JP2016012094A - Camera with contrast af function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a camera that performs AF processing by effectively applying contrast-based focus detection and phase difference-based focus detection.SOLUTION: A digital camera 10 has a photometric sensor 20A and a ranging sensor 18A, and selectively performs phase difference-based focus detection using the ranging sensor 18A and contrast-based focus detection using the photometric sensor 20A in accordance with a user setting. When a focus detection mode is set to a phase difference-based focus detection mode, and if object properties and object area make it difficult to determine an in-focus point in the phase difference-based focus detection mode, the focus detection mode is switched to a contrast-based focus detection mode.

Description

  The present invention relates to an imaging apparatus applicable to a digital camera or the like, and more particularly to an autofocus (AF) process.

  A digital camera or the like includes an AF device that automatically focuses a subject image by driving a focus lens. A single-lens reflex camera is equipped with an AF device based on a phase difference method, and guides subject light to a distance measuring sensor module disposed below a movable mirror. Then, the subject light is divided into pupils, and the focus is determined based on the phase difference of the projected image.

  On the other hand, in the case of a compact camera, a mirrorless camera, or the like, AF processing is performed by a contrast method (mountain climbing method) using an image sensor for photographing. In the contrast method, the brightness difference (contrast) of the image signal read from the image sensor is detected while moving the focus lens in one direction, and the position where the brightness difference reaches a peak is determined as the focus position.

  Even in a digital camera that is not provided with a movable mirror and a dedicated distance measuring sensor module, it is possible to perform focus adjustment based on a phase difference method (see Patent Document 1). In this case, ranging pixels are arranged on a part of the light receiving surface of the imaging element for photographing. Then, the phase difference is detected based on the pixel signal output from the ranging pixel.

  Further, even in a single-lens reflex camera, focus adjustment based on a contrast method can be performed (see Patent Document 2). In this case, a sensor is arranged outside the phase difference type distance measuring sensor module, and focusing is determined based on a pixel signal output from the sensor.

Japanese Patent No. 3761383 JP 2000-156823 A

  In the case of a single-lens reflex camera, the user cannot check the subject through the optical viewfinder when the movable mirror is raised. Therefore, in a configuration in which the distance measuring sensor is arranged on a part of the light receiving surface of the image sensor, display by live view is indispensable. This does not match the user's preference for determining the composition of the subject through the eyepiece before shooting, and the characteristics of the single-lens reflex camera cannot be utilized.

  On the other hand, when a dedicated ranging sensor different from the conventional AF sensor module is provided outside in a single-lens reflex camera, a problem of parallax occurs, and from the necessity such as adjustment of the ranging sensor with the photographing lens, Manufacturing costs increase.

  Therefore, it is necessary to be able to select the AF process using the contrast method and the AF process using the phase difference method according to the shooting situation without greatly changing the conventional camera configuration.

  The imaging apparatus of the present invention forms an image of a subject light guided to the optical finder and a mirror (such as a movable mirror) that selectively guides the subject light that has passed through the imaging optical system to the optical finder and the distance measuring image sensor. A focus detection method selection unit for selecting and setting as a focus detection method one of a two-dimensional image sensor, a phase difference focus detection using a ranging image sensor, and a contrast focus detection using a two-dimensional image sensor; According to the set focus detection method, either focus detection based on a phase difference method based on a pixel signal read out from a ranging image sensor or focus detection based on a contrast method based on a pixel signal read out from a two-dimensional image sensor A focus detection unit that executes the focus detection unit, and a focus adjustment unit that drives the photographing optical system to perform a focusing operation.

  The two-dimensional image sensor is constituted by a photometric two-dimensional image sensor (such as a photometric sensor) that measures the brightness of a subject image. The focus detection method selection unit may set either phase difference focus detection or contrast focus detection according to a setting operation by the user. It is also possible to provide a display control unit that displays a subject image in a live view on a display unit provided on the back of the camera based on a pixel signal output from the two-dimensional image sensor.

  Considering that phase-difference focus detection is impossible or difficult, the focus detection method selection unit switches from phase-difference focus detection to contrast focus detection in a state where phase-difference focus detection is set. Switching setting is possible.

