Abstract:
An imager is provided having an imaging sensor, a pupil divider and a display. The imaging sensor photographs a subject image obtained through a photographing lens, and outputs image data. The pupil divider has shutters positioned in a light path between the photographing lens and the imaging sensor. The display displays an image using the image data photographed by the imaging sensor. The shutters periodically blocks part of the light path. The imaging sensor outputs multiple image data by photographing a subject image passing through a light path that is not blocked by the shutters. The display displays multiple image data that is compensated for shifts between subject images in the multiple image data.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an imager equipped with an imaging sensor that captures an image using a pupil-dividing auto focus mechanism. 
         [0003]    2. Description of the Related Art 
         [0004]    A well-known imager provides a pupil divider between a photographing lens and an imaging sensor to open and close a light path, and determines whether a subject image is in focus by comparing images passing through different light paths. The pupil divider comprises a liquid crystal shutter array that divides the light path from the photographing lens to the imaging sensor. The subject images passing through different light paths are formed on the same position of the imaging sensor when the photographing lens is focused accurately, but they are not formed on the same position when the photographing lens is not properly focused. Japanese Unexamined Patent Publication No. H06-175015 discloses an imager that exhibits on a display a through image photographed by an imaging sensor. 
         [0005]    In the case that such an imager displays through images comprising images that have passed through different paths, the subject images arriving through different optical paths overlap with one another when the photographing lens is not accurately focused. Therefore, the displayed through image is unsightly. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to provide an imager that has a pupil-dividing auto focus mechanism and displays a through image so that the subject images do not overlap when the photographing lens is not accurately focused. 
         [0007]    An imager is provided having an imaging sensor, a pupil divider and a display. The imaging sensor photographs a subject image obtained through a photographing lens, and outputs image data. The pupil divider has shutters positioned in a light path between the photographing lens and the imaging sensor. The display displays an image using the image data photographed by the imaging sensor. The shutters periodically blocks part of the light path. The imaging sensor outputs multiple image data by photographing a subject image passing through a light path that is not blocked by the shutters. The display displays multiple image data that is compensated for shifts between subject images in the multiple image data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The objects and advantages of the present invention will be better understood from the following description, with references to the accompanying drawings in which: 
           [0009]      FIG. 1  is a perspective view of an imager as seen from a rear surface according to the present embodiment; 
           [0010]      FIG. 2  is a block diagram of the imager; 
           [0011]      FIG. 3  is a perspective view of a pupil divider; 
           [0012]      FIG. 4  shows a light path when the photographing lens is not accurately focused; 
           [0013]      FIG. 5  shows a light path when the photographing lens is not accurately focused; 
           [0014]      FIG. 6  shows overlapping subject images; 
           [0015]      FIG. 7  is a flowchart of a preparation process; 
           [0016]      FIG. 8  shows subject images for which an overlap has been rectified; 
           [0017]      FIG. 9  is a flowchart of a display process; and 
           [0018]      FIG. 10  shows subject images for which an overlap has been rectified by the display process. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The present invention is described below with references to the embodiment shown in the drawings. 
         [0020]      FIG. 1  shows a digital camera  100  that is an imager according to the first embodiment. For example, the digital camera  100  is a single-lens reflex camera. 
         [0021]    The digital camera  100  is equipped with a main power switch  111  that activates and deactivates a main power source, a release button  112 , a LCD monitor  114 , a card slot  116 , and a photographing lens  121  that projects from the front surface of the digital camera. The main power switch  111  and the release button  112  manipulate an operation switch  110 . 
         [0022]    The main power switch  111  is a momentary switch projecting from the back surface of the digital camera  100 . The digital camera is powered on when a user depresses the main power switch  111 . In the case that a user depresses the main power switch  111  while the digital camera  100  is powered, the digital camera  100  is powered off. 
         [0023]    The release button  112  is a two-step momentary switch provided on the top of the digital camera  100 . In the case that a user depresses the release button  112  halfway, the digital camera carries out photometry and distance surveying processes. In the case that a user fully depresses the release button  112 , the digital camera captures an image. 
         [0024]    The LCD monitor  114  is rectangular-shaped with the same 3:4 aspect ratio as a photographed image. As illustrated in  FIG. 1 , it is a rectangle of which the long sides extend in the longitudinal direction of the digital camera  100 , and it is provided near the center on the back surface of the digital camera  100 . It displays a through image and an image obtained through the photographing lens  121 , a photographed image, and configuration settings of the digital camera  100 . 
