Patent Publication Number: US-2011069155-A1

Title: Apparatus and method for detecting motion

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2009-0088633, filed on Sep. 18, 2009, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments relate to detecting and recognizing motion of a person. 
     2. Description of the Related Art 
     A service providing system provides services desired by a user by recognizing presence and location of the user and a direction or type of motion of the user, which contributes to more convenient use of the system. 
     Examples of such a system include a secure entrance control system that recognizes a face of a visitor to the secure entrance, a notebook computer with a camera that senses a face of a user for log-in, and a camera that detects a face to capture a smile. 
     Recently, the motion of a user has also been detected using image information acquired from a camera mounted in a system. 
     In this case, motion of the user is recognized by calculating an optical flow obtained by detecting feature points from an image and tracking locations of the feature points. 
     This technology may be applied when a background image for the user is relatively simple or stationary, but not when the background image includes the same iterative patterns or a moving image (e.g., a television screen). 
     SUMMARY 
     According to one or more embodiments, there is provided an apparatus for detecting a motion, including an object image acquiring unit acquiring object images using distance information for an object included in images obtained from at least two cameras, the object image including only the object without a background, a motion-detection-area setting unit setting a motion detection area in the acquired object image, and a motion detecting unit detecting a motion of the object based on an amount of an image change in the motion detection area between the acquired object images. 
     The object image acquiring unit may include a first image acquiring unit, a second image acquiring unit, a facial area detecting unit detecting a facial area from the image obtained from the first image acquiring unit or the second image acquiring unit, a distance image acquiring unit acquiring a distance image from the images obtained from the first image acquiring unit and the second image acquiring unit, and an image filtering unit producing the object image using the detected facial area and the acquired distance image. 
     The object image acquiring unit may include a first image acquiring unit, a second image acquiring unit, a facial area detecting unit detecting a facial area from the image obtained from the first image acquiring unit or the second image acquiring unit, a distance image acquiring unit acquiring a distance image from the images obtained from the first image acquiring unit and the second image acquiring unit, a mask creating unit creating an image mask using the detected facial area and the acquired distance image, and an image filtering unit producing the object image from the image obtained from the first image acquiring unit or the second image using the created image mask. 
     The motion detection area may be set around a face of the object. The image change amount may be defined as an optical flow between the images, or a location of a feature point or a distance change amount. 
     According to one or more embodiments, there is provided a method of detecting a motion, including acquiring object images using distance information for an object included in images obtained from at least two cameras, the object image including only the object without a background, setting a motion detection area in the acquired object image, and detecting a motion of the object based on an amount of an image change in the motion detection area between the acquired object images. 
     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 embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a distance image, according to one or more embodiments; 
         FIG. 2  illustrates an acquiring of a distance image, according to one or more embodiments; 
         FIG. 3  is a block diagram of a motion detection apparatus, according to one or more embodiments; 
         FIG. 4  is a block diagram of an object image acquiring unit, according to one or more embodiments; 
         FIG. 5  is a block diagram of an object image acquiring unit, according to one or more embodiments; 
         FIG. 6  illustrates an operation of a motion detection method, according to one or more embodiments; 
         FIG. 7  illustrates an operation of a motion detection method, according to one or more embodiments; and 
         FIG. 8  is a flowchart illustrating a motion detection method, according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to embodiments set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects of the present invention. 
       FIG. 1  illustrates a distance image, according to one or more embodiments. 
     In  FIG. 1 , the distance image  101  may be defined as an image in which respective points are represented by distance information. In the distance image  101 , the distance information may be represented by colors or different shades of gray. For example, the respective points of the distance image  101  may be represented by colors or different shades of gray having different brightness depending on distances. 
       FIG. 2  illustrates an acquiring of a distance image, according to one or more embodiments. 
     In  FIG. 2 , the distance image may be obtained from first and second images  102  and  103 , respectively acquired by left and right cameras of a stereo camera, for example. The stereo camera may have the left and right camera combined as in eyes of a person. For example, the left camera may be located at point C and the right camera may be located at point C′. In this case, a distance from the first image  102  or the second image  103  to a specific point M may be obtained by the below Equation 1, for example. 
         z= ( B/d ) *F    Equation 1
 
     In Equation 1, with regards to  FIG. 2 , z denotes the distance from the image to point M, B denotes a distance between point C and point C′, d denotes a difference between location coordinates of point M in the respective images (i.e., a difference between X 1  and X 2 ), and F denotes a focal length of a camera lens. B may be a constant or a measured value, d may be obtained using a sum of squared difference (SSD) scheme, and F may depend on the camera lens, as only examples. Based on the values, the distances z from each image to the specific point can be obtained. 
     Thus, the two images  102  and  103  may be acquired by the stereo camera, the distances of the respective points of the images are calculated, and the points are represented by different colors or shades of gray according to the distances, and thus a distance image such as shown in  FIG. 1  can be acquired. 
