Patent Publication Number: US-2006008264-A1

Title: Image taking apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATON  
      This application is based on Japanese Patent Application No. 2004-199512 filed in Japan on Jul. 6, 2004, the entire content of which is hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image taking apparatus having an automatic focusing function.  
      2. Description of the Related Art  
      A digital camera has conventionally been known that uses, for focus adjustment, a focus adjustment area fixed in a central part of the captured image. Moreover, a digital camera has been used that is provided with a plurality of focus adjustment modes including a focus adjustment mode in which the position of the focus adjustment area is movable, in order to enable precise focusing on a specific subject.  
      However, in the conventional digital camera, since the position of the focus adjustment area is fixed immediately after the shift to the focus adjustment mode in which the position of the focus adjustment area is movable, there are cases where the user is forced to largely move the position of the focus adjustment area after the shift to the focus adjustment mode by a manual operation. For this reason, in the conventional digital camera, it is required to reduce the trouble of performing the operation associated with the movement of the position of the focus adjustment area.  
     SUMMARY OF THE INVENTION  
      A main object of the present invention is to provide an image taking apparatus capable of maintaining the continuity of the operation associated with the movement of the position of the focus adjustment area.  
      Another object of the present invention is to provide an image taking apparatus capable of reducing the trouble of performing the operation associated with the movement of the position of the focus adjustment area.  
      The above-mentioned objects of the present invention are attained by providing an image taking apparatus having a movement instruction member configured to receive, from a user, an instruction to move a position of a focus adjustment area within a captured image, a switching instruction member configured to receive, from the user, an instruction to switch among a plurality of focus adjustment modes according to the same focus detection method, the plurality of focus adjustment modes including a position non-fixed focus adjustment mode in which the position of the focus adjustment area is moved in response to the movement instruction received by the movement instruction member, and a controller configured to perform focus adjustment based on image information in the focus adjustment area within the captured image in response to the movement instruction from the movement instruction member as well as the focus adjustment mode switching instruction from the switching instruction member, when detecting an instruction to switch to the position non-fixed focus adjustment mode from the switching instruction member, the controller determining an initial position of the focus adjustment area in the position non-fixed focus adjustment mode immediately after mode switching based on a position of a representative point of the focus adjustment area immediately before the mode switching.  
      These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings, which illustrate specific embodiments of the invention. 
    
    
     BRIEF DESCRIPTON OF DRAWINGS  
      These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a front view of a digital camera  1 A;  
       FIG. 2  is a rear view of the digital camera  1 A;  
       FIG. 3  is a block diagram showing the internal structure of a digital camera  1 A;  
       FIG. 4  is a view showing the transition, in the image capturing mode, of the screen displayed on an LCD  180 ;  
       FIG. 5  is a view showing an AF area AR 1  indicated by a wide focus frame WFF, and sub blocks SB 1  to SB 11 ;  
       FIG. 6  is a view showing an AF area AR 2  indicated by a focus frame FF 11  (FF 1  to FF 10 );  
       FIG. 7  is a view showing the screen transition when a shift button  207   a  and an enter button  200  are simultaneously depressed;  
       FIG. 8  is a view showing an AF area AR 3  indicated by a cursor KR;  
       FIG. 9  is a view showing the screen transition when the shift button  207   a  and the enter button  200  are simultaneously depressed;  
       FIG. 10  is a view showing the position of the AF area when the AF mode is switched from a multi-segment AF mode to an FFP AF mode;  
       FIG. 11  is a view showing the position of the AF area AR 2  when the AF mode is switched from the FFP AF mode to the multi-segment AF mode;  
       FIG. 12  is a view showing the position of the AF area when the AF mode is switched from a wide AF mode to the FFP AF mode;  
       FIG. 13  is a view showing the position of the AF area AR 2  when the AF mode is switched from the wide AF mode to the multi-segment AF mode;  
       FIG. 14  is a flowchart explaining an AF mode switching operation;  
       FIG. 15  is a flowchart explaining the AF mode switching operation; and  
       FIG. 16  is a flowchart explaining the AF mode switching operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, an embodiment of the image forming apparatus according to the present invention will be described with reference to the attached drawings.  
      A digital camera  1 A according to the embodiment of the present invention has an AF (automatic focusing) function, and is provided with a plurality of AF modes (focus adjustment modes) associated with AF. These plurality of AF modes include a multi-segment AF mode and an FFP (flex focus point) AF mode in which the position of the AF area (focus adjustment area) within the captured image is movable. In the digital camera  1 A, when the AF mode is switched to the multi-segment AF mode or to the FFP AF mode, the position of the AF area immediately after the switching is determined based on the position of the representative point of the AF area immediately before the switching. The structure and operation of the digital camera  1 A will be described below. The multi-segment AF mode referred to here is an AF mode in which the AF area can be selected from among preset AF area candidates, and the FFP AF mode referred to here is an AF mode in which the position of the AF area can be more minutely specified than in the multi-segment AF mode.  
      &lt;External Structure&gt; 
      The external structure of the digital camera  1 A will be described below with reference to the front view of  FIG. 1  and the rear view of  FIG. 2 .  
