Patent Publication Number: US-6707489-B1

Title: Automatic voice tracking camera system and method of operation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional from U.S. patent application Ser. No. 08/509,228, filed Jul. 31, 1995, and entitled “Automatic Voice Tracking Camera System and Method of Operation.” 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to the field of video conferencing, and more particularly an automatic voice tracking camera system and method of operation. 
     BACKGROUND OF THE INVENTION 
     In conventional video conferencing systems, infrared technology has been employed to track the position of a speaker in the video conference. This conventional method uses an IR transmitter and three IR receivers to triangulate the position of the IR transmitter which is carried by the speaker. This type of system may not work well in a conference room environment where a number of persons may talk at any given time. 
     A second conventional method for tracking a speaker is the use of touch-to-talk microphones. The position of each microphone is preset in order to direct a camera when a speaker touches a microphone to talk. The positions of the microphones are preloaded in the system so that the system knows where each speaker is to be located. This may be undesirable because it requires fixed positions of speakers, limits the movement of speakers, and is not easily portable. 
     Microphone array technology is being introduced in the video conferencing field in order to improve the reception of a sound and to allow location of the position of the source of the sound. This microphone array technology can be used in both conference room and classroom environments. The position information from such a microphone array is problematic if used to direct a camera because the position information changes continuously due to the movement of speakers and due to errors in locating the position of the speakers. 
     It is desirable in a video conferencing environment to provide automatic voice tracking of a speaker in order to control cameras such that there is natural camera movement in viewing a given speaker. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an automatic voice tracking camera system and method of operation are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed video conferencing systems. 
     According to one aspect of the present invention, an automatic voice tracking camera system includes a first camera and a camera controller. The first camera is operable to receive control signals for controlling a view of the first camera. The camera controller is operable to determine a responsive camera movement of the first camera based upon coordinates for a point in space where the determination comprises comparing the coordinates with a first spacial region defined around a current speaker position. The camera controller is then operable to generate camera control signals based upon the appropriate responsive camera movement and to provide the camera control signals to the first camera. In one embodiment, the camera controller is further operable also to compare the coordinates with a second spacial region defined around the current speaker position. 
     According to another aspect of the present invention, a method is provided for automatically controlling a camera. The method includes determining an appropriate responsive camera movement from coordinates for a point in space where the coordinates are compared with a first spacial region defined around a current speaker position. Camera control signals are then generated based upon the appropriate responsive camera movement, and the camera control signals are provided to a first camera. 
     A technical advantage of the present invention is the automation of tracking a speaker in a video conference such that the camera views the speaker using only the voice of the speaker to determine the speaker&#39;s position. 
     Another technical advantage of the present invention is the use of two cameras whereby a non-active camera can be used to find and view a new speaker prior to switching between the two cameras. In this manner, a switch to a new speaker does not include a scan between the two speakers. 
     A further technical advantage of the present invention is the movement of a camera to a new view only if the speaker&#39;s position moves outside of a defined window. Thus, a minor position change is not translated into movement of the camera. 
     An additional technical advantage of the present invention is the use of a second defined window to determine whether a current camera or other camera should be used to view the speaker when the speaker&#39;s position moves outside of the first defined window. 
     Another technical advantage of the present invention is the filtering of speaker position information to delay movement of the camera until a new position is verified. In this manner, insignificant noises that might otherwise result in a camera movement are filtered. 
