phase difference focus detection unit 129, and a TVAF focus detection unit 130.

  The image sensor drive circuit 123 controls the operation of the image sensor 122, A / D converts the acquired image signal, and transmits it to the camera MPU 125. The image processing circuit 124 performs γ conversion, color interpolation, JPEG compression, and the like of the image acquired by the image sensor 122.

  A camera MPU (processor) 125 having functions of a first control unit, a second control unit, and a third control unit performs all computations and controls related to the camera body 120, and includes an image sensor driving circuit 123, an image The processing circuit 124, the display 126, the operation SW 127, the memory 128, the imaging plane phase difference focus detection unit 129, and the TVAF focus detection unit 130 are controlled.

  The first control means performs the phase difference AF based on the first pixel signal output from the focus detection pixel that detects a plurality of light beams passing through different pupil regions of the photographing optical system.

  The second control means performs contrast AF based on the second pixel signal output from the imaging pixel that detects a plurality of light beams passing through the pupil region of the imaging optical system.

  The second control unit varies the driving width of the lens driving amount of the focus lens based on at least one of the contrast information of the subject image and the luminance information of the subject image.

  The third control means switches between the phase difference AF and the contrast AF using subject information extracted from the second pixel signal.

  The subject information extracted from the second pixel signal is information correlated with the focus detection accuracy of the focus detection pixel or information correlated with the focus detection accuracy of the imaging pixel.

  The subject information extracted from the second pixel signal includes contrast information correlated with the focus detection accuracy of the focus detection pixel, and spatial frequency information and focus of the subject image correlated with the focus detection accuracy of the focus detection pixel. This is at least one of the stray light information included in the subject image correlated with the focus detection accuracy of the detection pixel.

  The subject information extracted from the second pixel signal includes the luminance information of the subject image correlated with the focus detection accuracy of the shooting pixel and the change amount of the subject image correlated with the focus detection accuracy of the shooting pixel over time. This is at least one of the information and the contrast information of the subject image correlated with the focus detection accuracy of the photographing pixels.

  The camera MPU 125 having the functions of the first control means, the second control means, and the third control means is connected to the lens MPU 117 via the signal line of the mount M, and obtains the lens position with respect to the lens MPU 117 and performs predetermined processing. The lens drive request is issued with the drive amount of ## EQU2 ## or the optical information specific to the lens unit 100 is acquired.

  The camera MPU 125 having the functions of the first control means, the second control means, and the third control means includes a ROM 125a that stores a program for controlling camera operation, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters. Is built-in.

  Further, the camera MPU 125 executes focus detection processing by a program stored in the ROM 125a. Details of the focus detection process will be described later. The camera MPU 125 also corrects the imaging plane phase difference AF because the influence of vignetting is large and the reliability decreases when the image height at the focus detection position is large.

  The display 126 is configured by an LCD or the like, 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. The operation switch group 127 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The memory 128 of this embodiment is a detachable flash memory, and records captured images.

  The imaging plane phase difference focus detection unit (first focus detection unit) 129 uses a phase difference AF method based on image signals of focus detection pixels discretely arranged in a plurality of imaging pixels of the image sensor 122. Focus detection processing is performed. More specifically, the imaging surface phase difference focus detection unit 129 is based on the deviation amount of the pair of images formed on the focus detection pixels by the light flux passing through the pair of pupil regions of the imaging optical system. Perform AF.

  The principle of the imaging surface phase difference AF is the same as that described in FIG. 5 to FIG. 7, FIG.

  The TVAF focus detection unit (second focus detection unit) 130 performs a contrast-type focus detection process using the contrast component of the image information obtained by the image processing circuit 124. In contrast-type focus detection processing, the focus lens 104 is moved to detect the position of the focus lens where the contrast evaluation value reaches a peak.

  As described above, the present embodiment combines the imaging surface phase difference AF and the contrast AF, and since any focus detection means is based on the information on the imaging surface, the phase difference AF and the contrast AF (TVAF) are combined. Focus detection accuracy can be improved.

