Abstract:
An image capturing apparatus includes an image capturing unit, a designating unit configured to designate a main-area or a position to which a moving object is to reach, in each captured image captured by the image capturing unit, an image capturing control unit configured to control the image capturing unit to continuously capture the moving object at a predetermined frame rate, a position specifying unit configured to specify a position of the moving object in the image captured by the image capturing unit, and a frame rate control unit configured to control the predetermined frame rate, based on the specified position of the moving object, and either the main-area or position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2010-251646, filed Nov. 10, 2010; and No. 2011-187972, filed Aug. 30, 2011, the entire contents of all of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image capturing apparatus which captures, for example, a moving object, an image capturing control method, and a recording medium. 
     2. Description of the Related Art 
     As a conventional technique, Jpn. Pat. Appln. KOKAI Publication No. 2010-166304 discloses a technique of setting a main image capturing area to capture a moving object within the image capturing area in order to improve the quality of an image acquired by panning. In this patent literature, while the main image capturing area is exposed by a plurality of number of times, the background area other than the main image capturing area is exposed once, and a composited image is generated, acquiring an image in which the moving object stands still while the background is moving. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an image capturing apparatus, an image capturing control method, and a recording medium, capable of easily capturing a plurality of images of a moving object in a composition the user wants. 
     According to one aspect of the present invention, there is provided an image capturing apparatus comprising: an image capturing unit; a designating unit configured to designate a main-area or a position to which a moving object is to reach, in each captured image captured by the image capturing unit; an image capturing control unit configured to control the image capturing unit to continuously capture the moving object at a predetermined frame rate; a position specifying unit configured to specify a position of the moving object in the image captured by the image capturing unit; and a frame rate control unit configured to control the predetermined frame rate, based on the specified position of the moving object, and either the main-area or position. 
     According to one aspect of the present invention, there is provided an image capturing apparatus comprising: an image capturing unit; a detection unit configured to detect a position of a moving object in an image capturing area of the image capturing unit; a speed obtaining unit configured to obtain information indicative of a moving speed of the moving object; a first setting unit configured to set an area, which has a size based on the information indicative of the moving speed of the moving object obtained by the speed obtaining unit, in the image capturing area of the image capturing unit; a determination unit configured to determine a relationship between the position of the moving object detected by the detection unit in the image capturing area of the image capturing unit and a position of the area set by the first setting unit; and a control unit configured to control a frame rate, which is used to record an image to be captured by the image capturing unit, based on a result of the determination by the determination unit. 
     According to another aspect of the present invention, there is provided an image capturing control method for use in an apparatus including an image capturing unit, the method comprising: detecting a position of a moving object in an image capturing area of the image capturing unit; obtaining information indicative of a moving speed of the moving object; setting a first area, which has a size based on the obtained information indicative of the moving speed of the moving object, in the image capturing area of the image capturing unit; determining a relationship between the detected position of the moving object in the image capturing area of the image capturing unit and a position of the set first area; and controlling a frame rate, which is used to record an image to be captured by the image capturing unit, based on a result of the determining. 
     According to still another aspect of the present invention, there is provided a non-transitory computer-readable storage medium having a program stored thereon, the program being executable to control an apparatus including an image capturing unit to perform functions comprising: detecting a position of a moving object in an image capturing area of the image capturing unit; obtaining information indicative of a moving speed of the moving object; setting a first area, which has a size based on the obtained information indicative of the moving speed of the moving object, in the image capturing area of the image capturing unit; determining a relationship between the detected position of the moving object in the image capturing area of the image capturing unit and a position of the set first area; and controlling a frame rate, which is used to record an image to be captured by the image capturing unit, based on a result of the determining. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing the arrangement of the functional circuit of a digital camera according to first and second embodiments of the present invention; 
         FIG. 2  is a flowchart showing a series of processing items in the continuous capturing mode according to the first embodiment; 
         FIGS. 3A ,  3 B and  3 C are view each showing a main object which moves on the monitor screen in continuous capturing according to the first embodiment; 
         FIG. 4  is a view showing a change of the continuous capturing speed according to the first embodiment; 
         FIG. 5  is a flowchart showing a series of processing items in the continuous capturing mode according to a second embodiment of the present invention; and 
         FIGS. 6A ,  6 B and  6 C are views each showing a main object which moves on the monitor screen in continuous capturing according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     (First Embodiment) 
     The first embodiment in which the present invention is applied to a digital camera will be described with reference to several views of the accompanying drawing. 