  For example, the focus detection method selection unit switches from phase difference focus detection to contrast focus detection when the focus detection target area set in the subject image deviates from the focus detectable area of the ranging image sensor. Alternatively, the focus detection method selection unit shifts from the phase difference type focus detection to the contrast type focus detection when it is difficult or difficult to determine whether the phase difference type focus detection is performed, such as a subject having a high spatial frequency pattern. Can be switched.

  The focus detection method selection unit uses a contrast-type focus detection using a two-dimensional image sensor and a photographing image sensor that is arranged behind the camera with respect to the movable mirror and forms an image of subject light that has passed through the photographing optical system. Any one of the image sensor target controlled focus detections can be selected and set as the contrast focus detection.

  The focus detection unit performs contrast type focus detection based on the pixel signal read from the two-dimensional image sensor and image sensor target contrast type focus detection based on the pixel signal read from the imaging image sensor according to the set focus detection method. Do one. At this time, the focus detection method selection unit may move the movable mirror to the optical path retracted position.

  The display control unit can selectively perform live view display on the display unit of the subject image by the imaging imaging device or the subject image by the two-dimensional imaging device in accordance with the set contrast type focus detection method.

  An image pickup apparatus according to another aspect of the present invention is based on a two-dimensional image sensor on which subject light guided through an imaging optical system and guided to an optical finder is imaged, and a pixel signal read from the two-dimensional image sensor. A brightness detection unit that detects brightness and a focus detection unit that performs focus detection by a contrast method based on pixel signals read from the two-dimensional image sensor while the focus position is continuously changing.

  According to another aspect of the present invention, an imaging method includes subject light guided through an imaging optical system and guided to an optical finder to form an image on a two-dimensional image sensor, based on pixel signals read from the two-dimensional image sensor. The brightness is detected, and the focus detection by the contrast method is executed based on the pixel signal read from the two-dimensional image sensor while the focus position (lens position) is continuously changing.

  According to the present invention, AF processing can be performed by effectively applying contrast focus detection and phase difference focus detection.

It is a schematic internal block diagram of the digital camera which is 1st Embodiment. It is a block diagram of a digital camera. It is the figure which showed the focusing frame visually recognized through an optical finder. It is the figure which showed the focus detection range of the phase difference type distance measuring sensor. It is the figure which showed AF frame in a photometric sensor. It is the figure which showed the fractional focus area of the photometry sensor. It is a timing chart at the time of contrast type AF processing. It is a flowchart of AF processing. It is a subroutine of contrast type focus detection processing in Step S107 of FIG. It is a figure showing AF area display by live view display and AF area display by optical finder display. It is a figure showing AF area display by live view display and AF area display by optical viewfinder display when a face is detected.

  Below, the digital camera which is this embodiment is demonstrated with reference to drawings.

  FIG. 1 is a schematic internal configuration diagram of a digital camera according to the present embodiment.

  The digital camera 10 is a single-lens reflex camera in which a photographic lens (lens barrel) 11 that houses a photographic optical system 12 can be detachably attached to a main body 10B. The shooting mode, playback mode, and the like can be set. The photographing optical system 12 includes a zoom lens 12A, a diaphragm 12B, and a focus lens 12C.

  When the photographing mode is set with the power turned on, the reflected light from the subject passes through the photographing optical system 12, and a part thereof is guided toward the optical finder 15 by the quick return mirror (movable mirror) 19. . Part of the reflected light is transmitted through the quick return mirror 19 and guided to the AF sensor module 18 by the half mirror 17. The AF sensor module 18 includes a distance measuring sensor 18A corresponding to phase difference type focus detection, and the two-dimensional distance measuring sensor 18A is configured by an imaging element such as a CCD.

  The light incident on the focus plate 15E of the optical viewfinder 15 is reflected by the pentaprism 15A and the half mirror 15B, and is emitted from the eyepiece 15D via the focusing screen 15C. Thereby, the user can confirm the subject image through the eyepiece 15D. Further, part of the subject light transmitted through the half mirror 15B is guided to the photometric sensor (two-dimensional imaging device) 20A of the AE sensor module 20 disposed in the optical viewfinder 15, and the subject light is on the light receiving surface of the photometric sensor 20A. Is imaged.

