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Lectures 1-3
MAN 325
Mathematical Imaging
Techniques
Instructor
► Dr. Sanjeev Kumar
Associate Professor
Department of Mathematics, IIT Roorkee
Can catch at : Room No. 302
mail at: malikfma@iitr.ac.in
gtalk: MALIKDMA@GMAIL
Lectures 1 3 final (4)
Lectures 1 3 final (4)
S. No.
Contents
1. Image fundamentals: A simple image formation model, sampling and quantization,
connectivity and adjacency relationships between pixels
2. Spatial domain filtering: Basic intensity transformations: negative, log, power-law and
piecewise linear transformations, bit-plane slicing, histogram equalization and matching,
smoothing and sharpening filtering in spatial domain, unsharp masking and high-boost
filtering
3. Frequency domain filtering: Fourier Series and Fourier transform, discrete and fast
Fourier transform, sampling theorem, aliasing, filtering in frequency domain, lowpass
and highpass filters, bandreject and bandpass filters, notch filters
4. Image restoration: Introduction to various noise models, restoration in presence of
noise only, periodic noise reduction, linear and position invariant degradation,
estimation of degradation function
5. Image reconstruction: Principles of computed tomography, projections and Radon
transform, the Fourier slice theorem, reconstruction using parallel-beam and fan-beam
by filtered backprojection methods
6. Mathematical morphology: Erosion and dilation, opening and closing, the Hit-or-Miss
transformation, various morphological algorithms for binary images
7. Wavelets and multiresolution processing: Image pyramids, subband coding,
multiresolution expansions, the Haar transform, wavelet transform in one and two
dimensions, discrete wavelet transform
Gonzalez, R. C. and Woods, R. E., "Digital Image
Processing", Prentice Hall, 3rd Ed.
Jain, A. K., "Fundamentals of Digital Image Processing",
PHI Learning, 1st Ed.
Bernd, J., "Digital Image Processing", Springer, 6th Ed.
Burger, W. and Burge, M. J., "Principles of Digital Image
Processing", Springer
Scherzer, O., " Handbook of Mathematical Methods in
Imaging", Springer
Lectures 1 3 final (4)
Weeks 1 & 2 8
Image Acquisition Process
Weeks 1 & 2 9
Introduction
► What is Digital Image Processing?
Digital Image
— a two-dimensional function
x and y are spatial coordinates
The amplitude of f is called intensity or gray level at the point (x, y)
Digital Image Processing
— process digital images by means of computer, it covers low-, mid-, and high-level
processes
low-level: inputs and outputs are images
mid-level: outputs are attributes extracted from input images
high-level: an ensemble of recognition of individual objects
Pixel
— the elements of a digital image
( , )
f x y
Weeks 1 & 2 10
A Simple Image Formation Model
( , ) ( , ) ( , )
( , ): intensity at the point ( , )
( , ): illumination at the point ( , )
(the amount of source illumination incident on the scene)
( , ): reflectance/transmissivity
f x y i x y r x y
f x y x y
i x y x y
r x y

at the point ( , )
(the amount of illumination reflected/transmitted by the object)
where 0 < ( , ) < and 0 < ( , ) < 1
x y
i x y r x y

Weeks 1 & 2 11
Some Typical Ranges of Reflectance
► Reflectance
 0.01 for black velvet
 0.65 for stainless steel
 0.80 for flat-white wall paint
 0.90 for silver-plated metal
 0.93 for snow
Weeks 1 & 2 12
Image Sampling and Quantization
Digitizing the
coordinate
values
Digitizing the
amplitude
values
Weeks 1 & 2 13
Image Sampling and Quantization
Weeks 1 & 2 14
Representing Digital Images
►The representation of an M×N numerical
array as
(0,0) (0,1) ... (0, 1)
(1,0) (1,1) ... (1, 1)
( , )
... ... ... ...
( 1,0) ( 1,1) ... ( 1, 1)
f f f N
f f f N
f x y
f M f M f M N

 
 

 

 
 
   
 
Weeks 1 & 2 15
Representing Digital Images
►The representation of an M×N numerical
array as
0,0 0,1 0, 1
1,0 1,1 1, 1
1,0 1,1 1, 1
...
...
... ... ... ...
...
N
N
M M M N
a a a
a a a
A
a a a


   
 
 
 

 
 
 
Weeks 1 & 2 16
Representing Digital Images
►The representation of an M×N numerical
array in MATLAB
(1,1) (1,2) ... (1, )
(2,1) (2,2) ... (2, )
( , )
... ... ... ...
( ,1) ( ,2) ... ( , )
f f f N
f f f N
f x y
f M f M f M N
 
 
 

 
 
