Patent Publication Number: US-2011069074-A1

Title: Image Display Device And Image Display Method

Description:
This application is based on Japanese Patent Application No. 2009-217709 filed on Sep. 18, 2009 and No. 2010-169704 filed on Jul. 28, 2010, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image display device which displays an image and an image display method. 
     2. Description of Related Art 
     In recent years, digital imaging devices, which record taken images (including moving images and still images) as data on a recording medium instead of recording on a film, have been widely spread. This type of imaging device is capable of recording a large amount of image data that is obtained by taking images and capable of deleting any image data item recorded. The device thus allows a user to casually take as many images as he/she likes until a satisfactory image is obtained. 
     The user uses an image display device attached to the imaging device, typically, a viewer such as a monitor or a photo frame, to reproduce image data (to play moving images or to display still images). The user selects image data to be reproduced with the use of an operation unit constituted of, for example, a touch panel. Some image display devices facilitate the selection process by displaying images corresponding to image data items (hereinafter referred to as corresponding images) such as thumbnail images. 
     However, clearly displaying a large number of corresponding images at once is difficult because of the limited display screen size of the attached image display device. The user therefore needs to operate the operation unit to switch displayed corresponding images one after another until the corresponding image of desired image data is displayed. 
     When the number of image data items is large in this case, the user may need to perform the switching many times to find and select desired image data. Specifically, the user may need to go forward (to display the next corresponding image), or go backward (to display the preceding corresponding image), through corresponding images many times. This makes the operation of selecting desired image data laborious, which is a problem. 
     In the case where there is a plurality of image data items obtained by taking images from the same angle, in the same location, at the same time of day, or the like and the user decides that the desired image data is not among this set of image data items, the user will feel no need to examine the corresponding images of this set of image data items carefully, and is likely to fast forward or fast back (to go forward or backward through many corresponding images in one operation) through the set of image data items in the hope of quickly finding and selecting the desired image data. Then the user may accidentally go past the displayed corresponding image of the desired image data (“forward overshoot” or “backward overshoot”) and take longer to select the desired image data, which is another problem. 
     To address the problems, an image display device has been proposed which allows a user to select desired image data quickly in just a few operations by displaying reduced images of image data items that resemble a selected image data item in the order of similarity, and subsequently displaying only reduced images of image data items relevant to an image data item that is selected from among the first displayed reduced images. 
     In another image display device that has been proposed, a representative image data item is determined for each group of a plurality of image data items, and reduced images of the determined image data items are displayed side by side. When a user selects an image data item that is the representative of one group, this image display device displays reduced images of image data items that belong to the same group as the selected image data item. 
     A drawback of the former image display device is that searching for an image data item to which only a few image data items are similar or relevant is difficult because their reduced images cannot be displayed preferentially. A drawback of the latter image display device is that an image data item is difficult to search for when to which group the image data item belongs is unknown. A user trying to select such an image data item as those has no choice but to search for the image to be selected by going forward or backward through many corresponding images the same way as in conventional devices. The problem of laborious operation and the problem of prolonged image data selection due to “forward overshoot” or “backward overshoot” arise as a result. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an image display device, including: 
     a display unit which displays at least one of corresponding images which are in a given order; 
     an input unit to which a switching instruction is input to switch the at least one corresponding image displayed on the display unit in the given order: and 
     a switching control unit which switches the at least one corresponding image displayed on the display unit in accordance with the switching instruction, 
     in which, when the at least one corresponding image displayed on the display unit does not have a close correlation with at least a corresponding image to be displayed next, the switching control unit switches the corresponding images by a first switching amount, which is determined based on the switching instruction, and 
     in which, when the correlation is close, the switching control unit switches the corresponding images by a second switching amount, which is determined by a method different from that of the first switching amount. 
     According to the present invention, there is also provided an image display method, including: 
     a first step of displaying at least one of corresponding images which are in a given order; 
     a second step of inputting a switching instruction which switches the at least one corresponding image displayed in the first step in the given order; and 
     a third step of switching the at least one corresponding image displayed in the first step, 
     in which, when the at least one corresponding image displayed in the first step does not have a close correlation with at least a corresponding image to be displayed next, the corresponding images are switched in the third step by a first switching amount, which is determined based on the switching instruction input in the second step, and 
     in which, when the correlation is close, the corresponding images are switched in the third step by a second switching amount, which is determined by a method different from that of the first switching amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of the structure of an image display device according to an embodiment of the present invention. 
         FIGS. 2A to 2C  are diagrams illustrating an example of how display by a display unit looks in a search for image data to be reproduced. 
         FIGS. 3A and 3B  are graphs showing examples of a basic relation between an instruction amount and a switching amount. 
         FIG. 4  is a diagram illustrating an example of a feature vector calculation method. 
         FIG. 5  is a diagram illustrating the example of the feature vector calculation method. 
         FIGS. 6A and 6B  are graphs showing examples of a relation of the instruction amount to the switching amount that is set for the switching of closely correlated corresponding images. 
         FIG. 7  is a diagram illustrating an example of a set of corresponding images and the order of the corresponding images. 
         FIGS. 8A to 8D  are diagrams illustrating a first display example. 
         FIGS. 9A to 9C  are diagrams illustrating a second display example. 
         FIGS. 10A to 10D  are diagrams illustrating a third display example. 
         FIGS. 11A to 11C  are diagrams illustrating a fourth display example. 
         FIGS. 12A and 12B  are graphs showing examples of a relation between the instruction amount and the switching amount to illustrate a modification example of switching control. 
         FIG. 13  is a diagram illustrating an example of how corresponding images are switched when various instruction amounts are input. 
         FIG. 14  is a flow chart illustrating an action of the image display device in which whether the correlation between corresponding images is close or not is determined at the time of switching the corresponding images and then the corresponding images are switched. 
         FIG. 15  is a flow chart illustrating an action of the image display device in which whether there is a close correlation or not is determined at the time image data is transferred. 
         FIG. 16  is a flow chart illustrating an action of the image display device in which whether image data that has just been taken has a close correlation or not is determined. 
         FIG. 17  is a flow chart illustrating a corresponding image switching action that is executed when whether the correlation between corresponding images is close or not is determined in advance. 
         FIGS. 18A and 18B  are diagrams illustrating a first example of a composite corresponding image selection detection action. 
         FIGS. 19A and 19B  are diagrams illustrating a second example of the composite corresponding image selection detection action. 
         FIGS. 20A to 20C  are diagrams illustrating a first example of a post-composite corresponding image selection action. 
         FIGS. 21A to 21C  are diagrams illustrating a third example of the post-composite corresponding image selection action. 
         FIGS. 22A to 22C  are diagrams illustrating a fifth example of the post-composite corresponding image selection action. 
         FIGS. 23A to 23C  are diagrams illustrating a first modification example of the action executed when the selected image is a composite corresponding image. 
         FIGS. 24A and 24B  are diagrams illustrating a third modification example of the action executed when the selected image is a composite corresponding image. 
         FIGS. 25A and 25B  are graphs showing other examples of the basic relation between the instruction amount and the switching amount. 
         FIG. 26  is a diagram illustrating another example of how display by the display unit looks in a search for image data to be reproduced. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     The significance and effects of the present invention are clarified by the following description of an embodiment. However, the embodiment given below is merely one of possible embodiments of the present invention, and terms describing the present invention and its components are not limited to the meaning written in the following embodiment. 
     &lt;&lt;Overview of an Image Display Device&gt;&gt; 
     An embodiment of the present invention is described below with reference to the drawings. First, an overview of an image display device according to the present invention is given with reference to  FIG. 1 .  FIG. 1  is a block diagram illustrating an example of the structure of the image display device according to the embodiment of the present invention. 
     As illustrated in  FIG. 1 , an image display device  1  includes an image recording unit  2 , which records image data, an operation unit  3 , to which an instruction from a user is input, a display unit  4 , which displays images, and a display control unit  5 , which reads necessary information out of the image recording unit  2  in accordance with various instructions input from the user via the operation unit  3 , and which controls images displayed by the display unit  4 . 
     The image display device  1  causes the user to select an image data item to be reproduced from among image data items recorded in the image recording unit  2 . To this end, the display control unit  5  causes the display unit  4  to display at least one corresponding image of an image data item (for example, a thumbnail image attached as one of the contents of the image data item, or an image obtained by the display control unit  5  by adjusting the image data item (e.g., a reduced image of a still image or a reduced image of one frame contained in a moving image)). 
     Image data items recorded in the image recording unit  2  are in a given order. The given order can be any order, for example, the order of image taking date/time, the order of image taking, the order of image data names, the order of file formats, an arbitrary order set by the user, or a combination of those orders. A corresponding image which corresponds to an image data item can be interpreted as occupying the same place in the order as its image data item. In addition to the image data item&#39;s place in the order, the corresponding image is interpreted as having various relations its image data item has (for example, a correlation and a category). The following description is simplified by assuming that a corresponding image occupies the same place in the order and has the same relations as its image data item. 
     In a search for image data to be reproduced, display by the display unit  4  looks, for example, as illustrated in  FIGS. 2A to 2C .  FIGS. 2A to 2C  are diagrams illustrating an example of how display by the display unit  4  looks in a search for image data to be reproduced. 
     As illustrated in  FIG. 2A , the display unit  4  in this example displays three corresponding images, that is, a reproduction candidate image C 10 , a preceding candidate image B 10 , and a next candidate image A 10 . Specifically, the reproduction candidate image C 10  is displayed substantially at the center of the display unit  4 , with the preceding candidate image B 10  and the next candidate image A 10  displayed on the left and right side thereof. The corresponding images are successive to one another in the order of the preceding candidate image B 10 , the reproduction candidate image C 10 , and the next candidate image A 10 . 
     When the user operates the operation unit  3  to input a “selection instruction,” an image data item to which the reproduction candidate image C 10  corresponds is reproduced. As illustrated in  FIG. 2B , when the user operates the operation unit  3  to input an instruction for “moving the reproduction candidate image forward by one image,” the next candidate image A 10  turns into a reproduction candidate image C 11 , the reproduction candidate image C 10  turns into a preceding candidate image B 11 , and a corresponding image that immediately follows the next candidate image A 10  in the order turns into a next candidate image A 11 . As illustrated in  FIG. 2C , when the user operates the operation unit  3  to input an instruction for “moving the reproduction candidate image backward by one image,” the preceding candidate image B 10  turns into a reproduction candidate image C 12 , the reproduction candidate image C 10  turns into a next candidate image A 12 , and a corresponding image that precedes the preceding candidate image A 10  in the order turns into a preceding candidate image B 12 . 
