Abstract:
An image converter includes an image converting unit and a determining unit. The image converting unit acquires frame image groups each including one or more frame images from original image data, and outputs the frame image(s) of each acquired group, converting its/their image quality based on determination by the determining unit, generating foreign-device-use image data including the frame image groups including the frame image(s). The determining unit determines necessity of first-image-quality retention of the frame image(s) of each group based on whether it/they satisfies/satisfy a condition. The image converting unit outputs the frame image(s) of the group at the first image quality if it/they is/are determined by the determining unit as necessary to retain at the first image quality, or a second image quality if determined as unnecessary to retain at the first image quality.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image converter, an image reproducer, an image conversion/reproduction system, and a program. 
     2. Description of the Related Art 
     Recently, image display devices such as TVs have progressed remarkably, and various types of devices with a capability of high resolution or high pixel count display have been developed and used in ordinary households. Display devices mounted on mobile terminals such as cellular phones, etc. have also come with upgraded capabilities. 
     However, cellular phones, etc. are more preferable if they are smaller and lighter, and hence usually mounted with a CPU, a memory device, etc. that are lower-powered than those mounted on TVs, etc. Therefore, when transferring image data having a high image quality that is created for reproduction on TVs, DVD recorders, etc., to cellular phones, etc. to reproduce the image data on the cellular phones, etc., it is necessary to convert or degrade the image quality of the image data to an image quality matching the capabilities of the cellular phones, etc., i.e., to a lower image quality. Degrading is to lower, for example, resolution, bit rate, etc. Degrading can compress the overall size of the image data and reduce the decoding load. 
     For example, Unexamined Japanese Patent Application KOKAI Publication No. 2001-45436 discloses a digital broadcast receiver that converts received image data to image data adapted to an external device connected to it. 
     Conventional data conversion techniques degrade uniformly all the frames that constitute high quality image data (e.g., MPEG data). Therefore, cellular phones, etc. will reproduce image data whose image quality has been lowered uniformly for all the frames. Image data that has been recorded at a high image quality can only be viewed at a low image quality when users reproduce the image data on a cellular phone, etc. If image data that has been degraded uniformly throughout its frames contains information with a very small size, e.g., small-sized letters, users cannot understand it. On the other hand, if image data with a high image quality uniformly is reproduced on a cellular phone, etc., a large load is imposed on the device, which therefore may not be able to reproduce the image data smoothly or store the image data. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the problems described above, and an object of the present invention is to provide an image converter, an image reproducer, an image conversion/reproduction system, and a program for enabling reproduction of image data that has a small overall image size as having been partially degraded but has had a desired data portion thereof upgraded to an image quality that is not beyond the capability of a reproducing device. 
     To achieve the above object, an image converter according to a first aspect of the present invention includes an image converting unit and a determining unit. 
     The image converting unit sequentially acquires frame image groups each including one or a plurality of frame image(s) from original image data that is constituted by these frame image groups, and outputs the frame image(s) included in each of the acquired frame image groups by converting an image quality of the frame image(s) based on a result of determination by the determining unit, thereby to generate a foreign-device-use image data that is constituted by the frame image groups including the frame image(s). 
     The determining unit determines whether it is necessary to retain the frame image(s) of each frame image group at a first image quality or not based on whether the frame image(s) of the frame image group satisfies/satisfy a predetermined condition or not. 
     In a case where the determining unit determines that it is necessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at the first image quality. 
     In a case where the determining unit determines that it is unnecessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at a second image quality. 
     The first image quality may be higher than the second image quality. 
     The first image quality may be equal to the image quality of the frame image(s) of each of the acquired frame image groups. 
     The determining unit may perform determination only on a frame image that is decodable without requiring other frames, of the frame image(s) included in each frame image group. 
     The determining unit may calculate a time interval between a reproduction start time of the frame image group that is currently the determination target and a reproduction start time of the most recent frame image group that has been determined as necessary to retain at the first image quality, and determine that it is unnecessary to retain the determination-target frame image group at the first image quality in a case where the time interval is shorter than a preset time period. 
