Patent Publication Number: US-2011069156-A1

Title: Three-dimensional image pickup apparatus and method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a three-dimensional image pickup apparatus and method. More particularly, the present invention relates to a three-dimensional image pickup apparatus and method in which it is possible reliably to photograph an object which moves at a high speed and simultaneous is framed in a telephoto setting. 
     2. Description Related to the Prior Art 
     A three-dimensional camera or three-dimensional image pickup apparatus is known. A first camera unit and a second camera unit pick up images of an object simultaneously. The images with parallax are combined to obtain a three-dimensional image. An example of the three-dimensional camera is described in the following websites. 
     http://www.fujifilm.co.jp/corporate/news/article/ffnr0226.html 
     http://www.fujifilm.com/photokina2008/pdf/release/finepix_real3d_e.pdf 
     An LCD display panel on a rear surface of the three-dimensional camera displays first and second images for being viewed discretely by eyes of a viewer. The viewer can observe the three-dimensional image according to the plural images photographed by the three-dimensional camera autostereoscopically without specific eyewear. 
     In JP-A 9-005643, a three-dimensional endoscope as the three-dimensional camera is disclosed. The first camera unit has a wide-angle first lens system with a small first focal length. The second camera unit has a second lens system of a normal angle of view with a great second focal length. The first and second camera units pick up images of common the object. An image processor corrects the first image from the first camera unit for an equivalent angle of view after the second camera unit of the normal angle of view in an apparent manner. A second image from the second camera unit and the corrected image are combined with one another, viewed by the viewer&#39;s eyes, to photograph the object stereoscopically. In the endoscope, the first camera unit of the wide-angle setting is used at first for image pickup of a large area for searching the object. Then the second camera unit of the normal angle of view is used together for detailed observation, so that a small area in the body cavity is enlarged for three-dimensional image pickup. 
     U.S. Pat. No. 7,701,491 (corresponding to JP-A 2006-211489) discloses the three-dimensional camera for obtaining plural images at one time with a difference in the angle of view. It is possible with the three-dimensional camera to obtaining a first image without trimming and a second image of a telephoto view according partial trimming of the first image. 
     There is a special scene in which the object moves very quickly and is followed for image pickup in a telephoto setting. If a user is rather unskilled, the object abruptly comes out of a viewing area of the three-dimensional camera when he or she depresses the shutter. It is likely that the object is missed in the image pickup in spite of his or her intention. There may be great importance of image pickup of the object even from a scene with high difficulty in photographing the object. 
     In JP-A 9-005643, the image pickup can be changed over between the two-dimensional image mode of a wide-angle setting and the three-dimensional image mode of the normal angle of view in a telephoto setting. If a user wishes to keep an image of the object, possibility of photographing the object in a viewing area will be high upon changeover to the two-dimensional image mode of the wide-angle setting. However, the object may be incidentally missed from the viewing area even after attempt of photographing the object in the three-dimensional image mode of the normal angle of view in the telephoto setting. Such a problem cannot be prevented reliably. 
     In U.S. P. No. 7,701,491 (corresponding to JP-A 2006-211489), images handled for display of live images are stored. Should the object be missed from an image of a telephoto setting according to the trimming, there is possibility of presence of the object in an image without trimming according to handling for live images. However, the images for live images are field images having only considerably low image quality in comparison with frame images which are generally used for main image pickup. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, an object of the present invention is to provide a three-dimensional image pickup apparatus and method in which it is possible reliably to photograph an object which moves at a high speed and simultaneous is framed in a telephoto setting. 
     In order to achieve the above and other objects and advantages of this invention, a three-dimensional image pickup apparatus is provided, and includes first and second camera units for receiving entry of object light, and for picking up first and second images with parallax simultaneously. First and second lens systems are incorporated in respectively the first and second camera units, and have a focal length changeable in a zooming range for zooming. A focal length adjusting device changes the focal length of the second lens system toward a wider-angle side than the focal length of the first lens system. A processor forms a third image from the second image with an angle of view equal to an angle of view of the first image. A three-dimensional image processor produces a three-dimensional image from the first and third images. There is a medium controller for storage processing of the first, second and third images, or the first and second images and a value of the focal length upon picking up the first image. 
     The processor forms the third image by trimming of the second image. 
     The focal length adjusting device enlarges a lens moving distance for zooming the second lens system toward a wide-angle side according to zooming of the first lens system toward a telephoto end position. 
     The zooming range is equal between the first and second lens systems. The focal length adjusting device, if the first lens system is in a wide-angle end position in the zooming range, sets the second lens system in a wide-angle end position, and if the first lens system is deviated from the wide-angle end position, sets the second lens system nearer to the wide-angle end position than the first lens system. 