      As shown in  FIG. 1 , a taking lens system  110  is provided on the front surface of a camera body  100  of the digital camera  1 A. The taking lens system  110  comprises lens units  112  and  113  held by a lens barrel  130 , and a diaphragm  114  (see  FIG. 3 ), and images light incident from the front of the digital camera  1 A, on the light receiving surface of a CCD (charge coupled device)  120 , (see  FIG. 3 ) which is an image sensor.  
      Further, an AF fill-in light lamp  140  that applies AF fill-in light to the subject is provided on the front surface of the camera body  100 . The AF fill-in light lamp  140  having a light emitting diode as the light source automatically emits light in low light conditions and in low contrast conditions to apply AF fill-in light to the subject.  
      On the top surface of the camera body  100 , the following are provided: an AF mode setting dial  145  for setting the AF mode of the digital camera  1 A; a mode setting dial  160  for setting the operation mode of the digital camera  1 A; a release button  150  for providing a image capturing start instruction to the digital camera  1 A; and a pop-up flash  170  that emits light at the time of fill-flash photography.  
      The AF mode setting dial  145  is used for switching the AF mode among a wide AF mode, the multi-segment AF mode and the FFP AF mode.  
      The mode setting dial  160  is a rotary switch for switching the operation mode of the digital camera  1 A among a still image capturing mode to perform sill image capturing, a moving image capturing mode to perform moving image capturing and a playback mode to perform playback display of recorded images.  
      The shutter button  150  is a two-stroke push button switch whose half depressed condition (hereinafter, referred to also as “S 1  condition”) and fully depressed condition (hereinafter, referred to also as “S 2  condition”) can be determined. The digital camera  1 A starts the image capturing preparation operation when detecting that the shutter button  150  is brought into the S 1  condition, and starts image capturing for recording when detecting that the shutter button  150  is brought into the S 2  condition.  
      As shown in  FIG. 2 , an LCD (liquid crystal display)  180  that performs live view display of captured images and playback display of recorded images is provided on the back surface of the camera body  100 . An EVF (electronic view finder)  190  for displaying the live view of captured images is provided above the LCD  180 .  
      Further, on the back surface of the camera body  100 , a four-way switch  205  having four upper, lower, left and right push buttons UP, DN, LF and RT is provided, and in the center of the four-way switch  205 , an enter button  200  is provided. In the image capturing mode, the upper and lower push buttons UP and DN of the four-way switch  205  are used for changing the zoom magnification, and in the playback mode, the left and right push buttons LF and RT of the four-way switch  205  are used for the frame advance of played back images.  
      The digital camera  1 A has an AF area transition mode in which the AF mode can be switched by the AF mode setting dial  145 , and the enter button  200  is used for setting the digital camera  1 A in the AF area transition mode and for canceling the setting of the AF area transition mode in the digital camera  1 A. The four-way switch  205  serves also as an instruction member for providing an instruction to move the AF area to the digital camera  1 A in the AF area transition mode.  
      Below the LCD  180 , buttons  207  used for various operations are provided. The buttons  207  include a shift button  207   a  for changing the function assigned to the button.  
      &lt;Internal Structure&gt; 
      Subsequently, the internal structure of the digital camera  1 A will be described with reference to the block diagram of  FIG. 3 .  
      A controller  250  is a microcomputer having at least a CPU  251 , a RAM  252  and a ROM  253 , and executes a program stored in the ROM  253  to thereby perform centralized control of components of the digital camera  1 A. An AF controller  254  shown in  FIG. 3  schematically shows the function associated with AF realized by the controller  250  executing the program.  
      In the digital camera  1 A, AF control (automatic focus adjustment) according to the contrast method is performed by the AF controller  254  in any of the wide AF mode, the multi-segment AF mode and the FFP AF mode. That is, the AF controller  254  calculates the contrast value in the AF area while changing the lens position of the focusing lens unit  113 , and moves the focusing lens unit  113  to an in-focus lens position where the contrast value is highest. While the contrast value in the AF area is adopted as the focus evaluation value in the digital camera  1 A, the focus evaluation value based on which AF is performed is not limited to the contrast value; it may be a parameter representative of the in-focus degree, for example, the edge width or the number of edges calculated from image information in the AF area. In addition, the AF controller  254  performs the processing to move the AF area in the multi-segment AF mode and the FFP AF mode.  
      In the lens barrel  130  of the taking lens system  110 , the zoom lens unit  112  for changing the zoom magnification (focal length) and the focusing lens unit  113  for performing the focus adjustment of the taking lens system  110  are provided. The zoom lens unit  112  and the focusing lens unit  113  are respectively connected to a zoom motor M 1  and a focusing motor M 3  for performing driving in the direction of the optical axis. The taking lens system  110  has the diaphragm  114  for changing the quantity of light incident on the CCD  120 . The diaphragm  114  is disposed midway between the zoom lens unit  112  and the focusing lens unit  113 , and connected to a diaphragm motor M 2  for changing the aperture.  
      Further, the digital camera  1 A has a zoom motor controller  260 , a shutter diaphragm controller  270  and a focus adjustment controller  280 . The zoom motor controller  260 , the shutter diaphragm controller  270  and the focus adjustment controller  280  supply driving power to the zoom motor M 1 , the diaphragm motor M 2  and the focusing motor. M 3  based on a control signal supplied from the controller  250 , respectively. This enables the controller  250  to perform the driving of the zoom lens unit  112  and the focusing lens unit  113  and change the aperture of the diaphragm  114 .  