 
Weeks 1 & 2 17
Representing Digital Images
► Discrete intensity interval [0, L-1], L=2k
► The number b of bits required to store a M × N
digitized image
b = M × N × k
Weeks 1 & 2 18
Representing Digital Images
Lectures 1 3 final (4)
Lectures 1 3 final (4)
Lectures 1 3 final (4)
What is a Digital Image? (cont…)
►Common image formats include:
 1 sample per point (B&W or Grayscale)
 3 samples per point (Red, Green, and Blue)
 4 samples per point (Red, Green, Blue, and “Alpha”,
a.k.a. Opacity)
►For most of this course we will focus on grey-scale
Image processing
► An image processing operation typically defines
a new image g in terms of an existing image f.
► We can transform either the range of f.
► Or the domain of f:
► What kinds of operations can each perform?
What is DIP? (cont…)
►The continuum from image processing to
computer vision can be broken up into low-,
mid- and high-level processes
Low Level Process
Input: Image
Output: Image
Examples: Noise
removal, image
sharpening
Mid Level Process
Input: Image
Output: Attributes
Examples: Object
recognition,
segmentation
High Level Process
Input: Attributes
Output:
Understanding
Examples: Scene
understanding,
autonomous navigation
In this course we will
stop here
Key Stages in Digital Image Processing
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Key Stages in Digital Image Processing:
Image Aquisition
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Image Enhancement
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Image Restoration
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Morphological Processing
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Segmentation
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Object Recognition
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Representation & Description
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Images
taken
from
Gonzalez
&
Woods,
Digital
Image
Processing
(2002)
Key Stages in Digital Image Processing:
Image Compression
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Key Stages in Digital Image Processing:
Colour Image Processing
Image
Acquisition
Image
Restoration
Morphological
Processing
Segmentation
Representation
& Description
Image
Enhancement
Object
Recognition
Problem Domain
Colour Image
Processing
Image
Compression
Applications
&
Research Topics
Document Handling
Signature Verification
Biometrics
Fingerprint Verification /
Identification
Fingerprint Identification Research at
UNR
Minutiae Matching
Delaunay Triangulation
Object Recognition
Object Recognition Research
reference view 1 reference view 2
novel view recognized
Indexing into Databases
►Shape content
Indexing into Databases
(cont’d)
►Color, texture
Target Recognition
►Department of Defense (Army, Airforce,
Navy)
Interpretation of aerial photography is a problem domain in both
computer vision and registration.
Interpretation of Aerial
Photography
Autonomous Vehicles
►Land, Underwater, Space
Traffic Monitoring
Face Detection
Face Recognition
Face Detection/Recognition Research
at UNR
Facial Expression Recognition
Face Tracking
Face Tracking (cont’d)
Hand Gesture Recognition
► Smart Human-Computer User Interfaces
► Sign Language Recognition
Human Activity Recognition
Medical Applications
► skin cancer breast cancer
Morphing
Inserting Artificial Objects into a Scene
Companies In this Field In India
► Sarnoff Corporation
► Kritikal Solutions
► National Instruments
► GE Laboratories
► Ittiam, Bangalore
► Interra Systems, Noida
► Yahoo India (Multimedia Searching)
► nVidia Graphics, Pune (have high requirements)
► Microsoft research
► DRDO labs
► ISRO labs
► …
Neighborhood Operations in Images
Weeks 1 & 2 62
Basic Relationships Between Pixels
► Neighborhood
► Adjacency
► Connectivity
► Paths
► Regions and boundaries
Weeks 1 & 2 63
Basic Relationships Between Pixels
► Neighbors of a pixel p at coordinates (x,y)
 4-neighbors of p, denoted by N4(p):
(x-1, y), (x+1, y), (x,y-1), and (x, y+1).
 4 diagonal neighbors of p, denoted by ND(p):
(x-1, y-1), (x+1, y+1), (x+1,y-1), and (x-1, y+1).
 8 neighbors of p, denoted N8(p)
N8(p) = N4(p) U ND(p)
Weeks 1 & 2 64
Basic Relationships Between Pixels
► Adjacency
Let V be the set of intensity values
 4-adjacency: Two pixels p and q with values from V are
4-adjacent if q is in the set N4(p).
 8-adjacency: Two pixels p and q with values from V are
8-adjacent if q is in the set N8(p).
Weeks 1 & 2 65
Basic Relationships Between Pixels
► Adjacency
Let V be the set of intensity values
 m-adjacency: Two pixels p and q with values from V are
m-adjacent if
(i) q is in the set N4(p), or
(ii) q is in the set ND(p) and the set N4(p) ∩ N4(p) has no pixels whose
values are from V.
Weeks 1 & 2 66
Basic Relationships Between Pixels
► Path
 A (digital) path (or curve) from pixel p with coordinates (x0, y0) to pixel
q with coordinates (xn, yn) is a sequence of distinct pixels with
coordinates
(x0, y0), (x1, y1), …, (xn, yn)
Where (xi, yi) and (xi-1, yi-1) are adjacent for 1 ≤ i ≤ n.
 Here n is the length of the path.
 If (x0, y0) = (xn, yn), the path is closed path.
 We can define 4-, 8-, and m-paths based on the type of adjacency
used.
Weeks 1 & 2 67
Examples: Adjacency and Path
0 1 1 0 1 1 0 1 1
0 2 0 0 2 0 0 2 0
0 0 1 0 0 1 0 0 1
V = {1, 2}
Weeks 1 & 2 68
Examples: Adjacency and Path
0 1 1 0 1 1 0 1 1
0 2 0 0 2 0 0 2 0
0 0 1 0 0 1 0 0 1
V = {1, 2}
8-adjacent
Weeks 1 & 2 69
Examples: Adjacency and Path
0 1 1 0 1 1 0 1 1
0 2 0 0 2 0 0 2 0
0 0 1 0 0 1 0 0 1
V = {1, 2}
8-adjacent m-adjacent
Weeks 1 & 2 70
Examples: Adjacency and Path
01,1 11,2 11,3 0 1 1 0 1 1
02,1 22,2 02,3 0 2 0 0 2 0
03,1 03,2 13,3 0 0 1 0 0 1
V = {1, 2}
8-adjacent m-adjacent
The 8-path from (1,3) to (3,3):
(i) (1,3), (1,2), (2,2), (3,3)
(ii) (1,3), (2,2), (3,3)
The m-path from (1,3) to (3,3):
(1,3), (1,2), (2,2), (3,3)
Weeks 1 & 2 71
Basic Relationships Between Pixels
► Connected in S
Let S represent a subset of pixels in an image. Two pixels
p with coordinates (x0, y0) and q with coordinates (xn, yn)
are said to be connected in S if there exists a path
(x0, y0), (x1, y1), …, (xn, yn)
Where ,0 ,( , )
i i
i i n x y S
   