     The reproduction candidate images C 10  to C 12  are preferred to be distinguishable from other corresponding images such as the preceding candidate images B 10  to B 12  and the next candidate images A 10  to A 12 . In the example of  FIGS. 2A to 2C , the display control unit  5  adjusts the size of each corresponding image such that the reproduction candidate images C 10  to C 12  are displayed larger than the other corresponding images A 10  to A 12  and B 10  to B 12 . In addition to this (or instead of this), other methods may be employed to differentiate the reproduction candidate images C 10  to C 12 , including giving the displayed reproduction candidate images C 10  to C 12  an outer frame different from that of the other corresponding images A 10  to A 12  and B 10  to B 12 . 
     The image display device  1  can be a part of some device (for example, the image display device  1  can be a monitor of an imaging device). The components illustrated in  FIG. 1  can therefore be put to other uses as well. A corresponding image is not limited to a thumbnail image attached to image data or a reduced image, and may be an image of characters, an icon, or a combination thereof. 
     In  FIGS. 2A to 2C , the image data items reproduced are ones associated with images that are the reproduction candidate images C 10  to C 12  upon input of a “selection instruction”. In addition to this (or instead of this), the image data item reproduced may be one associated with an arbitrary corresponding image specified by the user from among displayed corresponding images. In the case where the operation unit  3  is, for example, a touch panel, the user may touch (tap) a place where a desired corresponding image is displayed to thereby input a selection instruction for selecting this corresponding image. In the case where the operation unit  3  is, for example, a tracking ball or a set of keys (including keys displayed on a touch panel, which is true also in the following description), the user may specify a desired corresponding image via the operation unit  3  and simultaneously press a given key to thereby input a selection instruction for selecting this corresponding image. The user may instead press a given key to input a selection instruction for selecting a corresponding image that is the reproduction candidate image C 10 , C 11 , or C 12  at the time the key is pressed. 
     While  FIGS. 2A to 2C  illustrate a case where the display unit  4  displays three corresponding images at a time, the number of corresponding images displayed may be one, two, or equal to or larger than four. 
     &lt;&lt;Switching Control of Corresponding Images&gt;&gt; 
     The description given next with reference to the drawings is about details of corresponding image switching control in a search for image data to be reproduced. 
     &lt;Switching Control: Basics&gt; 
     The basics of switching control are described first with reference to the drawings.  FIGS. 3A and 3B  are graphs showing examples of a basic relation between an instruction amount and a switching amount. 
     The “instruction amount” is the signal value of a switching instruction which is input to the display control unit  5  by the user by operating the operation unit  3 . In principle, the instruction amount increases as the amount of the user&#39;s operation of the operation unit  3  at a time (or per unit time) is increased or the length of operation at a time is prolonged. For example, in the case where the operation unit  3  is a touch panel, the instruction amount is larger when the user slides a finger, a stylus, or the like on the touch panel (strokes the touch panel) in one direction for a longer distance, or at a higher speed, at a time. To give another example, in the case where the operation unit  3  is a set of keys, the instruction amount is larger when the user keeps pressing one key for a longer period of time. In still another example where the operation unit  3  is a tracking ball, the instruction amount is larger when the user causes the tracking ball to rotate in one direction faster. Those are merely examples and the instruction amount can be set in any way. 
     The “switching amount” is a value set by the display control unit  5  based on the instruction amount which is input from the operation unit  3 , and indicates the amount of corresponding images displayed on the display unit  4  that are to be switched. To give a concrete example, the switching amount can be defined as the number of corresponding images that are switched per unit action or per unit time. The following description is made concrete by defining the switching amount as the number of corresponding images that are switched in one switching action and as an integer (which means that the screen scrolls forward or backward through corresponding images on an image basis). Defined as this, the switching amount in the switch from  FIG. 2A  to  FIG. 2B  is one. 
     The graphs of  FIGS. 3A and 3B  each have an axis of abscissa that represents the instruction amount per one operation or per unit time and an axis of ordinate that represents the switching amount. The switching amount increases in a stepped manner as the instruction amount increases. However, in the graph of  FIG. 3A , the increment in instruction amount necessary to increase the switching amount by one step is regular irrespective of how large or small the instruction amount is, whereas in the graph of  FIG. 3B , the increment in instruction amount necessary to increase the switching amount by one step grows smaller as the instruction amount increases. Another difference between  FIGS. 3A and 3B  is that, while the switching amount in the graph of  FIG. 3A  does not have an upper limit, the switching amount in the graph of  FIG. 3B  has an upper limit and becomes constant after the instruction amount reaches a certain value. 
       FIGS. 3A and 3B  are merely examples, and the relation between the instruction amount and the switching amount can be other than the basic relation shown in  FIGS. 3A and 3B . For instance, the switching amount in the graph of  FIG. 3A  may have an upper limit, and the switching amount in the graph of  FIG. 3B  may not have an upper limit. 
     The image display device  1  may switch corresponding images such that the user can view not only the display before and after the switching but also the process of the switching (the dynamic sequence of corresponding images being switched to go forward or backward). This structure allows the user to recognize the specifics of the switching with ease, and therefore is preferred. 
     &lt;Switching Control: Corresponding Images Having a Close Correlation&gt; 
     Corresponding images are switched, in principle, by a switching amount set in accordance with a basic relation as shown in  FIG. 3A  or  3 B. An exception is when corresponding images to be switched to go forward or backward are those having a close correlation (for example, image data items whose degree of correlation, which is described later, is equal to or larger than a threshold). Then the image display device  1  of this embodiment sets a switching amount that does not satisfy the basic relation described above. A description is given below with reference to the drawings on switching control that is executed when closely correlated corresponding images are switched. 
     [Calculation of the Degree of Correlation] 
     An example of how to calculate the degree of correlation is described first. The degree of correlation is calculated by comparing various types of information on a plurality of image data items. The degree of correlation may be calculated from two image data items that are consecutive in the order, or from three or more image data items that are consecutive in the order. 
     The calculation of the degree of correlation can use various types of information on image data, including the image taking date/time and image taking location of image data, the degree of similarity between images composed from image data items (for example, a still image or one frame contained in a moving image, which hereinafter may simply be referred to as image), settings set by the user, and a result of comprehensively weighing those points. To give a concrete example, the degree of correlation is higher when compared image data items have image taking dates/times closer to each other, have image taking locations closer to each other, and create images more similar to each other (e.g., images have a greater degree of similarity to each other). 
     In the case where the degree of correlation is calculated from the image taking date/time of image data, the image taking date/time used for the calculation is, for example, one that is recorded as part of image data when an image is taken. The calculation of the degree of correlation may be weighted such that compared image data items have a particularly high degree of correlation when the time difference between the image taking dates/times of the image data items is smaller than a reference time, which is a given length of time. 
     In the case where the degree of correlation is calculated from the location of image taking, the image taking location used for the calculation is, for example, one recorded as part of image data when an image is taken by an imaging device equipped with a global positioning system (GPS). The calculation of the degree of correlation may be weighted such that compared image data items have a particularly high degree of correlation when the distance difference between the image taking locations of the image data items is smaller than a reference distance, which is a given distance. 
     Methods of calculating the degree of similarity between images are described below. The degree of similarity between images can be calculated from various aspects. Three different methods of calculating the degree of similarity which are referred to as first method, second method, and third method are discussed in the following description. The calculation of the degree of similarity may use any of the first to third methods or a combination thereof. 
     Described first as the first method is a method of calculating the degree of similarity based on the number of people in each image. In this method of calculating the degree of similarity, the number of people is calculated for each compared image by performing face detection on each image and counting the number of faces detected in the image. When the number of people calculated for one image and the number of people calculated for another image are substantially equal to each other, the degree of similarity between the images is set high. The degree of similarity is set high also when the number of people calculated for one image and the number of people calculated for another image are both zero. 
     The first method can employ various known technologies for face detection. For example, AdaBoost (Yoav Freund, Robert E. Schapire, “A decision-theoretic generalization of on-line learning and an application to boosting,” European Conference on Computational Learning Theory, Sep. 20, 1995) may be used. In AdaBoost, a plurality of weak classifiers weighted by classifying a large number of training samples (face and non-face sample images) sequentially classifies parts of a frame of a moving image, to thereby detect a face. 
     Described next as the second method is a method of calculating the degree of similarity based on whether or not persons contained in images are the same person. In this method of calculating the degree of similarity, face recognition is perfoiined on each compared image to determine whether or not the same person is detected in the compared images. When the same person is detected in the compared images, the degree of similarity between the images is set high. 
     The second method can employ various known technologies for face recognition. For example, the face of a person which is detected in an image through face detection may be compared with a sample image of a specific person which is recorded in advance. To give another example, a person&#39;s face detected in one image and a person&#39;s face detected in another image may be compared with each other. 
     As the third method, a method of calculating the degree of similarity by utilizing a “feature vector” which indicates the feature amount of an image is described with reference to the drawings. The following description takes as an example a feature vector calculation method that uses the feature vector of a background region, which is a region remaining after a person region is removed from the whole image. A person region can be calculated by estimating which region contains a person based on the location and size of a face region that is detected by, for example, face detection as described above. In the case of an image that does not contain a person, the entire image can be a background region. 
       FIGS. 4 and 5  are diagrams illustrating an example of the method of calculating the feature vector. An image  100  illustrated in  FIG. 4  is a two-dimensional image including a plurality of pixels arranged in horizontal and vertical directions. Filters  111  to  115  are edge extracting filters which extract edges in a small region (for example, region in image  100  having 3×3 pixels) having a focused pixel  101  as a center thereof, in the image  100 . As the edge extracting filters, arbitrary spatial filters appropriate for edge extraction (for example, differential filters such as Sobel filter or Prewitt filter) may be used. Note that, the filters  111  to  115  are different from one another. Further, in  FIG. 4 , a filter size of the filters  111  to  115  and the small region where the filters are caused to function are assumed to be 3×3 pixels as the example, but may be other sizes such as 5×5 pixels. Further, the number of filters to be used may be a number other than five. 
     The filters  111 ,  112 ,  113 , and  114  extract edges extending in the horizontal direction, the vertical direction, a right oblique direction, and a left oblique direction of the image  100 , respectively, and output filter output values indicating intensity of the extracted edges. The filter  115  extracts an edge extending in a direction not classified in the horizontal direction, the vertical direction, the right oblique direction, and the left oblique direction, and outputs a filter output value indicating intensity of the extracted edge. 
     The intensity of the edge represents a gradient magnitude of a pixel signal (for example, luminance signal). For example, when there is an edge extending in the horizontal direction of the image  100 , a relatively large gradient occurs in the pixel signal in the vertical direction which is orthogonal to the horizontal direction. Further, for example, when spatial filtering is performed by causing the filter  111  to function on the small region having the focused pixel  101  at the center thereof, the gradient magnitude of the pixel signal along the vertical direction of the small region having the focused pixel  101  at the center thereof is obtained as the filter output value. Note that, this is common to the filters  112  to  115 . 