       FIG. 1  is a block diagram showing the circuit arrangement of a digital camera  10  according to the first embodiment. A CPU  20  controls an imaging lens unit  11  disposed on the front surface of a camera body to allow the optical image of an object to enter the image sensing surface of a solid-state image sensor (IS)  12  formed from a charge-coupled device (CCD), CMOS image sensor, or the like, thereby forming the image of the object. 
     In a monitor state also called live-view image display, the CPU  20  sends, to an AGC &amp; analog-to-digital converter  13 , an image signal obtained by image sensing on the solid-state image sensor  12 . Then, the CPU  20  executes correlated square sampling, automatic gain adjustment, and analog-to-digital conversion processing for the image signal, and digitizes the image signal. A buffer memory  14  holds the image data of the digital value via a system bus SB. 
     An image processing unit  15  properly performs necessary image processing for the image data held in the buffer memory  14 . The image processing unit  15  includes an object detection unit  15   a , motion vector analysis unit  15   b , and area entrance determination unit  15   c.    
     The image processing unit  15  executes de-mosaic processing including matrix operation, pixel interpolation processing, and gamma correction processing for image data (to be referred to as “Bayer data”) complying with the layout of a color filter with a Bayer array attached to the solid-state image sensor  12 . The image processing unit  15  performs development for the Bayer data serving as raw data, and converts it into image data of the luminance-color difference system (YUV). 
     The image processing unit  15  generates, from this image data, image data whose numbers of pixels and tone bits are greatly decreased for display. The image processing unit  15  sends the generated image data to a display unit  16  to display it as a live-view image. 
     Similar to the optical lens unit  11 , a microphone  17  is attached to the front surface of the camera body, and inputs sound from the object side. The microphone  17  converts the input sound into an electrical signal, and outputs the electrical signal to an audio processing unit  18 . 
     In audio recording, still image capturing with audio, and moving image capturing, the audio processing unit  18  converts an audio signal input from the microphone  17  into digital data. The audio processing unit  18  detects the sound pressure level of the digital audio data. Further, the audio processing unit  18  compresses the audio data in a predetermined data file format such as Moving Picture Experts Group-4 Advanced Audio Coding (AAC), generating an audio data file and sending it to a recording medium (to be described later). 
     The audio processing unit  18  includes an audio source circuit such as a pulse code modulation (PCM) audio source. The audio processing unit  18  decompresses a compressed audio data file sent in audio playback, and converts the decompressed audio data into an analog signal. A loudspeaker  19  attached to the rear surface of the housing of the digital camera  10  is driven to amplify and output the audio of the analog signal. 
     The CPU  20  comprehensively controls these circuits. The CPU  20  is directly connected to a work memory  21  and program memory  22 . The work memory  21  is formed from, for example, a DRAM. The program memory  22  is formed from, for example, an electrically programmable nonvolatile memory such as a flash memory. The program memory  22  permanently stores operation programs, data, and the like, including continuous capturing speed control (to be described later). 
     The CPU  20  executes the control operation of the overall digital camera  10  while reading necessary programs, data, and the like from the program memory  22 , and temporarily expanding and storing them in the work memory  21 , as needed. 
     The CPU  20  executes a control operation in correspondence with various key operation signals directly input from an operation unit  23 , and an operation signal from a touch input unit  24  arranged at one end on the display unit  16 . 
     The operation unit  23  includes, for example, a power key, shutter key, zoom-up/down key, capturing mode key, playback mode key, menu key, cursor (“↑”, “→”, “↓”, and “←”) keys, set key, cancel key, and display key. 
     The touch input unit  24  is integrally formed on the display unit  16  using a transparent conductive film. The touch input unit  24  sends, as an operation signal to the CPU  20 , coordinate information of a position touched by the user&#39;s hand or finger. 
     The CPU  20  is connected via the system bus SB to a lens driving unit  25 , an electronic flash driving unit  26 , an image sensor (IS) driving unit  27 , and a memory card controller  28  in addition to the AGC &amp; analog-to-digital converter  13 , the buffer memory  14 , the image processing unit  15 , the display unit  16 , the touch input unit  24 , and the audio processing unit  18 . 
     Upon receiving a control signal from the CPU  20 , the lens driving unit  25  controls rotation of a lens DC motor (M)  29 , and changes the positions of some of a plurality of lens units which form the optical lens unit  11 , for example, the positions of a zoom lens and focusing lens individually along the optical axis. 
