Abstract:
A method and apparatus for detecting motion in a large area with a single imaging device, such as a camera. A fixed object is located in the area and a camera is panned across the area with the fixed object remaining in the field of view of the camera. Successive images are adjusted based on the position of the fixed object within the image and the adjusted images are compared to detect movement with an area of overlap between the images.

Description:
BACKGROUND  
       [0001]     The invention relates generally to motion detection and more specifically to a surveillance system and method, for use in security systems or the like, in which a moving camera can be used to detect motion in an area.  
         [0002]     Conventional security systems typically protect an enclosed area using switches at doors, windows, and other potential entry points. When a switch is activated, an alarm is sounded, a message is generated, or some other means of notifying the appropriate persons and/or discouraging the persons breaching security is activated. It is also known to use passive infra red (PIR) sensors, which sense heat differences caused by animate objects such as humans or animals, to detect the presence of persons in unauthorized areas. Other sensors used in surveillance and security systems include vibration sensors, radio frequency sensors, laser sensors and microwave sensors. Sensors often can be activated erroneously by power surges or large electromagnetic fields, such as occur when lightening is present. Such activation of course can trigger a false alarm.  
         [0003]     To increase the reliability of security and surveillance systems, video cameras have been used to monitor premises. However, with camera surveillance, a constant communications channel must be maintained with the operator at the monitoring site. It is known to combine video camera surveillance with another sensing mechanism, a PIR sensor, for example, so actuation of the video camera is initiated by activation of the other sensor and the operator&#39;s attention is focused by sounding an alarm or delivering a message. However, when monitoring continuous video, even for relatively short periods of time, the operator must maintain a constant vigilance. However, an operator&#39;s ability to pay attention to a video display generally diminishes rapidly to the point where the operator is essentially ineffective after several minutes. Accordingly, video surveillance is labor intensive, expensive, and not always effective.  
         [0004]     More recently, video cameras have been used to monitor an area within a field of view and the resulting image signal is processed to detect any motion in the field of view. U.S. Pat. No. 4,408,224 is exemplary of such systems in which a video camera monitors an area, such as a parking lot, and produces a video signal. The video signal is digitized and stored in a memory and is compared with a previous video signal that has been digitized and stored in a memory. If any differences between the two signals exceeds a threshold, an output is generated and fed to an alarm generation circuit. Various algorithms can be used to compare video signals with one another to determine if motion has occurred in the monitored area. For example, U.S. Pat. No. 6,069,655 discloses comparing video signals on a pixel by pixel basis, generating a difference signal between the two signals, and interpreting any non-zero pixel in the difference signal to be a possible movement. U.S. Pat. No. 4,257,063 discloses a video monitoring system in which a video line from a camera is compared to the same video line viewed at an earlier time to detect motion. U.S. Pat. No. 4,161,750 teaches that changes in the average value of a video line can be used to detect motion.  
         [0005]     While the use of video cameras for detecting motion has solved many problems associated with surveillance, some limitations still exist. Specifically, a video camera can only monitor an area within its field of view. The field of view can be increased by locating the camera at a position far away from the area or by using wide angle optics. In either case, each pixel of the imager in the camera will correspond to a larger portion of the area as the field of view is increased. Therefore as the field of view is increased, resolution of the image signal decreases and the ability of the camera to accurately detect motion is reduced. To increase the area covered by a video camera surveillance system, it is well known to provide multiple video cameras. Of course, this increases the cost and complexity of the surveillance system. It is also known to utilize a moving camera to increase the field of view. For example, U.S. Pat. No. 5,473,364 discloses a surveillance system having moving cameras. However, the system disclosed in U.S. Pat. No. 5,473,364 requires complex algorithms, such as affine transforms, for adjusting images for camera movement. Accordingly, such systems are complex and require a great deal of processing power.  
       SUMMARY OF THE INVENTION  
       [0006]     An object of the invention is to improve surveillance systems. To achieve this and other objects, a first aspect of the invention is an apparatus for detecting motion in an area. The apparatus comprises an imaging device, such as a camera, having a field of view that is smaller than the area, means for moving the field of view to vary the portion of the area that is covered by the field of view, means for storing a first set of image data captured by the imaging device when the field of view covers a first portion of the area and for storing a second set of image data captured by the imaging device when the field of view covers a second portion of the area, means for determining a fixed object image portion in an overlapping area, means for adjusting at least one of the first set of image data and the second set of image data based on the fixed object image portion to obtain two sets of adjusted image data, and means for comparing the two sets of corrected image data to determine if any objects in the overlapping area have moved.  