         [0025]    Certain components provided in the digital camera are described with reference to  FIG. 2 . The digital camera  100  mainly comprises a DSP  131  that controls the operation of the digital camera  100 , an operation switch  110  that is used for operating the digital camera  100 , an imaging unit  120  that converts a subject image to a digital image signal, a memory  132  that stores data sent from the DSP  131 , a SD card  133  that stores a photographed image, the LCD monitor  114 , a pupil divider  126  that divides the light path from the photographing lens  121 , a liquid crystal driver  127  that drives the pupil divider  126 , a photographing lens  121 , and a lens driver  122  that drives the photographing lens  121 . 
         [0026]    The imaging unit  120  mainly comprises an imaging sensor  124  and an AFE (Analog Front End)  125 . 
         [0027]    The imaging sensor  124  comprises a CCD or CMOS, and has an imaging area that converts an incoming subject image to an analog image signal. The photographing lens  121  focuses a subject image on the imaging area of the imaging sensor  124 . The imaging area is rectangular-shaped, and is configured in the digital camera  100  so that the long side of the imaging area is coincident with the direction from right to left of  FIG. 1  and the short side of the imaging area is coincident with the direction from top to bottom of  FIG. 1 . 
         [0028]    The imaging sensor  124  converts a subject image formed on the imaging area to an analog image signal, and sends it to the AFE  125 . The AFE  125  converts an analog image signal to a digital image signal after adjusting the gain of the analog image signal, and then sends the digital image signal to the DSP  131 . 
         [0029]    The pupil divider  126 , which has a first liquid crystal shutter  126   a  and a second liquid crystal shutter  126   b , is provided in the light path of the photographing lens  121  and blocks the light path to the imaging sensor  124 . The first liquid crystal shutter  126   a  and second liquid crystal shutter  126   b  are aligned in the horizontal direction, i.e. in the transversal direction of the digital camera  100 . When the photographing lens  121  is seen from the imaging sensor  124 , the first liquid crystal shutter  126   a  is provided in the right half of the light path, and the second liquid crystal shutter  126   b  is provided in the left half of the light path. The first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  divide the light path in two. The first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  each comprise liquid crystal. When the liquid crystal driver  127  applies voltage to them, they block the light path. When the DSP  131  sends a switching signal to the liquid crystal driver  127 , the liquid crystal driver  127  applies voltage to the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b . The first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  alternatingly shield the light path. That is, when the first liquid crystal shutter  126   a  opens the light path the second liquid crystal shutter  126   b  blocks the light path, and when the first liquid crystal shutter  126   a  blocks the light path the second liquid crystal shutter  126   b  opens the light path. 
         [0030]    Before imaging, the DSP  131  carries out photometry processing of a subject using the quantity of light from the subject image that is included in the digital image signal. It calculates an exposure value using the photometry value, and then calculates the shutter speed and aperture value that are used in photographing. Afterward, a photograph is taken based on the calculated shutter speed and aperture value. 
         [0031]    The DSP  131  executes a phase difference AF process. The phase difference AF process focuses the photographing lens  121  on a subject using the pupil divider  126 . More precisely, the DSP drives the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  so as to alternatingly block the light path per a predetermined cycle. When the first liquid crystal shutter  126   a  opens the light path, light passes through the first liquid crystal shutter  126   a  and strikes the imaging sensor  124  (refer to  FIG. 4 ). Similarly, when the second liquid crystal shutter  126   b  opens the light path, light passes through the second liquid crystal shutter  126   b  and strikes the imaging sensor  124  (refer to  FIG. 5 ). When a subject image is focused on the imaging sensor  124 , a subject image passing through the first liquid crystal shutter  126   a  and a subject image passing through the second liquid crystal shutter  126   b  correspond to each other on the imaging surface  124 . The DSP  131  processes a digital image signal received from the AFE  125  and drives the photographing lens  121  to focus a subject image on the imaging sensor  124 , so that a subject image passing through the first liquid crystal shutter  126   a  and a subject image passing through the second liquid crystal shutter  126   b  correspond to each other on the imaging surface  124 . After the photographing lens  121  is focused on a subject, the DSP  131  executes an AF lock, which locks in place the focusing optical system of the photographing lens  121 . 
