Patent Publication Number: US-9892606-B2

Title: Video surveillance system employing video primitives

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/098,385, filed on Apr. 5, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/057,154, filed on Feb. 15, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 09/987,707, filed Nov. 15, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/694,712, filed on Oct. 24, 2000, all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a system for automatic video surveillance employing video primitives. 
     REFERENCES 
     For the convenience of the reader, the references referred to herein are listed below. In the specification, the numerals within brackets refer to respective references. The listed references are incorporated herein by reference. 
     The following references describe moving target detection: 
     {1} A. Lipton, H. Fujiyoshi and R. S. Patil, “Moving Target Detection and Classification from Real-Time Video,”  Proceedings of IEEE WACV &#39; 98, Princeton, N.J., 1998, pp. 8-14. 
     {2} W. E. L. Grimson, et al., “Using Adaptive Tracking to Classify and Monitor Activities in a Site”,  CVPR , pp. 22-29, June 1998. 
     {3} A. J. Lipton, H. Fujiyoshi, R. S. Patil, “Moving Target Classification and Tracking from Real-time Video,”  IUW , pp. 129-136, 1998. 
     {4} T. J. Olson and F. Z. Brill, “Moving Object Detection and Event Recognition Algorithm for Smart Cameras,”  IUW , pp. 159-175, May 1997. 
     The following references describe detecting and tracking humans: 
     {5} A. J. Lipton, “Local Application of Optical Flow to Analyse Rigid Versus Non-Rigid Motion,”  International Conference on Computer Vision , Corfu, Greece, September 1999. 
     {6} F. Bartolini, V. Cappellini, and A. Mecocci, “Counting people getting in and out of a bus by real-time image-sequence processing,”  IVC,  12(1):36-41, January 1994. 
     {7} M. Rossi and A. Bozzoli, “Tracking and counting moving people,”  ICIP 94, pp. 212-216, 1994. 
     {8} C. R. Wren, A. Azarbayejani, T. Darrell, and A. Pentland, “Pfinder: Real-time tracking of the human body,”  Vismod,  1995. 
     {9} L. Khoudour, L. Duvieubourg, J. P. Deparis, “Real-Time Pedestrian Counting by Active Linear Cameras,”  JEI,  5(4):452-459, October 1996. 
     {10} S. Ioffe, D. A. Forsyth, “Probabilistic Methods for Finding People,”  IJCV,  43(1):45-68, June 2001. 
     {11} M. Isard and J. MacCormick, “BraMBLe: A Bayesian Multiple-Blob Tracker,”  ICCV,  2001. 
     The following references describe blob analysis: 
     {12} D. M. Gavrila, “The Visual Analysis of Human Movement: A Survey,”  CVIU,  73(1):82-98, January 1999. 
     {13} Niels Haering and Niels da Vitoria Lobo, “Visual Event Detection,”  Video Computing Series , Editor Mubarak Shah, 2001. 
     The following references describe blob analysis for trucks, cars, and people: 
     {14} Collins, Lipton, Kanade, Fujiyoshi, Duggins, Tsin, Tolliver, Enomoto, and Hasegawa, “A System for Video Surveillance and Monitoring: VSAM Final Report,” Technical Report CMU-RI-TR-00-12, Robotics Institute, Carnegie Mellon University, May 2000. 
     {15} Lipton, Fujiyoshi, and Patil, “Moving Target Classification and Tracking from Real-time Video,” 98  Darpa IUW , Nov. 20-23, 1998. 
     The following reference describes analyzing a single-person blob and its contours: 
     {16} C. R. Wren, A. Azarbayejani, T. Darrell, and A. P. Pentland. “Pfinder: Real-Time Tracking of the Human Body,”  PAMI , vol 19, pp. 780-784, 1997. 
     The following reference describes internal motion of blobs, including any motion-based segmentation: 
     {17} M. Allmen and C. Dyer, “Long—Range Spatiotemporal Motion Understanding Using Spatiotemporal Flow Curves,”  Proc. IEEE CVPR , Lahaina, Maui, Hi., pp. 303-309, 1991. 
     {18} L. Wixson, “Detecting Salient Motion by Accumulating Directionally Consistent Flow”, IEEE Trans. Pattern Anal. Mach. Intell., vol. 22, pp. 774-781, August, 2000. 
     BACKGROUND OF THE INVENTION 
     Video surveillance of public spaces has become extremely widespread and accepted by the general public. Unfortunately, conventional video surveillance systems produce such prodigious volumes of data that an intractable problem results in the analysis of video surveillance data. 
     A need exists to reduce the amount of video surveillance data so analysis of the video surveillance data can be conducted. 
     A need exists to filter video surveillance data to identify desired portions of the video surveillance data. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to reduce the amount of video surveillance data so analysis of the video surveillance data can be conducted. 
     An object of the invention is to filter video surveillance data to identify desired portions of the video surveillance data. 
     An object of the invention is to produce a real time alarm based on an automatic detection of an event from video surveillance data. 
     An object of the invention is to integrate data from surveillance sensors other than video for improved searching capabilities. 
     An object of the invention is to integrate data from surveillance sensors other than video for improved event detection capabilities 
     The invention includes an article of manufacture, a method, a system, and an apparatus for video surveillance. 
     The article of manufacture of the invention includes a computer-readable medium comprising software for a video surveillance system, comprising code segments for operating the video surveillance system based on video primitives. 
     The article of manufacture of the invention includes a computer-readable medium comprising software for a video surveillance system, comprising code segments for accessing archived video primitives, and code segments for extracting event occurrences from accessed archived video primitives. 
     The system of the invention includes a computer system including a computer-readable medium having software to operate a computer in accordance with the invention. 
     The apparatus of the invention includes a computer including a computer-readable medium having software to operate the computer in accordance with the invention. 
     The article of manufacture of the invention includes a computer-readable medium having software to operate a computer in accordance with the invention. 
     Moreover, the above objects and advantages of the invention are illustrative, and not exhaustive, of those that can be achieved by the invention. Thus, these and other objects and advantages of the invention will be apparent from the description herein, both as embodied herein and as modified in view of any variations which will be apparent to those skilled in the art. 
     Definitions 
     A “video” refers to motion pictures represented in analog and/or digital form. Examples of video include: television, movies, image sequences from a video camera or other observer, and computer-generated image sequences. 
     A “frame” refers to a particular image or other discrete unit within a video. 
     An “object” refers to an item of interest in a video. Examples of an object include: a person, a vehicle, an animal, and a physical subject. 
     An “activity” refers to one or more actions and/or one or more composites of actions of one or more objects. Examples of an activity include: entering; exiting; stopping; moving; raising; lowering; growing; and shrinking. 
     A “location” refers to a space where an activity may occur. A location can be, for example, scene-based or image-based. Examples of a scene-based location include: a public space; a store; a retail space; an office; a warehouse; a hotel room; a hotel lobby; a lobby of a building; a casino; a bus station; a train station; an airport; a port; a bus; a train; an airplane; and a ship. Examples of an image-based location include: a video image; a line in a video image; an area in a video image; a rectangular section of a video image; and a polygonal section of a video image. 
     An “event” refers to one or more objects engaged in an activity. The event may be referenced with respect to a location and/or a time. 
     A “computer” refers to any apparatus that is capable of accepting a structured input, processing the structured input according to prescribed rules, and producing results of the processing as output. Examples of a computer include: a computer; a general purpose computer; a supercomputer; a mainframe; a super mini-computer; a mini-computer; a workstation; a micro-computer; a server; an interactive television; a hybrid combination of a computer and an interactive television; and application-specific hardware to emulate a computer and/or software. A computer can have a single processor or multiple processors, which can operate in parallel and/or not in parallel. A computer also refers to two or more computers connected together via a network for transmitting or receiving information between the computers. An example of such a computer includes a distributed computer system for processing information via computers linked by a network. 
     A “computer-readable medium” refers to any storage device used for storing data accessible by a computer. Examples of a computer-readable medium include: a magnetic hard disk; a floppy disk; an optical disk, such as a CD-ROM and a DVD; a magnetic tape; a memory chip; and a carrier wave used to carry computer-readable electronic data, such as those used in transmitting and receiving e-mail or in accessing a network. 
     “Software” refers to prescribed rules to operate a computer. Examples of software include: software; code segments; instructions; computer programs; and programmed logic. 
     A “computer system” refers to a system having a computer, where the computer comprises a computer-readable medium embodying software to operate the computer. 
     A “network” refers to a number of computers and associated devices that are connected by communication facilities. A network involves permanent connections such as cables or temporary connections such as those made through telephone or other communication links. Examples of a network include: an internet, such as the Internet; an intranet; a local area network (LAN); a wide area network (WAN); and a combination of networks, such as an internet and an intranet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are explained in greater detail by way of the drawings, where the same reference numerals refer to the same features. 
         FIG. 1  illustrates a plan view of the video surveillance system of the invention. 
         FIG. 2  illustrates a flow diagram for the video surveillance system of the invention. 
         FIG. 3  illustrates a flow diagram for tasking the video surveillance system. 
         FIG. 4  illustrates a flow diagram for operating the video surveillance system. 
         FIG. 5  illustrates a flow diagram for extracting video primitives for the video surveillance system. 
         FIG. 6  illustrates a flow diagram for taking action with the video surveillance system. 
         FIG. 7  illustrates a flow diagram for semi-automatic calibration of the video surveillance system. 
         FIG. 8  illustrates a flow diagram for automatic calibration of the video surveillance system. 
         FIG. 9  illustrates an additional flow diagram for the video surveillance system of the invention. 
         FIGS. 10-15  illustrate examples of the video surveillance system of the invention applied to monitoring a grocery store. 
