Chapter2 Eye

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ImageProcessingImageProcessingDigitalImageFundamentalsDigitalImageFundamentals

apterapterProf.Vidya Manian

Dept.of

Electrical

and

Comptuer Engineering

INEL5327(Spring2009) Introduction 1ECE,UPRM


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Light

Imagingsensors

Imagesampling

and

intensity

quantization

Pixelrelationships

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Retinainnermostmembraneofeye

Lightreceptors

are

cones

and

rods

Conessensitivetocolor(photopic orbrightlight

Rodssensitivetolowlevelsofillumination(scotopic or

dimllight vision)

Foveasquaresensorarrayof1.5mmx1.5mm

Densityis150,000elements/mm2

,

comparedtocurrentelectronicimagingsensor(CCDarray)of5mmx5mm



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Theshapeofthelensisadjustedforfocusingonnearordistantobject

Contrarytophotographiccamerawherelenshasa

Focallengthofeye=17mm

h=15

m

height

of

the

object,

distance

of

person

from

o ect= m

15/100=h/17,h=2.55mm

Perceptionexcitationoflightreceptors,signalspassedtothebrainwheretheyaredecoded(V1,ITandPFC)



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Sub ectivebri htness lo arithmicfunctionof

the

light

intensity

incident

on

the

eye Rangeofintensities 106

Currentsensitivitylevel brightnessadaptationlevel(Ba)

,

WhenIisstrongenough,thesubjectwillres ond es

Weberratio

:c/I

increment

of

illumination

discriminable



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Highlevels

of

illumination

by

cones

Perceive rig tnessisnotasimp e unction

ofintensity

HVSundershootsorovershootsaroundthe

boundaryofregionsofdifferentintensities

Machbands

scalloped

intensities



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Simultaneouscontrast



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RadiowavesWavelen thslon erthanvisible

light Gammarayswavelengthssmallthanvisiblelight

=c ;wavelength(m),frequency,cspeedoflight

, Electromagneticwavesstreamofmassless

articleswithener movin ats eedofli ht

Higherfrequency

(shorter

wavelength)

carry

moreenergyperphoton



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Electroma neticWavelen th

Li ht


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Electromagneticspectrumsensedbythehuman

Visible(0.43m)

to

red

(0.79

m)

Whitecolorob ectthatreflectsli htbalancedinallvisiblewavelengths

Greenobjects

reflect

wavelengths

in

500

570

,

Monochromatic(achromatic) lightwithoutcolor

Intensity

denotedby

gray

levels

Gra scale ran eofmeasuredvaluesofmonochromaticlightfromblacktowhite



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L ( ) =

Object


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fromthe

light

source

(Watts)

observer,lumens(lm)

Brig tness:su jective escriptoro ig t

perception

Infraredband

radiates

heat

useful

in

imaging

applicationsthatrelyonheatsignatures



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onthe

size

of

the

object

,

10m

Hence,sourcetostu ywaternee semitting

infarUVorsoftXrayregion

Imagegeneration



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absorptionof

energy

by

elements

of

the

scene

, , ,

Objects:

real

world,

molecules,

cells,

biological Incomingenergyistransformedtoavoltage

bycombinationofelectricalpowerandsensor

material

Theout utvolta ewaveformisdi itized



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voltageproportional

to

light

For

2

D

imaging:

lead

screw

rovides

motion

in

perpen icu ar irection

Microdensitometers:sensorsmovingintwo

lineardirections



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SingleSensorwithmotiontogenerate

2D

image



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Perpendicularmotion

provides

imaging

in

4000inlinesensors:airborneimaging

a lication 1Dimagingsensorstripsmounted

er endicular to direction of fli ht

Lensesareusedforfocusingareatobescanned on to sensor



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Linearsensorstripandcircularsensor

strip



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Rin confi urationusedinmedicalandindustrial

imaging:crosssection (slice

of

3D

objects)

