Patent Publication Number: US-2007115351-A1

Title: Methods and systems for enhanced motion detection

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to video surveillance systems and, more particularly, to video surveillance systems with enhanced motion detection.  
      At least some known video surveillance systems include one or more video cameras mounted in a housing along with a pan, tilt, and zoom (PTZ) assembly. The PTZ permits controlling a movement of the camera to align a viewing area of the camera with an object of interest or location of interest. The zoom portion of the mechanism may be used to adjust a field of view of the camera. The housing protects the camera from the environment in the location where the camera and PTZ assembly are mounted.  
      The speed at which an area larger than the field of view of the camera can be viewed is limited by the visual perception of the operator. If the camera motion is too fast the operator cannot distinguish items and quickly losses attention. Some known motion detection is performed by fixed cameras. The cameras store one still image as the reference and continuously compare new images with this reference. In PTZ cameras the camera can move to cover a surveillance area larger than the camera field of view and the reference image needs to be correlated to the current view of the camera.  
     BRIEF DESCRIPTION OF THE INVENTION  
      In one embodiment, a video surveillance system includes a pan/tilt/zoom video camera assembly and a processor configured to control the pan/tilt/zoom video camera assembly to generate a panoramic reference image of a selectable motion detection area, acquire images of the motion detection area, and determine a motion in the motion detection area using a comparison of the acquired images of the motion detection area and the panoramic reference image.  
      In another embodiment, a pan/tilt/zoom video camera assembly includes a video camera, a pan/tilt assembly configured to rotate said video camera about a substantially vertical pan axis and a substantially horizontal tilt axis, and a processor configured to control said pan/tilt assembly and said video camera assembly to generate a panoramic reference image of a selectable motion detection area, acquire images of the motion detection area, and determine a motion in the motion detection area using a comparison of the acquired images of the motion detection area and the panoramic reference image.  
      In yet another embodiment, a method of operating a pan/tilt/zoom video camera assembly includes generating a panoramic reference image of a selectable motion detection area, acquiring images of the motion detection area, and determining a motion in the motion detection area using a comparison of the acquired images of the motion detection area and the panoramic reference image. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of an exemplary video surveillance system in accordance with an embodiment of the present invention;  
       FIG. 2  is a schematic diagram of an exemplary embodiment of pan/tilt/zoom video camera assembly shown in  FIG. 1 ; and  
       FIG. 3  is a flowchart of an exemplary method of operating the pan/tilt/zoom video camera assembly for enhanced motion detection. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.  
       FIG. 1  is a schematic view of an exemplary video surveillance system  100  in accordance with an embodiment of the present invention. Video surveillance system  100  includes a control panel  102 , a display monitor  104 , and a pan/tilt/zoom video camera assembly  105 . Typically, a camera  106  is housed in an enclosure  108  having a dome  110  for protecting camera  106  from the environment where camera  106  is located. In one embodiment, dome  110  is tinted to allow camera  106  to acquire images of the environment outside of enclosure  108  and simultaneously prevent individuals in the environment being observed by camera  106  from determining the orientation of camera  106 . In various alternative embodiments, dome  110  is not tinted. In the exemplary embodiment, camera  106  includes capabilities to pan about a vertical axis  112 , tilt about a horizontal axis  114 , and control a lens assembly  116  to cause camera  106  to zoom. For example, pan/tilt/zoom video camera assembly  105  includes a pan motor and encoder (not shown) and tilt motor and encoder (not shown). The encoders determine an angular position of the pan and tilt motor and generate position signals that are used with a zoom setting to determine an area in the field of view. Panning movement of camera  106  is represented by an arrow  118 , tilting movement of camera  106  is represented by arrow  120  and the changing of the focal length of lens assembly  116  of camera  106 , i.e., zooming, is represented by arrow  122 . As shown with reference to a coordinate system  124 , panning motion may track movement along the x-axis, titling motion may track movement along the y-axis and focal length adjustment may be used to track movement along the z-axis. Signals representing commands to control such capabilities are transmitted from control panel  102  through a control data line  126 . Image data signals are transmitted from camera  106  to display monitor  104  and a storage device  128  through a video data line  130 .  
      Lens assembly  116  views an area of a location  132 , which may be remote from control panel  102  and is in a field of view  134  and along a viewing axis  136  of lens assembly  116 . Images of location  132  are converted by camera  106  into an electrical video signal, which is transmitted to display monitor  104 .  