  When a release button (not shown) is operated, a series of shooting operations are performed. That is, when the release button is half-pressed, AF processing, photometry, and exposure calculation processing are executed, and when the release button is fully pressed, the quick return mirror 19 is moved up, the diaphragm 12B is driven, and the shutter 13 is opened and closed. The subject light is imaged on the light receiving surface of the image sensor (imaging imaging device) 14.

  When the reproduction mode is set, the recorded image can be reproduced and displayed on the image LCD 60 installed on the back side of the main body 10B. In the photographing mode, a see-through image can be displayed as a moving image on the image LCD 60, and a subject image obtained by the image sensor 14 and the photometric sensor 20A can be displayed.

  When the menu setting mode is selected, the user can select and set either the contrast-type focus detection or the phase-difference focus detection as the focus detection method by an input operation. Furthermore, when contrast focus detection is set, an optical finder mode using the optical finder 15 and a live view display mode using the image LCD 60 can be selected and set as display modes during AF processing.

  FIG. 2 is a block diagram of the digital camera.

  The controller 30 including a CPU outputs a control signal to the exposure control unit 32, the finder LCD 33, the photographing lens driving unit 36, the image signal processing circuit 40, etc., and a release operation detected by the release switch 37, a mode dial switch 42 Based on a user input operation detected by the button switch 44 or the like, operation control of the entire camera such as exposure control, photographing / recording operation, reproduction display, and phase difference AF processing is performed. The camera operation control program is stored in a non-volatile memory (not shown).

  When the phase difference type focus detection is set as the focus detection method, the focus lens 12C is driven by the AF driver 34 based on the phase difference detected by the AF sensor module 18. When the defocus amount is calculated based on the pixel signal output from the AF sensor module 18, the movement direction and the drive amount along the optical axis of the focus lens 12C are obtained according to the defocus amount.

  The photometric sensor 20A is a two-dimensional sensor composed of a CCD or CMOS sensor, and a color filter array in which color elements of R, Gr, Gb, and B are arranged in a Bayer array is arranged in the photometric sensor 20A. . In the photometric sensor 20A, a pixel signal corresponding to a subject image visually recognized by the user through the optical finder 15 is output and sequentially sent to an image signal processing circuit 40 configured by a DSP (Digital Signal Processor) or the like.

  In the photometric sensor 20A, a plurality of divided photometric areas are defined, and a representative luminance value (such as an average value) is calculated in each divided photometric area. When the brightness of the subject area to be photographed is detected, the exposure control unit 32 calculates an exposure value such as a shutter speed and an aperture value, and the aperture 12B and the shutter 13 are driven and controlled based on the exposure value during the photographing operation. The

  The image signal processing circuit 40 calculates the luminance value of each of the divided photometry areas based on the G component pixel signal of the transmitted pixel signal, and obtains the brightness of the subject. On the other hand, in the case of live view display and photographing operation, a pixel signal corresponding to the subject image generated by the image sensor 14 is sent to the image signal processing circuit 40.

  When a photographing operation is performed, the image signal processing circuit 40 performs image signal processing such as white balance adjustment and color conversion processing on the pixel signal for one frame output from the image sensor 14 to generate image data. To do. The generated image data is temporarily stored in a memory (not shown) and recorded on the memory card 46 in a compressed or non-compressed state.

  On the other hand, when contrast type focus detection is set as the focus detection method, the image signal processing circuit 40 detects the brightness of the subject from the transmitted pixel signal, while performing contrast type focus detection based on the pixel signal. Do. A program relating to focus detection is stored in the ROM 48 in advance.

  Specifically, while the focus lens 12C is driven so that the focal position moves along any one of the proximity point to infinity (∞) and the infinity to the proximity point, the focal position changes continuously. Then, the brightness difference of the subject portion which is the AF processing target is calculated, and in-focus / in-focus determination is performed. Then, the position where the peak value of the luminance difference is detected is determined as the in-focus position, and the focus lens 12C is driven by the drive amount to the in-focus position. The controller 30 drives and controls the focus lens 12C during contrast focus detection.