     In a state in which a certain pixel in the image  100  is determined as the focused pixel  101 , the filters  111  to  115  are caused to function on the small region having the focused pixel  101  at the center thereof, to thereby obtain five filter output values. Among the five filter output values, the maximum filter output value is extracted as an adopted filter value. When the maximum filter output value is the filter output value obtained from one of the filters  111  to  115 , the adopted filter value is called one of a first adopted filter value to a fifth adopted filter value. Therefore, for example, when the maximum filter output value is the filter output value from the filter  111 , the adopted filter value is the first adopted filter value, and when the maximum filter output value is the filter output value from the filter  112 , the adopted filter value is the second adopted filter value. 
     The position of the focused pixel  101  is caused to move from one pixel to another in the horizontal direction and the vertical direction in the background region of the image  100 , for example. In each movement, the filter output values of the filters  111  to  115  are obtained, to thereby determine the adopted filter value. After the adopted filter values with respect to all the pixels in the background region of the image  100  are determined, histograms  121  to  125  of the first to fifth adopted filter values as illustrated in  FIG. 5  are individually created. 
     The histogram  121  of the first adopted filter value is a histogram of the first adopted filter value obtained from the image  100 . In the example illustrated in  FIG. 5 , the number of bins of the histogram is 16 (this is common to histograms  122  to  125 ). In this case, 16 frequency data items may be obtained from one histogram, and hence 80 frequency data items may be obtained from the histograms  121  to  125 . An 80-dimensional vector having the 80 frequency data items as elements thereof is obtained as a shape vector H E . The shape vector H E  is a vector corresponding to a shape of an object existing in the image  100 . 
     In addition, color histograms representing a state of color in the background region of the image  100  are created. For example, when pixel signals in each pixel forming the image  100  include an R signal representing intensity of red color, a G signal representing intensity of green color, and a B signal representing intensity of blue color, a histogram HST R  of an R signal value, a histogram HST G  of a G signal value, and a histogram HST B  of a B signal value in the background region of the image  100  are created as the color histograms of the image  100 . For example, when the number of bins of each color histogram is 16, 48 frequency data items may be obtained from the color histograms HST R , HST G , and HST B . A vector (for example, 48-dimensional vector) having the frequency data items obtained from the color histograms as elements thereof is obtained as a color vector H C . 
     When the feature vector of the image  100  is expressed by H, the feature vector H is obtained by an expression “H=k C ×H C +k E ×H E ”, where k C  and k E  denote predetermined coefficients (note that, k C ≠0 and k E ≠0). Therefore, the feature vector H of the image  100  represents the image feature amounts in accordance with a shape and color of an object in the image  100 . 
     A method of calculating the degree of similarity by using the feature vector H which is calculated in the manner described above is now described. To calculate the degree of similarity between two images, for example, feature vectors H 1  and H 2  of the respective images are calculated first. The feature vectors H 1  and H 2  are placed into a space where the feature vector H is to be defined. The start points of the feature vectors H 1  and H 2  are placed at the origin, and the distance (Euclidean distance) between the end point of the feature vector H 1  and the end point of the feature vector H 2  in the feature space is calculated. The calculation of the degree of similarity is then performed so that the degree of similarity is larger when this distance is shorter. The calculation of the degree of similarity may be performed such that the degree of similarity is particularly high when this distance is shorter than a reference distance, which is a given distance. 
     Note that, in a moving picture experts group (MPEG)  7 , the derivation of the feature vector H (feature amount) of the image is performed by using five edge extracting filters. Moreover, the five edge extracting filters may be applied to the filters  111  to  115 . In addition, the feature vector H (feature amount) of the image  100  may be derived by applying a method standardized in MPEG  7  to the image  100 . Further, the feature vector H may be calculated by using only one of the feature amounts of a shape and color. 
     The degree of correlation between image data items recorded in the image recording unit  2  may be calculated in advance. Alternatively, the display control unit  5  may calculate the degree of correlation at the time corresponding images displayed on the display unit  4  are switched. Details of when to calculate the degree of correlation (when to determine whether there is a close correlation or not) are described later. 
     [Switching Amount] 
     Described next with reference to the drawings is the switching amount that is set when corresponding images to be switched have a close correlation.  FIGS. 6A and 6B  are graphs showing examples of a relation of the instruction amount to the switching amount that is set for the switching of closely correlated corresponding images.  FIGS. 6A and 6B  correspond to  FIGS. 3A and 3B , which show the basic relation between the instruction amount and the switching amount. 
     The case where corresponding images to be switched have a close correlation is, for example, a case where the correlation is close between an image data item to which the current reproduction candidate image corresponds and an image data item that precedes (when going backward) or follows (when going forward) this image data item in the order (i.e., the image data item of a corresponding image that turns into a reproduction candidate image at least next to the current reproduction candidate image). To give a concrete example, corresponding images to be switched have a close correlation when the correlation is close at least between an image data item to which the current reproduction candidate image corresponds and an image data item that is immediately before or after this image data item in the order. Corresponding images to be switched do not have a close correlation when the correlation between those image data items is not close. 
     To switch corresponding images that do not have a close correlation, the switching amount is set in accordance with the basic relation described above. Specifically, switching amounts E 1  and E 2 , for example, are set with respect to an instruction amount D as shown in  FIGS. 6A and 6B . To switch corresponding images that have a close correlation, on the other hand, the switching amount set is EC which does not satisfy the basic relation described above and which is determined by a method different from the one for the switching amounts E 1  and E 2 . 
     The image display device  1  structured as above can vary how corresponding images are switched depending on whether the correlation between the corresponding images is close or not. Switching suited to each specific set of corresponding images is thus executed. In particular, corresponding images that have a close correlation can be switched quickly by setting a large switching amount for the switching of closely correlated corresponding images. This allows the user to easily and quickly switch corresponding images that are not wanted at the moment, with the result that desired corresponding images are displayed easily and quickly. The user can accordingly select desired image data easily and quickly. 
     [Display Example] 
     Concrete examples of how display looks when corresponding images displayed on the display unit  4  are switched (first to fourth display examples) are described next with reference to the drawings.  FIG. 7  is a diagram illustrating an example of a set of corresponding images and their order. In  FIG. 7 , a corresponding image  201  is the first in the order, a corresponding image  202  is the second in the order, a corresponding image  203  is the third in the order, a corresponding image  204  is the fourth in the order, a corresponding image  205  is the fifth in the order, a corresponding image  206  is the sixth in the order, and a corresponding image  207  is the seventh in the order. 
     The corresponding image  203  and the corresponding image  204  can be determined as having a close correlation. Similarly, the corresponding image  204  and the corresponding image  205  can be determined as having a close correlation. It can therefore be determined that the corresponding images  203  to  205  have a close correlation. The determination that the corresponding images  203  to  205  have a close correlation may be made as a result of directly comparing image data items to which the corresponding images  203  to  205  respectively correspond. 
     In the first to fourth display examples described below, the corresponding images  201  to  207  are each checked in advance before switching (for example, at the time of image taking or transferring; details are described later) for whether or not the corresponding image has a close correlation with other corresponding images, unless otherwise stated. 
     {First Display Example} 
       FIGS. 8A to 8D  are diagrams illustrating the first display example. The example of  FIGS. 8A to 8D  uses the same display method as the one illustrated in  FIGS. 2A to 2C  to display corresponding images. 
     In  FIG. 8A , the corresponding image  201  is a preceding candidate image B 20 , the corresponding image  202  is a reproduction candidate image C 20 , and the corresponding image  203  is a next candidate image A 20 . Discussed below is a case where switching instructions having the instruction amount D of  FIGS. 6A and 6D  are sequentially input in this state to go forward through the corresponding images in order. 
     The corresponding image  202  (reproduction candidate image C 20 ) and the corresponding image  203  (next candidate image A 20 ) do not have a close correlation as described above. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 8A , as many corresponding images as indicated by the switching amounts E 1  and E 2  (in this example, one) of  FIGS. 6A and 6B  are switched to go forward and reach a state of  FIG. 8B , where the corresponding image  202  is a preceding candidate image B 21 , the corresponding image  203  is a reproduction candidate image C 21 , and the corresponding image  204  is a next candidate image A 21 . 
     As described above, the corresponding image  203  (reproduction candidate image C 21 ), the corresponding image  204  (next candidate image A 21 ), and the corresponding image  205  have a close correlation. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 8B , as many corresponding images as indicated by the switching amount EC of  FIGS. 6A and 6B  are switched. The switching amount EC in this example is large enough to switch all of the corresponding images  203  to  205  which have a close correlation (in this example, three). 
     This switching brings  FIG. 8B  to a state of  FIG. 8C  and then to a state of  FIG. 8D , where the corresponding image  205  is a preceding candidate image B 22 , the corresponding image  206  is a reproduction candidate image C 22 , and the corresponding image  207  is a next candidate image A 22 .  FIG. 8C  is a transition state from  FIG. 8B  to  FIG. 8D  which includes a state in which the corresponding image  203  is the preceding candidate image, the corresponding image  204  is the reproduction candidate image, and the corresponding image  205  is the next candidate image, and a subsequent state in which the corresponding image  204  is the preceding candidate image, the corresponding image  205  is the reproduction candidate image, and the corresponding image  206  is the next candidate image. 
     When images are displayed and switched in the manner described above, it seems to the user as if the corresponding images  203  to  205  are switched at high speed. 
     In the case where the determination of whether there is a close correlation or not is performed at the time of switching in this example, executing the determination can be difficult, in terms of calculation amount and calculation speed, for other correlations than the correlation between the current reproduction candidate image and few corresponding images preceding (in the case of going backward) or following (in the case of going forward) the reproduction candidate image in the order. A countermeasure is, for example, to set the switching amount EC to a value based on the instruction amount D or to a given value. The switching amount EC may be set to a value based on the instruction amount D or to a given value also when whether there is a close correlation or not is determined in advance. 
     Setting the switching amount EC to a value based on the instruction amount D or to a given value may cause a situation where the corresponding images  203  to  205  which have a close correlation are not switched at once to go forward (in other words, one of the states of  FIG. 8C  is reached in one switching but no further), or a situation where the corresponding images  206  and  207  which do not have a close correlation with the reproduction candidate image C 21  (corresponding image  203 ) are switched to go forward together with the corresponding images  203  to  205 . When the latter situation occurs, there is a chance of overlooking a corresponding image that is important to a search for an image data item, which is a problem. This problematic situation can be avoided by setting the switching amount EC to a value that is within the limit of the number of corresponding images for which the determination of whether or not there is a close correlation can be performed, and that equals the number of corresponding images determined as having a close correlation and switched at once. 