Weeks 1 & 2 72
Basic Relationships Between Pixels
Let S represent a subset of pixels in an image
► For every pixel p in S, the set of pixels in S that are connected to p is
called a connected component of S.
► If S has only one connected component, then S is called Connected
Set.
► We call R a region of the image if R is a connected set
► Two regions, Ri and Rj are said to be adjacent if their union forms a
connected set.
► Regions that are not to be adjacent are said to be disjoint.
Weeks 1 & 2 73
Basic Relationships Between Pixels
Weeks 1 & 2 74
Basic Relationships Between Pixels
Weeks 1 & 2 75
Basic Relationships Between Pixels
Weeks 1 & 2 76
Basic Relationships Between Pixels
BW = imread('text.png');
imshow(BW);
CC = bwconncomp(BW);
numPixels =
cellfun(@numel,CC.PixelIdxList);
[biggest,idx] = max(numPixels);
BW(CC.PixelIdxList{idx}) = 0;
figure, imshow(BW);
Weeks 1 & 2 77
Basic Relationships Between Pixels
► Boundary (or border)
 The boundary of the region R is the set of pixels in the region that
have one or more neighbors that are not in R.
 If R happens to be an entire image, then its boundary is defined as the
set of pixels in the first and last rows and columns of the image.
► Foreground and background
 An image contains K disjoint regions, Rk, k = 1, 2, …, K. Let Ru denote
the union of all the K regions, and let (Ru)c denote its complement.
All the points in Ru is called foreground;
All the points in (Ru)c is called background.
Weeks 1 & 2 78
Question 1
► In the following arrangement of pixels, are the two
regions (of 1s) adjacent? (if 8-adjacency is used)
1 1 1
1 0 1
0 1 0
0 0 1
1 1 1
1 1 1
Region 1
Region 2
Weeks 1 & 2 79
Question 2
► In the following arrangement of pixels, are the two
parts (of 1s) adjacent? (if 4-adjacency is used)
1 1 1
1 0 1
0 1 0
0 0 1
1 1 1
1 1 1
Part 1
Part 2
Weeks 1 & 2 80
► In the following arrangement of pixels, the two
regions (of 1s) are disjoint (if 4-adjacency is used)
1 1 1
1 0 1
0 1 0
0 0 1
1 1 1
1 1 1
Region 1
Region 2
Weeks 1 & 2 81
► In the following arrangement of pixels, the two
regions (of 1s) are disjoint (if 4-adjacency is used)
1 1 1
1 0 1
0 1 0
0 0 1
1 1 1
1 1 1
foreground
background
Weeks 1 & 2 82
Question 3
► In the following arrangement of pixels, the circled
point is part of the boundary of the 1-valued pixels
if 8-adjacency is used, true or false?
0 0 0 0 0
0 1 1 0 0
0 1 1 0 0
0 1 1 1 0
0 1 1 1 0
0 0 0 0 0
Weeks 1 & 2 83
Question 4
► In the following arrangement of pixels, the circled
point is part of the boundary of the 1-valued pixels
if 4-adjacency is used, true or false?
0 0 0 0 0
0 1 1 0 0
0 1 1 0 0
0 1 1 1 0
0 1 1 1 0
0 0 0 0 0
Weeks 1 & 2 84
Distance Measures
► Given pixels p, q and z with coordinates (x, y), (s, t),
(u, v) respectively, the distance function D has
following properties:
a. D(p, q) ≥ 0 [D(p, q) = 0, iff p = q]
b. D(p, q) = D(q, p)
c. D(p, z) ≤ D(p, q) + D(q, z)
Weeks 1 & 2 85
Distance Measures
The following are the different Distance measures:
a. Euclidean Distance :
De(p, q) = [(x-s)2 + (y-t)2]1/2
b. City Block Distance:
D4(p, q) = |x-s| + |y-t|
c. Chess Board Distance:
D8(p, q) = max(|x-s|, |y-t|)
Weeks 1 & 2 86
Question 5
► In the following arrangement of pixels, what’s the
value of the chessboard distance between the
circled two points?
0 0 0 0 0
0 0 1 1 0
0 1 1 0 0
0 1 0 0 0
0 0 0 0 0
0 0 0 0 0
Weeks 1 & 2 87
Question 6
► In the following arrangement of pixels, what’s the
value of the city-block distance between the circled
two points?
0 0 0 0 0
0 0 1 1 0
0 1 1 0 0
0 1 0 0 0
0 0 0 0 0
0 0 0 0 0
Weeks 1 & 2 88
Introduction to Mathematical Operations in
DIP
► Array vs. Matrix Operation
11 12
21 22
b b
B
b b
 