     Furthermore, a number input device inputs a pixel number of pixels of an image for storage processing with the medium controller, to change a lens moving distance for zooming the second lens system toward a wide-angle side according to the pixel number. 
     Furthermore, a principal object detector detects a principal object from the first image, to change a lens moving distance for zooming the second lens system toward a wide-angle side if the principal object is in a first condition. 
     The first condition is at least one selected from a group including a condition in which the principal object is positioned at an end of the first image, a condition of the principal object with motion, and a condition in which an object distance of the principal object is equal to or smaller than a predetermined distance. 
     Also, a three-dimensional image pickup method is provided, and includes a step of picking up first and second images with parallax simultaneously by use of first and second camera units including respectively first and second lens systems of which a focal length is changeable in a zooming range for zooming. The focal length of the second lens system is changed toward a wider-angle side than the focal length of the first lens system. A third image is formed from the second image with an angle of view equal to an angle of view of the first image. A three-dimensional image is produced from the first and third images. The first, second and third images are written to a storage medium, or the first and second images and a value of the focal length upon picking up the first image are written to a storage medium. 
     The third image is formed by trimming of the second image. 
     In the changing step for the focal length, a lens moving distance for zooming the second lens system toward a wide-angle side is enlarged according to zooming of the first lens system toward a telephoto end position. 
     The zooming range is equal between the first and second lens systems. In the changing step for the focal length, if the first lens system is in a wide-angle end position in the zooming range, the second lens system is set in a wide-angle end position, and if the first lens system is deviated from the wide-angle end position, the second lens system is set nearer to the wide-angle end position than the first lens system. 
     Furthermore, there is a step of determining a pixel number of pixels of an image in the storing step, to change a lens moving distance for zooming the second lens system toward a wide-angle side according to the pixel number. 
     Furthermore, there is a step of detecting a principal object from the first image, to change a lens moving distance for zooming the second lens system toward a wide-angle side if the principal object is in a first condition. 
     The first condition is at least one selected from a group including a condition in which the principal object is positioned at an end of the first image, a condition of the principal object with motion, and a condition in which an object distance of the principal object is equal to or smaller than a predetermined distance. 
     Also, a computer executable program for three-dimensional image pickup is provided, and includes a program code for picking up first and second images with parallax simultaneously by use of first and second camera units including respectively first and second lens systems of which a focal length is changeable in a zooming range for zooming. A program code is for changing the focal length of the second lens system toward a wider-angle side than the focal length of the first lens system. A program code is for forming a third image from the second image with an angle of view equal to an angle of view of the first image. A program code is for producing a three-dimensional image from the first and third images. A program code is for writing the first, second and third images to a storage medium, or the first and second images and a value of the focal length upon picking up the first image to a storage medium. 
     Also, a user interface for three-dimensional image pickup is provided, and includes a region for picking up first and second images with parallax simultaneously by use of first and second camera units including respectively first and second lens systems of which a focal length is changeable in a zooming range for zooming. A region is for changing the focal length of the second lens system toward a wider-angle side than the focal length of the first lens system. A region is for forming a third image from the second image with an angle of view equal to an angle of view of the first image. A region is for producing a three-dimensional image from the first and third images. A region is for writing the first, second and third images to a storage medium, or the first and second images and a value of the focal length upon picking up the first image to a storage medium. 
