Patent Publication Number: US-2012032988-A1

Title: Display control apparatus that displays list of images onto display unit, display control method, and storage medium storing control program therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to display control for displaying a list of images onto a display unit, and particularly, relates to a technique about display control for scrolling images. 
     2. Description of the Related Art 
     Some digital cameras have an index function that lists reduced picked-up images when displaying the picked-up images read from a recording medium onto a display unit like a liquid crystal display. 
     For example, Japanese Laid-Open Patent Publication (Kokai) No. 2000-125251 (JP 2000-125251A) discloses a technique that displays thumbnail images onto a display unit in a two-dimensional rectangular arrangement so as to enable to scroll a screen of the display unit in at least one of vertical and horizontal directions. 
     This technique keeps continuity among screens by displaying thumbnail images, which were located at a bottom in a screen before scrolling, at a top of a screen after scrolling. 
     Japanese Laid-Open Patent Publication (Kokai) No. 2005-275034 (JP 2005-275034A) discloses a technique that displays desired images, which have been selected by a user from thumbnail images displayed on a display unit, in a screen one by one. 
     This technique enables to operate a desired image efficiently by enlarging only the selected image and arranging it at the top of the screen. 
     Incidentally, when checking massive images stored in a mass storage medium, it is efficient to search by scrolling thumbnail images displayed on a display unit. Here, quick search for a desired image from massive thumbnail images requires to accelerate scrolling. 
     However, JP 2000-125251A is difficult to grasp a content of a thumbnail image when increasing the scrolling speed of the thumbnail images because of small size of the thumbnail image during scrolling. 
     JP 2005-275034A displays only the thumbnail image selected by a user in large size, which increases workload for selecting the desired image to be displayed in large size. Particularly, when a plurality of images are desired to be enlarged, it becomes difficult to search desired images quickly from massive thumbnail images. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mechanism that is capable of searching for a desired image from massive images listed by scrolling on a display unit. 
     Accordingly, a first aspect of the present invention provides a display control apparatus that controls a display unit to display a list of images, comprising a display control unit configured to control so that the images are displayed in a predetermined order on the display unit, a scrolling control unit configured to control so as to scroll the images displayed on the display unit, and a control unit configured to control the display control unit to decrease the number of images displayed in a screen and to increase a size of the displayed images when the scrolling control unit changes scrolling speed from low speed to high speed. 
     Accordingly, a second aspect of the present invention provides a control method for a display control apparatus that controls a display unit to display a list of images, the control method comprising a display control step of controlling so that the images are displayed in a predetermined order on the display unit, a scrolling control step of controlling so as to scroll the images displayed on the display unit, and a control step of controlling so as to decrease the number of images displayed in a screen in the display control step and to increase a size of the displayed images when the scrolling speed is changed from low speed to high speed in the scrolling control step. 
     Accordingly, a third aspect of the present invention provides A non-transitory computer-readable storage medium storing a control program causing a computer to execute a control method for a display control apparatus that displays a list of images on a display unit, the control method comprising a display control step of controlling so that the images are displayed in a predetermined order on the display unit, a scrolling control step of controlling so as to scroll the images displayed on the display unit, and a control step of controlling so as to decrease the number of images displayed in a screen in the display control step and to increase a size of the displayed images when the scrolling speed is changed from low speed to high speed in the scrolling control step. 
     According to the present invention, since the variation of the scrolling speed of the index screen from low speed to high speed increases the image size and decreases the number of images displayed in a screen, the visibility of picked-up images during scrolling improves. Accordingly, a user can quickly search a desired image from massive images listed onto the display unit during scrolling. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an external view showing a digital camera as an example of a display control apparatus to which embodiments of the present invention can be applied. 
         FIG. 1B  is a block diagram schematically showing an electrical configuration of the digital camera shown in  FIG. 1A . 
         FIG. 2A ,  FIG. 2B , and  FIG. 2C  are views showing an example of time-variations of an index screen displayed onto a display unit when a user performs a scrolling operation to a cross key of an operation unit of the digital camera shown in  FIG. 1A . 
         FIG. 3A  through  FIG. 3F  are views showing an example of display modes of the index screen on the display unit corresponding to scrolling speed changed by an operation of the cross key. 
         FIG. 4  is a graph showing a relationship between a period during which the cross key is pushed and held in a predetermined direction (a holding time) and a scrolling time per screen. 
         FIG. 5  is a flowchart showing an example of an operation of the digital camera shown in  FIG. 1A . 
         FIG. 6  is a view showing a list of priority flags determined by the process in  FIG. 5 . 
         FIG. 7  is a view showing an example of priority order table used in the process in  FIG. 5 . 
         FIG. 8  is a flowchart showing a displaying image selection/enlargement process executed in the step S 1005  in  FIG. 5 . 
         FIG. 9A  through  FIG. 9D  are views showing an example of display modes of the index screen corresponding to moving speed of a finger on a touch sensor. 
         FIG. 10  is a flowchart showing an example of an operation of a digital camera as a display control apparatus according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereafter, embodiments according to the present invention will be described in detail with reference to the drawings. 