       FIG. 3  illustrates a motion detection apparatus, according to one or more embodiments. 
     In  FIG. 3 , a motion detection apparatus  100  may include an object image acquiring unit  301 , a motion-detection-area setting unit  302 , and a motion detecting unit  303 , for example. 
     The object image acquiring unit  301  may acquire an object image that is an image including only the object without a background, using distance information for an object included in images obtained from at least two cameras. 
     In an embodiment, the object image may include only an object by removing a background from any image including the background and the object. The object image may be acquired through facial area information and a distance image obtained based on the respective images obtained from the stereo camera, for example. In an embodiment, the object image may be obtained continuously at certain time intervals by the object image acquiring unit  301 . That is, in such an embodiment, a first object image may be acquired at time t 0  and a second object image may be obtained at time t 1 . 
     The motion-detection-area setting unit  302  sets a motion detection area in the acquired object image. The motion detection area may be a reference area for recognizing an amount of an image change between the first object image and the second object image. The motion detection area may be formed around a face in each object image, for example. 
     The motion detecting unit  303  recognizes an amount of an image change between the acquired object images to detect a motion of an object. For example, the motion detecting unit  303  may detect the motion of the object based on the image change amount in the motion detection area set in each of the first and second object images. In this case, the image change amount may be defined as an optical flow between images, a location of a specific feature point, or a distance change amount, for example. 
     The detected motion may include a type of the motion, such as a moving direction of a person&#39;s hand. The motion detection apparatus  300  may further include a motion controller generating a predetermined control command according to the motion detected by the motion detecting unit  303 . 
     Thus, since the motion detection apparatus  300 , according to an embodiment, acquires the first and second object images including only the object without a background at certain time intervals, sets the motion detection area around the face of each object image, and detects the motion of the object through the image change amount in the motion detection area, the motion detection apparatus  300  can detect the motion of the object with a limited amount of computation irrespective of a change of the background. 
       FIG. 4  is a block diagram of an object image acquiring unit, according to one or more embodiments. 
     Referring to  FIG. 4 , an object image acquiring unit  400  may include a first image acquiring unit  401 , a second image acquiring unit  402 , a facial area detecting unit  403 , a distance image acquiring unit  404 , and an image filtering unit  405 , for example. 
     The first image acquiring unit  401  and the second image acquiring unit  402  may be a stereo camera that simultaneously photographs the same area. For example, the first image acquiring unit  401  may be a left camera of a stereo camera and the second image acquiring unit may be a right camera of the stereo camera, both being spaced a predetermined distance apart. For convenience of illustration, an image obtained by the first image acquiring unit  401  is referred to as an L image and an image obtained by the second image acquiring unit  402  is referred to as an R image. 
     The facial area detecting unit  403  detects a facial area from the L image. A variety of face detection algorithms, such as a boosted cascade scheme for a feature point, may be employed. For example, the facial area detecting unit  403  can detect the facial area by scanning a predetermined search window in the L image. 
     The distance image acquiring unit  404  may acquire a distance image using the L and R images. Here, the definition and acquisition of the distance image may be similar to the above descriptions of  FIGS. 1 and 2 . 
     The image filtering unit  405  may produce the above-described object image using the facial area detected by the facial area detecting unit  403  and the distance image acquired by the distance image acquiring unit  404 . For example, the image filtering unit  405  may identify an area in the distance image corresponding to the detected facial area, calculate a distance to the object using the distance information of the distance image corresponding to the facial area, and then remove a portion corresponding to the background other than the object. If the calculated distance to the object is d, a distance image consisting of distances greater than d−th and smaller than d+th may be used as the object image. Here, the thresholds d−th and d+th denote previously determined threshold values. 
       FIG. 5  is a block diagram of an object image acquiring unit, according to one or more embodiments. 
     In  FIG. 5 , an object image acquiring unit  500  may include a first image acquiring unit  401 , a second image acquiring unit  402 , a facial area detecting unit  403 , a distance image acquiring unit  404 , a mask creating unit  501 , and an image filtering unit  502 , for example. 
     The first image acquiring unit  401 , the second image acquiring unit  402 , the facial area detecting unit  403 , and the distance image acquiring unit  404  may be similar to those illustrated in  FIG. 4 , and accordingly further discussion will not be set forth. 
     The mask creating unit  501  creates a filtering mask using a facial area detected by the facial area detecting unit  403  and a distance image acquired by the distance image acquiring unit  404 . For example, the mask creating unit  501  may identify an area in the distance image corresponding to the detected facial area, calculate the distance to the object using the distance information of the distance image corresponding to the facial area, and then remove a portion corresponding to the background other than the object. If the calculated distance to the object is d, a portion corresponding to a distance greater than d−th and smaller than d+th may be set to 1 and other portions are set to 0 to create the filtering mask. Here, again, the thresholds d−th and d+th denote previously determined threshold values. 
