CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the Korean Patent Application No. 10-2010-0111952, filed on Nov. 11, 2010, and 10-2010-0111954, filed on Nov. 11, 2010, the contents of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments described herein relate to a display device. 
     2. Background 
     A variety of display devices have been proposed in order to meet consumer demand and provide new products and services. These devices include high-definition televisions, computer monitors and mobile terminals and as well as a myriad of others. In spite of their commercial success, many improvements are needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows one embodiment of a multimedia system. 
         FIG. 2  shows an example of a multimedia device in the system. 
         FIG. 3  shows a multimedia device using a plurality of heterogeneous images sensors and camera-taking screens. 
         FIG. 4  shows a procedure of using detection and recognition data in connection with a plurality of heterogeneous image sensors. 
         FIG. 5  shows a list of face vectors stored in a database. 
         FIG. 6  shows operation of a plurality of heterogeneous image sensors, which interact with a multimedia device in accordance with hardware and software. 
         FIG. 7  shows one embodiment which includes a plurality of heterogeneous image sensors and a multimedia device. 
         FIG. 8  shows another embodiment which includes a plurality of heterogeneous image sensors and a multimedia device. 
         FIG. 9  shows another embodiment which includes a plurality of heterogeneous image sensors. 
         FIG. 10  shows an example of an image sensor. 
         FIG. 11  shows another example of an image sensor. 
         FIG. 12  shows a method for calculating a distance using an image sensor. 
         FIG. 13  shows an image taken by an image sensor. 
         FIG. 14  shows another image sensor. 
         FIG. 15  shows a procedure of recognizing a user through a multimedia device that uses a plurality of heterogeneous image sensors. 
         FIG. 16  shows a procedure of performing a function customized to a recognized user. 
         FIG. 17  shows a procedure of recognizing a plurality of users through a multimedia device that uses a plurality of heterogeneous image sensors. 
         FIG. 18  shows a procedure of performing a function customized to a plurality of recognized users. 
         FIG. 19  to  FIG. 21  show procedures of registering a new user. 
         FIG. 22  shows one embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
         FIG. 23  shows another embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
         FIG. 24  shows scenes where a depth image and a color image based on a first pose of a user are taken by a plurality of heterogeneous image sensors. 
         FIG. 25  shows scenes where a depth image and a color image based on a second pose of a user are taken by a plurality of heterogeneous image sensors. 
         FIG. 26  shows scenes where a depth image and a color image based on a third pose of a user are taken by a plurality of heterogeneous image sensors. 
         FIG. 27  shows a database that stores feature information of each user according to pose information, generated based on scenes in  FIG. 24  to  FIG. 26 . 
         FIG. 28  shows a scene where first body information of a user is taken by a first image sensor. 
         FIG. 29  shows a scene where second body information of a user is taken by a first image sensor. 
         FIG. 30  shows a scene where third body information of a user is taken by a first image sensor. 
         FIG. 31  shows a scene where fourth body information of a user is taken by a first image sensor. 
         FIG. 32  shows a database that stores body information of a plurality of users generated based on scenes taken in  FIG. 28  to  FIG. 31 . 
         FIG. 33  shows one embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
         FIG. 34  shows another embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
         FIG. 35  shows another embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
         FIG. 36  shows another embodiment of a method of recognizing a user using a plurality of heterogeneous image sensors. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows one embodiment of a multimedia system including a multimedia device in the form of a connected TV. The system includes a content provider (CP)  10 , a service provider (SP)  20 , a network provider (NP)  30 , and a home network end user (FINED)  40 . The HNED  40  corresponds to, for example, a client  100  which is the multimedia device. 
     The content provider  10  manufactures various contents and provides them. Examples of the content provider  10  include a terrestrial broadcaster, a cable system operator (SO), a multiple system operator (MSO), a satellite broadcaster, and an Internet broadcaster, as illustrated in  FIG. 1 . Also, the content provider  10  may provide various applications in addition to broadcast contents. 
     The service provider  20  can provide contents provided by the content provider  10  by service-packaging them. For example, the service provider  20  of  FIG. 1  can package first terrestrial broadcasting, second terrestrial broadcasting, cable MSO, satellite broadcasting, various kinds of Internet broadcasting, application, etc. and provide the packaged one to a user. 
     The network provider  30  may provide a network for providing a service to the client  100 . The client  100  may construct a home network end user (HNED) to receive a service. 
     The client  100  may provide contents through the network. In this case, the client  100  may be a content provider contrary to the above. The content provider  10  may receive contents from the client  100 . In this case, it is advantageous in that bidirectional content service or data service is available. 
       FIG. 2  shows an example of a multimedia device which includes a network interface  201 , a TCP/IP manager  202 , a service delivery manager  203 , a demultiplexer (Demux)  205 , a PSI&amp; (PSIP and/or SI) decoder  204 , an audio decoder  206 , a video decoder  207 , a display A/V and OSD module  208 , a service control manager  209 , a service discovery manager  210 , a metadata manager  212 , an SI&amp;Metadata DB  211 , a UI manager  214 , and a service manager  213 . 
     Moreover, a plurality of heterogeneous image sensors  260  are connected with the multimedia device  200 , by a connection mode of a USB mode, for example. Also, although the plurality of heterogeneous image sensors  260  are designed as separate modules in  FIG. 2 , the plurality of heterogeneous images sensors  260  may be designed in such a manner that they are housed in the multimedia device  200 . 
     The network interface  201  receives packets from a network, and transmits the packets to the network. In other words, the network interface  201  receives services, contents, etc. from the service provider through the network. 
     The TCP/IP manager  202  is involved in packets received in the multimedia device  200  and packets transmitted from the multimedia device  200 , i.e., packet transfer from the source to the destination. The service delivery manager  203  takes the role of control of received service data. For example, if the service delivery manager  203  controls real-time streaming data, it can use RTP/RTCP. If the service delivery manager  203  transmits the real time streaming data by using RTP, it parses the received packets in accordance with RTP and transmits the parsed packets to the demultiplexer  205  or stores the parsed packets in the SI&amp;Metadata DB  211  under the control of the service manager  213 . The service delivery manager  203  feeds the received information back to a server, which provides a service, by using RTCP. 