       FIG. 1A  is an external view showing a digital camera  100  as an example of a display control apparatus to which embodiments of the present invention can be applied. A display unit  110  displays an image and a variety of information. A touch panel is overlaid on the display unit  110  to enable a touch operation to the display unit  110 . 
     A shutter button  61  is an operation unit for instructing shooting. A mode dial  60  is an operation unit for changing various modes. A connector  130  connects a communication I/F (interface)  107  mentioned later to a connecting cable  131 . A cross key  70  is a direction button that receives various operations from a user, and can be operated in four directions including an up direction, a down direction, a left direction, and a right direction. Although the cross key  70  is described as a single operating member here, as long as it can operate in the four directions, four independent buttons arranged at a cross are sufficient. 
     A controller wheel  73  is an operating member that can receive a rotary operation, and is used for instructing selections in cooperation with the cross key  70 . A rotary operation of the controller wheel  73  generates an electric pulse signal by which a CPU  101  controls units of the digital camera  100 . A rotation angle and the number of rotation of the controller wheel  73  can be determined based on the pulse signal. 
     It should be noted that the controller wheel  73  may be any operating member that can detect a rotary operation. For example, the controller wheel  73  may be a dial operating member that generates the pulse signal by a rotation of itself according to a user&#39;s rotary operation. Alternatively, the controller wheel  73  may be an operating member that consists of touch sensors and detects a rotary operation of a user&#39;s finger on the controller wheel  73  without rotating the controller wheel  73  itself (a touch wheel). 
     A power switch  72  switches ON/OFF of a power supply. The touch panel overlaid on the display unit  110 , the power switch  72 , the shutter button  61 , the mode dial  60 , the cross key  70 , and the controller wheel  73  are operating members included in an input unit  105  mentioned later. 
     An external storage medium  108  is a memory card, a hard disk, etc. A storage medium slot  201  is a slot for storing the external storage medium  108 . The external storage medium  108  stored in the storage medium slot  201  can communicate with the digital camera  100  via a storage-medium I/F  106 . A cover  202  closes the storage medium slot  201 . 
       FIG. 1B  shows an example of an electrical configuration of the digital camera  100  shown in  FIG. 1A . 
     In  FIG. 1B , the CPU  101 , a nonvolatile memory  102 , a memory  103 , a display control part  104 , the input unit  105 , the storage-medium I/F  106 , the communication I/F  107 , an image pickup unit  115 , and an image processing unit  116  are connected to an internal bus  111 . The units that are connected to the internal bus  111  can mutually exchange data via the internal bus  111 . 
     The image pickup unit  115  comprises an image pickup lens, an image pickup device, etc. The image processing unit  116  applies a pixel interpolation process, a development process, a color process, a reducing process, an encoding process, a compression process, etc. to image data of a moving image or a static image picked up by the image pickup unit  115 . The processed image data is recorded into the external storage medium  108  as an image file. The image processing unit  116  applies various processes, such as a decompression process, a decoding process, the color process, a resizing process, for displaying an image on the display unit  110  to the image file read from the external storage medium  108 . It should be noted that the display unit  110  functions as an electronic view finder (a through image display) by converting the image signal picked up by the image pickup unit  115  into a digital image signal by an A/D conversion, storing the digital image signal into the memory  103 , converting the digital image signal stored into an analog image signal, and transmitting the analog image signal sequentially to the display unit  110  for displaying. 
     The nonvolatile memory  102  stores image data, other data, various programs for operating the CPU  101 , etc. The nonvolatile memory consists of a hard disk (HD), a ROM, etc. The memory  103  consists of a RAM, for example. The CPU  101  controls the units of the digital camera  100  according to the programs stored in the nonvolatile memory  102 , for example, while using the memory  103  as a work memory. 
     The input unit  105  receives a user&#39;s operation, generates a control signal corresponding to the operation, and supplies it to the CPU  101 . For example, the input unit  105  has the above-mentioned various operating members like the touch panel as input devices that receive user&#39;s operations. It should be noted that the touch panel is an input device that outputs coordinate information corresponding to a position at which a user&#39;s fingertip contacts in the planar input unit, for example. The CPU  101  controls the units of the digital camera  100  according to the program based on the control signal that is generated by the input unit  105  corresponding to the user&#39;s operations to the input devices and is supplied from the input unit  105 . Accordingly, the digital camera  100  acts according to the user&#39;s operations. 
     The display control unit  104  outputs a display signal for displaying an image on the display unit  110 . For example, a display control signal generated by the CPU  101  according to the program is supplied to the display control unit  104 . The display control unit  104  generates a display signal based on the display control signal, and outputs it to the display unit  110 . For example, the display control unit  104  controls the display unit  110  to display a GUI (Graphical User Interface) screen based on the display control signal generated by the CPU  101 . 
     When the input unit  105  is provided with the touch panel, the input unit  105  and the display unit  110  can be united. For example, the touch panel of which transmittance is high so as not to obstruct the display of the display unit  110  is overlaid on the display surface of the display unit  110 . Then, the input coordinate on the touch panel is associated with the display coordinate on the display unit  110 . This can constitute a GUI that looks as if a user can directly operate the screen displayed on the display unit  110 . 