  Next, the focus detection range of the distance measuring sensor 18A and the photometric sensor 20A will be described with reference to FIGS. 3A to 3D and FIG.

  FIG. 3A is a diagram showing a focusing frame visually recognized through the optical viewfinder. FIG. 3B is a diagram showing a focus detection range of the phase difference type distance measuring sensor 18A.

  When the user confirms the subject image with the optical viewfinder 15, the AF frame F0 is visually recognized. In the distance measuring sensor 18A, as shown in FIG. 3B, a fractional focusing area DT0 including 20 pixel blocks in the center and two pixel blocks in the left and right is set and visually recognized through the optical viewfinder 15 shown in FIG. 3A. Corresponds to the AF frame T0.

  FIG. 3C is a diagram showing an AF frame in the photometric sensor 20A. In the image area for one frame obtained from the photometric sensor 20A, an area having a length X along the horizontal direction and a length Y along the vertical direction around the image center point is defined as an AF frame F1. . However, X and Y represent ratios when the horizontal length and vertical length of the image data are set to 1. For example, X and Y are 0.4 and 0.3, respectively.

  FIG. 3D is a diagram showing a fractional focusing area of the photometric sensor 20A. The AF frame F1 indicates an area where a focusing operation based on the contrast / luminance difference is performed, and a plurality of (here 6 × 10) like the fractional focusing area DT0 defined for the phase difference AF sensor module 18. The fractional focus area DT1 is defined as the AF frame F1.

  Each fractional focus area is composed of pixel blocks having the same number of pixels as the fractional focus area defined for the distance measuring sensor 18A, and the pixel block is in a different section from the 16 × 16 divided photometry area at the time of photometry processing. Is configured. In the contrast AF process, a focusing operation can be performed in the AF frame F1, and the AF frame F1 is larger than the AF frame F0 in the distance measuring sensor 18A.

  FIG. 4 is a timing chart during contrast AF processing. The photometric sensor 20A sequentially reads pixel signals for one frame at 1/30 second intervals. After outputting the charge sweep pulse by the electronic shutter function, a pixel signal for one frame is generated by exposure in the exposure period ET.

  The drive pulse signal DS for driving the focus lens 12C is output in synchronization with the fall of the vertical synchronization signal VD. Focusing is repeatedly determined based on the pixel signal for one frame output from the photometric sensor 20A, and the drive pulse signal DS is output until the peak position is detected. The number of pulses of the drive pulse signal DS is determined based on the amount of extension of the focus lens 12C.

  The contrast AF process using the photometric sensor 20A and the phase difference AF process using the AF sensor module 18 can be selected by user settings as described above, and can be set and switched according to the shooting situation. Hereinafter, the AF process will be described with reference to FIGS.

  FIG. 5 is a flowchart of the AF process. FIG. 6 is a subroutine for contrast-type focus detection processing in step S107 of FIG. FIG. 7 is a diagram showing AF area display by live view display and AF area display by optical viewfinder display. In this case, a mode for displaying a subject image by the photometric sensor 20A in live view is set.

  When the release button is pressed halfway, it is determined which one of the contrast method and the phase difference method is set as the AF method (S101, S102). If it is determined that the contrast AF method has been selected and set, the process proceeds to step S107, and a contrast method AF process to be described later is executed. On the other hand, if the conventional phase difference AF method is set, the process proceeds to step S103.

  In step S103, an AF area preset by the user is detected. Then, in step S104, it is determined whether or not the detected AF area is out of the focus determination area in the phase difference AF. The AF area is composed of a predetermined number of fractional focus areas and defines a subject area to be an AF target. Here, the AF area is defined by four fractional focus areas.

  As shown in FIGS. 3B and 3D, the region where the focus determination can be made in the phase difference AF processing is narrower than the region determined in the contrast AF processing. Therefore, when the AF area set by the user exceeds the in-focus determination possible area of the phase difference AF, the mode is switched to the contrast AF method, and the process proceeds to step S107.