     The demultiplexer  205  demultiplexes the received packets to audio, video and PSI (Program Specific information) data and then transmits the demultiplexed data to the audio decoder  206 , the video decoder  207 , and the PSI&amp;(PSIP and/or SI) decoder  204 , respectively. 
     The PSI&amp; (PSIP and/or SI) decoder  204  receives and decodes PSI section, PSIP (Program and Service information Protocol) section or SI (Service Information) section, which is demultiplexed by the demultiplexer  205 . 
     Also, the PSI&amp;(PSIP and/or SI) decoder  204  decodes the received sections to make a database for service information, and stores the database for service information in the SI&amp;Metadata DB  211 . 
     The audio/video decoders  206 / 207  decode the video data and the audio data, which are received from the demultiplexer  205 . 
     The UI manager  214  provides a graphic user interface (GUI) for the user by using an on screen display (OSD), etc. and performs a receiving operation based on a key input from the user. For example, if a key input signal for channel selection is input from the user, the UI manager  214  transmits the key input signal to the service manager  213 . 
     The service manager  213  controls managers related to the service, such as the service delivery manager  203 , the service discovery manager  210 , the service control manager  209 , and the metadata manager  212 . 
     Also, the service manager  213  makes a channel map and selects a channel by using the channel map in accordance with the key input signal received from the UI manager  214 . The service discovery manager  210  provides information required to select the service provider that provides services. If a signal related to channel selection is received from the service manager  213 , the service discovery manager  210  discovers a corresponding service by using the received information. 
     The service control manager  209  takes the role of selection and control of the service. For example, if the user selects a live broadcasting service like the existing broadcasting mode, the service control manager  209  uses IGMP or RTSP. If the user selects a video on demand (VOD) service, the service control manager  209  selects and controls the service by using RTSP. The metadata manager  212  manages metadata related to the service and stores the metadata in the SI&amp;Metadata DB  211 . 
     The SI&amp;Metadata DB  211  stores the service information decoded by the PSI&amp; (PSIP and/or SI) decoder  204 , the metadata managed by the metadata manager  212 , and the information required to select the service provider provided by the service discovery manager  210 . Also, the SI&amp;Metadata DB  211  may store setup data for the system. 
     The IG  250  is a gateway where functions required to access IMS based IPTV services are collected. 
     The plurality of heterogeneous image sensors  260  illustrated in  FIG. 2  are designed to take a single image or a plurality of images of a person or object located in the periphery of the multimedia device  200 . In more detail, the plurality of heterogeneous image sensors  260  are designed to operate the single image or the plurality of images continuously, periodically, at a selected time, or at a specific condition only, as described later in more detail. 
       FIG. 3  shows one embodiment of a multimedia device based on a plurality of heterogeneous images sensors and camera-taking screens. The sensors include one or more first image sensors related to depth data processing include a field not suitable for long-distance face recognition due to limited resolution (for example, maximum VGA level) and a recognition distance (for example, 3.5 m). 
     The sensors also include one or more second image sensors related to color data processing have drawbacks in that they have a slow recognition speed and are not robust to light condition. Accordingly, in order to solve the drawbacks of the image sensors, the multimedia device is designed to interact with a hybrid type image sensor module that is a hybrid type of the first image sensor and the second image sensor. 
     An IR camera or depth camera is used as the first image sensor. In more detail, a time of flight (TOF) type IR camera or depth camera and a structured light type IR camera or depth camera have been discussed. The TOF type IR camera or depth camera calculates distance information by using the time difference resulting from emission of infrared rays. The structured light type IR camera or depth camera calculates distance information by emitting infrared rays to a specific pattern and analyzing a modified pattern. The first image sensor is advantageous in view of depth data recognition and processing speed, and easily senses object, person, etc. even at a dark place. However, the first image sensor has a drawback in that it has low resolution at a long distance. 
     Moreover, a color camera or RGB camera is used as the second image sensor. In more detail, a stereo camera type color camera or RGB camera and a mono camera type color camera or RGB camera have been discussed. The stereo camera type color camera or RGB camera detects and traces the hand or face based on image time comparison information taken through two cameras. The mono camera type color camera or RGB camera detects and traces the hand or face based on shape and color information taken through one camera. The second image sensor is advantageous in that it has more improved resolution than that of the first image sensor, whereas the second image sensor has drawbacks in that it is vulnerable to peripheral lighting and it is difficult to recognize the corresponding object at a dark place. In particular, the second image sensor has a drawback in that it is difficult to recognize exact depth. 
     As illustrated in  FIG. 3 , the multimedia device is designed to have both the first image sensor and the second image sensor. The image sensors may be designed in such a manner that they are embedded in the multimedia device, or may be designed as separate hardware modules. First of all, as illustrated in (b) of  FIG. 3 , the first image sensor takes images that include users located in the periphery of the multimedia device. Detailed taking-images are illustrated in ( 1 ), ( 2 ), ( 3 ) and ( 4 ) of  FIG. 3  in due order. 
     If image-taking and data analysis of the first image sensor are completed, as illustrated in (a) of  FIG. 3 , the second image sensor takes images of a face of a specific user. Detailed taking-images are illustrated in ( 5 ), ( 6 ), and ( 7 ) of  FIG. 3  in due order. 
     The first image sensor of the plurality of heterogeneous image sensors according to one embodiment of the present invention takes first images located in the periphery of the multimedia device and extracts depth data from the taken first images. As illustrated in ( 1 ) of  FIG. 3 , the first image sensor can be designed in such a manner that a field of each object is displayed at different contrast ratios depending on the distance. 