     The external storage media  108  like a memory card can be connected to the storage-medium I/F  106 . The CPU  101  controls the storage-medium I/F  106  to read data from the external storage medium  108  connected, and to write data into the external storage medium  108  concerned. The CPU  101  controls the communication I/F  107  so as to communicate with an external device connected via a communication cable  131 , and with networks  120  such as a LAN and the Internet. 
     It should be noted that the CPU  101  can detect the following operations to the touch panel included in the input unit  105 . An operation of a finger or a pen to touch the touch panel (referred to as a touch-down hereafter). A state to keep the finger or the pen touching the touch panel (referred to as a touch-on hereafter). An operation of the finger or the pen to move while touching the touch panel (referred to as a move hereafter). An operation to detach the finger or the pen that has touched the touch panel (referred to as a touch-up hereafter). A state where nothing touches the touch panel (referred to as a touch-off hereafter). 
     These operations and the position coordinate at which the finger or the pen are touching the touch panel are notified to the CPU  101  through the internal bus  111 , and the CPU  101  determines what operations were given on the touch panel based on the notified information. Regarding the move operation, the direction of the movement of the finger or the pen that moves on the touch panel can be determined as a vertical component and a horizontal component based on the change of the position coordinate. 
     A continuous operation of the touch-down, the move, and the touch-up on the touch panel draws a stroke. An operation to draw a stroke quickly is called a flick. The flick is an operation to move a finger while touching the touch panel in a certain distance quickly, and to detach the finger. In the other words, the flick is an operation to follow the touch panel quickly so as to snap the touch panel with the finger. 
     When the move operation beyond a predetermined distance and beyond a predetermined speed is detected and the touch-up is then detected, it is determined that the flick operation has been performed. When the move operation beyond the predetermined distance in speed less than the predetermined speed is detected, it is determined that a drag has been performed. The touch panel can use any of various systems such as a resistance film system, a capacitive sensing method, a surface acoustic wave system, an infrared system, an electromagnetic induction type, an image recognition system, a photosensor system. 
     Next, operations of first and second embodiments according to the present invention will be described. 
     In the first embodiment, when the scrolling speed becomes higher when index images are displayed in the scrolling process, the number of images displayed in one screen decreases and the size of each image increases. This improves the visibility even if the scrolling speed becomes high, which enables a user to find a desired image certainly and quickly. In this embodiment, a user can instruct vertical scrolling by one of the following methods. 
     (1) An operation (push) of the cross key  70  upward instructs a downward scrolling (a scrolling for moving displayed images from top to bottom, and for displaying hidden images arranged over the top). Conversely, an operation (push) of the cross key  70  downward instructs an upward scrolling (a scrolling for moving displayed images from bottom to top, and for displaying hidden images arranged under the bottom). The scrolling speed increases as the time of pushing the cross key  70  in the same direction becomes longer. 
     (2) A rotary operation of the controller wheel  73  clockwise instructs the upward scrolling, and a rotary operation of the controller wheel  73  counterclockwise instructs the downward scrolling. The scrolling speed increases as the rotation speed of the rotary operation increases. 
     (3) An upward drag or an upward flick on the touch panel instructs the upward scrolling. A downward drag or a downward flick instructs the downward scrolling. The scrolling speed increases as the moving speed of the touch position by the drag or the flick becomes faster. 
       FIG. 2A ,  FIG. 2B , and  FIG. 2C  are views showing an example of time-variations of an index screen displayed onto the display unit  110  when a user performs the scrolling operation. 
     Massive images stored in the external storage medium  108  are fitted in rectangular frames  203  arranged across an index screen  202  displayed on the display unit  110  as shown in  FIG. 2A  through  FIG. 2C . In  FIG. 2A , the display unit  110  displays the index screen  202  that consists of 64 images (the numbers  1  through  64 ) that are arranged by 8 images in vertical and 8 images in horizontal (eight lines x eight columns). The lines in the display area are called L 1 , L 2 , . . . , L 8  in the order from the top. Here, when the cross key  70  is pushed downward, the images in the index screen  202  move upward as shown in  FIG. 2B . 
       FIG. 2B  is a schematic view showing a state after scrolling by one line from the state in  FIG. 2A . In  FIG. 2B , the images (the numbers  1  through  8 ) on the top line (L 1 ) in  FIG. 2A  move out of the index screen  202  and are disappeared due to the upward scrolling. Instead, the images of the numbers  65  through  72  newly move into the bottom line (L 8 ) and are displayed on the index screen  202 . When a user keeps pushing the cross key  70  downward, the images continue scrolling upward.  FIG. 2C  is a schematic view showing a state after scrolling by eight lines (namely, the images exactly displayed on one screen simultaneously) from the state in  FIG. 2A  by continuing scrolling upward. The images of the numbers  1  through  64  on eight lines move out of the index screen  202  and are disappeared, and the images of the numbers  65  through  72  move to the top line (L 1 ) instead. 
