Patent Publication Number: US-2011074923-A1

Title: Image transmission system of network-based robot and method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2009-0091261, filed on Sep. 25, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments relate to a system and method of transmitting an image using a lossless compression method in a robot to provide a service over a network. 
     2. Description of the Related Art 
     In general, a mechanical device which performs motion similar to human motion using an electrical or magnetic mechanism is called a robot. Recently, with development of a sensor and a controller, the robot is utilized in various fields. For example, there are household robots, guide robots for public places, transportation robots for manufacturing plants and operator supporting robots. These example robots may provide various services to a user using mobility and motion. Recently, with development of a network such as the Internet, a robot to provide an image service over the network has been developed. 
     The robot to provide the image service over the network acquires an image using a camera and transmits the acquired camera image to a server in one format. Accordingly, the server provides the image service used for face recognition, object recognition, navigation and remote monitoring in the transmitted image format. However, in order to perform the service such as face recognition, object recognition, navigation or monitoring, various image formats are necessary. For example, image formats (size of 320*240, color and frame rate of 15 frames per second (fps) or more) are used in face recognition and image formats (size of 640*480, color, frame rate of 5 fps or more) are used in object recognition. In other words, various image formats are required to provide optimal services. For instance, transmitting a color image with a size of 640*480 and a frame rate of 15 fps satisfies all the above services and may be used for including face recognition and object recognition. However, an original image may not be transmitted and a lossy compressed image may be transmitted using a compression method. If compression is performed, gain is obtained in terms of network transmission, but deterioration (about −10% to −3%) in recognition performance may be caused due to data loss. As network bandwidth of 802.11n is improved, small sized image may be transmitted in a lossless manner for a robot. However, it is inefficient to transmit an image which satisfies all formats in a lossless transmission manner as described above. 
     SUMMARY 
     Therefore, it is an aspect of the example embodiments to provide an image transmission system of a network-based robot having a stereo camera mounted therein, which separates and synthesizes an image acquired by the stereo camera to efficiently transmit an image satisfying all formats using a lossless method, and a method thereof. 
     The foregoing and/or other aspects are achieved by providing an image transmission system, including: a camera configured to acquire an image, an image separation unit configured to separate the image acquired by the camera into a plurality of image formats, an image transmission/reception unit configured to store the plurality of separated image formats and to transmit the plurality of stored image formats according to an image request, an image synthesis unit configured to synthesize the plurality of image formats transmitted by the image transmission/reception unit into an image suitable for the image request; and a service server configured to provide an image service using the synthesized image. 
     The camera may be a stereo camera which is provided in the network-based robot to acquire a color image with a size of 640(X)*480(Y). 
     The image separation unit may separate the color image with the size of 640(X)*480(Y), which is acquired by the stereo camera, into parts including a monochrome image with a size of 640(X)*480(Y)/color component and a monochrome image with a size of 320(x)*240(y)/color component and transmit the parts to the image transmission/reception unit. 
     The image separation unit may separate the color image with the size of 640(X)*480(Y) into the monochrome image and the color component, obtain a difference between the color image with the size of 640(X)*480(Y) and an image component with the size of 320(x)*240(y), and transmit the difference to the image transmission/reception unit. 
     The image transmission/reception unit may include an image transmission unit configured to transmit the plurality of separated image formats over a network according to the image request, and an image reception unit configured to receive and store the plurality of image formats transmitted over the network. 
     The image transmission unit may further include buffers configured to store the plurality of separated image formats and an image processing unit configured to determine a frame rate to be transmitted by the buffers according to an image reception request of the service server. 
     The image transmission unit may compress the plurality of image formats to be transmitted by the buffers using a lossless compression method. 
     The image reception unit may further include buffers configured to store the plurality of image formats transmitted by the image transmission unit and an image client configured to analyze the image request of the service server and to determine the image formats to be transmitted by the buffers. 