     A further technical advantage of the present invention is the use of zoning of a conference room. A conference room is divided into a number of zones each associated with one camera. Each camera is then controlled to view speakers within its associated zone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present, invention and advantages thereof may be acquired by reference to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein: 
     FIG. 1 is a block diagram of a video conferencing system including an automatic voice tracking camera system according to the present invention; 
     FIG. 2 is a block diagram of one embodiment of an automatic voice tracking camera system of the present invention; 
     FIG. 3 is a flow chart of one embodiment of a process for initializing and controlling cameras according to the present invention; 
     FIG. 4 is a flow chart of one embodiment of the camera control process of FIG. 3; 
     FIG. 5 is a flow chart of the select and move camera process of FIG. 4; 
     FIG. 6 is a two-dimensional view of one embodiment of the use of windowing for camera selection and movement according to the present invention; 
     FIG. 7 illustrates one embodiment of camera selection and windowing criteria according to the present invention; 
     FIG. 8 is a flow chart of one embodiment of a process for generating control signals to move a camera according to the present invention; 
     FIG. 9 illustrates conversion of Cartesian coordinates to polar coordinates for use in camera control according to the present invention; and 
     FIG. 10 illustrates one embodiment of zoning a conference room according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of a video conferencing system, indicated generally at  10 , including an automatic voice tracking camera system  12  according to the present invention. Note that the illustrated embodiment of FIG. 1 shows use of the invention with a video conferencing system. This illustration, however, is not meant to limit the scope of the invention. The present invention may be practiced with many types of video systems. For example, an automatic tracking system for showing an individual in an auditorium or other grouping of people may effectively use the present invention. 
     System  12  comprises a microphone array  14 . Microphone array  14  includes a plurality of microphones positioned in a room in which one party to a video conference is serviced by system  12 . In one embodiment of the present invention, microphone array  14  comprises from twelve to sixteen microphones. This number of microphones is not, in any way, intended to be limiting. As many as 500 microphones or more may be used with the present invention. Microphone array  14  provides an audio signal to an automatic camera controller  16 . The audio signal represents received sound from the room including the voice of a speaker in the room. 
     System  12  comprises a plurality of cameras  18  located in the video conference room. Cameras  18  include a first camera, CAMERA  1 , through an Nth camera, CAMERA N. In one embodiment of the present invention, each camera  18  comprises a pan-tilt-zoom (PTZ) camera. In other embodiments, one or more camera  18  may comprise a wide angle camera or other suitable type of camera. 
     Automatic camera controller  16  is coupled to and communicates with a host video conference system  20 . Automatic camera controller  16  provides video and audio signals  22  to host video conference system  20 . Automatic camera controller  16  also communicates with host video conference system  20  through a communication link  24 . In the illustrated embodiment, communication link  24  comprises an RS-232 communication link. Cameras  18  communicate with automatic camera controller  16  through communication links  26 . In the illustrated embodiment, communication links  26  comprise RS-232 communication links. Cameras  18  also provide video signals  28  to automatic camera controller  16  that represent the picture viewed by each camera  18 . 
     In operation, microphone array  14  receives sound from within a room in which part of a video conference takes place. Microphone array  14  then provides an audio signal to automatic camera controller  16  representing the received sound. Automatic camera controller  16  operates to automatically point and track cameras  18  to the source of the sound. In a video conference, the sound received comprises the voice of a speaker which is used to track the speaker&#39;s position. In one embodiment of the present invention, system  12  comprises only one camera  18  which is automatically directed to the speaker. In other embodiments, system  12  comprises two or more cameras  18  from which a camera is automatically selected and directed to track the speaker. 
     Automatic camera controller  16  processes the audio signal provided by microphone array  14 . Automatic camera controller  16  then generates control signals to cameras  18  to automatically track cameras  18  to the source of the sound. In this manner, automatic camera controller  16  operates to point an active camera  18  to a speaker based upon reception of the voice of that speaker. Automatic camera controller  16  provides the processed audio signal from microphone array  14  and the video signal from the active camera  18  to host system  20 . In the illustrated embodiment, the audio signal and video signal are one-way signals from automatic camera controller system  16  to host system  20 . Communication link  24  is used for communication between host system  20  and automatic camera controller  16 . 
