Patent Publication Number: US-8525870-B2

Title: Remote communication apparatus and method of estimating a distance between an imaging device and a user image-captured

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a remote communication apparatus, and more particularly to a remote communication apparatus for use in video conference. The present invention also relates to a remote communication method for such apparatus. 
     2. Description of the Background Art 
     In recent years, remote communication systems for communication for participants in remote locations have been actively researched. Such a remote communication system catches the voice of a participant by a microphone, captures the image of the participant by an imaging device, and transmits the voice and image to a remote location, where they are reproduced in real time, thus being able to convey the state of the participant to another participant in the remote location. 
     Japanese patent laid-open publication No. 223551/1996 to Shimada discloses a remote communication system implementing remote communication with the feeling of on-site conversation. Specifically, Shimada discloses a video conference system applicable to a remote location where plural participants stay, and directing a video camera to one of the participants who speaks more or most loudly to be considered as a predominant talker in the conversation. On the video monitor of the video conference system, the user can focally watch the image of the predominant participant talking in the remote location. 
     More specifically, the video conference system taught by Shimada includes, in addition to a video camera, a couple of microphones, one for capturing voice and the other for sensing the direction of a predominant speaker talking louder. The other, or direction-sensing microphone, captures voice, from which the maximum sound pressure is detected to determine which of the participants speaks most loudly, i.e. predominant talker. Then, according to the determination, the video camera and the one microphone, i.e. sound-collecting microphone, are controlled so as to be oriented to the direction of the predominant talker. 
     In the video conference system of Shimada, the video camera captures the prevailing talker, whose image is used to extract the edge or outline of a subject whose image is to be captured, while the video camera is controlled in its orientation so as to render the edge thus extracted match with a predetermined pattern. This enables the image of the predominant talker to be viewed at the proper position on the screen of a video monitor. 
     However, although the video conference system of the prior art can thus determine the detection of a predominant talker, it fails to detect the distance from the video camera to a predominant participant. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a new and improved remote communication apparatus and a method therefor capable of estimating the distance of an imaging device to a participant to be captured by an imaging device. 
     In accordance with the present invention, a remote communication apparatus for receiving an image signal representing an image of a first participant captured by an imaging device to show the image to a second participant includes a zoom controller for controlling a zoom ratio defining an angle of view of the imaging device; and an estimator for estimating a distance between the imaging device and the first participant on the basis of the zoom ratio of the imaging device. 
     The estimator may estimate the distance between the imaging device and the first participant by assuming that the zoom ratio is adjusted so that, if an object of a predetermined size is virtually at a position of the first participant, an image of the object acquired by the imaging device would occupy a predetermined range in the whole image acquired by the imaging device. 
     The remote communication apparatus may further include a coordinate obtainer for using a pan and a tilt angle of the imaging device, and the distance between the imaging device and the first participant estimated by the estimator to obtain a coordinate position of the first participant in a coordinate system where the imaging device resides. The coordinate obtainer may obtain, rather than the coordinate position, a coordinate range of the first participant in the coordinate system. 
     The remote communication apparatus may further include a sound collector for capturing a voice of the second participant; a plurality of loudspeakers located around the first participant; and an output controller for transmitting the voice captured by the sound collector to at least one of the plurality of loudspeakers, wherein the output controller holds data of coordinates of the loudspeakers in the coordinate system and transmits the voice captured by the sound collector to one of the loudspeakers which has a coordinate position that is closest to the coordinate position of the first participant obtained by the coordinate obtainer. 
     The remote communication apparatus may further include a voice detector for detecting a volume level of the voice of the second participant captured by the sound collector, and the estimator may estimate the distance between the imaging device and the first participant on the basis of the volume level of the voice of the second participant detected by the voice detector in addition to the zoom ratio of the imaging device. 