     The digital camera of this embodiment moves the images on the index screen  202  at the speed that takes 0.5 seconds to scroll by one line in the first stage in which the user starts to push the cross key  70  downward. Therefore, it takes 4.0 seconds (=0.5 seconds×8 lines) from the state in  FIG. 2A  to the state in  FIG. 2C . 
     Next, display modes of the index screen  202  on the display unit  110  according to a scroll speed will be described with reference to  FIG. 3A  through  FIG. 3F . 
     In an initial state shown in  FIG. 3A , a total of 64 images in which 8 images per line (8 columns) are multiplied by 8 lines of L 1  through L 8  are arranged in the index screen  202  displayed on the display unit  110 . 
     When the cross key  70  is kept pushing downward beyond 4 seconds in this state, the scrolling speed of the index screen  202  upward increases. In connection with it, as shown in  FIG. 3B , the number of the images displayed on the index screen  202  becomes a total of 36 images in which 6 images per line (6 columns) are multiplied by 6 lines of L 1  through L 6 , and the size of an image is enlarged. Here, the number of the images to be displayed is reduced as compared with the state shown in  FIG. 3A  by thinning out the images while leaving high priority images. Accordingly, the moving speed of the display area in all the images by scrolling increases while displaying the images in the larger size than the state shown in  FIG. 3A . The moving speed of the display area here is the moving speed of the display area in all the images that are targets to be displayed in the initial state shown in  FIG. 3A  rather than the moving speed of the images displayed on the display unit  110 . For example, the moving speed is the speed of the display area moved from the state displaying the images of the numbers around  1  through  64  to the state displaying the images of the numbers around  641  through  704 , when 1000 images of the numbers  1  through  1000  are targets to be displayed in the initial state. If the moving speed becomes faster, all the 64 images of the numbers  641  through  704  are not displayed as the images of the numbers around  641  through  704 , the fewer numbers of images are displayed in larger size. The method of thinning out according to the priority of the images to display will be mentioned later. 
     When the cross key  70  is kept pushing downward beyond 8 seconds from the initial state, the scrolling speed of the images upward on the index screen  202  further increases as shown in  FIG. 3C . The number of the images displayed on the index screen  202  is further reduced to a total of 16 images in which 4 images per line are multiplied by 4 lines of L 1  through L 4 , and the size of an image becomes larger than that in  FIG. 3B . 
     When the cross key  70  is kept pushing downward beyond 12 seconds from the initial state, the scrolling speed of the images upward on the index screen  202  becomes higher than that in  FIG. 3C  as shown in  FIG. 3D . The number of the images displayed on the index screen  202  is further reduced to a total of 9 images in which 3 images per line are multiplied by 3 lines of L 1  through L 3 , and the size of an image becomes larger than that in  FIG. 3C . 
     In  FIG. 3C  and  FIG. 3D , date indications  300  and  301  are superimposed on the index screen  202  so as to grasp shooting dates of the images displayed on the index screen  202  during the high speed scrolling. 
     When the date indications  300  and  301  are superimposed on the index screen  202 , the display areas of the date indications  300  and  301  can be translucent so as to keep the visibility of the background images. The date indications  300  and  301  can be displayed on the index screen  202  only in predetermined periods when the year or the month of the shooting dates of the background images changes by scrolling. It should be noted that the date indications  300  and  301  can be displayed at any positions in the index screen  202 . 
     When the cross key  70  is kept pushing downward beyond 16 seconds from the initial state, the scrolling speed of the images upward on the index screen  202  becomes higher than that in  FIG. 3D  as shown in  FIG. 3E . The number of the images displayed on the index screen  202  is further reduced to a total of 4 images in which 2 images per line are multiplied by 2 lines of L 1  and L 2 , and the size of an image becomes larger than that in  FIG. 3D . 
     When the cross key  70  is kept pushing downward beyond 20 seconds from the initial state, the scrolling speed of the images upward on the index screen  202  becomes higher than that in  FIG. 3E  as shown in  FIG. 3F . The number of the images displayed on the index screen  202  is further reduced to a total of 1 image in which 1 image per line is multiplied by 1 line of L 1 , and the size of an image becomes larger than that in  FIG. 3E  and an image occupies the whole screen. 
       FIG. 4  is a graph showing a relationship between a period during which the cross key  70  is pushed and held in a predetermined direction (a holding time) and a scrolling time per screen of the display unit  110 . 
     As shown in  FIG. 4 , when the holding time of the cross key  70  is not beyond 4 seconds, the scrolling time (a time period while the same image data moves from the bottom to the top of the display area and then disappears) is 4 seconds, and the number of images per screen of the display unit  110  is 64 images that are arranged by 8 images in vertical and 8 images in horizontal. Namely, the moving speed (scrolling speed) V 1  of the images is given by V1=H/4 (m/s), where H (m) is a height of the display area for one screen on the display unit  110 . 
     When the holding time of the cross key  70  exceeds 4 seconds and is not beyond 8 seconds, the scrolling time per screen of the display unit  110  is 3 seconds, and the number of the images per screen is 36 images that are arranged by 6 images in vertical and 6 images in horizontal. That is, the scrolling speed V 2  is given by V2=H/3 (m/s). 
