image processing

1. Image Formation & System
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2. Light And The Electromagnetic Spectrum
Light: just a particular part of electromagnetic spectrum that can be sensed
by the human eye
The electromagnetic spectrum is split up according to the wavelengths of different
forms of energy
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3. • Wavelength - Wavelength is the distance between two
successive wave crests or wave troughs in the direction
of travel.
• Amplitude - Amplitude is the maximum distance the
oscillation travels, away from its horizontal axis.
• Frequency - The frequency of vibration is the number of
waves crossing at a point
Nature of Light

4. Frequency
Velocity of light= frequency x wavelength

v
c 

5. Reflected Light
The colours humans perceive are determined by nature of light
reflected from an object
For example, if white light (contains all
wavelengths) is shone onto green object
it absorbs most wavelengths absorbed
except green wavelength (color)
Colours
Absorbed
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6. Electromagnetic Spectrum and IP
 Images can be made from any form of EM radiation

7. Images from Different EM Radiation
 Radar imaging (radio waves)
 Magnetic Resonance Imaging (MRI) (Radio waves)
 Microwave imaging
 Infrared imaging
 Photographs
 Ultraviolet imaging telescopes
 X‐rays and Computed tomography
 Positron emission tomography (gamma rays)
 Ultrasound (not EM waves)

8. Examples of DIP:
CT: Computer Tomography
• http://www.nlm.nih.gov/research/vi
sible/image/head.jpg
• Section through Visible Human
Male - head, including cerebellum,
cerebral cortex, brainstem, nasal
passages (from Head subset)
• This is an example of the “visible
human project” sponsored by NIH
• DIP techniques applicable:
– Enhancement
– Segmentation

9. Ultrasound Image
• Profiles of a fetus
at 4 months, the
face is about 4cm
long
• Ultra sound image
is another imaging
modality
• The fetal arm with
the major arteries
(radial and ulnar)
clearly delineated.
http://www.parenthood.com/us.html

10. )
(
)
,
,
(
)
,
,
( 


 L
y
x
y
x
I 


11. BIOLOGICAL ASPECTS OF IMAGE ACQUISITION
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13. MMR,CSE4105,MBSTU

14. Muscles in eye can change the shape of the lens allowing us
focus on near or far objects
An image is focused onto retina exciting the rods and cones and
send signals to the brain
Image Formation In The Eye

15.  The Pinhole Camera (abstraction)
 First described by ancient Chinese and Greeks (300‐400AD)
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16. Simple Image Formation Process

19. Monochrome and Color Image Models

20. MMR,CSE4105,MBSTU

21. Image Formation

24. IMAGE FORMATION MODEL
• 𝑓 𝑥, 𝑦 = 𝑖 𝑥, 𝑦 × 𝑟 𝑥, 𝑦
ℎ𝑒𝑟𝑒 0 < 𝑖 𝑥, 𝑦 <∝ 𝑎𝑛𝑑 0 < 𝑟 𝑥, 𝑦 < 1
i(x,y) is determined by illumination source-illumination component
r(x ,y) is reflected component
0/total absorption, 1/total reflectance
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25. Visual Phenomena

26. • Image Brightness : Brightness of a grayscale image is the average
intensity of all pixels in image . Relative term depends on visual
perception
• So, brightness can be defined as the amount of energy output by a
source of light relative to the source we are comparing it to.
Brightness

27. Contrast
• Contrast generally refers to the difference in luminance or grey level
values in an image and is an important characteristic. It can be
defined as the ratio of the maximum intensity to the minimum
intensity over an image.
• Contrast= maximum pixel intensity - minimum pixel intensity
• Contrast ratio has a strong bearing on the resolving power and
detectability of an image. Larger this ratio, more easy it is to interpret
the image
• Contrast increase then light area lighter dark area darker

28. CONTRAST SENSITIVITY
Weber Ratio =
∆𝐼𝐶
𝐼
I= Constant
illumination
Ic= Illumination
increased
LOW Weber ratio means low variation is detected by observer/ good discernible
HIGH Weber ratio means large variation is required to notice the change
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29. Brightness Adaptation & Discrimination
The human visual system can perceive approximately 1010 different
light intensity levels
However, at any one time we can only discriminate between a much
smaller number – brightness adaptation
Similarly, perceived intensity of a region is related to the light
intensities of the regions surrounding it
A Phenomenon is observed when power supply is cut-off in the night Stare at the sun for a couple of seconds

30. Brightness Adaptation & Discrimination:
Mach Band Effect
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
 Perceived intensity overshoots or
undershoots at areas of intensity change
 For eight strips together, visual
appearance is that each strip looks
darker at the right side than its left
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31. Simultaneous contrast. All small squares have exactly the same intensity
but they appear progressively darker as background becomes lighter.
Brightness Adaptation of Human Eye : Simultaneous Contrast

32. Brightness Adaptation & Discrimination
An example of simultaneous contrast
All inner squares have same intensity but appear darker as outer
square (surrounding area) gets lighter
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
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33. Imaging System
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34. REVIEW OF DIGITAL CAMERA
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35. Digital Camera
• Aperature, a hole, through which light passes. It
determines how much light is focused onto the image
plane.
• Has a series of lenses that focus the light onto the
subject. Instead of focusing the light onto a film, a digital
camera focuses the light onto sensors.
• Heart of camera image sensor, converts the light energy
into an electrical charge. CCD and CMOs
• CCD produces more high quality images and more
immune to noise but consumes more power than
CMOs.

36. Image Sensing
Incoming energy (e.g. light) lands on a sensor material
responsive to that type of energy, generating a voltage
Collections of sensors are arranged to capture images
Imaging Sensor
Line of Image Sensors
Array of Image Sensors