     Also in accordance with the present invention, a method for remote communication includes the steps of controlling a zoom ratio defining an angle of view of the imaging device; and estimating a distance between the imaging device and the first participant on the basis of the zoom ratio of the imaging device. 
     Further in accordance with the present invention, a remote communication system includes an imaging device for capturing an image of a first participant; and the remote communication apparatus described above. 
     As described above, in accordance with the present invention, a distance between an imaging device and a participant whose image is to be captured by the imaging device can be estimated. 
     The inventive concept disclosed in the application may also be defined in ways other than in the claims presented below. The inventive concept may consist of several separate inventions particularly if the invention is considered in light of explicit or implicit subtasks or from the point of view of advantages achieved. In such a case, some of the attributes included in the claims may be superfluous from the point of view of separate inventive concepts. Within the framework of the basic inventive concept, features of different embodiments are applicable in connection with other embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  schematically shows a specific configuration of an illustrative embodiment of a remote communication system in accordance with the present invention; 
         FIG. 2  is a functional block diagram showing a specific detailed configuration of the remote communication apparatus shown in  FIG. 1 ; 
         FIG. 3  shows in a plan view an exemplary layout of the control panel shown in  FIG. 2 ; 
         FIG. 4  shows a specific detailed configuration of the system controller shown in  FIG. 2 ; 
         FIGS. 5 and 6  are plan views showing the relationship between the angle of view of the imaging device, the position of an object to be shot by the imaging device, and the image of the object captured by the imaging device; 
         FIG. 7  shows in a plan view an example of image field captured by the imaging device shown in  FIG. 1  and displayed on the screen of the display monitor shown in  FIG. 2 ; 
         FIG. 8  shows in a perspective view an example of coordinate system in the remote location shown in  FIG. 1 ; 
         FIGS. 9 and 10  are plan views, like  FIGS. 5 and 6 , showing an example of correction for a distance estimated by the relative position estimator shown in  FIG. 4 ; 
         FIGS. 11 and 12  are plan views, like  FIGS. 5 and 6 , showing examples of range hailed by the user of the remote communication apparatus shown in  FIG. 1 ; and 
         FIG. 13  is a flowchart useful for understanding the operation of the remote communication apparatus shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Well, reference will be made to the accompanying drawings to describe in detail a preferred embodiment of the present invention. In the following description and the accompanying drawings, like components or constituent elements are designated with the same reference numerals and repetitive descriptions thereon will be omitted. However, like components or constituent elements may sometimes be distinguished by letters following the same reference numerals but being different from each other. Plural components or constituent elements having substantially the same functional configuration may, if necessary, be distinguished in such a way as loudspeakers  24 A,  24 B and  24 C, which may, however, be designated generally with just reference numerals  24 . 
     First, reference will be made to  FIG. 1  to describe the outline of a remote communication system  1  in accordance with a preferred embodiment of the present invention.  FIG. 1  shows a configuration of the remote communication system  1  specifically implemented as a video conference system in accordance with the preferred embodiment. As seen from the figure, the remote communication system  1  in accordance with the preferred embodiment includes a remote communication apparatus  10  disposed to be manipulated by a user, or participant,  12  staying near the remote communication apparatus  10 . The remote communication system  10  further includes an imaging device  22 , and loudspeakers  24 A,  24 B and  24 C, which are positioned near remote participants  14 A to  14 D staying at the distance from the user  12  and interconnected to a communication device  26 . The remote communication system  1  thus structured is intended to allow the user  12  to communicate in real time with the remote participants  14 A to  14 D. 
     The remote communication apparatus  10  is adapted to transmit to the communication device  26  a control signal  27  for controlling the orientation, such as panning and tilting, and the angle of view, i.e. zoom factor or ratio, of the imaging device  22 , as well as to receive from the communication device  26  an image signal  30  representative of an image captured by the imaging device  22  in response to the control signal  27  to visualize the received image on its display unit  150 ,  FIG. 2 . This enables the user  12  on the remote communication apparatus  10  to watch the images of the remote participants  14 A to  14 D. The remote communication apparatus  10  is also adapted to transmit to the communication device  26  a voice signal  32  representing a voice or sound caught by a microphone  120 ,  FIG. 2 , from the user  12 . Signals or data are designated with reference numerals of connections on which they are conveyed. 