     When the holding time of the cross key  70  exceeds 8 seconds and is not beyond 12 seconds, the scrolling time per screen of the display unit  110  is 2.5 seconds, and the number of the images per screen is 16 images that are arranged by 4 images in vertical and 4 images in horizontal. That is, the scrolling speed V 3  is given by V3=H/2.5 (m/s). 
     When the holding time of the cross key  70  exceeds 12 seconds and is not beyond 16 seconds, the scrolling time per screen of the display unit  110  is 1.5 seconds, and the number of the images per screen is 9 images that are arranged by 3 images in vertical and 3 images in horizontal. That is, the scrolling speed V 4  is given by V4=H/1.5 (m/s). 
     When the holding time of the cross key  70  exceeds 16 seconds and is not beyond 20 seconds, the scrolling time per screen of the display unit  110  is 1 second, and the number of the images per screen is 4 images that are arranged by 2 images in vertical and 2 images in horizontal. That is, the scrolling speed V 5  is given by V5=H (m/s). 
     When the holding time of the cross key  70  exceeds 20 seconds, the scrolling time per screen of the display unit  110  is 0.5 seconds, and the number of the images per screen is 1 image. That is, the scrolling speed V 6  is given by V6=2H (m/s). 
     Thus, in this embodiment, the higher the scrolling speed is, the fewer the number of the displaying images is, and the larger the size of the images is. Since the number of the displaying images decreases as the scrolling speed becomes higher, the moving speed of the display area in all the images by scrolling becomes higher while enlarging the image size. It should be noted that the above mentioned relationship among the holding time of the cross key  70 , the scroll time per screen, and the scrolling speed is one example, and can be changed arbitrarily. 
     Next, an operation example of the digital camera of this embodiment will be described with reference to  FIG. 5 . Each process in  FIG. 5  is achieved because the CPU  101  develops the program recorded in the nonvolatile memory  102  onto the memory  103  and executes. 
     In step S 501 , the CPU  101  reads attribution information of an image file of a static image or a moving image from the external storage medium  108  into the memory  103 , and proceeds with the process to step S 502 . The attribution information has Exif (Exchangeable Image File Format) information about an image, attribution information like tag information recorded inside the image file, and attribution information about another file associated with the image file, for example. The attribution information has “date and time of shooting”, “a flag showing whether a person&#39;s face is included in image data”, “image quality at the time of shooting”, “zoom magnification”, “a counted value showing the number of person&#39;s faces included in image data”, “thumbnail (reduction image)”, etc. Moreover, the attribution information has “an ID value identifying a person registered in image data”, “a marker showing display in an index screen with a priority (set by a user)”, “F value showing an aperture of a lens at the time of shooting”, etc. 
     In the step S 502 , the CPU  101  determines the priority flag of each image according to addition conditions of the priority flag shown in  FIG. 6  based on the attribution information read from the external storage medium  108 . 
     The priority flag is used to select images displayed during a scroll operation mentioned later.  FIG. 6  shows a list of the addition conditions of the priority flag. 
     In  FIG. 6 , the left column describes definitions that are used when the flag is given by evaluating attribution information, and the right column describes values of the priority flags. The flag value has five levels of  1  through  5 , and the level  1  means the highest priority. The larger the flag value is, the lower the priority is. 
     The priority flag of the level  1  is given to an image that is designated by a user&#39;s predetermined operation to display preferentially. The CPU  101  determines whether the user has set to display the image preferentially based on whether the “marker showing display in an index screen with a priority (set by a user)” among the attribution information is ON. 
     The priority flag of the level  2  is given to an image of which the number of face detection is more than N 1 . When N 1  is 5, an image in which many persons are shot can be selected. The priority flag of level  3  is given to an image of which the number of face detection is more than N 2 . When N 2  is 1, an image in which a person is shot can be selected. 
     The priority flag of level  4  is given to an image of which a shooting date is in a boundary between years. For example, it is given to an image of the first date among images shot in each year like the image of the first date among images shot in 2008. The priority flag of level  5  is given to an image of which a shooting date is in a boundary between months. For example, it is given to an image of the first date among images shot in each month like the image of the first date among images shot in May in 2008. 
     In step S 503  in  FIG. 5 , the CPU  101  generates a priority table by classifying the images by the level of the priority flag according to the level of the priority flag given to each image in the step S 502 , and stores (keeps) the generated table into the memory  103 .  FIG. 7  shows an example of the priority table. In  FIG. 7 , the left column describes the level of the priority flag and the right column describes the numbers of the images corresponding to the levels of the priority flag. 
     In step S 504 , the CPU  101  displays an initial screen of the index screen mentioned above in  FIG. 3A  onto the display unit  110 . The initial screen of the index screen displays all the images that are targets to be displayed on the index screen, without referring to the priority table held in the step S 503 . The CPU  101  acquires data of a main image included in an image file or a thumbnail included in attribution information from the external storage medium  108 , decodes and resizes the acquired data to form an image, and displays the image on the index screen. Although the images are sorted by date and time of shooting (an order of the file number) basically, they may be sorted by another sorting order. 
