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Encyclopedia > Flicker fusion threshold

The flicker fusion threshold (or flicker fusion rate) is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer (this article centers around human observers). Flicker fusion threshold is related to Persistence of vision. Image File history File links Broom_icon. ... Psychophysics is the branch of cognitive psychology dealing with the relationship between physical stimuli and their perception. ... This does not cite any references or sources. ... In general, an observer is any system which receives information from an object. ... According to the theory of persistence of vision, the perceptual processes of the brain or the retina of the human eye retains an image for a brief moment. ...

Contents

Explanation

Like all psychophysical thresholds, the flicker fusion threshold is a statistical rather than an absolute quantity. There is a range of frequencies within which flicker sometimes will be seen and sometimes will not be seen, and the threshold is the frequency at which flicker is detected on 50% of trials. Leonardo da Vincis Vitruvian Man, an important early achievement in the study of physiology. ...


The flicker fusion threshold is proportional to the amount of modulation; if brightness is constant, a brief flicker will manifest a much lower threshold frequency than a long flicker. The threshold also varies with brightness (it is higher for a brighter light source) and with location on the retina where the perceived image falls: the rod cells of the human eye have a faster response time than the cone cells, so flicker can be sensed in peripheral vision at higher frequencies than in foveal vision. The flicker fusion threshold also is higher for a fatigued observer. [[Amplitude modulation]] (AM) is a technique used in electronic communication, most commonly for transmitting information via a carrier wave wirelessly. ... Human eye cross-sectional view. ... Normalised absoption spectra of human rod (R) and cone (S,M,L) cells. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... Peripheral vision is a part of vision that occurs outside the very center of gaze. ... The fovea, a part of the eye, is a spot located in the center of the macula. ...


The flicker fusion threshold also varies between species. Pigeons have been shown to have higher threshold than humans, and the same is probably true of all birds. Many mammals have a higher proportion of rods in their retinae than humans do, and it is likely that they would also have higher flicker fusion thresholds. In biology, a species is one of the basic units of biodiversity. ... Pigeon redirects here. ... “Aves” redirects here. ... Subclasses Subclass Allotheria* Order Docodonta (extinct) Order Multituberculata (extinct) Order Palaeoryctoides (extinct) Order Triconodonta (extinct) Order Volaticotheria (extinct) Subclass Prototheria Order Monotremata Subclass Theria Infraclass Trituberculata (extinct) Infraclass Metatheria Infraclass Eutheria Mammals are a class of vertebrate animals characterized by the production of milk in females for the nourishment of...


Importance

Flicker fusion is important in all technologies for presenting moving images, nearly all of which depend on presenting a rapid succession of static images (e.g. the frames in a cinema film, TV show, or a digital video file). If the frame rate falls below the flicker fusion threshold for the given viewing conditions, flicker will be apparent to the observer, and movements of objects on the film will appear jerky. For the purposes of presenting moving images, the human flicker fusion threshold is usually taken as 16 hertz (Hz). In actual practice, movies are recorded at 24 frames per second, and TV cameras operate at 25 or 30 frames per second, depending on the TV system used. Even though motion may seem to be continuous at 25 or 30 fps, the brightness may still seem to flicker objectionably. By showing each frame twice in cinema projection (48 Hz), and using interlace in television (50 or 60 Hz), a reasonable margin for error or unusual viewing conditions is achieved in minimising subjective flicker effects. Image File history File links Information_icon. ... In film, video production, animation, and related fields, a frame is one of the many still images which compose the complete moving picture. ... Digital video is a type of video recording system that works by using a digital, rather than analog, representation of the video signal. ... Frame rate, or frame frequency, is the measurement of how quickly an imaging device produces unique consecutive images called frames. ... The hertz (symbol: Hz) is the SI unit of frequency. ... For the method of incrementally displaying raster graphics, see Interlace (bitmaps). ...


Flicker is also important in the field of domestic (alternating current) lighting, where noticeable flicker can be caused by varying electrical loads, and hence can be very disturbing to electric utility customers. Most electricity providers have maximum flicker limits that they try to meet for domestic customers. City lights viewed in a motion blurred exposure. ...


Subjectivity of flicker

Computer CRT displays usually operate at a vertical scan rate well over 60 Hz (modern ones are around 100Hz), and can thus be considered flicker-free. Other display technologies do not flicker noticeably so the frame rate is less important. LCD flat panels do not seem to flicker at all as the backlight of the screen operates at a very high frequency of nearly 200 Hz, and each pixel is changed on a scan rather than briefly turning on and then off as in CRT displays. Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT Electron guns Electron beams Focusing coils Deflection coils Anode connection Mask for separating beams for red, green, and blue part of displayed image Phosphor layer with red, green, and blue zones Close-up of the phosphor... The terms scan and scanning have several meanings: In telecommunication: The term scan has the following meanings: To examine sequentially, part by part. ... LCD redirects here. ...


Some individuals, particularly autistics[citation needed], can still notice a flicker in CRTs or even in fluorescent lights; a few find fluorescent lights generally uncomfortable for this reason. Autism is classified by the World Health Organization (WHO) and American Psychological Association as a developmental disability that results from a disorder of the human central nervous system. ...


In some cases, it is possible to indirectly detect flicker at rates well beyond 60 Hz in the case of high-speed motion, via the stroboscopic effect. Human factors experts refer to this effect as a Phantom Array. Fast-moving flickering objects zooming across view (either by object motion, or by eye motion such as rolling eyes), can cause a dotted or multicolored blur instead of a continuous blur. A common example of this phenomenon is the DLP Rainbow Effect. Some special effects, such as certain kinds of electronic glowsticks commonly seen at outdoor events, have the appearance of a solid color when motionless but produce a multicolored or dotted blur when waved about in motion. Some particularly sensitive people claim to be able to see the flicker of office fluorescent lighting or street lighting, which occur at 100 or 120 Hz. Other times, people can indirectly detect the presence of a high-speed flicker via the mere existence of a wagon-wheel effect. Temporal aliasing is the term applied to a visual phenomenon also known as the stroboscopic effect. It also accounts for the wagon-wheel effect, so called because in video or motion pictures, spoked wheels on horse-drawn wagons sometimes appear to be turning backwards. ... The DLP Logo Digital Light Processing (DLP) is a technology used in projectors and video projectors. ... A classic glowsticking dancemove called the Figure 8. ... Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... The wagon-wheel effect, (alternatively, waggon-wheel effect, stagecoach-wheel effect, stroboscopic effect) is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. ...


See also

According to the theory of persistence of vision, the perceptual processes of the brain or the retina of the human eye retains an image for a brief moment. ... This animated GIF demonstrates the effects of Adobe Flash shape, motion and color tweening. ...

External links

  • IEC Flicker Meter
  • The Flicker Fusion Factor Why we can't drive safely at high speed

  Results from FactBites:
 
NationMaster - Encyclopedia: Flicker fusion (516 words)
The flicker fusion threshold varies with brightness (it is higher for brighter lights) and with location on the retina where the light falls: the rod cells have a faster response than the cone cells, so flicker can be seen in peripheral vision at higher frequencies than in foveal vision.
Flicker fusion is important in all technologies for presenting moving images, nearly all of which depend on presenting a rapid succession of static images (e.g.
Entropy of fusion The Entropy of fusion of a substance represents the increase in the degree of disorder involved in the...
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