     The communication device  26  is adapted to transmit the image signal  30  to and receive the voice signal  32  from the remote communication apparatus  10 . For example, the communication device  26  transmits the image signal  30  produced by the imaging device  22  to the remote communication apparatus  10 , and receives the voice signal  32  representing a voice captured from the user  12  from the remote communication apparatus  10  to transmit the voice signal  32  to the loudspeakers  24 A,  24 B and  24 C. The communication device  26  may symbolically depicted as a single block  26 , but may include any telecommunications circuits and/or networks. 
     The imaging device  22  may advantageously be a video camera adapted to be responsive to the control signal  27  transmitted from the remote communication apparatus  10  to capture the image of a participant  14  specifically with its orientation and angle of view controlled. 
     The loudspeakers  24 A,  24 B and  24 C are adapted to receive the voice signal  32  received by the communication device  26  from the remote communication apparatus  10  to produce the inputted voice signal  32  in the form of audible sound. This enables the participants  14 A to  14 D to hear the voice uttered by the user  12  remote therefrom. 
     Although being not depicted in  FIG. 1 , the remote communication system  1  may include microphones for capturing the voice of the participants  14 A to  14 D, and display devices for displaying the image of the user  12  captured by the remote communication apparatus  10 . 
       FIG. 2  is a schematic functional block diagram showing a configuration of the remote communication apparatus  10  in accordance with this embodiment. As shown in the  FIG. 2 , the remote communication apparatus  10  includes an control panel  110 , a microphone  120 , a system controller  130 , an imaging device controller  140 , a display unit  150  and an output controller  160 , which are interconnected as illustrated. In the figure, the communication device  26  is omitted just for simplification from depiction between the remote communication device  10  and the imaging device  22  and loudspeakers  24 A,  24 B and  24 C. Also omitted are other functional blocks and/or interconnections not directly necessary for understanding the invention. 
     The control panel  110  is manipulable by the user  12  to output a signal  34  corresponding to a content of the user&#39;s operation to the system controller  130 . The user&#39;s operation on the control panel  110  is exemplified by a key operation for controlling the orientation or attitude and angle of view of the imaging device  22 . 
       FIG. 3  schematically shows in a plan view an exemplary layout of the control panel  110 . As seen from  FIG. 3 , the control panel  110  specifically includes thereon a zoom switcher  112 , a tilt switcher  114  and a pan switcher  116 . 
     The zoom switcher  112  has a knob slidable in the up and down direction by the user&#39;s manipulation to make the imaging device  22  zoom in and out. The zoom switcher  112  outputs, when manipulated, to the system controller  130  operational information  34  representing the manipulation and the zooming position of the knob of the zoom switcher  112 . 
     Also, the tilt switcher  114  has a knob slidable in the up and down direction by the user&#39;s operation to make the imaging device tilt. The tilt switcher  114  outputs, when manipulated, to the system controller  130  operational information  34  representing the manipulation and the tilting position of the knob of the tilt switcher  114 . 
     Similarly, the pan switcher  116  has a knob slidable in the left and right direction by the user&#39;s operation to make the imaging device pan. The pan switcher  116  outputs, when manipulated, to the system controller  130  operational information  34  representing the manipulation and the panning position of the knob of the pan switcher  116 . 
       FIG. 3  merely shows an example of control panel  110 . Therefore, the control panel  110  may be, for example, in the form of touch-screen, push-buttons, changeover switches, toggle switches or dial switchers. Furthermore, the control panel  110  may include, for example, an optical sensor or a wireless receiver for receiving an infrared or radio-wave signal emitted by a remote control handset in response to the user&#39;s operation. 
     Returning to  FIG. 2 , the microphone  120  is a sound capturing unit for receiving the voice of the user  12  on the remote communication apparatus  10 . The microphone  120  is connected to the system controller  130  and the output controller  160 , and transduces the captured voice of the user  12  to the corresponding electric signal  32 , which is outputted to the system controller  130  and the output controller  160 . 
     The system controller  130  is adapted to be operative in response to the information signal  34  provided from the control panel  110  and the microphone  120  to produce from the operational information  34  control amounts  36  such as a zooming factor or ratio, a tilt angle and a pan angle to the imaging device controller  140 . The system controller  130  is also responsive to the information signal  34  to select appropriate one of the loudspeakers  24 A,  24 B and  24 C and send an information signal  38  representing the selected loudspeaker  24  to the output controller  160 . A detailed configuration of the system controller  130  will be described later with reference to  FIGS. 5 to 13 . 
