Motion Detection with Sophisticated Video Security Systems
At one time, a computer was only needed by NASA or science fiction movies. Now a computer is nearly as common as a television. Likewise, video security systems have been combined with computer technology to provide intelligent monitors outside of the high-profile environments.
We all have noted the security cameras at the
airport and bank. The newest generation
of video security equipment is taking advantage of technology that was
developed for high definition television and satellite TV: digital video.
Once the signal is in digital format, it can easily be combined with computer
technology to produce capabilities that seem at home in a
First generation motion detection systems were plagued by a tendency to respond late to events. If, for example, an auto passed the field of view, by the time the logic measured the movement and started recording, the auto was almost out of view. Engineers solved this problem by continuously saving 1-2 seconds of data to a buffer (short-term storage). Once the logic of motion detection reacted, the data in the buffer is added to the record, and so the response time appears to be negligible.
Motion Detection Variable Sensitivity
Modern motion detection systems are much more sophisticated than the motion sensors we know from burglar alarms. A video motion detector can be configured with variable sensitivity over the area. This allows us to realize some interesting possibilities.
Motion detection video surveillance systems save imagery only when triggered, providing a time stamped record of events as they occur without recording inactivity between events. Before the capabilities of motion detection, video cassette recorders would run continuously, and hours and hours of video would have to be viewed to find a specific event.
With this technology, each image received by the camera is processed by software and compared to the previous image. If the system detects changes that exceed the threshold (a parameter set by the user), the system implements the predefined action. The action could be simply that the video is saved, and/or a cell-phone text message or email is sent, or a relay is activated to turn on lights or an alarm.
Motion Detection Setup for Video Security Systems
Areas of the image can be set as insensitive by excluding certain portions of the screen. For example, motion of specific objects that must be protected in an environment where other movement should be ignored can be performed (a painting surrounded by visitors in a museum). Another example is the monitoring of a parking lot surrounded by trees; the area of the image that encompasses the trees could be set off-limits, so that only vehicles and pedestrians activate the motion detection. It should be noted that outdoor monitoring is inherently more prone to false alarms than indoor monitoring. For example lightning in a thunderstorm will almost always cause the detection of motion.
During setup, the image is separated into grids (grid patterns of 100-500 zones are common). Setup is simple. A static image is displayed with a grid overlay. A mouse is used to select areas, and only the highlighted boxes are active. Each grid can be set with the appropriate sensitivity.
Time limits can be set so that the motion detection is not active until defined periods, and these periods can be different for each day of the week. This feature could be used for the monitor of a warehouse that is busy during the day, but is idle at night.
Because of advances in technology, systems that once seemed appropriate only for Mission Impossible movies can be implemented by a small business or homeowner. Someday, these systems will be as commonplace as the old-fashioned burglar alarm is today.