     In still image capturing, upon receiving a control signal from the CPU  20 , the electronic flash driving unit  26  drives to turn on, in synchronism with a capturing timing, an electronic flash  30  made up of a plurality of white high-intensity LEDs. 
     The image sensor driving unit  27  scans and drives the solid-state image sensor  12  in accordance with currently set capturing conditions and the like. 
     The image processing unit  15  performs de-mosaic processing for image data which has been sent from the AGC &amp; analog-to-digital converter  13  upon image capturing in response to a shutter key operation on the touch input unit  24  and is held in the buffer memory  14 . Further, the image processing unit  15  performs data compression processing in a predetermined data file format, such as discrete cosine transform (DCT) format or Huffman coding for Joint Photographic Experts Group (JPEG) format, thereby generating an image data file whose data amount is greatly reduced. The generated image data file is recorded on a memory card  31  via the system bus SB and memory card controller  28 . 
     Also, the image processing unit  15  receives, via the system bus SB, image data which is read from the memory card  31  via the memory card controller  28  in the playback mode. The image processing unit  15  stores the image data in the buffer memory  14 . Then, the image processing unit  15  obtains image data of an original size by decompression processing of decompressing compressed image data held in the buffer memory  14  by procedures reverse to those in recording. The image processing unit  15  outputs the obtained image data to the display unit  16  via the system bus SB to display it. 
     The memory card controller  28  is connected to the memory card  31  via a card connector C. The memory card  31  is a recording memory for image data and the like that is detachably mounted in the digital camera  10  and serves as a recording medium for the digital camera  10 . The memory card  31  incorporates a flash memory serving as a nonvolatile memory electrically programmable for each block, and its driving circuit. 
     An operation in the embodiment will be described below. 
     Note that the following operation is executed after the CPU  20  reads an operation program and data stored in the program memory  22 , expands them in the work memory  21 , and stores them when capturing a plurality of still images temporally in the continuous capturing mode. 
     Operation programs and the like stored in the program memory  22  are those stored in the program memory  22  in shipment from the manufacturing factory of the digital camera  10 . In addition, the operation programs and the like include new operation programs, data, and the like which are downloaded from the outside by connecting the digital camera  10  to a personal computer in, for example, upgrading of the digital camera  10 . 
       FIG. 2  shows a series of processing items regarding capturing and subsequent recording in the continuous capturing mode. At the beginning of processing, the CPU  20  scans and drives the solid-state image sensor  12  via the IS driving unit  27  at a predetermined frame rate of, for example, 60 frames/second. While images obtained by the solid-state image sensor  12  are sequentially buffered in the buffer memory  14 , the CPU  20  controls the display unit  16  to display these images as live-view images in real time (step S 101 ). The CPU  20  controls the display unit  16  to display a character string such as “designate the range of an area to capture a main object” as a guide message at part of the display unit  16  such as the bottom of the screen to prompt the user of the digital camera  10  to designate the image capturing area of the object (step S 102 ). In this way, the CPU  20  notifies the user to designate the image capturing area of the object. After the notification, the CPU  20  determines whether the user has actually designated the area (step S 103 ). More specifically, the CPU  20  determines the designation of the image capturing position based on whether the user has performed a touch operation indicating a rectangular range in accordance with a coordinate signal output from the touch input unit  24  integrally formed with the display unit  16 . 
     If the user has not designated the area, the CPU  20  returns the process to step S 101  to repetitively execute the same process. 
     If the user has designated the area by a touch operation on the touch input unit  24 , the CPU  20  determines it in step S 103 . Then, the CPU  20  specifies the area of the main object by controlling the object detection unit  15   a  and motion vector analysis unit  15   b  of the image processing unit  15  to analyze a motion vector in time series images buffered in the buffer memory  14  (step S 104 ). 
     More specifically, the CPU  20  controls the object detection unit  15   a  and motion vector analysis unit  15   b  to analyze motion vectors in a plurality of block areas within an image, and specifies a block area having a specific motion vector as the area of the main object. 
     Details of motion vector analysis processing executed by the motion vector analysis unit  15   b  is a well-known technique generally executed in a moving picture compression encoding technique such as Moving Picture Experts Group (MPEG), and a description thereof will be omitted. 
     After the main object is specified by its motion vector, the CPU  20  sets a sub-area surrounding the designated area on the display unit  16  in accordance with the magnitude of specified motion vector, that is to say, the moving speed of the main object within the image (step S 105 ). 