     Moreover, the first image sensor can recognize a face of at least one user by using the extracted depth data. In other words, the first image sensor extracts body information (for example, face, hand, foot, joint, etc.) of the user by using the database, etc., as illustrated in ( 2 ) of  FIG. 3 , and acquires location coordinates and distance information of a face of a specific user as illustrated in ( 3 ) of  FIG. 3 . In more detail, the first image sensor is designed to calculate values x, y, and z which are location information on the face of the user, wherein the x means the location on a horizontal axis of the face in the taken first image, the y means the location on a vertical axis of the face in the taken first image, and the z means the distance between the face of the user and the first image sensor. 
     Also, among the plurality of heterogeneous image sensors according to one embodiment of the present invention, the second image sensor for extracting color images takes second images of the recognized face of the user, and is illustrated in ( 5 ) of  FIG. 3 . 
     If the first image sensor and the second image sensor illustrated in  FIG. 3  are designed to adjoin each other, an error due to the difference in physical location may be disregarded. However, according to another embodiment, the second image sensor is designed to compensate for the coordinate information or distance information acquired by the first image sensor by using the information on the difference in physical location and to take the user by using the compensated coordinate information or distance information. 
     Also, if the first image sensor and the second image sensor are designed to be arranged horizontally from the ground, the information on the difference in physical location can be set based on a horizontal frame. The second image sensor, as illustrated in ( 7 ) of  FIG. 3 , extracts feature information from the taken second image. The feature information is data corresponding to a specific part (for example, mouse, nose, eye, etc.) for identifying a plurality of users who use the multimedia device. Moreover, the second image sensor may zoom in a zone corresponding to the face of the user based on the coordinate values (the values x, y, and z) obtained through image-taking of the first image sensor. This means a procedure of switching from ( 5 ) of  FIG. 3  to ( 6 ) of  FIG. 3 . 
     If image-taking and analysis of the first image sensor and the second image sensor are completely performed, the multimedia device according to one embodiment of the present invention accesses a memory that stores data corresponding to the extracted feature information, and extracts information for identifying a specific user stored in the memory. 
     If the information for identifying a specific user exists in the memory, the multimedia device provides a service previously set for the specific user. On the other hand, if the information for identifying a specific user does not exist in the memory, the multimedia device is designed to display a guide message for storing the recognized user information in the memory. 
     As described above, according to one embodiment, the first image sensor is designed to detect user location information or coordinate information on the face of the user while the second image sensor is designed to recognize the face by using the data acquired by the first image sensor. 
     Moreover, according to another embodiment, the second image sensor is designed in such a manner that it is operated only in case of a specific condition. For example, if the distance information acquired by the operation of the first image sensor between the user and the first image sensor is less than a first reference value, or if a recognition rate on the face of the user, which is acquired by the operation of the first image sensor, is more than a second reference value, the face of the user located in the periphery of the multimedia device is detected and recognized by the first image sensor only. 
     On the other hand, if the distance information acquired by the operation of the first image sensor exceeds the first reference value, or if the recognition rate on the face of the user, which is acquired by the operation of the first image sensor, is less than the second reference value, the second image sensor is additionally used to recognize the face of the user. 
     According to another embodiment, the second image sensor is designed to perform zoom-in by using the distance information acquired by the first image sensor in the procedure of recognizing the face of the user and to take the face only by using face coordinate information acquired by the first image sensor. 
     Accordingly, the different types of heterogeneous image sensors are used as above, it is advantageous in that it enables long-distance face recognition and data processing speed is improved. 
       FIG. 4  shows one embodiment of a procedure of using detection data and recognition data in a plurality of heterogeneous image sensors and a multimedia device. Face detection is performed by a process different from that of face recognition. 
     The face detection includes a process of detecting a face zone within one image, whereas the face recognition is a process of recognizing whether the detected face corresponds to which specific user. In particular, the procedure of performing face detection by using the first image sensor and the procedure of performing face recognition by using the second image sensor in accordance with one embodiment of the present invention will be described with reference to  FIG. 4 . 
     As illustrated in  FIG. 4 , the multimedia device includes a detection module  301 , a recognition module  302 , a database (DB)  303 , a first image sensor  304 , and a second image sensor  305 . The multimedia device uses detection data  306  and recognition data  307  if necessary. The detection data  306 , for example, may be generated based on knowledge-based detection techniques, feature-based detection techniques, template matching techniques, and appearance-based detection techniques. Also, the recognition data  307 , for example, include data for identifying a specific user, such as eyes, nose, mouse, jaw, zone, distance, shape, and angle. 
     Moreover, the detection module  301  determines the presence of the face of the user by using the image data received from the first image sensor  304 . Also, in a procedure of estimating the zone where the face of the user is located, data related to the aforementioned knowledge-based detection techniques, feature-based detection techniques, template matching techniques, and appearance-based detection techniques are used. 
     The recognition module  302  identifies whether the recognized user is a specific user by using the image data received from the second image sensor  305 . At this time, the recognition module  302  compares the received image data with face vector information stored in the DB  303  based on the aforementioned recognition data  307 . This will be described in more detail with reference to  FIG. 5 . 
       FIG. 5  shows a list of face vectors stored in a database. The face vectors are of users who use a multimedia device, which vectors are stored in the database. The face vectors, for example are a data set of feature information appearing on the faces of the users, and are used to identify each of the specific users. 
       FIG. 6  shows an operation of a plurality of heterogeneous image sensors, which interact with a multimedia device according to one embodiment in accordance with a hardware field and a software field. 
     As illustrated in  FIG. 6 , the operation of the multimedia device, which is performed through images input by the plurality of heterogeneous image sensors, will be described depending on a hardware field  360  of the image sensor and a software field  350  of the multimedia device that processes the data received from the image sensor. Although the hardware field  360  is illustrated as a separate module in  FIG. 6 , it may be embedded in the multimedia device that processes the software field  350 . 
     First of all, the hardware field  360  includes a data collection field  340  and a firmware field  330 . The data collection field  340  receives original data recognized by the multimedia device from the image sensor, and includes an IR light projector, a depth image sensor, a color image sensor (RGB image sensor), a microphone, and a camera chip. 
     Also, the firmware field  330  serves to connect the hardware field with the software field. Also, the firmware field  330  may be used as a host application required by a specific application, and performs downsamphng and mirroring. 