     The image synthesis unit may fetch and synthesize the image formats stored in the buffers into an image suitable for the image request according to the image request of the service server. 
     The service server may include a face recognition server, an object recognition server, a navigation server and a monitoring server. 
     The foregoing and/or other aspects are achieved by providing an image transmission system of a network-based robot, including: a robot configured to separate an image acquired by a camera into a plurality of image formats and to transmit the plurality of image formats, and a server configured to synthesize the plurality of image formats and to provide a service, wherein the robot transmits the plurality of image formats to the server over a network. 
     The robot may include an image separation unit configured to separate the image acquired by the camera into the plurality of image formats, and an image transmission unit configured to store the plurality of separated image formats and to transmit the plurality of stored image formats to the server according to an image request of the server. 
     The server may include an image reception unit configured to receive and store the plurality of image formats transmitted from the image transmission unit over the network, and an image synthesis unit configured to fetch and synthesize the plurality of stored image formats into an image suitable for the image request according to the image request. 
     The foregoing and/or other aspects are achieved by providing a method of transmitting an image between a robot and a server over a network, the method including: at the robot, separating, by a first processor, an image acquired by a camera into a plurality of image formats and transmitting the plurality of image formats to the server; and, at the server, synthesizing, by a second processor, the plurality of image formats and providing a service according to an image request. 
     The robot may separate the color image with a size of 640(X)*480(Y), which is acquired by the camera, into parts including a monochrome image with a size of 640(X)*480(Y)/color component and a monochrome image with a size of 320(x)*240(y)/color component and transmit the parts to the server. 
     The robot may compress the plurality of image formats using a lossless compression method and transmit the compressed plurality of image formats to the server. 
     The server may synthesize the plurality of transmitted image formats into an image suitable for the image request and provide a service. 
     According to an image transmission system of a network-based robot and a method thereof, the network-based robot separates an image acquired by a stereo camera into various image formats and transmits the various image formats to a service server. The service server synthesizes the separated image formats to be suitable for an image request such as face recognition, object recognition, navigation or monitoring to restore and provide an original image as a service. When the network-based robot transmits the separated image formats to the server, the original image is transmitted using the lossless method to improve the performance of the server. Even when a service using a new image is added, separated images are transmitted with respect to the image format requested by this service to more flexibly cope with the service using the new image. Since channels are separated in order to receive lossless data, network gain is obtained. 
     Additional aspects, features, and/or advantages of embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an appearance view showing an example of a network-based robot according to example embodiments; 
         FIG. 2  is a view showing the overall configuration of an image transmission system of a network-based robot according to example embodiments; 
         FIG. 3  is a control block diagram showing an image transmission system of a network-based robot according to example embodiments; 
         FIG. 4  is a control block diagram of an image separation unit to separate a camera image in a network-based robot according to example embodiments; 
         FIG. 5  is a detailed block diagram showing the control configuration of an image transmission system of a network-based robot according to example embodiments; 
         FIG. 6  is a control block diagram of an image synthesis unit to synthesize an image in a network-based robot according to example embodiments; and 
         FIG. 7  is a flowchart illustrating an image transmission method of a network-based robot according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  is an appearance view showing an example of a network-based robot according to example embodiments. 
     In  FIG. 1 , the network-based robot  10  according to the example embodiments is a bipedal robot which walks erect using two legs  11 L and  11 R similar to a human, and includes a trunk  12 , two arms  13 L and  13 R and a head  14 . Feet  15 L and  15 R and hands  16 L and  16 R are included on the front ends of the legs  11 L and  11 R and the arms  13 L and  13 R, respectively. 
     A stereo camera  20  to acquire an image through two left and right cameras  20 L and  20 R is placed on the upper side of the trunk  12 . The location of the stereo camera  20  is not limited to the trunk  12  of the network-based robot  10  and may be placed at any location where an image may be acquired. For example, the stereo camera may be placed on the head  14 . 