     The determining unit may calculate the degree of image similarity between the frame image group that is currently the determination target and the most recent frame image group that has been determined as necessary to retain at the first image quality, and determine that it is unnecessary to retain the determination-target frame image group at the first image quality in a case where the degree of image similarity is equal to or greater than a preset value. 
     The determining unit may acquire the number of letters included in the frame image(s) of the frame image group that is currently the determination target, and determine that it is unnecessary to retain the frame image group at the first image quality in a case where the acquired number of letters is smaller than a preset number. 
     The image converter may further include an imaging unit that generates the original image data by imaging. 
     An image reproducer according to a second aspect of the present invention includes: 
     a reproducing unit that sequentially acquires frame image groups each including one or a plurality of frame images from image data that is constituted by these frame image groups, where a frame image group that is designated by a user is acquired first, and reproduces the image data; 
     a storage unit that temporarily stores at least one frame image of each of the frame image groups, in a case where the frame image group has a first image quality; and 
     a zooming unit that suspends reproduction of the image data in response to an instruction of the user, and displays one or a plurality of frame image(s) that is/are temporarily stored by expanding or reducing the frame image(s). 
     An image conversion/reproduction system according to a third aspect of the present invention includes an image converter and an image reproducer. 
     The image converter includes an image converting unit and a determining unit. 
     The image converting unit sequentially acquires frame image groups each including one or a plurality of frame image(s) from original image data that is constituted by these frame image groups, and outputs the frame image(s) included in each of the acquired frame image groups by converting an image quality of the frame image(s) based on a result of determination by the determining unit, thereby to generate a foreign-device-use image data that is constituted by the frame image groups including the frame image(s). 
     The determining unit determines whether it is necessary to retain the frame image(s) of each frame image group at a first image quality or not based on whether the frame image(s) of the frame image group satisfies/satisfy a predetermined condition or not. 
     In a case where the determining unit determines that it is necessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at the first image quality. 
     In a case where the determining unit determines that it is unnecessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at a second image quality. 
     The image reproducer includes a reproducing unit, a storage unit, and a zooming unit. 
     The reproducing unit sequentially acquires the frame image groups from the foreign-device-use image data, where a frame image group that is designated by a user is acquired first, and reproduces the foreign-device-use image data. 
     The storage unit temporarily stores at least one frame image of each of the frame image groups, in a case where the frame image group has the first image quality. 
     The zooming unit suspends reproduction of the foreign-device-use image data in response to an instruction of the user, and displays one or a plurality of frame image(s) that is/are temporarily stored by expanding or reducing the frame image(s). 
     In a case where the determining unit determines any frame image group as necessary to retain at the first image quality, the image converting unit may arrange position information and a reproduction start time of a predetermined frame image of the frame image group to be stored in the storage unit, 
     the image reproducer may include a list displaying unit that displays the frame image having the position information and the reproduction start time in the form of a list, and 
     the user may designate any frame image that is displayed by the list displaying unit in the form of a list. 
     A recording medium according to a fourth aspect of the present invention stores a program that controls a computer to function as an image converter including an image converting unit and a determining unit, in a manner described below. 
     The image converting unit sequentially acquires frame image groups each including one or a plurality of frame image(s) from original image data that is constituted by these frame image groups, and outputs the frame image(s) included in each of the acquired frame image groups by converting an image quality of the frame image(s) based on a result of determination by the determining unit, thereby to generate a foreign-device-use image data that is constituted by the frame image groups including the frame image(s). 
     The determining unit determines whether it is necessary to retain the frame image(s) of each frame image group at a first image quality or not based on whether the frame image(s) of the frame image group satisfies/satisfy a predetermined condition or not. 
     In a case where the determining unit determines that it is necessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at the first image quality. 
     In a case where the determining unit determines that it is unnecessary to retain the frame image(s) of the frame image group at the first image quality, the image converting unit outputs the frame image(s) of the frame image group at a second image quality. 