  
 
11 12
21 22
a a
A
a a
 
  
 
11 11 12 21 11 12 12 22
21 11 22 21 21 12 22 22
*
a b a b a b a b
A B
a b a b a b a b
 
 
  
 
 
11 11 12 12
21 21 22 22
.*
a b a b
A B
a b a b
 
  
 
Array product
Matrix product
Array
product
operator
Matrix
product
operator
Weeks 1 & 2 89
Introduction to Mathematical Operations in
DIP
► Linear vs. Nonlinear Operation
H is said to be a linear operator;
H is said to be a nonlinear operator if it does not meet the
above qualification.
 
( , ) ( , )
H f x y g x y

Additivity
Homogeneity
 
 
( , ) ( , )
( , ) ( , )
( , ) ( , )
( , ) ( , )
i i j j
i i j j
i i j j
i i j j
H a f x y a f x y
H a f x y H a f x y
a H f x y a H f x y
a g x y a g x y
 

 
 
   
 
   
 
Weeks 1 & 2 90
Arithmetic Operations
► Arithmetic operations between images are array
operations. The four arithmetic operations are denoted
as
s(x,y) = f(x,y) + g(x,y)
d(x,y) = f(x,y) – g(x,y)
p(x,y) = f(x,y) × g(x,y)
v(x,y) = f(x,y) ÷ g(x,y)
Weeks 1 & 2 91
Example: Addition of Noisy Images for Noise Reduction
Noiseless image: f(x,y)
Noise: n(x,y) (at every pair of coordinates (x,y), the noise is uncorrelated
and has zero average value)
Corrupted image: g(x,y)
g(x,y) = f(x,y) + n(x,y)
Reducing the noise by adding a set of noisy images, {gi(x,y)}
1
1
( , ) ( , )
K
i
i
g x y g x y
K 
 
Weeks 1 & 2 92
Example: Addition of Noisy Images for Noise Reduction
 
 
1
1
1
1
( , ) ( , )
1
( , ) ( , )
1
( , ) ( , )
( , )
K
i
i
K
i
i
K
i
i
E g x y E g x y
K
E f x y n x y
K
f x y E n x y
K
f x y



 
  
 
 
 
 
 
 
   
 




1
1
( , ) ( , )
K
i
i
g x y g x y
K 
 
2
( , ) 1
( , )
1
1
( , )
1
2
2 2
( , )
1
g x y K
g x y
i
K i
K
n x y
i
K i
n x y
K
 
 





 
Weeks 1 & 2 93
Example: Addition of Noisy Images for Noise Reduction
► In astronomy, imaging under very low light levels
frequently causes sensor noise to render single images
virtually useless for analysis.
► In astronomical observations, similar sensors for noise
reduction by observing the same scene over long
periods of time. Image averaging is then used to
reduce the noise.
Weeks 1 & 2 94
Weeks 1 & 2 95
An Example of Image Subtraction: Mask Mode Radiography
Mask h(x,y): an X-ray image of a region of a patient’s body
Live images f(x,y): X-ray images captured at TV rates after injection of
the contrast medium
Enhanced detail g(x,y)
g(x,y) = f(x,y) - h(x,y)
The procedure gives a movie showing how the contrast medium
propagates through the various arteries in the area being observed.
Weeks 1 & 2 96
Weeks 1 & 2 97
An Example of Image Multiplication
Weeks 1 & 2 98
Set and Logical Operations
Weeks 1 & 2 99
Set and Logical Operations
► Let A be the elements of a gray-scale image
The elements of A are triplets of the form (x, y, z), where
x and y are spatial coordinates and z denotes the intensity
at the point (x, y).
► The complement of A is denoted Ac
{( , , ) | ( , , ) }
2 1; is the number of intensity bits used to represent
c
k
A x y K z x y z A
K k z
  
 
{( , , ) | ( , )}
A x y z z f x y
 
Weeks 1 & 2 100
Set and Logical Operations
► The union of two gray-scale images (sets) A and B is
defined as the set
{max( , ) | , }
z
A B a b a A b B
   
