Human visual system model: Difference between revisions

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'''Psychovisual''' study is the study of the psychology of vision.

The human visual system model can be used to produce desired effects in perception and vision. Examples of using an HVS model include [[color television]], [[lossy compression]], and [[Cathode-ray tube]] (CRT) television.

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]].

Another example is lossy image compression, like [[JPEG]]. Our HVS model says that we cannot see high- frequency detail, so in JPEG we can quantize 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 bandstopband-stop filtered.

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.

==Block diagram of HVS==

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==Assumptions about the HVS==

* [[Low-pass filter]] characteristic (limited number of rods in the human eye): see [[Mach bands]]

* Lack of color resolution (fewer cones in the human eye than rods)

* Motion sensitivity

** More sensitive in [[peripheral vision]]

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==Examples of taking advantage of an HVS model==

* [[Flicker fusion threshold|Flicker frequency of film and television using persistence of vision to fool viewersviewer into seeing a continuous image]]

* [[Interlaced video|Interlaced television]] painting half images to give the impression of a higher flicker frequency

* Color television (chrominance at half resolution of luminance corresponding to proportions of rods and cones in the eye)

* Image compression (difficult to see higher frequencies more harshly quantized)

* [[Motion estimation]] (use luminance and ignore color)