      A lens position detector  290  comprising an encoder or the like detects the lens positions of the zoom lens unit  112  and the focusing lens unit  113 , and outputs the information on the detected lens positions to the controller  250 .  
      The CCD  120  photoelectrically converts the light image formed by the taking lens system  110  into an image signal having color components of R (red), G (green) and B (blue), and outputs it to a signal processor  210 . The image signal is a string of pixel signals corresponding to the quantity of light received by the light receiving cells (pixels) constituting the CCD  120 .  
      The signal processor  210  performs predetermined analog signal processings on the image signal inputted from the CCD  120 . The signal processor  210  has a CDS (correlated double sampling) circuit and an AGC (automatic gain control) circuit. The CDS circuit reduces the sampling noise of the image signal. The AGC circuit adjusts the level of the image signal. The gain control in the AGC circuit is also used for increasing the level of the image signal when appropriate exposure cannot be obtained by the adjustment of the aperture of the diaphragm  114  and the exposure time of the CCD  120 .  
      An A/D converter  220  converts the analog image signal inputted from the signal processor  210  into-a digital image signal, and outputs it to an image processor  230  as image data.  
      The CCD  120 , the signal processor  210  and the A/D converter  220  operate in synchronism with a reference clock inputted from a timing control circuit  240 . The timing control circuit  240  generates the reference clock based on a control signal inputted from the controller  250 .  
      The image processor  230  has a black level correction circuit  231 , a WB (white balance) circuit  232 , a gamma correction circuit  233  and an image memory  234 .  
      The black level correction circuit  231  corrects the black level of the image data inputted from the A/D converter  220  to a predetermined black level.  
      The WB circuit  232  performs level conversion of the color components of R, G and B of the image data. The level conversion is performed by use of a level conversion table inputted from the controller  250 . The level conversion table is set for each captured image by the controller  250 .  
      The gamma correction circuit  233  converts the gradation of the image data inputted from the WB circuit  232 . The gradation conversion is performed based on a predetermined level conversion table.  
      The image memory  234  temporarily stores the image data inputted from the gamma correction circuit  233 . The image memory  234  has a storage capacity capable of storing image data corresponding to one frame.  
      An operation portion  320  includes the previously-described shutter button  150 , mode setting dial  160 , AF mode setting dial  145 , buttons  207 , four-way switch  205  and enter button  200 . The controller  250  detects the conditions of these operation members, and makes the detection result reflected in the operation of the digital camera  1 A.  
      A flash circuit  310  supplies power for flash emission to the pop-up flash  170  in response to a flash control signal inputted from the controller  250 .  
      An EVF VRAM  330  and an LCD VRAM  340  have storage capacities capable of storing image data whose numbers of pixels are the same as those of the EVF  190  and the LCD  180 , respectively, and serve as the buffer memories of the images displayed on the EVF  190  and the LCD  180 .  
      Moreover, the digital camera  1 A has a card I/F (interface)  350  and a communication I/F  361 . The card I/F  350  is an interface for writing image data onto a memory card  360  and reading image data from the memory card  360 . The memory card  360  is a nonvolatile memory for storing image data of captured images. The communication I/F  361  is an interface for performing communication with an external apparatus connected to the digital camera  1 A.  
      &lt;Basic Operation of the Digital Camera&gt; 
      During image capturing standby in the image capturing mode, the image signals generated at predetermined time intervals by the CCD  120  are processed by the signal processor  210  to the gamma correction circuit  233 , and then, temporarily stored in the image memory  234  as image data. The image data is read out by the controller  250 , and converted into pieces of image data whose numbers of pixels are the same as those of the EVF  190  and the LCD  180 , respectively. The converted pieces of image data are transferred to the EVF VRAM  330  and the LCD VRAM  340 , and the image corresponding to the image data is displayed on the EVF  190  and the LCD  180  as the live view.  
      In addition, the digital camera  1 A adopts so-called continuous AF, and continuously performs AF control based on the image information, in the AF area, of the image after processed by the black level correction circuit  231 , also during image capturing standby.  
      When it is detected that the shutter button  150  is brought into the S 1  condition in the image capturing mode, the image signal generated by the CCD  120  is processed by the signal processor  210  to the black level correction circuit  231 , and exposure control, AF control and white balance adjustment are performed based on the image information corresponding to the image after the processing. Then, when it is detected that the shutter button  150  is brought into the S 2  condition, the image signal generated by the CCD  120  is processed by the signal processor  210  to the gamma correction circuit  233 , and then, temporarily stored in the image memory  234  as image data. The image data is read out by the controller  250 , undergoes compression processing, tag information addition processing and the like, and then, stored onto the memory card  360  through the card I/F  350 .  
      On the other hand, in the playback mode, the image data stored on the memory card  360  is read out by the controller  250  through the card I/F  350 , and undergoes decompression processing. The image data having undergone the decompression processing is converted into pieces of image data whose numbers of pixels are the same as those of the EVF  190  and the LCD  180 , and transferred to the EVF VRAM  330  and the LCD VRAM  340 . Then, the image corresponding to the image data is played back on the EVF  190  and the LCD  180 .  
      &lt;Screen Transition in the Image Capturing Mode&gt; 
      The switching of the AF mode in the image capturing mode and the screen transition that occurs in response thereto will be described below with reference to  FIG. 4 .  FIG. 4  is a view showing the transition, in the image capturing mode, of the screen (hereinafter, also referred to merely as “display screen”) displayed on the LCD  180 .  