     Consequently, it is possible reliably to photograph an object which moves at a high speed and simultaneous is framed in a telephoto setting, because the use of the third image formed by wide-angle setting of the second lens system can cause enhanced viewing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating a three-dimensional camera; 
         FIG. 2  is a perspective view illustrating the three-dimensional camera; 
         FIG. 3A  is an explanatory view illustrating right and left eye images; 
         FIG. 3B  is an explanatory view illustrating a state of viewing the images of  FIG. 3A  to clarify stereoscopy; 
         FIG. 4  is a block diagram schematically illustrating the three-dimensional camera; 
         FIG. 5  is a flow chart illustrating a sequence in a three-dimensional still image mode; 
         FIG. 6A  is an explanatory view illustrating a first image formed through the first lens system in a wide-angle setting; 
         FIG. 6B  is an explanatory view illustrating lens movement of the lens groups in the second lens system at the time of  FIG. 6A ; and 
         FIGS. 7A and 7B  are explanatory views illustrating lens movement of the lens groups in the second lens system in a telephoto setting; 
         FIG. 8  is a block diagram schematically illustrating a second preferred three-dimensional camera; 
         FIG. 9  is a flow chart illustrating a sequence in the three-dimensional still image mode; 
         FIG. 10A  is an explanatory view illustrating a first image formed through the first lens system in a state of a large number of pixels; 
         FIG. 10B  is an explanatory view illustrating lens movement of the lens groups in the second lens system at the time of  FIG. 10A ; 
         FIGS. 11A and 11B  are explanatory views illustrating lens movement of the lens groups in the second lens system in a state of a small number of pixels; 
         FIG. 12  is a block diagram schematically illustrating a third preferred three-dimensional camera; 
         FIG. 13  is a flow chart illustrating a sequence in the three-dimensional still image mode; 
         FIG. 14A  is an explanatory view illustrating a first image formed through the first lens system in presence of the object at the center; 
         FIG. 14B  is an explanatory view illustrating lens movement of the lens groups in the second lens system at the time of  FIG. 14A ; and 
         FIGS. 15A and 15B  are explanatory views illustrating lens movement of the lens groups in the second lens system in presence of the object at a frame end. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION 
     In  FIG. 1 , a three-dimensional camera  10  or stereoscopic camera is illustrated. A camera body  11  of the three-dimensional camera  10  has a front surface. There are a first camera unit  12 , a second camera unit  13 , and a flash light source  14  arranged on the front surface. The first and second camera units  12  and  13  are arranged to set their optical axes parallel with one another. A shutter button  15  and a power switch  16  are disposed on an upper side of the camera body  11 . 
     In  FIG. 2 , an LCD or display panel  18  and an input panel  19  are disposed on a rear surface of the camera body  11 . A card slot (not shown) is disposed on a lower surface of the camera body  11 . A memory card  20  as storage medium is removably loaded in the card slot. A lid is disposed to close a lower opening of the card slot. 
     In the three-dimensional camera  10 , the first and second camera units  12  and  13  pick up images of one object from points with a small distance, and with parallax. The display panel  18  is used to reproduce and display the two images for a viewer&#39;s eyes to view those in a discrete manner. Thus, a three-dimensional image is displayed for the viewer. 
     In  FIGS. 3A and 3B , a view of a three-dimensional image on the display panel  18  is illustrated. In  FIG. 3A , right and left eye images  21 L and  21 R are depicted. In  FIG. 3B , a state of the view is depicted. Right and left eyes  22 L and  22 R of the viewer view the images. A display surface  23  of the display panel  18  displays the right and left eye images  21 L and  21 R in a combined manner. In  FIG. 3A , an object  24  or object A appears in the right eye image  21 R. In  FIG. 3B , an object  25  or object A appears in the left eye image  21 L. In  FIG. 3B , a position of the object A is deviated at an amount of the parallax. Lines of eye gaze of the viewer cross over one another at a point in front of the display surface  23 . An image of the object A apparently protrudes forwards to give a stereoscopic form. 
     To clarify the description of a three-dimensional image, the right and left eye images  21 L and  21 R have one viewing area. Namely, a magnification of zooming is equal between the first and second camera units  12  and  13 . In the embodiment, a viewing area of the second camera unit  13  is set larger than a viewing area of the first camera unit  12  (zoomed toward the wide-angle side). A viewing area of the first camera unit  12  is retrieved by trimming from a viewing area of the second camera unit  13  to form right and left images for stereoscopy. Even when an object is missed from the viewing area of the first camera unit  12 , probability of presence of the object in a viewing area with the second camera unit  13  is increased, to prevent missing of the object in the two-dimensional image. The two-dimensional image has a sufficiently high image quality, because of image data of a frame image for recording instead of image data of a field image for use as a live image. 
     During standby for image pickup, the display panel  18  is an electronic viewfinder for displaying a live image of a three-dimensional or two-dimensional form. For the reproduction, the display panel  18  displays an image two or three-dimensionally according to image data stored in the memory card  20 . 
     The input panel  19  includes a mode designation switch  26 , a menu button  27 , a cross shaped key  28  and a start key  29 . The mode designation switch  26  is operable for changing over the operation modes of the three-dimensional camera  10 . The operation modes include a two-dimensional still image mode, a two-dimensional moving image mode, a three-dimensional still image mode, a three-dimensional moving image mode and a reproduction mode. In the two-dimensional still image mode, a two-dimensional still image is picked up. In the two-dimensional moving image mode, a two-dimensional moving image is picked up. In the three-dimensional still image mode, a three-dimensional still image is picked up. In the three-dimensional moving image mode, a three-dimensional moving image is picked up. In the reproduction mode, any of the images obtained by image pickup is displayed on the display panel  18 . In a default status directly after turning on the power switch  16 , the three-dimensional still image mode is set. 