     {Second Display Example} 
       FIGS. 9A to 9C  are diagrams illustrating the second display example and correspond to  FIGS. 8A to 8D , which illustrate the first display example. As in  FIGS. 8A to 8D , the example of  FIGS. 9A to 9C  also uses the same display method that is illustrated in  FIGS. 2A to 2C  to display corresponding images. 
     In  FIG. 9A , the corresponding image  201  is a preceding candidate image B 30  and the corresponding image  202  is a reproduction candidate image C 30 . A next candidate image A 30  in  FIG. 9A  is constituted of the closely correlated corresponding images  203  to  205  which are overlaid on top of one another to be grouped together into one stack. Discussed below is a case where switching instructions having the instruction amount D of  FIGS. 6A and 6D  are sequentially input in this state to go forward through the corresponding images in order. 
     The corresponding image  202  (reproduction candidate image C 30 ) and the corresponding images  203  to  205  (next candidate image A 30 ) do not have a close correlation as described above. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 9A , as many corresponding images as indicated by the switching amounts E 1  and E 2  (in this example, one) of  FIGS. 6A and 6B  are switched to go forward and reach a state of  FIG. 9B , where the corresponding image  202  is a preceding candidate image B 31 , a stack of corresponding images obtained by overlaying the corresponding images  203  to  205  on top of one another to be grouped together into one stack is a reproduction candidate image C 31 , and the corresponding image  206  is a next candidate image A 31 . 
     As described above, the corresponding images  203  to  205  (reproduction candidate image C 31 ) have a close correlation. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 9B , as many corresponding images as indicated by the switching amount EC of  FIGS. 6A and 6B  are switched. The switching amount EC in this example is large enough to switch all of the corresponding images  203  to  205  which have a close correlation (in this example, three). 
     This switching brings  FIG. 9B  to a state of  FIG. 9C , where the corresponding images  203  to  205  which are overlaid on top of one another to be grouped together into one stack are a preceding candidate image B 32 , the corresponding image  206  is a reproduction candidate image C 32 , and the corresponding image  207  is a next candidate image A 32 . 
     When images are displayed and switched in the manner described above, it seems to the user as if the corresponding images  203  to  205  are switched in a mass to go forward. 
     In this example, one representative corresponding image (corresponding image  205 ) selected out of the corresponding images  203  to  205  which are overlaid on top of one another to be grouped together into one stack is displayed in the same way as other corresponding images. The representative corresponding image can be any of the corresponding images  203  to  205  and, in this example, the corresponding image  205  which is the last of the three corresponding images in the order serves as the representative corresponding image. In the case where corresponding images are arranged in the order of image taking time or the order of image taking, for example, an image data item that is the last in the order is likely to be one with which the person who took the image is satisfied, and is not likely to be image data obtained from failed image taking. Therefore, selecting a corresponding image that is the last in the order as the representative corresponding image enables the user to grasp the entire set of corresponding images that have a close correlation when the corresponding images are thumbnail images or reduced images. 
     The stack of corresponding images obtained by overlaying the corresponding images  203  to  205  on top of one another may always be displayed as a stack irrespective of whether the switching of corresponding images is to be executed or not. Alternatively, the corresponding images  203  to  205  may be displayed individually instead of as a stack when the switching of images is not planned. 
     {Third Display Example} 
       FIGS. 10A to 10D  are diagrams illustrating the third display example and correspond to  FIGS. 8A to 8D  and  FIGS. 9A to 9C , which illustrate the first display example and the second display example, respectively. As in  FIGS. 8A to 8D  and  FIGS. 9A to 9D , the example of  FIGS. 10A to 10D  uses the same display method that is illustrated in  FIGS. 2A to 2C  to display corresponding images. 
     In  FIG. 10A , the corresponding image  201  is a preceding candidate image B 40 , the corresponding image  202  is a reproduction candidate image C 40 , and the corresponding image  203  is a next candidate image A 40 . Discussed below is a case where switching instructions having the instruction amount D of  FIGS. 6A and 6D  are sequentially input in this state to go forward through the corresponding images in order. 
     The corresponding image  202  (reproduction candidate image C 40 ) and the corresponding image  203  (next candidate image A 40 ) do not have a close correlation as described above. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 10A , as many corresponding images as indicated by the switching amounts E 1  and E 2  (in this example, one) of  FIGS. 6A and 6B  are switched to go forward and reach a state of  FIG. 10B , where the corresponding image  202  is a preceding candidate image B 41 , the corresponding image  203  is a reproduction candidate image C 41 , a combined corresponding image obtained by grouping together the corresponding images  204  and  205  into one group is a next candidate image A 41 . 
     As described above, the corresponding image  203  (reproduction candidate image C 41 ), and the corresponding image  204  and the corresponding image  205  (next candidate image A 41 ) have a close correlation. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 10B , as many corresponding images as indicated by the switching amount EC of  FIGS. 6A and 6B  are switched. The switching amount EC in this example is large enough to switch all of the corresponding images  203  to  205  which have a close correlation (in this example, three). 
     This switching brings  FIG. 10B  to a state of  FIG. 10C  and then to  FIG. 10D , where the combined corresponding image obtained by grouping together the corresponding images  204  and  205  into one group is a preceding candidate image B 42 , the corresponding image  206  is a reproduction candidate image C 42 , and the corresponding image  207  is a next candidate image A 42 .  FIG. 10C  is a transition state from  FIG. 10B  to  FIG. 10D  which includes a state where the corresponding image  203  is the preceding candidate image, the combined corresponding image obtained by grouping together the corresponding images  204  and  205  into one group is the reproduction candidate image, and the corresponding image  206  is the next candidate image. 
     When images are displayed and switched in the manner described above, it seems to the user as if the corresponding images  203  to  205  are switched in a mass to go forward. 
     In this display example, the first corresponding image  230  in order among the corresponding images  203  to  205 , which have a close correlation to one another, is displayed independently without being grouped together. The corresponding images  204  and  205  are displayed as a combined image obtained by grouping the corresponding images  204  and  205  into one group. Displaying independently the corresponding image  230  which is the first in the order enables the user to easily grasp that the corresponding images grouped together relate with the preceding corresponding image  203 . 
     The combined corresponding image obtained by grouping the corresponding images  204  and  205  into one group may always be displayed as a group irrespective of whether the switching of corresponding images is to be executed or not. Alternatively, the corresponding images  204  and  205  may be displayed individually instead of as a group when the switching of images is not planned. 
     The corresponding images that are combined into one corresponding image may be the corresponding images  203  to  205  as in the second display example described above, or it may be the corresponding images  204  and  205  that are overlaid on each other to be one corresponding image. The corresponding image that is displayed independently instead of as part of a combined image may be the corresponding image  205 , while the corresponding images  203  and  204  are combined into one corresponding image. 
     {Fourth Display Example} 
       FIGS. 11A to 11C  are diagrams illustrating the fourth display example and correspond to  FIGS. 8A to 8D ,  FIGS. 9A to 9C , and  FIGS. 10A to 10D , which illustrate the first to third display examples, respectively. As in  FIGS. 8A to 8D ,  FIGS. 9A to 9C , and  FIGS. 10A to 10D , the example of  FIGS. 11A to 11C  uses the same display method that is illustrated in  FIGS. 2A to 2C  to display corresponding images. 
     In  FIG. 11A , the corresponding image  201  is a preceding candidate image B 50  and the corresponding image  202  is a reproduction candidate image C 50 . A next candidate image A 50  in  FIG. 11A  is a grouped corresponding image obtained by displaying only one of the corresponding images  203  to  205  which have a close correlation (by omitting the display of the other two of the corresponding images  203  to  205 ). Discussed below is a case where switching instructions having the instruction amount D of  FIGS. 6A and 6D  are sequentially input in this state to go forward through the corresponding images in order. 
     The corresponding image  202  (reproduction candidate image C 50 ) and the corresponding images  203  to  205  (next candidate image A 50 ) do not have a close correlation as described above. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 11A , as many corresponding images as indicated by the switching amounts E 1  and E 2  (in this example, one) of  FIGS. 6A and 6B  are switched to go forward and reach a state of  FIG. 11B , where the corresponding image  202  is a preceding candidate image B 51 , a grouped corresponding image obtained by displaying only one of the corresponding images  203  to  205  is a reproduction candidate image C 51 , and the corresponding image  206  is a next candidate image A 51 . 
     As described above, the corresponding images  203  to  205  (reproduction candidate image C 31 ) have a close correlation. Therefore, when a switching instruction having the instruction amount D is input in  FIG. 11B , as many corresponding images as indicated by the switching amount EC of  FIGS. 6A and 6B  are switched. The switching amount EC in this example is large enough to switch all of the corresponding images  203  to  205  which have a close correlation (in this example, three). 
     This switching brings  FIG. 11B  to a state of  FIG. 11C , where a grouped corresponding image obtained by displaying only one of the corresponding images  203  to  205  is a preceding candidate image B 52 , the corresponding image  206  is a reproduction candidate image C 52 , and the corresponding image  207  is a next candidate image A 52 . 
     When images are displayed and switched in the manner described above, it seems to the user as if the corresponding images  203  to  205  are switched in a mass to go forward. 
     In this example, the grouped corresponding image obtained by displaying only one of the corresponding images  203  to  205 , namely, one representative corresponding image to be displayed, is the corresponding image  205 . The representative corresponding image can be any of the corresponding images  203  to  205 . However, as described in the second display example, selecting a corresponding image that is the last in the order as the representative corresponding image enables the user to grasp the entire set of corresponding images that have a close correlation. 
     The grouped corresponding image of this display example which is obtained by displaying only one of the corresponding images  203  to  205  is difficult to distinguish from other corresponding images if displayed as it is. The grouped corresponding image therefore is preferred to announce itself as a grouped corresponding image in some way. An image can be announced as a grouped corresponding image by, for example, displaying the image in a frame wider than that of other corresponding images as illustrated in  FIGS. 11A to 11C , or by displaying the image in a frame different in color or design from that of other corresponding images, or by displaying the image together with an icon or the like. 
     The grouped corresponding image obtained by displaying only one of the corresponding images  203  to  205  may always be displayed as a group irrespective of whether the switching of corresponding images is to be executed or not. Alternatively, the corresponding images  203  to  205  may be displayed individually instead of as a group when the switching of images is not planned. 
     The announcement of a grouped corresponding image described above is not limited to the fourth display example and may be employed in the first to third display examples, where the grouped corresponding image displays the closely correlated corresponding images  203  to  205  directly (first display example) or indirectly (second and third display examples). 