         [0007]     A second aspect of the invention is a method for detecting motion in an area of interest. The method comprises recording test image data of a portion of the area having a fixed object therein, selecting a portion of the test image data corresponding to the fixed object, storing the portion of the test image data as learned image data, recording first image data at a first field of view, changing the field of view to a second field of view including the fixed object, recording second image data at the second field of view, recognizing the fixed object in the first image data and the second image data, adjusting at least one of the first image data and the second image data for position based on the position of the fixed object in the first image data and the second image data, and comparing the first image data and the second image data after the adjusting step to determine if motion has occurred in an area encompassed by both the first field of view and the second field of view.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     The invention is described through a preferred embodiment and the attached drawing in which:  
         [0009]      FIG. 1  is a black diagram of a surveillance system of the preferred embodiment;  
         [0010]      FIG. 2  is a diagram illustrating the moving field of view of the preferred embodiment; and  
         [0011]      FIG. 3  is a flow chart of the surveillance method of the preferred embodiment; 
     
    
     DETAILED DESCRIPTION  
       [0012]      FIG. 1  illustrates a surveillance system in accordance with a preferred embodiment of the invention. Surveillance system  10  utilizes a single imaging device, camera  20  in the preferred embodiment, to detect motion over a large area. Camera  20  includes imaging section  22  and optics section  24  and has field of view F. The phrase “field of view,” as used herein, refers to the effective area of a scene that can be imaged on the image plane of camera  20  at a given time. Imaging section  22  includes an imager, such as a known solid state imager, for sensing light at a plurality of points in a scene. For example, the imager can be an active pixel Complementary Metal Oxide Semiconductor (CMOS) sensor, such as that described in U.S. Pat. No. 6,215,113, or the imager can be a Charge Coupled Device (CCD). Optics section  24  serves to focus light from the scene in the field of view of camera  20  onto the imager. For example, optics section  24  can include a lens system, aperture diaphragm, and the like for focusing the image and adjusting exposure. Imaging section  22  can include appropriate imaging electronics, such as an A/D converter, for outputting an image signal corresponding to light sensed by the imager. Optics section  24  can also include mirrors, prisms, or other elements as necessary to accomplish the functions set forth herein.  
         [0013]     Imaging section  22  and/or optics section  24  are coupled to panning mechanism  30  which comprises a motive device to move the field of view as desired by moving camera  20 , imaging section  22 , or optic section  24 . For example, the motive device can be the output shaft of a transmission coupled to a motor to rotate camera  20  about an axis or move camera  20  linearly. Further, the motive device can be coupled to a mirror or other element of optics section  24  to change the field of view without the need to move imaging section  22 . Panning mechanism  30  can be any device or combination of devices for moving the field of view of camera  20  across a desired area.  
         [0014]     Processor  40  of the preferred embodiment can comprise a microprocessor based device, such as a general purpose programmable computer. For example, processor  40  can be embodied in a personal computer, a server, or a dedicated programmable device. Processor  40  includes storage device  42 , determining module,  44 , adjusting module  46 , comparing module  48 , messaging layer  50 , and user interface  52 . The various components of processor  40  can be embodied as hardware and/or software, as will become apparent below. Such components are described as separate entities for the clarity. However, the components need not be embodied in separate hardware and/or software and the functionality thereof can be combined or further separated. For example, all of the modules can be embodied in a single executable program file of a control program running on processor  40 .  
         [0015]     Camera  20  generates a set of image data as an image signal based on the image in the field of view and communicates the signal to processor  40  for processing. As the field of view changes, by virtue of panning mechanism  30 , the image signal changes accordingly.  
         [0016]     Storage device  42  can include a Random Access Memory (RAM), a magnetic disk, such as a hard disk, or any other device capable of retaining image data. Image data corresponding to the image signal is stored in storage device  42 . The image data can be updated periodically, such as every second, every minute, or the like. Because the field of view is changing, the image signal will change over time. Storage device  42  preferably is capable of storing at least two sets of image data at a time for reasons which will become apparent below.  
         [0017]     Determining module  44  can include any algorithm or other logic for determining a static portion of an image corresponding to an image signal stored in memory device  42 . For example, Principal Component Analysis (PCA) techniques can be used. PCA distributes image data of a multidimensional image space and converts the image data into feature space. The principal components of eigenvectors which serve to characterize such space are then used for processing. More specifically, the eigenvectors are defined respectively by the amount of change in pixel intensity corresponding to changes within the image group, and can thus be thought of as characteristic axes for explaining the image.  
         [0018]     A large number of eigenvectors are required to accurately reproduce an image. However, if one only desires to express the characteristics of the outward appearance of an image, the image can be sufficiently expressed using a smaller number of eigenvectors to thereby reduce the required processing power. Known PCA techniques can be used to compare a “learned” image with a current image to recognize patterns in the present image that are similar or identical to the learned image. In the preferred embodiment, the learned image is a designated portion of a previous image signal taken by camera  20  as described in detail below.  
         [0019]     The learned image can be obtained by directing camera  20  toward an area including a substantially fixed object, such as a tree, a sign, a building, or a portion of such an object. The resulting image can be displayed on a screen in user interface  52 , such as a CRT display or the like. The operator can then designate the portion of the image representing the fixed object by selecting that portion of the image with a mouse pointer or other input device in a known manner. The portion of the image data representing the fixed object is then stored as a learned image. This learned image can be recognized in subsequent images by determining module  44 , using PCA techniques for example, and the position of the learned image in the current image can be output to adjusting module  46 .  