      Of the six screens SC 1  to SC 6  shown in  FIG. 4 , the screens SC 1  to SC 3  are display screen examples when the digital camera  1 A is set in the AF area transition mode, and the screens SC 4  to SC 6  are display screen examples when the digital camera  1 A is not set in the AF area transition mode. Moreover, of the screens SC 1  to SC 6 , the screens SC 1  and SC 4 , the screens SC 2  and SC 5  and the screens SC 3  and SC 6  are display screen examples when the AF mode is the wide AF mode, the multi-segment AF mode and the FFP AF mode, respectively.  
      When the digital camera  1 A is set in the AF area transition mode, the display screen is switched among the screens SC 1  to SC 3  in response to a rotation in a clockwise direction or a counterclockwise direction (hereinafter, sometimes referred to as “clockwise rotation” and “counterclockwise rotation”) of the AF mode setting dial  145 . That is, every time a clockwise rotation is made, the AF mode is circularly switched in the order of the wide AF mode, the multi-segment AF mode and the FFP AF mode, and the display screen is circularly changed in the order of the screen SC, the screen SC 2  and the screen SC 3 . Conversely, every time a counterclockwise rotation is made, the AF mode is circularly switched in the order of the FFP AF mode, the multi-segment AF mode and the wide AF mode, and the display screen is circularly changed in the order of the screen SC 3 , the screen SC 2  and the screen SC 1 .  
      When the enter button  200  is depressed under a condition where the digital camera  1 A is set in the AF area transition mode, the setting of the AF area transition mode in the digital camera  1 A is canceled (the screen SC 1 →the screen SC 4 , the screen SC 2 →the screen SC 5 , the screen SC 3 →the screen SC 6 ). When the enter button  200  is depressed under a condition where the digital camera  1 A is not set in the AF area transition mode, the digital camera  1 A is set in the AF area transition mode (the screen SC 4 →the screen SC 1 , the screen SC 5 →the screen SC 2 , the screen SC 6 →the screen SC 3 ). The AF mode is not changed by a depression of the enter button  200 .  
      &lt;Display Screens&gt; 
      The screens SC 1  to SC 6  of  FIG. 4  will be severally described below.  
      Wide AF Mode (Screens SC 1  and SC 4 )  
      On the screen SC 1  in the wide AF mode, a wide focus frame WFF indicating a cross-shaped AF area (see  FIG. 5 ) AR 1  set within the captured image is displayed so as to be superimposed on the live view. In the wide AF mode, since the position of the AF area AR 1  within the captured image is fixed in a central part, the position of the wide focus frame WFF within the screen SC 1  is also fixed in the central part. The shape of the AF area AR 1  is not limited to a cross shape; it may be, for example, a rectangular.  
      Since the AF area AR 1  occupies a comparatively large area, in the wide AF mode, the subject can be easily included in the AF area AR 1 . On the other hand, in the wide AF mode, it is difficult to bring a specific subject within the screen SC 1  precisely in focus.  
      As shown in  FIG. 5 , a plurality of (in this example, eleven) sub blocks SB 1  to SB 11  are set within the AF area AR 1  (see  FIG. 5 ). When the digital camera  1 A is set in the wide AF mode, the AF controller  254  identifies, of the sub blocks SB 1  to SB 11 , the sub block including the subject, and performs AF control based on the contrast value in the identified sub block. Further, with the central point (or the point of center of gravity; ditto in the description that follows) of the identified sub block (in this example, the sub block SC 10 ) as the representative point RP 1  of the AF area AR 1 , the AF controller  254  stores the position (coordinates) of the representative point RP 1  into the RAM  252 . The position stored in the RAM  252  is updated every time the sub block including the subject is changed, so that the information is always the latest. When the AF controller  254  cannot detect the subject and cannot identify the sub block including the subject, the representative point RP 1  is the central point C of the AF area AR 1 .  
      When a sub block including the subject is present, although the sub block is displayed on the screen SC 1 , the other sub blocks (in  FIG. 5 , the sub blocks indicated by the dotted lines) are not displayed on the screen SC 1 . This sub block display enables the user to recognize the area where AF control is performed within the screen SC 1 .  
      The method of identifying the sub block including the subject is not limited, and various known methods may be adopted. For example, a sub block containing a specific color (for example, skin color) in large parts may be set as the sub block including the subject.  
      On the other hand, on the screen SC 4  in the wide AF mode, various pieces of image capturing information INF are displayed in addition to the wide focus frame WFF.  
      Multi-Segment AF Mode (Screens SC 2  and SC 5 )  
      On the screen SC 2  in the multi-segment AF mode, eleven focus frames FF 1  to FF 11  indicating candidates of a rectangular AF area (see  FIG. 6 ) AR 2  are displayed so as to be superimposed on the live view. Nine (the focus frames FF 1  to FF 9 ) of the focus frames FF 1  to FF 11  are spaced in a matrix with three rows and three columns. The remaining two (the focus frames FF 10  and FF 11 ) of the focus frames FF 1  to FF 11  are disposed adjacent to the focus frames FF 4  and FF 6  at both ends of the second row of the matrix. In the multi-segment AF mode, one (in this example, the focus frame FF 11 ) of the focus frames FF 1  to FF 11  is highlighted, and the AF controller  254  performs AF control based on the contrast value in the AF area AR 2  indicated by the highlighted focus frame (hereinafter, sometimes referred to also as “selected focus frame”).  