  As shown in FIG. 7, when the AF area T1 is switched from the image center position to the upper right direction by the position change of the cross mark CR representing the AF area T1 by the user, the AF area at that position is the phase difference type AF. The in-focus determination possible area is exceeded (see FIG. 3B). Therefore, the phase difference AF is switched to the contrast AF.

  In step S105, phase difference AF processing is executed. At this time, if the subject to be AF processed is a subject for which it is difficult to determine the focus in the case of phase difference AF processing, it is determined that focus detection is impossible, and the phase difference AF method is switched to the contrast AF method (S106). ).

  For example, in the case of a subject in which a pattern with a high spatial frequency is repeated, it is difficult to determine whether or not the subject is in focus in the phase difference AF process, so that the contrast AF method is switched. When the process proceeds to the contrast AF process in step S107, execution of the subroutine of FIG. 6 is started.

  In step S <b> 201, it is determined which one of the AF finder display method and the live view display method is set. In the case of the optical viewfinder display method using the photometric sensor 20A, the process proceeds to step S204, and AF area setting processing is executed. For example, when a face is detected within the AF target range shown in FIG. 3C, the AF area T2 is set (see FIG. 8). As described above, when the user selects a specific AF area T1, that area is set. In the default state without face detection and user setting, the entire AF frame F1 shown in FIG. 3C is set as the AF area T1.

  In step S205, the luminance difference between the maximum luminance value and the minimum luminance value in the AF area is sequentially calculated while driving the focus lens 12C in one direction. Then, a position where the luminance difference reaches a peak is detected. In step S206, the driving amount of the focus lens in the reverse direction is calculated with the peak position as the focal position.

  On the other hand, when the live view display method for performing contrast AF processing using the image sensor 14 is selected, the quick return mirror 19 is raised (S202), and the image sensor 14A is driven to use the photometric sensor 20A. The live view display is switched to the live view display using the image sensor 14 (S203). Then, based on the pixel signal of the subject image read from the image sensor 14, AF processing according to steps S204 to S206 is executed.

  When the driving amount of the focus lens 12C up to the focal position is determined, in the case of the optical finder display method, the subroutine ends as it is (S207). On the other hand, when the live view display method is selected, the quick return mirror 19 is lowered and switched to the live view display method using the photometric sensor 20A (S208, S209).

  In step S108 in FIG. 5, the focus lens 12C moves by a predetermined lens driving amount. In step S109, the focused AF area is displayed on the finder LCD 33 and the image LCD 60. In the optical finder display, the finder LCD 33 is driven to display a fractional focus area corresponding to the AF area T1 (four fractional focus areas dt in FIG. 7). Note that the brightness of the subject is detected based on the pixel signal read from the photometric sensor 20A in the focused state.

  As described above, according to the present embodiment, in the single-lens reflex digital camera 10 including the photometric sensor 20A and the distance measuring sensor 18A, the phase difference type focus detection using the distance measuring sensor 18A and the contrast using the photometric sensor 20A. Expression focus detection can be selectively performed by user settings. Even when the phase difference focus detection is set, when the subject characteristic and the subject area are difficult to determine the focus by the phase difference focus detection, the focus detection is switched to the contrast focus detection.

  By selectively setting the two focus detection methods, it is possible to set a focus detection method suitable for various shooting situations. Since contrast-type focus detection is performed using the photometric sensor 20A provided in association with exposure control, the parallax problem does not occur. Furthermore, it is possible for the user to check the focused subject image and its area using the optical viewfinder, and to perform contrast AF processing without a sense of incongruity while performing the same shooting operation as a conventional single-lens reflex camera. Can do. Further, since the photometric sensor 20A for detecting the brightness of the subject is used, there is no need to provide a new circuit such as an image sensor.

  In live view display, it is possible to selectively set the contrast AF processing using the photometric sensor 20A or the image sensor 14, and by using the image sensor 14 having a large number of pixels, more accurate focus detection can be performed. Can be performed. At this time, the live view display by the photometric sensor 20A and the live view display by the image sensor 14 can be switched continuously, so that the live view display is not interrupted.