     Accordingly, the data collection field  340  and the firmware field  330  interact with each other. The data collection field  340  and the firmware field  330  can control the hardware field  360  through their interaction. Also, the firmware field can be driven by a camera chip. 
     Also, the software field  350  includes an application programming interface (API) field  320 , and a middleware field  310 . The API field  320  can be implemented by the controller of the multimedia device. Also, if a camera module is configured as an external device separately from the multimedia device, the API field can be implemented by a personal computer, a game console, a set-top box, etc. Also, the API field  320  could be a simple API that allows the multimedia device to drive the sensor of the hardware field. 
     The middleware field  310  is a recognition algorithm field and can include a depth processing middleware. Also, the middleware field can provide an application together with an explicit user control API even if the user inputs gesture through either his (her) hand or his (her) whole body. Also, the middleware field can include an algorithm that performs an operation for searching for the location of the hand of the user, an operation for tracing the location of the user, an operation for extracting skeleton features of the user, and an operation for respectively recognizing the user and background from the input image. The algorithm can be operated by using depth information, color information, IR information, and audio information, which are acquired from the hardware field. 
       FIG. 7  shows one embodiment having a plurality of heterogeneous image sensors and a multimedia device. Although the image sensors and multimedia device are shown to be separate in this embodiment, multiple image sensors/cameras may be designed in such a manner that they are embedded in the multimedia device in other embodiments. 
     As illustrated in  FIG. 7 , the multimedia device  400  according to one embodiment of the present invention is designed to include modules such as a central processing unit (CPU)  401  and a graphic processing unit  404 , wherein the CPU  401  includes an application  402  and a face recognition processing module  403 . In the mean time, a plurality of heterogeneous image sensors  420  are designed to include modules such as an application specific integrated circuit (ASIC)  421 , an emitter  422 , a first image sensor  423 , and a second image sensor  424 . 
     The multimedia device  400  is connected with the plurality of heterogeneous image sensors  420  through a wire or wireless interface  410 . For example, a universal serial bus (USB) interface may be used as the wire or wireless interface  410 . 
     The emitter  422  emits light to at least one user located in the periphery of the multimedia device  400 . The first image sensor  423  takes a first image by using the emitted light, extracts depth data from the taken first image, and detects a face of the at least one user by using the extracted depth data. Also, the second image sensor  424  takes a second image on the face of the detected user and extracts feature information from the taken second image. 
     The extracted feature information is transmitted to the face recognition processing module  403  of the multimedia device through the interface  410 . Although not illustrated in  FIG. 7 , the face recognition processing module  403  is designed to include a receiver, a memory, an extractor, and a controller. 
     The receiver of the face recognition processing module  403  receives feature information transmitted through the plurality of hetero image sensors  420  and the interface  410 . Moreover, the memory of the face recognition processing module  403  stores feature information on at least one user and ID corresponding to the feature information. 
     Accordingly, the extractor of the face recognition processing module  403  extracts the ID corresponding to the received feature information from the memory, and the controller of the face recognition processing module  403  is designed to automatically perform previously set functions corresponding to the ID. 
     If the face recognition processing module is designed to be performed by the CPU of the multimedia device as illustrated in  FIG. 7 , it is advantageous in that the design cost of the camera is lowered, and it is also advantageous in view of extensibility such as recognition of various faces and addition of functions. 
       FIG. 8  shows another embodiment which includes a plurality of heterogeneous image sensors and a multimedia device. Although the image sensors and the multimedia device are separately illustrated in  FIG. 8 , multiple image sensors/cameras may be embedded in the multimedia device in other embodiments. 
     As illustrated in  FIG. 8 , multimedia device  500  is designed to include modules such as a central processing unit (CPU)  501  and a graphic processing unit  503 , wherein the CPU  501  includes an application  502 . In the mean time, a plurality of heterogeneous image sensors  520  are designed to include modules such as a face recognition processing module  521 , an application specific integrated circuit (ASIC)  522 , an emitter  523 , a first image sensor  524 , and a second image sensor  525 . 
     The multimedia device  500  is connected with the plurality of heterogeneous image sensors  520  through a wire or wireless interface  510 . For example, a universal serial bus (USB) interface may be used as the wire or wireless interface  510 . It is to be understood that the modules of  FIG. 8  are only exemplary and the scope of the present invention should be defined basically by claims. 
       FIG. 8  is different from  FIG. 7  in that the face recognition module  521  is built in the plurality of heterogeneous image sensors  520 . As illustrated in  FIG. 8 , if the face recognition processing module is designed to be performed by the plurality of heterogeneous image sensors  520 , various types of cameras can be designed through an independent platform. 
       FIG. 9  shows an embodiment having a plurality of heterogeneous image sensors. The plurality of heterogeneous image sensors include a first image sensor group  610 , a second image sensor  620 , a controller  630 , a memory  640 , and an interface  650 , and are designed to receive audio data from a microphone  670  and an external audio source  660  under the control of the controller  630 . 
     The memory  640 , for example, may be designed as a flash memory. The interface  650  is designed as a USB interface and is connected with an external multimedia device. The first image sensor group  610  includes am emitter  680  and a first image sensor  690 . The emitter can be designed as an infra-red (IR) emitter, for example. 
     Moreover, a light projector  682  of the emitter  680  projects a lens  681  to emit light to at least one user located in the periphery of the multimedia device, under the control of the controller  630 . 
     Also, under the control of the controller  630 , the first image sensor  690  takes a first image by using the light received through a lens  691 , extracts depth data from the taken first image, and transmits the extracted data to the controller  630 . The controller  630  detects a face of the at least one user by using the transmitted depth data, and controls the second image sensor  620 . 
     The second image sensor  620  takes a second image on the face of the detected user applied through a lens  621 , under the control of the controller  630 . Moreover, the second image sensor  620  transmits feature information extracted from the taken second image to the controller  630 . 
