Patent Publication Number: US-9420161-B2

Title: Image-capturing apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an image-capturing apparatus. 
     BACKGROUND ART 
     Japanese Patent Laid-Open Publication No. 2011-15163 discloses an image-capturing apparatus that employs a system of depth From Defocus (DFD) method. This image-capturing apparatus implements a focus control that obtains plural defocusing, and includes an image-capturing device for capturing plural images defocusing differently from each other. The image-capturing apparatus then determine an object distance based on the plural images defocusing differently from each other. The image-capturing apparatus performs the focus control based on the determined object distance. 
     SUMMARY 
     An image-capturing apparatus is configured to capture an image of an object, an object. The image-capturing apparatus includes a focus lens, an image sensor configured to capture an object image of the object to produce image data, and a controller. The controller is operable to detect a speed at which the image-capturing apparatus is panned, and determine, in response to the detected speed, a control amount corresponding to a moving speed at which the controller moves the focus lens until causing the focus lens to focusing on a target object. 
     The image-capturing apparatus performs a convenient focusing operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a digital video camera in accordance with an exemplary embodiment for illustrating an electrical structure of the digital video camera. 
         FIG. 2  is a block diagram of the digital video camera in accordance with the embodiment for illustrating an operation of the digital video camera. 
         FIG. 3  is a schematic view of the operation of the digital video camera in accordance with the embodiment. 
         FIG. 4  is a schematic view of a DFD calculation executed by the digital video camera in accordance with the embodiment. 
         FIG. 5  is a zoom tracking table with respect to distances to plural object distances of the digital video camera in accordance with the embodiment. 
         FIG. 6  is a flowchart of the operation of the digital video camera in accordance with the embodiment. 
         FIG. 7  is a flowchart of an operation of the digital video camera in accordance with the embodiment. 
         FIGS. 8A to 8C  are schematic view of a screen of a display monitor of the digital video camera in accordance with the embodiment. 
         FIG. 9  is a schematic view of the digital video camera in accordance with the embodiment for illustrating an operation of calculating a lens moving speed of the digital video camera. 
     
    
    
     DETAIL DESCRIPTION OF PREFERRED EMBODIMENT 
     An exemplary embodiment of the present invention will be detailed below with reference to the accompanying drawings. An excessive description is omitted. For instance, a description of a well-known subject in a public domain is omitted, or a description of a similar element to that discussed previously is omitted for avoiding redundancy and facilitating an ordinary skilled person in the art to understand the present invention. 
     The inventor(s) provides the accompanying drawings and the description for the ordinary skilled person in the art to fully understand the disclosure, so that these materials may not limit the scope of the claims. 
     A number of methods for measuring an object distance, a distance from an image-capturing apparatus to an object includes a depth from Defocus (DFD) method that utilizes correlation values of defocusing amounts generated in image captured with a camera. In general, a defocusing amount is uniquely determined for each image-capturing apparatus in response to a relation between a focal position and the object distance. In the DFD method utilizing the above characteristics, two images having different defocus amounts are produced, and the object distance is measured based on a point-spread function (PSF) and a difference in the defocusing amounts. The image-capturing apparatus in accordance with this embodiment measures the object distance by utilizing the DFD calculation to perform an auto-focus control. 
     A structure and operation of the image-capturing apparatus in accordance with the embodiment will be described below. 
     1. Electrical Structure of Image-Capturing Apparatus 
       FIG. 1  is a block diagram of digital video camera  100 , an image-capturing apparatus in accordance with the embodiment, for illustrating an electrical structure of digital video camera  100 . Digital video camera  100  includes optical system  110  including at least one lens. Optical system  110  forms an object image on CMOS image sensor  140  by utilizing light from an object. The object image is captured with an image sensor, CMOS image sensor  140 . CMOS image sensor  140  produces image data based on the captured object image. The image data produced by CMOS image sensor  140  is converted into a digital signal with ADC  150 , and processed with image processor  160 . The digital signal is stored in memory card  200 . The structure of digital video camera  100  will be detailed below. 
     Optical system  110  in accordance with the embodiment includes zoom lens  111 , camera-shake correcting lens  112 , focus lens  113 , and iris  114 . Zoom lens  111  moves along optical axis  110 A to enlarge and reduce the object image. Focus lens  113  moves along optical axis  110 A to adjust a focus of the object image. Camera-shake correcting lens  112  is movable within a plane perpendicular to optical axis  110 A of optical system  110 . Camera-shake correcting lens  112  moves along a direction in which a shake of digital video camera  100  is cancelled as to reduce an influence caused by the shake of camera  100  on the captured image. Iris  114  has opening  114 A therein disposed on optical axis  110 A, and adjusts the size of opening  114 A automatically or according to a user&#39;s setting, so that iris  114  can adjust an amount of light transmitting through iris  114 . 
     Lens driver  120  includes a zoom actuator that drives zoom lens  111 , a camera-shake correcting actuator that drives camera-shake correcting lens  112 , a focus actuator that drives focus lens  113 , and an iris actuator that drives iris  114 . Lens driver  120  controls the zoom actuator, the camera-shake correcting actuator, the focus actuator, and the iris actuator. 
     CMOS image sensor  140  captures the object image formed by optical system  110 , and produces analog image data in form of an analog signal. Image sensor  140  performs various operations, such as exposure, transfer, and electronic shutter. 
     A/D converter  150  converts the analog image data produced by CMOS image sensor  140  into digital image data in form of a digital signal. 
     Image processor  160  processes the image data produced by CMOS image sensor  140  to produce image data to be displayed on monitor display  220  and to produce image data to be stored in memory card  200 . For instance, image processor  160  performs a gamma correction, a white-balance correction, and a flaw correction on the image data produced by CMOS image sensor  140 . Image processor  160  compresses the image data produced by CMOS image sensor  140  by a compression method in accordance with H.264 standard or MPEG2 standard. Image processor  160  may be implemented by a DSP or a microprocessor. 
     Controller  180  controls entire digital video camera  100 , and can be implemented by a semiconductor element. Controller  180  can be implemented by hardware, or by a combination of hardware and software. Controlled may be implemented by a microprocessor. 
     Buffer  170  functions as a working memory of image processor  160  and controller  180 , and can be implemented by, e.g. a DRAM or a ferroelectric memory. 
     Card slot  190  holds memory card  200  detachably, and is mechanically or electrically connectable to memory card  200 . Memory card  200  contains a flash memory or a ferroelectric memory therein, and stores data, such as an image file produced in image processor  160 . 
     Internal memory  240  is implemented by a flash memory or a ferroelectric memory, and stores a control program that controls entire digital video camera  100 . Internal memory  240  also stores point spread functions (PSFs). 
     Operational actuator  210  includes user interfaces, such as a cross key, an enter-button, for accepting operations by users. 
     Monitor display  220  has screen  220 A that displays thereon an image indicated by the image data produced by CMOS image sensor  140  and an image indicated by the image data read out from memory card  200 . Monitor display  220  displays various menus for setting functions of camera  100  on screen  220 A. Touch panel  220 B is disposed on screen  220 A. Touch panel  220 B is touched by a user for receiving various touch actions. An instruction entering through touch panel  220 B as a touch action is supplied to controller  180  to be processed. 
     Angular velocity sensor  250  detects an angular velocity produced in digital video camera  100  due to a camera shake. The angular velocity detected by sensor  250  is supplied to controller  180 . Controller  180  drives camera-shake correcting lens  112  to cancel a camera shake produced in digital video camera  100  due to the angular velocity. 
     2. Operations of Digital Video Camera  100   
     2-1. Auto-Focus Operations Utilizing a Result of the DFD Calculation 
     Digital video camera  100  performs an auto-focus operation utilizing a result of the DFD calculation.  FIG. 2  is a block diagram of digital video camera  100  for illustrating a control of the focus lens by utilizing the result of the DFD calculation. 
     DFD processor  161  is disposed in image processor  160 , and performs the DFD calculation to produce a depth map. To be more specific, DFD processor  161  uses two images: observed image PA and reference image PB having different defocusing amounts produced intentionally by changing focal positions. DFD processor  161  produces the depth map based on observed image PA, reference image PB, and point spread functions (PSFs). The depth map indicates object distances at respective ones of pixels of observed image PA (reference image PB). 
     Then, DFD processor  161  supplies the depth map to controller  180 . Controller  180  controls lens driver  120  as to drive focus lens  113  based on the depth map. 
     The DFD calculation performed by DFD processor  161  shown in  FIG. 2  and the determination of the object distance by controller  180  will be detailed below. 
     First, the DFD calculation performed by DFD processor  161  will be detailed.  FIG. 3  is a schematic view of focus lens  113  of digital video camera  100  in accordance with the embodiment for illustrating the movement of focus lens  113  for the DFD calculation. Controller  180  changes a focal position based on the DFD calculation to intentionally produce two images having different defocusing amounts. To be more specific, as shown in  FIG. 3 , controller  180  controls lens driver  120  to locate focus lens  113  at focusing position L 1  at time point t 1 . Similarly, focus lens  113  is located at focusing position L 2  different from focusing position L 1  at time point t 2 . CMOS image sensor  140  captures an image of the object when focus lens  113  is positioned at focusing position L 1  for producing observed image PA. Similarly, image sensor  140  captures the image of the object when focus lens  113  is positioned at focusing position L 2  for producing reference image PB. Although being produced by capturing the same object, images PA and PB have defocusing amounts different from each other due to different positions of focus lens  113  for the capturing. 
       FIG. 4  is a schematic view for illustrating the calculation of the object distance by utilizing the DFD calculation performed by digital video camera  100  in accordance with the embodiment. DFD processor  161  performs the DFD calculation on observed pixels SA constituting observed image PA and reference pixels SB constituting reference image PB to determine the distances from respective ones of pixels SA (SB). DFD processor  161  produces plural observed pixels CA by convolutions of plural PSFs with observed pixels SA. DFD processor  161  compares plural observed pixels CA with reference pixels SB located at the same coordinates as pixels CA on the image. The above operation will be detailed below. 
     A point spread function (PSF) indicates a response to a point light source of an optical system, and indicates a change in a defocusing amount. A convolution of the PSF with an image corresponding to a combination of point light sources can intentionally produce a defocused image. According to the embodiment, a large number of point spread functions corresponding to a large number of distances to an object are previously provided in internal memory  240 . Controller  180  separates distances to an object into sixteen steps, namely from the closest point to the farthest point, and selects sixteen point spread functions PSF 1  to PSF 16  corresponding to the sixteen steps out of the large number of point spread functions stored in memory  240 . Controller  180  then supplies selected point spread functions PSF 1  to PSF 16  to DFD processor  161 . 
     DFD processor  161  performs convolutions of point spread functions PSF 1  to PSF 16  with observed pixels SA as to produce sixteen observed pixels CA 1  to CA 16  corresponding to the object distances at respective ones of observed pixel SA. Since observed pixels CA 1  to CA 16  have point spread functions different from each other for convolution, observed pixels CA 1  to CA 16  form different defocused images. 
     DFD processor  161  then compares observed pixels CA 1  to CA 16  with reference pixel SB, and selects observed pixel CAn that has the smallest difference from reference pixel SB among observed pixels CA 1  to CA 16 . DFD processor  161  determines the object distance corresponding to the point spread function for convolution producing observed pixel CAn as the distance to the object at observed pixel SA. For instance, if the difference between observed pixel CA 3  and reference pixel SB is smaller than differences between reference pixel SB and each of other observed pixels CA 1  to CA 2 , CA 4  to CA 16 , then, DFD processor  161  determines that an object distance corresponding to point spread function PSF 3  for convolution with observed pixel SA to produce observed pixel CA 3  is the object distance at observed pixel SA. DFD processor  161  outputs distance data corresponding to the determined object distance. 
     DFD processor  161  performs the above operation on each observed pixels PA and reference pixels PB as to produce a depth map plotting respective object distances at the pixels. According to the embodiment, since sixteen point spread functions corresponding to distances to the object are used, the depth map exhibits sixteens levels of the object distances. 
     Next, based on the object distance determined by the DFD calculation, controller  180  determines an in-focus position to which focus lens  113  is to move. To be more specific, controller  180  refers to a tracking table for calculating the in-focus position based on the determined object distance as well as a current position of focus lens  111 .  FIG. 5  is the zoom tracking table for plural object distances of digital video camera  100  in accordance with the embodiment. As shown in  FIG. 5 , profiles DM 1  to DM 4  indicate in-focus positions corresponding to a position of zoom lens  111  for typical distances DL to an object (1 m, 2 m, 3 m, and infinite shown in  FIG. 5 ). Controller  180  can calculate in-focus positions for object distances other than the typical object distances DL by interpolation to the profiles shown in  FIG. 5  with respect to the object distances. 
     Controller  180  determines the in-focus position based on the calculated object distance and the zoom tracking table, and controls lens controller  120  to move focus lens  113  to the in-focus position as to cause focus lens  113  to focus on the object. 
     2-2. Control of Focus Lens  113  in Response to Panning 
     Controller  180  can determine, based on an output from angular velocity sensor  250 , whether or not a user pans digital video camera  100 . Controller  180  can detect a panning speed by calculating the output from angular velocity sensor  250 . The determination of the panning and the panning speed are not limited to the use of the output from angular velocity sensor  250 . For instance, controller  180  detects a moving object in an image captured by CMOS image sensor  140  or uses another method, thereby determining whether or not camera  100  is panned, and detecting a panning speed. 
     The user captures images of objects with digital video camera  100  while panning camera  100  right and left directions.  FIG. 6  is a schematic view of digital video camera  100  and objects A 1 , A 2 , A 3  located on image-capturing directions D 1  that agree with optical axis  110 A shown in  FIG. 1  while being panned  FIG. 7  is a flowchart of calculating a lens moving speed of focus lens  113  that follows the panning of digital video camera  100 .  FIGS. 8A to 8C  are schematic view of screen  220 A of display monitor  220  while camera  100  is panned. 
     As shown in  FIG. 6 , objects A 1 , A 2 , and A 3  are located at different distances from camera  100 . The user pans digital video camera  100  to right direction R 1 , so that a state of capturing object A 1  changes to a state of capturing object A 3  via a state of capturing object A 3  in the frame. At this moment, digital video camera  100  controls focus lens  113  such that a focusing speed at which object A 1 , A 2 , A 3  is focused on can be adjusted in accordance with the panning speed. 
     As shown in  FIG. 7 , the user starts panning camera  100  when camera is ready to capture an object (step S 301 ). At this moment, controller  180  starts calculating the panning speed of camera  100  based on a change in the output from angular velocity sensor  250 . 
     During the panning, the user selects target object A 2 , which is a focusing target, from through-images displayed on screen  220 A of display monitor  220  (step S 302 ). In screen  220 A shown in  FIG. 8A , object image PA 1  of object A 1  is captured. From this state, digital video camera  100  is panned to right direction R 1 , and then, object image PA 2  of object A 2  appears in screen  220 A. At this moment, the user selects target object A 2  (i.e. the focusing target) from a through-image by, for instance, operating touch-panel  220 B disposed on screen  220 A with a finger. 
     Controller  180  obtains position F 1  of focus lens  113  (step S 303 ). The position F 1  is an in-focus position at a certain time point when target object A 2  is selected by the user. Controller  180  then obtains an object distance from digital video camera  100  to target object A 2  by the DFD calculation (step S 304 ). Controller  180  obtains a focal distance that is determined based on a position of zoom lens  111  at the certain time point when target object A 2  is selected by the user. Controller  180  then calculates a half-picture angle α (degree) in a horizontal direction by using dimension d in the horizontal direction of CMOS image sensor  140  and the obtained focal distance f by Formula 1. 
     
       
         
           
             
               
                 
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     Controller  180  detects the position, in the horizontal direction, of the image of object A 2  displayed on screen  220 A.  FIG. 9  shows an operation of calculating a lens moving speed of focus lens  113  in accordance with the panning. In  FIG. 9 , screen  220 A of display monitor  220  is a form of 180 pixels in the vertical direction) by 1980 pixels in the horizontal direction. Image-capturing direction D 1  of camera  100  corresponds to a predetermined position in screen  220 A. According to this embodiment, the predetermined position is center P 1  of screen  220 A. As shown in  FIG. 9 , position P 2 , in the horizontal direction, of the image of selected object A 2  on screen  220 A is away from center P 1  toward the right by 420 pixels in the horizontal direction. Angle θ (degree) between position P 2  and center P 1  is expressed by Formula 2. 
     
       
         
           
             
               
                 
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     A necessary duration τ (seconds) for the image of object A 2  to move to center P 1  of screen  220 A is calculated by using angle θ and panning speed β (deg/sec) in Formula 3. 
     
       
         
           
             
               
                 
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     Controller  180  refers to the zoom tracking curve for obtaining position F 2  of focus lens  113  at an object distance to object A 2 . Controller  180  thus can calculate, by using duration τ, a lens moving speed at which focus lens  113  moves during the panning, and positions F 1  and F 2  of focus lens  113  (step S 306 ). Controller  180  moves focus lens  113  at the calculated lens moving speed at the certain time point during the panning (step S 307 ). Object A 2  is not in focus at the certain time point when the user selects target object A 2 ; however, while the image capturing apparatus is panned to right direction R 1 , when target object A 2  is positioned in image-capturing direction D 1  from digital video camera  100  during this panning, the image of target object A 2  is located at center P 1  of screen  220 A as shown in  FIG. 8C  and is focused on. 
     3. Advantage 
     As discussed above, the image capturing apparatus, i.e., digital video camera  100 ), in accordance with the embodiment includes focus lens  113 , an image sensor, i.e., CMOS image sensor  140  that captures an object image formed through focus lens  113  for producing image data, and controller  180 . Controller  180  detects a panning speed. Controller  180  determines the lens moving speed of the focus lens based on the detected panning speed. To be more specific, controller  180  determines the moving speed of focus lens  113  in response to the panning speed detected at the certain time point when object A 2  is selected during the panning. 
     In other words, the image capturing apparatus, i.e., digital video camera  100  in accordance with this embodiment includes focus lens  113 , an image sensor, i.e., CMOS image sensor  140  configured to capture an object image of the object to produce image data, and controller  180 . Controller  180  is operable to detect a speed at which the image-capturing apparatus is panned. Controller  180  is operable to determine, in response to the detected speed, a control amount corresponding to a moving speed at which the controller moves the focus lens until causing the focus lens to focusing on a target object. 
     The control amount may be the lens moving speed of focus lens  113 . In this case, controller  180  moves focus lens  113  at the lens moving speed, thereby causing focus lens  113  to focus on target object A 2 . 
     The above structure allows digital video camera  100  to focus on target object A 2  in accordance with the panning speed of camera  100  panned by the user. Digital video camera  100  thus focuses on object A 2  in accordance with the panning speed at which the user pans camera  100 , so that camera  100  can focus on object A 2  while camera  100  is panned according to a framing policy of the user. As a result, an ordinary user of digital video camera  100  can track a transition of object A 2  easily like a professional cameraman practices. 
     Controller  180  may be operable to cause CMOS image sensor  140  to capture object image PA 2  of target object A 2  at a certain time point while digital video camera  100  is panned, to detect a position of object image PA 2  on the screen  220 A at the certain time point, to obtain a certain focusing position (position F 1 ) of focus lens  113  at the certain time point, and to determine the control amount based on the detected position of object image PA 2 , the certain focusing position (position F 1 ), and the detected speed β. 
     Controller  180  may be operable to cause CMOS image sensor  140  to capture object image PA 2  of target object A 2  at a certain time point while digital video camera  100  is panned, to detect an object distance to the target object A 2  at the certain time point, to obtain a certain focusing position (position F 1 ) of the focus lens  113  at the certain time point, and to determine the control amount based on the certain focusing position (position F 1 ), the object distance, and the detected speed β. 
     Target object A 2  may be selected at the certain time point by touching screen  220 A. 
     4. Other Embodiments 
     In the above embodiment, an example of a technique disclosed in this patent application is described; however, the technique disclosed in this application is not limited to the above embodiment and is applicable to other embodiments with a change, replacement, supplement, or omission. The structural elements described in the embodiment can be combined for establishing a new embodiment. 
     An example of embodiments will be described below. 
     According to the above embodiment, the point spread functions are stored in internal memory  240 ; however, the present invention is not limited to this structure, for instance, the point spread functions may be stored in a memory of image processor  160 . Digital video camera  100  in accordance with the above embodiment selects sixteen point spread functions; however, the number of the selected point spread functions may be larger than sixteen or smaller than sixteen in response to the number of levels of the depth map. 
     The image-capturing apparatus in accordance with the above embodiment is a digital video camera. The lens of this camera cannot be replaced; however, the camera is not limited to this structure, and the present invention is applicable to a digital video camera with a replaceable lens. 
     In the above embodiment, examples of the technique disclosed in the present invention are described with accompanying drawings and detailed descriptions. The structural elements in the drawings or the detailed descriptions include not only elements essential for problems to be solved but also other elements necessary for detailing the examples but not necessary for solving the problems. Although these elements not necessary for solving the problems are described here, they should not be construed as essential elements for the problems to be solved. 
     The above embodiments only describe examples of the technique disclosed in the present invention, so that various changes, replacements, supplements, or omissions are allowed in the scope of claims described later or an equivalent scope thereto. 
     The image-capturing apparatus of the present invention is applicable to digital video cameras, digital still cameras, portable-phones with camera function, or smart-phones with camera function.