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A '''human visual system model''' (HVS model) is used by [[image processing]], [[video processing]] and [[computer vision]] experts to deal with biological and psychological processes that are not yet fully understood. Such a model is used to simplify the
'''Psychovisual''' study is the study of the psychology of vision.
It is common to think of "taking advantage" of the HVS model to produce desired effects. Examples of taking advantage of an HVS model include colour television. Originally it was thought that colour television required too high a bandwidth for the then available technology. Then it was noticed that the colour resolution of the HVS was much lower than the brightness resolution; this allowed colour to be squeezed into the signal by [[chroma subsampling]]. Another example is image compression, like [[JPEG]]. Our HVS model says that we cannot see high frequency detail so in JPEG we can quantise these components without a perceptible loss of quality. Similar concepts are applied in [[Data compression#Lossy audio compression|audio compression]], where sound frequencies inaudible to humans are bandstop filtered.▼
The human visual system model can produce desired effects in perception and vision. Examples of using an HVS model include [[color television]], [[lossy compression]], and [[Cathode-ray tube]] (CRT) television.
Several HVS features are derived from evolution, when we needed to defend ourselves or hunt for food. We often see demonstrations of HVS features when we are looking at optical illusions.▼
Originally, it was thought that color television required too high a bandwidth for the then available technology. Then it was noticed that the color resolution of the HVS was much lower than the brightness resolution; this allowed color to be squeezed into the signal by [[chroma subsampling]].
▲
▲Several HVS features are derived from evolution
==Block diagram of HVS==
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* [[Low-pass filter]] characteristic (limited number of rods in human eye): see [[Mach bands]]
* Lack of
* Motion sensitivity
** More sensitive in [[peripheral vision]]
** Stronger than texture sensitivity, e.g. viewing a camouflaged animal
* Texture stronger than disparity
* Integral Face recognition (babies smile at faces)
** [[Hollow-face illusion|Depth inverted face looks normal]] (facial features overrule depth information)
*** Upside down face with inverted mouth and eyes looks normal<ref>[http://www.moillusions.com/2006/09/margaret-thatcher-illusion.html Margaret Thatcher Illusion
==Examples of taking advantage of an HVS model==
* [[Flicker fusion threshold|Flicker frequency of film and television using persistence of vision to fool viewer into seeing a continuous image]]
* [[
*
* Image compression (difficult to see higher frequencies more harshly
* [[Motion estimation]] (use luminance and ignore
* [[
==See also==
* [[Psychoacoustics]]
* [[Visual system]]
* [[Visual perception]]
* [[Depth perception]]
==References==
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