     The menu button  27  is operated to display information on the display panel  18 , such as a menu screen and input screen. The cross shaped key  28  is operated to zoom the first and second camera units  12  and  13  and to move a cursor displayed in the menu screen and input screen. The start key  29  is depressed to confirm a condition or mode set in the camera. 
     In  FIG. 4 , circuit elements in the three-dimensional camera  10  are illustrated. A CPU  30  operates in response to input signals from the shutter button  15  and the input panel  19 . A ROM  31  stores various programs and data. The CPU  30  reads the programs and data, and controls the circuit elements entirely by running the programs. A look-up table memory  32  or LUT is connected to the CPU  30  as described later. A flash control unit  33  is connected with the CPU  30  and controls the flash light source  14 . 
     A data bus  35  connects various elements to the CPU  30 . The elements include an input controller  37 , a signal processor  38 , an AF evaluator  39 , an AE/AWB evaluator  40 , an SDRAM  41 , a VRAM  42 , a trimming processor  44  as processor for a third image, a compressor/expander  45 , a medium controller  46  and a display control unit  47  as three-dimensional image processor. Also, the first and second camera units  12  and  13 , the shutter button  15 , the input panel  19 , the ROM  31 , the look-up table memory  32  and the flash control unit  33  are connected to the CPU  30 . 
     The shutter button  15  is a two step switch, and depressible at two levels by half depression and full depression. In the still image mode, the shutter button  15  is depressed halfway to perform tasks required for image pickup, for example, AE (auto exposure) control, AF (autofocus) control, AWB (automatic white balance) control, and the like. When the shutter button  15  is depressed fully, a still image is picked up and stored. In the moving image mode, the shutter button  15  is depressed fully to start recording a moving image. When the shutter button  15  is depressed fully again, the image pickup of the moving image is terminated. 
     The first camera unit  12  includes a first lens system  52 , a CCD image sensor  53  and an AFE or analog front end  54 . Lenses/lens groups  51  as focal length adjusting device are incorporated in the first lens system  52  as a zoom lens system of which a focal length is changeable in a zoom range. Also, an MOS image sensor may be used instead of the CCD image sensor. 
     The first lens system  52  includes various elements, such as the lens groups  51 , a zoom mechanism, focusing mechanism, aperture stop device and the like. The zoom mechanism drives the lens groups  51  for zooming. A focal length of the lens groups  51  is fed back to the CPU  30 . The focusing mechanism moves the focus lens in the lens groups  51  for adjusting the focus. The aperture stop device adjusts a diameter of its opening to adjust strength of object light incident on the CCD image sensor  53 . A lens driver  55  is controlled by the CPU  30  to actuate the zoom mechanism, the focusing mechanism and the aperture stop device. 
     The CCD image sensor  53  converts object light from the lens groups  51  into an image signal as an output. A CCD driver  56  is connected with the CCD image sensor  53 , and controlled by the CPU  30 . A timing generator  57  or TG generates a sync pulse with which the CCD driver  56  is driven, and controls charge storing time and transfer timing of charge reading of the CCD image sensor  53 . 
     An image signal generated by the CCD image sensor  53  is input to the analog front end  54 . The analog front end  54  includes a correlated double sampling circuit, an automatic gain control circuit, and an A/D converter. When the sync pulse is generated by the timing generator  57 , responsively the analog front end  54  operates in synchronism with transfer in the CCD image sensor  53  in charge reading. The correlated double sampling circuit eliminates noise from the image signal. The automatic gain control circuit amplifiers the image signal at an input gain according to sensitivity determined by the CPU  30 . The A/D converter converts the image signal of the analog form from the automatic gain control circuit into a first image signal of a digital form, which is input to the input controller  37 . 
     The second camera unit  13  is structurally equal to the first camera unit  12 , and includes a second lens system  62 , a CCD image sensor  63 , an AFE or analog front end  64 , a lens driver  65 , a CCD driver  66  and a timing generator  67  or TG. Lenses/lens groups  61  as focal length adjusting device are incorporated in the second lens system  62  in the same manner as the lens groups  51 . A second image signal is output by the analog front end  64  to the input controller  37 . 
     In the second camera unit  13 , the CPU  30  obtains the focal length of the lens groups  51  fed back from the first lens system  52 , and zooms the lens groups  61  in the second camera unit  13  at a focal length which is on a wider-angle side than the obtained focal length. The distance of the zooming changes according to the focal length of the lens groups  51 . A difference of the focal length of the lens groups  61  from that of the lens groups  51 , when the zoom position of the lens groups  51  is on the wide-angle side, is set small, and when the zoom position of the lens groups  51  is on the telephoto side, is set large. 