       FIG. 3A  shows the relationship between a main object MO, a designated area TA, and a sub-area SA which are extracted from a screen displayed on the display unit  16 . The CPU  20  sets the sub-area SA on the display unit  16  to be larger than the designated area TA when the magnitude of motion vector is larger than a predetermined value, and smaller than the designated area TA when the magnitude of motion vector is smaller than a predetermined value. The motion vector and the size of the sub-area SA with respect to the designated area TA may be set stepwise using a plurality of thresholds set in advance. 
     Note that the main object MO in the screen of the display unit  16  is an object moving in a direction indicated by an arrow A 1 . The moving direction of the main object MO is not limited to one obtained when the digital camera  10  is fixed by a tripod or the like and captures an image, and a real moving object serving as the main object MO moves within the screen. That is, the movement of the main object MO includes even relative movement within the screen when the user holds the digital camera  10  in his or her hands and captures an image, and the composition is changed so that the main object MO moves to a position the user wants within the capturing range. 
     In  FIG. 3A , lines C 1  to C 4  indicated by two vertical lines and two horizontal lines, that is to say, a total of four broken lines are set to assist capturing in a composition at the golden ratio. For example, whether to display C 1  to C 4  on the display unit  16  can be switched by a display key operation on the operation unit  23 . 
     After that, the CPU  20  sets two types of image capturing rates FR 1  and FR 2  (FR 1 &lt;FR 2 ) in continuous capturing based on the set motion vector and the position of the designated area (step S 106 ). 
     Image capturing rate FR 1  is an image capturing frame rate used in continuous capturing when a partial area of the main object MO enters the sub-area SA. Image capturing rate FR 2  is an image capturing frame rate used in continuous capturing when the entire area of the main object MO enters the designated area TA. 
     Upon completion of various settings, the CPU  20  suspends continuous capturing processing until it is determined using the area entrance determination unit  15   c  of the image processing unit  15  that a partial area of the main object MO in the image has reached the sub-area SA, in order to start actual continuous capturing (step S 107 ). 
     In step S 107 , the area entrance determination unit  15   c  determines that a partial area of the main object MO in the image has reached the sub-area SA. The CPU  20  starts continuous capturing at image capturing rate FR 1  of, for example, 15 frames/second set in step  5106  (step S 108 ). The CPU  20  sequentially stores the raw data acquired by capturing in the buffer memory  14 . 
     Then, the area entrance determination unit  15   c  determines whether the entire area of the main object MO in the image has entered the designated area TA (step S 109 ). If the area entrance determination unit  15   c  determines that the entire area of the main object MO in the image has not entered the designated area TA, the CPU  20  returns the process to step S 108 . 
     While controlling the image sensor driving unit  27  to maintain continuous capturing at image capturing rate FR 1 , the CPU  20  repetitively executes the processes of steps S 108  and S 109  until the area entrance determination unit  15   c  determines that the entire area of the main object MO in the image has entered the designated area TA. 
       FIG. 3B  shows a state in which the main object MO further moves down to the right within the screen from the state of  FIG. 3A  and crosses the sub-area SA, and its partial area has reached the designated area TA. As shown in  FIG. 3B , the main object MO further moves within the screen in a direction indicated by an arrow A 2 , and enters the designated area TA, obtaining a capturing composition the user intends. 
     After the main object MO further moves within the screen of the display unit  16  and completely enters the designated area TA, as shown in  FIG. 3C , the CPU  20  determines it in step S 109 , and controls the image sensor driving unit  27  to maintain continuous capturing at image capturing rate FR 2  of, for example, 30 frames/second set in step S 106  instead of image capturing rate FR 1  (step S 110 ). 
     The area entrance determination unit  15   c  determines whether a partial area of the main object MO in the image has exited the designated area TA (step S 111 ). If the area entrance determination unit  15   c  determines that a partial area of the main object MO in the image has not exited the designated area TA, the CPU  20  returns the process to step S 110 . 
     By repetitively executing the processes of steps S 110  and S 111 , the CPU  20  controls the image sensor driving unit  27  to maintain continuous capturing at image capturing rate FR 2  while the entire area of the main object MO in the image entered the designated area TA. 
     If a partial area of the main object MO in the image has exited the designated area TA, the CPU  20  determines it in step S 111 , and controls the image sensor driving unit  27  to again maintain continuous capturing at image capturing rate FR 1  set in step S 106  (step S 112 ). 
