Human Eye-Digital Image Processing-Lecture Slides, Slides of Digital Image Processing

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Human eye

Shape is nearly a Sphere

Three membranes: 

Cornea and Sclera:opaque, tough tissue  Choroid: have bloodvessels, heavily pigmented.  Ciliary body  Iris diaphragm  Retina

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Human eye: Retina Two types of visual receptors 

Cones (Photopic or bright-light vision) 

6-7 million cones  One per nerve  High resolution - give fine details  Located in fovea (central portion)  Sensitive to color

Rods (Scotopic or dim-light vision) 

75-150 million rods  Several per nerve  Low resolution – give overall field view

Blind spot (absence of receptors area) ~ 17 degrees off axis

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Human eye 

We can consider Fovea as a square sensor array ofsize 1.5mm x 1.5mm



Density of Cones: 150,000 elements/mm

2 

Cones are 337,000 elements



Charged Coupled Devices (CCD) can achieve this in5mm x 5mm

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Image formation Q. Compute the height of tree in the image

formed at the retina.

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Brightness perception 

I is the uniform illumination on the flat area



I

c

is the change in the object brightness required to

just distinguish object from the background



Weber Ratio:

I

c

/ I

where

I

c

is the increment of

illumination discriminable 50%of the time with backgroundillumination I.

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Brightness perception 

Good brightness discrimination

I

c

/ I is small



Bad brightness discrimination

I

c

/ I is large

RODS CONS Discrimination Illumination Level High Low Bad Good

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Mach Band pattern: Details

Is it the same level ofdarkness around D andB? The brightness patternperceived is a darkerstripe in region D and abrighter one in theregion B whereasactually the region fromD to B has the sameintensity.

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Brightness perception Brightness is not a simple function of intensitySecond Phenomenon: Simultaneous Contrast

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Optical illusions

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Image sources 

Electromagnetic (EM) band imaging 

Gamma ray band images

X-ray band images

Ultra violet band images

Visual light and infra-red images

Images based on micro waves or radio waves



Non-EM band imaging 

Acoustic and ultrasonic images

Electron microscopy

Computer generated images (synthetic)

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Applications:EM-Band Imaging 

Gamma ray band imaging 

Nuclear medicine, Astronomical observations



X-ray imaging 

Medical diagnostics, Industry, Astronomy



Ultra violet imaging 

Fluorescence microscopy, Astronomy



Visible and Infra-red imaging 

Remote sensing, industry, surveillance, military, lightmicroscopy, Astronomy



Microwave and Radio band imaging 

RADAR, Medical (MRI), Astronomy

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Applications:Non EM-Band Imaging 

Acoustic imaging (hundreds of Hz) 

Geological exploration (oil, gas, …)



Ultrasound imaging (millions of Hz) 

Industry and medicine



Electron microscopic imaging 

Employed to achieve magnification of 10000x or more

(light microscope is limited to 1000x approx.)



Synthetic imaging 

3D modeling or visualization systems, Machine design,Architecture, Special effects and animations, Gaming, etc.

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Image acquisition

Single sensore.g. a photodiodeLine sensor Array sensor

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Image acquisition