     In the reference numerals, L and R denote left and right, respectively. 
       FIG. 2  is a view showing the overall configuration of an image transmission system of a network-based robot according to example embodiments. 
     In  FIG. 2 , the network-based robot  10  separates an image acquired by the stereo camera  20  into various image formats and transmits the various image formats to a server unit  200 . The server unit  200  synthesizes the various image formats into an image format suitable for a service request and provides an image service such as face recognition, object recognition, navigation or monitoring. 
       FIG. 3  is a control block diagram showing an image transmission system of a network-based robot according to example embodiments. 
     In  FIG. 3 , the network-based robot  10  includes a stereo camera  20  to acquire an image, an image separation unit  30  to separate the acquired image into various image formats, and an image transmission unit  40  to transmit the separated various image formats to a service server. 
     The stereo camera  20  acquires a color image with a size of 640(X)*480(Y) through two left and right cameras  20 L and  20 R and inputs the color image to the image separation unit  30 . 
     The image separation unit  30  includes a left image separator  30 L to separate the color image with the size of 640(X)*480(Y), which is received from the left camera  20 L, into various image formats and to store the various image formats and a right image separator  30 R to separate the color image with the size of 640(X)*480(Y), which is received from the right camera  20 R, into various image formats and to store the various image formats. 
     The server unit  200  includes an image reception unit  210  to receive the various image formats transmitted from the network-based robot  10  over a network, an image synthesis unit  230  to synthesize the received various image formats into an image suitable for an image request such as face recognition, object recognition, navigation or monitoring, and a service server  240  to provide an image service using the synthesized image suitable for the image request. 
     The image synthesis unit  230  includes a first image synthesizer  231  to synthesize the image formats into an image format (e.g., 320*240, color, and 10 fps) suitable for face recognition, a second image synthesizer  232  to synthesize the image formats into an image format (e.g., 640*480, color, and 5 fps) suitable for object recognition, a third image synthesizer  233  to synthesize the image formats into an image format (e.g., 320*240, monochrome, and 20 fps) suitable for navigation, and a fourth synthesizer  234  to synthesize the image formats into an image format (e.g., 640*480, color, and 10 fps) suitable for remote monitoring. If a service using a new image is added, an image synthesizer to synthesize the image formats into an image format requested by this service may be further provided. 
     The service server  240  includes a face recognition server  241  to provide an image service for face recognition, an object recognition server  242  to provide an image service for object recognition, a navigation server  243  to provide an image service for navigation, and a monitoring server  244  to provide an image service for remote monitoring. Even in the service server  240 , similar to the image synthesis unit  230 , if a service server  240  using a new image is added, the image formats may be synthesized into an image format requested by this service server  240  to provide a service. 
       FIG. 4  is a control block diagram of an image separation unit to separate a camera image in a network-based robot according to example embodiments. 
     In  FIG. 4 , the image separation unit  30  includes a down-sampling unit  31  to reduce a color image with a size of 640(X)*480(Y) received from the stereo camera  20  (left or right camera) to a color image with a size of 320(x)*240 (y); a first monochrome/color component separation unit  32  to separate the color image with the size of 320(x)*240 (y) into a monochrome component and a color component; an x*y monochrome image storage unit  33  to store the monochrome image with the size of 320(x)*240(y), which is separated by the first monochrome/color component separation unit  32 , in a buffer; an x*y color component storage unit  34  to store the color component with the size of 320(x)*240(y), which is separated by the first monochrome/color component separation unit  32 , in a buffer; a second monochrome/color component separation unit  35  to separate the color image with the size of 640(X)*480(Y), which is received from the stereo camera  20 , into a monochrome component and a color component; an X*Y monochrome image storage unit  36  to store the monochrome image with the size of 640(X)*480(Y), which is separated by the second monochrome/color component separation unit  35 , in a buffer; an X*Y color component storage unit  37  to store the color component with the size of 640(X)*480(Y), which is separated by the second black/color component separation unit  35 , in a buffer; a first calculation unit  38  to obtain a difference between the monochrome image with the size of 320(x)*240(y) stored in the x*y monochrome image storage unit  33  and the monochrome image with the size of 640(X)*480(Y) stored in the X*Y monochrome image storage unit  36 ; and a second calculation unit  39  to obtain a difference between the color component with the size of 320(x)*240(y) stored in the x*y color component storage unit  34  and the color component with the size of 640(X)*480(Y) stored in the X*Y color component storage unit  37 . The first calculation unit  38  and the second calculation unit  39  convert the monochrome image and the color component with the size of 320(x)*240(y) into the size of 640(X)*480(Y) using linear up-sampling and then obtain a difference therebetween. 