     A recording medium according to a fifth aspect of the present invention stores a program that controls a computer to function as: 
     a reproducing unit that sequentially acquires frame image groups each including one or a plurality of frame images from image data that is constituted by these frame image groups, where a frame image group that is designated by a user is acquired first, and reproduces the image data; 
     a storage unit that temporarily stores at least one frame image of each of the frame image groups, in a case where the frame image group has a first image quality; and 
     a zooming unit that suspends reproduction of the image data in response to an instruction of the user, and displays one or a plurality of frame image(s) that is/are temporarily stored by expanding or reducing the frame image(s). 
     Effect of the Invention 
     In accordance with the present invention, it is possible to reduce the overall size of image data by degrading a portion of the image data to a lower image quality while upgrading a different portion of the image data to a higher image quality or keeping it as it is, enabling that portion of the image data to be viewed at a high image quality or to be expanded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings in which: 
         FIG. 1  is a diagram showing the configuration of an image conversion/reproduction system according to one embodiment of the present invention; 
         FIG. 2  is a block diagram showing the configuration of a HDD recorder of  FIG. 1 ; 
         FIG. 3  is a block diagram showing the configuration of a cellular phone of  FIG. 1 ; 
         FIG. 4  is a diagram conceptually showing an operation of the image conversion/reproduction system of  FIG. 1 ; 
         FIG. 5  is a flowchart showing the procedures of an image data converting process; 
         FIG. 6A  is a diagram showing the structure of recorded image data; 
         FIG. 6B  is a diagram showing the structure of mobile-device-use image data; 
         FIG. 7  is a diagram showing an example of a high resolution scene managing table; 
         FIG. 8  is a flowchart showing the procedures of a scene determining process; 
         FIG. 9  is a flowchart showing the procedures of a list displaying process; 
         FIG. 10  is a flowchart showing the procedures of an image reproducing process; 
         FIG. 11A  is a diagram showing an example of an output screen when an image is reproduced normally in a reproduction control process; 
         FIG. 11B  is a diagram showing an example of the output screen in a zooming mode in the reproduction control process; 
         FIG. 11C  is a diagram showing an example of the output screen when an image is zoomed up in the reproduction control process; 
         FIG. 12  is a flowchart showing the procedures of a zooming process; 
         FIG. 13  is a diagram showing a modification (part  1 ) of the structure of the mobile-device-use image data; 
         FIG. 14  is a diagram showing a modification (part  2 ) of the structure of the mobile-device-use image data; 
         FIG. 15A  is a diagram showing a modification of the high resolution scene managing table corresponding to the mobile-device-use image data of  FIG. 13 ; and 
         FIG. 15B  is a diagram showing a modification of the high resolution scene managing table corresponding to the mobile-device-use image data of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An image conversion/reproduction system according to one embodiment of the present invention will be explained with reference to the drawings. As shown in  FIG. 1 , an image conversion/reproduction system  1  according to the present embodiment includes a HDD recorder  10  as one embodiment of an image converter and a cellular phone  20  as one embodiment of an image reproducer. The HDD recorder  10  and the cellular phone  20  can exchange data via a home network  30 . The home network  30  is constituted by, for example, a wireless LAN. 
     As shown in  FIG. 2 , the HDD recorder  10  includes a communication unit  101  comprising a network card or the like, a main memory  102 , a CPU  103 , an output unit  104 , a secondary storage device  105 , and a content receiving unit  106 . These components are connected to an internal bus  107 . 
     The secondary storage device  105  stores an image converting program  109  and a scene determining program  110 . These programs will be loaded onto the main memory  102  as needed. The CPU  103  operates in accordance with these programs and performs an image data converting process and a scene determining process, which are to be described later. The secondary storage device  105  stores image data (e.g., content data compliant with a digital terrestrial broadcasting standard) received by the content receiving unit  106  as recorded image data  111 . The secondary storage device  105  also stores image data obtained by converting the recorded image data  111  for use by the cellular phone  20  as mobile-device-use image data  112 . In the present embodiment, the recorded image data  111  and the mobile-device-use image data  112  are both moving image data in MPEG2 format. 
     The recorded image data  111  is output via the output unit  104  to a TV monitor or the like unillustrated and reproduced thereon. In the present embodiment, the TV monitor or the like has a screen resolution of 1920×1080 dots. Correspondingly, the recorded image data  111  has a resolution of 1920×1080 dots. 