     The imaging device controller  140  is adapted to be responsive to a control signal representing the control amounts  36  from the system controller  130  to control the imaging device  22 . In this embodiment, the imaging device controller  140  receives the control amount  36  from the system controller  130 , and outputs, according to the received control amounts  36 , the control signal  27  for controlling the orientation, e.g. the pan and tilt angles, and the angle of view of the imaging device  22  defined by the zoom ratio. In other words, the imaging device controller  140  functions as a zoom, a tilt and a pan controller. The imaging device  22  is responsive to the control signal  27  from the imaging device controller  140  to capture the image of the participants  14 . 
     The display monitor  150  is adapted to receive the image signal  30  representing the image captured by the imaging device  22  to display the image to the user  12  on the remote communication apparatus  10 . Therefore, the user  12 , while checking the image on the display monitor  150 , can operate the control panel  110  to control the imaging device  22 . The display monitor  150  may be, for example, a CRT (Cathode Ray Tube) display device, an LCD (Liquid Crystal Display) device, or an OLED (Organic Light Emitting Diode) device. 
     The output controller  160  is adapted to be responsive to the control output  38  from the system controller  130  to transmit the voice signal  32  inputted from the microphone  120  to at least one of the loudspeakers  24 A,  24 B and  24 C which is selected by the system controller  130 . Specifically, each of the loudspeakers  24 A,  24 B and  24 C has its own address specific thereto allotted. The output controller  160  transmits the voice signal  32  to the loudspeaker  24  having its address corresponding to that designated by the information signal  38  from the system controller  130 . 
     Now, with reference to  FIG. 4  showing a detailed configuration of the system controller  130 , the system controller  130  comprises a control amount calculator  132 , a voice detector  134 , a relative position estimator  136 , and an address translator  138 , which are interconnected as depicted. 
     The control amount calculator  132  is adapted to be responsive to the input  34  from the control panel  110  to calculate the control amounts  36  on the imaging device  22 . Specifically, the control amount calculator  132  has data stored in advance which define the relationships between the positions of the knobs of the zoom switcher  112 , tilt switcher  114  and pan switcher  116 , and the zoom ratio, tilt angle and pan angle, respectively, of the imaging device  22 , and the control amount calculator  132  converts the input  34  from the control panel  110  to the control amounts  36  such as the zoom ratio, tilt angle and pan angle according to the relationships stored. The control amount calculator  132  outputs the control amounts  36  to the imaging device controller  140  and the relative position estimator  136 . 
     The voice detector  134  is adapted to determine whether or not the voice signal  32  inputted from the microphone  120  includes a word or words hailing another participant. For example, when the word “Hey” is registered as a word hailing another participant, the voice detector  134  may be responsive to the voice sounding “Hey” in the voice signal  32  inputted from the microphone  120  to determine that the voice signal  32  is of a hail to one or ones of the participants  14 A to  14 D. When the voice signal  32  inputted from the microphone  120  is determined as including a hail to another participant, the voice detector  134  outputs a starting signal  40  to cause the relative position estimator  136  to start its processing. 
     The relative position estimator  136  is adapted to use the control amounts  36  inputted from the control amount calculator  132  to estimate the relative position of the hailed participant from the imaging device  22  to produce an information signal  41  representing the estimated relative position. For example, the pan and tilt angles may be used to determine the direction of the hailed participant from the imaging device  22 . However, by simply using the pan and tilt angles, the distance of a hailed participant from the imaging device  22  would not be determined. Therefore with the illustrative embodiment, the relative position estimator  136  uses the zoom ratio to estimate the distance of a hailed participant from the imaging device  22 . 
     Specifically, the relative position estimator  136  first finds an angle of view θ,  FIG. 5 , on the basis of the zoom ratio included in the control amounts  36 . The relative position estimator  136  may be adapted to hold a look-up table defining the relationship between the values of zoom ratio and the values of angle of view so as to reference the table to thereby find a value of angle of view θ corresponding to an input value of zoom ratio. 
     Next, the relative position estimator  136  estimates, on the basis of the angle of view θ, the distance of the hailed participant from the imaging device  22 . Specifically with reference to  FIG. 5 , the relative position estimator  136  assumes that the user  12  adjusts the zoom ratio, i.e. angle of view θ, of the imaging device  22  so that, if a certain object having a predetermined size, e.g. sphere  42  having its diameter equal to M cm, is virtually at the position of a hailed participant, the width of an image of the sphere  42  acquired by the imaging device  22  would occupy a portion a % of the width of the screen  152  of the monitor  150 . Now, the relationship between the angle of view θ and the distance L cm is represented by the following expression (1): 
     