      In the multi-segment AF mode, the selected focus frame is not fixed but can be moved vertically and horizontally by an operation of the four-way switch  205 . That is, in the multi-segment AF mode, the position of the AF area AR 2  can be moved in response to an instruction to change the selected focus frame, that is, an instruction to move the AF area AR 2  by the four-way switch  205 .  
      In addition, as shown by the screen transition in  FIG. 7 , irrespective of which frame is the selected focus frame, the focus frame FF 5  in the center of the screen can be set as the selected focus frame by simultaneously depressing the shift button  207   a  and the enter button  200 .  
      While the size of the AF area AR 2  varies also according to the number of pixels of the CCD  120 , when the number of pixels of the CCD  120  is several millions, the size is generally selected from among 400×300 pixels to 600×400 pixels. Since this size is set so as to be smaller than the size of the AF area AR 1  of the wide AF mode, not only the position of the AF area AR 2  can be moved but also in the multi-segment AF mode, it is easier to bring a specific subject precisely in focus than in the wide AF mode.  
      Moreover, as shown in  FIG. 6 , a plurality of (in this example, nine) sub blocks SB 21  to SB 29  not displayed on the screen SC 2  are set within the AF area AR 2  of the multi-segment AF mode. When performing AF control based on the contrast value in the AF area AR 2 , the AF controller  254  calculates the contrast value in each sub block, and identifies, as the in-focus point, the central point of the sub block (in this example, the sub block SB 28 ) where the contrast value is the highest, that is, in-focus state is realized in the AF area AR 2 . Then, with the identified in-focus point as the representative point RP 2  of the AF area AR 2 , the AF controller  254  stores the position (coordinates) of the representative point RP 2  into the RAM  252 . The position stored in the RAM  252  is updated every time the sub block where in-focus state is realized is changed, so that the information is always the latest. In cases such as a case where the contrast value in the sub block is lower than a predetermined threshold value, it is determined that there is no sub block where in-focus state is realized, and the representative point RP 2  is a central point C′ whose relative position with respect to the AF area AR 2  is fixed.  
      On the other hand, on the screen SC 5  of the multi-segment AF mode, only the above-mentioned selected focus frame, that is, the focus frame indicating the AF area AR 2  actually used for AF control (in this example, the focus frame FF 11 ) is displayed, and the remaining focus frames FF 1  to FF 10  are not displayed. Moreover, on the screen SC 5 , image capturing information INF similar to that displayed on the screen SC 4  is displayed in addition to the selected focus frame (see  FIG. 4 ).  
      FFP AF Mode (Screens SC 3  and SC 6 )  
      On the screen SC 3  of the FFP AF mode, a cursor KR indicating a rectangular AF area (see  FIG. 8 ) AR 3  is displayed so as to be superimposed on the live view. The cursor-KR is the central point of the AF area AR 3 . In the FFP AF mode, the AF controller  254  performs focus adjustment based on the contrast value in the AF area AR 3  indicated by the cursor KR.  
      In the FFP AF mode, the position of the cursor KR on the screen SC 3  is not fixed but can be moved vertically and horizontally by an operation of the four-way switch  205 . That is, in the FFP AF mode, the position of the AF area AR 3  can be moved in response to a movement instruction by the four-way switch  205 . The resolution (step width) of the position movement of the AF area AR 3  of the FFP AF mode is higher than that of the position movement of the AF area AR 2  of the multi-segment AF mode. For this reason, in the FFP AF mode, it is easier to bring a specific subject precisely in focus than in the multi-segment AF mode.  
      In the FFP AF mode, the cursor KR can be moved to the center of the screen by simultaneously depressing the shift button  207   a  and the enter button  200  like in the multi-segment AF mode (see  FIG. 9 ).  
      While the size of the AF area AR 3  varies also according to the number of pixels of the CCD  120 , when the number of pixels of the CCD  120  is 2000×1500, the size is 250×150 pixels, when the number of pixels of the CCD  120  is 2400×1800, the size is 300×180 pixels, and when the number of pixels of the CCD  120  is 2560×1920, the size is approximately 300×190 pixels. In the FFP AF mode, since focus adjustment is minutely performed, the size of the AF area is set so as to be smaller than that in the multi-segment AF mode within the bounds where a bad influence of camera shake can be avoided.  
      On the other hand, on the screen SC 6  of the FFP AF mode, image capturing information INF similar to that displayed on the screen SC 4  is displayed in addition to the cursor KR (see  FIG. 4 ).  
      &lt;Switching of the AF Mode and the Position of the AF Area Before and After the Switching&gt; 
      In the digital camera  1 A, when the AF mode is switched to the multi-segment AF mode or the FFP AF mode in which the position of the AF area is not fixed by a clockwise or counterclockwise rotation of the AF mode setting dial  145 , the position of the AF area immediately after the switching is determined based on the position of the representative point of the AF area immediately before the switching. This determination of the position of the AF area will be described below.  
      Multi-Segment AF Mode→FFP AF Mode  
       FIG. 10  is a view showing the position of the AF area when the AF mode is switched from the multi-segment AF mode to the FFP AF mode.  