     &lt;Modification Example of Switching Control&gt; 
     A description is given below with reference to the drawings on a modification example of switching control that is executed when corresponding images having a close correlation are switched.  FIGS. 12A and 12B  are graphs showing examples of a relation between the instruction amount and the switching amount to show a modification example of the switching control.  FIGS. 12A and 12B  correspond to  FIGS. 3A and 3B , which show the basic relation between the instruction amount and the switching amount, and  FIGS. 6A and 6B , which show examples of switching control. 
     As shown in  FIGS. 12A and 12B , upon input of an instruction amount D 1  which is equal to or smaller than a threshold Dth 1 , switching amounts E 11  and E 21  which satisfy the basic relation are set in this modification example irrespective of whether corresponding images to be switched have a close correlation or not (in other words, the switching amount EC equals the switching amounts E 11  and E 21 ). 
     When the input instruction amount is an instruction amount D 2  which is larger than the threshold Dth 1  and smaller than a threshold Dth 2 , the same switching control as in the examples of  FIGS. 6A and 6B  is executed. Specifically, switching amounts E 12  and E 22  are set in accordance with the basic relation when corresponding images to be switched do not have a close correlation and, when corresponding images to be switched have a close correlation, the switching amount EC that is equal to or larger than the switching amounts E 12  and E 22  is set instead of adhering to the basic relation. 
     In this modification example, the screen jumps to an image in the next category when an instruction amount D 3  which is equal to or larger than the threshold Dth 2  is input. A “category” is, for example, a group of image data items that have the same image taking date, the same image taking location, the same event where image taking took place, or the like. A “jump” is a switch to a corresponding image that belongs to the next category (for example, a corresponding image that is the first in the order within the category). A jump is executed by, for example, setting a switching amount (y−x+1), which is based on the order (x) of the current reproduction candidate image in a category and the number (y) of corresponding images belonging to this category. 
     A description is given below with reference to the drawing on a concrete example of how corresponding images are switched when the instruction amounts D 1  to D 3  of  FIGS. 12A and 12B  are each input continuously to the display control unit  5 .  FIG. 13  is a diagram showing an example of how corresponding images are switched when various instruction amounts are input. 
     In  FIG. 13 , a corresponding image  301  is the first in the order, a corresponding image  302  is the second in the order, a corresponding image  303  is the third in the order, a corresponding image  304  is the fourth in the order, a corresponding image  305  is the fifth in the order, a corresponding image  306  is the sixth in the order, a corresponding image  307  is the seventh in the order, and a corresponding image  308  is the eighth in the order. The corresponding images  304  and  305  can be determined as having a close correlation, as are the corresponding images  305  and  306  and the corresponding images  306  and  307 . It can therefore be determined that the corresponding images  304  to  307  have a close correlation. The determination that the corresponding images  304  to  307  have a close correlation may be made as a result of directly comparing image data items to which the corresponding images  304  to  307  respectively correspond. 
     The corresponding images  301  and  302  belong to the same category. The corresponding image  303  belongs to a category of its own. The corresponding images  304  to  307  belong to the same category. The corresponding image  308  belongs to a category of its own. In  FIG. 13 , one category is separated from another by a broken line. 
       FIG. 13  illustrates switching in which corresponding images are switched in order with the corresponding image  301  as the start point. Unlike  FIGS. 8A to 8D ,  FIGS. 9A to 9C ,  FIGS. 10A to 10D , and  FIGS. 11A to 11C ,  FIG. 13  focuses on switching (going forward by) one corresponding image (for example, the reproduction candidate image) in order to simplify the illustration. 
     When the input instruction amount is D 1 , the switching amounts E 11  and E 21  which satisfy the basic relation are set. In the example of  FIG. 13 , corresponding images are switched one by one to go forward (E 11 =E 21 =1). The corresponding images  301  to  308  are therefore switched to go forward in order one at a time whenever the instruction amount D 1  is input (whenever the user operates the operation unit  3 ). 
     In this example, although the corresponding image  304  and the corresponding image  305  which follows the corresponding image  304  in the order have a close correlation, the switching amounts E 11  and E 21  which satisfy the basic relation are set as described above. The corresponding images  304  and  305  are accordingly switched to go forward one at a time (the same is true when the corresponding images  306  and  307  are switched to go forward). 
     When the instruction amount D 2  is input to switch the corresponding image  301  to go forward, the switching amounts E 12  and E 22  which satisfy the basic relation are set because the corresponding image  301  and the corresponding image  302  which follows the corresponding image  301  in the order do not have a close correlation (the same is true when the corresponding image  303  is switched to go forward). In the example of  FIG. 13 , two corresponding images are switched to go forward at a time (E 12 =E 22 =2). 
     When the instruction amount D 2  is input to switch the corresponding image  305  to go forward, the switching amount EC which does not satisfy the basic relation is set because the corresponding image  305  and the corresponding images  306  and  307  which follow the corresponding image  305  in the order have a close correlation. As in the first to fourth display examples, the switching amount EC in the example of  FIG. 13  is set large enough to switch all of the closely correlated corresponding images  305  to  307  to go forward (in this example, three). 
     When the input instruction amount is D 3 , corresponding images are switched to go forward on a category basis. Each time the instruction amount D 3  is input (each time the user operates the operation unit  3 ), corresponding images are switched to go forward and reach one that is the first in the order among corresponding images belonging to the next category. Specifically, in the example of  FIG. 13 , the corresponding image  301  is switched first to go forward, followed by the switching of the corresponding image  303 , and then  304 , and then  308 . 
     As described above, when the input instruction amount is D 1  which is equal to or smaller than the threshold Dth 1 , the closely correlated corresponding images  304  to  307  can be switched separately (for example, in a manner that turns each into the reproduction candidate image separately) by setting the switching amounts E 11  and E 21 , which satisfy the basic relation, irrespective of whether corresponding images to be switched have a close correlation or not. Therefore, in the case where an image data item to be selected is among image data items to which the corresponding images  304  to  307  correspond, the image data item of interest is easily selected by simply reducing the instruction amount (for example, by reducing the amount of the user&#39;s operation of the operation unit  3  at a time (or per unit time), or by shortening the length of operation at a time). 
     When the input instruction amount is D 3  which is equal to or larger than the threshold Dth 2  and corresponding images are switched on a category basis, one of the advantages is that candidates can be narrowed down at an early stage of a search for an image data item to be selected. The image data item is therefore selected easily and quickly. 
     The threshold Dth 2  may not be provided. In this case, when the input instruction amount is larger than the threshold Dth 1  and corresponding images to be switched do not have a close correlation, a switching amount that satisfies the basic relation may be set whereas the switching amount EC which does not satisfy the basic relation is set when the correlation is close. 
     The thresholds Dth 1  and Dth 2  can take any values. The thresholds Dth 1  and Dth 2  may be values that are different from the values at steps of the stepped basic relation as in  FIG. 12A , or may be values that match the values at steps of the stepped basic relation as in  FIG. 12B . 
     This modification example is applicable to the second to fourth display examples. In this case, a grouped corresponding image may be broken into its constituent corresponding images to be displayed and switched separately at least when, for example, the input instruction amount is equal to or smaller than the threshold Dth 1 . 
     &lt;When to Calculate the Presence or Absence of Correlation&gt; 
     When to execute the determination of whether corresponding images have a close correlation or not is described next with reference to the drawings. 
     [At the Time of Switching] 
       FIG. 14  is a flow chart illustrating an action of the image display device  1  in which whether the correlation between corresponding images is close or not is determined at the time of switching the corresponding images and then the corresponding images are switched. The action of  FIG. 14  is executed when, for example, image data is to be reproduced on the image display device  1 , and executed when the user operates the operation unit  3  once. 
     As illustrated in  FIG. 14 , a switching instruction is first input to the image display device  1  by the user operating the operation unit  3  (STEP  1 ). The display control unit  5  checks the instruction amount described above at this point. The display control unit  5  also determines whether or not the correlation is close between a pre-switching corresponding image (for example, the reproduction candidate image in STEP  1  or the reproduction candidate image in STEP  2 ) and a switching candidate corresponding image which precedes or follows this corresponding image in the order (for example, the preceding candidate image or the next candidate image in STEP  2 ) (STEP  2 ). 
     Based on the instruction amount and the result of the determination in STEP  2 , the display control unit  5  determines whether to switch the pre-switching corresponding image to the switching candidate corresponding image (STEP  3 ). This determination of whether to execute a switch can be made based on whether or not the switch to the switching candidate corresponding image is within the range of the switching amount described above. Specifically, when the switching of corresponding images is within the range of the switching amount, it is determined that the corresponding images are to be switched. 
     As described above, the number of corresponding images, for which whether or not there is a close correlation can be determined, is limited in some cases due to the calculation amount and the calculation speed. In such cases, in STEP  3 , a switching amount is set based on whether or not the determination of whether there is a close correlation or not can be executed (whether or not STEP  2  can be executed further), and whether to execute the switch is determined. 
     When it is determined that the corresponding images are not to be switched (STEP  3 : NO), switching is ended. When it is determined that the corresponding images are to be switched (STEP  3 : YES), on the other hand, the pre-switching corresponding image is switched to the switching candidate corresponding image (STEP  4 ). The corresponding images are switched at high speed as in the first display example. After the corresponding images are switched in STEP  4 , the processing returns to STEP  2  to subsequently repeat STEP  3  and STEP  4 . 
     The switching control described above can thus be performed on corresponding images of any kind (for example, image data items taken by a plurality of imaging devices and image data items whose information such as their order have been changed) by executing the determination of whether corresponding images (image data items) have a close correlation or not at the time of switching. 
     [At the Time of Transfer] 
       FIG. 15  is a flow chart illustrating an action of the image display device  1  in which whether there is a close correlation or not is determined at the time image data is transferred. The action of  FIG. 15  is executed when, for example, image data obtained by image taking is transferred from the imaging device to a viewer (the image display device  1 ) or a recording device. 
     As illustrated in  FIG. 15 , a transfer instruction specifying which image data item is to be transferred is input first (STEP  11 ). The presence or absence of the image data item to be transferred is then checked (STEP  12 ). When the image data item to be transferred is not found (STEP  12 : NO), the transfer is ended. When the image data item to be transferred is found (STEP  12 : YES), whether or not the image data item to be transferred has a close correlation with an image data item that precedes or follows the image data item to be transferred in the order is determined (STEP  13 ). 
     When the correlation between the image data item to be transferred and its preceding or following image data item is close (STEP  14 : YES), the image data items are recorded as ones that have a close correlation in the image display device or the recording device (STEP  15 ). At this point, information indicating that the correlation is close may be recorded in a part of each image data item such as a header, or may be recorded in a system recording area of the image display device or the recording device. 