      In the exemplary embodiment, control panel  102  includes an X-Y control joystick  140  that is used to generate pan and tilt commands. A plurality of rocker-type switches  142  are used to control a zoom  144 , a focus  146 , and an iris  148  of lens assembly  116 . In an alternative embodiment, joystick  140  includes a twist actuation that is used to control the zoom of camera  106 . Joystick  140  may also incorporate triggers and/or buttons to facilitate operating various controls associated with system  100 . Control panel  102  also includes a numeric keypad  150  for entering numbers and values. In an alternative embodiment, control panel  102  may include an alpha or alphanumeric keypad (not shown) for entering text as well as numbers. Control panel  102  further includes a plurality of preset switches  152  that may be programmed to execute macros that automatically control the actions of camera  106  and/or lens assembly  116 . A plurality of buttons  154  may be used, for example, for predetermined control functions and/or user-defined functions, for example, a camera selection in a multi-camera video surveillance system. A display  156  may be used to display a status of video surveillance system  100  or may be used to display parameters associated with a selected camera.  
      A processor  158  receives programmed instructions, from software, firmware, and data from memory  160  and performs various operations using the data and instructions. Processor  158  may include an arithmetic logic unit (ALU) that performs arithmetic and logical operations and a control unit that extracts instructions from memory  160  and decodes and executes them, calling on the ALU when necessary. Memory  160  generally includes a random-access memory (RAM) and a read-only memory (ROM), however, there may be other types of memory such as programmable read-only memory (PROM), erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM). In addition, memory  160  may include an operating system, which executes on processor  158 . The operating system performs basic tasks that include recognizing input, sending output to output devices, keeping track of files and directories and controlling various peripheral devices.  
      The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein. Memory  160  may include storage locations for the preset macro instructions that may be accessible using one of the plurality of preset switches  142 .  
      As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by processor  158 , including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.  
      In various embodiments, processor  158  and memory  160  are located external to camera  106  such as in control panel  102  or in a PC or other standalone or mainframe computer system capable of performing the functions described herein.  
      In the exemplary embodiment, video surveillance system  100  is a single camera application, however, various embodiments of the present invention may be used within a larger surveillance system having additional cameras which may be either stationary or moveable cameras or some combination thereof to provide coverage of a larger or more complex surveillance area. In an alternative embodiment, one or more video recorders (not shown) are connected to control panel  102  to provide for recording of video images captured by camera  106  and other cameras in system  100 .  
       FIG. 2  is a schematic diagram of an exemplary embodiment of pan/tilt/zoom video camera assembly  105  (shown in  FIG. 1 ). Pan/tilt/zoom video camera assembly  105  includes a camera  106 , a pan mechanism  202  that is configured to rotate the video camera about a pan axis  204  in a clockwise and a counter clockwise pan direction  206 . In the exemplary embodiment, pan mechanism  202  is configured to pan continuously about pan axis  204 . In an alternative embodiment, pan mechanism  202  is configured to pan less than a full rotation about pan axis  204 . Pan/tilt/zoom video camera assembly  105  also includes a tilt mechanism  208  coupled to the pan mechanism and configured to rotate video camera  106  about a tilt axis  210  (illustrated normal to the figure). In the exemplary embodiment, tilt mechanism  208  is configured to rotate camera  106  about tilt axis  210  greater than ninety degrees through an angle  212  and an angle  214  with respect to pan axis  204 . In such embodiment, the total tilt of camera  106  is greater than one hundred eighty degrees. A controller, such as control panel  102 , is communicatively coupled to pan mechanism  202  and tilt mechanism  208 . Controller  102  is configured to receive a first image of a view acquired from a first address wherein the address indicates a pan rotation angle with respect to an index, such as an initial starting or “parked” position. The address also indicates a tilt angle with respect to pan axis  204 , and a zoom setting of lens assembly  116 . In the exemplary embodiment, when camera  106  is rotated about tilt axis  210  through zero degrees with respect to pan axis  204 , for example camera  106  is oriented pointing vertically downward, the video image is electronically flipped, such that the image, as perceived by the user, is oriented right side up.  