  The focus detection process executed by the camera MPU (processor) 125 having the functions of the first control unit, the second control unit, and the third control unit will be described below with reference to FIGS. In FIG. 1, “S” is an abbreviation for a step. FIG. 1 is a flowchart for explaining a focus detection process executed by the camera MPU 125.

  When the camera MPU 125 starts the focus detection process (S100), the camera MPU 125 first searches for the focus detection pixel row of the imaging plane phase difference AF included in the currently selected focus detection region, and can detect the focus detection pixel row. A maximum detected defocus amount is acquired (S101). The maximum defocus amount that can be detected by the focus detection pixels is determined from the length of the focus detection pixel row and the coefficient (K value) for converting the image shift amount into the defocus amount. The K value is stored in advance in the EEPROM 125c for each focus detection pixel column.

  Next, the image sensor 122 is exposed (S102). As a result, not only output signals used for imaging plane phase difference AF and TVAF but also information on nearby subjects including a focus detection area for TVAF and a focus detection area for imaging plane phase difference AF can be obtained. In order to determine the reliability of TVAF or imaging plane phase difference AF, which will be described later, the pixel area on the imaging plane for obtaining subject information is a focus detection area for TVAF or a focus detection area for imaging plane phase difference AF. It is desirable to include.

  Further, TVAF and imaging surface phase difference AF may be used by thinning out the number of output signals of the imaging pixels in accordance with the required focus adjustment accuracy. Even in this case, it is desirable that the output signal for obtaining subject information is composed of a larger number of pixels than the output signal of TVAF or imaging plane phase difference AF. Thereby, information that cannot be obtained from the output signals of TVAF and imaging plane phase difference AF can be obtained, and the reliability of the focus detection result of TVAF and imaging plane phase difference AF described later can be determined.

  The first pixel signal used for the imaging plane phase difference AF corresponds to the first image signal. Further, the pixel signal used for contrast AF (TVAF) and the second pixel signal for obtaining information from the subject correspond to the second image signal.

  Next, the camera MPU 125 performs focus detection processing based on the imaging plane phase difference AF (S103), and determines whether a defocus amount has been detected (S104).

  If it is determined that the defocus amount has not been detected (No in S104), the camera MPU 125 drives the focus lens 104 so that the subject image is not detected from the maximum detected defocus amount acquired in S101 (S105). The flow returns to S102.

  FIG. 3A is a diagram showing the relationship between the lens driving timing and the driving position of the focus lens 104 in S105. The camera MPU 125 drives the focus lens 104 with a drive amount U corresponding to twice the maximum detected defocus amount that can be detected by the imaging plane phase difference AF. An interval between two adjacent focus detection points T1 is a drive amount U, and a defocus amount corresponding to U / 2 before and after the focus detection point T1 is acquired. The focus lens driving based on the result of the imaging surface phase difference AF performed here is referred to as lens driving by the first lens control. Since the first lens control is based on the result of the imaging plane phase difference AF, it is possible to perform lens driving with a relatively large driving amount, and to realize high-speed lens driving.

  On the other hand, if it is determined that the defocus amount has been detected (Yes in S104), the camera MPU 125 detects the vicinity including the focus detection area for TVAF and the focus detection area for imaging surface phase difference AF acquired during the exposure in S102. The reliability of the imaging surface phase difference AF result is calculated from the subject information (S106).

  In general, the detection accuracy of the imaging surface phase difference AF differs depending on the state of the subject. For example, the focus detection accuracy may be lowered due to a low contrast of the subject, a strong light source near the subject, and the influence of a ghost. In Patent Document 2 described above, whether or not the focus detection accuracy of the imaging surface phase difference AF is lowered is determined from the contrast of the pixel signal of the imaging surface phase difference AF to control the driving of the focus lens. .