     The controller  630  is designed to transmit the extracted feature information to the multimedia device by using the interface  650 . Accordingly, the multimedia device that has received the feature information can quickly identify which user of users stored in the DB is the one corresponding to the taken image. 
       FIG. 10  shows an example of a first image sensor. In  FIG. 10 , an IR source  710  may correspond to the emitter  680  of  FIG. 9 , and a depth image processor  720  may correspond to the first image sensor  690  of  FIG. 9 . Accordingly, the description of  FIG. 9  and  FIG. 10  may complementarily be applied to this embodiment. Also, the camera illustrated in  FIG. 10  may be designed in accordance with the aforementioned structured light type. 
     The IR source  710  is designed to continuously project a coded pattern image to a target user  730 . The depth image processor  720  estimates the location of the user by using information of an initial pattern image distorted by the target user  730 . 
       FIG. 11  shows another example of a first image sensor. In  FIG. 11 , an LED  810  may correspond to the emitter  680  of  FIG. 9 , and a depth image processor  820  may correspond to the first image sensor  690  of  FIG. 9 . Accordingly, the description of  FIG. 9  and  FIG. 11  may complementarily be applied to this embodiment. Also, the camera illustrated in  FIG. 11  may be designed in accordance with the aforementioned TOF type. 
     The light emitted by the LED  810  is transmitted to a target user  830 . The light reflected by the target user  830  is transmitted to the depth image processor  820 . The modules illustrated in  FIG. 11  calculate the location of the target user  830  by using information on the time difference, unlike  FIG. 10 . This will be described in more detail with reference to  FIG. 12 . 
       FIG. 12  shows a method of calculating a distance using a first image sensor in  FIG. 11 . As illustrated in a left graph of  FIG. 12 , a value t which is the arrival time can be obtained through the time difference between the emitted light and the reflected light. 
     As illustrated in an equation at the right side of  FIG. 12 , the distance between the LED  810  and the target user  830  and the distance between the target user  830  and the depth image processor  820  are calculated by multiplication of the speed of light and the value t. Accordingly, the distance between the LED  810  or the depth image processor  820  and the target user  830  is estimated as 1/d. 
       FIG. 13  shows an image taken by a first image sensor of a plurality of heterogeneous image sensors according to one embodiment. As illustrated in  FIG. 13 , color information such as RGB is not expressed from the image taken by the first image sensor. However, the image taken by the first image sensor is advantageous in that a rough location of an individual object can be identified quickly through differential contrast depending on the distance. 
     For example, as illustrated in  FIG. 13 , the farthest hall way is expressed by the darkest contrast, and it is noted that the hall way is away at the distance of 10 m range from the first image sensor. Moreover, a wall located at an intermediate distance level is expressed by contrast of a middle tone, and it is noted that the wall is away at the distance of 5 m range from the first image sensor. A TV viewer located at the relatively closest distance is expressed by contrast of the brightest tone, and it is noted that the TV viewer is away at the distance of 4 m range from the first image sensor. 
       FIG. 14  shows an image taken by a second image sensor of a plurality of heterogeneous image sensors according to one embodiment. Unlike the first image sensor, since the second image sensor uses bright RGB colors, it is advantageous in that main elements of a face of a user can be identified easily. 
     In particular, as illustrated in  FIG. 14 , the second image sensor is designed in such a manner that data in the periphery of eyes, nose, and mouse used to identify a person are processed to be used as feature information for face recognition. Although eyes, nose, and mouse are illustrated in  FIG. 14 , other elements of the face, such as ears, forehead, hair color, wrinkle, skin color, face shape, and face size, may be used. 
       FIG. 15  shows a procedure of recognizing a user through a multimedia device that uses a plurality of heterogeneous image sensors, and  FIG. 16  shows a procedure of performing a function customized to a recognized user in accordance with the recognized result of  FIG. 15 . 
     If a specific user located before the multimedia device is recognized by using the plurality of heterogeneous image sensors according to one embodiment of the present invention, corresponding ID ‘father’  1201  is displayed in the periphery of the specific user on the screen taken as illustrated in  FIG. 15 . According to another embodiment, instead of the screen taken as illustrated in  FIG. 15 , a guide message that the specific user ‘father’ has been recognized may be displayed while a broadcast screen currently viewed by the specific user is being output. 
     As illustrated in  FIG. 16 , in a state that the current channel  1301  is normally displayed, if the specific user ‘father’ is recognized, the multimedia device may be designed in such a manner that the broadcast screen is converted to a sports channel  1302  preferred by the specific user ‘father’. In this case, it is supposed that the information as to that the preference channel of the specific user ‘father’ is the sports channel is previously stored in the DB of the multimedia device. 
       FIG. 17  shows a procedure of recognizing a plurality of specific users through a multimedia device that uses a plurality of heterogeneous image sensors according to one embodiment of the present invention. And,  FIG. 18  shows a procedure of performing a function customized to a plurality of recognized users. Hereinafter, additional idea for utilizing the aforementioned face recognition result (in particular, the case where multiple users are recognized) will be described with reference to  FIG. 17  and  FIG. 18 . 
     If three specific users located before the multimedia device are recognized by using the plurality of heterogeneous image sensors according to one embodiment of the present invention, corresponding IDs ‘son’  1401 , ‘daughter’  1402  and ‘father’  1403  are displayed in the periphery of the specific users on the screen taken as illustrated in  FIG. 17 . According to another embodiment, instead of the screen taken as illustrated in  FIG. 17 , a guide message that the three specific users haven been recognized may be displayed while a broadcast screen currently viewed by the specific users is being output. 
     Moreover, as illustrated in  FIG. 18 , in a state that the current channel  1501  is normally displayed, if the plurality of specific users are recognized as described above, the multimedia device may be designed in such a manner that the broadcast screen is converted to a movie channel  1502  preferred by all the specific users. In this case, it is supposed that the information as to that the preference channel of the specific users is the movie channel is previously stored in the DB of the multimedia device. 
