A human visual system model (HVS model) is used by
image processing
An image or picture is a visual representation. An image can be two-dimensional, such as a drawing, painting, or photograph, or three-dimensional, such as a carving or sculpture. Images may be displayed through other media, including a pr ...
,
video processing In electronics engineering, video processing is a particular case of signal processing, in particular image processing, which often employs filter (video), video filters and where the input and output Signal (electrical engineering), signals are vid ...
and
computer vision
Computer vision tasks include methods for image sensor, acquiring, Image processing, processing, Image analysis, analyzing, and understanding digital images, and extraction of high-dimensional data from the real world in order to produce numerical ...
experts to deal with biological and psychological processes that are not yet fully understood. Such a model is used to simplify the behaviors of what is a very
complex system
A complex system is a system composed of many components that may interact with one another. Examples of complex systems are Earth's global climate, organisms, the human brain, infrastructure such as power grid, transportation or communication sy ...
. As our knowledge of the true
visual system
The visual system is the physiological basis of visual perception (the ability to perception, detect and process light). The system detects, phototransduction, transduces and interprets information concerning light within the visible range to ...
improves, the model is updated.
Psychovisual study is the study of the psychology of vision.
The human visual system model can produce desired effects in perception and vision. Examples of using an HVS model include
color television
Color television (American English) or colour television (British English) is a television transmission technology that also includes color information for the picture, so the video image can be displayed in color on the television set. It improv ...
,
lossy compression
In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
, and
Cathode-ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a ...
(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
Chroma subsampling is the practice of encoding images by implementing less resolution for Chrominance, chroma information than for luma (video), luma information, taking advantage of the human visual system's lower acuity for color differences t ...
.
Another example is lossy image compression, like
JPEG
JPEG ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...
. Our HVS model says 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
audio compression, where sound frequencies inaudible to humans are band-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
Assumptions about the HVS
*
Low-pass filter
A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filt ...
characteristic (limited number of rods in human eye): see
Mach bands
* Lack of color resolution (fewer cones in human eye than rods)
* Motion sensitivity
** More sensitive in
peripheral vision
Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...
** Stronger than texture sensitivity, e.g. viewing a camouflaged animal
* Texture stronger than disparity 3D depth resolution does not need to be so accurate
* Integral Face recognition (babies smile at faces)
**
Depth inverted face looks normal (facial features overrule depth information)
*** Upside down face with inverted mouth and eyes looks normal
Margaret Thatcher Illusion – Mighty Optical Illusions
/ref>
Examples of taking advantage of an HVS model
* Flicker frequency of film and television using persistence of vision to fool viewer into seeing a continuous image
* 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 eye)
* Image compression (difficult to see higher frequencies more harshly quantized)
* Motion estimation
In computer vision and image processing, motion estimation is the process of determining ''motion vectors'' that describe the transformation from one 2D image to another; usually from adjacent video frame, frames in a video sequence. It is an wel ...
(use luminance and ignore color)
* Watermark
A watermark is an identifying image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, atop a dark background), caused by thickness or density variations i ...
ing and Steganography
Steganography ( ) is the practice of representing information within another message or physical object, in such a manner that the presence of the concealed information would not be evident to an unsuspecting person's examination. In computing/ ...
See also
* Psychoacoustics
Psychoacoustics is the branch of psychophysics involving the scientific study of the perception of sound by the human auditory system. It is the branch of science studying the psychological responses associated with sound including noise, speech, ...
* Visual system
The visual system is the physiological basis of visual perception (the ability to perception, detect and process light). The system detects, phototransduction, transduces and interprets information concerning light within the visible range to ...
* Visual perception
Visual perception is the ability to detect light and use it to form an image of the surrounding Biophysical environment, environment. Photodetection without image formation is classified as ''light sensing''. In most vertebrates, visual percept ...
* Depth perception
Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions.
Depth sensation is the corresponding term for non-hum ...
References
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Computer vision
Computer vision tasks include methods for image sensor, acquiring, Image processing, processing, Image analysis, analyzing, and understanding digital images, and extraction of high-dimensional data from the real world in order to produce numerical ...