  However, it is difficult to determine all the situations of the subject that cause a decrease in focus detection accuracy from the pixel signal of the imaging plane phase difference AF. For example, as a situation of a subject in which a decrease in focus detection accuracy is expected, a subject having a contrast in an oblique direction with respect to the contrast detection direction (pupil division direction) of the imaging plane phase difference AF, or the imaging plane phase difference AF can be detected. A subject including a spatial frequency component higher than the spatial frequency information of the subject can be considered.

  FIG. 4 and FIG. 5 show examples of the situation of the subject in which a decrease in focus detection accuracy is expected.

  FIG. 4 shows a state in which an optical image (shaded portion) is formed on a part of the imaging surface of the imaging element 122. The hatched portion indicating the optical image of the subject is a portion having higher luminance on the subject, and the luminance is lower except for the hatched portion.

  Each square indicates a pixel, and each pixel written as R, G, B indicates a pixel mainly having sensitivity to red, green, and blue light. As described above, of the 2 rows × 2 columns of pixels, the pair of G pixels arranged diagonally is left as a photographing pixel, and the R pixel and the B pixel are replaced with focus detection pixels, as shown in FIG. AF1 and AF2 are arranged as a pair of focus detection pixels that perform pupil division in the left-right direction. Four pairs of AF pixels are depicted in FIG. 4, but the number of pixels used for focus detection may be larger, and may be continuous in the left-right direction in FIG. 4. .

  FIG. 4 shows a state in which the focus is adjusted so that the optical image of the subject is focused on the imaging surface of the image sensor 122 in a focused state. In the in-focus state, optical images are formed in the same position and in the same shape with respect to the pair of AF pixels, and FIG. 4 shows only the common optical image for the pair of AF pixels. Yes.

  4A shows an optical image of a subject, in which a subject optical image having luminance in a relatively wide range in the vertical direction is formed on a part of the imaging surface of the image sensor 122. Shows the case. In this case, among the four pairs of AF pixels, the second and third pairs of AF pixels are included in a part of the optical image, so the output of the four pixels in the figure is as shown in FIG. become. Details of FIG. 5A will be described later.

  FIG. 4B shows a case where an optical image of a subject having luminance in a relatively wide range in an oblique direction is formed on a part of the image sensor 122 as an optical image of the subject. ing. In this case, among the four pairs of AF pixels, only the AF pixel of the third AF1 and the AF pixel of the second AF2 are included in a part of the optical image. It becomes like 5 (B). Details of FIG. 5B will be described later.

  FIG. 4C illustrates a case where an optical image of a subject having luminance within a relatively narrow range in the vertical direction is formed on a part of the imaging surface of the image sensor 122 as an optical image of the subject. Is shown. In this case, among the four pairs of AF pixels, only the AF pixel of the third AF1 and the AF pixel of the second AF2 are included in a part of the optical image. It becomes like 5 (B). Details of FIG. 5B will be described later.

  FIG. 5 shows a pixel signal as an output signal obtained from the image sensor 122 by the optical image formed on the image sensor 122 shown in FIG. The horizontal axis represents the pixel number indicating the pixel position, and the vertical axis represents the pixel signal as an output signal indicating the light amount. In FIG. 5, the square mark represents the output of the AF pixel of AF1, and the circle mark represents the output of the AF pixel of AF2.

  FIG. 5A shows the output when an optical image is formed as shown in FIG. 4A, and the outputs of AF1 and AF2 are almost the same because of the in-focus state.

  FIG. 5B shows the output when an optical image is formed as shown in FIGS. 4B and 4C. The outputs of the AF1 and AF2 pixels are different regardless of the in-focus state. In this case, according to the formed output, since the image is shifted by one pixel, the imaging surface phase difference focus detection unit 129 determines that the image is in the defocus state, and performs erroneous focus detection and focus adjustment. will have to go. However, such focus detection error cannot be detected by using only the AF pixel signal.