         FIG. 16 a    shows a flow diagram of a video analysis subsystem according to an embodiment of the invention. 
         FIG. 16 b    shows the flow diagram of the event occurrence detection and response subsystem according to an embodiment of the invention. 
         FIG. 17  shows exemplary database queries. 
         FIG. 18  shows three exemplary activity detectors according to various embodiments of the invention: detecting tripwire crossings ( FIG. 18 a   ), loitering ( FIG. 18 b   ) and theft ( FIG. 18 c   ). 
         FIG. 19  shows an activity detector query according to an embodiment of the invention. 
         FIG. 20  shows an exemplary query using activity detectors and Boolean operators with modifiers, according to an embodiment of the invention. 
         FIGS. 21 a  and 21 b    show an exemplary query using multiple levels of combinators, activity detectors, and property queries. 
         FIG. 22  shows an exemplary configuration of a video surveillance system according to an embodiment of the invention. 
         FIG. 23  shows another exemplary configuration of a video surveillance system according to an embodiment of the invention. 
         FIG. 24  shows another exemplary configuration of a video surveillance system according to an embodiment of the invention. 
         FIG. 25  shows a network that may be used in exemplary configurations of embodiments of the invention. 
         FIG. 26  shows an exemplary configuration of a video surveillance system according to an embodiment of the invention. 
         FIG. 27  shows an exemplary configuration of a video surveillance system according to an embodiment of the invention. 
         FIG. 28  shows an exemplary configuration of a video surveillance system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The automatic video surveillance system of the invention is for monitoring a location for, for example, market research or security purposes. The system can be a dedicated video surveillance installation with purpose-built surveillance components, or the system can be a retrofit to existing video surveillance equipment that piggybacks off the surveillance video feeds. The system is capable of analyzing video data from live sources or from recorded media. The system is capable of processing the video data in real-time, and storing the extracted video primitives to allow very high speed forensic event detection later. The system can have a prescribed response to the analysis, such as record data, activate an alarm mechanism, or activate another sensor system. The system is also capable of integrating with other surveillance system components. The system may be used to produce, for example, security or market research reports that can be tailored according to the needs of an operator and, as an option, can be presented through an interactive web-based interface, or other reporting mechanism. 
     An operator is provided with maximum flexibility in configuring the system by using event discriminators. Event discriminators are identified with one or more objects (whose descriptions are based on video primitives), along with one or more optional spatial attributes, and/or one or more optional temporal attributes. For example, an operator can define an event discriminator (called a “loitering” event in this example) as a “person” object in the “automatic teller machine” space for “longer than 15 minutes” and “between 10:00 p.m. and 6:00 a.m.” Event discriminators can be combined with modified Boolean operators to form more complex queries. 
     Although the video surveillance system of the invention draws on well-known computer vision techniques from the public domain, the inventive video surveillance system has several unique and novel features that are not currently available. For example, current video surveillance systems use large volumes of video imagery as the primary commodity of information interchange. The system of the invention uses video primitives as the primary commodity with representative video imagery being used as collateral evidence. The system of the invention can also be calibrated (manually, semi-automatically, or automatically) and thereafter automatically can infer video primitives from video imagery. The system can further analyze previously processed video without needing to reprocess completely the video. By analyzing previously processed video, the system can perform inference analysis based on previously recorded video primitives, which greatly improves the analysis speed of the computer system. 
     The use of video primitives may also significantly reduce the storage requirements for the video. This is because the event detection and response subsystem uses the video only to illustrate the detections. Consequently, video may be stored or transmitted at a lower quality. In a potential embodiment, the video may be stored or transmitted only when activity is detected, not all the time. In another potential embodiment, the quality of the stored or transmitted video may be dependent on whether activity is detected: video can be stored or transmitted at higher quality (higher frame-rate and/or bit-rate) when activity is detected and at lower quality at other times. In another exemplary embodiment, the video storage and database may be handled separately, e.g., by a digital video recorder (DVR), and the video processing subsystem may just control whether data is stored and with what quality. In another embodiment, the video surveillance system (or components thereof) may be on a processing device (such as general purpose processor, DSP, microcontroller, ASIC, FPGA, or other device) on board a video management device such as a digital video camera, network video server, DVR, or Network Video Recorder (NVR), and the bandwidth of video streamed from the device can be modulated by the system. High quality video (high bit-rate or frame-rate) need only be transmitted through an IP video network only when activities of interest are detected. In this embodiment, primitives from intelligence-enabled devices can be broadcast via a network to multiple activity inference applications at physically different locations to enable a single camera network to provide multi-purpose applications through decentralized processing. 
       FIG. 22  shows one configuration of an implementation of the video surveillance system. Block  221  represents a raw (uncompressed) digital video input. This can be obtained, for example, through analog to digital capture of an analog video signal or decoding of a digital video signal. Block  222  represents a hardware platform housing the main components of the video surveillance system (video content analysis—block  225 —and activity inference—block  226 ). The hardware platform may contain other components such as an operating system (block  223 ); a video encoder (block  224 ) that compresses raw digital video for video streaming or storage using any available compression scheme (JPEG, MJPEG, MPEG1, MPEG2, MPEG4, H.263, H.264, Wavelet, or any other); a storage mechanism (block  227 ) for maintaining data such as video, compressed video, alerts, and video primitives—this storage device may be, for example, a hard-disk, on-board RAM, on-board FLASH memory, or other storage medium; and a communications layer (block  228 ) which may, for example, packetize and/or digitize data for transmission over a communication channel (block  229 ). 
     There may be other software components residing on computational platforms at other nodes of a network to which communications channel  229  connects. Block  2210  shows a rule management tool which is a user interface for creating video surveillance rules. Block  2211  shows an alert console for displaying alerts and reports to a user. Block  2212  shows a storage device (such as DVR, NVR, or PC) for storing alerts, primitives, and video for further after-the-fact processing. 
     Components on the hardware platform (block  222 ) may be implemented on any processing hardware (general purpose processor, microcontroller, DSP, ASIC, FPGA, or other processing device) on any video capture, processing, or management device such as a video camera, digital video camera, IP video camera, IP video server, digital video recorder (DVR), network video recorder (NVR), PC, laptop, or other device. There are a number of different possible modes of operation for this configuration. 
     In one mode, the system is programmed to look for specific events. When those events occur, alerts are transmitted via the communication channel (block  229 ) to other systems. 
     In another mode, video is streamed from the video device while it is analyzing the video data. When events occur, alerts are transmitted via the communication channel (block  229 ). 
     In another mode, video encoding and streaming is modulated by the content analysis and activity inference. When there is no activity present (no primitives are being generates), no video (or low quality, bit-rate, frame rate, resolution) is being streamed. When some activity is present (primitives are being generated), higher quality, bit-rate, frame rate, resolution video is streamed. When events of interest are detected by the event inference, very high quality, bit-rate, frame rate, resolution video is streamed. 
     In another mode of operation, information is stored in the on-board storage device (block  227 ). Stored data may consist of digital video (raw or compressed), video primitives, alerts, or other information. The stored video quality may also be controlled by the presence of primitives or alerts. When there are primitives and alerts, higher quality, bit-rate, frame rate, resolution video may be stored. 
       FIG. 23  shows another configuration of an implementation of the video surveillance system. Block  231  represents a raw (uncompressed) digital video input. This can be obtained, for example, through analog to digital capture of an analog video signal or decoding of a digital video signal. Block  232  represents a hardware platform housing the analysis component of the video surveillance system (block  235 ). The hardware platform may contain other components such as an operating system (block  233 ); a video encoder (block  234 ) that compresses raw digital video for video streaming or storage using any available compression scheme (JPEG, MJPEG, MPEG1, MPEG2, MPEG4, H.263, H.264, Wavelet, or any other); a storage mechanism (block  236 ) for maintaining data such as video, compressed video, alerts, and video primitives—this storage device may be, for example, a hard-disk, on-board RAM, on-board FLASH memory, or other storage medium; and a communications layer (block  237 ) that may, for example, packetize and/or digitize data for transmission over a communication channel (block  238 ). In the embodiment of the invention shown in  FIG. 23 , the activity inference component (block  2311 ) is shown on a separate hardware component (block  239 ) connected to a network to which communication channel  238  connects. 
     There may also be other software components residing on computational platforms at other nodes of this network (block  239 ). Block  2310  shows a rule management tool, which is a user interface for creating video surveillance rules. Block  2312  shows an alert console for displaying alerts and reports to a user. Block  2313  shows a storage device that could be physically located on the same hardware platform (such as a hard disk, floppy disk, other magnetic disk, CD, DVD, other optical disk, MD or other magneto-optical disk, solid state storage device such as RAM or FLASH RAM, or other storage device) or may be a separate storage device (such as external disk drive, PC, laptop, DVR, NVR, or other storage device). 
     Components on the hardware platform (block  222 ) may be implemented on any processing platform (general purpose processor, microcontroller, DSP, FPGA, ASIC or any other processing platform) on any video capture, processing, or management device such as a video camera, digital video camera, IP video camera, IP video server, digital video recorder (DVR), network video recorder (NVR), PC, laptop, or other device. Components on the back-end hardware platform (block  239 ) may be implemented on any processing hardware (general purpose processor, microcontroller, DSP, FPGA, ASIC, or any other device) on any processing device such as PC, laptop, single-board computer, DVR, NVR, video server, network router, hand-held device (such as video phone, pager, or PDA). There are a number of different possible modes of operation for this configuration. 
     In one mode, the system is programmed on the back-end device (or any other device connected to the back-end device) to look for specific events. The content analysis module (block  235 ) on the video processing platform (block  232 ) generates primitives that are transmitted to the back-end processing platform (block  239 ). The event inference module (block  2311 ) determines if the rules have been violated and generates alerts that can be displayed on an alert console (block  2312 ) or stored in a storage device (block  2313 ) for later analysis. 