     When the correlation between the image data item to be transferred and its preceding or following image data item is not close (STEP  14 : NO), the image data items are recorded as ones that do not have a close correlation in the image display device or the recording device (STEP  16 ). At this point, as in STEP  15 , information indicating that the correlation is not close may be recorded in the header or in the system recording area. Alternatively, the distant correlation may be indicated by not recording information about the correlation. 
     After STEP  15  or STEP  16  is finished, the processing returns to STEP  12  to check whether or not another image data item is to be transferred, and the subsequent steps are repeated. 
     With this structure, whether the correlation between image data items is close or not is determined prior to image data reproduction in the image display device  1 . Accordingly, there is no need to execute the determination of whether or not there is a close correlation at the time of switching, and the switching control described above is completed quickly. 
     In STEP  15  and STEP  16 , in which information indicating that the correlation is close is recorded, the degree of correlation may be recorded instead. The determination of whether there is a close correlation or not may be executed by the imaging device, or by the image display device or the recording device. 
     [At the Time of Image Taking] 
       FIG. 16  is a flow chart illustrating an action of the image display device  1  in which whether image data that has just been taken has a close correlation or not is determined. The action of  FIG. 16  is executed when one image data item is obtained by image taking. 
     As illustrated in  FIG. 16 , an image is taken first to obtain an image data item (STEP  21 ). The next step is to determine whether or not the image data item obtained by the image taking in STEP  21  has a close correlation with an image data item that precedes the obtained image data item in the order (STEP  22 ). When there is an image data item that follows the obtained image data item in the order, STEP  22  may include determining whether or not the obtained image data item has a close correlation with its following image data item. 
     When the correlation is close between the image data item obtained by image taking and the image data item that precedes (or follows) the obtained image data item in the order (STEP  23 : YES), the image data items are recorded as ones that have a close correlation in a recording unit of the imaging device (STEP  24 ). At this point, information indicating that the correlation is close may be recorded in a part of each image data item such as a header, or may be recorded in a system recording area of the imaging device. 
     When the correlation is not close between the image data item obtained by image taking and the image data item that precedes (or follows) the obtained image data item in the order (STEP  23 : NO), the image data items are recorded as ones that do not have a close correlation in the recording unit of the imaging device (STEP  25 ). At this point, as in STEP  24 , information indicating that the correlation is not close may be recorded in the header or in the system recording area. Alternatively, the distant correlation may be indicated by not recording information about the correlation. After STEP  24  or STEP  25  is finished, the action is ended. 
     With this structure, as in the case where the determination is made at the time of transfer in the manner described above, whether the correlation between image data items is close or not is determined prior to image data reproduction in the image display device  1 . Accordingly, there is no need to execute the determination of whether or not there is a close correlation at the time of switching, and the switching control described above is completed quickly. 
     In STEP  24  and STEP  25 , where information indicating that the correlation is close is recorded, the degree of correlation may be recorded instead. 
     [Switching of Corresponding Images for Which Whether the Correlation is Close or Not is Determined in Advance] 
     Described next with reference to  FIG. 17  is an action of switching corresponding images for which whether the correlation is close or not is determined in advance and recorded at the time of transfer or at the time of image taking (see the sections [At the Time of Transfer] and [At the Time of Image Taking]).  FIG. 17  is a flow chart illustrating a corresponding image switching action that is executed when whether the correlation between corresponding images is close or not is determined in advance. The action of  FIG. 17  is executed when, for example, image data is to be reproduced in the image display device  1 , and executed each time the user operates the operation unit  3 . 
     As illustrated in  FIG. 17 , a switching instruction is first input to the image display device  1  by the user operating the operation unit  3  (STEP  31 ). The display control unit  5  checks the instruction amount described above at this point. The display control unit  5  also checks whether or not the correlation is close between a pre-switching corresponding image (for example, the reproduction candidate image in STEP  31  or the reproduction candidate image in STEP  32 ) and a switching candidate corresponding image which precedes or follows this corresponding image in the order (for example, the preceding candidate image or the next candidate image in STEP  32 ) (STEP  32 ). 
     Based on the instruction amount and the correlation checked in STEP  32 , the display control unit  5  determines whether to switch the pre-switching corresponding image to the switching candidate corresponding image (STEP  33 ). This determination of whether to execute a switch can be made based on whether or not the switching of the switching candidate corresponding image is within the range of the switching amount described above. Specifically, when the switch to the switching candidate corresponding image is within the range of the switching amount, it is determined that the corresponding images are to be switched. 
     When it is determined that the corresponding images are not to be switched (STEP  33 : NO), switching is ended. When it is determined that the corresponding images are to be switched (STEP  33 : YES), on the other hand, the pre-switching corresponding image is switched to the switching candidate corresponding image (STEP  34 ). The corresponding image is switched at high speed as in the first display example, or switched together with other corresponding images as in the second to fourth display examples. After the corresponding images are switched in STEP  34 , the processing returns to STEP  32  to subsequently repeat STEP  33  and STEP  34 . 
     As described above, when whether a corresponding image has a close correlation or not is determined in advance, the image display device  1  only needs to check the correlation at the time of switching. This allows the image display device  1  to speed up switching control and to have a simpler structure. 
     &lt;Examples of an Action Executed When the User Selects a Composite Corresponding Image&gt; 
     In the description given above, image data reproduced is one to which a corresponding image selected by the user (by inputting a selection instruction via the operation unit  3 ) corresponds. However, the user may select one corresponding image in which at least two corresponding images are grouped together (see the second to fourth display examples,  FIG. 7 ,  FIGS. 9A to 9C ,  FIGS. 10A to 10D , and  FIGS. 11A to 11C . Hereinafter, this type of corresponding image is referred to as composite corresponding image and discriminated from a single corresponding image.). The image display device  1  is preferably structured to take a different action in this case from the case where the user selects a single corresponding image. 
     Examples of an action executed when the image selected by the user is a composite corresponding image are described below. The following action examples, whether they be of the same kind or of different kinds, can be combined unless there is a contradiction. What follows are mainly examples of applying the action examples to the second display example (see  FIGS. 9A to 9C ) and the third display example (see  FIGS. 10A to 10D ), and a description on the application of the action examples to the fourth display example (see  FIGS. 11A to 11C ) is omitted because it is similar to the application of the action examples to the second display example. In the following description of the action examples, elements in the drawings that are similar to ones in  FIG. 7 ,  FIGS. 9A to 9C , and  FIGS. 10A to 10D  are denoted by the same reference symbols in order to simplify the description by omitting a detailed description on those elements. 
     [Composite Corresponding Image Selection Detection Action] 
     Examples of an action executed by the display control unit  5  to detect that the user has selected a composite corresponding image are described first with reference to the drawings. 
     {Composite Corresponding Image Selection Detection Action: First Example} 
       FIGS. 18A and 18B  are diagrams illustrating a first example of a composite corresponding image selection detection action.  FIG. 18A  corresponds to the second display example, and  FIG. 18B  corresponds to the third display example. As illustrated in  FIGS. 18A and 18B , in this action example, the display control unit  5  detects that a composite corresponding image has been selected when a composite corresponding image is situated in a selection detection range S and an instruction from the user has not been input via the operation unit  3  for a given period of time or longer. Specifically, the display control unit  5  detects that a composite corresponding image has been selected when, for example, a composite corresponding image is a reproduction candidate image C 6  or C 7  and an instruction from the user has not been input for a given period of time or longer. 
     The selection detection range S is not limited to the area where the reproduction candidate image is displayed, and may be set to the area where the preceding candidate image or the next candidate image is displayed. The selection detection range S may also be set to not one but a plurality of areas. For instance, the selection detection range S may be set to each of, or two of, the areas where the preceding candidate image, the reproduction candidate image, and the next candidate image are respectively displayed. 
     The state in this action example where a composite corresponding image is situated in the selection detection range S and an instruction from the user has not been input via the operation unit  3  for a given period of time or longer is similar to and interchangeable with a state in a fourth example of a post-composite corresponding image selection action which is described later. 
     {Composite Corresponding Image Selection Detection Action: Second Example] 
       FIGS. 19A and 19B  are diagrams illustrating a second example of the composite corresponding image selection detection action.  FIG. 19A  corresponds to the second display example, and  FIG. 19B  corresponds to the third display example. As illustrated in  FIGS. 19A and 19B , in this action example, the display control unit  5  detects that a composite corresponding image has been selected when a selection instruction for selecting a composite corresponding image is input from the user via the operation unit  3 . Specifically, the display control unit  5  detects that a composite corresponding image has been selected upon input of a selection instruction for selecting a composite corresponding image, for example, a reproduction candidate image C 8  of  FIG. 19A  or a next candidate image A 9  of  FIG. 19B . 
     {Composite Corresponding Image Selection Detection Action: Third Example} 
     In this action example, the display control unit  5  detects that a composite corresponding image has been selected when a composite corresponding image is situated in the selection detection range S described in the first example of the composite corresponding image selection detection action (see  FIGS. 18A and 18B ) and an instruction that is not a switching instruction is input from the user via the operation unit  3 . 
     Specifically, the display control unit  5  detects that a composite corresponding image has been selected when, for example, a composite corresponding image is the reproduction candidate image C 6  and the user operates the operation unit  3  in a direction different from one for inputting a switching instruction (hereinafter referred to as switching instruction direction) (e.g., a direction perpendicular to the switching instruction direction or a direction between this direction and the switching instruction direction, which is hereinafter referred to as non-switching instruction direction.). 
     For example, in the case where the operation unit  3  is a touch panel and a switching instruction is input when the user slides a finger, a stylus, or the like on the touch panel (strokes the touch panel) in a direction in which a preceding candidate image B 6  (B 7 ), the reproduction candidate image C 6  (C 7 ), and a next candidate image A 6  (A 7 ) are aligned on the display unit  4  (the left-right direction in the drawings, i.e., the switching instruction direction), the user operates the operation unit  3  in a non-switching instruction direction by sliding a finger, a stylus, or the like on the display unit  4  (strokes the touch panel) along a direction that is not the switching instruction direction (the top-bottom direction or oblique direction in the drawings, i.e., a non-switching instruction direction). To give another example, in the case where the operation unit  3  is a tracking ball or a set of keys and a switching instruction is input by rolling the tracking ball in the alignment direction (switching instruction direction) or by pressing a key that is allocated to the switching instruction direction, the user operates the operation unit  3  in a non-switching instruction direction by rolling the tracking ball along a direction that is not the switching instruction direction (non-switching instruction direction) or by pressing a key that is allocated to a non-switching instruction direction. 
     An instruction that is not a switching instruction in this action example is similar to and interchangeable with an instruction in a third example of the post-composite corresponding image selection action which is described later. 