     Automatic camera controller  16  processes the audio signal received from microphone array  14  in order to determine a position of a speaker. Automatic camera controller  16  then operates to control cameras  18  based on the speaker position information obtained from the audio signal processing In general, automatic camera controller  16  determines whether a camera  18  needs to move in order to view the speaker, selects an appropriate camera  18  to move if necessary, and moves the appropriate camera  18 . 
     FIG. 2 is a block diagram of an embodiment of automatic camera controller  16  of FIG. 1 according to the present invention. As shown in FIG. 2, automatic camera controller  16  comprises a beamformer  30 . Beamformer  30  is coupled to microphone array  14 . Beamformer  30  receives the audio signal provided by microphone array  14 . Beamformer  30  provides a processed audio signal  32  to host system  20 . Beamformer  30  also provides speaker position data  34 . Speaker position data  34  represents the position of the source of the sound represented by the audio signal received from microphone array  14 . In a video conference, the sound comprises the voice of a speaker and the position of the voice coincides with the position of the speaker. The word “speaker” is used herein generally to refer to the source of the sound tracked by the cameras although that sound could include sounds other than the voice of a speaker. 
     A camera controller  36  receives speaker position data  34 . Camera controller  36  is coupled to an interface  38  and to camera  18 . As discussed above, other embodiments of the present invention comprise more than one camera  18 . Camera controller  36  generates and provides control signals  40  to camera  18  in order to direct the view of camera  18 . Interface  38  is coupled to host system  20  to provide a communication link. As shown, camera  18  provides video signal  42  to automatic camera controller  16  which is, in turn, provided to host system  20 . 
     The operation of microphone array  14  and beamformer  30  in FIG. 2 are described in more detail in U.S. patent application Ser. No. 08/399,427, entitled “Methods and Apparatus for Source Location Estimation From Microphone Array Time Delay Estimates” and U.S. patent application Ser. No. 08/231,646 entitled “Method and Apparatus for adoptive Beamforming” the disclosures of which are incorporated herein by reference. 
     Beamformer  30  determines the position of the speaker by processing the audio signal received from microphone array  14 . Beamformer  30  then transfers the processed audio signal to host system  20  and transfers the position of the speaker to camera controller  36  in the form of speaker position data  34 . In one embodiment of the present invention, speaker position data  34  comprises Cartesian coordinates defining the location of the speaker and accuracy of prediction of the speaker position. 
     Camera controller  36  determines an appropriate responsive camera movement based upon speaker position data  34 . Camera controller  36  then generates camera control signals  26  and provides camera control signals  26  to camera  18  such that the view of camera  18  automatically tracks the position of the speaker. In other embodiments of the present invention, camera controller  36  controls two or more cameras  18  in order to track the speaker. In one embodiment of the present invention, camera controller  36  generates pan-tilt-zoom control commands for moving camera  18  which comprises a pan-tilt-zoom (PTZ) camera. 
     Camera controller  36  communicates with host system  20  using interface  38 . Interface  38  provides a communication link  24  between host system  20  and camera controller  36  in order to allow download of new software and transmission of host commands as well as other communication functions. 
     FIG. 3 shows a flow of a process for initializing and controlling cameras. When voice tracking system  12  is turned on, camera controller  36  within automatic camera controller  16  goes through initialization process  52  to set up register values, determine number of cameras to be controlled, and geometric relationship between the microphone array  14  and the cameras  18 . Once the initialization process  52  is complete, the controller  36  move to control process  54  and starts taking position data of a speaker from the beamformer  30  as well as control commands from the host  20  through the interface  38 . 
     A technical advantage of the present invention is the automation of tracking a speaker in a video conference such that the camera views the speaker using only the voice of the speaker to determine the speaker&#39;s position. 
     FIG. 3 is a flow chart of one embodiment of a process for controlling cameras according to the present invention. The automatic control of cameras is accomplished by the camera controller described above. In step  50 , the power for the camera controller is turned on. After power-on, the camera controller executes an initialization process in step  52 . Then, in step  54 , the camera controller executes a camera control process. In step  56 , the camera controller determines whether the video conference has ended. If so, the camera controller has completed camera control. If not, the camera controller repeats the camera control process of step  54  until the video conference has ended. 