  In S106, the reliability of the imaging surface phase difference AF result is calculated from the imaging pixels around the AF pixel in consideration of the focus detection error as described above. For example, in the situation of the subject as shown in FIGS. 4B and 4C, the direction and position of the high-contrast portion of the signal of the photographic pixel near the AF pixel are recognized, as shown in FIG. It is possible to detect the presence or absence of a significant focus detection error. In FIG. 5B, a focus shift corresponding to the image shift amount for one pixel is obtained as a focus detection error.

  4C is converted into a spatial frequency component by a known Fourier transform or the like, and whether or not a higher frequency component than the spatial frequency component that can be detected by the AF pixel is included. A detection error may be set. When the focus detection error is set by such a method, the focus detection error can be estimated by storing the focus detection error corresponding to the spatial frequency of the subject in advance.

  As shown in FIG. 4, a subject having a spatial frequency of 1/2 or more of the distance between the centers of the focus detection directions (pupil division directions) of the pair of focus detection pixels cannot be detected in principle. In principle, a subject having a high spatial frequency that is 1/2 or more of the distance between the center of the first pair of AF pixels and the center of the second pair of AF pixels cannot be detected. In general, the white and black edges of the free color include spatial frequency components of various spatial frequency information from low frequency to high frequency, so that the above-described focus detection error occurs.

  In addition to the situation of the subject shown in FIG. 4, a situation where stray light from a strong light source in the vicinity of the subject arrives at the paired AF pixels unevenly is also conceivable. Even in such a case, the outputs of the paired AF pixels do not match and a focus detection error occurs. However, since the position of the strong light source can be specified from the signal of the imaging pixel, the focus detection according to the position of the light source Since the imaging surface phase difference focus detection unit 129 stores the influence in advance, the focus detection error can be estimated. For example, a correspondence table of focus detection error amounts corresponding to strong light source positions is stored in the EEPROM 125c.

  In S106, the reliability of the imaging surface phase difference AF result is calculated as a possible focus detection error. The processing for calculating the reliability of the imaging surface phase difference AF result described above is performed by the camera MPU 125. In S106, the focus detection error is calculated using the following equation (1).

  As described above, the subject contrast direction error is calculated for each subject by storing information on the focus detection error amount associated with the direction of the high-contrast portion of the signal of the imaging pixel in the EEPROM 125c. Similarly, the subject spatial frequency error is calculated for each subject by storing information on the focus detection error amount associated with the signal amount of the high-frequency component detected from the signal of the photographing pixel in the EEPROM 125c. Further, the error due to stray light is similarly calculated for each subject using the focus detection error amount corresponding to the position of the strong light source and the amount of light stored in the EEPROM 125c.

  In S107, the lens driving amount of the focus lens 104 is calculated from the defocus amount calculated in S104 and the focus detection error calculated in S106. FIG. 3B is a diagram showing details of drive control of the focus lens 104 when the defocus amount is detected in S104. T2 which is the first focus position in FIG. 3B indicates the lens position at the time of focus detected by the imaging plane phase difference AF based on the defocus amount calculated in S104.

  In S107, the position T2 is driven so as to reach the lens position T3 before the lens driving amount T4 in view of the focus detection error calculated in S106. When the focus detection error calculated in S106 is larger than the defocus amount calculated in S104, the calculated defocus amount is determined to be unreliable, and the lens driving amount calculated in S107 is set to 0. The lens driving based on the result of the imaging surface phase difference AF is not performed.

  As described above, since the lens driving amount is set in accordance with the focus detection accuracy of the imaging surface phase difference AF, high-speed focus detection in accordance with the state of the subject can be performed. The camera MPU 125 determines whether to use such imaging plane phase difference AF.

  In S108, it is determined whether the lens driving amount has a finite value other than zero. When the lens driving amount has a finite value (Yes in S108), lens driving is performed by lens control (first lens control) based on the result of the imaging surface phase difference AF. (S109) If the lens drive amount is 0 (No in S108), S109 is skipped.

