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Digital Image Processing
Human Visual System
Human Visual System
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Human Visual System
In many image processing applications, the objective
In many image processing applications, the objective
is to help a
is to help a human observer
human observer perceive the visual
perceive the visual
information in an image. Therefore, it is important to
information in an image. Therefore, it is important to
understand the human visual system.
understand the human visual system.
The human visual system consists mainly of the eye
The human visual system consists mainly of the eye
(image sensor or camera), optic nerve (transmission path),
(image sensor or camera), optic nerve (transmission path),
and brain (image information processing unit or computer).
and brain (image information processing unit or computer).
It is one of the most sophisticated image processing
It is one of the most sophisticated image processing
and analysis systems.
and analysis systems.
Its understanding would also help in the design of
Its understanding would also help in the design of
efficient, accurate and effective computer/machine vision
efficient, accurate and effective computer/machine vision
systems.
systems.
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Cross-section
Cross-section
of the Human Eye
of the Human Eye
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Cross-section
Cross-section
of the Human Eye
of the Human Eye
Nearly spherical with a diameter of 20 mm (approx.).
Nearly spherical with a diameter of 20 mm (approx.).
Cornea
Cornea --- Outer tough transparent membrane, covers anterior
--- Outer tough transparent membrane, covers anterior
surface.
surface.
Sclera
Sclera --- Outer tough opaque membrane, covers rest of the optic
--- Outer tough opaque membrane, covers rest of the optic
globe.
globe.
Choroid
Choroid --- Contains blood vessels, provides nutrition.
--- Contains blood vessels, provides nutrition.
Iris
Iris --- Anterior portion of choroid, pigmented, gives color to the eye.
--- Anterior portion of choroid, pigmented, gives color to the eye.
Pupil
Pupil --- Central opening of the Iris, controls the amount of light
--- Central opening of the Iris, controls the amount of light
entering the eye (diameter varies from 2-8 mm).
entering the eye (diameter varies from 2-8 mm).
Lens
Lens --- Made of concentric layers of fibrous cells, contains 60-70%
--- Made of concentric layers of fibrous cells, contains 60-70%
water.
water.
Retina
Retina --- Innermost layer, “screen” on which image is formed by the
--- Innermost layer, “screen” on which image is formed by the
lens when properly focussed, contains photoreceptors (cells sensitive
lens when properly focussed, contains photoreceptors (cells sensitive
to light).
to light).
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Light and EM Spectrum
Light and EM Spectrum
Electromagnetic (EM) waves or radiation can be
Electromagnetic (EM) waves or radiation can be
visualized as propogating sinusoidal waves with
visualized as propogating sinusoidal waves with
some wavelength l or equivalently a frequency n
some wavelength l or equivalently a frequency n
where
where c
c = ln ,
= ln , c
c being the velocity of light.
being the velocity of light.
Equivalently, they can be considered as a stream
Equivalently, they can be considered as a stream
of (massless) particles (or photons), each having
of (massless) particles (or photons), each having
an energy
an energy E
E proportional to its frequency n; n =
proportional to its frequency n; n = h
h
E
E , where
, where h
h is Planck’s constant.
is Planck’s constant.