     The initialization process of step  52  includes initialization and position alignment of the camera or cameras in the room. Alignment includes determining the relationship between the microphone array and each camera. The camera controller is then initialized appropriately One method for determining the relationship is to have a person talk in the video conference room. The camera is then forced to point to and view the person. The differences between position data obtained by the beamformer and the pan, tilt, and zoom values read from the camera is the offset. The offset obtained therefrom is used as the relationship of the camera relative to the microphone array and to initialize the camera controller. 
     The camera control process of step  54  involves determining whether a command has been received from the host system through the interface. If so, the host command is interpreted by the camera controller and passed to the camera or used to control the microphone array as appropriate. 
     FIG. 4 is a flow chart of one embodiment of the camera control process of step  54  of FIG. 3. A user may turn off the auto-tracking capability and manually control the camera. If the host command is not a command requiring action by the camera controller, the camera controller forwards the host command to the camera and turns off automatic control until the host turns on the automatic tracking. In step  60 , the camera controller determines whether a command was received from the host system. If not, in step  62 , the camera controller determines whether the speaker has moved to a new position. If not, then the current iteration of the camera control process is completed and the camera controller continues at step  56  in FIG.  3 . 
     If, in step  64 , the speaker has changed position, the camera controller executes the select and move camera process of step  64 . The process of step  64  is described in more detail below. In general, in step  64 , the camera controller determines whether a camera should be moved, selects the camera to move, controls the appropriate camera to view the new position and switches between cameras if necessary. 
     If, in step  60 , a command was received from the host system, then the camera controller determines whether realignment is necessary in step  66 . If so, the camera controller returns to the initialization process of step  52  in FIG.  3 . If not, in step  68 , the camera controller determines whether manual tracking is indicated by the host command. If so, in step  70 , the camera controller passes the host command to the camera and turns off automatic control until the host turns on the automatic tracking. Following step  70 , the camera controller returns to step  56  of FIG.  3 . 
     If, in step  68 , manual tracking is not indicated, then in step  72 , the camera controller determines whether the host command is a change of zoom. If so, the camera controller changes the zoom in step  74  and uses it as a new zoom set up. If not, the camera controller returns to step  62 . After changing the zoom in step  74 , the camera controller also returns to step  62 . 
     In step  62 , the camera controller determines whether the speaker has moved to a new position by processing the position information representing the position of the voice of the speaker. In one embodiment of the present invention, the camera controller receives new position information from the beamformer. In one embodiment, the camera controller receives two pieces of information from the beamformer. One piece is the position of the speaker when that position changes, and the other piece is an accuracy indicator associated with the position information. The accuracy indicator represents how accurately the position information represents the position of the speaker. 
     In the select and move camera process of step  64 , the camera controller uses different methods to select and move cameras depending on the number of cameras coupled to the camera controller. One embodiment of the select and move camera process is described in more detail below. In this embodiment of the present invention, this process for a one-camera system is a subset of that for a two-camera system. 
     In a one-camera embodiment, the camera controller determines whether the camera needs to be moved when the camera controller receives new position information. This determination is accomplished by examining whether the new position is outside a window defined with respect to the current camera position. This use of a defined window is important because a speaker may move slightly and remain inside the frame of the picture viewed by the camera. The defined window prevents an attempt to center the camera continuously, which would be distracting to the users. The size of the defined window can be varied according to the zoom range of the camera. If the camera is zoomed-in, the window can be defined smaller so a small change in position triggers a movement of the camera. On the other hand, if the camera is zoomed-out, the window can be defined larger so only a relatively large change in position triggers a movement of the camera. The windowing is used in this manner because a zoomed-out camera covers a larger area than a zoomed-in camera. 