     In step S 505 , the CPU  101  acquires the scrolling speed v. A scrolling can be performed by the operation to the cross key  70 , the controller wheel  73 , or the touch panel, as mentioned above. The scrolling speed is determined by the holding time to push the cross key  70 , the rotation speed of the rotary operation to the controller wheel  73 , or the moving speed of the touch position to the touch panel. The CPU  101  acquires the current scrolling speed v determined by these operations by the user. 
     In step S 506 , the CPU  101  executes a displaying image selection/enlargement process for 6 speed ranges S 1  through S 6  based on the scrolling speed acquired in the step S 505 . Details of the process will be described later with reference to  FIG. 8 . 
     In step S 507 , the CPU  101  displays the images set in the step S 506  on the index screen. That is, the CPU  101  reads the main image or the thumbnail of the image set in the step S 506  from the external storage medium  108 , decodes, resizes, and displays it. Then, since the CPU  101  returns the process to the step S 505  and repeats the process, the index screen is dynamically updated according to the scrolling speed. 
       FIG. 8  shows an example of the displaying image selection/enlargement process executed for the 6 speed ranges S 1  through S 6 . The definitions of the speed ranges S 1  through S 6  are as follows. 
         S 1:  |v|≦V 1 
         S 2:  V 1&lt; |v|≦V 2 
         S 3:  V 2&lt; |v|≦V 3 
         S 4:  V 3&lt; |v|≦V 4 
         S 5:  V 4&lt; |v|≦V 5 
         S 6:  V 5&lt; |v|   
     In step S 1001  in  FIG. 8 , the CPU  101  determines which of the speed ranges S 1  through S 6  corresponds to the scrolling speed acquired in the step S 505 . When it is determined that the scrolling speed falls within the speed range S 1 , the process proceeds to step S 1007 . 
     In the step S 1007 , the CPU  101  sets 64 images in an 8×8 matrix that will be displayed on the index screen  202  according to date and time of shooting. All the images become targets to be displayed on the index screen. In this case, the priority table is not referred. Next, the process returns to the step S 507  in  FIG. 5 . 
     When the CPU  101  determines that the scrolling speed falls within the speed range S 2  in the step S 1001 , the process proceeds to step S 1008 . 
     In the step S 1008 , the CPU  101  sets 36 images in a 6×6 matrix that will be displayed on the index screen  202  by selecting images in the decreasing order of the level of the priority flag with reference to the priority table stored in the memory  103  in the step S 503 , and proceeds with the process to step S 1013 . When the CPU  101  detects scrolling by the operation of the cross key  70  under the condition where the 36 images are displayed on the index screen  202 , images are selected from the images that are displayed at the speed range S 1 . For example, when one-line scrolling is detected under the condition where 36 images are displayed, the CPU  101  selects 36 images from 64 images from the number  9  through the number  72  (see  FIG. 2B ), which will be displayed when scrolling one line at the speed range  1 , according to the level of the priority flag defined in the priority table. 
     In step S 1013 , the CPU  101  determines whether the number of the images set in the step S 1008  is less than 36 images of the 6×6 matrix. If the number of images to which the priority flags are attached among the images included in the display area defined by the current scroll position is less than 36, the number of the images set in the step S 1008  is less than 36. When the number of the set images is not less than 36, the CPU  101  returns the process to the step S 507  in  FIG. 5 . When the number of the set images is less than 36, the CPU  101  selects and set images from images other than the images set in the step S 1008  so that the number of the set images reaches 36, and then, returns the process to the step S 507  in  FIG. 5 . 
     The images may be selected in the order of the shooting date, may be selected by every fixed number, or may be selected at random. However, the images that have been scrolled and moved out of the screen are excepted from the parent population for selection during a period of continuous scrolling in the same direction. This is to prevent the images that were scrolled out of the screen from displaying again during the scrolling in the same direction. 
     When the CPU  101  determines that the scrolling speed falls within the speed range S 3  in the step S 1001 , the process proceeds to step S 1009 . 
     In the step S 1009 , the CPU  101  sets 16 images in a 4×4 matrix that will be displayed on the index screen  202  by selecting images in the decreasing order of the level of the priority flag with reference to the priority table stored in the memory  103  in the step S 503 , and proceeds with the process to step S 1014 . 
     In step S 1014 , the CPU  101  determines whether the number of the images set in the step S 1009  is less than 16 images of the 4×4 matrix. When the number of the set images is not less than 16, the CPU  101  returns the process to the step S 507  in  FIG. 5 . When the number of the set images is less than 16, the CPU  101  selects and set images from images other than the images set in the step S 1009  so that the number of the set images reaches 16, and then, returns the process to the step S 507  in  FIG. 5 . 
     When the CPU  101  determines that the scrolling speed falls within the speed range S 4  in the step S 1001 , the process proceeds to step S 1010 . 
     In the step S 1010 , the CPU  101  sets 9 images in a 3×3 matrix that will be displayed on the index screen  202  by selecting images in the decreasing order of the level of the priority flag with reference to the priority table stored in the memory  103  in the step S 503 , and proceeds with the process to step S 1015 . 