     In another mode, video primitives and video can be stored in a storage device on the back-end platform ( 2313 ) for later analysis. 
     In another mode, stored video quality, bit-rate, frame rate, resolution can be modulated by alerts. When there is an alert, video can be stored at higher quality, bit-rate, frame rate, resolution. 
     In another mode, video primitives can be stored on the video processing device (block  236  in block  232 ) for later analysis via the communication channel. 
     In another mode, the quality of the video stored on the video processing device (in block  236  in block  232 ) may be modulated by the presence of primitives. When there are primitives (when something is happening) the quality, bit-rate, frame rate, resolution of the stored video can be increased. 
     In another mode, video can be streamed from the video processor via the encoder ( 234 ) to other devices on the network, via communication channel  238 . 
     In another mode, video quality can be modulated by the content analysis module ( 235 ). When there are no primitives (nothing is happening), no (or low quality, bit-rate, frame rate, resolution) video is streamed. When there is activity, higher quality, bit-rate, frame rate, resolution video is streamed. 
     In another mode, streamed video quality, bit-rate, frame rate, resolution can be modulated by the presence of alerts. When the back end event inference module (block  2311 ) detects an event of interest, it can send a signal or command to the video processing component (block  232 ) requesting video (or higher quality, bit-rate, frame rate, resolution video). When this request is received, the video compression component (block  234 ) and communication layer (block  237 ) can change compression and streaming parameters. 
     In another mode the quality of video stored on board the video processing device (block  236  in block  232 ) can be modulated by the presence of alerts. When an alert is generated by the event inference module (block  2311 ) on the back end processor (block  239 ) it can send a message via the communication channel (block  238 ) to the video processor hardware (block  232 ) to increase the quality, bit-rate, frame rate, resolution of the video stored in the on board storage device ( 238 ). 
       FIG. 24  shows an extension of the configuration described in  FIG. 23 . By separating the functionality of video content analysis and back end activity inference, it is possible to enable a multi-purpose intelligent video surveillance system through the process of late application binding. A single network of intelligence-enabled cameras can broadcast a single stream of video primitives to separate back-end applications in different parts of an organization (at different physical locations) and achieve multiple functions. This is possible because the primitive stream contains information about everything going on in the scene and is not tied to specific application areas. The example depicted in  FIG. 24  pertains to a retail environment but is illustrative of the principal in general and is applicable to any other application areas and any other surveillance functionality. Block  241  shows an intelligence-enabled network of one or more video cameras within a facility or across multiple facilities. The content analysis component or components may reside on a processing device inside the cameras, in video servers, in network routers, on DVRs, on NVRs, on PCs, on laptops or any other video processing device connected to the network. From these content analysis components, streams of primitives are broadcast via standard networks to activity inference modules on back end processors (blocks  242 - 245 ) residing in physically different areas used for different purposes. The back end processors may be in computers, laptops, DVRs, NVRs, network routers, handheld devices (phones, pagers, PDAs) or other computing devices. One advantage to this decentralization is that there need not be a central processing application that must be programmed to do all the processing for all possible applications. Another advantage is security so that one part of an organization can perform activity inference on rules that are stored locally so that no one else in the network has access to that information. 
     In block  242  the primitive stream from the intelligent camera network is analyzed for physical security applications: to determine if there has been a perimeter breach, vandalism, and to protect critical assets. Of course, these applications are merely exemplary, and any other application is possible. 
     In block  243  the primitive stream from the intelligent camera network is analyzed for loss prevention applications: to monitor a loading dock; to watch for customer or employee theft, to monitor a warehouse, and to track stock. Of course, these applications are merely exemplary, and any other application is possible. 
     In block  244  the primitive stream from the intelligent camera network is analyzed for public safety and liability applications: to monitor for people or vehicle moving too fast in parking lots, to watch for people slipping and falling, and to monitor crowds in and around the facility. Of course, these applications are merely exemplary, and any other application is possible. 
     In block  245  the primitive stream from the intelligent camera network is analyzed for business intelligence applications: to watch the lengths of queues, to track consumer behavior, to learn patterns of behavior, to perform building management tasks such as controlling lighting and heating when there are no people present. Of course, these applications are merely exemplary, and any other application is possible. 
       FIG. 25  shows a network (block  251 ) with a number of potential intelligence-enabled devices connected to it. Block  252  is an IP camera with content analysis components on board that can stream primitives over a network. Block  253  is an IP camera with both content analysis and activity inference components on board that can be programmed directly with rules and will generate network alerts directly. Block  254  is a standard analog camera with no intelligent components on board; but it is connected to an IP video management platform (block  256 ) that performs video digitization and compression as well as content analysis and activity inference. It can be programmed with view-specific rules and is capable of transmitting primitive streams and alerts via a network. Block  255  is a DVR with activity inference components that is capable of ingesting primitive streams from other devices and generating alerts. Block  257  is a handheld PDA enabled with wireless network communications that has activity inference algorithms on board and is capable of accepting video primitives from the network and displaying alerts. Block  258  is complete intelligent video analysis system capable of accepting analog or digital video streams, performing content analysis and activity inference and displaying alerts on a series of alert consoles. 
       FIG. 26  shows another configuration of an implementation of the video surveillance system. Block  2601  represents a hardware platform that may house the main components of the video surveillance system, as well as additional processing and interfacing components. Block  2602  represents a hardware sub-platform housing the main components of the video surveillance system (video content analysis—block  2603 —and activity inference—block  2604 ), and may also include an application programming interface (API), block  2605 , for interfacing with these components. Raw (uncompressed) digital video input may be obtained, for example, through analog to digital capture of an analog video signal or decoding of a digital video signal, at block  2607 . The hardware platform  2601  may contain other components such as one or more main digital signal processing (DSP) applications (block  2606 ); a video encoder (block  2609 ) that may be used to compress raw digital video for video streaming or storage using any available compression scheme (JPEG, MJPEG, MPEG1, MPEG2, MPEG4, H.263, H.264, Wavelet, or any other); a storage mechanism (not shown) for maintaining data such as video, compressed video, alerts, and video primitives—this storage device may be, for example, a hard-disk, on-board RAM, on-board FLASH memory, or other storage medium; and a communications layer, shown in  FIG. 26  as TCP/IP stack  2608 , which may, for example, packetize and/or digitize data for transmission over a communication channel. 
     Hardware platform  2601  may be connected to a sensor  2610 . Sensor  2610  may be implemented in hardware, firmware, software, or combinations thereof. Sensor  2610  may serve as an interface between hardware platform  2601  and network  2611 . Sensor  2610  may include a server layer, or a server layer may be implemented elsewhere, for example, between sensor  2610  and network  2611  or as part of network  2611 . 
     There may be other software components residing on computational platforms at other nodes of network  2611 . Block  2612  shows a rule management tool, which, again, is a user interface for creating video surveillance rules. Block  2613  shows an alert console for displaying alerts and reports to a user. 
     Components on the hardware platform (block  2601 ) may be implemented on any processing hardware (general purpose processor, microcontroller, DSP, ASIC, FPGA, or other processing device) on any video capture, processing, or management device such as a video camera, digital video camera, IP video camera, IP video server, digital video recorder (DVR), network video recorder (NVR), PC, laptop, or other device. There are a number of different possible modes of operation for this configuration, as discussed above. 
     In the configuration of  FIG. 26 , alerts may be handled at the DSP level, and API framework  2605  may include alert API support. This may support use of alerts for various command and control functions within the device. 
     For example, in some embodiments of the invention, main DSP application  2606  may take an alert and send it to another algorithm running on hardware platform  2601 . This may, for example, be a facial recognition algorithm to be executed upon a person-based rule being triggered. In such a case, the handoff may be made if the alert contains an object field that indicates that the object type is a person. 
     Another example that may implemented in some embodiments of the invention is to use the alert to control video compression and/or streaming. This may, for example, be simple on/off control, control of resolution, etc.; however, the invention is not necessarily limited to these examples. Such control may, for example, be based upon presence of an alert and/or on details of an alert. 
     In general, alerts may be used for a variety of command and control functions, which may further include, but are not limited to, controlling image enhancement software, controlling pan-tilt-zoom (PTZ) functionality, and controlling other sensors. 
       FIG. 27  shows yet another configuration of an implementation of the video surveillance system. Block  2701  represents a hardware platform that may house the main components of the video surveillance system, as well as additional processing and interfacing components. Block  2702  represents a hardware sub-platform housing the main components of the video surveillance system (video content analysis—block  2703 —and activity inference—block  2704 ), and may also include an application programming interface (API), block  2705 , for interfacing with these components. Raw (uncompressed) digital video input may be obtained, for example, through analog to digital capture of an analog video signal or decoding of a digital video signal, at block  2707 . The hardware platform  2701  may contain other components such as one or more main digital signal processing (DSP) applications (block  2706 ); a video encoder (block  2709 ) that may be used to compress raw digital video for video streaming or storage using any available compression scheme (JPEG, MJPEG, MPEG1, MPEG2, MPEG4, H.263, H.264, Wavelet, or any other); a storage mechanism (not shown) for maintaining data such as video, compressed video, alerts, and video primitives—this storage device may be, for example, a hard-disk, on-board RAM, on-board FLASH memory, or other storage medium; and a communications layer, shown in  FIG. 27  as TCP/IP stack  2708 , which may, for example, packetize and/or digitize data for transmission over a communication channel. 