     In  FIG. 4 , either the left or right image separator  30 L and  30 R may be the image separation unit  30 . The components of  FIG. 4  are provided in the left or right image separator  30 L or  30 R to separate the image using the same method. 
       FIG. 5  is a detailed block diagram showing the control configuration of an image transmission system of a network-based robot according to example embodiments. 
     In  FIG. 5 , the image transmission unit  40  of the network-based robot  10  includes left and right 320(x)*240(y) monochrome image buffers  41 L and  41 R to receive and store the monochrome images with the size of 320(x)*240(y), which are separated by the left and right image separators  30 L and  30 R of the image separation unit  30 ; left and right 320(x)*240(y) color component buffers  42 L and  42 R to receive and store the color components with the size of 320(x)*240(y), which are separated by the left and right image separators  30 L and  30 R; left and right 640(X)*480(Y) monochrome difference image buffers  43 L and  43 R to receive and store the difference between the monochrome images with the size of 640(X)*480(Y), which are separated by the left and right image separators  30 L and  30 R; left and right 640(X)*480(Y) color difference component buffers  44 L and  44 R to receive and store the difference between the color components with the size of 640(X)*480(Y), which are separated by the left and right image separators  30 L and  30 R; and a 640(X)*480(Y) color image buffer  45  which is a path to transfer the color image with the size of 640(X)*480(Y), which is separated by the left image separator  30 L. 
     The image transmission unit  40  further includes an image processing unit  46  to determine the frame rate (fps) to be transmitted by the left and right 320(x)*240(y) monochrome image buffers  41 L and  41 R, the left and right 320(x)*240(y) color component buffers  42 L and  42 R, the left and right 640(X)*480(Y) monochrome difference image buffers  43 L and  43 R, and the left and right 640(X)*480(Y) color difference component buffers  44 L and  44 R, according to an image reception request of the image synthesis unit  230 . If the image processing unit  46  determines the frame rate (fps) to be transmitted, the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R, and  44 L and  44 R synchronously transmit the images. At this time, each of the transmitted images has a frame number. 
     In addition, the image transmission unit  40  further includes source encoders  51 L and  51 R,  52 L and  52 R,  53 L and  53 R, and  54 L and  54 R to compress the images transmitted from the left and right 320(x)*240(y) monochrome image buffers  41 L and  41 R, the left and right 320(x)*240(y) color component buffers  42 L and  42 R, the left and right 640(X)*480(Y) monochrome difference image buffers  43 L and  43 R, and the left and right 640(X)*480(Y) color difference component buffers  44 L and  44 R through respective channels using a lossless compression method; and a source encoder  55  to compress the 640(X)*480(Y) color image transmitted from the 640(X)*480(Y) color image buffer  45  using a lossy compression method. 
     Although in the example embodiments the 640(X)*480(Y) color image separated by the left image separator  30 L is used in the 640(X)*480(Y) color image buffer  45 , the example embodiments are not limited thereto and the 640(X)*480(Y) color image separated by the right image separator  30 R may be used. 
     In  FIG. 5 , the image reception unit  210  of the server unit  200  includes left and right 320(x)*240(y) monochrome image buffers  211 L and  211 R, left and right 320(x)*240(y) color component buffers  212 L and  212 R, left and right 640(X)*480(Y) monochrome difference image buffers  213 L and  213 R and left and right 640(X)*480(Y) color difference component storage units  214 L and  214 R and a 640(X)*480(Y) color image buffer  215  to receive and store the images through the left and right 320(x)*240(y) monochrome image buffers  41 L and  41 R, the left and right 320(x)*240(y) color component buffers  42 L and  42 R, the left and right 640(X)*480(Y) monochrome difference image buffers  43 L and  43 R, the left and right 640(X)*480(Y) color difference component buffers  44 L and  44 R, and the 640(X)*480(Y) color image buffer  45 . 
     In addition, the image reception unit  210  further includes an image client  216  to analyze the request of the accessed service server  240  ( 241  to  244 ), to determine data to be transmitted by the left and right 320(x)*240(y) monochrome image buffers  41 L and  41 R, the left and right 320(x)*240(y) color component buffers  42 L and  42 R, the left and right 640(X)*480(Y) monochrome difference image buffers  43 L and  43 R, and the left and right 640(X)*480(Y) color difference component buffers  44 L and  44 R of the image transmission unit  40 , and to transmit the frame rate satisfying all requirements. 