     In step S 1015 , the CPU  101  determines whether the number of the images set in the step S 1010  is less than 9 images of the 3×3 matrix. When the number of the set images is not less than 9, the CPU  101  returns the process to the step S 507  in  FIG. 5 . When the number of the set images is less than 9, the CPU  101  selects and set images from images other than the images set in the step S 1010  so that the number of the set images reaches 9, and then, returns the process to the step S 507  in  FIG. 5 . 
     When the CPU  101  determines that the scrolling speed falls within the speed range S 5  in the step S 1001 , the process proceeds to step S 1011 . 
     In the step S 1011 , the CPU  101  sets 4 images in a 2×2 matrix that will be displayed on the index screen  202  by selecting images in the decreasing order of the level of the priority flag with reference to the priority table stored in the memory  103  in the step S 503 , and proceeds with the process to step S 1016 . 
     In step S 1016 , the CPU  101  determines whether the number of the images set in the step S 1011  is less than 4 images of the 2×2 matrix. When the number of the set images is not less than 4, the CPU  101  returns the process to the step S 507  in  FIG. 5 . When the number of the set images is less than 4, the CPU  101  selects and set images from images other than the images set in the step S 1011  so that the number of the set images reaches 4, and then, returns the process to the step S 507  in  FIG. 5 . 
     When the CPU  101  determines that the scrolling speed falls within the speed range S 6  in the step S 1001 , the process proceeds to step S 1012 . 
     In the step S 1012 , the CPU  101  sets an image that will be displayed on the index screen  202  by selecting an image having the highest level of the priority flag with reference to the priority table stored in the memory  103  in the step S 503 , and proceeds with the process to step S 1017 . 
     In step S 1017 , the CPU  101  determines whether no image is set in the step S 1012 . When the image is set, the CPU  101  returns the process to the step S 507  in  FIG. 5 . When no image is set, the CPU  101  selects and set an image from other images, and then, returns the process to the step S 507  in  FIG. 5 . 
     Although this embodiment determines the speed ranges S 1  through S 6  based on the scrolling speeds, the factor of the determination is not limited to the scrolling speed. For example, the holding time of the cross key  70 , the rotation speed of the rotary operation to the controller wheel  73 , or the moving speed of the touch position by a drag or a flick onto the touch panel is acquired, and the speed ranges S 1  through S 6  can be directly determined by the acquired value. 
     Here, an image in the index screen  202  displayed on the display unit  110  at the speed range S 2  is larger than an image at the speed range S 1 . In the same manner, an image at the speed range S 3  is larger than an image at the speed range S 2 , an image at the speed range S 4  is larger than an image at the speed range S 3 , an image at the speed range S 4  is larger than an image at the speed range S 5 , an image at the speed range S 6  is larger than an image at the speed range S 5 . 
     When the user cancels the operation of instructing the scrolling, the CPU  101  gradually reduces the size of images in the index screen  202  displayed on the display unit  110  and increases the number of images that are displayed per screen as a lapsed time, and then shifts to the initial state. 
     For example, when the holding state of the cross key  70  is canceled under the condition where 4 images of the 2×2 matrix are displayed as shown in  FIG. 3E , the index screen  202  is changed to display 9 images of the 3×3 matrix as shown in  FIG. 3D  after a predetermined time lapses. Then, whenever the predetermined time lapses, the index screen  202  is changed to display 16 images as shown in  FIG. 3C , to display 36 images as shown in  FIG. 3B , and to display 64 images as shown in  FIG. 3A . In this case, it is possible to apply known screen effects such as fading, zooming when the index screen is changed. 
     Here, in order to show intuitively that the images displayed on one screen are thinned out as the scrolling speed increases, the displays shown in  FIGS. 3A through 3F  may be replaced with the displays shown in FIGS.  9 A through  9 D. In the display method shown in  FIGS. 9A through 9D , the images displayed on one screen are thinned out and the size of the displayed image increases as the scrolling speed increases, and an overlap of the disappeared images are expressed in a depth direction in order to showing that the number of thinned out images increases as the scrolling speed increases.  FIG. 9A  and  FIG. 3A  show the similar display states.  FIGS. 9B ,  9 C, and  9 D are displayed under the corresponding conditions in  FIGS. 3C ,  3 E, and  3 D, respectively. Even if scrolling speed goes up by displaying in this way and the display size per image is large by it, the movement speed of the display rectangle in all the images by scroll is also quick simultaneously—to that extent—it can be shown to both users. 
     As described above, according to the embodiment, since the variation of the scrolling speed of the index screen from low speed to high speed increases the image size and decreases the number of images displayed in the screen, the visibility of picked-up images during the scrolling operation improves. Accordingly, a user can quickly search a desired image from massive images listed onto the display unit  110  during the scrolling operation. 
     Next, an operation of the digital camera  100  as a second embodiment of the display control apparatus according to the present invention will be described with reference to  FIG. 10 . It should be noted that duplicated sections or corresponding section with respect to the above-mentioned first embodiment will be described by diverting the figures and the signs. 