Weeks 1 & 2 101
Set and Logical Operations
Weeks 1 & 2 102
Set and Logical Operations
Weeks 1 & 2 103
Spatial Operations
► Single-pixel operations
Alter the values of an image’s pixels based on the intensity.
e.g.,
( )
s T z

Weeks 1 & 2 104
Spatial Operations
► Neighborhood operations
The value of this pixel is
determined by a specified
operation involving the pixels in
the input image with coordinates
in Sxy
Weeks 1 & 2 105
Spatial Operations
► Neighborhood operations
Weeks 1 & 2 106
Geometric Spatial Transformations
► Geometric transformation (rubber-sheet transformation)
— A spatial transformation of coordinates
— intensity interpolation that assigns intensity values to the spatially
transformed pixels.
► Affine transform
( , ) {( , )}
x y T v w

   
11 12
21 22
31 32
0
1 1 0
1
t t
x y v w t t
t t
 
 
  
 
 
Weeks 1 & 2 107
Weeks 1 & 2 108
Image Registration
► Input and output images are available but the
transformation function is unknown.
Goal: estimate the transformation function and use it to
register the two images.
► One of the principal approaches for image registration is
to use tie points (also called control points)
 The corresponding points are known precisely in the
input and output (reference) images.
Weeks 1 & 2 109
Image Registration
► A simple model based on bilinear approximation:
1 2 3 4
5 6 7 8
Where ( , ) and ( , ) are the coordinates of
tie points in the input and reference images.
x c v c w c vw c
y c v c w c vw c
v w x y
   


   

Weeks 1 & 2 110
Image Registration
Weeks 1 & 2 111
Image Transform
► A particularly important class of 2-D linear transforms,
denoted T(u, v)
1 1
0 0
( , ) ( , ) ( , , , )
where ( , ) is the input image,
( , , , ) is the ker ,
variables and are the transform variables,
= 0, 1, 2, ..., M-1 and = 0, 1,
M N
x y
T u v f x y r x y u v
f x y
r x y u v forward transformation nel
u v
u v
 
 
 
..., N-1.
Weeks 1 & 2 112
Image Transform
► Given T(u, v), the original image f(x, y) can be recoverd
using the inverse tranformation of T(u, v).
1 1
0 0
( , ) ( , ) ( , , , )
where ( , , , ) is the ker ,
= 0, 1, 2, ..., M-1 and = 0, 1, ..., N-1.
M N
u v
f x y T u v s x y u v
s x y u v inverse transformation nel
x y
 
 
 
Weeks 1 & 2 113
Image Transform
Weeks 1 & 2 114
Example: Image Denoising by Using DCT Transform
Weeks 1 & 2 115
Forward Transform Kernel
1 1
0 0
1 2
1 2
( , ) ( , ) ( , , , )
The kernel ( , , , ) is said to be SEPERABLE if
( , , , ) ( , ) ( , )
In addition, the kernel is said to be SYMMETRIC if
( , ) is functionally equal to ( ,
M N
x y
T u v f x y r x y u v
r x y u v
r x y u v r x u r y v
r x u r y v
 
 



1 1
), so that
( , , , ) ( , ) ( , )
r x y u v r x u r y u

Weeks 1 & 2 116
The Kernels for 2-D Fourier Transform
2 ( / / )
2 ( / / )
The kernel
( , , , )
Where = 1
The kernel
1
( , , , )
j ux M vy N
j ux M vy N
forward
r x y u v e
j
inverse
s x y u v e
MN


 




Weeks 1 & 2 117
2-D Fourier Transform
1 1
2 ( / / )
0 0
1 1
2 ( / / )
0 0
( , ) ( , )
1
( , ) ( , )
M N
j ux M vy N
x y
M N
j ux M vy N
u v
T u v f x y e
f x y T u v e
MN


 
 
 
 

 




Weeks 1 & 2 118
Probabilistic Methods
Let , 0, 1, 2, ..., -1, denote the values of all possible intensities
in an digital image. The probability, ( ), of intensity level
occurring in a given image is estimated as
i
k
k
z i L
M N p z
z


( ) ,
where is the number of times that intensity occurs in the image.
k
k
k k
n
p z
MN
n z

1
0
( ) 1
L
k
k
p z




1
0
The mean (average) intensity is given by
= ( )
L
k k
k
m z p z



Weeks 1 & 2 119
Probabilistic Methods
1
2 2
0
The variance of the intensities is given by
= ( ) ( )
L
k k
k
z m p z





th
1
0
The moment of the intensity variable is
( ) = ( ) ( )
L
n
n k k
k
n z
u z z m p z




Weeks 1 & 2 120
Example: Comparison of Standard Deviation
Values
31.6
 
14.3
  49.2
 

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Lectures 1 3 final (4)