     In a two-camera embodiment, there are two selection criteria with respect to the windowing function. The camera controller first checks if the new position is within the defined window of the active or current camera as described above. If not, one of the two cameras needs to be moved to track the new position of the speaker. The camera controller determines which camera to move by applying a second defined window. The second window is defined with respect to the current camera and encompasses a larger area than the first window. If the new position is relatively close to the current camera, the new position falls within the second window. In this case, the current camera is moved to track the new position. If the new position is not within the second window, the camera controller moves the second or other camera to track the new position and switches the active video after the other camera has moved to cover the new position. After this switch, the other camera becomes the current camera. 
     Another technical advantage of the present invention is the use of two cameras whereby a non-active camera can be used to find and view a new speaker prior to switching between the two cameras. In this manner, a switch to a new speaker does not include a scan between the two speakers. 
     FIG. 5 is a flow chart of one embodiment of the select and move camera process of step  64  of FIG.  4 . In step  80 , the camera controller determines whether or not a camera needs to be moved by analyzing the new position with respect to the defined window of the current camera. If not, then no camera selection or movement is necessary. If so, in step  82 , the camera controller determines whether there is one or there are two available cameras. It should be understood that embodiments comprising more than two cameras can also be implemented according to the present invention. 
     If there is one camera, the camera controller moves the current camera in step  84 . Of course, the current camera is the only camera. If there are two available cameras, the camera controller determines whether or not to use the current camera in step  86 . This determination uses a second defined window as described above. If the current camera is to be moved, the camera controller moves the current camera in step  84 . Otherwise, in step  88 , the camera controller moves the other camera, and then sets the other camera to be the current camera. This switch means that the previously current camera becomes the other camera. 
     FIG. 6 is a two-dimensional view of one embodiment of the use of windowing for camera selection and movement according to the present invention. It should be understood that three dimensional windows can be used by adding a third coordinate. 
     As shown in FIG. 6, the current camera is directed to view a position P c  and the other camera is directed to view a position P o . The position of the current camera P c , coincided with the position of the speaker prior to movement of the speaker to a new position. The new position, P n , represents the new position of the speaker after movement. 
     With respect to the current camera, a first window, WINDOW  1 , and a second window, WINDOW  2 , are defined. The first window defines a region  90 , and the second window defines a region  92 . Region  90  of WINDOW  1  represents the area in which no camera movement is needed. Region  92  of WINDOW  2  represents the area in which the current camera will be moved to track the new position, and the remaining area is the region in which the other camera will be moved. It should be understood that other embodiments having more than two cameras can also be implemented. 
     In FIG. 6, if new position P n  falls within region  90 , there is no change in camera position. If new position P n  falls within region  92 , the current camera is moved to be directed to and viewing the new position P n . After this movement, the position of the current camera P c  is the same as the new position P n . Lastly, if the new position P n  falls outside of region  92 , the other camera is moved. In this case, the position of the other camera P c  coincides with the new position P n . The other camera becomes the current camera, and the current camera becomes the other camera. The newly defined current camera is directed to and viewing the current position of the speaker. 
     A technical advantage of the present invention is the movement of a camera to a new view only if the speaker&#39;s position moves outside of a defined window. Thus, a minor position change is not translated into movement of the camera. 
     An additional technical advantage of the present invention is the use of a second defined window to determine whether a current camera or other camera should be used to view the speaker when the speaker&#39;s position moves outside of the first defined window. 
     FIG. 7 illustrates one embodiment of camera selection and windowing criteria according to the present invention. As shown, a new position P n , a current camera position P c , an other camera position P o , and a new average position P a  are maintained. In addition, temporary positions P 0 , P 1 , and P 2  are maintained. The window regions, WINDOW  1  and WINDOW  2 , are defined with respect to an allowable difference between two coordinates. The defined differences are used to determine whether a point is too far from a center point of a window to be considered within the window. As shown, the differences, (x_diff 1 ,y_diff 1 ,z_diff 1 ) and (x_diff 2 ,y_diff 2 ,z_diff 2 ), are defined as the product of constants, A to F, and function, f a  to f f , zoom setting. 