     The image reception unit  210  further includes source decoders  221 L and  221 R,  222 L and  222 R,  223 L and  223 R,  224 L and  224 R, and  225  respectively corresponding to the source encoders  51 L and  51 R,  52 L and  52 R,  53 L and  53 R,  54 L and  54 R, and  55 , in order to restore the images compressed by the source encoders  51 L and  51 R,  52 L and  52 R,  53 L and  53 R,  54 L and  54 R, and  55  of the image transmission unit  40 . 
     In  FIG. 5 , the image synthesis unit  230  of the server unit  200  includes a first image synthesizer  231  to request a 320(x)*240(y) color separation image necessary for synthesizing the image formats into the image format (e.g., 320*240, color, and 10 fps) suitable for face recognition (left camera and 10 fps); a second image synthesizer  232  to request a 640(X)*480(Y) color separation image necessary for synthesizing the image formats into the image format (e.g., 640*480, color, and 5 fps) suitable for object recognition (left and right cameras, and 5 fps); a third image synthesizer  233  to request a 320(x)*240(y) color separation image necessary for synthesizing the image formats into the image format (e.g., 320*240, monochrome, and 20 fps) suitable for navigation (left and right cameras, and 20 fps); and a fourth image synthesizer  234  to request a 640(X)*480(Y) color separation image necessary for synthesizing the image formats into the image format (e.g., 640*480, color, and 10 fps) suitable for remote monitoring (left camera, and 10 fps). 
     The first to fourth image synthesizers  231  to  234  are provided in correspondence with the face recognition server  241 , the object recognition server  242 , the navigation server  243  and the monitoring server  244  of the service server  240  to transmit an image request signal to the client processing unit  216  of the image reception unit  210  in order to synthesize the images requested by the service server  240  ( 241  to  244 ). 
       FIG. 6  is a control block diagram of an image synthesis unit to synthesize an image in a network-based robot according to example embodiments. 
     In  FIG. 6 , the image synthesis unit  230  includes a first up-sampling unit  231   a  to enlarge the 320(x)*240(y) monochrome image transmitted from the left or right 320(x)*240(y) monochrome image buffer  211 L or  211 R of the image reception unit  210  to a 640(X)*480(Y) monochrome image; a second up-sampling unit  232   a  to enlarge the 320(x)*240(y) color component transmitted from the left or right 320(x)*240(y) color component buffer  212 L or  212 R of the image reception unit  210  to a 640(X)*480(Y) color component; a first calculation unit  233   a  to add the 640(X)*480(Y) monochrome image enlarged by the first up-sampling unit  231   a  and the 640(X)*480(Y) monochrome difference image transmitted from the left or right 640(X)*480(Y) monochrome difference image buffer  213 L or  213 R of the image reception unit  210 ; a second calculation unit  234   a  to add the 640(X)*480(Y) color component enlarged by the second up-sampling unit  232   a  and the 640(X)*480(Y) color difference component transmitted from the left or right 640(X)*480(Y) color difference component buffer  214 L or  214 R of the image reception unit  210 ; a first monochrome/color synthesis unit  235   a  to synthesize the 320(x)*240(y) monochrome image transmitted from the left or right 320(x)*240(y) monochrome image buffer  211 L or  211 R of the image reception unit  210  and the 320(x)*240(y) color component transmitted from the left or right 320(x)*240(y) color component buffer  212 L or  212 R of the image reception unit  210  and to output a 320(x)*240(y) color image; and a second monochrome/color synthesis unit  236   a  to synthesize the 640(X)*480(Y) monochrome image obtained by the first calculation unit  233   a  and the 640(X)*480(Y) color component obtained by the second calculation unit  232   a  and to output a 640(X)*480(Y) color image. 
     Although, in  FIG. 6 , the image synthesis unit  230  using one of the left and right images is described, the components of  FIG. 6  may be provided with respect to both the left and right images to restore the original image using the same method and transmit the original image as a service. 
     Hereinafter, the operation and effect of the image transmission system of the network-based robot having the above configuration and the method thereof will be described. 
     The network-based robot  10  including one stereo camera  20  transmits the image acquired by the stereo camera  20  to the server unit  200  which will use the image for a robot service as shown in  FIG. 2 . The server unit  200  analyzes the image transmitted from the network-based robot  10  and informs the network-based robot  10  of information regarding the image or provides an image service to a user. The service server  240  ( 241  to  244 ) for the image service requests the image which may be maximally processed by the service server in consideration of a difference in a desired image size/monochrome or color/fps. 
     For example, the network-based robot  10  may provide four different services using the image acquired using the stereo camera  20 . These services are described below. 
     The image format varies according to the types of the services provided by the network-based robot  10  using the image. Accordingly, in order to provide respective services, different image formats are necessary. For example, Table 1 shows image formats suitable for services such as face recognition, object recognition, navigation and monitoring. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Number  
                   