  • 2. Instructor ► Dr. Sanjeev Kumar Associate Professor Department of Mathematics, IIT Roorkee Can catch at : Room No. 302 mail at: malikfma@iitr.ac.in gtalk: MALIKDMA@GMAIL
  • 5. S. No. Contents 1. Image fundamentals: A simple image formation model, sampling and quantization, connectivity and adjacency relationships between pixels 2. Spatial domain filtering: Basic intensity transformations: negative, log, power-law and piecewise linear transformations, bit-plane slicing, histogram equalization and matching, smoothing and sharpening filtering in spatial domain, unsharp masking and high-boost filtering 3. Frequency domain filtering: Fourier Series and Fourier transform, discrete and fast Fourier transform, sampling theorem, aliasing, filtering in frequency domain, lowpass and highpass filters, bandreject and bandpass filters, notch filters 4. Image restoration: Introduction to various noise models, restoration in presence of noise only, periodic noise reduction, linear and position invariant degradation, estimation of degradation function 5. Image reconstruction: Principles of computed tomography, projections and Radon transform, the Fourier slice theorem, reconstruction using parallel-beam and fan-beam by filtered backprojection methods 6. Mathematical morphology: Erosion and dilation, opening and closing, the Hit-or-Miss transformation, various morphological algorithms for binary images 7. Wavelets and multiresolution processing: Image pyramids, subband coding, multiresolution expansions, the Haar transform, wavelet transform in one and two dimensions, discrete wavelet transform
  • 6. Gonzalez, R. C. and Woods, R. E., "Digital Image Processing", Prentice Hall, 3rd Ed. Jain, A. K., "Fundamentals of Digital Image Processing", PHI Learning, 1st Ed. Bernd, J., "Digital Image Processing", Springer, 6th Ed. Burger, W. and Burge, M. J., "Principles of Digital Image Processing", Springer Scherzer, O., " Handbook of Mathematical Methods in Imaging", Springer
  • 8. Weeks 1 & 2 8 Image Acquisition Process
  • 9. Weeks 1 & 2 9 Introduction ► What is Digital Image Processing? Digital Image — a two-dimensional function x and y are spatial coordinates The amplitude of f is called intensity or gray level at the point (x, y) Digital Image Processing — process digital images by means of computer, it covers low-, mid-, and high-level processes low-level: inputs and outputs are images mid-level: outputs are attributes extracted from input images high-level: an ensemble of recognition of individual objects Pixel — the elements of a digital image ( , ) f x y
  • 10. Weeks 1 & 2 10 A Simple Image Formation Model ( , ) ( , ) ( , ) ( , ): intensity at the point ( , ) ( , ): illumination at the point ( , ) (the amount of source illumination incident on the scene) ( , ): reflectance/transmissivity f x y i x y r x y f x y x y i x y x y r x y  at the point ( , ) (the amount of illumination reflected/transmitted by the object) where 0 < ( , ) < and 0 < ( , ) < 1 x y i x y r x y 
  • 11. Weeks 1 & 2 11 Some Typical Ranges of Reflectance ► Reflectance  0.01 for black velvet  0.65 for stainless steel  0.80 for flat-white wall paint  0.90 for silver-plated metal  0.93 for snow
  • 12. Weeks 1 & 2 12 Image Sampling and Quantization Digitizing the coordinate values Digitizing the amplitude values
  • 13. Weeks 1 & 2 13 Image Sampling and Quantization
  • 14. Weeks 1 & 2 14 Representing Digital Images ►The representation of an M×N numerical array as (0,0) (0,1) ... (0, 1) (1,0) (1,1) ... (1, 1) ( , ) ... ... ... ... ( 1,0) ( 1,1) ... ( 1, 1) f f f N f f f N f x y f M f M f M N                   
  • 15. Weeks 1 & 2 15 Representing Digital Images ►The representation of an M×N numerical array as 0,0 0,1 0, 1 1,0 1,1 1, 1 1,0 1,1 1, 1 ... ... ... ... ... ... ... N N M M M N a a a a a a A a a a                   
  • 16. Weeks 1 & 2 16 Representing Digital Images ►The representation of an M×N numerical array in MATLAB (1,1) (1,2) ... (1, ) (2,1) (2,2) ... (2, ) ( , ) ... ... ... ... ( ,1) ( ,2) ... ( , ) f f f N f f f N f x y f M f M f M N             
  • 17. Weeks 1 & 2 17 Representing Digital Images ► Discrete intensity interval [0, L-1], L=2k ► The number b of bits required to store a M × N digitized image b = M × N × k
  • 18. Weeks 1 & 2 18 Representing Digital Images
  • 22. What is a Digital Image? (cont…) ►Common image formats include:  1 sample per point (B&W or Grayscale)  3 samples per point (Red, Green, and Blue)  4 samples per point (Red, Green, Blue, and “Alpha”, a.k.a. Opacity) ►For most of this course we will focus on grey-scale
