1. what is vision ? vision “a process that produces form images of the external world, a...
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What is
Vision ?
VISION“A process that produces
form images of the external world, a description which is useful to the viewer and
not cluttered with the irrelevant information.”
David Marr
What is
Light ?
LIGHT
Part of
Electro Magnetic Spectrum to which the
Eyes are sensitive
What is
Electromagnetic Spectrum ?
X-rays1
Gamma-3
Cosmic-6
Radar6
Micro3
TV9 Radio
12200nm 10,000nm
780nm400nm
VisibleLight
OpticalRadiations
U V I R
Properties of light
• Travels in straight lines
surface
i r angle of incidence (i)=
angle of reflection (r)
Properties of light
• Reflects from surfaces
sin (i) = n sin (r)
surface
i
r
air
densemedium
n is refractive indexof dense material
n ≈ 1.1 - 1.3
(depends on material)
Properties of Light
• Refracts at boundaries of transparent materials
Frequency corresponds to colour
OPTICAL MEDIA
REFRACTION
Human eye
Fovea
Optic nervefibers
Retina
Vitreoushumor
Lens
Iris
Pupil
Cornea
Aqueoushumor
Refraction quizA
BC
1
2 3
n1n
2
Refraction review
n1n
2
n1<n2
The eyesreceivers of information
Shaping and transforming light into sensory perceptions for nearly
600 million years.
The eye - receiver of information
sun observer
• Light sources: sun, light bulbs, candles, moon
• Light reflects off of objects in environment
The eye - receiver of information
observersun observer
• Light sources: sun, light bulbs, candles, moon
• Light reflects off of objects in environmentobjects effectively become light sources
Photoreceptor“receptor of light [photons]”
• photoreceptor cell transforms light into nerve impulses
incoming light ray
output of cell(signal along axon)
photoreceptor
Implications for vision
• Does not matter if an object is a source or a reflector of light
• Strength of reflection is a function of:– color of object– smoothness of object– relative orientation between light rays, surface
normal, and observer
Human Eye
• lens eye
• array of photoreceptors: retina– rods and cones
• focusing: cornea plus crystalline lens
• photoreceptors are “backwards”– axons (nerves) leave through blind spot
cornea
crystallinelens
retina: photoreceptors = rods + cones
opticnerve
Representing objects by edges
• Very efficient compression
• 100 million axons from photo receptors per eye
• 1 million axons from ganglion cells per eye
• Reduction by a factor of 100!!
LIGHT
Retina
Receptors
Brain
Process
Vision
Sunset
What will happen if
Colors are not perceived ?
RECEPTORS
100 Million Rods & ConesBillion Cells in Three Layers10 Billion Calculations /Sec
1.2 Million AxonsOptic Nerve
> Dozen Vision Centers
Three Dimensional World
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Three Dimensional World
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Global Facts
BLIND
VISION 3/60 OR LOW
IN BEST SEEING EYE
WHO ESTIMATES
42 – MILLION BLINDS IN THE WORLD
HALF ARE DUE TO CATARACT
CATARACT WITH VISION 3/60 OR LOW
20 M WILL INCREASE TO 40 M IN YEAR 2020
• Globally, at least 100 million eyes have visual acuity < 6 / 60 due to cataract.
• Annually, at least 25 million eyes develop visual acuity < 6/60 due to cataract.
ONE MILLION OPERATEDEVERY YEAR
BUT1.5 M ADDED EVERY YEAR
SOWORLD IS BECOMING MORE
BLIND
NUMBER OF EYE SURGEONS
UK - 14 PER MILLIONAFRICA – 1 PER MILLIONSUDAN – 3 PER MILLION
CATARACT SURGURY RATECSR
UK – 4500 PER MILLIONAUSTRALIA – 6500 PER MILLIONAFRICA – 200-400 PER MILLION
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