     Hardware platform  2701  may be connected to a sensor  2710 . Sensor  2710  may be implemented in hardware, firmware, software, or combinations thereof. Sensor  2710  may serve as an interface between hardware platform  2701  and network  2711 . Sensor  2710  may include a server layer, or a server layer may be implemented elsewhere, for example, between sensor  2610  and network  2711  or as part of network  2711 . 
     As before, there may be other software components residing on computational platforms at other nodes of network  2711 . Block  2715  shows an alert console for displaying alerts and reports to a user. Block  2712  shows a partner rule user interface, coupled to a rule software development kit (SDK)  2713  and appropriate sensor support  2714  for the SDK  2713 . Sensor support  2714  may remove dependency on a server (as discussed in the immediately preceding paragraph), which may thus permit standalone SDK capability. 
     The components  2712 - 2714  may be used to permit users or manufacturers to create rules for the system, which may be communicated to event inference module  2704 , as shown. Components  2712 - 2714  may be hosted, for example, on a remote device, such as a computer, laptop computer, etc. 
     Rule SDK  2713  may actually take on at least two different forms. In a first form, rule SDK  2713  may expose to a user fully formed rules, for example, “person crosses tripwire.” In such a case, a user may need to create a user interface (UI) on top of such rules. 
     In a second form, SDK  2713  may expose to a user an underlying rule language and/or primitive definitions. In such a case, the user may be able to create his/her own rule elements. For example, such rule language and primitive definitions may be combined to define object classifications (e.g., “truck” or “animal”), new types of video tripwires (video tripwires are discussed further below), or new types of areas of interest. 
     Components on the hardware platform (block  2701 ) may be implemented on any processing hardware (general purpose processor, microcontroller, DSP, ASIC, FPGA, or other processing device) on any video capture, processing, or management device such as a video camera, digital video camera, IP video camera, IP video server, digital video recorder (DVR), network video recorder (NVR), PC, laptop, or other device. There are a number of different possible modes of operation for this configuration, as discussed above. 
       FIG. 28  shows still another configuration of an implementation of the video surveillance system. The configuration shown in  FIG. 28  may be used to permit the system to interface with a remote device via the Internet. The configuration of  FIG. 28  may generally be similar to the previously-discussed configurations, but with some modifications. Block  2801  represents a hardware platform that may house the main components of the video surveillance system, as well as additional processing and interfacing components. Block  2802  represents a hardware sub-platform housing the main components of the video surveillance system (video content analysis—block  2803 —and activity inference—block  2804 ), and may also include an application programming interface (API), block  2805 , for interfacing with these components. Block  2802  may further include a rule SDK  2806  to permit creation of new rules for event inference module  2804 . Raw (uncompressed) digital video input may be obtained, for example, through analog to digital capture of an analog video signal or decoding of a digital video signal, at block  2809 . The hardware platform  2801  may contain other components such as one or more main digital signal processing (DSP) applications (block  2807 ); a video encoder (block  2811 ) that may be used to compress raw digital video for video streaming or storage using any available compression scheme (JPEG, MJPEG, MPEG1, MPEG2, MPEG4, H.263, H.264, Wavelet, or any other); a storage mechanism (not shown) for maintaining data such as video, compressed video, alerts, and video primitives—this storage device may be, for example, a hard-disk, on-board RAM, on-board FLASH memory, or other storage medium; and a communications layer, shown in  FIG. 28  as TCP/IP stack  2810 , which may, for example, packetize and/or digitize data for transmission over a communication channel. In the configuration of  FIG. 28 , hardware platform  2801  may further include a hypertext transport protocol (HTTP) web service module  2808  that may be used to facilitate communication with an Internet-based device, via TCP/IP stack  2810 . 
     Components on the hardware platform (block  2801 ) may be implemented on any processing hardware (general purpose processor, microcontroller, DSP, ASIC, FPGA, or other processing device) on any video capture, processing, or management device such as a video camera, digital video camera, IP video camera, IP video server, digital video recorder (DVR), network video recorder (NVR), PC, laptop, or other device. There are a number of different possible modes of operation for this configuration, as discussed above. 
     As discussed above, the configuration of  FIG. 28  is designed to permit interaction of the system with remote devices via the Internet. While such remote devices are not to be thus limited,  FIG. 28  shows a web browser  2812 , which may be hosted on such a remote device. Via web browser  2812 , a user may communicate with the system to create new rules using rule SDK  2806 . Alerts may be generated by the system and communicated to one or more external devices (not shown), and this may be done via the Internet and/or via some other communication network or channel. 
     As another example, the system of the invention provides unique system tasking. Using equipment control directives, current video systems allow a user to position video sensors and, in some sophisticated conventional systems, to mask out regions of interest or disinterest. Equipment control directives are instructions to control the position, orientation, and focus of video cameras. Instead of equipment control directives, the system of the invention uses event discriminators based on video primitives as the primary tasking mechanism. With event discriminators and video primitives, an operator is provided with a much more intuitive approach over conventional systems for extracting useful information from the system. Rather than tasking a system with an equipment control directives, such as “camera A pan 45 degrees to the left,” the system of the invention can be tasked in a human-intuitive manner with one or more event discriminators based on video primitives, such as “a person enters restricted area A.” 
     Using the invention for market research, the following are examples of the type of video surveillance that can be performed with the invention: counting people in a store; counting people in a part of a store; counting people who stop in a particular place in a store; measuring how long people spend in a store; measuring how long people spend in a part of a store; and measuring the length of a line in a store. 
     Using the invention for security, the following are examples of the type of video surveillance that can be performed with the invention: determining when anyone enters a restricted area and storing associated imagery; determining when a person enters an area at unusual times; determining when changes to shelf space and storage space occur that might be unauthorized; determining when passengers aboard an aircraft approach the cockpit; determining when people tailgate through a secure portal; determining if there is an unattended bag in an airport; and determining if there is a theft of an asset. 
     An exemplary application area may be access control, which may include, for example: detecting if a person climbs over a fence, or enters a prohibited area; detecting if someone moves in the wrong direction (e.g., at an airport, entering a secure area through the exit); determining if a number of objects detected in an area of interest does not match an expected number based on RFID tags or card-swipes for entry, indicating the presence of unauthorized personnel. This may also be useful in a residential application, where the video surveillance system may be able to differentiate between the motion of a person and pet, thus eliminating most false alarms. Note that in many residential applications, privacy may be of concern; for example, a homeowner may not wish to have another person remotely monitoring the home and to be able to see what is in the house and what is happening in the house. Therefore, in some embodiments used in such applications, the video processing may be performed locally, and optional video or snapshots may be sent to one or more remote monitoring stations only when necessary (for example, but not limited to, detection of criminal activity or other dangerous situations). 
     Another exemplary application area may be asset monitoring. This may mean detecting if an object is taken away from the scene, for example, if an artifact is removed from a museum. In a retail environment asset monitoring can have several aspects to it and may include, for example: detecting if a single person takes a suspiciously large number of a given item; determining if a person exits through the entrance, particularly if doing this while pushing a shopping cart; determining if a person applies a non-matching price tag to an item, for example, filling a bag with the most expensive type of coffee but using a price tag for a less expensive type; or detecting if a person leaves a loading dock with large boxes. 
     Another exemplary application area may be for safety purposes. This may include, for example: detecting if a person slips and falls, e.g., in a store or in a parking lot; detecting if a car is driving too fast in a parking lot; detecting if a person is too close to the edge of the platform at a train or subway station while there is no train at the station; detecting if a person is on the rails; detecting if a person is caught in the door of a train when it starts moving; or counting the number of people entering and leaving a facility, thus keeping a precise headcount, which can be very important in case of an emergency. 
     Another exemplary application area may be traffic monitoring. This may include detecting if a vehicle stopped, especially in places like a bridge or a tunnel, or detecting if a vehicle parks in a no parking area. 
     Another exemplary application area may be terrorism prevention. This may include, in addition to some of the previously-mentioned applications, detecting if an object is left behind in an airport concourse, if an object is thrown over a fence, or if an object is left at a rail track; detecting a person loitering or a vehicle circling around critical infrastructure; or detecting a fast-moving boat approaching a ship in a port or in open waters. 
     Another exemplary application area may be in care for the sick and elderly, even in the home. This may include, for example, detecting if the person falls; or detecting unusual behavior, like the person not entering the kitchen for an extended period of time. 
       FIG. 1  illustrates a plan view of the video surveillance system of the invention. A computer system  11  comprises a computer  12  having a computer-readable medium  13  embodying software to operate the computer  12  according to the invention. The computer system  11  is coupled to one or more video sensors  14 , one or more video recorders  15 , and one or more input/output (I/O) devices  16 . The video sensors  14  can also be optionally coupled to the video recorders  15  for direct recording of video surveillance data. The computer system is optionally coupled to other sensors  17 . 
     The video sensors  14  provide source video to the computer system  11 . Each video sensor  14  can be coupled to the computer system  11  using, for example, a direct connection (e.g., a firewire digital camera interface) or a network. The video sensors  14  can exist prior to installation of the invention or can be installed as part of the invention. Examples of a video sensor  14  include: a video camera; a digital video camera; a color camera; a monochrome camera; a camera; a camcorder, a PC camera; a webcam; an infra-red video camera; and a CCTV camera. 
     The video recorders  15  receive video surveillance data from the computer system  11  for recording and/or provide source video to the computer system  11 . Each video recorder  15  can be coupled to the computer system  11  using, for example, a direct connection or a network. The video recorders  15  can exist prior to installation of the invention or can be installed as part of the invention. The video surveillance system in the computer system  11  may control when and with what quality setting a video recorder  15  records video. Examples of a video recorder  15  include: a video tape recorder; a digital video recorder; a network video recorder; a video disk; a DVD; and a computer-readable medium. The system may also modulate the bandwidth and quality of video streamed over a network by controlling a video encoder and streaming protocol. When activities of interest are detected, higher bit-rate, frame-rate, or resolution imagery may be encoded and streamed. 