       FIG. 19  to  FIG. 21  show procedures of registering a new user if a multimedia device that uses a plurality of heterogeneous image sensors. In  FIG. 15  to  FIG. 18  as described above, it is supposed that user(s) who has recognized the plurality of heterogeneous image sensors according to one embodiment of the present invention is previously stored in the memory or DB. However, in case of a user who has never been made on face recognition, a procedure of registering the user is required. 
     First of all, if information of corresponding to data recognized by the plurality of heterogeneous image sensors does not exist in the DB of the multimedia device, a message indicating an unknown user is displayed as illustrated in  FIG. 19 . 
     Moreover, as illustrated in  FIG. 20 , a guide message to register information of a user initially taken is displayed, and the taken user can input its identification information as illustrated in  FIG. 21 . In this case, it is not necessarily required that name should be used as the identification information. The user can optionally use desired information such as occupation, relationships with family, and rank. 
       FIG. 22  shows one embodiment of a method of recognizing a user by using a plurality of heterogeneous image sensors. The method of recognizing a user includes taking a first image located in the periphery of the multimedia device by using the first image sensor (S 1901 ). The method includes extracting depth data from the taken first image (S 1902 ). The method includes detecting a face of at least one user by using the extracted depth data (S 1903 ). The method includes taking a second image on the face of the detected user by using the second image sensor (S 1904 ). 
     The method includes extracting feature information from the taken second image (S 1905 ). The method includes accessing the memory that stores data corresponding to the extracted feature information (S 1906 ). And, the method includes extracting information identifying a specific user stored in the memory (S 1907 ). 
       FIG. 23  shows another embodiment of a method of recognizing a user per device using a plurality of heterogeneous image sensors. In this embodiment, the emitter emits the light to at least one user located in the periphery of the multimedia device (S 2001 ). The first image sensor takes a first image by using the emitted light, extracts depth data from the taken first image, and detects a face of the at least one user by using the extracted depth data (S 2002 ). 
     The second image sensor takes a second image on the face of the detected user, extracts feature information from the taken second image (S 2003 ), and transmits the extracted feature information to the multimedia device. 
     Accordingly, the multimedia device detects a specific user by using the received feature information and performs a control operation to allow a function of the detected specific user to be performed automatically (S 2004 ). 
     According to another embodiment, the first image sensor calculates the values x, y and z which are location information on the face of the user, wherein the x means the location on a horizontal axis of the face in the taken first image, the y means the location on a vertical axis of the face in the taken first image, and the z means the distance between the face of the user and the first image sensor. 
     Moreover, according to another embodiment, the second image sensor takes a zone on the face of the user through zoom-in based on the calculated values x, y and z. 
     According to another embodiment, the plurality of heterogeneous image sensors that include the emitter, the first image sensor, and the second image sensor are designed to further include a compensation module that compensates for the taken second image based on the physical distance between the location of the first image sensor and the location of the second image sensor. 
     The emitter corresponds to IR emitter, for example, the first image sensor corresponds to a depth camera, for example, and the second image sensor corresponds to RGB camera, for example. 
       FIG. 24  shows scenes where a depth image and a color image based on a first pose of a user are taken by a plurality of heterogeneous image sensors. As illustrated in &lt;depth image&gt; of  FIG. 24 , if the image is taken using the first image sensor, body, skeleton, joint information, etc. of the user in addition to the location of the face of the user can be extracted. Accordingly, it is noted from the joint information, etc. taken in the &lt;depth image&gt; of  FIG. 24  that the user currently poses lying. As illustrated in &lt;color image&gt; of  FIG. 15 , the face of the user who is currently lying is closed-up, and feature information is extracted. 
       FIG. 25  shows scenes where a depth image and a color image based on a second pose of a user are taken by a plurality of heterogeneous image sensors. As illustrated in &lt;depth image&gt; of  FIG. 25 , if the image is taken using the first image sensor, body, skeleton, joint information, etc. of the user in addition to the location of the face of the user can be extracted. Accordingly, it is noted from the joint information, etc. taken in the &lt;depth image&gt; of  FIG. 25  that the user currently poses standing. As illustrated in &lt;color image&gt; of  FIG. 25 , the face of the user who is currently standing is closed-up, and feature information is extracted. 
       FIG. 26  shows scenes where a depth image and a color image based on a third pose of a specific user are taken by using a plurality of heterogeneous image sensors. As illustrated in &lt;depth image&gt; of  FIG. 26 , if the image is taken using the first image sensor, body, skeleton, joint information, etc. of the user in addition to the location of the face of the user can be extracted. Accordingly, it is noted from the joint information, etc. taken in the &lt;depth image&gt; of  FIG. 26  that the user currently poses sitting. As illustrated in &lt;color image&gt; of  FIG. 26 , the face of the user who is currently sitting down is closed-up, and feature information is extracted. 
       FIG. 27  shows contents of a database that includes feature information of each user according to pose information generated based on scenes in  FIG. 24  to  FIG. 26 . For example, the pose information could be face rotation information of the taken user. In other words, if the taken face of the user is inclined toward the left side based on the multimedia device, it is expressed by minus (−) information. If the taken face of the user is inclined toward the right side based on the multimedia device, it is expressed by plus (+) information. 
     As illustrated in  FIG. 18 , feature information (a, b, c, d) on a face of a father, which corresponds to the pose information (−15, −30, +15, +30) taken and recognized in  FIG. 15  to  FIG. 17  is stored in the DB. Also, as illustrated in  FIG. 18 , feature information (e, f, g, h) on a face of a mother, which corresponds to the pose information (−15, −30, +15, +30) taken and recognized in  FIG. 24  to  FIG. 26  is stored in the DB. 
     Moreover, as illustrated in  FIG. 27 , feature information (i, j, k, l) on a face of a son  1 , which corresponds to the pose information (−15, −30, +15, +30) taken and recognized in  FIG. 24  to  FIG. 26  is stored in the DB. As illustrated in  FIG. 27 , feature information (m, n, o, p) on a face of a son  2 , which corresponds to the pose information (−15, −30, +15, +30) taken and recognized in  FIG. 24  to  FIG. 26  is stored in the DB. 
