1. 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.

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Presentation transcript:

1

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-rays 1 Gamma -3 Cosmic -6 Radar 6 Micro 3 TV 9 Radio nm10,000nm 780nm 400nm Visible Light Optical Radiations U VI R

Properties of light Travels in straight lines

angle of incidence (i) = angle of reflection (r) Properties of light Reflects from surfaces

sin (  i ) = n sin (  r ) n is refractive index of dense material n ≈ (depends on material) Properties of Light Refracts at boundaries of transparent materials

Frequency corresponds to colour

OPTICAL MEDIA REFRACTION

Human eye Fovea Optic nerve fibers Retina Vitreous humor Lens Iris Pupil Cornea Aqueous humor

Refraction quiz A B C n1n1 n2n2

Refraction review n1n1 n2n2 n 1 <n 2

The eyes receivers of information Shaping and transforming light into sensory perceptions for nearly 600 million years.

Seeing physical recording of the pattern of light energy received from the world that consists of: 1.Selective gathering of the light 2.Projection or focusing of the light on a photosensitive surface 3.Conversion of the light into a pattern of chemical or electrical activity

The eye - receiver of information Light sources: sun, light bulbs, candles, moon Light reflects off of objects in environment

The eye - receiver of information Light sources: sun, light bulbs, candles, moon Light reflects off of objects in environment objects effectively become light sources

Photoreceptor “receptor of light [photons]” photoreceptor cell transforms light into nerve impulses

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

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 & Cones Billion Cells in Three Layers 10 Billion Calculations /Sec 1.2 Million Axons Optic Nerve > Dozen Vision Centers

Three Dimensional World \FantasticTrip.pp sFantasticTrip.pp s Three Dimensional World \FantasticTrip.pp sFantasticTrip.pp s

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 OPERATED EVERY YEAR BUT 1.5 M ADDED EVERY YEAR SO WORLD IS BECOMING MORE BLIND

NUMBER OF EYE SURGEONS  UK - 14 PER MILLION  AFRICA – 1 PER MILLION  SUDAN – 3 PER MILLION

CATARACT SURGURY RATE CSR  UK – 4500 PER MILLION  AUSTRALIA – 6500 PER MILLION  AFRICA – PER MILLION

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