  When the lens driving is finished in S109, next, exposure to the image sensor 122 is performed as in S102 (S110). As a result, not only output signals used for imaging plane phase difference AF and TVAF but also information on nearby subjects including a focus detection area for TVAF and a focus detection area for imaging plane phase difference AF can be obtained.

  Next, the reliability of TVAF is determined from subject information at the time of the previous exposure (S111).

  The reliability of the TVAF determined in S111 determines whether the focus detection process is finished using the TVAF or the imaging plane phase difference AF. This processing is performed by the camera MPU 125 as subject information extraction means. As described above, the contrast-type focus detection process detects the focus lens position where the contrast evaluation value reaches a peak by moving the focus lens 104.

  Therefore, there are some issues that depend on this method. For example, when a high-brightness point light source exists as a subject in a focus detection area for TVAF that performs contrast evaluation, the output signal of the point light source may be saturated depending on exposure conditions. In such a case, when the point light source is slightly blurred, the output signal remains saturated and the area of the subject in the focus detection area for TVAF for performing contrast evaluation increases, resulting in an edge with high contrast. Many are detected. As a result, the contrast evaluation value becomes larger in a slightly blurred state, and erroneous focus adjustment is performed.

  Another problem is that a stable contrast evaluation value cannot be obtained because the subject in the focus detection area for TVAF that performs contrast evaluation shakes due to movement of the subject or camera shake of the photographer. . In such a case, it can be easily imagined that the peak of the contrast evaluation value cannot be detected with high accuracy. The same applies to a flashing subject.

  For this reason, in S111, it is determined whether or not high-accuracy contrast focus detection can be performed from an image signal obtained in advance exposure. Specifically, as to the presence or absence of a point light source, it is determined in Japanese Patent Application Laid-Open No. 2007-33735 whether or not there is a saturated signal in the focus detection area for TVAF that performs contrast evaluation using the disclosed technique. it can. When it is determined that a point light source exists, it is determined that the reliability of TVAF is low. For example, the reliability of TVAF related to the point light source is calculated using the following Equation 2.

  In the above formula, the evaluation value of the row including the high luminance portion corresponds to the TE line peak integration evaluation value Hi in Japanese Patent Application Laid-Open No. 2007-33735. In addition, the evaluation value of the entire focus detection area corresponds to the TE line peak integration evaluation value.

  Thus, by calculating the ratio of the high luminance part in the focus detection area as the reliability of TVAF, when the high luminance part is large, the reliability of TVAF takes a large value. If the reliability of the TV AF of the point light source takes a value equal to or greater than a predetermined threshold, it is determined in step S111 that the imaging plane phase difference AF is used.

  In addition, in order to detect a change in the subject in the focus detection area for TVAF that performs contrast evaluation, an image in the focus detection area for TVAF that performs contrast evaluation is pattern-matched to a reference image acquired in advance. (Normalization correlation) processing is performed to detect the position or range of the subject image in the reference image. If the change in position or range (change in the size of the subject) is larger than the predetermined threshold, it is determined that the reliability of TVAF is low.

  In addition, after the pattern matching process, when a predetermined condition is satisfied, the reference image is updated. The updated reference image may be an image signal obtained by newly exposing or an image used for the previous pattern matching process. The case where the predetermined condition is satisfied is, for example, a case where the size of the subject area changes or a case where the similarity is lowered due to a change in the direction of the subject.

  In order to more easily detect changes in the subject in the focus detection area, the camera unit 120 detects the amount of camera shake that the photographer generates at the time of shooting, and changes the subject in the focus detection area. It is good.

  The reliability of TVAF due to the change of the subject in the focus detection area for TVAF is calculated using Equation 3 below.

  In contrast AF, a high-frequency spatial frequency component at a boundary with contrast such as the contour of a subject is evaluated. Therefore, the change in the position of the subject outline due to the change in the position and size of the subject described above affects the reliability of the TVAF. When the change in the position of the subject contour is calculated as the amount of change on the image sensor, and the amount of change is larger than the subject detection range on the image sensor, focus detection is performed on a completely different subject.

