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U M E R J AV E D( U M E R . J AV E D @ I I U . E D U . P K )
D E PA RT M E N T O F E L E C T R O N I C
E N G I N E E R I N G ,
FA C U LT Y O F E N G I N E E R I N G & T E C H N O L O G Y,
I I U I
FA L L 2 0 1 2
CS-407: Digital Image Processing
U M E R J AV E D( U M E R . J AV E D @ I I U . E D U . P K )
C H A P T E R : 2
D I G I TA L I M A G E F U N D A M E N TA L S
CS-407: Digital Image Processing
Human Eye
Umer Javed, CS: 407: Digital Image Processing
Courtesy: DIP 3/Edition
Chapter:2, Slide # 3
Human Eye
Umer Javed, CS: 407: Digital Image Processing
Iris:
Controls amount of light entering in eye by contraction or expansion.
Retina:
Inner most layer
Contains 2 type of receptors
Cones
Rods
Chapter:2, Slide # 4
Human Eye
Umer Javed, CS: 407: Digital Image Processing
Cones: Exist a number of 6~7 Million in each eye.
Central Position at Fovea.
Highly sensitive to color.
Helps in resolving fine details.
Cone vision is known as Phototopic or Bright light vision.
Rods: 75~150 Million, Residing all over retina
Reduce Amount of detail.
Creates general overview of picture
Sensitive to low level intensitites.
In low light, objects appear colorless, because only Rods are active.
Vision is called Scotopic or Dim Light Vision.
Chapter:2, Slide # 5
Human Eye
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 6
Courtesy: DIP 3/Edition
Human Eye
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 7
Courtesy: DIP 3/Edition
Brightness Adaptation
Umer Javed, CS: 407: Digital Image Processing
Light Intensity vs
Subjective Brightness.
mL= millilambert.
In high brightness range Photopic
vision is active.
In Low Brightness range Scopic
vision is active.
Human vision system cannot operate
over such range simultaneously, rather
it adjusts its sesitivity.
Chapter:2, Slide # 8
Courtesy: DIP 3/Edition
Weber Ratio
Umer Javed, CS: 407: Digital Image Processing
Introduce bright light, , if increment is not brighter,change wont be detectable.
Smaller WB, means small change is detectable.
Larger WB, means only large change is detectable.
I
cIWeberRatio :I
Chapter:2, Slide # 9
Limitations of Eye
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 10
Courtesy: DIP 3/Edition
Limitations of Eye
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 11
Courtesy: DIP 3/Edition
Limitations of Eye
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 12
Courtesy: DIP 3/Edition
Electromagnetic Spectrum
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 13
Courtesy: DIP 3/Edition
Image Sensing
Umer Javed, CS: 407: Digital Image Processing
Single image sensor:
Incoming energy transforms into voltage by Combination of Input electrical power and sensor material.
Output voltage can be digitized.
Photodiode follows this kind of behavior.
Colored sensors give maximum voltage for similar colors and minimum for others.
Chapter:2, Slide # 14
Image Sensing
Chapter:2, Slide # 15Umer Javed, CS: 407: Digital Image Processing
Sensor Strips:
Courtesy: DIP 3/Edition
Image Sensing
Umer Javed, CS: 407: Digital Image Processing
Sensor Arrays:
Charged Coupled Devices (CCD)
Widely used in digital cameras
Complimentary Metal Oxide Semiconductor (CMOS)
CMOS doesn’t require charged couples
Application Areas:
Air Borne Imaging
X-Rays Scan
Computerized Axial Tomography (CAT)
Positron Emission tomography (PET)
Magnetic Resonance Imaging (MRI)
Chapter:2, Slide # 16
Image Formation
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 17
Courtesy: DIP 3/Edition
Image Formation
Umer Javed, CS: 407: Digital Image Processing
Image as a function should be positive and finitei.e.
Two key components play their role
Amount of source illumination, incident
Amount of source illumination, reflected
Function results in
Chapter:2, Slide # 18
0 < f(x, y)<
i(x, y)
r(x, y)
0 <i(x, y)<
0 < r(x, y)<1
f(x, y)= i(x, y)r(x, y)
Intensity Measures
Umer Javed, CS: 407: Digital Image Processing
Image intensity/gray scale as a functioni.e.
Intensity ranges
Where
Gray Scale Range
generally used as: OR
Chapter:2, Slide # 19
0 0= f(x , y )
min maxL L
min min minL = i rmax max maxL = i r
,min maxL L 0, L -1
Sampling and Quantization
Umer Javed, CS: 407: Digital Image Processing
Creates digital image from sensed data.
Image may be continuous w.r.t x, y-axis and amplitude .
Sampling:
Digitizing the Coordinate values.
Equally spaced samples taken for Figure 2.16.
Practically, Sampling depends upon sensor arrangement.
Quantization:
Digitizing the Amplitude values.
8 Level quantization is performed on Figure 2.16.
Chapter:2, Slide # 20
Sampling and Quantization
Umer Javed, CS: 407: Digital Image Processing Chapter:2, Slide # 21
Courtesy: DIP 3/Edition
Sampling and Quantization
Umer Javed, CS: 407: Digital Image Processing
Courtesy: DIP 3/Edition
Digital Image Values
Introduction 23Umer Javed, CS: 407: Digital Image Processing
Courtesy: DIP 3/Edition