     The area entrance determination unit  15   c  determines whether the entire area of the main object MO in the image has exited the sub-area SA (step S 113 ). If the area entrance determination unit  15   c  determines that the entire area of the main object MO in the image has not exited the sub-area SA, the CPU  20  returns the process to step S 112 . 
     By repetitively executing the processes of steps S 112  and S 113 , the CPU  20  controls the image sensor driving unit  27  to maintain continuous capturing at image capturing rate FR 1  until the entire area of the main object MO in the image exited the sub-area SA. 
     After the entire area of the main object MO in the image exits the sub-area SA, the CPU  20  determines it in step S 113  and controls the image sensor driving unit  27  to stop continuous capturing (step S 114 ). 
       FIG. 4  shows the relationship between the image capturing frame rate and the positions of the sub-area SA and designated area TA with respect to the moving position of the main object MO. 
     As shown in  FIG. 4 , when a partial area of the main object MO enters the sub-area SA, continuous capturing starts at frame rate FR 1 . In a period M during which the entire area of the main object MO enters the designated area TA, the composition is highly likely to be one the user intends. Thus, frame rate FR 1  is changed to higher frame rate FR 2 , and continuous capturing is maintained. 
     Even after a partial area of the main object MO exits the designated area TA, continuous capturing is maintained at frame rate FR 1  until the entire area of the main object MO exits the sub-area SA. When the entire area of the main object MO exits the sub-area SA, continuous capturing stops. 
     After the stopping of continuous capturing, the CPU  20  controls the image processing unit  15  to generate reduced images by greatly decreasing the number of pixels in each of image data which are obtained by a series of continuous capturing operations and held in the buffer memory  14  (step S 115 ). 
     The CPU  20  controls the display unit  16  to display a list of generated reduced images, and display a guide message such as “touch the ‘save’ button after touching all images to be saved” to prompt the user to select images to be saved. In synchronism with this display, the CPU  20  controls the display unit  16  to display a “save” button at, for example, the lower right end of the display unit  16  to designate the end of selection and execution of save (step S 116 ). 
     At this time, the CPU  20  controls the display unit  16  to also display an empty check box at, for example, the upper left portion of each reduced image. For a touched reduced image, the CPU  20  controls the display unit  16  to display a check “✓” in the check box. The user can easily discriminate an image to be saved from one not to be saved. 
     Alternatively, for a reduced image touched to be saved, the entire reduced image may be displayed semi-transparently, and a legend such as “RECORD” may be displayed in red to overlap the image. 
     Then, the CPU  20  waits until the user touches the “save” button and ends selection of reduced images (step S 117 ). If selection of reduced images is designated, the CPU  20  determines it in step S 117 . The CPU  20  converts image data which corresponds to each selected reduced image and is held in the buffer memory  14 , into an image data file in a predetermined data file format such as JPEG. The CPU  20  records the obtained image data file on the memory card  31  (step S 118 ), ending a series of processes in the continuous capturing mode. 
     In the operation example of  FIG. 2 , images to be saved are individually selected from reduced images. Alternatively, the user may select two, start and end images indicating the range of time series successive images considered to match a composition the user wants, out of a displayed list of reduced images. In this case, a plurality of images within the continuous range defined by the two, start and end images are selected at once. 
     In any case, the user can select an image to be recorded from successive images to be recorded. 
     As described above in detail, according to the first embodiment, a plurality of images of a moving object can be captured easily in a composition the user wants. 
     In addition, in the first embodiment, when the main object MO enters the designated area TA, the current frame rate automatically switches to a higher frame rate and continuous capturing is maintained. A larger number of images of the main object MO in a composition the user wants can be acquired. As a result, the user can capture satisfactory images with a high success rate. 
     In the first embodiment, when setting frame rates for continuous capturing, the motion vector of the main object MO in the screen is calculated, and frame rate FR 2  used when the main object MO exists in the designated area TA and frame rate FR 1  before and after this state are set in accordance with the magnitude of motion vector. 
     By using a motion vector calculation algorithm popular in moving image processing, appropriate frame rates can be set in accordance with the moving speed of the main object MO serving as a moving object within the screen. 
     In the above description of the embodiment, the user sets the arbitrary designated area TA. However, it is also possible to prepare a plurality of designated area patterns in advance and select an arbitrary one of them by the user. 