     The I/O devices  16  provide input to and receive output from the computer system  11 . The I/O devices  16  can be used to task the computer system  11  and produce reports from the computer system  11 . Examples of I/O devices  16  include: a keyboard; a mouse; a stylus; a monitor; a printer; another computer system; a network; and an alarm. 
     The other sensors  17  provide additional input to the computer system  11 . Each other sensor  17  can be coupled to the computer system  11  using, for example, a direct connection or a network. The other sensors  17  can exit prior to installation of the invention or can be installed as part of the invention. Examples of another sensor  17  include, but are not limited to: a motion sensor; an optical tripwire; a biometric sensor; an RFID sensor; and a card-based or keypad-based authorization system. The outputs of the other sensors  17  can be recorded by the computer system  11 , recording devices, and/or recording systems. 
       FIG. 2  illustrates a flow diagram for the video surveillance system of the invention. Various aspects of the invention are exemplified with reference to  FIGS. 10-15 , which illustrate examples of the video surveillance system of the invention applied to monitoring a grocery store. 
     In block  21 , the video surveillance system is set up as discussed for  FIG. 1 . Each video sensor  14  is orientated to a location for video surveillance. The computer system  11  is connected to the video feeds from the video equipment  14  and  15 . The video surveillance system can be implemented using existing equipment or newly installed equipment for the location. 
     In block  22 , the video surveillance system is calibrated. Once the video surveillance system is in place from block  21 , calibration occurs. The result of block  22  is the ability of the video surveillance system to determine an approximate absolute size and speed of a particular object (e.g., a person) at various places in the video image provided by the video sensor. The system can be calibrated using manual calibration, semi-automatic calibration, and automatic calibration. Calibration is further described after the discussion of block  24 . 
     In block  23  of  FIG. 2 , the video surveillance system is tasked. Tasking occurs after calibration in block  22  and is optional. Tasking the video surveillance system involves specifying one or more event discriminators. Without tasking, the video surveillance system operates by detecting and archiving video primitives and associated video imagery without taking any action, as in block  45  in  FIG. 4 . 
       FIG. 3  illustrates a flow diagram for tasking the video surveillance system to determine event discriminators. An event discriminator refers to one or more objects optionally interacting with one or more spatial attributes and/or one or more temporal attributes. An event discriminator is described in terms of video primitives (also called activity description meta-data). Some of the video primitive design criteria include the following: capability of being extracted from the video stream in real-time; inclusion of all relevant information from the video; and conciseness of representation. 
     Real-time extraction of the video primitives from the video stream is desirable to enable the system to be capable of generating real-time alerts, and to do so, since the video provides a continuous input stream, the system cannot fall behind. 
     The video primitives should also contain all relevant information from the video, since at the time of extracting the video primitives, the user-defined rules are not known to the system. Therefore, the video primitives should contain information to be able to detect any event specified by the user, without the need for going back to the video and reanalyzing it. 
     A concise representation is also desirable for multiple reasons. One goal of the proposed invention may be to extend the storage recycle time of a surveillance system. This may be achieved by replacing storing good quality video all the time by storing activity description meta-data and video with quality dependent on the presence of activity, as discussed above. Hence, the more concise the video primitives are, the more data can be stored. In addition, the more concise the video primitive representation, the faster the data access becomes, and this, in turn may speed up forensic searching. 
     The exact contents of the video primitives may depend on the application and potential events of interest. Some exemplary embodiments are described below 
     An exemplary embodiment of the video primitives may include scene/video descriptors, describing the overall scene and video. In general, this may include a detailed description of the appearance of the scene, e.g., the location of sky, foliage, man-made objects, water, etc; and/or meteorological conditions, e.g., the presence/absence of precipitation, fog, etc. For a video surveillance application, for example, a change in the overall view may be important. Exemplary descriptors may describe sudden lighting changes; they may indicate camera motion, especially the facts that the camera started or stopped moving, and in the latter case, whether it returned to its previous view or at least to a previously known view; they may indicate changes in the quality of the video feed, e.g., if it suddenly became noisier or went dark, potentially indicating tampering with the feed; or they may show a changing waterline along a body of water (for further information on specific approaches to this latter problem, one may consult, for example, co-pending U.S. patent application Ser. No. 10/954,479, filed on Oct. 1, 2004, and incorporated herein by reference). 
     Another exemplary embodiment of the video primitives may include object descriptors referring to an observable attribute of an object viewed in a video feed. What information is stored about an object may depend on the application area and the available processing capabilities. Exemplary object descriptors may include generic properties including, but not limited to, size, shape, perimeter, position, trajectory, speed and direction of motion, motion salience and its features, color, rigidity, texture, and/or classification. The object descriptor may also contain some more application and type specific information: for humans, this may include the presence and ratio of skin tone, gender and race information, some human body model describing the human shape and pose; or for vehicles, it may include type (e.g., truck, SUV, sedan, bike, etc.), make, model, license plate number. The object descriptor may also contain activities, including, but not limited to, carrying an object, running, walking, standing up, or raising arms. Some activities, such as talking, fighting or colliding, may also refer to other objects. The object descriptor may also contain identification information, including, but not limited to, face or gait. 
     Another exemplary embodiment of the video primitives may include flow descriptors describing the direction of motion of every area of the video. Such descriptors may, for example, be used to detect passback events, by detecting any motion in a prohibited direction (for further information on specific approaches to this latter problem, one may consult, for example, co-pending U.S. patent application Ser. No. 10/766,949, filed on Jan. 30, 2004, and incorporated herein by reference). 
     Primitives may also come from non-video sources, such as audio sensors, heat sensors, pressure sensors, card readers, RFID tags, biometric sensors, etc. 
     A classification refers to an identification of an object as belonging to a particular category or class. Examples of a classification include: a person; a dog; a vehicle; a police car; an individual person; and a specific type of object. 
     A size refers to a dimensional attribute of an object. Examples of a size include: large; medium; small; flat; taller than 6 feet; shorter than 1 foot; wider than 3 feet; thinner than 4 feet; about human size; bigger than a human; smaller than a human; about the size of a car; a rectangle in an image with approximate dimensions in pixels; and a number of image pixels. 
     Position refers to a spatial attribute of an object. The position may be, for example, an image position in pixel coordinates, an absolute real-world position in some world coordinate system, or a position relative to a landmark or another object. 
     A color refers to a chromatic attribute of an object. Examples of a color include: white; black; grey; red; a range of HSV values; a range of YUV values; a range of RGB values; an average RGB value; an average YUV value; and a histogram of RGB values. 
     Rigidity refers to a shape consistency attribute of an object. The shape of non-rigid objects (e.g., people or animals) may change from frame to frame, while that of rigid objects (e.g., vehicles or houses) may remain largely unchanged from frame to frame (except, perhaps, for slight changes due to turning). 
     A texture refers to a pattern attribute of an object. Examples of texture features include: self-similarity; spectral power; linearity; and coarseness. 
     An internal motion refers to a measure of the rigidity of an object. An example of a fairly rigid object is a car, which does not exhibit a great amount of internal motion. An example of a fairly non-rigid object is a person having swinging arms and legs, which exhibits a great amount of internal motion. 
     A motion refers to any motion that can be automatically detected. Examples of a motion include: appearance of an object; disappearance of an object; a vertical movement of an object; a horizontal movement of an object; and a periodic movement of an object. 
     A salient motion refers to any motion that can be automatically detected and can be tracked for some period of time. Such a moving object exhibits apparently purposeful motion. Examples of a salient motion include: moving from one place to another; and moving to interact with another object. 
     A feature of a salient motion refers to a property of a salient motion. Examples of a feature of a salient motion include: a trajectory; a length of a trajectory in image space; an approximate length of a trajectory in a three-dimensional representation of the environment; a position of an object in image space as a function of time; an approximate position of an object in a three-dimensional representation of the environment as a function of time; a duration of a trajectory; a velocity (e.g., speed and direction) in image space; an approximate velocity (e.g., speed and direction) in a three-dimensional representation of the environment; a duration of time at a velocity; a change of velocity in image space; an approximate change of velocity in a three-dimensional representation of the environment; a duration of a change of velocity; cessation of motion; and a duration of cessation of motion. A velocity refers to the speed and direction of an object at a particular time. A trajectory refers a set of (position, velocity) pairs for an object for as long as the object can be tracked or for a time period. 
     A scene change refers to any region of a scene that can be detected as changing over a period of time. Examples of a scene change include: an stationary object leaving a scene; an object entering a scene and becoming stationary; an object changing position in a scene; and an object changing appearance (e.g. color, shape, or size). 
     A feature of a scene change refers to a property of a scene change. Examples of a feature of a scene change include: a size of a scene change in image space; an approximate size of a scene change in a three-dimensional representation of the environment; a time at which a scene change occurred; a location of a scene change in image space; and an approximate location of a scene change in a three-dimensional representation of the environment. 
     A pre-defined model refers to an a priori known model of an object. Examples of a pre-defined model may include: an adult; a child; a vehicle; and a semi-trailer. 
     In block  31 , one or more objects types of interests are identified in terms of video primitives or abstractions thereof. Examples of one or more objects include: an object; a person; a red object; two objects; two persons; and a vehicle. 
     In block  32 , one or more spatial areas of interest are identified. An area refers to one or more portions of an image from a source video or a spatial portion of a scene being viewed by a video sensor. An area also includes a combination of areas from various scenes and/or images. An area can be an image-based space (e.g., a line, a rectangle, a polygon, or a circle in a video image) or a three-dimensional space (e.g., a cube, or an area of floor space in a building). 