       
         
           
             
               
                 
                   M 
                   = 
                   
                     
                       ( 
                       
                         L 
                         × 
                         2 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         tan 
                         ⁢ 
                         
                           θ 
                           2 
                         
                       
                       ) 
                     
                     × 
                     
                       a 
                       100 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Therefore, the relative position estimator  136  estimates the distance L according to the following expression (2): 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       50 
                       × 
                       M 
                     
                     
                       a 
                       × 
                       tan 
                       ⁢ 
                       
                         θ 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Therefore, for example, when the diameter M of the sphere  42  is equal to 30 cm, and the ratio a in width of the sphere image  44  to the screen  152  is equal to 50%, the distance L is represented by the following expression (3): 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     30 
                     
                       tan 
                       ⁢ 
                       
                         θ 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
       FIGS. 5 and 6  show the relationship between the angle of view θ of the imaging device  22 , the distance of the sphere  42  from the imaging device  22 , and the size of the image  44  of the sphere  42 . When the ratio a in width of the sphere image  44  to the screen  152  is equal to 50%, for the angle of view θ shown in  FIG. 5 , the distance L estimated by the relative position estimator  136  is equal to a distance between a position B and the imaging device  22 . Similarly, when the ratio a in width of the sphere image  44  to the screen  152  is equal to 50%, for the angle of view shown in  FIG. 6  which is larger than that in  FIG. 5 , the distance L estimated by the relative position estimator  136  is equal to a distance between a position C and the imaging device  22  which is shorter than that in  FIG. 5 . 
     Meanwhile, the relative position estimator  136  may hold a table defining the relationship between the zoom ratio and the distance, and reference the table to thereby estimate the distance between a hailed participant and the imaging device  22 . 
     Additionally, a manner for estimating the distance between a hailed participant and the imaging device  22  is not limited to the manner using the above-described expressions. For example, the relative position estimator  136  may be adapted to receive and analyze an image captured by the imaging device  22  to thereby estimate the distance L between a hailed participant  14  and the imaging device  22 . With reference to  FIG. 7 , a specific description will be made below. 
       FIG. 7  shows in a plan view a specific example of image  46  of a participant  14  captured by the imaging device  22  and carried on the image signal  30  to be displayed on the screen  152  of the display monitor  150 . In  FIG. 7 , the width of the head of the participant image  46  is represented by x. The relative position estimator  136  in this case further obtains from the image signal  30  the image field  152  captured by the imaging device  22  and analyzes the latter to obtain the value of width x. This width x depends on the zoom ratio or the angle of view θ. Therefore, assuming that the actual width of the head of the participant is equal to a value y, the relative position estimator  136  can estimate the distance L between the hailed participant and the imaging device  22  using a ratio a % of the width x to the width of the screen  152 . In this case, the relationship between the angle of view θ and the distance L is represented by the following expression (4): 
     
       
         
           
             
               
                 
                   
                     y 
                     
                       L 
                       × 
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       tan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         θ 
                         2 
                       
                     
                   
                   = 
                   
                     a 
                     100 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Therefore, the relative position estimator  136  estimates the distance L according to the following expression (5): 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       50 
                       ⁢ 
                       y 
                     
