Motion detection
Encyclopedia
Motion
detection is a process of confirming a change in position of an object relative to its surroundings or the change in the surroundings relative to an object. This detection can be achieved by both mechanical
and electronic
methods. In addition to discrete
, on or off motion detection, it can also consist of magnitude detection that can measure and quantify the strength or speed of this motion or the object that created it.
When motion detection is accomplished by natural organisms, it is called motion perception
.
Motion can be detected by: sound (acoustic sensors), opacity (optical and infrared sensors and video image processors), geomagnetism (magnetic sensors, magnetometers), reflection of transmitted energy (infrared laser radar, ultrasonic sensors, and microwave radar sensors), electromagnetic induction (inductive-loop detectors), and vibration (triboelectric, seismic, and inertia-switch sensors). Acoustic sensors are based on: electret
effect, inductive coupling
, capacitive coupling
, triboelectric effect, piezoelectric effect, and fiber optic transmission
. Radar
intrusion sensors have the lowest rate of false alarms.
, or even the keys on the keyboards used to type this article employ a mechanical method of detecting motion. Each key is a manual switch that is either off or on. Each letter that appears is a result of motion on that corresponding key and the switch being turned on. This simple binary code
concept is at the heart of the digital age, with mechanical switches being replaced by ever shrinking Transistors.
can be electronically identified are optical detection and acoustical detection. Infrared
light or laser
technology may be used for optical detection. Motion detection devices, such as PIR motion detectors, have a sensor that detects a disturbance in the infrared spectrum, such as a person or an animal. Once detected, an electronic signal can activate an alarm or a camera
that can capture an image or video of the motioner.
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 linchpin of electronic security systems, but is also a valuable tool in preventing the illumination of 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 pixel
s. Since images will naturally differ due to factors such as varying lighting, camera flicker
, and CCD
dark current
s, 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
.
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
detection is a process of confirming a change in position of an object relative to its surroundings or the change in the surroundings relative to an object. This detection can be achieved by both mechanical
Mechanical
Mechanical may refer to:* Mechanical engineering, a branch of engineering concerned with the application of physical mechanics* HVAC , the mechanical systems of a building...
and electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
methods. In addition to discrete
Discrete
Discrete in science is the opposite of continuous: something that is separate; distinct; individual.Discrete may refer to:*Discrete particle or quantum in physics, for example in quantum theory...
, on or off motion detection, it can also consist of magnitude detection that can measure and quantify the strength or speed of this motion or the object that created it.
When motion detection is accomplished by natural organisms, it is called motion perception
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...
.
Motion can be detected by: sound (acoustic sensors), opacity (optical and infrared sensors and video image processors), geomagnetism (magnetic sensors, magnetometers), reflection of transmitted energy (infrared laser radar, ultrasonic sensors, and microwave radar sensors), electromagnetic induction (inductive-loop detectors), and vibration (triboelectric, seismic, and inertia-switch sensors). Acoustic sensors are based on: electret
Electret
Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885...
effect, inductive coupling
Inductive coupling
In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...
, capacitive coupling
Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...
, triboelectric effect, piezoelectric effect, and fiber optic transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
. Radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
intrusion sensors have the lowest rate of false alarms.
Mechanical Detection
The most basic form of mechanical motion detection is in the form of a switch or trigger. These motion detection devices are common in our everyday lives. The keys of a typewriterTypewriter
A typewriter is a mechanical or electromechanical device with keys that, when pressed, cause characters to be printed on a medium, usually paper. Typically one character is printed per keypress, and the machine prints the characters by making ink impressions of type elements similar to the pieces...
, or even the keys on the keyboards used to type this article employ a mechanical method of detecting motion. Each key is a manual switch that is either off or on. Each letter that appears is a result of motion on that corresponding key and the switch being turned on. This simple binary code
Binary code
A binary code is a way of representing text or computer processor instructions by the use of the binary number system's two-binary digits 0 and 1. This is accomplished by assigning a bit string to each particular symbol or instruction...
concept is at the heart of the digital age, with mechanical switches being replaced by ever shrinking Transistors.
Electronic Detection
The principal methods by which motionMotion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
can be electronically identified are optical detection and acoustical detection. Infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
light or laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
technology may be used for optical detection. Motion detection devices, such as PIR motion detectors, have a sensor that detects a disturbance in the infrared spectrum, such as a person or an animal. Once detected, an electronic signal can activate an alarm or a camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
that can capture an image or video of the motioner.
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
Motion detector
A motion detector is a device for motion detection. That is, it is a device that contains a physical mechanism or electronic sensor that quantifies motion that can be either integrated with or connected to other devices that alert the user of the presence of a moving object within the field of view...
is thus a linchpin of electronic security systems, but is also a valuable tool in preventing the illumination of unoccupied spaces
Over-illumination
Over-illumination is the presence of lighting intensity beyond that required for a specified activity. Over-illumination was commonly ignored between 1950 and 1995, especially in office and retail environments; only since then has the interior design community begun to reconsider this practice.The...
.
A simple algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
for motion detection by a fixed camera compares the current image with a reference image and simply counts the number of different pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s. Since images will naturally differ due to factors such as varying lighting, camera flicker
Flicker (screen)
Flicker is a visible fading between cycles displayed on video displays, especially the refresh interval on cathode ray tube based computer screens. Flicker occurs on CRTs when they are driven at a low refresh rate, allowing the brightness to drop for time intervals sufficiently long to be noticed...
, and CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
dark current
Dark current
Dark current is the constant response exhibited by a receptor of radiation during periods when it is not actively being exposed to light. It may refer to:...
s, pre-processing is useful to reduce the number of false positive
Type I and type II errors
In statistical test theory the notion of statistical error is an integral part of hypothesis testing. The test requires an unambiguous statement of a null hypothesis, which usually corresponds to a default "state of nature", for example "this person is healthy", "this accused is not guilty" or...
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
Art gallery
An art gallery or art museum is a building or space for the exhibition of art, usually visual art.Museums can be public or private, but what distinguishes a museum is the ownership of a collection...
.