     Accordingly, the possibility of error is lowered even though the user or viewers located before the multimedia device change their pose more freely. Also, in order to ensure more improved performance, the multimedia device according to another embodiment can update the users&#39; poses (for example, face rotation angle, etc.) by continuously monitoring them. 
       FIG. 28  shows a scene where first body information of a specific user is taken by using a first image sensor according to one embodiment. As described above, information on the joint of a specific user can be predicted by using the first image sensor. Accordingly, as illustrated in  FIG. 19 , information on an arm&#39;s length of the specific user located before the multimedia device can be detected. 
       FIG. 29  shows a scene where second body information of a user is taken by a first image sensor according to one embodiment. As described above, information on the joint of a specific user can be predicted by using the first image sensor. Accordingly, as illustrated in  FIG. 29 , information on a width of shoulders of the specific user located before the multimedia device can be detected. 
       FIG. 30  shows a scene where third body information of a user is taken by a first image sensor, and  FIG. 31  shows a scene where fourth body information of a specific user is taken by a first image sensor. 
     As described above, information on the joint of a specific user can be predicted by using the first image sensor. Accordingly, as illustrated in  FIG. 31 , information on an face size of the specific user located before the multimedia device can be detected. 
       FIG. 32  shows contents of a database that includes body information of each user, which is generated based on scenes taken in  FIG. 28  to  FIG. 31 . As illustrated in  FIG. 32 , body information of each user, which is taken and recognized in  FIG. 28  to  FIG. 31 , is stored in the DB. 
     In other words, if a specific user cannot be detected or a user currently located before the multimedia device cannot be identified, even using the aforementioned feature information and the aforementioned pose information (for example, face rotation information), the DB illustrated in  FIG. 23  can be used. In particular, family members located before the multimedia device may be similar to one another in view of face shape. In this case, if the DB illustrated in  FIG. 20  is used, it is advantageous in that user recognition performance can be improved. Also, in order to ensure more improved performance, the multimedia device can update the users&#39; pose information by continuously monitoring them. 
     In  FIG. 28  to  FIG. 32 , body information (for example, cm unit) of the taken user can be estimated using a scheme that is performed in proportional to the distance between the image sensor and the user. However, according to another embodiment, the body information can be calculated and expressed in a pixel unit. For example, two or more points that express each of face, knees, ankle, wrist, the palm of the hand, pelvis, etc., which are specific body parts of the user, can be detected using the first image sensor. 
     And, specific body information of the taken user can be estimated by calculating the distance between the detected points. Also, the face size of the user taken using the second image sensor can be estimated by calculating the distance between two eyes of the taken user. Of course, even in case of another embodiment, specific body information calculated by the distance between pixels can be estimated using the scheme that is performed in proportional to the distance between the image sensor and the user. 
       FIG. 33  shows one embodiment of a method of recognizing a user by a plurality of heterogeneous image sensors. Although  FIG. 33  to  FIG. 36  relate to the description of a method, their description can be analyzed by mutual complementary application with the description of the aforementioned product. 
     The multimedia device that uses a plurality of heterogeneous image sensors takes a first image located in front of the multimedia device by using the first image sensor (S 2201 ). Moreover, the multimedia device extracts depth data from the taken first image (S 2202 ), and detects a face of at least one user and pose information (for example, face angle) by using the extracted depth data (S 2203 ). 
     Also, the multimedia device takes a second image on the detected face of the user by using the second image sensor (S 2204 ), and extracts feature information from the taken second image (S 2205 ). 
     And, the multimedia device extracts information identifying a specific user stored in the memory based on the pose information acquired through the first image sensor and the feature information acquired through the second image sensor (S 2206 ). 
     Moreover, the second image sensor is designed to take a specific zone through zoom-in by using the depth data (for example, distance information, location information, etc.) acquired through the first image sensor. Accordingly, it is advantageous in that the second image sensor can accurately take the face only of the user located before the multimedia device. Also, the feature information corresponds to facial information that can identify each of taken users. 
     In particular, since the multimedia device is designed to simultaneously use the feature information on the face and the pose information corresponding to the feature information, it is advantageous in that face recognition performance can be improved and the user is not required to be limited to a specific pose. 
       FIG. 34  shows another embodiment of a method of recognizing a user by a plurality of heterogeneous image sensors. In this embodiment, the multimedia device maps pose information of the specific user and feature information corresponding to the pose information and stores them in the memory (S 2301 ). For example, the memory may be the one that includes the database illustrated in  FIG. 27 . 
     Moreover, the multimedia device compares the pose information and feature information stored in the memory with pose information acquired through the first image sensor and feature information acquired through the second image sensor (S 2302 ). And, the multimedia device is designed to recognize the specific user as a viewer by using the compared result (S 2303 ). 
       FIG. 35  shows another embodiment of a method of recognizing a user by a plurality of heterogeneous image sensors. In this embodiment, the multimedia device maps body information of the specific user and feature information corresponding to the pose information and stores them in the memory (S 2401 ). For example, the memory may be the one that includes the database illustrated in  FIG. 32 . 
     Moreover, the multimedia device compares the body information and feature information stored in the memory with body information acquired through the first image sensor and feature information acquired through the second image sensor (S 2402 ). If the former body information and feature information stored in the memory are identical with the latter body information and feature information, the multimedia device is designed to recognize the specific user as a viewer (S 2403 ). 
     In particular, according to another embodiment, since the multimedia device is designed to simultaneously use the feature information on the face and the body information, it is advantageous in that face recognition performance can be improved and family members having similar faces can be identified more perfectly. 
       FIG. 36  shows another embodiment of a method of recognizing a user per device by using a plurality of heterogeneous image sensors. In this embodiment, the first image sensor takes a first image by using an emitter that emits the light to at least one user located in front of the multimedia device, and extracts depth data from the taken first image. 
     Accordingly, detection and tracking of the at least one user are performed (S 2501 ). Also, the first image sensor the face, body information and pose information of the at least one user by using the extracted depth data (S 2503 ). In particular, coordinate information on the location of the face is transmitted to the second image sensor (for example, color camera). 