       FIG. 12  illustrates identifying areas along an aisle in a grocery store. Four areas are identified: coffee; soda promotion; chips snacks; and bottled water. The areas are identified via a point-and-click interface with the system. 
     In block  33 , one or more temporal attributes of interest are optionally identified. Examples of a temporal attribute include: every 15 minutes; between 9:00 p.m. to 6:30 a.m.; less than 5 minutes; longer than 30 seconds; over the weekend; and within 20 minutes of. 
     In block  34 , a response is optionally identified. Examples of a response includes the following: activating a visual and/or audio alert on a system display; activating a visual and/or audio alarm system at the location; activating a silent alarm; activating a rapid response mechanism; locking a door; contacting a security service; forwarding data (e.g., image data, video data, video primitives; and/or analyzed data) to another computer system via a network, such as the Internet; saving such data to a designated computer-readable medium; activating some other sensor or surveillance system; tasking the computer system  11  and/or another computer system; and directing the computer system  11  and/or another computer system. 
     In block  35 , one or more discriminators are identified by describing interactions between video primitives (or their abstractions), spatial areas of interest, and temporal attributes of interest. An interaction is determined for a combination of one or more objects identified in block  31 , one or more spatial areas of interest identified in block  32 , and one or more temporal attributes of interest identified in block  33 . One or more responses identified in block  34  are optionally associated with each event discriminator. 
       FIG. 16 a    shows an exemplary video analysis portion of a video surveillance system according to an embodiment of the invention. In  FIG. 16 a   , a video sensor (for example, but not limited to, a video camera)  1601  may provide a video stream  1602  to a video analysis subsystem  1603 . Video analysis subsystem  1603  may then perform analysis of the video stream  1602  to derive video primitives, which may be stored in primitive storage  1605 . Primitive storage  1605  may be used to store non-video primitives, as well. Video analysis subsystem  1603  may further control storage of all or portions of the video stream  1602  in video storage  1604 , for example, quality and/or quantity of video, as discussed above. 
     Referring now to  FIG. 16 b   , once the video, and, if there are other sensors, the non-video primitives  161  are available, the system may detect events. The user tasks the system by defining rules  163  and corresponding responses  164  using the rule and response definition interface  162 . The rules are translated into event discriminators, and the system extracts corresponding event occurrences  165 . The detected event occurrences  166  trigger user defined responses  167 . A response may include a snapshot of a video of the detected event from video storage  168  (which may or may not be the same as video storage  1604  in  FIG. 16 a   ). The video storage  168  may be part of the video surveillance system, or it may be a separate recording device  15 . Examples of a response may include, but are not necessarily limited to, the following: activating a visual and/or audio alert on a system display; activating a visual and/or audio alarm system at the location; activating a silent alarm; activating a rapid response mechanism; locking a door; contacting a security service; forwarding or streaming data (e.g., image data, video data, video primitives; and/or analyzed data) to another computer system via a network, such as, but not limited to, the Internet; saving such data to a designated computer-readable medium; activating some other sensor or surveillance system; tasking the computer system  11  and/or another computer system; and/or directing the computer system  11  and/or another computer system. 
     The primitive data can be thought of as data stored in a database. To detect event occurrences in it, an efficient query language is required. Embodiments of the inventive system may include an activity inferencing language, which will be described below. 
     Traditional relational database querying schemas often follow a Boolean binary tree structure to allow users to create flexible queries on stored data of various types. Leaf nodes are usually of the form “property relationship value,” where a property is some key feature of the data (such as time or name); a relationship is usually a numerical operator (“&gt;”, “&lt;”, “=”, etc); and a value is a valid state for that property. Branch nodes usually represent unary or binary Boolean logic operators like “and”, “or”, and “not”. 
     This may form the basis of an activity query formulation schema, as in embodiments of the present invention. In case of a video surveillance application, the properties may be features of the object detected in the video stream, such as size, speed, color, classification (human, vehicle), or the properties may be scene change properties.  FIG. 17  gives examples of using such queries. In  FIG. 17 a   , the query, “Show me any red vehicle,”  171  is posed. This may be decomposed into two “property relationship value” (or simply “property”) queries, testing whether the classification of an object is vehicle  173  and whether its color is predominantly red  174 . These two sub-queries can combined with the Boolean operator “and”  172 . Similarly, in  FIG. 17 b   , the query, “Show me when a camera starts or stops moving,” may be expressed as the Boolean “or”  176  combination of the property sub-queries, “has the camera started moving”  177  and “has the camera stopped moving”  178 . 
     Embodiments of the invention may extend this type of database query schema in two exemplary ways: (1) the basic leaf nodes may be augmented with activity detectors describing spatial activities within a scene; and (2) the Boolean operator branch nodes may be augmented with modifiers specifying spatial, temporal and object interrelationships. 
     Activity detectors correspond to a behavior related to an area of the video scene. They describe how an object might interact with a location in the scene.  FIG. 18  illustrates three exemplary activity detectors.  FIG. 18 a    represents the behavior of crossing a perimeter in a particular direction using a virtual video tripwire (for further information about how such virtual video tripwires may be implemented, one may consult, e.g., U.S. Pat. No. 6,696,945).  FIG. 18 b    represents the behavior of loitering for a period of time on a railway track.  FIG. 18 c    represents the behavior of taking something away from a section of wall (for exemplary approaches to how this may be done, one may consult U.S. patent application Ser. No. 10/331,778, entitled, “Video Scene Background Maintenance—Change Detection &amp; Classification,” filed on Jan. 30, 2003). Other exemplary activity detectors may include detecting a person falling, detecting a person changing direction or speed, detecting a person entering an area, or detecting a person going in the wrong direction. 
       FIG. 19  illustrates an example of how an activity detector leaf node (here, tripwire crossing) can be combined with simple property queries to detect whether a red vehicle crosses a video tripwire  191 . The property queries  172 ,  173 ,  174  and the activity detector  193  are combined with a Boolean “and” operator  192 . 
     Combining queries with modified Boolean operators (combinators) may add further flexibility. Exemplary modifiers include spatial, temporal, object, and counter modifiers. 
     A spatial modifier may cause the Boolean operator to operate only on child activities (i.e., the arguments of the Boolean operator, as shown below a Boolean operator, e.g., in  FIG. 19 ) that are proximate/non-proximate within the scene. For example, “and—within 50 pixels of” may be used to mean that the “and” only applies if the distance between activities is less than 50 pixels. 
     A temporal modifier may cause the Boolean operator to operate only on child activities that occur within a specified period of time of each other, outside of such a time period, or within a range of times. The time ordering of events may also be specified. For example “and—first within 10 seconds of second” may be used to mean that the “and” only applies if the second child activity occurs not more than 10 seconds after the first child activity. 
     An object modifier may cause the Boolean operator to operate only on child activities that occur involving the same or different objects. For example “and—involving the same object” may be used to mean that the “and” only applies if the two child activities involve the same specific object. 
     A counter modifier may cause the Boolean operator to be triggered only if the condition(s) is/are met a prescribed number of times. A counter modifier may generally include a numerical relationship, such as “at least n times,” “exactly n times,” “at most n times,” etc. For example, “or—at least twice” may be used to mean that at least two of the sub-queries of the “or” operator have to be true. Another use of the counter modifier may be to implement a rule like “alert if the same person takes at least five items from a shelf.” 
       FIG. 20  illustrates an example of using combinators. Here, the required activity query is to “find a red vehicle making an illegal left turn”  201 . The illegal left turn may be captured through a combination of activity descriptors and modified Boolean operators. One virtual tripwire may be used to detect objects coming out of the side street  193 , and another virtual tripwire may be used to detect objects traveling to the left along the road  205 . These may be combined by a modified “and” operator  202 . The standard Boolean “and” operator guarantees that both activities  193  and  205  have to be detected. The object modifier  203  checks that the same object crossed both tripwires, while the temporal modifier  204  checks that the bottom-to-top tripwire  193  is crossed first, followed by the crossing of the right-to-left tripwire  205  no more than 10 seconds later. 
     This example also indicates the power of the combinators. Theoretically it is possible to define a separate activity detector for left turn, without relying on simple activity detectors and combinators. However, that detector would be inflexible, making it difficult to accommodate arbitrary turning angles and directions, and it would also be cumbersome to write a separate detector for all potential events. In contrast, using the combinators and simple detectors provides great flexibility. 
     Other examples of complex activities that can be detected as a combination of simpler ones may include a car parking and a person getting out of the car or multiple people forming a group, tailgating. These combinators can also combine primitives of different types and sources. Examples may include rules such as “show a person inside a room before the lights are turned off;” “show a person entering a door without a preceding card-swipe;” or “show if an area of interest has more objects than expected by an RFID tag reader,” i.e., an illegal object without an RFID tag is in the area. 
     A combinator may combine any number of sub-queries, and it may even combine other combinators, to arbitrary depths. An example, illustrated in  FIGS. 21 a  and 21 b   , may be a rule to detect if a car turns left  2101  and then turns right  2104 . The left turn  2101  may be detected with the directional tripwires  2102  and  2103 , while the right turn  2104  with the directional tripwires  2105  and  2106 . The left turn may be expressed as the tripwire activity detectors  2112  and  2113 , corresponding to tripwires  2102  and  2103 , respectively, joined with the “and” combinator  2111  with the object modifier “same”  2117  and temporal modifier “ 2112  before  2113 ”  2118 . Similarly, the right turn may be expressed as the tripwire activity detectors  2115  and  2116 , corresponding to tripwires  2105  and  2106 , respectively, joined with the “and” combinator  2114  with the object modifier “same”  2119  and temporal modifier “ 2115  before  2116 ”  2120 . To detect that the same object turned first left then right, the left turn detector  2111  and the right turn detector  2114  are joined with the “and” combinator  2121  with the object modifier “same”  2122  and temporal modifier “ 2111  before  2114 ”  2123 . Finally, to ensure that the detected object is a vehicle, a Boolean “and” operator  2125  is used to combine the left-and-right-turn detector  2121  and the property query  2124 . 