  • 23. Image processing ► An image processing operation typically defines a new image g in terms of an existing image f. ► We can transform either the range of f. ► Or the domain of f: ► What kinds of operations can each perform?
  • 24. What is DIP? (cont…) ►The continuum from image processing to computer vision can be broken up into low-, mid- and high-level processes Low Level Process Input: Image Output: Image Examples: Noise removal, image sharpening Mid Level Process Input: Image Output: Attributes Examples: Object recognition, segmentation High Level Process Input: Attributes Output: Understanding Examples: Scene understanding, autonomous navigation In this course we will stop here
  • 25. Key Stages in Digital Image Processing Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression
  • 26. Key Stages in Digital Image Processing: Image Aquisition Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 27. Key Stages in Digital Image Processing: Image Enhancement Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 28. Key Stages in Digital Image Processing: Image Restoration Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 29. Key Stages in Digital Image Processing: Morphological Processing Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 30. Key Stages in Digital Image Processing: Segmentation Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 31. Key Stages in Digital Image Processing: Object Recognition Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 32. Key Stages in Digital Image Processing: Representation & Description Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression Images taken from Gonzalez & Woods, Digital Image Processing (2002)
  • 33. Key Stages in Digital Image Processing: Image Compression Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression
  • 34. Key Stages in Digital Image Processing: Colour Image Processing Image Acquisition Image Restoration Morphological Processing Segmentation Representation & Description Image Enhancement Object Recognition Problem Domain Colour Image Processing Image Compression
  • 40. Fingerprint Identification Research at UNR Minutiae Matching Delaunay Triangulation
  • 42. Object Recognition Research reference view 1 reference view 2 novel view recognized
  • 45. Target Recognition ►Department of Defense (Army, Airforce, Navy)
  • 46. Interpretation of aerial photography is a problem domain in both computer vision and registration. Interpretation of Aerial Photography
  • 55. Hand Gesture Recognition ► Smart Human-Computer User Interfaces ► Sign Language Recognition
  • 57. Medical Applications ► skin cancer breast cancer
  • 60. Companies In this Field In India ► Sarnoff Corporation ► Kritikal Solutions ► National Instruments ► GE Laboratories ► Ittiam, Bangalore ► Interra Systems, Noida ► Yahoo India (Multimedia Searching) ► nVidia Graphics, Pune (have high requirements) ► Microsoft research ► DRDO labs ► ISRO labs ► …
  • 62. Weeks 1 & 2 62 Basic Relationships Between Pixels ► Neighborhood ► Adjacency ► Connectivity ► Paths ► Regions and boundaries
  • 63. Weeks 1 & 2 63 Basic Relationships Between Pixels ► Neighbors of a pixel p at coordinates (x,y)  4-neighbors of p, denoted by N4(p): (x-1, y), (x+1, y), (x,y-1), and (x, y+1).  4 diagonal neighbors of p, denoted by ND(p): (x-1, y-1), (x+1, y+1), (x+1,y-1), and (x-1, y+1).  8 neighbors of p, denoted N8(p) N8(p) = N4(p) U ND(p)
  • 64. Weeks 1 & 2 64 Basic Relationships Between Pixels ► Adjacency Let V be the set of intensity values  4-adjacency: Two pixels p and q with values from V are 4-adjacent if q is in the set N4(p).  8-adjacency: Two pixels p and q with values from V are 8-adjacent if q is in the set N8(p).
  • 65. Weeks 1 & 2 65 Basic Relationships Between Pixels ► Adjacency Let V be the set of intensity values  m-adjacency: Two pixels p and q with values from V are m-adjacent if (i) q is in the set N4(p), or (ii) q is in the set ND(p) and the set N4(p) ∩ N4(p) has no pixels whose values are from V.
  • 66. Weeks 1 & 2 66 Basic Relationships Between Pixels ► Path  A (digital) path (or curve) from pixel p with coordinates (x0, y0) to pixel q with coordinates (xn, yn) is a sequence of distinct pixels with coordinates (x0, y0), (x1, y1), …, (xn, yn) Where (xi, yi) and (xi-1, yi-1) are adjacent for 1 ≤ i ≤ n.  Here n is the length of the path.  If (x0, y0) = (xn, yn), the path is closed path.  We can define 4-, 8-, and m-paths based on the type of adjacency used.
  • 67. Weeks 1 & 2 67 Examples: Adjacency and Path 0 1 1 0 1 1 0 1 1 0 2 0 0 2 0 0 2 0 0 0 1 0 0 1 0 0 1 V = {1, 2}
  • 68. Weeks 1 & 2 68 Examples: Adjacency and Path 0 1 1 0 1 1 0 1 1 0 2 0 0 2 0 0 2 0 0 0 1 0 0 1 0 0 1 V = {1, 2} 8-adjacent