     As shown in  FIG. 3 , the cellular phone  20  includes a communication unit  201  comprising a network card or the like, a main memory  202 , a CPU  203 , an input unit  204 , a display unit  205 , and a secondary storage device  206 . These components are connected to an internal bus  207 . 
     The input unit  204  is constituted by a keypad  211  or the like, and receives an input from a user. The display unit  205  is constituted by a liquid crystal display (LCD)  212  or the like, and displays, for example, an image based on the mobile-device-use image data  112  in accordance with an instruction from the CPU  203 . The LCD  212  has a screen resolution of 600×480 dots. 
     The secondary storage device  206  stores a list displaying program  216 , an image reproducing program  217 , and a still image reproducing program  218 , as a reproduction control program  215 . These programs will be loaded onto the main memory  202  as needed. The CPU  203  operates in accordance with these programs and performs a reproduction control process, which is to be described later. The secondary storage device  206  stores the mobile-device-use image data  112  received from the HDD recorder  10  via the home network  30 . 
       FIG. 4  is a diagram that conceptually shows the operation of the image conversion/reproduction system  1  according to the present embodiment. The HDD recorder  10  performs the image data converting process to generate the mobile-device-use image data  112  based on the recorded image data  111 . Specifically, an image converting unit  115  and a scene determining unit  116 , which are functional units of the CPU  103 , perform the image data converting process. 
     The cellular phone  20  sends a command (image data request command) for requesting the mobile-device-use image data  112  to the HDD recorder  10  via the home network  30 , in response to an operation of the user. The HDD recorder  10  receives the image data request command, reads out the mobile-device-use image data  112  stored in the secondary storage device  105 , and sends it to the cellular phone  20  via the home network  30 . The cellular phone  20  stores the received mobile-device-use image data  112  in the secondary storage device  206 . 
     The cellular phone  20  performs the reproduction control process, which is to be described later, in response to an operation of the user. The reproduction control process includes a list displaying process, an image reproducing process, and a zooming process. Specifically, a list displaying unit  221 , an image reproducing unit  222 , and a still image reproducing unit  223 , which are functional units of the CPU  203 , perform the list displaying process, the image reproducing process, and the zooming process. 
     The above-mentioned process performed by the HDD recorder  10  and the cellular phone  20  will now be explained in detail. First, the image data converting process performed by the HDD recorder  10  will be explained. 
       FIG. 5  is a flowchart showing the procedures of the image data converting process. In the present embodiment, the image converting unit  115  of the CPU  103  starts up in response to an operation of the user (including a command from the cellular phone  20 ), and performs the image data converting process described below. The image converting unit  115  may start up at an arbitrary timing and be designed to start up regularly (at regular intervals). 
     First, the image converting unit  115  determines whether any recorded image data  111  is stored in the secondary storage device  105  or not (step S 101 ). In a case where no recorded image data  111  is stored in the secondary storage device  105  (step S 101 ; NO), the image data converting process terminates here. In a case where any recorded image data  111  is stored in the secondary storage device  105  (step S 101 ; YES), the image converting unit  115  sequentially acquires the image frames (frame blocks  601  shown in  FIG. 6A ) that constitute the recorded image data  111  (step S 102 ). 
     Frame blocks to be sequentially acquired by the image converting unit  115  will now be explained. Each of the frame blocks  601  shown in  FIG. 6A  is a group of frames that are organized together based on significance to each other, out of all the frames that constitute the image data. The frame blocks  601  are equivalent to, for example, Groups of Pictures (GOP) in MPEG2. In compression coding, frames to be organized into any frame block  601  will be compressed without having any dependency on frames to be organized into other frame blocks  601 . That is, in reproducing images, the frames can be decoded within their own frame block  601 . The resolution needs only to be uniform within each frame block  601 ; different frame blocks  601  may have different resolutions. 