                     
                       a 
                       × 
                       tan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         θ 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Returning to  FIG. 4 , the address translator  138  is adapted to select one of the loudspeakers  24 A,  24 B and  24 C which corresponds to the relative position  41  estimated by the relative position estimator  136 , and output an address  38  of the selected loudspeaker  24  to the output controller  160 . Specifically, the address translator  138  holds data of positions, i.e. spatial coordinates, of the loudspeakers  24 A,  24 B and  24 C in a coordinate system  48  of the remote location including the imaging device  22  and their addresses for communication. The address translator  138  also has the function of a coordinate obtainer for obtaining a coordinate in the remote location of a hailed participant on the basis of the relative position  41  (the pan angle, the tilt angle, and the distance L from the imaging device  22 ) estimated by the relative position estimator  136 . 
     Thus, the address translator  138  can calculate a distance in the space coordinate system between the hailed participant and each loudspeaker  24 , and select one of the loudspeakers  24  that is closest to the hailed participant. With reference to  FIG. 8 , a more specific description will be made below. 
       FIG. 8  shows a specific example of coordinate system  48  of the location remote from the remote communication apparatus  10 . The address translator  138  holds data of the positions, i.e. coordinates, of the loudspeakers  24 A,  24 B and  24 C in the coordinate system  48  shown in  FIG. 8 . When the participant  14 C is hailed, the address translator  138  obtains the coordinate position of the participant  14 C as shown in  FIG. 8  on the basis of the relative position  41  estimated by the relative position estimator  136 . 
     Furthermore, the address translator  138  calculates the distance between the coordinate positions of the participant  14 C and each of the loudspeakers  24 A,  24 B and  24 C. Now, since the loudspeaker  24 B is closest in coordinate position to the participant  14 C in this example as shown, the address translator  138  selects the loudspeaker  24 B and outputs the address  38  of the loudspeaker  24 B to the output controller  160 . 
     The above description is directed to an exemplified case of selecting the loudspeaker  24 C that is closest to a hailed participant, but this embodiment is not limited to this exemplified case. For example, the address translator  138  may select a predetermined number of loudspeakers  24  for a hailed participant. 
     The address translator  138  may be adapted to determine an allocation of volume level to the respective loudspeakers  24  depending on the distance in the spatial coordinate system  48  of a hailed participant to each loudspeaker  24 . For example, the address translator  138  may increase the allocation of volume levels for the loudspeakers  24  closer to a hailed participant, and decrease the allocation of volume levels for the loudspeakers  24  more distant from the hailed participant. Furthermore, the address translator  138  may provide the output controller  160  with the allocation of volume level of each loudspeaker  24  together with the address of that loudspeaker  24  associated therewith. 
     The above description is directed to an exemplified case of estimating the distance between a hailed participant and the imaging device  22  on the basis of the zoom ratio, but the embodiment is not limited to this exemplified case. As a modification, the voice detector  134  may be adapted to measure the volume level of the voice signal  32 , and the relative position estimator  136  may be adapted to use the volume level of the voice signal  32  detected by the voice detector  134  to correct the distance estimated on the basis of the zoom ratio. 
     Specifically, when a voice signal  32  detected by the voice detector  134  is higher in volume level than a predetermined reference value, it is considered to be hail to a participant who stays more distant from the imaging device  22  than estimated based only on the zoom ratio. In this case, the relative position estimator  136  may correct the distance estimated on the basis of the zoom ratio to a longer distance. With reference to  FIGS. 9 and 10 , a more specific description will be made below. 
       FIGS. 9 and 10  show an example of correction for estimated distance. The relative position estimator  136 , as shown in  FIG. 9 , when estimating that a participant exists at a position B whose distance from the imaging device  22  is defined on the basis of the zoom ratio in the case of the volume level of the voice signal  32  detected by the voice detector  134  being higher than the reference value, may correct the estimated position of the hailed participant to a position D that is more distant from the imaging device  22  than the position B. 
     Similarly, as shown in  FIG. 10 , when estimating that a participant exists at a position C whose distance from the imaging device  22  is defined on the basis of the zoom ratio in the case of the volume level of the voice signal  32  detected by the voice detector  134  being higher than the reference value, the relative position estimator  136  may correct the estimated position of the hailed participant to a position A that is more distant from the imaging device  22  than the position C. 