  In contrast AF, the in-focus position is determined by evaluating different blur states of the subject. Therefore, it is necessary to evaluate the same subject during the focus detection operation. Therefore, by calculating the TVAF reliability of the subject change as in Equation 3, if the TVAF reliability is greater than a predetermined threshold, it is determined in step S111 that the imaging plane phase difference AF is used.

  In the present invention, using an image signal including the vicinity of a focus detection area for TVAF that performs contrast evaluation, a subject such as a point light source or a subject for which an unstable contrast evaluation value is expected is avoided from being subjected to focus adjustment by TVAF control. be able to. Thereby, highly accurate focus adjustment is realizable.

  If it is determined in S111 that the reliability of TVAF is low (No in S111), the process proceeds to a subroutine for imaging surface phase difference AF control (S114). When the focus adjustment is completed in S114, the focus detection process ends. Such a determination regarding the reliability of TVAF is performed by the camera MPU 125.

  If it is determined in S111 that the reliability of TVAF is high (Yes in S111), the step width of the lens driving amount of the focus lens 104 when performing TVAF control is set (S112). FIG. 6 is a diagram for explaining the setting of the step width of the lens driving amount at the time of TVAF control. The horizontal axis represents the position of the focus lens 104, and the vertical axis represents the TVAF contrast evaluation value.

  In general, the contrast evaluation value of TVAF increases as the contrast, which is the difference in brightness of the subject, increases. Also, depending on the light source environment that illuminates the subject, the higher the brightness of the subject, the higher the contrast and the larger the TVAF evaluation value. Therefore, the TVAF evaluation value change according to the position change of the focus lens differs depending on the contrast information and luminance information of the subject.

  In FIG. 6, white circles represent examples of evaluation value transitions when the subject has high contrast and high brightness, and black circles represent subjects with low contrast and low contrast. It is an example of transition of the evaluation value when it is luminance.

  When the subject has high contrast and high brightness (white circles), the change in the contrast evaluation value due to the focus lens position is relatively large. Therefore, by setting the step width of the lens drive amount of the focus lens to a small value, Focus detection can be performed with high accuracy. On the other hand, if the subject has low contrast and low brightness (black circles), setting the drive width as the step width of the focus lens drive amount similar to that at high contrast and high brightness will change the contrast evaluation value. It does not appear greatly.

  In general, the contrast evaluation value includes noise of an output signal and noise due to a change in the subject situation in addition to a change in the contrast of the optical image of the subject. In TVAF control, the position of the focus lens is driven and controlled so as to search for the peak position of the contrast evaluation value. Therefore, when the optical contrast change for each position of the focus lens is small, it is greatly affected by other noises. If there is a peak of the contrast evaluation value in the wrong driving direction of the focus lens, it may be detected.

  Therefore, in this embodiment, the driving width as the step width of the lens driving amount is changed according to the condition of the subject. For example, in FIG. 6, when the subject has high contrast and high brightness (white circle), the small step amount is R1, and when the subject has low contrast and low brightness (black circle), the large step amount It shows that lens driving is performed as R2 which is twice R1.

  In this embodiment, the state of the subject is determined using an image signal including the vicinity of the contrast evaluation range, which is a focus detection area for TVAF. Specifically, the sum of the output differences between adjacent pixels is calculated as the contrast of the subject in the image signal within the focus detection area for TVAF, and the focus lens drive amount step is determined according to the magnitude of a predetermined threshold. The width may be set.

  In addition, the step width of the focus lens drive amount may be set more simply by the maximum output value of the image signal within the contrast evaluation range that is a focus detection area for TVAF. In addition, when a plurality of image signals having different positions of the focus lens 104 are obtained in advance by a plurality of exposures, the focus lens is driven according to the magnitude of the square sum of the output differences between adjacent pixels of the image signal. An amount step width may be set. This process is performed by the camera MPU 125.

  After setting the step width of the focus lens drive amount in S112, the process proceeds to a TVAF control subroutine (S113). When the focus adjustment is completed in S113, the focus detection process ends.