     It is likely that the recorded image data  111  includes a frame block  601  that requires a very long time period for reproduction. To deal with such a case, the image converting unit  115  may check the reproduction time period required by each frame block  601  of the recorded image data  111  before acquiring the first frame block  601  to determine whether or not there is any frame block  601  that requires equal to or longer than a preset time period. In a case where there is any frame block  601  that requires equal to or longer than the preset time period, the image converting unit  115  may divide the frame block  601  requiring equal to or longer than the preset time period into two or more new frame blocks  601  to generate new recorded image data  111 . The image converting unit  115  may generate the mobile-device-use image data  112  based on the new data. 
     Returning to the flowchart of  FIG. 5 , the scene determining unit  116  performs the scene determining process on the frame blocks acquired by the image converting unit  115  (step S 103 ). The scene determining unit  116  determines whether or not each acquired frame block  601  needs to be stored at a high resolution (the resolution of 1920×1080 dots in the present embodiment). The scene determining process performed by the scene determining unit  116  will be described in detail later. 
     In a case where the scene determining unit  116  determines a given frame block as necessary to store at a high resolution (step S 104 ; YES), the image converting unit  115  converts that frame block  601  at a high resolution (step S 106 ). Note that the recorded image data  111  has been already stored at a so-defined high resolution of the present embodiment (the resolution of 1920×1080 dots). Therefore, in the present embodiment, this frame block  601  will not have its resolution changed through the conversion. 
     The image converting unit  115  extracts an i frame from the frame block  601  converted at a high resolution, and temporarily stores it in the secondary storage device  105  (step S 107 ). The i frame stored here will be used in the scene determining process. An i frame is a frame that has been compressed within itself (equivalent to, e.g., i (intra) frame in MPEG2). In the present embodiment, it is assumed that the first frame of each frame block  601  is an i frame. 
     The image converting unit  115  registers annotation information (frame number and reproduction start time) that is related to the frame block  601  that has been converted at a high resolution in a high resolution scene managing table  602  shown in  FIG. 6B  (step S 108 ). The high resolution scene managing table  602  is stored in a predetermined area of the mobile-device-use image data  112 . As shown in  FIG. 7 , the high resolution scene managing table  602  has a field for “frame number” and a field for “reproduction start time”. The image converting unit  115  sets the number of the first frame (i.e., i frame) of that frame block  601  (the number being a numeral that indicates the order of that first frame in the recorded image data  111 ) in the frame number field, and the reproduction start time of that frame block  601  in the reproduction start time field. As will be described in detail later, the high resolution scene managing table  602  will be used for allowing the cellular phone  20  to reproduce the mobile-device-use image data  112  by cue playback of the frame block  601  converted at a high resolution. 
     Returning to the flowchart of  FIG. 5 , in a case where the scene determining unit  116  determines a given frame block as unnecessary to store at a high resolution (step S 104 ; NO), the image converting unit  115  converts that frame block to a low resolution (the resolution of 600×480 dots in the present embodiment) (step S 105 ). 
     The image converting unit  115  stores the frame blocks  601  that have been converted either at a high resolution or to a low resolution in the secondary storage device  105  as frame blocks  601  that constitute the mobile-device-use image data  112  (step S 109 ). The image converting unit  115  determines whether a frame block  601  extracted from the recorded image data  111  is the last frame block or not (step S 110 ). In a case where a frame block  601  extracted from the recorded image data  111  is not the last frame block (step S 110 ; NO), the flow returns to step S 102  to repeat the process described above. On the other hand, in a case where a frame block  601  extracted from the recorded image data  111  is the last frame block (step S 110 ; YES), the image data converting process ends. The mobile-device-use image data  112  is obtained through the above-described image data converting process. 
     The scene determining process will now be explained in detail with reference to the flowchart of  FIG. 8 . First, the scene determining unit  116  acquires the reproduction start time of the frame block  601  that is currently the conversion target and that of the most recent frame block  601  that has been converted at a high resolution, and calculates the time interval between these reproduction start times (step S 201 ). In a case where the calculated interval is shorter than a preset time period (step S 202 ; NO), the scene determining unit  116  determines that the conversion target frame block  601  needs not be stored at a high resolution (step S 203 ). This can prevent the mobile-device-use image data  112  from being large-sized. 