     Preparing patterns of the designated area TA in advance can reduce the load on the user in capturing in a general composition. capturing can more easily and quickly shift to continuous capturing. 
     Although not described in the embodiment, the frame rate of continuous capturing may be set aiming at a composition in which a main object and a characteristic object in the background coexist. For example, characteristic objects whose patterns can be extracted from images, such as various structural landmarks including a tower and a building, and animals such as a pet are considered to belong to the background area. When a main object overlaps a characteristic object, the frame rate of continuous capturing is intentionally decreased. This enables reliably capturing an image in a more expressive composition without missing a good shot. 
     When extracting the pattern of the characteristic object from the image, the user may directly designate the characteristic object on the touch input unit  24  integrally formed with the display unit  16 , as described in the embodiment. This can further reduce the load of image processing calculation for pattern extraction. 
     (Second Embodiment) 
     The second embodiment in which the present invention is applied to a digital camera will be described with reference to several views of the accompanying drawing. 
     The circuit arrangement of a digital camera  10  according to the second embodiment is basically the same as that shown in  FIG. 1 . The same reference numerals denote the same parts, and an illustration and description thereof will not be repeated. 
     In the second embodiment, an area entrance determination unit  15   c  of an image processing unit  15  determines how much the main object has entered a specified image capturing position, based on whether the distance between the position of the main object and an image capturing position specified by the user that is calculated by processes of an object detection unit  15   a  and motion vector analysis unit  15   b  becomes less than or equal to first and second set distances r 1  and r 2 . 
     An operation in the second embodiment will be explained. 
     Note that the following operation is executed after a CPU  20  reads an operation program and data stored in a program memory  22 , expands them in a work memory  21 , and stores them when capturing a plurality of still images temporally continuous in the continuous capturing mode. 
     Operation programs and the like stored in the program memory  22  are those stored in the program memory  22  in shipment from the manufacturing factory of the digital camera  10 . In addition, the operation programs and the like include new operation programs, data, and the like which are downloaded from the outside by connecting the digital camera  10  to a personal computer in, for example, upgrading of the digital camera  10 . 
       FIG. 5  shows a series of processing items regarding capturing and subsequent recording in the continuous capturing mode. At the beginning of processing, the CPU  20  scans and drives a solid-state image sensor  12  via an image sensor driving unit  27  at a predetermined frame rate of, for example, 60 frames/second. While obtained images are sequentially buffered in a buffer memory  14 , the CPU  20  controls a display unit  16  to display these images as live-view images in real time (step S 201 ). The CPU  20  controls the display unit  16  to display a character string such as “designate a position to capture a main object” as a guide message at part of the display unit  16  such as the bottom of the screen to prompt the user of the digital camera  10  to designate the image capturing position of the object (step S 202 ). In this manner, the CPU  20  notifies the user to designate the image capturing area of the object. 
     After the notification, the CPU  20  determines whether the user has actually designated the image capturing position (step S 203 ). More specifically, the CPU  20  determines the designation of the image capturing position based on whether the user has performed a touch operation to designate an arbitrary position in accordance with a coordinate signal output from a touch input unit  24  integrally formed with the display unit  16 . 
     If the user has not designated the position, the CPU  20  returns the process to step S 201  to repetitively execute the same process. 
     If the user has designated the position by a touch operation on the touch input unit  24 , the CPU  20  determines it in step S 203 . Then, the CPU  20  controls the object detection unit  15   a  and motion vector analysis unit  15   b  of the image processing unit  15  to analyze a motion vector in time series images buffered in the buffer memory  14  for each predetermined block area (not shown). The CPU  20  specifies, as the position of the main object, the position of a block area analyzed to have a specific motion vector (step S 204 ). 
     When there are a plurality of block areas having a specific motion vector, for example, the center of a block which has the specific motion vector and exists at the shortest distance from a position designated by the touch operation can be employed as the position of the main object. As the object position, the average of the center positions of a plurality of block areas having a specific motion vector may be adopted. 
     In the second embodiment, the CPU  20  uses, for example, 16 pixels in the vertical direction×16 pixels in the horizontal direction as a basic block, divides an image into a plurality of block areas, and controls the motion vector analysis unit  15   b  to analyze a motion vector in each divided block area. From the analysis result, the CPU  20  specifies, as the area of the main object, a block area having a specific motion vector in comparison with the remaining block areas. 