  A focus adjustment subroutine by TVAF control will be described with reference to FIGS. FIG. 7 shows a flow of a focus adjustment processing subroutine by TVAF control. FIG. 8 is a diagram for explaining TVAF control, where the horizontal axis represents the position of the focus lens 104 and the vertical axis represents the TVAF evaluation value. The step width of the focus lens drive amount set in S112 in FIG. 1 is represented as T8 as the number of pulses for one lens drive.

  The camera MPU 125 drives the focus lens 104 from the start position T7 to the in-focus position T2 of the imaging surface phase difference AF at the drive interval T8 set in S112, and acquires the TVAF evaluation value at each drive interval T8 (S301). ).

  Next, the camera MPU 125 determines whether or not a peak has been detected, that is, whether or not the TVAF evaluation value has been switched from increase to decrease, and whether or not the peak determination threshold T9 has been decreased (S302). As the first TVAF evaluation value for detecting the peak, the TVAF evaluation value obtained by the exposure in S110 of FIG. 1 may be used. If the camera MPU 125 determines that no peak is detected (No in S302), the flow returns to S301.

  On the other hand, if it is determined that a peak has been detected (Yes in S302), the camera MPU 125 determines whether the current driving interval T8 is narrow (S303).

  If the camera MPU 125 determines that a peak is detected at a narrow drive interval T8 (Yes in S303), the camera MPU 125 drives the focus lens 104 to the peak position (S304).

  On the other hand, if the camera MPU 125 determines that a peak is detected at a wide driving interval T8 (No in S303), the camera MPU 125 sets the driving interval T8 narrow (S305) and climbs toward the TVAF in-focus position T11. Driving is performed to obtain an evaluation value (S306).

  Next, the camera MPU 125 determines whether or not a peak has been detected, that is, whether or not the TVAF evaluation value has been switched from increasing to decreasing and the peak determination threshold T9 has been decreased (S307). If the camera MPU 125 determines that no peak is detected (No in S307), the flow returns to S306. On the other hand, when the camera MPU 125 determines that a peak has been detected (Yes in S307), it drives the focus lens 104 to the peak position (S304).

  In this way, if the camera MPU 125 is expected to increase the contrast change of the subject image, the step size of the focus lens 104 in the TVAF is set narrow to ensure detection accuracy, and the contrast evaluation value change is expected to be small. , Improve the responsiveness by setting a wide step width, and reset the step width narrowly after peak detection. Such determination regarding TVAF control is performed by the camera MPU 125.

  When the driving of the focus lens 104 is finished in S304, the focus adjustment process by the TVAF control is finished.

  The driving of the focus lens based on the result of TVAF performed here is referred to as lens driving by second lens control. Since the second lens control is based on the result of TVAF, the second lens control is configured by repeated lens driving with a relatively small driving amount, and the lens driving is relatively slow.

  Next, a focus adjustment subroutine by the imaging plane phase difference AF control will be described. FIG. 9 shows a flow of a focus adjustment processing subroutine by the imaging surface phase difference AF control.

  A lens driving amount corresponding to the defocus amount calculated using the output signal used for the imaging plane phase difference AF obtained by the exposure performed in S110 of FIG. 1 is calculated.

  Thus, the output signal at the time of exposure in S110 may be used for either imaging plane phase difference AF or TVAF. Therefore, for each exposure, the calculation of the defocus amount by the imaging surface phase difference focus detection unit and the contrast evaluation value by the TVAF detection unit are both calculated.

  Thereby, focus detection can always be performed by both focus detection methods. However, the embodiment of the present invention is not limited to this, and only one of the focus detections may be performed for each exposure. In that case, an effect of reducing the amount of calculation required for focus detection can be obtained.

  Next, the focus lens is driven by the first lens control based on the calculated lens driving amount (S402).