     Meanwhile, when the volume level of the voice signal  32  detected by the voice detector  134  is lower than the reference value, the relative position estimator  136  may correct the distance estimated on the basis of the zoom ratio to a shorter distance. 
     The relative position estimator  136  may also be adapted to estimate a hailed range instead of the relative position of a hailed participant. In this case, the address translator  138  may select a loudspeaker  24  residing in the hailed range, and output the address  38  of the selected loudspeaker  24  to the output controller  160 . With reference to  FIGS. 11 and 12 , a specific description will be made below. 
       FIGS. 11 and 12  show specific examples of hailed range. The relative position estimator  136  may be adapted to estimate as a hailed range a range  28  between the positions B and D, as shown in  FIG. 11 , estimated on the basis of the zoom ratio. Similarly, the relative position estimator  136  may estimate as a hailed range a range  28  formed, as shown in  FIG. 12 , between the positions C and A estimated on the basis of the zoom ratio. 
     Next, with reference to  FIG. 13 , the operation of the remote communication apparatus  10  in accordance with this embodiment will be described.  FIG. 13  is a flowchart useful for understanding the operation of the remote communication apparatus  10 . At first, the user  12  operates the control panel  110  in order to control the imaging device  22  (step S 210 ). Then, the content  34  of the user&#39;s operation on the operating panel  110  is inputted into the control amount calculator  132  to be converted to the control amounts  36  such as the zoom ratio, the tilt angle and the pan angle (S 220 ). 
     Then, the control amounts  36  are inputted into the imaging device controller  140 , which in turn outputs the control signal  27  to the imaging device  22  to thereby control the imaging device  22  according to the control amounts  36  (S 230 ). This causes the image in the range intended by the user  12  to be captured by the imaging device  22  to be viewed on the display monitor  150 . 
     Next, when a voice signal  32  representing a user&#39;s voice hailing another participant is inputted from the microphone  120  (S 240 ) into the voice detector  134  and the output controller  160 , the instruction signal  40  is outputted from the voice detector  134  to the relative position estimator  136  to instruct the relative position estimator  136  to estimate the relative position  41  of the hailed participant from the imaging device  22 . 
     Then, in the address translator  138 , selected is one of the loudspeakers  24  which corresponds to the relative position  41  estimated by the relative position estimator  136 , and then the address  38  of the selected loudspeaker  24  is outputted to the output controller  160  (S 260 ). In the address translator  138 , the coordinate position of the hailed participant in the spatial coordinate system  48  of the remote location is obtained on the basis of the relative position  41  estimated by the relative position estimator  136 . Thus, calculated is a distance between the hailed participant and each loudspeaker  24  in the spatial coordinate system  48 , and selected is one of the loudspeakers  24  that is closest to the hailed participant. 
     Then, from the output controller  160 , the voice signal  32  of the user is transmitted to the loudspeaker  24  selected by the address translator  138  (S 270 ). This enables the user&#39;s voice to be outputted from the loudspeaker  24  that is closest to the hailed participant. 
     In summary, in accordance with the instant embodiment, on the basis of the current value of zoom ratio of the imaging device  22 , the distance between the hailed participant and the imaging device  22  can be estimated. Furthermore, in accordance with this embodiment, the user&#39;s voice can be outputted from one of the loudspeakers  24  which is appropriate for the position of a hailed participant. The distance between a hailed participant and the imaging device  22  can be corrected depending on the volume level of the user&#39;s voice. 
     For example, those control steps processed by the remote communication apparatus  10  not always have to be performed in the temporal order depicted in the flowchart, but may be performed, for example, in the order different therefrom or even partly or entirely in parallel. 
     Additionally, it should be noted that the above depiction and description do not restrict the remote communication apparatus  10  to an implementation only in the form of hardware but at least a part or the entirety of the apparatus  10  may be implemented by software, i.e. a computer program that enables hardware such as a processor system including a CPU (Central Processor Unit), a ROM (Read-Only Memory) and a RAM (Random-Access Memory) built in the remote communication apparatus  10  to implement the functions similar to those of the above-described constituent elements of the remote communication apparatus  10 . In such a case, storage media storing the computer program sequences are also provided. 
     The entire disclosure of Japanese patent application No. 2009-191349 filed on Aug. 20, 2009, including the specification, claims, accompanying drawings and abstract of the disclosure, is incorporated herein by reference in its entirety. 
     While the present invention has been described with reference to the particular illustrative embodiment, it is not to be restricted by the embodiment. It is to be appreciated that those skilled in the art can change or modify the embodiment without departing from the scope and spirit of the present invention.