JP5366643B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus.

  Patent Document 1 proposes a hybrid focus detection means of a phase difference detection type focus detection means (phase difference AF) and a contrast detection type focus detection means (TVAF). In Patent Document 2, a focus detection pixel is provided in an image sensor to realize a phase difference detection function (imaging surface phase difference AF).

JP 2003-295047 A JP 2009-003122 A

  The hybrid focus detection means described in Patent Document 1 has an optical path difference between the phase difference AF and the TVAF. Further, in Patent Document 1, there is a case where TVAF is performed on an unnecessarily large range after driving the lens to the in-focus position obtained by the phase difference AF.

  An object of the present invention is to provide an imaging apparatus excellent in focus detection accuracy and responsiveness.

An imaging apparatus according to an aspect of the present invention includes a plurality of shooting pixels that each receive light passing through an exit pupil of a shooting lens to generate an image of a subject, and each of which is a part of the exit pupil of the shooting lens And detecting a shift amount of the pair of images of the subject formed on the plurality of focus detection pixels. A first focus detection unit for detecting a focal position; a second focus detection unit for detecting a contrast peak position of the image of the subject formed by the plurality of imaging pixels as a second focus position; and the pair of images. The start position of the second focus detection unit when the reliability of focus detection by the first focus detection unit is high and the reliability is not high. Start of the second focus detection unit Than location, a processor for setting near the first focus position, have a, wherein the processor, when the contrast of the image of the subject obtained by the focus detection by the first focus detection unit is not steep When the focus is detected by the second focus detection unit, the driving interval for driving the focus lens included in the photographing lens from the start position toward the first focus position in the focus detection is determined. When it is determined that the focus lens is present, the focus detection by the second focus detection unit is set to be wider than the drive interval for driving the focus lens from the start position toward the first focus position .

  The present invention can provide an imaging apparatus with excellent focus detection accuracy and responsiveness.

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 graph explaining the correction method of imaging surface phase difference AF. It is a figure explaining the drive of the focus lens in the imaging surface phase difference AF of FIG. It is a figure explaining operation | movement of TVAF.

  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 a drive / control system. As described above, the lens unit 100 includes the focus lens 104 and includes a photographing lens that forms an image of the 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 drive / control system 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 lens, 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 drive / control system.

  The optical low-pass filter 121 and the imaging element 122 function as an imaging optical system that forms a subject image with the light flux from the lens unit 100.

  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 circuits, and one photoelectric conversion element is arranged on the 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. Also, some pixels are focus detection pixels, and focus detection (imaging surface phase difference AF) using a phase difference detection method is possible on the imaging surface.

  More specifically, the image sensor 122 includes a plurality of photographing pixels that each receive light passing through the entire exit pupil of the photographing lens that forms an image of the subject and generate an image of the subject. The image sensor 122 further includes a plurality of focus detection pixels that each receive light passing through a partial region of the exit pupil of the photographing lens. The plurality of focus detection pixels as a whole can receive light passing through the entire exit pupil of the photographing lens. 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 drive / control system includes an image sensor driving circuit 123, an image processing circuit 124, a camera MPU 125, 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.

  The camera MPU (processor) 125 performs all calculations and controls related to the camera body 120, and includes an image sensor driving circuit 123, an image processing circuit 124, a display 126, an operation SW 127, a memory 128, and an imaging surface phase difference focus detection unit 129. The TVAF focus detection unit 130 is controlled. The camera MPU 125 is connected to the lens MPU 117 via the signal line of the mount M, and obtains the lens position, issues a lens driving request with a predetermined driving amount to the lens MPU 117, and transmits optical information specific to the lens unit 100. Or get it. The camera MPU 125 includes a ROM 125a that stores a program for controlling camera operations, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters.

  Further, the camera MPU 125 executes focus detection processing by a program stored in the ROM 125a. Specifically, the camera MPU 125 changes the moving range of the focus lens 104 in TVAF based on the reliability of the imaging plane phase difference AF. Note that this change may be performed by the TVAF focus detection unit 130. 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. Furthermore, the camera MPU 125 adjusts the reliability threshold value of the imaging plane phase difference AF according to the image height (that is, sets so as to increase with the image height).

  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 surface phase difference focus detection unit (first focus detection unit) 129 performs focus detection processing by the phase difference AF method based on the image signal of the focus detection pixels embedded in the image sensor 122. 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 FIGS.

  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 a focus lens position where the contrast reaches a peak.

  As described above, the present embodiment combines the imaging surface phase difference AF and TVAF, and since each focus detection unit is based on information on the imaging surface, the focus detection accuracy is improved as compared with the combination of the phase difference AF and TVAF. be able to.

  A light beam limited by several constituent members such as a lens holding frame of the lens unit 100 and an aperture / shutter is incident on the image sensor 122. When the pair of pupil-divided focus detection pixels used in the imaging plane phase difference AF is positioned around the imaging region, the light beam incident on one pixel is vignetted. In the imaging plane phase difference AF, the shift amount (defocus amount) of the pair of images is detected by detecting the relative positions of the pair of images detected by the pair of focus detection pixels. However, if the light flux incident on one focus detection pixel is vignetted, the degree of coincidence between the two images decreases, and the defocus amount detection accuracy also decreases. In order to prevent this, it is effective to correct the asymmetry of both images and increase the degree of coincidence of the images.