  Note that it is possible to switch to phase difference focus detection in a state where contrast focus detection is set. For example, when it is assumed that the subject is at a long distance, it may be automatically switched to phase difference type focus detection.

  Contrast focus detection can be configured using only a photometric sensor. Further, a two-dimensional image sensor other than the photometric sensor may be separately provided in the vicinity of the optical finder, and the subject light guided to the optical finder may be imaged on the image sensor.

10 Digital Camera 12 Shooting Optical System 14 Image Sensor (Image Sensor for Shooting)
15 Optical Finder 18 AF Sensor Module 18A Distance Sensor (Image Sensor for Distance Measurement)
19 Quick return mirror (movable mirror)
20 AE sensor module 20A Photometric sensor (two-dimensional image sensor)
30 controller (focus adjustment unit, focus detection method selection unit)
40 Image signal processing circuit (focus detection unit, brightness detection unit, display control unit)
60 Image LCD (Display unit)

Claims (9)

A mirror that selectively guides the subject light that has passed through the photographing optical system to an optical finder and an image sensor for phase difference ranging;
A two-dimensional image sensor for photometry on which subject light guided to the optical finder is imaged;
A focus detection method selection unit that selects and sets one of a phase difference type focus detection using the distance measuring image sensor and a contrast type focus detection using the two-dimensional image sensor as a focus detection method;
According to the set focus detection method, either focus detection based on a phase difference method based on a pixel signal read from the ranging image sensor or focus detection based on a contrast method based on a pixel signal read from the two-dimensional image sensor A focus detection unit for executing
And a focus adjustment unit that drives the photographing optical system to perform a focusing operation.   2. The camera according to claim 1, wherein the focus detection method selection unit can be switched from phase difference focus detection to contrast focus detection in a state where phase difference focus detection is set. 3.   The focus detection method selection unit switches from phase difference focus detection to contrast focus detection when the focus detection target area set in the subject image deviates from the focus detectable area of the ranging image sensor. The camera according to claim 2.   4. The focus detection method selection unit switches from phase difference focus detection to contrast focus detection when focusing / non-focusing cannot be determined by phase difference focus detection. Camera described in.   5. The camera according to claim 1, wherein the focus detection method selection unit sets one of phase difference focus detection and contrast focus detection according to a setting operation by a user. An image sensor for photographing, which is disposed behind the camera with respect to the mirror and forms an image of subject light passing through the photographing optical system;
The focus detection method selection unit selects one of contrast focus detection using the two-dimensional image sensor and image sensor target controlled focus detection using the imaging image sensor as contrast focus detection. Set,
In accordance with the set focus detection method, the focus detection unit detects contrast based focus detection based on the pixel signal read from the two-dimensional image sensor, and image sensor target contrast type based on the pixel signal read from the imaging image sensor. 6. The camera according to claim 1, wherein any one of focus detection is executed. Based on the pixel signal output from the two-dimensional image sensor, further comprising a display control unit for live view display of the subject image on a display unit provided on the back of the camera,
The display control unit selectively displays a subject image by the imaging imaging device or a subject image by the two-dimensional imaging device on the display unit in a live view according to a set contrast type focus detection method. The camera according to claim 1. A two-dimensional image sensor for photometry on which subject light guided through an imaging optical system and guided to an optical viewfinder is imaged;
A brightness detection unit that detects the brightness of a subject based on pixel signals read from the two-dimensional image sensor;
An imaging apparatus comprising: a focus detection unit configured to perform focus detection by a contrast method based on a pixel signal read from the two-dimensional image sensor while a focal position is continuously changing. The subject light that has passed through the photographic optical system and led to the optical viewfinder is imaged on a two-dimensional image sensor for photometry,
Based on the pixel signal read from the two-dimensional image sensor, the brightness of the subject is detected,
An imaging method comprising: performing focus detection by a contrast method based on a pixel signal read from the two-dimensional image sensor while a focal position is continuously changing.

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