IlluminationbyrotatingXraysource,s ensoroppositecolects Xrayenergythatpassesthrough

the

object. CAT:Computerizedaxialtomography

Requireextensiveprocessingofthe3Ddigital

vo umeo

s ac e

mages

MRI,PET(PositronEmissionTomography)



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Electroma neticandultrasonicsensin devices

havesensors

in

2D

array

Digitalcamera: CCDarray(4000x4000elements)

Completeimageisobtainedbyfocusingenergy

patternon

surface

of

array

Forlightillumination,opticallensprojectstheviewedsceneonlensfocalplane

Outputis

integral

of

light

received

at

each

sensor

Digitizedbyothersectionofimagingsystem



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Imageacquisitionprocess

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(Spring

2009) ECE,

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CurrentstateoftheartinHuman

Visual

Perception

and

Digital

Perce tualModels

Supplementmaterialforreading

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(Spring

2009) ECE,

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HumanVisualPerception

A

summary

TheHVShasahierarchicalorganization withgradualincreaseinnvar ancean comp ex yo es mu a ong ev sua s ream.

Earlyor

low

level

processing

occurs

in

retina,

Lateral

Geniculate

Nucleus(LGN)andprimaryvisualcortex(V1)cells. Forexample,.

V1,fromV2toV4cellsareresponsivetocomplexfeaturesoftheobject.

InInterotemporal (IT) cortex

cells

are

selective

to

color,

orientation

texture,pose,illumination,directionofmotionandshapetuning.InAnteriorInterotemporal cortex(AIT)cellsaretunedtobodypartssuchasfacesandhands. InvariantrecognitiontakesplaceinIT.

,performed

based

on

learning

the

target

object

from

previous

layers

inthehierarchy.Thislayerperformsimmediaterecognition,identificationandcategorization(classification).

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2009) ECE,

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2009) ECE,

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2009) ECE,

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Recentadvancesinmodelingof

Humanvisual

perception

T.Serre,Learningadictionaryofshapecomponentsinvisualcortex:comparisonwithneurons,humansand

machines,PhD

Thesis,

MIT,

2000.

R.Raizada andS.Grossberg,ContextsensitivebindingsbythelaminarcircuitsofV1andV2:Aunifiedmodelofperceptualgrouping,attention,andorientationcontrast,

Vis.Cognition,Vol.8,pp.431466,2001. M.Riesenhuber andT.Poggio,Neuralmechanismsof

objectrecognition,Neurobiology,Vol.12,pp162168,2002.

R.

P.

N.

Rao,

Brain:

the

next

generation,

MIT

Press,

Cambridge,Mass.,2002.

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(Spring

2009) ECE,

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T.Serre,Learningadictionaryofshapecomponentsinvisualcortex:comparisonwithneurons,humansand

machines,PhD

Thesis,

MIT,

2000.

R.Raizada andS.Grossberg,ContextsensitivebindingsbythelaminarcircuitsofV1andV2:Aunifiedmodelofperceptualgrouping,attention,andorientationcontrast,

Vis.Cognition,Vol.8,pp.431466,2001. M.Riesenhuber andT.Poggio,Neuralmechanismsof

objectrecognition,Neurobiology,Vol.12,pp162168,2002.

R.P.

N.

Rao,

Brain:

the

next

generation,

MIT

Press,

Cambridge,Mass.,2002.

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(Spring

2009) ECE,

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When ouenteradarktheateronabri htda it

takes

an

appreciable

interval

of

time

before

you

canseewellenoughtofindanemptyseat.Whichofthevisualprocessesexplainedisatplayinthissituation?

erna ngcurren cer a n y spar o eelectromagneticspectrum.CommercialACinthe

wavelengthin

kilometers

of

this

component

of

thespectrum.

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2009) ECE,

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perceptionand

perceptual

model

for

image

classon23January2009.

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(Spring

2009) ECE,

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Chapter2 Eye

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