  For example, image signal information when an object with uniform brightness is imaged is recorded. In FIG. 3, a solid line A is image signal information obtained when an object with uniform brightness is imaged, and a dotted line B is obtained as a result of partial vignetting when an object with uniform brightness is imaged. This is image signal information. The vertical axis represents the output (contrast) of the image signal, and the horizontal axis represents the position of the subject. By dividing the dotted line B by the solid line A, image signal information in which the vignetting component of the light beam is approximately corrected can be obtained. Since the vignetting component is determined by the lens aperture and the image height, the correction coefficients for several representative points are stored in the EEPROM 125c, and the camera MPU 125 may refer to them during correction.

  Hereinafter, the focus detection process executed by the camera MPU (processor) 125 will be described with reference to FIGS. 1, 4, and 5. 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 sequence of the imaging plane phase difference AF included in the currently selected TVAF evaluation area, and can detect the focus detection pixel sequence. 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 camera MPU 125 performs focus detection processing based on the imaging plane phase difference AF (S102), and determines whether or not a defocus amount has been detected (S103).

  If it is determined that the defocus amount is not detected (No in S103), the camera MPU 125 drives the focus lens 104 so as not to miss the detection of the subject image from the maximum detected defocus amount acquired in S101 (S104). The flow returns to S102.

  FIG. 4A is a diagram illustrating the relationship between the lens driving timing and the driving position of the focus lens 104 in S104. 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.

  On the other hand, if it is determined that the defocus amount is detected (Yes in S103), the camera MPU 125 acquires the correction coefficient described in FIG. 3 from the EEPROM 125c (S105), and corrects the image signal using the acquired correction coefficient (S105). S106). FIG. 4B is a diagram showing details of drive control of the focus lens 104 when the defocus amount is detected in S103.

  Next, the camera MPU 125 acquires a reliability threshold value for TVAF operation determination corresponding to the image height from the EEPROM 125c so that a higher reliability is required as the image height of the focus detection pixel is larger (S107). This is because when focus detection is performed at a position where the image height is large, an error is likely to occur in the reliability obtained from the correction coefficient used in S106 and the image signal after correction.

  Next, the camera MPU 125 determines whether or not the reliability of the imaging plane phase difference AF is higher than the reliability threshold value set according to the image height (S108). The reliability includes information on the degree of coincidence and contrast between a pair of images obtained as a result of the imaging plane phase difference AF. The contrast information is used because of the characteristics of phase difference AF, a high-contrast subject has characteristics that are easier to detect.

  If the camera MPU 125 determines that the reliability of the imaging surface phase difference AF is high (Yes in S108), the reliability of the in-focus position (first focusing position) T2 obtained by the imaging surface phase difference AF is high. The focus lens 104 is driven so as to perform TVAF limited to the vicinity thereof. Thereby, the responsiveness of focus detection can be improved. That is, as shown in FIG. 4B, the camera MPU 125 drives the focus lens 104 from the position T1 where the imaging surface phase difference AF detects the defocus amount to the position T3 that is separated from the position T2 by the distance T4. This is the TVAF start position (S109). The camera MPU 125 stores the distance T4 in the EEPROM 125c in advance.

  On the other hand, if the camera MPU 125 determines that the reliability of the imaging plane phase difference AF is not high (No in S108), the reliability of the in-focus position T2 obtained by the imaging plane phase difference AF is low, and thus a relatively wide range. The focus lens 104 is driven so as to perform TVAF. Thereby, focus detection accuracy can be improved. That is, as shown in FIG. 4B, the camera MPU 125 drives the focus lens 104 from the position T1 to the position T5 that is separated from the position T2 by a distance T6 that is larger than the distance T4. To do. The camera MPU 125 stores the distance T6 in the EEPROM 125c in advance.

  However, since the direction from the position T1 to the in-focus position T2 is reliable, the camera MPU 125 next determines whether or not the maximum detected defocus amount is the distance T6 (S110), and determines that it is so. In this case, the focus lens is driven to the position T5 (S111). On the other hand, if it is determined that the maximum detected defocus amount is smaller than the distance T6 and the position T5 is located on the left side of the position T1 in FIG. 4B, the camera MPU 125 sets the current position T1 as the TVAF start position. To do.

  Next, the camera MPU 125 determines whether the contrast of the subject image obtained by the imaging plane phase difference AF is steep (S112). The camera MPU 125 determines that the image is steep when the integrated amount of the secondary contrast component obtained by differentiating the contrast value is large or when the difference amount between the peak value and the bottom value of the image is large.

  FIG. 5 is a diagram for explaining TVAF, in which the horizontal axis represents the position of the focus lens 104 and the vertical axis represents the evaluation value of TVAF.