               
               
                   
                   
                   
                 Frame 
                 of  
                 Recommended 
               
               
                 Type 
                 Size 
                 Color 
                 (fps) 
                 cameras 
                 compression 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Navigation 
                 320(x) * 240(y) 
                 Mono- 
                 &gt;20 
                 2EA 
                 Lossless 
               
               
                   
                   
                 chrome 
                   
                   
                   
               
               
                 Face 
                 320(x) * 240(y) 
                 Mono- 
                 &gt;10 
                 1EA 
                 Lossless 
               
               
                 recognition 
                   
                 chrome 
                   
                   
                   
               
               
                 Object 
                 640(X) * 480(Y) 
                 Color 
                 &gt;5 
                 2EA 
                 Lossless 
               
               
                 recognition 
                   
                   
                   
                   
                   
               
               
                 Monitoring 
                 640(X) * 480(Y) 
                 Color 
                 &gt;10 
                 1EA 
                 Lossy 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the service server  240  ( 241  to  244 ) requests various images according to the size of the image, monochrome and color, fps, number of cameras  20  and a compression method. Since data recognition performance is influenced by a lossless compression method and a lossy compression method, for face recognition and object recognition, better performance may be obtained when the image is processed using the lossless compression method. 
     In order to satisfy all the conditions of Table 1, a color image with a size of 640(X)*480(Y) and a frame rate of 30 fps is transmitted and a color image with a size of 320(x)*240(y) and a frame rate of 30 fps is transmitted to satisfy the four services. 
     In the existing method, the amount of dummy data is increased when the image of the stereo camera  20  is transmitted to the network-based robot  10 . For example, if an image suitable for face recognition has a size of 320(x)*240(y) and the frame rate of 10 fps and an image suitable for object recognition has a size of 640(X)*480(Y) and a frame rate of 5 fps, an image with a size of 640(X)*480(Y) and frame rate of 10 fps is transmitted in order to transmit an image suitable for both the face recognition server  241  and the object recognition server  242 . Since the face recognition server  241  receives the image having a size greater than a desired size and reduces the image to an image with a size of 320(x)*240(y), the amount of dummy data is significantly increased. The object recognition server  242  receives an image with a size of 640(X)*480(Y) and the frame rate of 10 fps and uses only 5 frames. 
     For reference, a color image with a size of 640(X)*480(Y) and the frame rate of 30 fps is necessary for satisfying an image having the frame rate of 30 fps and a color image with a size of 640(X)*480(Y) and the frame rate of 10 fps. In this case, if network bandwidth necessary for transmitting a color image with a size of 640(X)*480(Y) and the frame rate of 30 fps is calculated using one channel, data processing of 640*480*3*30=27.648 MB=221.184 Mbps is necessary. If such data processing is performed using the network, transmission is not substantially performed and the amount of unnecessary data is increased. Even when an image with a size of 320(x)*240(y) is transmitted and an image with a size of 640(X)*480(Y) is transmitted through multiple channels, the image needs to be repeatedly transmitted. 
     In contrast, in the example embodiments, the network-based robot  10  including one stereo camera  20  separates the image acquired by the stereo camera  20  and transmits the images satisfying various formats using a lossless method as shown in  FIG. 5 , in order to efficiently satisfy various image formats. 
     Referring to  FIG. 5 , the images input through the left camera  20 L and the right camera  20 R of the stereo camera  20  are separated and transmitted by the image separation unit  30  as follows: 