      The position of the AF area AR 3 , that is, the position of the cursor KR in the FFP AF mode immediately after the switching is the same as the position of the representative point RP 2  of the AF area AR 2  (in this example, the AF area indicated by the focus frame FF 9 ) of the multi-segment AF mode immediately before the switching.  
      The representative point RP 2  is the in-focus point or the central point (the point of center of gravity; ditto in the description that follows) of the AF area AR 2 . While the central point is a fixed point whose relative position with respect to the AF area AR 2  is fixed, the relative position of the in-focus point with respect to the AF area AR 2  changes as occasion arises. When the in-focus point can be identified, the representative point RP 2  is the in-focus point, and when the in-focus point cannot be identified and when an instruction to switch the AF mode is provided before the identification of the in-focus point is completed, the representative point RP 2  is the central point.  
      By thus making the position of the AF area AR 3  immediately after the switching to the FFP AF mode the same as the position of the representative point RP 2  of the AF area of the multi-segment AF mode immediately before the switching, since the position of the AF area AR 3  after the switching is not largely changed from the position of the AR area AR 2  before the switching, the continuity of the operation associated with the determination of the position of the AF area is maintained, so that the trouble of performing the operation can be reduced. In particular, when the representative point RP 2  is the in-focus point, the position where the subject is highly likely to be present is the position of the AF area AR 3 , so that the trouble of performing the operation can be further reduced.  
      FFP AF Mode→Multi-Segment AF Mode  
       FIG. 11  is a view showing the position of the AF area AR 2  when the AF mode is switched from the FFP AF mode to the multi-segment AF mode. In  FIG. 11 , the focus frames indicated by the dotted lines within the screen SC 3  of the FFP AF mode are shown for convenience&#39;s sake for ease of understanding, and are not displayed on the actual screen SC 3 .  
      The position of the AF area AR 2 , that is, the position of the selected focus frame in the multi-segment AF mode immediately after the switching is determined based on the position of the representative point of the AF area AR 3  of the FFP AF mode immediately before the switching. The representative point is the central point of the AF area AR 3 , that is, the position of the cursor KR.  
      More specifically, when the position of the cursor KR immediately before the switching is included within any of the candidates of the AF area AR 2  of the multi-segment AF mode immediately after the switching, the candidate of the AF area AR 2  including the position of the cursor KR is set as the AF area AR 2 . On the other hand, when the position is not included, the candidate of the AR area AR 2  closest to the position of the cursor KR immediately before the switching is set as the AF area AR 2 . The distance between the position of the cursor KR and the candidate of the AF area AR 2  is the distance between the position of the cursor KR and the central point of the candidate of the AF area AR 2 .  
      By thus setting the position of the AF area AR 2  immediately after the switching to the multi-segment AF mode to the position closest to the position of the representative point of the AF area AR 3  of the FFP AF mode immediately before the switching, since the position of the AF area AR 2  after the switching is not largely changed from the position of the AF area AR 3  immediately before the switching, the continuity of the operation associated with the determination of the position of the AF area is maintained, so that the trouble of performing the operation can be reduced. In addition, by setting the candidate of the AF area AR 2  closest to the position of the representative point as the AF area, even when the position the same as the position of the representative point cannot be set as the position of the AF area, the position of the AF area AR 2  after the switching can be prevented from being largely changed from the position of the AF area AR 3  before the switching. That is, even when the step width of the position movement of the AF area is large, the continuity of the operation associated with the determination of the position of the AF area can be maintained.  
      Wide AF Mode→FFP AF Mode  
       FIG. 12  is a view showing the position of the AF area AR 3  when the AF mode is switched from the wide AF mode to the FFP AF mode. The wide focus frame and the sub blocks indicated by the dotted lines within the screen SC 3  of the FFP AF mode in  FIG. 12  are shown for convenience&#39;s sake for ease of understanding, and are not displayed on the actual screen SC 3 .  
      The position of the AF area AR 3 , that is, the position of the cursor KR in the FFP AF mode immediately after the switching is the same as the position of the representative point RP 1  of the AF area AR 1  of the wide AF mode immediately before the switching. The representative point RP 1  is the position of the central point of the sub block including the subject within the AF area AR 1 .  
      By thus making the position of the AF area AR 3  immediately after the switching to the FFP AF mode the same as the position of the representative point of the AF area of the wide AF mode immediately before the switching, since the position where the subject is highly likely to be present is the position of the AF area AR 3 , the continuity of the operation associated with the determination of the position of the AF area can be maintained, so that the trouble of performing the operation can be reduced.  
      Wide AF Mode→Multi-Segment AF Mode  
       FIG. 13  is a view showing the position of the AF area AR 2  when the AF mode is switched from the wide AF mode to the multi-segment AF mode. In  FIG. 13 , the focus frames indicated by the dotted lines within the screen SC 1  of the wide AF mode are shown for convenience&#39;s sake for ease of understanding, and are not displayed on the actual screen SC 1 .  
      The position of the AF area AR 2 , that is, the position of the selected focus frame in the multi-segment AF mode immediately after the switching is determined based on the position of the representative point RP 1  of the AF area AR 1  of the wide AF mode immediately before the switching. The representative point RP 1  is the central point of the sub block including the subject.  
