Motion detection is the process of detecting a change in the position of an object relative to its surroundings or a change in the surroundings relative to an object. It can be achieved by either mechanical or electronic methods.[1] When it is done by natural organisms, it is called motion perception.
See also: Motion detector § Technology |
Motion can be detected by monitoring changes in:
The most basic forms of mechanical motion detection utilize a switch or trigger. For example, the keys of a typewriter use a mechanical method of detecting motion, where each key is a switch that is either off or on, and each letter that appears is a result of the key's motion.
See also: Motion estimation and Moving object detection |
The principal methods by which motion can be electronically identified are optical and acoustic. Infrared light or laser technology can be used for optical detection. Motion-detection devices such as PIR motion detectors have a sensor that detects a disturbance in the infrared spectrum. A signal can then activate an alarm, and/or a camera to capture an image or video of the event.[3][4]
This method's chief applications are:
A simple algorithm for motion detection by a fixed camera compares the current image with a reference image and monitors the number of different pixels. Since images 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 panning, or when a specific object's motion must be detected in a field containing other, irrelevant movement—for example, a painting surrounded by visitors in an art gallery. With a panning camera, models based on optical flow are used to distinguish between apparent background motion caused by the camera's movement and that of independently moving objects.[5]
Motion detectors are often integrated components of systems that automatically perform tasks, or alert users of motion in an area. An occupancy sensor detects the entry or movement of a person or thing within a certain space.
Motion controllers are also used for video game consoles as game controllers. A camera can also allow the body's movements to be used for control, such as in the Kinect system.