     On the other hand, in a case where the interval between them is equal to or longer than the present time period (step S 202 ; YES), the scene determining unit  116  reads out the i frame of the most recent frame block  601  that has been converted at a high resolution, and calculates the degree of similarity between the i frame image of the conversion target frame block  601  and the i frame image of the most recent frame block  601  converted at a high resolution (step S 204 ). The present embodiment is not limited in how to calculate the degree of similarity and can employ a known technique. 
     The scene determining unit  116  compares the calculated degree of similarity with a preset threshold to determine whether the i frame images are similar or not (step S 205 ). In a case where the i frames are similar (step S 205 ; YES), the scene determining unit  116  determines that the conversion target frame block  601  needs not be stored at a high resolution (step S 203 ). Generally, in a situation where frames of information that are displayed continuously are similar, i.e., a situation where images do not change greatly from scene to scene, it can be determined that such images need not be displayed at a high resolution. Therefore, it is possible to prevent unnecessary increase of the size of the mobile-device-use image data  112 , by avoiding a high resolution storing in such a case. 
     On the other hand, in a case where the i frame images are not similar (step S 205 ; NO), the scene determining unit  116  acquires the number of letters included in the i frame image converted at a high resolution by a know technique (step S 206 ). In a case where the acquired number of letters is smaller than a preset number (step S 207 ; NO), the scene determining unit  116  determines that the conversion target frame block  601  needs not be stored at a high resolution (step S 203 ). On the other hand, in a case where the acquired number of letters is equal to or greater than the preset number (step S 207 ; YES), the scene determining unit  116  determines that the conversion target frame block  601  needs to be stored at a high resolution (step S 208 ). As a result, when a user reproduces, for example, an image that contains small letters to be displayed closely on the cellular phone  20 , he/she can zoom it up so he/she can see it well. 
     In the scene determining process described above, the scene determining unit  116  determines that a frame block needs to be stored at a high resolution in a case where three conditions, namely the interval between reproduction start times, the degree of similarity between images, and the number of letters included in an image are all satisfied. However, this is one example, and it may be determined that a frame block needs to be stored at a high resolution in a case where any one or more of these conditions is/are satisfied. In a case where more than one conditions are used in combination, they need not be used in a specific order. For example, the degree of similarity may be checked first. Then, if the images are not similar, the number of letters may be checked. If the number of letters is equal to or greater than the preset number, the interval may then be checked. If the interval is equal to or longer than the preset time period, the conversion target frame block may be determined as necessary to store at a high resolution. 
     The operation of the cellular phone  20  for reproducing the mobile-device-use image data  112  will now be explained. First, the list displaying process performed by the list displaying unit  221  will be explained with reference to the flowchart of  FIG. 9 . The list displaying unit  221  starts in response to a user&#39;s operation via the keypad  211 , and performs the list displaying process described below. 
     The list displaying unit  221  reads out the high resolution scene managing table  602  from the mobile-device-use image data  112  stored in the secondary storage device  206  (step S 301 ). The list displaying unit  221  acquires the frames (i frames) corresponding to the frame numbers set in the frame number field of the high resolution scene managing table  602  (step S 302 ). The list displaying unit  221  displays images (scenes), which are the respective i frame images affixed with their own reproduction start time, on the display unit  205  in the form of thumbnails (step S 303 ). After displaying the thumbnails, the list displaying unit  221  enters into a state ready to receive a selection operation of the user (a selection operation awaiting state) (step S 304 ). The user can select a desired scene by operating the keypad  211  to use for example, a cursor moving key and move the cursor from scene to scene. 
     When the user selects a scene and presses an enter key or the like of the keypad  211 , the list displaying unit  221  notifies the user&#39;s selection to the image reproducing unit  222 . The image reproducing unit  222  starts to reproduce the image data from the frame block  601  corresponding to the selected scene (step S 305 ). 
     The image reproducing process performed by the image reproducing unit  222  will now be explained with reference to the flowchart of  FIG. 10 . The image reproducing unit  222  sequentially acquires frame blocks  601  from the mobile-device-use image data  112  (step S 401 ). In a case where, as described above, the image reproducing unit  222  reproduces image data from the scene selected by the user, the image reproducing unit  222  sequentially acquires frame blocks  601  from the frame block  601  corresponding to the selected scene. 