      More specifically, when the position of the representative point RP 1  immediately before the switching is included within any of the candidates of the AF area AR 2  of the multi-segment AF mode immediately after the switching (the upper row in  FIG. 13 ), the candidate of the AF area AR 2  including the position of the representative point RP 1  (in this example, the candidate of the AF area AR 2  indicated by the focus frame FF 6 ) is set as the AF area AR 2 . On the other hand, when the position is not included (the lower row in  FIG. 13 ), the candidate of the AR area AR 2  closest to the position of the representative point RP 1  immediately before the switching is set as the AF area AR 2  (in this example, the candidate of the AF area AR 2  indicated by the focus frame FF 2 ). The distance between the position of the representative point RP 1  and the candidate of the AF area AR 2  is the distance between the position of the representative point RP 1  and the central point of the candidate of the AF area AR 2 .  
      By thus determining the position of the AF area AR 2  immediately after the switching to the multi-segment AF mode based on the position of the representative point of the AF area of the wide AF mode immediately before the switching, since the position where the subject is highly likely to be present is the position of the AF area AR 2 , the continuity of the operation associated with the determination of the position of the AF area can be maintained, so that the trouble of performing the operation can be reduced.  
      &lt;AF Mode Switching Operation&gt; 
      The AF mode switching operation will be described below with reference to the flowcharts of FIGS.  14  to  16 . FIGS.  14  to  16  show the operation flows when the power is turned on or the mode setting dial  160  is operated and the operation mode of the digital camera  1 A is set in the image capturing mode.  
      In the operation flows shown in FIGS.  14  to  16 , first, the digital camera  1 A is set in the image capturing mode [step ST 1 ], and the live view is displayed on the LCD  180  [step ST 2 ]. Then, the digital camera  1 A detects the presence or absence of the operation of the AF mode setting dial  145 , that is, detects the presence or absence of an AF mode switching instruction [step ST 3 ]. When no AF mode switching instruction is detected at step ST 3 , the process shifts to step ST 4 . When an instruction to switch the AF mode to the multi-segment AF mode or to the FFP AF mode is detected, the process shifts to step ST 21  or step ST 41 , respectively. In the stage of step ST 3 , since the position of the representative point is maintained at the default position (the center of the screen), in the operation flow to which the process shifts, the position of the selected focus frame or the cursor KR is the center of the screen as described later (see step ST 23  or ST 43 ).  
      At step ST 4 , the AF mode is set to the wide AF mode. Then, the detection of the subject and the identification of the sub block including the subject are performed [step ST 5 ], AF control is performed based on the contrast value in the identified sub block [step ST 6 ], and the position of the central point of the identified sub block is stored in the RAM  252  as the position of the representative point RP 1  [step ST 7 ]. Then, the digital camera  1 A again detects the presence or absence of the AF mode switching instruction [step ST 8 ]. When no AF mode switching instruction is detected at step ST 8 , the process shifts to step ST 9 . When an instruction to switch the AF mode to the multi-segment AF mode or to the FFP AF mode is detected, the process shifts to step ST 24  or step ST 44 , respectively. At step ST 8 , since the position of the representative point is moved from the default position (the center of the screen), in the operation flow to which the process shifts, the position of the selected focus frame or the cursor is not always the center of the screen as mentioned later.  
      At step ST 9 , the condition of the release button  150  is detected. When it is detected that the release button  150  is brought into the S 2  condition, image capturing for recording [step ST 10 ] and the recording of the captured image onto the memory card  360  [step ST 11 ] are successively performed. When it is not detected at step ST 9  that the release button  150  is brought into the S 2  condition, the process returns to step ST 5 , and the detection of the subject and so forth are repeated.  
      Steps ST 21  to ST 31  show the operation flow associated with the operation in the multi-segment AF mode.  
      At step ST 21 , the AF mode is set to the multi-segment AF mode, and then, the presence or absence of an AF mode switching instruction is detected [step ST 22 ]. When no AF mode switching instruction is detected at step ST 22 , the focus frame FF 5  in the center of the screen is set as the selected focus frame [step ST 23 ]. When an instruction to switch the AF mode to the FFP AF mode or to the wide AF mode is detected at step ST 22 , the process shifts to step ST 41  or step ST 4 , respectively. In the stage of step ST 22 , since the position of the representative point is maintained at the default position (the center of the screen), at the step to which the process shifts, the position of the cursor KR is the center of the screen as described later (see step ST 43 ).  
      On the other hand, at step ST 24 , the AF mode is set to the multi-segment AF mode, the focus frame closest to the position of the representative point stored in the RAM  252  is set as the selected focus frame [step ST 25 ]. Since the position of the AF area AR 2  indicated by the selected focus frame becomes the position of the representative point of the FFP AF mode (the central point of the AF area AR 3 =the position of the cursor KR) or the position of the representative point of the wide AF mode (the position of the central point of the sub block including the subject) by step ST 25 , even if the AF mode is switched, the continuity of the operation associated with the position of the AF area is realized.  