     Left/right camera  20 L or  20 R: Monochrome image with a size of 320(x)*240(y), 
     Left/right camera  20 L or  20 R: Color-component image (excluding a monochrome component) with a size of 320(x)*240(y), 
     Left/right camera  20 L or  20 R: Monochrome difference image with a size of 640(X)*480(Y) (difference with monochrome image with a size of 320(x)*240(y)), 
     Left/right camera  20 L or  20 R: Color difference component with a size of 640(X)*480(Y) (difference with color component with a size of 320(x)*240(y)). 
     Each channel is compressed using a lossless compression method in order to prevent image loss. The service server  240  ( 241  to  244 ) using the image requests a necessary separation image and the frame rate through the image synthesis unit  230  ( 231  to  234 ). Accordingly, the image synthesis unit  230  ( 231  to  234 ) requests and synthesizes necessary images through communication with the image transmission unit  40  to transmit the separated image and transmits the synthesized image to the service server  240  ( 241  to  244 ) to provide a service. 
     The image output from the stereo camera  20  is separated by the left and right image separators  30 L and  30 R and the separated images are stored in the image buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R and  45  of the image transmission unit  40 . 
     The image processing unit  46  of the image transmission unit  40  receives an image reception request of the image client  216  and transmits the image to the image reception unit  210 . The image client  216  receives the request of the service server  240  ( 241  to  244 ) connected thereto and determines data to be transmitted by the image buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45  of the image transmission unit  40 . 
     For example, in Table 1, the first image synthesizer  231  of the face recognition server  241  requests a size of 320(x)*240(y), color, the left camera  20 L, and 10 fps, the second image synthesizer  232  of the object recognition server  242  requests a size of 640(X)*480(Y), color, the left and right cameras  20 L and  20 R, and 5 fps, the third image synthesizer  233  of the navigation server  243  requests a size of 320(x)*240(y), monochrome, the left and right cameras  20 L and  20 R, and 20 fps, and the fourth image synthesizer  234  of the monitoring server  244  requests a size of 640(X)*480(Y), color, the left camera  20 L, and 10 fps. 
     The image client  216  of the image reception unit  210  analyzes the request and transmits the frame rate satisfying all requirements through the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45  of the image transmission unit  40 . 
     Requested maximum values are as follows according to the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45 : 
     Left camera  20 L, size of 320(x)*240(y), monochrome: 20 fps, 
     Left camera  20 L, size of 320(x)*240(y), color: 10 fps, 
     Left camera  20 L, size of 640(X)*480(Y), monochrome: 5 fps, 
     Left camera  20 L, size of 640(X)*480(Y), color: 5 fps, 
     Right camera  20 R, size of 320(x)*240(y), monochrome: 20 fps, 
     Right camera  20 R, size of 320(x)*240(y), color: 5 fps, 
     Right camera  20 R, size of 640(X)*480(Y), monochrome: 5 fps, 
     Right camera  20 R, size of 640(X)*480(Y), color: 5 fps. 
     When the image processing unit  46  of the image transmission unit  40  determines the frame rate to be transmitted by the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45 , the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45  synchronously transmit the images. Each of the transmitted, images has a frame number. 
     The image reception unit  210  receives and stores the transmitted image in the buffers  211 L and  211 R,  212 L and  212 R,  213 L and  213 R,  214 L and  214 R, and  215 . The image synthesis unit  230  ( 231  to  234 ) of the service server  240  ( 241  to  244 ) fetches the stored images in a desired format, synthesizes the images, and transmits the synthesized image to the service server  240  ( 241  to  244 ). The service server  240  ( 241  to  244 ) performs a service using the received image. The overall flow is shown in  FIG. 7 . 
       FIG. 7  is a flowchart illustrating an image transmission method of a network-based robot according to example embodiments. 
     In  FIG. 7 , the stereo camera  20  acquires a color image with a size of 640(X)*480(Y) through two left and right cameras  20 L and  20 R and transmits the color image to the image separation unit  30  ( 1 ). 