     Initially, the current camera position P c  is set equal to the other camera position P o  which is set equal to the new position P n  In addition, the temporary position marker, t, is set to position “0.” 
     When the camera controller receives a new speaker position, the camera controller determines whether or not a camera needs to move and selects which camera to move. The camera controller first determines whether the absolute value of the difference between one of the coordinates (x c ,y c ,z c ) of the current camera position P c  and the corresponding coordinate (x n ,y n ,z n ) of the new position P n , is greater than the allowed differences defined by WINDOW  1  (x_diff 1 ,y_diff 1 ,z_diff 1 ). If so, then the new position P n  is stored in temporary position P o  and the index of the temporary position is incremented by one. This process is repeated until the index reaches the number three. The accuracy information may be used to determine if the new position should even be considered as a valid position. This may be performed by establishing a threshold region. If the accuracy information exceeds the threshold, the process responds by discarding a position with a large error. 
     When all three temporary positions P 0 , P 1  and P 2  are filled, there have been three new positions P n  outside the range of WINDOW  1 . The camera controller sets the new average position P a  equal to the average of the three temporary positions P 0 , P 1  and P 2  It should be understood that, in other embodiments, the number of temporary positions can be higher or lower than three. 
     After the new average position P a  is set, the camera controller determines whether the absolute value of the difference between one of the coordinates (x a , Y a ,z a ) of the new average position P a  and a corresponding coordinate (x c ,y c ,z c ) of the current camera position P c  is greater than the differences defined by WINDOW  2  (x_diff 2 ,y_diff 2 ,z_diff 2 ). If so, then the camera controller moves the other camera to be directed to view the new average position P a . The camera controller then sets the other camera position P o  equal to the current camera position P c  and sets the current camera position P c  equal to the new average position P a . The active video signal is then switched between the two cameras to the new current camera. 
     If, however, the difference between the new average position P a  and the current camera position P c  is not greater than the differences defined by WINDOW  2 , the camera controller moves the current camera to be directed to view the new average position P a . The camera controller then sets the current camera position P c  equal to the new average position P a  After a movement of either of the cameras, the camera controller returns to the initial step of measuring new positions versus the differences defined by WINDOW  1 . 
     In this embodiment there are three temporary positions used to produce an average new position. The number of temporary positions can be varied depending on at the time delay desired before moving a camera. In the illustrated embodiment, unless there are three consecutive new positions outside the WINDOW  1  range, the camera controller restarts the accumulation of temporary positions. Once a new average position P a  has been determined, the new average position P a  becomes the current position P c . Any newer position within WINDOW  1  from the new current position P c  is then ignored. WINDOW  1  is used to determine whether a new position should be accumulated, and WINDOW  2  is used to determine whether the current camera should be moved or the other camera should be moved. 
     A technical advantage of the present invention is the filtering of speaker position information to delay movement of the camera until a new position is verified. In this manner, insignificant noises that might otherwise result in a camera movement are filtered. 
     Once movement and camera selection have been determined, the camera controller converts the speaker position from Cartesian coordinates to polar coordinates. Depending on the type of camera, appropriate commands for changing the view of the selected camera are generated and provided to the camera. In one embodiment to the present invention, the camera has pan, tilt and zoom (PTZ) controls and comprises a CANON VC-C1 or a PANASONIC KXC-CM775 PTZ camera. It should be understood that where there is only one camera, the current camera position P c  is always set equal to the other camera position P o  in the process described above. 
     Another aspect of the present embodiment is that the camera used to locate the speaker may be a wide-angle camera. For example, the present embodiment includes the necessary instructions and controller functions so that when a signal appears for the pan-tilt-zoom camera to change its position to another position, the wide-angle camera may move until the desired object or speaker comes into view of the wide-angle picture. Once the speaker is within or near the center of the wide-angle picture, the camera controller will shift to the wide-angle pan-tilt-zoom camera for viewing to continue. 