     The second image sensor takes a second image by closing up the face zone of the detected user ( 82502 ). Also, the second image sensor extracts feature information from the taken second image (S 2504 ). 
     The body information and pose information acquired through the first image sensor and feature information acquired through the second image sensor are transmitted to the multimedia device through the interface such as USB. 
     The multimedia device accesses the DB related to face recognition (for example,  FIG. 18  or  FIG. 23 ), and searches and authenticates the user corresponding to the received pose information and body information (S 2505 ). Moreover, the multimedia device updates the authenticated information in the DB ( 82506 ). In this case, the update operation ( 82506 ) may be designed to be operated as background together with the step S 2505 . 
     The multimedia device is designed to provide a service customized for the authenticated user ( 82507 ). For example, automatic tuning to a preference channel previously set by the authenticated user may be performed, or preferred applications or contents may be implemented automatically. 
     Another embodiment may apply to a gaming context. For example, the first and second image sensors of the display device may recognize various gestures or motions made by a user, and then the processor may interpret these motions or gestures to correspond to specific commands or input values. These commands and/or values may then be used as a basis for controlling a function in a game application operating on the display device, and corresponding changes may appear, for example, in the game as various gaming screens are displayed. 
     Another embodiment may include automatically executing an application or program upon recognition of a specific user. The application may be virtually any application including but not limited to a scheduling or calendar application, a photo album application, e-mail application corresponding to that user&#39;s e-mail account, an instant messaging application, automatic execution or access to a social networking, video chat, financial, investment, webcam, or other type of website, automatic access to a predetermined web browser, as well as other Internet or application-based functions. 
     The aforementioned webcam may be remotely located from the display device or directed connected thereto. If remotely located, the display device may access and display webcam video based on recognition of a specific user. Data may be stored in a database included in or accessed by the display device linking the recognition of each of a plurality of user&#39;s to respective applications and/or programs. 
     Another embodiment involves controlling the movement, appearance, or other action in the screen of a video game or other game application based on poses recognized by the sensors and processor of the multimedia system. 
     One or more embodiments described herein provide a multimedia device with multiple image sensors of different types and a method for controlling the same, which provide a solution for exactly recognizing users located in the periphery of a multimedia device by using a plurality of heterogeneous image sensors. 
     One or more embodiments described herein provide a design method that can consider a recognition distance and recognition performance at the same time by solving problems occurring in a recognition procedure of a camera interacting with a multimedia device. 
     According to one embodiment, a method for controlling a multimedia device that uses a plurality of heterogeneous image sensors comprises the steps of taking a first image located in the periphery of the multimedia device by using a first image sensor, extracting depth data from the taken first image, detecting a face of at least one user by using the extracted depth data, taking a second image on the face of the detected user by using a second image sensor, extracting feature information from the taken second image, accessing a memory, which stores data corresponding to the extracted feature information, and extracting information identifying a specific user stored in the memory. 
     According to another embodiment, a plurality of heterogeneous image sensors, which recognize at least one user, in accordance with one embodiment of the present invention comprises an emitter emitting light to at least one user located in the periphery of the multimedia device, a first image sensor taking a first image by using the emitted light, extracting depth data from the taken first image, and detecting a face of the at least one user by using the extracted depth data, a second image sensor taking a second image on the face of the detected user and extracting feature information from the taken second image, and an interface transmitting the extracted feature information to the multimedia device. 
     According to another embodiment, a solution is provided for exactly recognizing users located in the periphery of the multimedia device by using a plurality of heterogeneous image sensors. 
     According to another embodiment, a design method is provided that can consider a recognition distance and recognition performance at the same time by solving problems occurring in a recognition procedure of a camera interacting with a multimedia device. 
     One or more embodiments disclosed herein also provide improved face recognition performance, data processing speed, and long distance based on mutual complementary use of a 3D depth camera and a 2D color camera. 
     The various embodiments described herein may be implemented in program instructions that can be executed by various computer and/or processing architectures, which instructions may be recorded on a computer readable recording medium. The computer readable recording medium can include program instructions, data files, and data structures, alone or in combination. The program instructions recorded in the computer readable recording medium may be designed specially for the embodiments described herein. 
     Examples of the computer readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROM and DVD, magneto-optical media such as floppy disks, and a hardware device such as ROM, RAM, and flash memory, which is configured to store and perform program instructions. Examples of the program instructions include a machine language code made by a compiler and a high-level language code implemented using an interpreter by a computer. The hardware device can be configured as at least one software module to perform the operation of the present invention, and vice versa. 
     When used herein, the suffixes “module” and “unit” for the elements used in the following description are given or used in common by considering facilitation in writing this disclosure only but fail to have meanings or roles discriminated from each other. The “module” and “unit” can be designed in hardware or software. 
     A multimedia device described in this specification may correspond to various types of devices that receive and process broadcast data, for example. Moreover, the multimedia device may correspond to a connected TV. The connected TV may be provided with, for example, a wire and wireless communication device in addition to a broadcasting receiving function. 
     Accordingly, the connected TV may be provided with a more convenient interface such as a manual input unit, a touch screen or a motion recognition remote controller. Also, the connected TV enables e-mailing, web browsing, banking or games by accessing Internet or computer in accordance with the support of wire or wireless Internet function. For these various functions, a standardized general-purpose operating system (OS) can be used. 
     Accordingly, since the connected TV can freely be provided with or delete various applications on a general-purpose OS kernel, it may perform user-friendly various functions. More detailed examples of the connected TV include a web TV, an Internet TV, an HBBTV, a smart TV, and a DTV. The connected TV may be applied to a smart phone as the case may be. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.
A multimedia device includes a first image sensor to acquire a first image, a second image sensor to acquire a second image, and a processor to determine coordinate information of the person in the first image and to extract a feature of the person in the second image based on the coordinate information. The first and second image sensors have overlapping fields of view, the coordinate information provides an indication of a distance to the person, and the processor compares the extracted feature to reference information and recognizes the person based on the comparison.