     For the image pickup on the telephoto side, the viewing area of the second camera unit  13  is set larger than the viewing area of the first camera unit  12  for enhanced viewing, which increases probability of presence of an object within the viewing area of the second camera unit  13  even upon missing of the object from the viewing area of the first camera unit  12 . However, when the lens groups  51  are set in the wide-angle end position (shortest focal length), the lens groups  61  are also set equally with the lens groups  51 , because the focal length of the lens groups  61  cannot be changed toward the wide-angle side in comparison with the shortest focal length of the lens groups  51 , and because there is low probability in missing of an object from the viewing area in the image pickup of the wide-angle end position (widest angle side). A relationship between focal lengths of the lens groups  51  and  61  is stored in the look-up table memory  32 , and is read by the CPU  30  for suitable situations. 
     The input controller  37  has a buffer with a predetermined capacity, and stores first and second images signals output by the first and second camera units  12  and  13 . Directly after the power switch  16  is turned on or upon halfway depression of the shutter button  15  for display of a live image, the input controller  37  sends the image signals of one field of storing to the signal processor  38 . When the shutter button  15  is depressed fully for recording by image pickup, the input controller  37  sends first and second signals of one frame being stored to the signal processor  38 . 
     The signal processor  38  processes the first and second image signals from the input controller  37  for various processing functions such as gradation conversion, white balance correction, gamma correction, Y-C conversion and the like, to form first and second image data corresponding to images of one field or one frame. The first and second image data are written to the VRAM  42 . 
     The AF evaluator  39  determines an AF evaluation value of information of the contrast for each of the first and second images according to the first and second image signals from the input controller  37 . The CPU  30  controls the lens drivers  55  and  65  according to the AF evaluation value from the AF evaluator  39  to adjust focus of the lens groups  51  and  61 . 
     The AE/AWB evaluator  40  detects object brightness and determines a WB evaluation value for use in the white balance correction in accordance with the first and second image signals. The CPU  30  controls the lens drivers  55  and  65  and the CCD drivers  56  and  66  according to information of the object brightness from the AE/AWB evaluator  40  to control the exposure. Also, the CPU  30  controls the signal processor  38  to optimize the white balance of an object according to the WB evaluation value from the AE/AWB evaluator  40 . 
     The trimming processor  44  is controlled by the CPU  30  and reads second image data from the VRAM  42 , to retrieve a third image from the second image at an area equal to that of the first image. Details of the retrieval will be described later. 
     For a main sequence of image pickup, the compressor/expander  45  compresses image data stored in the SDRAM  41 , the image data including the first and second image data, and the third image data produced by trimming of the second image data, to produce the first, second and third compressed image data of a predetermined file format. If the angle of view is set according to the wide-angle end position, the third image data is equal to the second image data. 
     The first, second and third compressed image data are written by the medium controller  46  to the memory card  20 . To reproduce images, the compressor/expander  45  expands the first, second and third compressed image data from the memory card  20 , to create first, second and third uncompressed image data. The medium controller  46  accesses the memory card  20  to write and read image data. 
     The display control unit  47  processes the first and third image data from the VRAM  42 , or uncompressed form of the first and third image data expanded by the compressor/expander  45 , to form a signal for image display by signal processing. The signal is output to the display panel  18  in a preset sequence. Thus, the first and third images are displayed on the display panel  18  in a three-dimensional still image mode as a default mode. A user can view a three-dimensional live image. 
     The operation of the three-dimensional camera  10  is described by referring to  FIGS. 5-7B . At first, the power switch  16  is operated to turn on the power source of the three-dimensional camera  10 . In a default state immediately after powering, the three-dimensional still image mode is set in the three-dimensional camera  10 . The first and second camera units  12  and  13  start picking up a live image. 
     When horizontal bars in the cross shaped key  28  are depressed for zooming, the first lens system  52  of the first camera unit  12  is controlled to change the focal length of the lens groups  51 . The focal length is fed back to the CPU  30  from the first lens system  52 . See the step st 1 . 
     The CPU  30  refers to the look-up table memory  32  according to the focal length of the lens groups  51  output by the first lens system  52 , and controls the second lens system  62  in the second camera unit  13  to set the lens groups  61  at a focal length of a wider-angle side than the lens groups  51 . See the step st 2 . 
     When the lens groups  51  are zoomed to the wide-angle side, likeliness of missing of an object  72  from a frame  74  is considerably low, the object  72  being present in a first image  71 L (of a field image) output by the first camera unit  12 . Thus, the focal length of the lens groups  61  becomes shorter toward the wide-angle side than that of the lens groups  51 . In  FIG. 6B , a second image  71 R (of a field image) output by the second camera unit  13  has a region slightly greater than the first image  71 L. 