      In the exemplary embodiment, a view  230  is the area within the field of view of camera  106  at a particular address, for example, at a pan angle, tilt angle, and zoom setting. An image is acquired of view  230  by camera  106 . The image may be stored, displayed, processed for enhancement, and/or combined with other images. In the exemplary embodiment, images of adjacent views are registered with respect to objects within each image and combined to form a larger panoramic image of multiple views. The images may be registered edge to edge  232  or may include an area of overlap  234  to facilitate registering the images. In the exemplary embodiment, a panoramic motion detection area  236  includes a plurality of views  230  contiguously oriented about a field of view of camera  106 . In an alternative embodiment, views  230  are not contiguously oriented.  
       FIG. 3  is a flowchart of an exemplary method  300  of operating a pan/tilt/zoom video camera assembly for enhanced motion detection. A motion detection algorithm is described wherein the area of motion detection to be covered is larger than any single camera field of view. The algorithm records a plurality of images of the motion detection area that are addressed as a single panoramic image. The camera is then moved in any direction. While in a motion detection mode, the video from camera is correlated with the pre-stored panoramic reference image. The images of the views acquired during a scan are compared to a corresponding location in the panoramic reference image. If the comparison determines the acquired images do not match the reference image, then motion is indicated and a motion detected event is triggered.  
      Method  300  includes generating  302  a panoramic reference image of a selectable motion detection area. In the exemplary embodiment, a user designates an area within the range of view of the pan/tilt/zoom video camera as a motion detection area by “painting the screen” while moving the pan/tilt/zoom video camera. Any area covered by the paint will be within the selected motion detection area. The painting is done similar to the privacy masks on some known cameras. In this instance, the paint is a transparent color however, thus allowing the user to see through the paint. The area painted is not limited to rectangular shapes.  
      During operation, the user initiates the motion detection mode. The camera will use the motion detection area defined in step  302  as the area to quickly obtain a record of as a single image. Multiple are images acquired  304  during a scan of the motion detection area and are registered into a panoramic reference image. The reference image is associated with the camera position and zoom where each image was acquired.  
      After entering the motion detection mode, the pan/tilt/zoom video camera automatically generates a scan that best fits the motion detection area selected above. The user does not need to specify the scan path precisely. The path is based on a constraint mapping of the camera motion to the area with the time duration of the scan as a minimizing factor. The camera is commanded to move substantially faster than in normal user observation operation permitting the motion detection area to be scanned faster than during normal user observation. In the exemplary embodiment, the scan time exceeds three times faster than during normal user observation. Additionally, the motion of the camera is randomized to facilitate reducing the possibility of targets defeating the surveillance by observing pan/tilt/zoom video camera motion. Areas outside the detect area are ignored. During motion detection mode, the rate of panning and tilting of the pan/tilt/zoom video camera precludes meaningful observation by the user, so a current still image of the scan is output to the display with a selectable periodicity and duration, for example, every one second to facilitate monitoring the motion detection area as well as giving reasonable indication that the system is operating satisfactorily.  
      During the time in this mode, received images from the pan/tilt/zoom video camera are compared to the reference image. In the exemplary embodiment, differences above a threshold stop the motion detect mode and the user is alerted that motion has been detected  306 . A programmed target tracking algorithm may also be initiated such that the cause of the motion detected is followed throughout the viewing area of the pan/tilt/zoom video camera and information about the target transmitted to other pan/tilt/zoom video cameras in the surveillance system such that there can be a handoff of tracking to a next pan/tilt/zoom video camera if the target moves into the next camera viewing area.  
      The above described surveillance method controls the video camera to move at a speed substantially faster than typical visual scanning speeds. The faster scanning speed permits a larger viewing area to be monitored in a shorter time thus facilitating reducing the probability of missing events. In the exemplary embodiment, the surveillance system alerts the operator only if the area under surveillance changes.  
      The above-described embodiments of a video surveillance system provide a cost-effective and reliable means for automating many of the surveillance operations of a security camera comparing current images during a motion detect scan to a panoramic reference image permits the surveillance system to cover a larger area in a shorter time span.  
      Exemplary embodiments of video surveillance systems and apparatus are described above in detail. The video surveillance system components illustrated are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. For example, the video surveillance system components described above may also be used in combination with different video surveillance system components. A technical effect of the various embodiments of the systems and methods described herein include facilitating operation and maintenance of video surveillance system by permitting relatively fast scanning of a viewing area larger than the field of view of the camera.  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.