  If it is determined that the subject image is steep (Yes in S112), the camera MPU 125 sets the drive interval T8 of the focus lens 104 for obtaining the TVAF evaluation value to be narrow (S113), otherwise. A wide driving interval T8 is set (S114). For example, when the focusing accuracy in the final TVAF is ± 50 μm in terms of defocus amount, T8 = 200 μm is set in S113, and T8 = 400 μm is set in S114. The setting width may be changed according to the steepness of the subject image.

  Next, the camera MPU 125 drives the focus lens 104 from the start position T7 in the direction of the focus position T2 of the imaging surface phase difference AF at the drive interval T8 set in S113 or S114, and the TVAF evaluation value at each drive interval T8. Is acquired (S115).

  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 whether or not the peak determination threshold T9 has been decreased (S116). If the camera MPU 125 determines that no peak is detected (No in S116), the flow returns to S204.

  On the other hand, if it is determined that a peak has been detected (Yes in S116), the camera MPU 125 determines whether the current drive interval T8 is narrow (S117).

  If the camera MPU 125 determines that a peak is detected at a narrow driving interval T8 (Yes in S117), the camera MPU 125 drives the focus lens 104 to the peak position (S122).

  On the other hand, if the camera MPU 125 determines that a peak is detected at a wide driving interval T8 (No in S117), the peak position (second in-focus position) T11 is more than the current position (for example, the position T10 in FIG. 5). The focus lens 104 is driven to a position T12 close to (S118). Next, the camera MPU 125 sets the drive interval T8 to be narrow (S119), performs hill-climbing drive toward the TVAF focus position T11, and acquires an evaluation value (S120). The responsiveness of focus detection can be improved by S118 and S119.

  Next, the camera MPU 125 determines whether or not a peak is detected, that is, whether or not the TVAF evaluation value is switched from increasing to decreasing and the peak determination threshold T9 is decreased (S121). If the camera MPU 125 determines that no peak is detected (No in S210), the flow returns to S120. On the other hand, when the camera MPU 125 determines that a peak has been detected (Yes in S121), it drives the focus lens 104 to the peak position (S122).

  As described above, the camera MPU 125 sets the movement range of the focus lens 104 in the TVAF to be narrow (that is, the start position is set to the position T3) if the reliability of the imaging plane phase difference AF is high, and improves the response when the reliability is low. That is, the start position is set to position T5) to ensure detection accuracy. In addition, if the subject image is steep, the camera MPU 125 secures the detection accuracy by setting the drive interval T8 of the focus lens 104 in TVAF to be narrow, and if it is not steep, the camera MPU 125 sets the drive interval T8 wide to improve the response. Then, after the peak detection, the driving interval T8 is narrowed again.

  In addition, if the difference in the amount of eccentricity of the focus detection pixel row in the imaging plane phase difference AF is increased, the focus detection accuracy increases. Therefore, when the focus detection pixel that detects the in-focus position T11 is this high-precision detection pixel. The distance T4 may be set narrower.

  The imaging device can be applied to imaging a subject.

100 Lens unit 104 Focus lens (group)
117 Lens MPU
120 Camera Body 122 Image Sensor 125 Camera MPU
125c EEPROM
129 Imaging surface phase difference focus detection unit 130 TVAF focus detection unit

Claims (4)

A plurality of imaging pixels each receiving light passing through the exit pupil of the photographic lens to generate an image of the subject, and a plurality of focal points each receiving light passing through a partial region of the exit pupil of the photographic lens An image sensor having a detection pixel;
A first focus detection unit that detects a first in-focus position by detecting a shift amount of a pair of images of the subject formed in the plurality of focus detection pixels;
A second focus detection unit for detecting a contrast peak position of the image of the subject formed by the plurality of shooting pixels as a second in-focus position;
The reliability of the start position of the second focus detection unit when the reliability of focus detection by the first focus detection unit including information on the degree of coincidence of the pair of images and the contrast of the image of the subject is high. A processor that sets the first focus position closer to the first focus position than the start position of the second focus detection unit when not higher;
I have a,
If the processor determines that the contrast of the image of the subject obtained by focus detection by the first focus detection unit is not steep, the processor detects the first alignment from the start position in focus detection by the second focus detection unit. When the driving interval for driving the focus lens of the photographing lens toward the focal position is determined that the contrast of the image of the subject is steep, the second focus detection unit performs focus detection from the start position in the focus detection. An image pickup apparatus characterized in that it is set wider than a driving interval for driving the focus lens toward one in-focus position .   The processor sets a driving interval set when the contrast of the image of the subject obtained by focus detection by the first focus detection unit is not steep, and sets the peak position by the second focus detection unit. The imaging apparatus according to claim 1, wherein the imaging apparatus narrows after detection.   The imaging apparatus according to claim 1, wherein the processor sets the start position by comparing the reliability with a reliability threshold that is set to increase with an image height.   The processor sets the start position after correcting the contrast of the pair of images of the subject in the focus detection by the first focus detection unit with a correction coefficient determined by an aperture and an image height of the photographing lens. The imaging apparatus according to claim 1.