     The image filtering unit  502  may mask the R image with the created filtering mask to produce the above-described object image. 
       FIG. 6  illustrates an operation of a motion detection method, according to one or more embodiments. 
     Referring to  FIG. 6 , the first image acquiring unit  401  and the second image acquiring unit  402  acquire an L image  601  and an R image  602 , respectively. In this case, the L image  601  and R image  602  may include both an object and a background. 
     The facial area detecting unit  403  may detect a facial area  603  from the L image  601 . 
     The distance image acquiring unit  404  may acquire a distance image  604  using the L image  601  and the R image  602 . 
     The image filtering unit  405  may further acquire an object image  605  using distance information of the distance image  604  corresponding to the facial area  603 . 
     When the object image  605  has been acquired, the motion-detection-area setting unit  302  may set a motion detection area  606  in the object image  605 . In this case, the motion detection area may be set around a face of the object in the object image  605 . 
     The acquisition of the object image  605  and the setting of the motion detection area  606  may be continuously performed at certain time intervals. That is, through the above-described process, in an embodiment, a first object image with the motion detection area may be acquired at time t 0 , and then a second object image with the motion detection area acquired at time t 1 . 
     Thus, here, the motion detecting unit  303  can detect the motion of the object through an amount of an image change in the motion detection area between the first object image and the second object image. 
       FIG. 7  illustrates an operation of a motion detection method, according to one or more embodiments. 
     Referring to  FIG. 7 , the first image acquiring unit  401  and the second image acquiring unit  402  may acquire an L image  701  and an R image  702 , respectively. In this case, the L image  701  and R image  702  may include both an object and a background. 
     The facial area detecting unit  403  may detect a facial area  703  from the L image  701 . 
     The distance image acquiring unit  404  may acquire a distance image  704  using the L image  701  and the R image  702 . 
     The mask creating unit  501  may create an image mask  705  using distance information of the distance image  704  corresponding to the facial area  703 . For example, the image mask  705  may be a filtering mask in which an area corresponding to the object is set to 1 and other areas are set to 0. 
     The image filtering unit  502  may further mask the R image  702  with the image mask  705  to produce an object image  706 . 
     When the object image  706  has been acquired, the motion-detection-area setting unit  302  may set a motion detection area  707  in the object image  706 . In this case, the motion detection area may be set around a face of the object in the object image  706 , for example. 
     The acquisition of the object image  706  and the setting of the motion detection area  707  may be continuously performed at certain time intervals. That is, through the process as described above, in an embodiment, a first object image with the motion detection may be acquired at time t 0 , and then a second object image with the motion detection area acquired at time t 1 . 
     Thus, the motion detecting unit  303  can detect the motion of the object through an amount of an image change in the motion detection area between the first object image and the second object image. 
       FIG. 8  is a flowchart illustrating a motion detecting method, according to one or more embodiments. 
     Referring to  FIG. 8 , first, an object image may be acquired ( 801 ). The object image may include only an object by removing a background from any image including the background and the object, and may be obtained through the configuration as shown in  FIG. 4  or  5 , for example. 
     A motion detection area may be set in the object image ( 802 ). The motion detection area may be a reference area for recognizing an amount of an image change between the object images. For example, the motion detection area may be set around a face of the object image by the motion-detection-area setting unit  302 . 
     The amount of the image change in the motion detection area between the object images may be detected to detect a motion of the object ( 803 ). For example, the motion detecting unit  303  can detect the motion of the object through an optical flow between the object images in the motion detection area, a location of a feature point, or a distance change amount, for example. 
     The detected motion may include a type of the motion. Accordingly, the method may further include generating a predetermined control command according to the type of the detected motion. Various functions of a system using the method of detecting a motion according to one or more embodiments may be controlled according to the control command generated according to the type of the detected motion, for example. 
     In addition to the above described embodiments, embodiments can also be implemented through computer readable code/instructions in/on a non-transitory medium, e.g., a computer readable medium, to control at least one processing device, such as a processor or computer, to implement any above described embodiment. The medium can correspond to any defined, measurable, and tangible structure permitting the storing and/or transmission of the computer readable code. 
     The media may also include, e.g., in combination with the computer readable code, data files, data structures, and the like. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. Examples of computer readable code include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter, for example. The media may also be a distributed network, so that the computer readable code is stored and executed in a distributed fashion. Still further, as only an example, the processing element could include a processor or a computer processor, and processing elements may be distributed and/or included in a single device. 
     Also, one or more of the above-described embodiments may be applied to air conditioners that recognize a motion of an object to control a blowing direction, e.g., to control a blowing direction of cooled air toward an identified object or person. 
     While aspects of the present invention has been particularly shown and described with reference to differing embodiments thereof, it should be understood that these embodiments should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in the remaining embodiments. 
     Thus, although a few embodiments have been shown and described, with additional embodiments being equally available, it would 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 invention, the scope of which is defined in the claims and their equivalents.