     The image separation unit  30  separates the color image with the size of 640(X)*480(Y), which is transmitted from the stereo camera  20  ( 20 L and  20 R), into a monochrome image with a size of 640(X)*480(Y) and a color component/monochrome image with a size of 320(x)*240(y) and a color component. After the color image with the size of 640(X)*480(Y) is separated into the monochrome image and the color component, a difference between the image with the size of 640(X)*480(Y) and the image component with the size of 320(x)*240(y) is obtained and is transmitted to the image transmission unit  40  ( 2 ). 
     The image transmission unit  40  receives the images having various formats separated by the image separation unit  30  ( 30 L and  30 R), stores the images in the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45 , and waits for transmission ( 3 ). 
     Thereafter, the service server  240  ( 241  to  244 ) requests a necessary separated image and the frame rate through the image synthesis unit  230  ( 231  to  234 ) ( 4 ), and the image client  216  of the image reception unit  210  analyzes the image reception request of the service server  240  ( 241  to  244 ) connected thereto and communicates with the image transmission unit  40  to transmit the separated image ( 5 ). 
     Accordingly, the image processing unit  46  of the image transmission unit  40  receives the image reception request of the image client  216  and the frame rates (fps) of the images stored in the buffers  41 L and  41 R,  42 L and  42 R,  43 L and  43 R,  44 L and  44 R, and  45 . When an image is transmitted, a frame number for synchronization is transmitted therewith. At this time, if a lossless compression is necessary for each separated image (if network bandwidth is insufficient), lossless compression is performed. If the lossless compression is performed, the image with a size of 640(X)*480(Y) has only a difference and thus a lossless compression ratio is excellent. If the service server  240  ( 241  to  244 ) for the image service of the network-based robot  10  is included in the network-based robot  10 , the image transmission unit  40  and the image reception unit  210  may be combined. At this time, a source encoder and a source decoder are not necessary and the request of the image synthesis unit  230  ( 231  to  234 ) may be directly transmitted. The image reception unit  210  receives and stores the transmitted images in the buffers  211 L and  211 R,  212 L and  212 R,  213 L and  213 R,  214 L and  214 R, and  215  ( 6 ). 
     Then, the image synthesis unit  230  ( 231  to  234 ) of the service server  240  ( 241  to  244 ) fetches the images stored in the buffers  211 L and  211 R,  212 L and  212 R,  213 L and  213 R,  214 L and  214 R, and  215  of the image reception unit  210  ( 7 ) and synthesizes the images ( 8 ). 
     For example, color images having a size of 640(X)*480(Y) and a frame rate of 5 fps, acquired by the left and right cameras  20 L and  20 R, are transmitted for object recognition. In the transmitted images, an image having a size of 320(x)*240(y) is input to the first monochrome/color synthesis unit  235   a  of the image synthesis unit  230  to output a color image having a size of 320(x)*240(y), an image enlarged by the first and second up-sampling units  231   a  and  232   a  and the monochrome/color image component having a size of 640(X)*480(Y) are synthesized, and an image having a size of 640(X)*480(Y) is output from the second monochrome/color synthesis unit  236   a  (see  FIG. 6 ). The same process is performed with respect to the left and right cameras of the stereo camera  20  to restore, transmit an original image, and provide a service. 
     Thereafter, the image synthesis unit  230  ( 231  to  234 ) transmits the synthesized image to the service server  240  ( 241  to  244 ) ( 9 ). The service server  240  ( 241  to  244 ) provides the service using the received image ( 10 ). 
     In example embodiments, if an image is transmitted, a lossless compression method is used in order to prevent image data from being lost. The lossless compression method is used with respect to a difference image between channels. Since the performance of the lossless compression method varies according to data, in the example embodiments, the description of gain due to lossless compression is omitted. Since image data of a difference may be compressed to a size significantly smaller than that of actual image data, gain may be obtained in terms of transmission of a large amount of data. 
     Although embodiments have been shown and described, it should be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.