     Details of motion vector analysis processing executed by the motion vector analysis unit  15   b  is a well-known technique generally executed in a moving picture compression encoding technique such as Moving Picture Experts Group (MPEG), and a description thereof will be omitted. 
     After a block area containing the main object is specified, the CPU  20  sets two types of image capturing rates FR 1  and FR 2  (FR 1 &lt;FR 2 ) in continuous capturing in accordance with the distance between a pixel position closest to the image capturing position designated by the user within the block area and the image capturing position designated by the user (step S 205 ). 
     Image capturing rate FR 1  is an image capturing frame rate used in continuous capturing when the distance between the position of a partial area of a main object MO and the designated image capturing position is within the first distance r 1 . Image capturing rate FR 2  is an image capturing frame rate used in continuous capturing when the distance between the position of a partial area of the main object MO and the designated image capturing position is within the second distance r 2  shorter than the first distance r 1  (r 1 &gt;r 2 ). 
     Upon completion of various settings, the CPU  20  suspends continuous capturing control until the area entrance determination unit  15   c  of the image processing unit  15  determines that the position of a partial area of the main object MO in the image exists within the first distance r 1  (step S 206 ). 
       FIG. 6A  shows the relationship between the position of the main object MO and a designated position TP in the screen displayed on the display unit  16 . In this state, a distance r from the front end position of the main object MO to the image capturing position TP has not reached either the first distance r 1  or second distance r 2 . Thus, the CPU  20  does not start continuous capturing control. 
     Note that the main object MO in the screen of the display unit  16  is an object moving in a direction indicated by an arrow A 11 . The moving direction of the main object MO is not limited to one obtained when the digital camera  10  is fixed by a tripod or the like and captures an image, and a real moving object serving as the main object MO moves within the screen. The movement of the main object MO includes even relative movement within the screen when the user holds the digital camera  10  in his hands and captures an image, and the composition is changed so that the main object MO moves to a position the user wants within the capturing range. 
     In  FIG. 6A , lines C 1  to C 4  indicated by two vertical lines and two horizontal lines, that is to say, a total of four broken lines are set to assist capturing in a composition at the golden ratio. For example, whether to display C 1  to C 4  on the display unit  16  can be switched by a display key operation on the operation unit  23 . 
     If the area entrance determination unit  15   c  determines that distance r from the position of a partial area of the main object MO in the image to the image capturing position TP becomes less than or equal to the first distance r 1 , the CPU  20  determines it in step S 206 , and starts continuous capturing control at image capturing rate FR 1  of, for example, 15 frames/second set in step S 205  (step S 207 ). The CPU  20  sequentially stores the raw data acquired by capturing in the buffer memory  14 . 
     Then, the area entrance determination unit  15   c  determines whether distance r from the position of a partial area of the main object MO in the image to the image capturing position TP becomes less than or equal to the second distance r 2  (step S 208 ). If the area entrance determination unit  15   c  determines that distance r has not become less than or equal to the second distance r 2 , the CPU  20  returns the process to step S 207 . 
     By repetitively executing the processes of steps S 207  and S 208 , the CPU  20  waits until the area entrance determination unit  15   c  determines that distance r from the position of a partial area of the main object MO to the image capturing position TP becomes less than or equal to the second distance r 2 , while continuing continuous capturing control at image capturing rate FR 1 . 
       FIG. 6B  shows a state in which the main object MO further moves down to the right within the screen from the state of  FIG. 6A , and distance r from the position of a partial area of the main object MO to the image capturing position TP has become less than or equal to the first distance r 1  but has not become less than or equal to the second distance r 2 . As shown in  FIG. 6B , since the main object MO further moves in a direction indicated by an arrow A 12  within the screen, distance r from the position of the main object MO to the image capturing position TP becomes less than or equal to the second distance r 2 , and the composition comes close to one the user intends. 
     When the main object MO further moves within the screen of the display unit  16  and distance r up to the image capturing position TP becomes less than or equal to the second distance r 2 , as shown in  FIG. 6C , the CPU  20  determines it in step S 208 , and maintains continuous capturing processing at image capturing rate FR 2  of, for example, 30 frames/second set in step S 205  instead (step S 209 ). 
     The area entrance determination unit  15   c  determines whether the distance between the position of the main object MO in the image and the image capturing position TP becomes longer than the second distance r 2  (step S 210 ). If the area entrance determination unit  15   c  determines that the distance from the position of a partial area of the main object MO to the image capturing position TP is less than or equal to the second distance r 2 , the CPU  20  returns the process to step S 209 . 