     The first to third examples of the composite corresponding image selection detection action are applicable not only to cases where a composite corresponding image is selected but also to cases where a corresponding image is selected. 
     [Post-composite Corresponding Image Selection Action] 
     Examples of an action executed by the display control unit  5  after the user selects a composite corresponding image are described next with reference to the drawings. 
     {Post-composite Corresponding Image Selection Action: First Example} 
       FIGS. 20A to 20C  are diagrams illustrating a first example of a post-composite corresponding image selection action, and correspond to the second display example.  FIG. 20A  is an example of how display by the display unit  4  looks prior to the composite corresponding image selection detection action.  FIG. 20B  is an example of how display by the display unit  4  looks immediately after the composite corresponding image selection detection action.  FIG. 20C  is an example of how display by the display unit  4  looks after the user inputs an instruction that is not a switching instruction via the operation unit  3  while the display unit  4  is as shown in  FIG. 20B . 
     As illustrated in  FIGS. 20A and 20B , in this action example, the composite corresponding image selection detection action described above executed in the display control unit  5  is followed by the reproduction on the display unit  4  of image data to which one of the corresponding images constituting the selected composite corresponding image corresponds. The image data reproduced may be, for example, one associated with the representative corresponding image  205  (see  FIG. 7 ), which is a constituent of the composite corresponding image. 
     While image data is being reproduced as illustrated in  FIG. 20B , the user inputs an instruction that is not a switching instruction via the operation unit  3 , thereby causing the display control unit  5  to reproduce on the display unit  4  image data that is not the currently reproduced image data and that is associated with one of the corresponding images constituting the selected composite corresponding image. In the example of  FIG. 20C , image data to which the corresponding image  203  (see  FIG. 7 ) corresponds is reproduced on the display unit  4 . 
     Subsequently, the user further inputs an instruction that is not a switching instruction (for example, the user operates the operation unit  3  in a non-switching instruction direction), causing the display control unit  5  to sequentially switch the image data reproduced on the display unit  4 . The image data reproduced is switched, for example, in the order of the degree of correlation, the order of the degree of similarity between images, the order of image taking date/time, or other orders described above. 
     This structure enables the user to easily reproduce and check image data items to which a plurality of closely correlated corresponding images respectively correspond. 
     In the case where the user&#39;s operation of the operation unit  3  in a non-switching instruction direction causes the switching of the image data reproduced on the display unit  4 , image data may be switched in a given order which is determined depending on the direction of the operation (for example, whether the operation direction is the upward direction or the downward direction, or whether the operation direction is the oblique upward direction or the oblique downward direction). To give a concrete example, the image data reproduced on the display unit  4  may be switched in ascending order when the user operates the operation unit  3  in the upward direction, whereas the image data reproduced on the display unit  4  is switched in descending order when the user operates the operation unit  3  in the downward direction. This structure facilitates the user&#39;s search for desired image data. 
     The operation direction may also determine which order index (e.g., the image taking date/time or the degree of similarity between images composed from image data items) is to be used in switching. To give a concrete example, the image data reproduced on the display unit  4  may be switched in the order of image taking date/time when the user operates the operation unit  3  in the upward direction, whereas the image data reproduced is switched in the order of the degree of similarity between images when the user operates the operation unit  3  in the downward direction. This structure allows the user to select an arbitrary index in a search for desired image data. 
     The image data reproduced on the display unit  4  may be switched in different methods associated with different general operation directions (for example, the top-bottom direction and the oblique direction) in which the user operates the operation unit  3 . To give a concrete example, the image data reproduced may be switched in a given order when the user operates the operation unit  3  in the top-bottom direction, whereas the image data reproduced is switched in an order of another index when the user operates the operation unit  3  in the oblique direction. 
     The general operation direction and the specific operation direction may respectively determine which order index is to be used and whether this order is an ascending order or a descending order. To give a concrete example, the image data reproduced on the display unit  4  may be switched in ascending order of image taking date/time when the user operates the operation unit  3  in the upward direction, whereas the image data reproduced on the display unit  4  is switched in descending order of image taking date/time when the user operates the operation unit  3  in the downward direction. The image data reproduced on the display unit  4  may be switched in ascending order of the degree of similarity between images when the user operates the operation unit  3  in the oblique upward direction, whereas the image data reproduced on the display unit  4  is switched in descending order of the degree of similarity between images when the user operates the operation unit  3  in the oblique downward direction. 
     When this action example is applied to the third display example, the same action as when this action example is applied to the second display example may be executed. In this case, the example may be modified such that image data items to which the corresponding images  204  and  205  (see  FIG. 7  and  FIGS. 10A to 10D ) constituting a composite corresponding image correspond are reproduced on the display unit  4 . The example may also be modified such that image data items to which the closely correlated corresponding images  203  to  205  (see  FIG. 7  and  FIGS. 10A to 10D ) correspond are reproduced on the display unit  4 . 
     {Post-composite Corresponding Image Selection Action: Second Example} 
     The display unit  4  in this action example executes the same action as in the first example of the post-composite corresponding image selection action (see  FIGS. 20A to 20C ). The difference between this action example and the first example is an action executed by the display control unit  5  to switch the image data reproduced on the display unit  4  (action of changing  FIG. 20B  to  FIG. 20C ). The rest of this action example is the same as the first example, and a description thereof is omitted. 
     In this action example, the image data reproduced on the display unit  4  is switched in a given order when the display control unit  5  detects that no instruction has been input from the user via the operation unit  3  for a given period of time or longer. The display control unit  5  can execute the switching repeatedly. 
     With this structure, the user can easily reproduce and check image data items to which a plurality of closely correlated corresponding images respectively correspond, without needing to perform a special operation. 
     {Post-composite Corresponding Image Selection Action: Third Example} 
       FIGS. 21A to 21C  are diagrams illustrating a third example of the post-composite corresponding image selection action, and correspond to the second display example. FIG.  21 A is an example of how display by the display unit  4  looks prior to the composite corresponding image selection detection action.  FIG. 21B  is an example of how display by the display unit  4  looks immediately after the composite corresponding image selection detection action.  FIG. 21C  is an example of how display by the display unit  4  looks after the user inputs an instruction that is not a switching instruction via the operation unit  3  while the display unit  4  is as shown in  FIG. 21B . 
     As illustrated in  FIGS. 21A and 21B , in this action example, the selected composite corresponding image is kept displayed after the display control unit  5  executes the composite corresponding image selection detection action described above. Various adjustments such as enlargement may be made to the composite corresponding image at this point, as long as a preceding candidate image B 112  and a next candidate image A 112  are at least partially displayed (in other words, as long as the user can see the order of the composite corresponding image and the corresponding images). 
     While the composite corresponding image is displayed as illustrated in  FIG. 21B , the user inputs an instruction that is not a switching instruction via the operation unit  3 , thereby causing the display control unit  5  to change display on the display unit  4  such that the representative corresponding image is one of the corresponding images constituting the selected composite corresponding image that is not the former representative corresponding image  205  (see  FIG. 7 ). In the example of  FIG. 21C , display on the display unit  4  is changed such that the corresponding image  203  (see  FIG. 7 ) is the representative corresponding image. 
     Subsequently, the user further inputs an instruction that is not a switching instruction, causing the display control unit  5  to sequentially switch the representative corresponding image of the selected composite corresponding image. The representative corresponding image is switched, for example, in the order of the degree of correlation, the order of the degree of similarity between images, the order of image taking date/time, or other orders described above. 
     This structure enables the user to check a plurality of corresponding images constituting a composite corresponding image with ease. 
     The action described in the first example of the post-composite corresponding image selection action, in which the user&#39;s operation of the operation unit  3  in a non-switching instruction direction causes the switching of image data reproduced on the display unit  4 , may be executed in this action example. However, the image switched in this action example is the representative corresponding image of the selected composite corresponding image. 
     When this action example is applied to the third display example, the same action as when this action example is applied to the second display example may be executed. In this case, the example may be modified such that how the corresponding images  204  and  205  (see  FIG. 7  and  FIGS. 10A to 10D ) constituting a composite corresponding image are displayed on the display unit  4  can be changed (for example, the order in which the images are arranged or the size of the images can be changed). The example may also be modified such that which of the closely correlated corresponding images  203  to  205  (see  FIG. 7  and  FIGS. 10A to 10D ) is displayed independently, instead of being grouped with the other corresponding images, can be changed by causing the corresponding image  203 , which has been displayed independently instead of being grouped together, and the corresponding images  204  and  205 , which have constituted a composite corresponding image, to switch places with each other. 
     {Post-composite Corresponding Image Selection Action: Fourth Example} 
     The display unit  4  in this action example executes the same action as in the third example of the post-composite corresponding image selection action (see  FIGS. 21A to 21C ). The difference between this action example and the third example is an action executed by the display control unit  5  to switch the representative corresponding image of a composite corresponding image (action of changing  FIG. 21B  to  FIG. 21C ). The rest of this action example is the same as the third example, and a description thereof is omitted. 
     In this action example, the representative corresponding image of a composite corresponding image is switched in a given order when the display control unit  5  detects that no instruction has been input from the user via the operation unit  3  for a given period of time or longer. The display control unit  5  can execute the switching repeatedly. 
     With this structure, the user can easily check a plurality of corresponding images constituting a composite corresponding image, without needing to perform a special operation. 
     {Post-composite Corresponding Image Selection Action: Fifth Example} 
       FIGS. 22A to 22C  are diagrams illustrating a fifth example of the post-composite corresponding image selection action, and correspond to the second display example.  FIG. 22A  is an example of how display by the display unit  4  looks prior to the composite corresponding image selection detection action.  FIG. 22B  is an example of how display by the display unit  4  looks immediately after the composite corresponding image selection detection action action.  FIG. 22C  is an example of how display by the display unit  4  looks after the user inputs a selection via the operation unit  3  while the display unit  4  is as shown in  FIG. 22B . 
     As illustrated in  FIGS. 22A and 22B , in this action example, the closely correlated corresponding images  203  to  205  (see  FIG. 7 . In this example, corresponding images that constitute a composite corresponding image.) are separately displayed as view-all images D 1221  to D 1223  when the display control unit  5  executes the composite corresponding image selection detection action described above. In displaying those images, the representative corresponding image  205  (see  FIG. 7 ) of the composite corresponding image which is the view-all image D 1223  may be positioned at the center of the display unit  4  or other places where the image will easily be spotted. 