     Image data of the first and second images  71 L and  71 R as field images output by the first and second camera units  12  and  13  in synchronism are input to the input controller  37 , processed by the signal processor  38  for various functions of signal processing, and written to the VRAM  42  in the step st 3 . 
     The trimming processor  44  reads image data of the second image  71 R output by the second camera unit  13 . The second image  71 R is processed for trimming in a trimming area or crop area  75  (indicated by the broken line) according to the first image  71 L. Image data of a third image  71 R′ (of a field image) is obtained and written to the VRAM  42 . See the step st 4 . 
     Image data of the first and third images  71 L and  71 R′ are read from the VRAM  42 , and output by the display control unit  47  to the display panel  18 . As there is parallax between the first and third images  71 L and  71 R′, a three-dimensional live image can be seen on the display panel  18 . See the step st 5 . 
     When the input panel  19  is left to stand without manual touch for a predetermined time, for example one minute, the display panel  18  is turned to an energy saving mode of display and comes not to display a live image. A user can depress the shutter button  15  halfway for the display panel  18  to restart displaying the live image again. 
     A first image  77 L is output by the first camera unit  12  as a field image. See  FIG. 7A . When the lens groups  51  are zoomed to the telephoto side, an object  78  in the first image  77 L is very likely to extend outside the frame  74 . The likeliness is specifically high if motion of the object  78  is quick. Thus, a focal length of the lens groups  61  is changed considerably to the wider-angle side than the focal length of the lens groups  51 . In  FIG. 73 , a second image  77 R as a field image is output by the second camera unit  13 , and covers a larger area than the first image  77 L. 
     The image data of the first and second images  77 L and  77 R output by the first and second camera units  12  and  13  in synchronism are input by the input controller  37 , processed by the signal processor  38  for various functions of signal processing, and written to the VRAM  42 . See the step st 3 . 
     Image data of the second image  77 R is read by the trimming processor  44 . A trimming area or crop area  79  is determined to correspond to a viewing area of the first image  77 L. The image data of the second image  77 R is processed by trimming with the trimming area  79 . A third image  77 R′ is obtained as a field image, of which image data is written to the VRAM  42 . See the step st 4 . The third image on the telephoto side has a high magnification of enlargement. So image data having passed through a low-pass filter is used because a component of high frequency should be treated as noise. 
     The image data of the first and third images  77 L and  77 R′ are read from the VRAM  42 , and output by the display control unit  47  to the display panel  18 . A user can view a three-dimensional live image on the display panel  18  at the step st 5  because of parallax between the first and third images  77 L and  77 R′. 
     He or she views the object  78  on the display panel  18 , and depresses the shutter button  15  fully at the step st 6 . Image data of first and second images as frame images output by the first and second camera units  12  and  13  in synchronism are sent through the input controller  37  and the signal processor  38  and written to the SDRAM  41 . See the step st 7 . 
     The trimming processor  44  reads the second image from the SDRAM  41 , processes the second image for trimming in a trimming area according to a viewing area of the first image, to produce image data of a third image, and outputs the image data to the SDRAM  41 . See the step st 8 . The first, second and third images are compressed as one image file in a predetermined file format by the compressor/expander  45 . The medium controller  46  writes the image file to the memory card  20  in the step st 9 . 
     The images may be stored in a different manner. For example, information of a tab can be created to associate the images with one another before storing in the memory card  20 . Also, it is possible in the memory card  20  to store a set of the first and second images and a focal length of the lens groups  51  at the time of image pickup of the first image instead of the first to third images. To reproduce a three-dimensional image, the second image is processed by trimming according to the focal length of the lens groups  51  to form the third image. 
     The shutter button  15  is depressed after zooming the lens groups  51  on the telephoto side. It is likely upon the depression of the shutter button  15  that the object  78  moves abruptly and becomes missed from a viewing area for a first image. Even though the object  78  is not present in an area viewable for a three-dimensional image, it is probable that an object  78 ′ is present in a viewing area for a second image from the second camera unit  13  in a two-dimensional form (frame image). 
     Even if the object  78  has not been photographed as a three-dimensional image, it is probable to keep an image of the object  78 ′ as two-dimensional image, and to prevent unwanted missing of the object  78  in image pickup. The two-dimensional image, according to image data of a frame image, has a sufficiently high image quality. 
