Patent Application
20050226338
1. Field of Invention
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.
2. Description of Related Art
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.
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.
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.
Related apparatuses are also presented.
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:
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.
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.
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.
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'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.
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.
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'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.
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'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.
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.
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.
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.
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.
Note that the steps regarding selecting a particular video source are not need when there is only one video source.
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.
