chapter2 eye
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ImageProcessingImageProcessingDigitalImageFundamentalsDigitalImageFundamentals
apterapterProf.Vidya Manian
Dept.of
Electrical
and
Comptuer Engineering
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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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CurrentstateoftheartinHuman
Visual
Perception
and
Digital
Perce tualModels
Supplementmaterialforreading
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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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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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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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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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perceptionand
perceptual
model
for
image
classon23January2009.
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