     By repetitively executing the processes of steps S 209  and S 210 , the CPU  20  maintains continuous capturing control at image capturing rate FR 2  while the position of a partial area of the main object MO in the image exists within the second distance r 2  from the image capturing position TP. 
     If the entire area of the main object MO in the image moves apart from the image capturing position TP by more than the second distance r 2 , the CPU  20  determines it in step S 210 , and again maintains continuous capturing at image capturing rate FR 1  set in step S 205  (step S 211 ). 
     After that, the area entrance determination unit  15   c  determines whether the distance between the entire main object MO in the image and the image capturing position TP becomes longer than the first distance r 1  (step S 212 ). If the area entrance determination unit  15   c  determines that the position of a partial area of the main object MO exists within the first distance r 1  and does not move apart, the CPU  20  returns the process to step S 211 . 
     By repetitively executing the processes of steps S 211  and S 212 , the CPU  20  maintains continuous capturing at image capturing rate FR 1  until the position of a partial area of the main object MO in the image exists within the first distance r 1  from the image capturing position TP. 
     If the area entrance determination unit  15   c  determines that the entire area of the main object MO in the image moves apart from the image capturing position TP by more than the first distance r 1 , the CPU  20  determines it in step S 212 , and stops continuous capturing control (step S 213 ). 
     After the stopping of continuous capturing, the CPU  20  generates reduced images by greatly decreasing the number of pixels in each of image data which are obtained by a series of continuous capturing operations and held in the buffer memory  14  (step S 214 ). 
     The CPU  20  controls the display unit  16  to display a list of generated reduced images, and display a guide message such as “touch the ‘save’ button after touching all images to be saved” to prompt the user to select images to be saved. In synchronism with this display, the CPU  20  controls the display unit  16  to display a “save” button at, for example, the lower right end of the display unit  16  to designate the end of selection and execution of save (step S 215 ). 
     At this time, the CPU  20  controls the display unit  16  to also display an empty check box at, for example, the upper left portion of each reduced image. For a reduced image touched by the user, the CPU  20  controls the display unit  16  to display a check “✓” in the check box. The user can easily discriminate an image to be saved from one not to be saved. 
     Alternatively, for a reduced image touched by the user to be saved, the entire reduced image may be grayed out, and a legend such as “RECORD” may be displayed in red to overlap the image. 
     Then, the CPU  20  waits until the user touches the “save” button and ends selection of reduced images (step S 216 ). If selection of reduced images is designated, the CPU  20  determines it in step  5216 . The CPU  20  converts image data which corresponds to each selected reduce image and is held in the buffer memory  14 , into an image data file in a predetermined data file format such as JPEG. The CPU  20  records the image data file on the memory card  31  (step S 217 ), ending a series of processes in the continuous capturing mode. 
     In the operation example of  FIG. 5 , images to be saved are individually selected from reduced images. Alternatively, the user may select two, start and end images indicating the range of time series successive images considered to match a composition the user wants, out of reduced images displayed in a list. In this case, a plurality of images within the continuous range defined by the two, start and end images are selected at once. 
     As described above in detail, according to the second embodiment, a plurality of images of a moving object can be captured easily in a composition the user wants. 
     In the second embodiment, the start and end of capturing and the image capturing frame rate in continuous capturing are variously set based on the distance between the closest position of the main object MO and the image capturing position TP designated by the user. Control by the CPU  20  using the image processing unit  15  can be further simplified. 
     Note that the first and second embodiments have described a method of controlling the image capturing frame rate at two stages, but the present invention is not limited to this. For example, in the above embodiments, finer image capturing frame rates may be set and changed at multiple stages in accordance with, for example, the distance between the position of the main object MO and the designated area TA or designated position TP. 
     In the above embodiments, the present invention is applied to a digital camera which performs continuous capturing. However, the present invention is not limited to this, and is similarly applicable to various devices such as a cellular phone, personal digital assistant (PDA), electronic book reader, portable game console, and portable computer as long as an electronic device has a camera function. 
     Further, the present invention is not limited to the above-described embodiments and can be variously modified without departing from the scope of the invention in practical use. Functions executed in the above-described embodiments may be combined as properly as possible. The embodiments include various stages, and various inventions can be extracted by an appropriate combination of components disclosed. For example, when effects are obtained even if several components are omitted from all those described in the embodiments, an arrangement from which these components are omitted can be extracted as an invention. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.