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 Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations ...

electronic Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor * ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electronic device *Electronic co ...

methods. When it is done by natural organisms, it is called

motion perception Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs. Although this process appears straightforward to most observers, it has proven to be a difficult ...

Methods

Motion can be detected by monitoring changes in: *Infrared light (passive and active sensors) *Visible light (video and camera systems) *Radio frequency energy (radar, microwave and tomographic motion detection) *Sound (microphones, other acoustic sensors) *Kinetic energy (

triboelectric The triboelectric effect (also known as triboelectric charging) is a type of contact electrification on which certain materials become electrically charged after they are separated from a different material with which they were in contact. Rub ...

, seismic, and inertia-switch sensors) *Magnetism (magnetic sensors, magnetometers) *Wi-Fi Signals ( WiFi Sensing)

Mechanical

The most basic forms of mechanical motion detection utilize a switch or trigger. For example, the keys of a

typewriter A typewriter is a mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of keys, and each one causes a different single character to be produced on paper by striking an inked ribbon selectivel ...

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.

Electronic

The principal methods by which

motion In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and m ...

can be electronically identified are optical and acoustic.

Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

light or

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...

technology can be used for optical detection. Motion-detection devices such as PIR

motion detector A motion detector is an electrical device that utilizes a sensor to detect nearby motion. Such a device is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. They form a vital c ...

s have a sensor that detects a disturbance in the

infrared spectrum Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

. A signal can then activate an alarm, and/or a

camera A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...

to capture an image or video of the event. This method's chief applications are: * Detection of unauthorized entry * Turning lights on/off when an area is entered/vacated * Activating a camera to record new events (e.g. human activity) A simple

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...

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 An art gallery is a room or a building in which visual art is displayed. In Western cultures from the mid-15th century, a gallery was any long, narrow covered passage along a wall, first used in the sense of a place for art in the 1590s. The lon ...

. With a panning camera, models based on

optical flow Optical flow or optic flow is the pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer and a scene. Optical flow can also be defined as the distribution of apparent veloci ...

are used to distinguish between apparent background motion caused by the camera's movement and that of independently moving objects.Bewley, A., Guizilini, V., Ramos, F., & Upcroft, B. (2014)
Online Self-Supervised Multi-Instance Segmentation of Dynamic Objects
In International Conference on Robotics and Automation (pp. 1296–1303). Hong Kong, China: IEEE.

Devices

Motion detectors are often integrated components of systems that automatically perform tasks, or alert users of motion in an area. An

occupancy sensor An occupancy sensor is an indoor motion detecting device used to detect the presence of a person to automatically control lights or temperature or ventilation systems. The sensors use infrared, ultrasonic, microwave, or other technology. The te ...

detects the entry or movement of a person or thing within a certain space.

Motion controllers In video games and entertainment systems, a motion controller is a type of game controller that uses accelerometers or other sensors to track motion and provide input. History Motion controllers using accelerometers are used as controllers for ...

are also used for

video game consoles A video game console is an electronic device that outputs a video signal or image to display a video game that can be played with a game controller. These may be home consoles, which are generally placed in a permanent location connected to a ...

game controller A game controller, gaming controller, or simply controller, is an input device used with video games or entertainment systems to provide input to a video game, typically to control an object or character in the game. Before the seventh generatio ...

s. A camera can also allow the body's movements to be used for control, such as in the

Kinect Kinect is a line of motion sensing input devices produced by Microsoft and first released in 2010. The devices generally contain RGB cameras, and infrared projectors and detectors that map depth through either structured light or time of fli ...

system.

References

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External links

Relational Motion Detection

Motion Detection Algorithms In Image Processing

Presence and Absence detection explained

Motion detection sample algorithm realization video
Security Motion in computer vision