     All these detectors may optionally be combined with temporal attributes. Examples of a temporal attribute include: every 15 minutes; between 9:00 pm and 6:30 am; less than 5 minutes; longer than 30 seconds; and over the weekend. 
     In block  24  of  FIG. 2 , the video surveillance system is operated. The video surveillance system of the invention operates automatically, detects and archives video primitives of objects in the scene, and detects event occurrences in real time using event discriminators. In addition, action is taken in real time, as appropriate, such as activating alarms, generating reports, and generating output. The reports and output can be displayed and/or stored locally to the system or elsewhere via a network, such as the Internet.  FIG. 4  illustrates a flow diagram for operating the video surveillance system. 
     In block  41 , the computer system  11  obtains source video from the video sensors  14  and/or the video recorders  15 . 
     In block  42 , video primitives are extracted in real time from the source video. As an option, non-video primitives can be obtained and/or extracted from one or more other sensors  17  and used with the invention. The extraction of video primitives is illustrated with  FIG. 5 . 
       FIG. 5  illustrates a flow diagram for extracting video primitives for the video surveillance system. Blocks  51  and  52  operate in parallel and can be performed in any order or concurrently. In block  51 , objects are detected via movement. Any motion detection algorithm for detecting movement between frames at the pixel level can be used for this block. As an example, the three frame differencing technique can be used, which is discussed in {1}. The detected objects are forwarded to block  53 . 
     In block  52 , objects are detected via change. Any change detection algorithm for detecting changes from a background model can be used for this block. An object is detected in this block if one or more pixels in a frame are deemed to be in the foreground of the frame because the pixels do not conform to a background model of the frame. As an example, a stochastic background modeling technique, such as dynamically adaptive background subtraction, can be used, which is described in {1} and U.S. patent application Ser. No. 09/694,712 filed Oct. 24, 2000. The detected objects are forwarded to block  53 . 
     The motion detection technique of block  51  and the change detection technique of block  52  are complimentary techniques, where each technique advantageously addresses deficiencies in the other technique. As an option, additional and/or alternative detection schemes can be used for the techniques discussed for blocks  51  and  52 . Examples of an additional and/or alternative detection scheme include the following: the Pfinder detection scheme for finding people as described in {8}; a skin tone detection scheme; a face detection scheme; and a model-based detection scheme. The results of such additional and/or alternative detection schemes are provided to block  53 . 
     As an option, if the video sensor  14  has motion (e.g., a video camera that sweeps, zooms, and/or translates), an additional block can be inserted before blocks between blocks  51  and  52  to provide input to blocks  51  and  52  for video stabilization. Video stabilization can be achieved by affine or projective global motion compensation. For example, image alignment described in U.S. patent application Ser. No. 09/609,919, filed Jul. 3, 2000, now U.S. Pat. No. 6,738,424, which is incorporated herein by reference, can be used to obtain video stabilization. 
     In block  53 , blobs are generated. In general, a blob is any object in a frame. Examples of a blob include: a moving object, such as a person or a vehicle; and a consumer product, such as a piece of furniture, a clothing item, or a retail shelf item. Blobs are generated using the detected objects from blocks  51  and  52 . Any technique for generating blobs can be used for this block. An exemplary technique for generating blobs from motion detection and change detection uses a connected components scheme. For example, the morphology and connected components algorithm can be used, which is described in {1}. 
     In block  54 , blobs are tracked. Any technique for tracking blobs can be used for this block. For example, Kalman filtering or the CONDENSATION algorithm can be used. As another example, a template matching technique, such as described in {1}, can be used. As a further example, a multi-hypothesis Kalman tracker can be used, which is described in {5}. As yet another example, the frame-to-frame tracking technique described in U.S. patent application Ser. No. 09/694,712 filed Oct. 24, 2000, can be used. For the example of a location being a grocery store, examples of objects that can be tracked include moving people, inventory items, and inventory moving appliances, such as shopping carts or trolleys. 
     As an option, blocks  51 - 54  can be replaced with any detection and tracking scheme, as is known to those of ordinary skill. An example of such a detection and tracking scheme is described in {11}. 
     In block  55 , each trajectory of the tracked objects is analyzed to determine if the trajectory is salient. If the trajectory is insalient, the trajectory represents an object exhibiting unstable motion or represents an object of unstable size or color, and the corresponding object is rejected and is no longer analyzed by the system. If the trajectory is salient, the trajectory represents an object that is potentially of interest. A trajectory is determined to be salient or insalient by applying a salience measure to the trajectory. Techniques for determining a trajectory to be salient or insalient are described in {13} and {18}. 
     In block  56 , each object is classified. The general type of each object is determined as the classification of the object. Classification can be performed by a number of techniques, and examples of such techniques include using a neural network classifier {14} and using a linear discriminatant classifier {14}. Examples of classification are the same as those discussed for block  23 . 
     In block  57 , video primitives are identified using the information from blocks  51 - 56  and additional processing as necessary. Examples of video primitives identified are the same as those discussed for block  23 . As an example, for size, the system can use information obtained from calibration in block  22  as a video primitive. From calibration, the system has sufficient information to determine the approximate size of an object. As another example, the system can use velocity as measured from block  54  as a video primitive. 
     In block  43 , the video primitives from block  42  are archived. The video primitives can be archived in the computer-readable medium  13  or another computer-readable medium. Along with the video primitives, associated frames or video imagery from the source video can be archived. This archiving step is optional; if the system is to be used only for real-time event detection, the archiving step can be skipped. 
     In block  44 , event occurrences are extracted from the video primitives using event discriminators. The video primitives are determined in block  42 , and the event discriminators are determined from tasking the system in block  23 . The event discriminators are used to filter the video primitives to determine if any event occurrences occurred. For example, an event discriminator can be looking for a “wrong way” event as defined by a person traveling the “wrong way” into an area between 9:00 a.m. and 5:00 p.m. The event discriminator checks all video primitives being generated according to  FIG. 5  and determines if any video primitives exist which have the following properties: a timestamp between 9:00 a.m. and 5:00 p.m., a classification of “person” or “group of people”, a position inside the area, and a “wrong” direction of motion. The event discriminators may also use other types of primitives, as discussed above, and/or combine video primitives from multiple video sources to detect event occurrences. 
     In block  45 , action is taken for each event occurrence extracted in block  44 , as appropriate.  FIG. 6  illustrates a flow diagram for taking action with the video surveillance system. 
     In block  61 , responses are undertaken as dictated by the event discriminators that detected the event occurrences. The responses, if any, are identified for each event discriminator in block  162 . 
     In block  62 , an activity record is generated for each event occurrence that occurred. The activity record includes, for example: details of a trajectory of an object; a time of detection of an object; a position of detection of an object, and a description or definition of the event discriminator that was employed. The activity record can include information, such as video primitives, needed by the event discriminator. The activity record can also include representative video or still imagery of the object(s) and/or area(s) involved in the event occurrence. The activity record is stored on a computer-readable medium. 
     In block  63 , output is generated. The output is based on the event occurrences extracted in block  44  and a direct feed of the source video from block  41 . The output is stored on a computer-readable medium, displayed on the computer system  11  or another computer system, or forwarded to another computer system. As the system operates, information regarding event occurrences is collected, and the information can be viewed by the operator at any time, including real time. Examples of formats for receiving the information include: a display on a monitor of a computer system; a hard copy; a computer-readable medium; and an interactive web page. 
     The output can include a display from the direct feed of the source video from block  41  transmitted either via analog video transmission means or via network video streaming. For example, the source video can be displayed on a window of the monitor of a computer system or on a closed-circuit monitor. Further, the output can include source video marked up with graphics to highlight the objects and/or areas involved in the event occurrence. If the system is operating in forensic analysis mode, the video may come from the video recorder. 
     The output can include one or more reports for an operator based on the requirements of the operator and/or the event occurrences. Examples of a report include: the number of event occurrences which occurred; the positions in the scene in which the event occurrence occurred; the times at which the event occurrences occurred, representative imagery of each event occurrence; representative video of each event occurrence; raw statistical data; statistics of event occurrences (e.g., how many, how often, where, and when); and/or human-readable graphical displays. 
       FIGS. 13 and 14  illustrate an exemplary report for the aisle in the grocery store of  FIG. 15 . In  FIGS. 13 and 14 , several areas are identified in block  22  and are labeled accordingly in the images. The areas in  FIG. 13  match those in  FIG. 12 , and the areas in  FIG. 14  are different ones. The system is tasked to look for people who stop in the area. 
     In  FIG. 13 , the exemplary report is an image from a video marked-up to include labels, graphics, statistical information, and an analysis of the statistical information. For example, the area identified as coffee has statistical information of an average number of customers in the area of 2/hour and an average dwell time in the area as 5 seconds. The system determined this area to be a “cold” region, which means there is not much commercial activity through this region. As another example, the area identified as sodas has statistical information of an average number of customers in the area of 15/hour and an average dwell time in the area as 22 seconds. The system determined this area to be a “hot” region, which means there is a large amount of commercial activity in this region. 
     In  FIG. 14 , the exemplary report is an image from a video marked-up to include labels, graphics, statistical information, and an analysis of the statistical information. For example, the area at the back of the aisle has average number of customers of 14/hour and is determined to have low traffic. As another example, the area at the front of the aisle has average number of customers of 83/hour and is determined to have high traffic. 
     For either  FIG. 13  or  FIG. 14 , if the operator desires more information about any particular area or any particular area, a point-and-click interface allows the operator to navigate through representative still and video imagery of regions and/or activities that the system has detected and archived. 
       FIG. 15  illustrates another exemplary report for an aisle in a grocery store. The exemplary report includes an image from a video marked-up to include labels and trajectory indications and text describing the marked-up image. The system of the example is tasked with searching for a number of areas: length, position, and time of a trajectory of an object; time and location an object was immobile; correlation of trajectories with areas, as specified by the operator; and classification of an object as not a person, one person, two people, and three or more people. 
     The video image of  FIG. 15  is from a time period where the trajectories were recorded. Of the three objects, two objects are each classified as one person, and one object is classified as not a person. Each object is assigned a label, namely Person ID  1032 , Person ID  1033 , and Object ID  32001 . For Person ID  1032 , the system determined the person spent 52 seconds in the area and 18 seconds at the position designated by the circle. For Person ID  1033 , the system determined the person spent 1 minute and 8 seconds in the area and 12 seconds at the position designated by the circle. The trajectories for Person ID  1032  and Person ID  1033  are included in the marked-up image. For Object ID  32001 , the system did not further analyze the object and indicated the position of the object with an X. 
     Referring back to block  22  in  FIG. 2 , calibration can be (1) manual, (2) semi-automatic using imagery from a video sensor or a video recorder, or (3) automatic using imagery from a video sensor or a video recorder. If imagery is required, it is assumed that the source video to be analyzed by the computer system  11  is from a video sensor that obtained the source video used for calibration. 
     For manual calibration, the operator provides to the computer system  11  the orientation and internal parameters for each of the video sensors  14  and the placement of each video sensor  14  with respect to the location. The computer system  11  can optionally maintain a map of the location, and the placement of the video sensors  14  can be indicated on the map. The map can be a two-dimensional or a three-dimensional representation of the environment. In addition, the manual calibration provides the system with sufficient information to determine the approximate size and relative position of an object. 
     Alternatively, for manual calibration, the operator can mark up a video image from the sensor with a graphic representing the appearance of a known-sized object, such as a person. If the operator can mark up an image in at least two different locations, the system can infer approximate camera calibration information. 
     For semi-automatic and automatic calibration, no knowledge of the camera parameters or scene geometry is required. From semi-automatic and automatic calibration, a lookup table is generated to approximate the size of an object at various areas in the scene, or the internal and external camera calibration parameters of the camera are inferred. 
     For semi-automatic calibration, the video surveillance system is calibrated using a video source combined with input from the operator. A single person is placed in the field of view of the video sensor to be semi-automatic calibrated. The computer system  11  receives source video regarding the single person and automatically infers the size of person based on this data. As the number of locations in the field of view of the video sensor that the person is viewed is increased, and as the period of time that the person is viewed in the field of view of the video sensor is increased, the accuracy of the semi-automatic calibration is increased. 
       FIG. 7  illustrates a flow diagram for semi-automatic calibration of the video surveillance system. Block  71  is the same as block  41 , except that a typical object moves through the scene at various trajectories. The typical object can have various velocities and be stationary at various positions. For example, the typical object moves as close to the video sensor as possible and then moves as far away from the video sensor as possible. This motion by the typical object can be repeated as necessary. 
     Blocks  72 - 75  are the same as blocks  51 - 54 , respectively. 
     In block  76 , the typical object is monitored throughout the scene. It is assumed that the only (or at least the most) stable object being tracked is the calibration object in the scene (i.e., the typical object moving through the scene). The size of the stable object is collected for every point in the scene at which it is observed, and this information is used to generate calibration information. 
     In block  77 , the size of the typical object is identified for different areas throughout the scene. The size of the typical object is used to determine the approximate sizes of similar objects at various areas in the scene. With this information, a lookup table is generated matching typical apparent sizes of the typical object in various areas in the image, or internal and external camera calibration parameters are inferred. As a sample output, a display of stick-sized figures in various areas of the image indicate what the system determined as an appropriate height. Such a stick-sized figure is illustrated in  FIG. 11 . 
     For automatic calibration, a learning phase is conducted where the computer system  11  determines information regarding the location in the field of view of each video sensor. During automatic calibration, the computer system  11  receives source video of the location for a representative period of time (e.g., minutes, hours or days) that is sufficient to obtain a statistically significant sampling of objects typical to the scene and thus infer typical apparent sizes and locations. 
       FIG. 8  illustrates a flow diagram for automatic calibration of the video surveillance system. Blocks  81 - 86  are the same as blocks  71 - 76  in  FIG. 7 . 
     In block  87 , trackable regions in the field of view of the video sensor are identified. A trackable region refers to a region in the field of view of a video sensor where an object can be easily and/or accurately tracked. An untrackable region refers to a region in the field of view of a video sensor where an object is not easily and/or accurately tracked and/or is difficult to track. An untrackable region can be referred to as being an unstable or insalient region. An object may be difficult to track because the object is too small (e.g., smaller than a predetermined threshold), appear for too short of time (e.g., less than a predetermined threshold), or exhibit motion that is not salient (e.g., not purposeful). A trackable region can be identified using, for example, the techniques described in {13}. 
       FIG. 10  illustrates trackable regions determined for an aisle in a grocery store. The area at the far end of the aisle is determined to be insalient because too many confusers appear in this area. A confuser refers to something in a video that confuses a tracking scheme. Examples of a confuser include: leaves blowing; rain; a partially occluded object; and an object that appears for too short of time to be tracked accurately. In contrast, the area at the near end of the aisle is determined to be salient because good tracks are determined for this area. 
     In block  88 , the sizes of the objects are identified for different areas throughout the scene. The sizes of the objects are used to determine the approximate sizes of similar objects at various areas in the scene. A technique, such as using a histogram or a statistical median, is used to determine the typical apparent height and width of objects as a function of location in the scene. In one part of the image of the scene, typical objects can have a typical apparent height and width. With this information, a lookup table is generated matching typical apparent sizes of objects in various areas in the image, or the internal and external camera calibration parameters can be inferred. 
       FIG. 11  illustrates identifying typical sizes for typical objects in the aisle of the grocery store from  FIG. 10 . Typical objects are assumed to be people and are identified by a label accordingly. Typical sizes of people are determined through plots of the average height and average width for the people detected in the salient region. In the example, plot A is determined for the average height of an average person, and plot B is determined for the average width for one person, two people, and three people. 
     For plot A, the x-axis depicts the height of the blob in pixels, and the y-axis depicts the number of instances of a particular height, as identified on the x-axis, that occur. The peak of the line for plot A corresponds to the most common height of blobs in the designated region in the scene and, for this example, the peak corresponds to the average height of a person standing in the designated region. 
     Assuming people travel in loosely knit groups, a similar graph to plot A is generated for width as plot B. For plot B, the x-axis depicts the width of the blobs in pixels, and the y-axis depicts the number of instances of a particular width, as identified on the x-axis, that occur. The peaks of the line for plot B correspond to the average width of a number of blobs. Assuming most groups contain only one person, the largest peak corresponds to the most common width, which corresponds to the average width of a single person in the designated region. Similarly, the second largest peak corresponds to the average width of two people in the designated region, and the third largest peak corresponds to the average width of three people in the designated region. 
       FIG. 9  illustrates an additional flow diagram for the video surveillance system of the invention. In this additional embodiment, the system analyzes archived video primitives with event discriminators to generate additional reports, for example, without needing to review the entire source video. Anytime after a video source has been processed according to the invention, video primitives for the source video are archived in block  43  of  FIG. 4 . The video content can be reanalyzed with the additional embodiment in a relatively short time because only the video primitives are reviewed and because the video source is not reprocessed. This provides a great efficiency improvement over current state-of-the-art systems because processing video imagery data is extremely computationally expensive, whereas analyzing the small-sized video primitives abstracted from the video is extremely computationally cheap. As an example, the following event discriminator can be generated: “The number of people stopping for more than 10 minutes in area A in the last two months.” With the additional embodiment, the last two months of source video does not need to be reviewed. Instead, only the video primitives from the last two months need to be reviewed, which is a significantly more efficient process. 
     Block  91  is the same as block  23  in  FIG. 2 . 
     In block  92 , archived video primitives are accessed. The video primitives are archived in block  43  of  FIG. 4 . 
     Blocks  93  and  94  are the same as blocks  44  and  45  in  FIG. 4 . 
     As an exemplary application, the invention can be used to analyze retail market space by measuring the efficacy of a retail display. Large sums of money are injected into retail displays in an effort to be as eye-catching as possible to promote sales of both the items on display and subsidiary items. The video surveillance system of the invention can be configured to measure the effectiveness of these retail displays. 
     For this exemplary application, the video surveillance system is set up by orienting the field of view of a video sensor towards the space around the desired retail display. During tasking, the operator selects an area representing the space around the desired retail display. As a discriminator, the operator defines that he or she wishes to monitor people-sized objects that enter the area and either exhibit a measurable reduction in velocity or stop for an appreciable amount of time. 
     After operating for some period of time, the video surveillance system can provide reports for market analysis. The reports can include: the number of people who slowed down around the retail display; the number of people who stopped at the retail display; the breakdown of people who were interested in the retail display as a function of time, such as how many were interested on weekends and how many were interested in evenings; and video snapshots of the people who showed interest in the retail display. The market research information obtained from the video surveillance system can be combined with sales information from the store and customer records from the store to improve the analysts understanding of the efficacy of the retail display. 
     The embodiments and examples discussed herein are non-limiting examples. 
     The invention is described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the claims is intended to cover all such changes and modifications as fall within the true spirit of the invention.