  After that, exposure to the image sensor 122 is performed to obtain at least an output signal of the imaging surface phase difference AF, and it is determined whether or not it is in focus from the calculated defocus amount (S403).

  If it is in focus (Yes in S403), the focus adjustment process by the imaging surface phase difference AF control is finished. If it is not in focus (No in S403), the process returns to S401. Here, the defocus amount is calculated again in order to always perform the focus determination after driving the lens, but the embodiment is not limited thereto. When the lens driving amount calculated in S401 is smaller than the predetermined value, it is determined that the detected defocus amount and lens driving error are small, and the focus determination can be omitted.

  As described above, by selecting each AF control from the output signals other than the signals used for imaging plane phase difference AF and TVAF in consideration of the reliability of each AF, both the accuracy and speed of focus adjustment are achieved. Focus adjustment can be performed.

122 Imaging element 100 Imaging optical system 129 Imaging surface phase difference focus detection unit (first focus detection unit)
130 TVAF focus detection unit (second focus detection unit)
125 camera MPU

Claims (8)

A plurality of photographic pixels for imaging a subject image formed by a photographic optical system having a focus lens; an imaging device having focus detection pixels discretely arranged in the plurality of photographic pixels; and the photographic optical system First control means for performing phase difference AF based on a first pixel signal output from the focus detection pixel that detects a plurality of light fluxes passing through different pupil regions, and a pupil region of the photographing optical system. Second control means for performing contrast AF based on a second pixel signal output from the photographing pixel for detecting a plurality of light beams passing therethrough, and subject information extraction for extracting subject information from the second pixel signal An imaging device comprising:
An image pickup apparatus comprising: third control means for switching between the phase difference AF and the contrast AF using subject information extracted from the second pixel signal.   When the third control means determines that the reliability of the phase difference AF calculated based on subject information extracted from the second pixel signal without using the first pixel signal is low, The imaging apparatus according to claim 1, wherein the phase difference AF is switched to the contrast AF.   If the third control means determines that the contrast AF calculated based on the subject information extracted from the second pixel signal without using the first pixel signal has low reliability, the contrast The imaging apparatus according to claim 1, wherein AF is switched to the phase difference AF.   The subject information extracted from the second pixel signal is information correlated with focus detection accuracy of the focus detection pixel or information correlated with focus detection accuracy of the photographing pixel. 4. The imaging device according to any one of 3.   The subject information extracted from the second pixel signal includes the contrast information correlated with the focus detection accuracy of the focus detection pixel and the spatial frequency of the subject image correlated with the focus detection accuracy of the focus detection pixel. The imaging apparatus according to claim 4, which is at least one of stray light information included in a subject image correlated with information and a focus detection accuracy of the focus detection pixel.   The subject information extracted from the second pixel signal includes the luminance information of the subject image correlated with the focus detection accuracy of the shooting pixel and the time-lapse of the subject image correlated with the focus detection accuracy of the shooting pixel. 6. The imaging apparatus according to claim 4, wherein at least one of the information on the amount of change due to the difference between the image and the contrast information of the subject image correlated with the focus detection accuracy of the imaging pixel.   The said 2nd control means changes the drive width of the lens drive amount of the said focus lens based on at least 1 of the contrast information of the said subject image, and the luminance information of the said subject image. The imaging device according to item. A plurality of photographic pixels for imaging a subject image formed by a photographic optical system having a focus lens; an imaging device having focus detection pixels discretely arranged in the plurality of photographic pixels; and the photographic optical system First control means for performing phase difference AF based on a first pixel signal output from the focus detection pixel that detects a plurality of light fluxes passing through different pupil regions, and a pupil region of the photographing optical system. Second control means for performing contrast AF based on a second pixel signal output from the photographing pixel for detecting a plurality of light beams passing therethrough, and subject information extraction for extracting subject information from the second pixel signal A method of controlling an imaging apparatus comprising:
A control method for an imaging apparatus, comprising: third control means for switching between the phase difference AF and the contrast AF using subject information extracted from the second pixel signal.

Images