         [0032]    After receiving a digital image signal from the AFE  125 , the DSP  131  processes the digital image signal and creates frame image data, which contains the data of one frame of an image. The frame image data is displayed on the LCD monitor  114  as a through image. 
         [0033]    During photographing the DSP  131  processes the received digital image signal and creates frame image data that contains the data of one frame of a captured image. The frame image data is stored in the SD card  133  and displayed on the LCD monitor  114 . The memory  132  is used as a working memory where intermediate data is temporarily stored while the DSP  131  carries out image processing. 
         [0034]    The SD card  133  is detachably stored in the card slot  116  provided on the side surface of the digital camera  100 . A user can change a SD card  133  by accessing the card slot  116  from the exterior of the digital camera  100 . 
         [0035]    In the case that the photographing lens  121  is focused on a subject with the pupil divider  126 , a subject image passing through the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  reach the imaging sensor  124  on an alternating basis. Therefore, when the photographing lens  121  is not accurately focused, subject images that are not in focus will appear as overlapping double images on the imaging sensor  124 . That is, In the case that the LCD monitor  114  displays a through image, the subject images that are not in focus are displayed as overlapping double images on the imaging sensor  124  (refer to  FIG. 6 ). It causes an unsightly image to be displayed and gives a user the impression that the digital camera  100  is broken. To prevent the display of such a degraded image, the process described hereinafter is performed. 
         [0036]    A preparation process is described hereinafter with reference to  FIG. 7 . The preparation process begins with the DSP  131  when the release button  112  is depressed halfway. 
         [0037]    In Step S 701 , a determination is made as to whether or not the photographing lens  121  is under the AF lock condition. In the case that the AF lock is in effect, the process proceeds to Step S 702  and the AF procedures, etc. in Steps S 703  to S 705  are not carried out because the photographing lens  121  is regarded as already being focused on a subject. 
         [0038]    In Step S 702 , the DSP  131  sends signal to the liquid crystal driver  127  for the pupil divider  126  to open the light path. The pupil divider  126  then opens the light path. After that, the process proceeds to Step S 706 . 
         [0039]    In the case that the AF lock is not in effect, the AF procedures, etc. in Steps S 703  to S 705  are carried out because the photographing lens  121  is not regarded as being focused on a subject. 
         [0040]    In Step S 703 , the DSP  131  sends a signal to the liquid crystal driver  127  for the pupil divider  126  to repetitively block and unblock the light path. The pupil divider  126  then repetitively blocks and unblocks the light path. 
         [0041]    Next in Step S 704 , the phase difference AF process is carried out. At the same time the phase difference AF process is carried out, the display process in Step S 705  and actual display on the monitor in Step S 706  are performed concurrently. 
         [0042]    A subject image is not in focus on the imaging sensor  124  while the display process in Step S 705  and actual display on the monitor in Step S 706  are performed. To prevent an overlapping double image of the subject from being displayed on the LCD monitor  114 , the display area of the LCD monitor  114  is divided in two so that a left side area and a right side area are created, where the left side area displays an image passing through the first liquid crystal shutter  126   a  while the right side area displays an image passing through the second liquid crystal shutter  126   b  (refer to  FIG. 8 ). Thereby, an overlapping double image of a subject is not displayed on the LCD monitor  114 . 
         [0043]    In Step S 707 , whether or not the release button  112  is depressed halfway is determined. In the case that it is not depressed halfway, the process ends. In the case that it is depressed halfway, the process proceeds to Step S 708 . 
         [0044]    In Step S 708 , whether or not the release button  112  is fully depressed is determined. In the case that it is not fully depressed, the process returns to Step S 701 . In the case that it is fully depressed, the process proceeds to Step S 709 . 
         [0045]    In Step S 709 , the DSP  131  sends a signal to the liquid crystal driver  127  for the pupil divider  126  to open the light path. The pupil divider  126  then opens the light path. Afterward, the process proceeds to Step S 710 . 
         [0046]    In Step S 710 , a subject is photographed by conducting the release process, and the photographed image data is stored in the SD card  133 . Afterward, the process ends. 