     FIG. 8 is a flow chart of one embodiment of a process for generating control signals to move a camera according to the present invention. In step  100 , the Cartesian coordinates are converted to polar coordinates including a position offset due to the relationship of the microphone array to the camera, if necessary. In step  102 , the polar coordinates are used to generate specific camera commands. These camera commands comprise appropriate control signals for the specific type of camera being used. In step  104 , the commands to move the camera are executed by the camera. Step  104  may comprise substeps which include transmitting commands to the camera in step  106 , receiving commands by the camera in step  108 , and assessing the PTZ range of the camera in step  110 . 
     FIG. 9 illustrates conversion of Cartesian coordinates to polar coordinates for use in camera control according to the present invention. As shown in FIG. 9, a Cartesian coordinate (x, y, z) is to be converted to polar coordinates (r, θ, Φ) in the polar coordinate system. The speaker&#39;s position is represented by (x, y, z). The camera is located at the origin, as shown. The polar coordinates represent the distance from the camera to the speaker (r), the pan angle of the camera from center to the speaker (θ), and the tilt angle of the camera from center to the speaker (Φ). 
     The distance (r) from the camera to the speaker is used to determine the appropriate zoom. This distance or range is defined as        r   =         x   2     +     y   2     +     z   2                         
     According to the illustrated convention, a centered camera represents a zero pan angle (θ), where the left side is negative and the right side is positive. Under this convention, the pan angle (θ) is defined as equal to the arctan of (x/y). The tilt angle (Φ) is defined to be zero when the camera is centered, where up is positive, and down is negative. The tilt angle (Φ) is defined to the arctan of        (     z   ÷       (       (       x   2     +     y   2       )       )     .                       
     The size of an object or speaker in the picture can be maintained by changing the zoom ratio according to the distance as long as the ratio is in the range of the camera. A default zoom ratio can be set in the initialization routine of the camera controller. The zoom can be adjusted by a user while the camera is in use. The camera controller detects changes and maintains the size of the picture until a user changes the zoom. It has been observed that accuracy of locating a speaker deteriorates, especially in estimating distance, when the speaker is further away from the microphone array. The camera controller can slightly reduce the zoom ratio from the desired value to ensure the size of the picture if the speaker is relatively far from the camera. 
     FIG. 10 illustrates one embodiment of zoning a conference room according to the present invention. Zoning can be applied to a video conference in which two or more cameras are used. As shown in FIG. 10, a conference room  120  includes a conference table  122 . There are four chairs  124  positioned in a first zone, ZONE  1 , and four chairs  126  positioned in a second zone, ZONE  2 . A first camera  130  is located on one side of the room, as shown, and a second camera  132  is located on the opposite side of the room. A TV monitor  128  for showing video received from the other video conference site is positioned at one end of conference table  122 . 
     In this embodiment, conference room  120  is divided into two zones. Zoning of the conference room avoids problems caused by using only one camera such as an inability to capture a full view of all speakers. A typical video conference room has a long conference table and two rows of chairs as shown in FIG.  10 . 
     According to the present invention, conference room  120  is divided into ZONE  1  and ZONE  2 . Camera  130  and camera  132  are used to track speakers depending upon the zone in which the speakers are positioned. For example, camera  130  is used to track speakers in ZONE  2 , and camera  132  is used to track speakers in ZONE  1 . Analogous zoning can be applied to multiple cameras each dedicated to one of a number of zones where a room is larger or where capturing a direct image of each speaker is important. Each speaker position will be located within a zone which then determines which camera or cameras are used to track that speaker position and view the speaker. 
     A technical advantage of the present invention is this use of zoning of a conference room. The conference room is divided into a number of zones each associated with one camera. Each camera is then controlled to view speakers within its associated zone. 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.