     In the two-dimensional still image mode, the first image from the first camera unit  12  is a main image. The second image from the second camera unit  13  synchronized with the first camera unit  12  is an auxiliary image. The main and subsidiary images are written to the memory card  20 . Except for the setting of the wide-angle end position (widest angle side), an area in the subsidiary image is always wider than that in the main image. This is effective in enhanced viewing, as it is highly probable that an object missed in the main image may be present in the subsidiary image. 
     A sequence in the three-dimensional moving image mode is similar to the three-dimensional still image mode. Image data of a three-dimensional moving image at a magnification set by a user is stored in the memory card  20 . Also, image data of a two-dimensional moving image from the second camera unit  13  upon image pickup with a greater angle of view than the three-dimensional moving image is stored in the memory card  20  in association with the three-dimensional moving image. Consequently, it is probable that an object is present in the two-dimensional moving image even after missing in the three-dimensional moving image. 
     In  FIG. 8 , a second preferred three-dimensional camera  80  or stereoscopic camera is illustrated. The three-dimensional camera  80  is characterized in that a change amount of the angle of view of an image for enhanced viewing (second image) is changed according to the number of pixels for an image to be written to the memory card  20 . 
     For the three-dimensional camera  80 , the three-dimensional camera  10  is repeated except for having a number input device  81  for inputting an active pixel number, and a look-up table memory  82  or LUT in  FIG. 18 . The number input device  81  sets the number of pixels to the input panel  19 . The look-up table memory  82  is instead of the look-up table memory  32 . Elements similar to those of the first embodiment are designated with reference numerals. 
     According to the data in the look-up table memory  82 , a lens moving distance for shift of an angle of view of the second image toward the wide-angle side becomes larger than a lens moving distance for shift of the angle of view of the first image according to zooming of the first image toward the telephoto side. This is the same as the condition of the first embodiment. However, the number of pixels is set smaller to lower the image quality relatively. Even if an enlargement factor is increased by increasing the ratio of the trimming, only small influence occurs to the drop of the image quality. In the present embodiment, a lens moving distance for shift of an angle of view of the second image toward the wide-angle side according to zooming of the first image toward the telephoto side is determined by referring to smallness of the input number of pixels, at a higher level than that according to the first embodiment, so as to increase probability of presence of an object within the second image. Note that a plurality of predetermined values of pixel numbers are stored and selectively designated. However, an adjusting structure can be incorporated for a user to determine a pixel number in a predetermined range. 
     He or she selects one of plural numbers of pixels before start. See the step st 11 . If he or she does not determine the number, a default number of pixels preset in the three-dimensional camera  80  is used. See the step st 12 . Note that signs st 11  and the like correspond to the signs st 11  and others in the flow chart of  FIG. 9 . Steps similar to those of the above embodiment are designated with identical signs or numbers. 
     When the user selects a high number as a pixel number for a relatively high resolution, a first image  83 L of  FIG. 10A  is obtained from the first camera unit  12 . A second image  83 R of  FIG. 10B  is obtained from the second camera unit  13 . A lens moving distance for zooming of the second image  83 R from the angle of view of the first image  83 L to the wide-angle side is set smaller. See the step st 13 . Thus, there occurs small drop in resolution of an enlarged third image  83 R′ according to a trimming area or crop area  84  in the second image  83 R. A three-dimensional image observable on the display panel  18  with simultaneous display of the first and third images  83 L and  83 R′ can have a high image quality with high resolution. 
     When the user selects a low number as a pixel number for a relatively low resolution, a first image  85 L of  FIG. 11A  is obtained from the first camera unit  12 . A second image  85 R of  FIG. 11B  is obtained from the second camera unit  13 . A lens moving distance for zooming of the second image  85 R from the angle of view of the first image  85 L to the wide-angle side is set larger. See the step st 13 . A viewing area of the second image  85 R can be still larger, and increases possibility of presence of the object  78  in the second image  85 R even after missing from the first image  85 L. Thus, there occurs considerable drop in resolution of an enlarged third image  85 R′ according to a trimming area or crop area  86  in the second image  85 R. However, there is no conspicuous drop in the resolution of a three-dimensional image displayed on the display panel  18  with the first and third images  85 L and  85 R′, because resolution of the first image  85 L is low. 
     In  FIG. 12 , a third preferred three-dimensional camera  87  or stereoscopic camera is illustrated. An offset amount of the angle of view of a second image as an image for enhanced viewing is changed according to a condition of a principal object. The condition is likeliness of coming away of a principal object from an viewing area. Specifically, the condition is nearness of the principal object to a frame end of the viewing area, or location of the principal object within a near distance as small as 2 meters from the three-dimensional camera  87 , or quick motion of the principal object. 