     Next, the image reproducing unit  222  determines whether or not each frame block  601  is a high resolution scene (step S 402 ). The image reproducing unit  222  makes this determination by determining whether the scene is higher than a predetermined resolution (in the present embodiment, 640×480 dots) or not. Needless to say, in a case where reproduction starts from the scene selected by the user, the frame block  601  acquired first is a high resolution scene. 
     In a case where the frame block  601  is not a high resolution scene (step S 402 ; NO), the image reproducing unit  222  goes to step S 403  and reproduces this frame block  601  (see  FIG. 11A ). On the other hand, in a case where the frame block  601  is a high resolution scene (step S 402 ; YES), the image reproducing unit  222  goes to step S 403  after performing steps S 404  to S 406 . 
     At step S 404 , the image reproducing unit  222  extracts the first frame (i.e., i frame) of the frame block  601  and temporarily stores the extracted first frame in the secondary storage device  206  as image data to be zoomed. At step S 405 , the image reproducing unit  222  sets a zooming mode as the control mode of the cellular phone  20 . When the zooming mode is set as the control mode, the still image reproducing unit  223 , which is to be described later, starts. At step S 406 , the image reproducing unit  222  displays a message that informs the user that zooming is available with a press of a predetermined key of the keypad  211  (e.g., “you can zoom up the image by the XX button”) on the LCD  212  (see  FIG. 11B ). 
     The zooming mode set here is automatically reset when a predetermined time period has passed. When the zooming mode is reset, the process (zooming process) performed by the still image reproducing unit  223  ends and the message is deleted (or hidden). 
     The zooming mode may be designed not to be reset while similar scenes are reproduced. Alternatively, the zooming mode may be designed not to be reset until the image reproducing process ends once it is set. 
     The image reproducing unit  222  repeatedly performs the above-described process until it reproduces the last frame block  601  (step S 407 ; YES), or until the user gives an operation to stop reproduction. 
     The zooming process performed by the still image reproducing unit  223  will be explained with reference to the flowchart of  FIG. 12 . When the user presses a predetermined key of the keypad  211  while in the zooming mode to enter a zooming instruction (step S 501 ; YES), the still image reproducing unit  223  makes the image reproducing unit  222  suspend the image reproducing process (step S 502 ). The still image reproducing unit  223  acquires the i frame stored in the secondary storage device  206  (see step S 404  of  FIG. 10 ), and displays the image of that i frame (i frame image) on the display unit  205  (step S 503 ). The still image reproducing unit  223  displays a message that notifies the user that reproduction will be resumed with a press of a predetermined key of the keypad  211  (e.g., “you can resume reproduction by the XX button”) on the LCD  212  (see  FIG. 11C ). 
     The still image reproducing unit  223  performs expansion, reduction, scrolling, etc. of the i frame image in accordance with an operation instruction of the user given via the keypad  211  or the like (step S 504 ). These processes will be continued until the user enters an instruction for resuming reproduction (step S 505 ; YES). 
     As explained above, the HDD recorder  10  (image converter) according to the present embodiment generates the mobile-device-use image data  112  for the cellular phone  20  from the recorded image data  111  recorded at a high resolution by performing the scene determining process to determine whether or not it is necessary to store each frame block  601  at a high resolution, taking into account various conditions. The HDD recorder  10  stores any frame block  601  that is determined to be necessary to store at a high resolution in the mobile-device-use image data  112  without degrading it. Therefore, the HDD recorder  10  according to the present embodiment can generate the mobile-device-use image data  112  that includes high-resolution scenes without increasing the data size. 
     The cellular phone  20  (image reproducer) according to the present embodiment can display an i frame image of a frame block that is stored at a high resolution by appropriately performing expansion, etc. of the image in accordance with an instruction of the user. Hence, the user can enjoy the merit of high quality images even when the reproducing device is the cellular phone  20 . 
     The present invention is not limited to the embodiment described above, but various modifications are available within the scope of the spirit of the present invention. 
     For example, in the embodiment described above, the image converting unit  115  of the HDD recorder  10  (image converter) generates the mobile-device-use image data  112  by reducing the resolution of the recorded image data  111 . However, the image quality parameter to be converted is not limited to resolution. For example, the parameter may be codec, bit rate, etc. 