     While the view-all images D 1221  to D 1223  are being displayed as illustrated in  FIG. 22B , the user inputs a selection instruction via the operation unit  3 , and the display control unit  5  reproduces on the display unit  4  image data associated with one of the corresponding images displayed as view-all images that is selected by the selection instruction. In the example of  FIG. 22C , the input selection instruction is for selecting the corresponding image  205  (see  FIG. 7 ) which is the view-all image D 1223 , and image data to which the corresponding image  205  corresponds is reproduced on the display unit  4 . 
     With this structure, corresponding images that have a close correlation with one another can easily be checked at once. 
     In the case where the user inputs a given instruction (for example, a selection instruction for selecting an arbitrary area on the display unit  4 ) while the display unit  4  is reproducing image data as in  FIG. 22C , the display control unit  5  may display corresponding images and a composite corresponding image on the display unit  4  as in  FIG. 22A , or may display view-all images on the display unit  4  as in  FIG. 22B . 
     In the case where the display unit  4  is as shown in  FIG. 22B  and the user inputs via the operation unit  3  a selection instruction for selecting an area that contains none of the view-all images D 1221  to D 1223 , the display control unit  5  may display on the display unit  4  corresponding images and a composite corresponding image as in  FIG. 22A . 
     When this action example is applied to the third display example, the same action as when this action example is applied to the second display example may be executed. In this case, the closely correlated corresponding images  203  to  205  (see  FIG. 7 ) may be displayed on the display unit  4  as view-all images as in  FIG. 23B , or only the corresponding images  204  and  205  which constitute a composite corresponding image (see  FIG. 7  and  FIGS. 10A to 10D ) may be displayed on the display unit  4  as view-all images. 
     [Modification Examples of the Actions] 
     {First Modification Example} 
     In the case where the action examples described above are applied to the third display example, the action executed in response to the user&#39;s selection of the corresponding image  203  (see  FIG. 7  and  FIGS. 10A to 10D ), which has a close correlation with the corresponding images  204  and  205  (see  FIG. 7  and  FIGS. 10A to 10D ) but is not displayed as part of a composite corresponding image constituted of the corresponding images  204  and  205 , may be the same as when the composite corresponding image is selected. The corresponding image  203  which is not displayed as part of the composite corresponding image may also be interpreted as an equivalent of the representative corresponding image in the second display example and the fourth display example. 
     A concrete description is given with reference to the drawings on an example of this action.  FIGS. 23A to 23C  are diagrams illustrating a first modification example of the action executed when the selected image is a composite corresponding image, and correspond to the third display example.  FIG. 23A  is an example of how display by the display unit  4  looks prior to the composite corresponding image selection detection action.  FIG. 23B  is an example of how display by the display unit  4  looks immediately after the composite corresponding image selection detection action.  FIG. 23C  is an example of how display by the display unit  4  looks after the user inputs a selection instruction via the operation unit  3  while the display unit  4  is as shown in  FIG. 23B . 
     In this modification example, as illustrated in  FIGS. 23A and 23B , the display control unit  5  displays view-all images D 1321  to D 1323  of the corresponding images  203  to  205  on the display unit  4  even when the input selection instruction is for selecting the corresponding image  203  (reproduction candidate image C 131 , see  FIG. 7 ), which has a close correlation with the corresponding images  204  and  205  (see  FIG. 7 ) but is not displayed as part of a composite corresponding image (next candidate image A 131 ) constituted of the corresponding images  204  and  205 . Subsequently, the same action as in the fifth example of the post-composite corresponding image selection action is executed as illustrated in  FIGS. 23B and 23C . 
     With this structure, the user can easily check corresponding images that have a close correlation to one another at once by selecting at least one of the closely correlated corresponding images. 
     This modification example corresponds to the second example of the composite corresponding image selection detection action and the fifth example of the post-composite corresponding image selection action, but can be adapted so as to correspond to other action examples as well. 
     {Second Modification Example} 
     The corresponding image that is displayed preferentially, such as the representative corresponding image in the second and fourth display examples or a corresponding image that has a close correlation with corresponding images constituting a composite corresponding image but is not displayed as part of the composite corresponding image in the third display example, may be variable. For instance, the corresponding image that is displayed preferentially may be one that has most recently been selected by the user, such as a corresponding image of image data most recently reproduced by the user, or a corresponding image most recently displayed preferentially in the third example of the post-composite corresponding image selection action. 
     This structure enables the image display device  1  to preferentially display a corresponding image that is likely to be selected by the user. Selecting a desired corresponding image is thus made easy for the user. 
     {Third Modification Example} 
     The display control unit  5  may additionally display operation methods of the operation unit  3  on the display unit  4  when a corresponding image and a composite corresponding image are displayed, when view-all images are displayed, when image data is reproduced, or the like. An example of how display by the display unit  4  looks in this case is described with reference to the drawings. 
       FIGS. 24A and 24B  are diagrams illustrating a third modification example of the action executed when the selected image is a composite corresponding image, and correspond to the second display example.  FIG. 24A  is an example of how display by the display unit  4  looks when corresponding images and a composite corresponding image are displayed.  FIG. 24B  is an example of how display by the display unit  4  looks when image data is reproduced. 
     As illustrated in  FIG. 24A , the display unit  4  displays images that indicate operation methods for giving a switching instruction (leftward arrow with “backward” and rightward arrow with “forward” in the drawing), and images that indicate operation methods for giving a selection instruction (black circle with “enlarge” in the drawing). 
     As illustrated in  FIG. 24B , the display unit  4  displays images that indicate operation methods for giving a switching instruction (leftward arrow with “backward” and rightward arrow with “forward” in the drawing), images that indicate operation methods for giving a selection instruction (black circle with “overlay” in the drawing), and images that indicate other instructions than a switching instruction (upward arrow with “similarity” and downward arrow with “time”). 
     This structure allows the user to operate the operation unit  3  while looking at the images indicating operation methods that are displayed on the display unit  4 . The user can thus easily bring the display unit  4  to a desired state. 
     The images indicating operation methods may be displayed on the display unit  4  all the time, or may be displayed only when a given condition is met, such as when the user operates the operation unit  3 . This modification example corresponds to the second example of the composite corresponding image selection detection action and the first example of the post-composite corresponding image selection action, but can be adapted so as to correspond to other action examples as well. This modification is applicable not only to cases where a composite corresponding image is displayed (e.g., the second to fourth display examples) but also to cases where a composite corresponding image is not displayed (e.g., the first display example). However, this modification example is more effective when applied to cases where a composite corresponding image is displayed and accordingly the operation of the operation unit  3  may become complicated (e.g., the second and third examples of the composite corresponding image selection detection action and the first, third, and fifth examples of the post-composite corresponding image selection action). 
     When the user inputs a switching instruction via the operation unit  3  while the display unit  4  is reproducing image data as in the display example of  FIG. 24B , the switching action described above is executed. Specifically, in the case where the state of  FIG. 24B  is one reached by, for example, inputting a selection instruction for selecting a reproduction candidate image C 141  of  FIG. 24A , when the user inputs a switching instruction (for going forward) via the operation unit  3 , the display control unit  5  reproduces on the display unit  4  image data associated with the corresponding image  206  (see  FIG. 7 ), which is a next candidate image A 141 . The display control unit  5  may also cause the display unit  4  to display a state (where the corresponding image  206  (see  FIG. 7 ) is the reproduction candidate image) reached after going forward in  FIG. 24A  in the manner described above. The same switching action may be executed also when a switching instruction is input while the display unit  4  is displaying view-all images. 
     &lt;&lt;Modification Example&gt;&gt; 
     In the description given above, the switching amount takes only an integer value so that corresponding images are switched on an image basis. Alternatively, the switching amount may be set to a decimal number so that corresponding images are switched on a partial-image basis. An example of this case is described with reference to the drawings.  FIGS. 25A and 25B  are graphs showing other examples of the basic relation between the instruction amount and the switching amount, and correspond to  FIGS. 3A and 3B .  FIG. 26  is a diagram illustrating another example of how display by the display unit looks in a search for image data to be reproduced, and corresponds to  FIGS. 2A to 2C . 
     As shown in  FIGS. 25A and 25B , a graph of the basic relation in this example takes continuous values. For instance, in the graph of  FIG. 25A , the switching amount increases linearly as the instruction amount increases. In the graph of  FIG. 25B , on the other hand, the switching amount increases non-linearly as the instruction amount increases. The switching amount in the graph of  FIG. 25A  does not have an upper limit, whereas the switching amount in the graph of  FIG. 25B  has an upper limit and becomes constant after the instruction amount reaches a certain value.  FIGS. 25A and 25B  are merely examples, and the relation between the instruction amount and the switching amount can be other than the basic relation shown in  FIGS. 25A and 25B . For instance, an upper limit may be set to the switching amount in the graph of  FIG. 25A , and an upper limit may not be set to the switching amount in the graph of  FIG. 25B . 
       FIG. 26  illustrates an example of how display by the display unit  4  looks when the switching amount is set in the manner described above. In  FIG. 26 , a corresponding image X 1  which has been the reproduction candidate image prior to a switch is partially moved to go forward, and a corresponding image X 2  which follows the corresponding image X 1  in the order is about to become a new reproduction candidate image. In this state, neither of the corresponding images X 1  and X 2  may be regarded as a reproduction candidate image, or one of the corresponding images X 1  and X 2  may be regarded as the reproduction candidate image. 
     The switching amount which is defined in the description given above as the number of corresponding images switched per switching action may be defined as the number of corresponding images switched per unit time. Defined as this, the switching amount is interpreted as a speed at which corresponding images are switched, and images are switched faster as the instruction amount increases (for example, corresponding images seemingly move fast on the display unit  4  to be switched). The switching speed during a switching action is not limited to a constant speed. For instance, when a plurality of corresponding images are to be switched at once, the switching speed may be increased for corresponding images that are switched nearer to the end of this switching action. 
     In some cases, the switching amount per unit time is inevitably increased as a result of increasing the switching amount per unit action, or the switching amount per unit action is inevitably increased as a result of increasing the switching amount per unit time. Those cases include the first display example when the length of one switching action is limited to a given range, and the second to fourth display examples. 
     In the image display device  1  according to the embodiment of the present invention, the actions executed by the display control unit  5  and the actions of other components may be implemented by a control device such as a microcomputer. Further, all or some of functions implemented by the control device may be written as a program so that all or some of the functions are implemented by running the program on a program executing device (e.g., a computer). 
     The image display device  1  of  FIG. 1  is not limited to those adaptations and can be implemented by hardware or a combination of hardware and software. In the case where software is a component of the image display device  1 , the block of a part implemented by the software represents the function block of the part. 
     The embodiment of the present invention has now been described. The present invention, however, is not limited thereto and can be carried out with various modifications, without departing from the spirit of the present invention. 
     The present invention is applicable to an image display device for displaying an image, typically, a display unit of an imaging device or a viewer, and to an image display method.