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The ''Human Visual System Model'', often referred to as the Human Visual System (HVS), is used by [[image processing]], [[video processing]] and [[Computer vision]] experts to deal with biological and psychological processes that are not yet fully understood. The model is used to simplify the behaviours of what is a very complex system. As our knowledge of the [[Visual system | true Human Visual System]] improves, the model is updated.
It is common to think of "taking advantage" of the HVS to produce desired effects. Examples of taking advantage of the HVS include colour television. Originally it was thought that colour television required too high a bandwidth for the then available technology. Then it was [[Chroma subsampling | noticed that the colour resolution of the HVS was much lower than the brightness resolution]]; this allowed colour to be squeezed into the signal. 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 [[Audio_data_compression#Lossy_audio_compression | audio compression]], where sound frequencies inaudible to humans are bandpass filtered.
Several HVS features are derived from avatisms, throwbacks to nature when we needed to defend ourselves or hunt for food. We often see demonstrations of HVS features when we are looking at optical illusions.
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==Assumptions about the HVS==
* [[Low pass filter]] characteristic (limited number of rods in human eye)
* Lack of colour resolution (less cones in human eye than rods)
* Motion sensitivity
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* Colour television (chrominance at half resolution of luminance)
* Image compression (higher frequencies more harshly quantised)
* [[Motion estimation]] (use luminance and ignore colour)
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