Motion detection

Motion detection is the sensing (usually by electronic devices) of physical movement in a given area. The principal methods by which motion can be identified are infra-red detection and acoustical detection. Motion detection sensors are available which can easily detect movement and produce an alarm or switch on an image recording device. There are motion detectors which employ cameras connected to a computer and this detects certain objects moving.

The chief applications for such detection are (a) detection of unauthorized entry, (b) detection of cessation of occupancy of an area to extinguish lighting and (c) detection of a moving object which triggers a camera to record subsequent events. The motion detector is thus a lynchpin of electronic security systems, but is also a valuable tool in preventing illuminating unoccupied spaces.

A simple algorithm for motion detection by a fixed camera compares the current image with a reference image and simply counts the number of different pixels. Since images will naturally differ due to factors such as varying lighting, camera flicker, and CCD dark currents, pre-processing is useful to reduce the number of false positive alarms.

More complex algorithms are necessary to detect motion when the camera itself is moving, or when the motion of a specific object must be detected in a field containing other movement which can be ignored. An example might be a painting surrounded by visitors in an art gallery.

When motion detection is accomplished by natural organisms, we speak of motion perception.

References

• Motion Detection Technologies
• Motion Detection and Recognition Research
• Passive Infrared Security Beams