      At step ST 26  following step ST 23  or ST 25 , the presence or absence of an operation of the four-way switch  205 , that is, the presence or absence of an AF area movement instruction is detected. When an AF area movement instruction is provided, the AF area is moved in response to the movement instruction [step ST 27 ], and AF control is performed [step ST 28 ]. When no AF area movement instruction is provided, AF control is performed without the AF area AR 2  being moved [step ST 28 ]. At step ST 29  following step ST 28 , the position of the in-focus point within the AF area AR 2  is stored into the RAM  252  as the position of the representative point RP 2 , and the presence or absence of an AF mode switching instruction is detected again [step ST 30 ]. At step ST 30 , since the position of the representative point RP 2  is moved from the default position (the center of the screen), in the operation flow to which the process shifts, the position of the focus frame or the cursor is not always the center of the screen as mentioned later. At step ST 31 , like at step ST 9 , the condition of the release button  150  is detected. When it is detected that the release button  150  is brought into the S 2  condition, the process shifts to image capturing for recording [step ST 10 ]. When it is not detected at step ST 9  that the release button  150  is brought into the S 2  condition, the process returns to step ST 26 , and the detection of the operation of the four-way switch and so forth are repeated.  
      Steps ST 41  to ST 51  show the operation flow associated with the operation in the FFP AF mode.  
      At step ST 41 , the AF mode is set to the FFP AF mode, and then, the presence or absence of an AF mode switching instruction is detected [step ST 42 ]. When no AF mode switching instruction is detected at step ST 42 , the cursor KR is set at the center of the screen [step ST 43 ]. When an instruction to switch the AF mode to the wide AF mode or to the multi-segment AF mode is detected at step ST 42 , the process shifts to step ST 4  or ST  21 , respectively. In the stage of step ST 42 , since the position of the representative point is maintained at the default position (the center of the screen), in the operation flow to which the process shifts, the position of the selected focus frame is the center of the screen as described later (see step ST 23 ).  
      On the other hand, at step ST 44 , the AF mode is set in the FFP AF mode, and the cursor KR is set in the position of the representative point stored in the RAM  252  [step ST 45 ]. Since the position of the AF area AR 3  indicated by the cursor KR becomes the position of the representative point of the wide AF mode (the position of the central point of the sub block including the subject) or the position of the in-focus point in the multi-segment AF mode (the position of the central point of the sub block where in-focus state is realized) by step ST 45 , even if the AF mode is switched, the continuity of the operation associated with the position of the AF area is realized.  
      At step ST 46  following step ST 43  or ST 45 , the presence or absence of an operation of the four-way switch  205 , that is, the presence or absence of an AF area movement instruction is detected. When an AF area movement instruction is provided, the cursor KR is moved in response to the movement instruction [step ST 47 ], and AF control is performed [step ST 48 ]. When no AF area movement instruction is provided, AF control is performed without the AF area being moved [step ST 48 ]. At step ST 49  following step ST 48 , the position of the in-focus point within the AF area AR 3  is stored into the RAM  252  as the position of the representative point, and the presence or absence of an AF mode switching instruction is detected again [step ST 50 ]. At step ST 50 , since the position of the representative point is moved from the default position (the center of the screen), in the operation flow to which the process shifts, the position of the selected focus frame is not always the center of the screen as mentioned later. At step ST 51 , like at step ST 9 , the condition of the release button  150  is detected. When it is detected that the release button  150  is brought into the S 2  condition, the process shifts to image capturing for recording [step ST 10 ]. When it is not detected that the release button  150  is brought into the S 2  condition, the process returns to step ST 46 , and the detection of the operation of the four-way switch and so forth are repeated.  
      &lt;Modifications&gt; 
      Regarding Wide AF Mode  
      While in the above-described embodiment, AF control is performed based on the contrast value in the sub block including the subject in the wide AF mode, it may be performed to perform AF control based on the contrast value in the entire AF area AR 1  and use the result of identification of the sub block including the subject only for the determination of the position of the representative point. Moreover, similar to the multi-segment AF mode, it may be performed to identify the in-focus point within the sub block and determine the position of the AF area immediately after the shift to the multi-segment AF mode or to the FFP AF mode, based on the identified in-focus point.  
      Regarding Continuous AF  
      While an example in which AF control is continuously performed during image capturing standby is shown in the above-described embodiment, it may be performed to execute AF control only when it is detected that the shutter button  150  is brought into the S 1  condition. In this case, a fixed point whose relative position with respect to the AF area is fixed such as the central point of the immediately preceding AF area is set as the representative point.  
      In the digital camera according to the embodiment of the present invention, since the position of the focus adjustment area immediately after the switching to the position non-fixed focus adjustment mode reflects the position of the representative point of the focus adjustment area immediately before the switching, the continuity of the operation associated with the determination of the position of the focus adjustment area is maintained. Consequently, the trouble of performing the operation can be reduced.  
      Moreover, in the digital camera according to the embodiment of the present invention, since the position of the focus adjustment area immediately after the switching to the position non-fixed focus adjustment mode reflects the position of the in-focus point within the focus adjustment area immediately before the switching, the position where the subject is highly likely to be present is the position of the focus adjustment area, so that the necessity for the position of the focus adjustment area to be moved immediately after the switching can be reduced. Consequently, the trouble of performing the operation can be further reduced.  
      Further, in the digital camera according to the embodiment of the present invention, even when the initial position cannot be made the same as the position of the representative point, since the initial position reflects the position of the representative point of the focus adjustment area immediately before the switching, the continuity of the operation associated with the determination of the position of the focus adjustment area can be more reliably maintained. Consequently, the trouble of performing the operation can be further reduced.  
      Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.