     For the three-dimensional camera  87 , the three-dimensional camera  10  is repeated except for having a principal object detector  88  and a look-up table memory  89 . The principal object detector  88  detects a principal object from a viewing area of framing. The look-up table memory  89  is used in place of the look-up table memory  32 . 
     A first image  91 L is obtained by the first camera unit  12  in  FIG. 14A . The principal object detector  88  detects a face  92   a  from the first image  91 L, and determines a principal object  92  according to the face  92   a  in the step st 21 . If plural faces are detected in the first image  91 L, one of those with a largest area is regarded as the principal object  92 . Note that signs st 21  and the like correspond to the signs st 21  and others in the flowchart of  FIG. 13 . Steps similar to those of the above embodiment are designated with identical signs or numbers. 
     For the face detection, candidate pixels of flesh color are extracted from all of the pixels in each image. The extracted pixels are combined to obtain flesh color portions in the image. The flesh color portions are compared with template information of a face according to a known technique of pattern recognition, and are evaluated for presence or absence of a face according to a result of the comparison. Furthermore, an area of the flesh color portions is compared to a threshold area. If the area is equal to or more than the threshold area, the flesh color portions are determined as a face. Also, a known technique of pattern recognition can be used to extracting eyes, a mouth or other specific parts of a face are extracted for the face detection. 
     Then the CPU  30  evaluates the condition of the principal object  92 . In  FIG. 14A , the principal object  92  does not shift in the presence at the center of the first image  91 L. The CPU  30  refers to the look-up table memory  89 , and changes the focal length of the lens groups  61  slightly farther toward the wide-angle side than the focal length of the lens groups  51  to set the lens groups  61 . See the step st 22 . Thus, a second image  91 R is obtained from the second camera unit  13  as illustrated in  FIG. 14B . A third image  91 R′ from a trimming area or crop area  93  in the second image  91 R has a low enlargement factor, has small degradation, so that a three-dimensional image of a high quality can be viewed. 
     In  FIG. 15A , a first image  95 L is illustrated. The principal object  92  is present near to an end of the first image  95 L. It is likely that the principal object  92  is missed from the area of the first image  95 L. Thus, the CPU  30  refers to the look-up table memory  89  and changes the focal length of the lens groups  61  to a considerably wider-angle side than that of the lens groups  51 . See the step st 22 . 
     Also, when the principal object  92  is moving or is located at a very near distance, the focal length of the lens groups  61  is changed toward the wider-angle side than the that of the lens groups  51 . An active or inactive state of motion of the principal object  92  can be found according to a position of the principal object  92  in a plurality of successive frames of a live image. For a location of the principal object  92  at a very near distance or within a distance of 2 meters, an output from the AF evaluator  39  can be checked for the evaluation. 
     In  FIG. 15B , a second image  95 R is obtained by the second camera unit  13  at a sufficiently larger angle of view than the first image  95 L. It is very probable that the principal object  92  is present in the second image  95 R even if the principal object  92  moves slightly or if a camera shake occurs with a user&#39;s hand. The display panel  18  displays the first image  95 L and an enlarged third image  95 R′ according to a trimming area  96  of the second image  95 R, so that he or she can view a three-dimensional image of the principal object  92 . 
     Also, it is possible in the present embodiment to add the structure for changing a lens moving distance for a shift of the focal length of the lens groups  61  toward the wide-angle side according to the focal length of the lens groups  51  of the first embodiment. It is also possible in the present embodiment to add the structure of the second embodiment for setting the number of pixels. 
     In the above embodiments, the first, second and third images are written to the memory card irrespective of presence of the principal object in the first, second and third images. Furthermore, it is possible to check whether a principal object is present in each of the first, second and third images by use of a principal object detection device with the CPU. For example, if the principal object is present in the second image but not present in the first and third images constituting a three-dimensional image, then it is possible to delete the first and third images and store only the second image in the memory card. Also, it is possible to check whether a principal object is present in each of the first, second and third images before writing to a memory card, and to store only images in presence of the principal object (for example, second image) in the memory card. 
     In the above embodiments, the second camera unit is constructed equally with the first camera unit. When the lens system of the first camera unit is zoomed to the wide-angle end position (widest angle side), the lens system of the second camera unit is also zoomed to the wide-angle end position. However, the second camera unit can be a type of which the lens system can be zoomed to the wider-angle side than that in the first camera unit. The lens system in the second camera unit can be moved to the wider-angle side than the wide-angle end position of the lens system in the first camera unit. Possibility of photographing an object missed from the first camera unit with the second camera unit can be increased. 
     Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein.