Abstract:
Image data from a video surveillance camera is moved from a volatile memory such as a circular buffer to a non-volatile memory such as a flash memory when a loss of signal from the camera is detected. The loss of signal may occur when an intruder disables the system such as by cutting a cable, by vandalizing the camera so that it no longer can transmit image data, or removing the camera altogether. The loss of signal is detected by determining whether a signal portion such as a start of active video code, end of active video code, or horizontal or vertical blanking interval, is present on a communication path of the camera. The system ensures that an image of the intruder is captured and stored before the system is disabled. Analog signals from the camera may be digitized for storage.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention relates generally to a method and system for storing data from a video surveillance camera when a signal from the camera is lost, such as due to power loss or vandalism.  
         [0003]     2. Description of Related Art  
         [0004]     Video surveillance cameras have become increasingly popular due to security concerns in businesses, homes and public spaces. Such cameras typically provide analog or digital images via a cable to a secure location where the images are monitored by personnel and/or stored in memory for subsequent viewing. However, this approach requires a substantial amount of data to be stored. To address this concern, schemes have been developed to store data only when a triggering event has occurred. For example, a motion detector or door or window detector may be coupled to a video surveillance system so that images are recorded only when the motion of an intruder is detected. This approach is problematic since the motion detector may provide false alarms when persons who are not intruders set off the motion detector. Moreover, the intruder may disable the system such as by cutting the cable, vandalizing the camera so that it no longer can transmit image data, or removing the camera altogether. In such cases, an image of the intruder may not be captured and stored before the system is disabled.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     To overcome these and other deficiencies in the prior art, the present invention describes a method and system for storing buffered data from a video surveillance camera when a loss of signal from the camera is detected.  
         [0006]     In one aspect of the invention, a method for storing image data from at least one camera includes: (a) monitoring a communication path of the at least one camera to determine whether a signal of the at least one camera is present on the communication path, (b) receiving image data from the signal of the at least one camera via the communication path when the signal of the at least one camera is present on the communication path, (c) storing the received image data in a first storage location, and (d) copying the received image data that is stored in the first storage location to a second storage location when the monitoring determines that the signal of the at least one camera is no longer present on the communication path.  
         [0007]     Related apparatuses are also presented. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     These and other features, benefits and advantages of the present invention will become apparent by reference to the following text and figures, with like reference numbers referring to like structures across the views, wherein:  
         [0009]      FIG. 1  illustrates an overview of an apparatus for storing data from a camera;  
         [0010]      FIG. 2  illustrates an overview of a method for storing data from a camera; and  
         [0011]      FIG. 3  illustrates a more detailed view of a method for storing data from a camera. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  illustrates an overview of an apparatus for storing data from a camera. Generally, the invention is suitable for use with any type of camera, including those that provide analog or digital data signals. For example, analog signals may be provided according to a conventional television format such as NTSC, PAL or SECAM. Moreover, interlaced or non-interlaced scanning may be used. Digital cameras, such as those using CCDs or CMOS sensors, may provide static images according to a format such as JPEG. Various type of cameras used for surveillance are known in the art. The invention is also suitable for use with one or multiple cameras.  
         [0013]     The data storage apparatus  100  is configured for the case where image data from multiple cameras is received in analog form. Multiple cameras, denoted in an example as camera A ( 170 ), camera B ( 180 ) and camera C ( 190 ) are provided. Each of the cameras  170 ,  180  and  190  communicates with the data storage apparatus  100  via respective communication paths  172 ,  182  and  192 , such as cables. Wireless paths may also be used. Typically, the cameras are positioned around a location to be monitored, such as the interior or exterior of a business. The cameras are mounted to a wall or ceiling and a cable is run from each camera to the data storage apparatus  100 , which may be in a secure location such as a locked office in the business. Separate wires are typically also run to the camera from a power supply to power the cameras.  
         [0014]     In one possible approach suitable for use with analog cameras, the cameras  170 ,  180  and  190  continuously send data signals to the data storage apparatus  100 . The data storage apparatus  100  includes a demultiplexer (demux)  105  that reads one of the signals at a time in a round robin manner. The demux  105  is not needed if there is only one camera. The signal that is being read is digitized at an analog-to-digital (A/D) converter  110  and decoded at a decoder  115 . As an example, the decoder  115  may use the Philips Semiconductor SAA7111A Enhanced Video Input Processor (EVIP) and SAA7114 PAL/NTSC/SECAM video decoder with adaptive PAL/NTSC comb filter, VBI-data slicer and high performance scaler. The decoder  115  provides digitized images from the analog signal as a series of static frames or snapshots. The digitized images may be provided as a CCIR656 bit stream, for instance. The analog signals from the different cameras may be processed in turn to obtain digital snapshot images at a fixed interval for each camera such as every second. Each snapshot image is derived from a frame or field of the analog signal.  
         [0015]     The processor  125  interacts with the decoder  115  to store the snapshot images in a volatile memory  120  such as a circular SDRAM buffer. To reduce costs, the volatile memory  120  has a capacity that is sufficient to store a limited number of frames, e.g., up to sixty frames total, or twenty frames, from each of the three cameras. When the volatile memory  120  becomes filled with image data, the older frames are removed while the newer frames are stored, in a first-in, first out manner. Thus, assuming there is a one second interval between frames, for instance, there is a twenty-second snapshot history stored in the volatile memory for each camera.  
         [0016]     In accordance with the invention, the data storage apparatus  100  detects when the signal from a camera is no longer present on the respective communication path. This may be achieved in various ways. For example, the processor  125  may detect whether a specified portion of the camera&#39;s signal is present on the respective communication path by detecting whether a specified code is output from the decoder  115 . The code may identify the end of active video (EAV), start of active video (SAV), or a horizontal or vertical blanking interval (HSYNC or VSYNC, respectively), for instance: In the CCIR  656  standard, for example, each line begins with an EAV code which indicates the end of active video for the previous line, a blanking interval, and an SAV code which indicates the start of active video for the current line, followed by the line of active video. EAV and SAV codes have a fixed format, including a 3-byte preamble of 0×FF, 0×00, 0×00 followed by the SAV or EAV code byte. It is also possible to detect other signal portions, such as color burst codes, when color images are used.  
         [0017]     The processor  125  detects the signal portion for each camera to confirm that the associated signal is present on the associated communication path. If the signal portion cannot be detected, the processor  125  initiates a copy or transfer of the image data stored in the volatile memory  120  to a non-volatile memory  130 , such as a flash memory. In one approach, when multiple cameras are used, the image data from each camera is transferred when the signal from only one camera is lost. In another approach, only the image data from each camera whose signal is lost is transferred. The image data associated with a particular camera may be identified by meta data associated with the image data.  
         [0018]     The non-volatile memory  130  provides a permanent storage of the currently buffered image data so the image data can subsequently be reviewed. If the buffered image data was not transferred to a permanent storage, the circular buffer  120  would continue to store blank or null images in place of the existing valid images until the buffer was eventually filled with useless blank images. The approach of the invention thus allows review of the area imaged by a camera for a period of time preceding the loss of the camera&#39;s signal, which could be caused, e.g., by an intruder or vandal cutting the cable used for the communication path or otherwise disabling the camera so that it no longer transmits a valid signal on the communication path to the data storage apparatus  100 . For instance, an image of the intruder or vandal is likely to be stored as the person approach the camera to disable it. The person can then be more easily identified and apprehended.  
         [0019]     Note also that the data storage apparatus  100  may communicate image data via a network such as the Internet or an intranet. For example, the non-volatile memory  130  may be located remotely from the data storage apparatus  100 , such as at a central location that is monitored by personnel. When a camera&#39;s signal is lost, the central location is notified via the network and the image data is communicated to the central location. An alarm message can also be communicated to the central location. This approach is advantageous since image data from different locations can be monitored centrally.  
         [0020]     In a configuration where the cameras provide digital images to the data storage apparatus  100 , the A/D converter  110  is not needed. Such digital data may be provided by the cameras in the CCIR656 format, for instance.  
         [0021]     The processor  125  may include a memory as a program storage device for storing software instructions that are executed to achieve the functionality described herein, including detecting the signal portions from the cameras and controlling the storage of the image data.  
         [0022]      FIG. 2  illustrates an overview of a method for storing data from a camera. At block  200 , a determination is made as to whether a signal is present from a camera on the associated communication path. This may involve determining whether a signal portion such as an SAV or EAV code is present, as discussed above, for instance. If the signal is present, an image from the signal, such as a frame, is stored in a volatile memory such as a circular buffer. After a waiting period, e.g., one second, at block  220 , the step of block  200  is repeated to again determine whether the signal is still present on the communication path. When the signal is no longer present, processing proceeds at block  230 . Specifically, the previously-cached frames in the circular buffer are copied to a non-volatile memory. Note that the steps shown may be repeated for each camera when there are multiple cameras.  
         [0023]      FIG. 3  illustrates a more detailed view of a method for storing data from a camera. Block  300  denotes a data process that may involve processing data in the CCIR 656 data format, for instance. At block  302 , the processor  125  looks for a portion of the camera&#39;s signal, such as an EAV/SAV code, HSYNC, VSYNC or color burst, in the bit stream that is output from the video decoder  115 . At block  304 , the bit stream is demultiplexed to recover separate Y, U and V data components, which are stored in the circular buffer  120  in planar format. At block  306 , a sub-sampling algorithm is applied to achieve a 4:2:2 planar format. Optionally, the data is scaled to Common Intermediate Format (CIF) video size. Note that signaling of the SAV or EAV to the DSPCPU, e.g., processor  125 , may be performed directly from the video decoder (e.g., the SAA7114). The data process at block  300  provides information including whether a signal source is detected, and whether a signal frame/field is acquired.  
         [0024]     Starting at block  310 , a main process or task runs. Such a task may run for each camera. The task waits for a request to acquire a digital video frame/field. At block  315 , a determination is made as to whether a video source, e.g., a particular camera, is already selected. If a video source is already selected, processing proceeds at block  330 , where a digital frame is acquired from the selected source. At block  335 , a determination is made as to whether the video source is detected. If the video source is detected, a digital frame from the video source is saved in the circular buffer at block  340 . The task may subsequently be repeated at block  310 . If the video source is not detected at block  335 , the entire contents of the circular buffer are saved to the non-volatile memory at block  345 .  
         [0025]     If the video source has not been selected at block  315 , the process switches to the selected video source at block  320 , and a digital frame is acquired from the selected source at block  330 . Processing then proceeds at block  335  as discussed above.  
         [0026]     Note that the steps regarding selecting a particular video source are not need when there is only one video source.  
         [0027]     The invention has been described herein with reference to particular exemplary embodiments. Certain alterations and modifications may be apparent to those skilled in the art, without departing from the scope of the invention. The exemplary embodiments are meant to be illustrative, not limiting of the scope of the invention, which is defined by the appended claims.