       FIG. 10  is a flowchart showing an example of an operation of the digital camera  100  of the second embodiment. Each process in  FIG. 10  is achieved because the CPU  101  develops the program stored in the nonvolatile memory  102  onto the memory  103  and executes. It should be noted that this embodiment is different from the first embodiment in the process after the step S 505  in the flowchart in  FIG. 5 . Therefore, only the different points will be described. 
     In step S 1301  in  FIG. 10 , the CPU  101  determines whether the user releases the hold of the cross key  70  to stop the scrolling operation on the index screen  202 . When the scrolling operation stops, the CPU proceeds with the process to step S 1310 . When the scrolling operation does not stop, the CPU  101  proceeds with the process to step S 1302 . Since the processes in steps S 1302  and S 1303  are identical to that in the steps S 506  and S 507 , respectively, the descriptions thereof are omitted. 
     In step S 1310 , the CPU  101  determines whether the index screen displayed on the display unit  110  includes only one image (see  FIG. 3F ). Then, when the index screen includes only one image, the CPU  101  proceeds with the process to step S 1311 . If not, the process proceeds to step S 1304 . 
     In the step S 1311 , the CPU  101  reproduces a moving image on the display unit  110 , when the main image corresponding to the thumbnail image currently displayed is a moving image. After reproduction is completed, it progresses to step S 1312 . 
     In the step S 1304 , the CPU  101  sets a fixed magnification mode, and proceeds with the process to step S 1305 . In the fixed magnification mode, the CPU  101  suspends the selection of displaying image and the change of the image size according to the scrolling speed, and keeps the display size at the time of stopping the scrolling operation in the step S 1301 . The CPU  101  displays all the images on the display unit  110  regardless of the priority after stopping the scrolling operation. For example, when the scrolling operation is stopped under the condition where 4 images of the 2×2 matrix, all the images are displayed on the display unit  110  in the 4 images format while scrolling after that. 
     In the step S 1305 , the CPU  101  detects the scrolling speed on the index screen  202  based on the operating condition of the cross key  70  by the user, and proceeds with the process to step S 1306 . 
     In the step S 1306 , the CPU  101  determines whether the scrolling operation on the index screen  202  is stopped by the user&#39;s operation of the cross key  70  and one image is selected to reproduce. Then, when the scrolling operation on the index screen  202  is stopped and one image is selected to reproduce, the CPU  101  reproduces the moving image selected in the step S 1311 . If not, the process proceeds to step S 1307 . 
     In the step S 1307 , the CPU  101  sets all the images to be displayed regardless of the priority flag, and proceeds with the process to step S 1308 . 
     In the step S 1308 , the CPU  101  updates the index screen displayed on the display unit  110  based on the images set in the step S 1307 , and proceeds with the process to step S 1309 . 
     In the step S 1309 , the CPU  101  determines whether a display reset button (not shown) is pushed to execute a reset operation. When the reset operation is not executed, the process returns to the step S 1305 . When the reset operation is executed, the process proceeds to step S 1312 . 
     In the step S 1312 , the CPU  101  resets the fixed magnification mode, and proceeds with the process to the step S 505 . Since the fixed magnification mode is reset according to the reset operation, 64 images of the 8×8 matrix are displayed on the index screen  202  that is displayed on the display unit  110 , and the initial screen state is set. 
     When returning to the initial screen state, the images displayed on the index screen  202  before the reset operation are also included and displayed on the display unit  110 . For example, when the reset operation is performed under the condition where the 4 images are displayed, 64 images including these 4 images are displayed on the display unit  110  to shift to the initial screen state. 
     As described above, in this embodiment, since the moving image is automatically reproduced when the scrolling operation stops under the condition where one image is enlarged and displayed on the index screen  202 , the operation is simplified. 
     In this embodiment, since the number of displaying images and the image size on the index screen  202  at the time of stopping the scrolling operation are kept, the search of the index screen  202  after stopping the scrolling operation can be performed comfortably. The other configurations and operation effects are the same as that of the above-mentioned first embodiment. 
     It should be noted that the control by the CPU  101  in the above-mentioned embodiments may be executed by one piece of hardware or may be shared by a plurality of pieces of hardware to control the whole apparatus. 
     Although the embodiments of the invention have been described, the present invention is not limited to the above-mentioned embodiments, the present invention includes various modifications as long as the concept of the invention is not deviated. The above mentioned embodiments are examples of the present invention, the embodiments can be combined suitably. 
     In the embodiments mentioned above, although the present invention is applied to the digital camera, it is not limited to this example. 
     That is, the present invention can be applied to any display control apparatuses that display images simultaneously, such as a PC, a PDA, a cell phone, a portable image viewer, a display unit of a printer for selecting a print image and for checking, and a digital photograph frame. Especially, it is more effective when the present invention is applied to small display units of portable electronic devices (a digital camera, a cell phone, a PDA, a portable music player, a handheld game machine, etc.). 
     Other Embodiments  
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2010-175571, filed on Aug. 4, 2010, which is hereby incorporated by reference herein in its entirety.