         [0047]    According to the embodiment, a through image is not displayed as an overlapping double image on the LCD monitor  114  while a subject is photographed using the pupil dividing auto focus mechanism. 
         [0048]    Note that, in the display process of Step S 705  and actual display on the monitor in Step S 706 , the display area of the LCD monitor  114  need not be divided in two areas, the display area may instead display either one of the images passing through the first liquid crystal shutter  126   a  or the second liquid crystal shutter  126   b . Thereby, a through image is not displayed as an overlapping double image on the LCD monitor  114 . 
         [0049]    Note that, in the display process of Step S 705  and the actual display on the monitor in Step S 706  the display area of the LCD monitor  114  need not be divided in two areas, the display area may instead display an image that is created from either the addition or average of the pixels that form an image passing through the first liquid crystal shutter  126   a  or the second liquid crystal shutter  126   b.    
         [0050]    The second embodiment according to the invention is described with references to  FIGS. 9 and 10 . The constructions of the second embodiment that are similar to the first embodiment have the same numeral applied and their descriptions have been omitted. 
         [0051]    In the second embodiment the display process is different from that of the first embodiment. Hereinafter, the display process is described with respect to the second embodiment. 
         [0052]    In Step S 901 , the DSP  131  calculates a shift length, which is the length on the imaging sensor  124  between the subject image passing through the first liquid crystal shutter  126   a  and the subject image passing through the second liquid crystal shutter  126   b . For example, the shift length is calculated for the image in the central portion of the imaging sensor  124 . As shown in  FIG. 6 , when subject images do not coincide on the imaging sensor  124 , the length between these images is defined as the shift length. 
         [0053]    In Step S 902 , a subject image passing through the first liquid crystal shutter  126   a  is shifted by one-half of the shift length in the right direction. Then, a subject image passing through the second liquid crystal shutter  126   b  is shifted by one-half of the shift length in the left direction. 
         [0054]    In Step S 903 , the two shifted images are added or averaged. Afterward, the added image or the averaged image is displayed on the LCD  114  in Step S 706  of the preparation process (refer to  FIG. 10 ). The addition or average calculations are based on every pixel. Thereby, a through image is not displayed as an overlapping double image on the LCD monitor  114 . 
         [0055]    According to the second embodiment, a through image is not displayed as an overlapping double image on the LCD monitor  114 , and the displayed position of the subject image is approximately the same as the position of a focused subject image on the LCD monitor  114  when the subject is photographed using the pupil dividing auto focus mechanism. 
         [0056]    An additional advantage of the embodiment is a faster focusing speed that uses the pupil-dividing auto focus mechanism to display a through image where subject images are not displayed as overlapping double images on the LCD monitor  114 , because a subject that is photographed using the pupil-dividing auto focus mechanism has a faster focusing speed than the contrast AF process. 
         [0057]    In the case that the reading period (frame rate) of the imaging sensor  124  is increased, the photographed image might darken because charging time is shortened and the amount of light received by the imaging sensor  124  is reduced accordingly. However, the darkened photographed image can be prevented by carrying out the additional procedure of Step S 903 . 
         [0058]    Note that, in the case of using the pupil dividing auto focus mechanism, the frame rate of the imaging sensor  124  may be increased. For example, the frame rate may be doubled from 30 fps to 60 fps. Therefore, a through image is smoothly displayed on the LCD monitor  114  without awkward movement. 
         [0059]    In Step S 902 , the subject images passing through the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  need not both be shifted, instead only one of either one of the subject images may be shifted by the shift length. 
         [0060]    Step S 903  need not be processed, instead any one of the subject images passing through the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  may be shifted by the shift length, and the shifted subject image and the unshifted subject image are displayed alternatingly on the LCD monitor  114 . 
         [0061]    The liquid crystal driver  127  may enable light to pass by applying voltage to the first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b.    
         [0062]    The first liquid crystal shutter  126   a  and the second liquid crystal shutter  126   b  need not be limited to a shutter having a liquid crystal, and may instead be a shutter having a shutter curtain. 
         [0063]    Although the embodiment of the present invention has been described herein with references to the accompanying drawings, obviously many modifications and changes may be made by those skilled in the art without departing from the scope of the invention. 
         [0064]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2009-143439 (filed on Jun. 16, 2009), which is expressly incorporated herein, by reference, in its entirety.