         [0020]     Alternatively a software algorithm of determining module  44  can automatically determine a portion of an image representing a fixed object using any known image analysis technique. For example, determining module  44  can determine a fixed object image portion by comparing successive image data of a test field of view to determine a reference image portion having a fixed object therein, i.e. a portion where data does not change in successive views. The reference image portion can then be compared with portions of the first and second image data to determine which portion of the first and second image data has the fixed object therein. Many reference images can be taken over time to eliminate false fixed objects, such as cars, that may appear fixed and then can be moved later on.  
         [0021]     Adjusting module  46  includes logic for adjusting images based on the determination of determining module  44 . In particular, adjusting module  46  compares the position of the learned image in two sets of image data and offsets the image data of at least one set of image data to locate the learned image in the same place in each set of image data. This operation permits the adjusted image data to be compared notwithstanding the fact that the field of view is different for each set of image data.  
         [0022]     The adjusted sets of image data are sent to comparing module  48  for comparison in a known manner to ascertain if an object in the area has moved, e.g., an animate object has entered the area of surveillance. Appropriate filters and other logic can be applied to the determination to reduce detection of motion caused by small animals, wind, or the like, in a known manner. In the case of motion detection, messaging layer  50  can send a message, or other signal, to annunciation device  60  which can include an audible alarm, an image display, a phone dialer, or the like, to notify the proper parties and provide the desired information thereto.  
         [0023]      FIG. 2  Illustrates the ability of the preferred embodiment to provide surveillance of a large area with a small amount of cameras by moving the field of view. In this example, the area to be converted by surveillance system  10  is area A (designated by the solid line in  FIG. 2 ). Field of view F 1  (designated by the dotted line in  FIG. 2 ) of camera  20  at a first position does not cover the entirety of area A. However, field of view F 1  does encompass tree T as a fixed object. The image of tree T can be selected as the learned image to be used for position adjustment by adjusting module  46 . The field of view of camera  20  can then be changed by panning mechanism  30  to be field of view F 2  (designated by the dashed line in  FIG. 2 ). Note that field of view F 2  also encompasses tree T. Accordingly, image data of overlapping portions of field of view F 1  and field of view F 2  can be compared after adjustment in the manner described above. It can be seen that the field of view can be changed incrementally to span the entirety of area A, as long as each field of view includes tree T, while comparing overlapping portions of successive sets of image data to thereby cover the entirety of area A with only camera  10 .  
         [0024]      FIG. 3  illustrates the method of surveillance of the preferred embodiment. In step  100 , a test image of the area to be monitored is taken and stored in storage device  42 . The test image can have any field of view of the area as long as there is a fixed object therein. The fixed object can be any object that is at least partially visible in all fields of view of camera  20  throughout panning of the area and is reasonably still and distinct to be discerned by analyzing image data. In step  110 , the portion of the test image having the fixed object therein is selected. For example, the test image can be displayed to a user through user interface  52  and the user can demarcate the fixed image with a mouse pointer, touch screen device, or the like. The image of the fixed object is then stored as a learned image in storage device  42 .  
         [0025]     In step  130 , a surveillance image N of the area is recorded with camera  20  at a first field of view and image N is stored in storage device  42 . In step  140 , the field of view of camera  20  is changed by an incremental amount by panning mechanism  30 , while still including the fixed object, and in step  150 , surveillance image N+1 is recorded at the new filed of view. In step  160 , adjusting module  46  adjusts one or both of images N and N+1 for position based on the position of the fixed object recognized by determining module  44  in each image. The images N and N+1 are compared after adjustment by comparing module  48  to determine if motion has occurred in the area based on a known algorithm. If it is determined that motion has occurred, annunciation device  60  is activated to sound an alarm or take any appropriate action to notify the proper persons or entities that motion has been detected.  
         [0026]     At this time, the mode of surveillance can be changed in step  200 . For example, an operator may now be given control of panning mechanism  30  to selectively view portions of the area to ascertain the source of motion or the operator may be presented with various displays automatically. If no motion is detected in step  170 , N is set to N−1, i.e. image N+1 becomes image N and surveillance continues in step  140  in the manner described above. This process can continue until panning mechanism has taken the field of view of camera  20  to the edge of the area and can continue with panning mechanism moving in a reverse direction back across the area.  
         [0027]     Note that steps  100  through  120 , i.e., the recording of the learned image, can be accomplished at the same time as step  130 . In other words, the learned image can be captured directly out of the first or subsequent surveillance images. Also, the learned image can be captured again periodically to improve performance. In fact, the learned image can be of plural objects as long as each successive surveillance image includes at least one fixed object in common.  
         [0028]     The logic of and data manipulation of the invention can be accomplished by any device, such as a general purpose programmable computer or hardwired devices. The imaging device can be any type of sensor for capturing image data, such as a still camera, a video camera, an x-ray imager, an acoustic imager, an electromagnetic imager, or the like. The camera can sense visible light, infra red light, or any other radiation or characteristic. The panning mechanism can comprise any type of motors, transmissions, and the like and can be coupled to any appropriate element to change the field of view of the camera. Any type of comparison and adjustment algorithm can be used with the invention.  
         [0029]     The invention has been described through a preferred embodiment. However, various modifications can be made without departing from the scope of the invention as defined by the appended claims and legal equivalents.