     In the embodiment described above, the high resolution scene managing table  602  is embedded in the mobile-device-use image data  112 . However, the high resolution scene managing table  602  may be generated by the HDD recorder  10  (image converter) separately from the mobile-device-use image data  112  and stored in the secondary storage device  105 . In this case, the cellular phone  20  (image reproducer) acquires the high resolution scene managing table  602  together when acquiring the mobile-device-use image data  112  from the HDD recorder  10 . 
     As shown in  FIG. 13 , the image converting unit  115  of the HDD recorder  10  (image converter) may change the position at which a frame block  601  is stored in the image track each time the frame block  601  is converted from a low resolution to a high resolution or from a high resolution to a low resolution. An example of the high resolution scene managing table  602  of this case is shown in  FIG. 15A . 
     Alternatively, as shown in  FIG. 14 , the image converting unit  115  may reduce the resolution of all the frame blocks  601 , and store the i frame of only such frame blocks  601  that are determined by the scene determining unit  116  to be necessary to store at a high resolution in different image tracks from that of moving image data. An example of the high resolution scene managing table  602  of this case is shown in  FIG. 15B . 
     In the scene determining process, the scene determining unit  116  may determine whether to store an image at a high resolution or not based on other elements in the image, such as the size of letters included in the image, the size and the kind of an object included in the image, etc. Other than elements in an image, the scene determining unit  16  may also make this determination based on audio information recorded synchronously with images (e.g., the loudness of a sound, etc.) 
     In the embodiment described above, the mobile-device-use image data  112  starts being reproduced when the user selects a scene from the displayed thumbnails. However, needless to say, the mobile-device-use image data  112  may also be reproduced from its first frame block  601  in accordance with an instruction of the user, with no thumbnails displayed. 
     In the list displaying process, the list displaying unit  221  may store the acquired i frames in the secondary storage device  206  separately in the form of a list of still images. Therefore, even if the mobile-device-use image data  112  is deleted, still images having a high resolution can be viewed. 
     The embodiment described above is an example where the mobile-device-use image data  112  is transferred from the HDD recorder  10  to the cellular phone  20  and the mobile-device-use image data  112  stored in the secondary storage device  206  is reproduced. However, the mobile-device-use image data  112  may be reproduced by a streaming reproduction manner by which the data is reproduced as it is transferred from the HDD recorder  10  to the cellular phone  20 . 
     The cellular phone  20  may have a feature for performing the image data converting process and convert image data such as content data that is acquired from another device into mobile-device-use image data  112 . 
     The cellular phone  20  may convert an image shot by a camera  208  into mobile-device-use image data  112  and reproduce the image data obtained from the conversion. 
     By applying a program, it is possible to make an existing video signal recorder or the like function as the image converter according to the present invention. That is, an existing video signal recorder or the like, to which programs as executed by the CPU  103  described above are applied, can realize the functional configuration and processes described above by the programs being executed by a computer (CPU or the like) that controls this video signal recorder or the like. Likewise, by applying a program, it is possible to make an existing cellular phone or the like function as the image reproducer according to the present invention. 
     Such programs may be distributed in arbitrary manners, and distributed as stored in a recording medium such as a memory card or distributed via a communication network such as the Internet. By applying the programs distributed in these manners to a video signal recorder or the like or a cellular phone or the like by installing the programs thereon, it is possible to realize functions similar to those of the HDD recorder  10  or the cellular phone  20  described above. 
     In accordance with the present invention, by generating a low quality image from a high quality image, it is possible to reduce the size of the image data, and at the same time, upgrade a necessary portion. Therefore, a high-definition image can be presented to the user even when the image is zoomed up. Accordingly, the present invention can be applied to a cellular phone, an image recorder, a video camcorder, etc. 
     Various embodiments and changes may be made thereunto without departing from the broad spirit and scope of the invention. The above-described embodiment is intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiment. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention. 
     This application is based on Japanese Patent Application No. 2008-293249 filed on Nov. 17, 2008 and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.