  • 69. Weeks 1 & 2 69 Examples: Adjacency and Path 0 1 1 0 1 1 0 1 1 0 2 0 0 2 0 0 2 0 0 0 1 0 0 1 0 0 1 V = {1, 2} 8-adjacent m-adjacent
  • 70. Weeks 1 & 2 70 Examples: Adjacency and Path 01,1 11,2 11,3 0 1 1 0 1 1 02,1 22,2 02,3 0 2 0 0 2 0 03,1 03,2 13,3 0 0 1 0 0 1 V = {1, 2} 8-adjacent m-adjacent The 8-path from (1,3) to (3,3): (i) (1,3), (1,2), (2,2), (3,3) (ii) (1,3), (2,2), (3,3) The m-path from (1,3) to (3,3): (1,3), (1,2), (2,2), (3,3)
  • 71. Weeks 1 & 2 71 Basic Relationships Between Pixels ► Connected in S Let S represent a subset of pixels in an image. Two pixels p with coordinates (x0, y0) and q with coordinates (xn, yn) are said to be connected in S if there exists a path (x0, y0), (x1, y1), …, (xn, yn) Where ,0 ,( , ) i i i i n x y S    
  • 72. Weeks 1 & 2 72 Basic Relationships Between Pixels Let S represent a subset of pixels in an image ► For every pixel p in S, the set of pixels in S that are connected to p is called a connected component of S. ► If S has only one connected component, then S is called Connected Set. ► We call R a region of the image if R is a connected set ► Two regions, Ri and Rj are said to be adjacent if their union forms a connected set. ► Regions that are not to be adjacent are said to be disjoint.
  • 73. Weeks 1 & 2 73 Basic Relationships Between Pixels
  • 74. Weeks 1 & 2 74 Basic Relationships Between Pixels
  • 75. Weeks 1 & 2 75 Basic Relationships Between Pixels
  • 76. Weeks 1 & 2 76 Basic Relationships Between Pixels BW = imread('text.png'); imshow(BW); CC = bwconncomp(BW); numPixels = cellfun(@numel,CC.PixelIdxList); [biggest,idx] = max(numPixels); BW(CC.PixelIdxList{idx}) = 0; figure, imshow(BW);
  • 77. Weeks 1 & 2 77 Basic Relationships Between Pixels ► Boundary (or border)  The boundary of the region R is the set of pixels in the region that have one or more neighbors that are not in R.  If R happens to be an entire image, then its boundary is defined as the set of pixels in the first and last rows and columns of the image. ► Foreground and background  An image contains K disjoint regions, Rk, k = 1, 2, …, K. Let Ru denote the union of all the K regions, and let (Ru)c denote its complement. All the points in Ru is called foreground; All the points in (Ru)c is called background.
  • 78. Weeks 1 & 2 78 Question 1 ► In the following arrangement of pixels, are the two regions (of 1s) adjacent? (if 8-adjacency is used) 1 1 1 1 0 1 0 1 0 0 0 1 1 1 1 1 1 1 Region 1 Region 2
  • 79. Weeks 1 & 2 79 Question 2 ► In the following arrangement of pixels, are the two parts (of 1s) adjacent? (if 4-adjacency is used) 1 1 1 1 0 1 0 1 0 0 0 1 1 1 1 1 1 1 Part 1 Part 2
  • 80. Weeks 1 & 2 80 ► In the following arrangement of pixels, the two regions (of 1s) are disjoint (if 4-adjacency is used) 1 1 1 1 0 1 0 1 0 0 0 1 1 1 1 1 1 1 Region 1 Region 2
  • 81. Weeks 1 & 2 81 ► In the following arrangement of pixels, the two regions (of 1s) are disjoint (if 4-adjacency is used) 1 1 1 1 0 1 0 1 0 0 0 1 1 1 1 1 1 1 foreground background
  • 82. Weeks 1 & 2 82 Question 3 ► In the following arrangement of pixels, the circled point is part of the boundary of the 1-valued pixels if 8-adjacency is used, true or false? 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 1 0 0 1 1 1 0 0 0 0 0 0
  • 83. Weeks 1 & 2 83 Question 4 ► In the following arrangement of pixels, the circled point is part of the boundary of the 1-valued pixels if 4-adjacency is used, true or false? 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 1 0 0 1 1 1 0 0 0 0 0 0
  • 84. Weeks 1 & 2 84 Distance Measures ► Given pixels p, q and z with coordinates (x, y), (s, t), (u, v) respectively, the distance function D has following properties: a. D(p, q) ≥ 0 [D(p, q) = 0, iff p = q] b. D(p, q) = D(q, p) c. D(p, z) ≤ D(p, q) + D(q, z)
  • 85. Weeks 1 & 2 85 Distance Measures The following are the different Distance measures: a. Euclidean Distance : De(p, q) = [(x-s)2 + (y-t)2]1/2 b. City Block Distance: D4(p, q) = |x-s| + |y-t| c. Chess Board Distance: D8(p, q) = max(|x-s|, |y-t|)
  • 86. Weeks 1 & 2 86 Question 5 ► In the following arrangement of pixels, what’s the value of the chessboard distance between the circled two points? 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
  • 87. Weeks 1 & 2 87 Question 6 ► In the following arrangement of pixels, what’s the value of the city-block distance between the circled two points? 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
  • 88. Weeks 1 & 2 88 Introduction to Mathematical Operations in DIP ► Array vs. Matrix Operation 11 12 21 22 b b B b b        11 12 21 22 a a A a a        11 11 12 21 11 12 12 22 21 11 22 21 21 12 22 22 * a b a b a b a b A B a b a b a b a b            11 11 12 12 21 21 22 22 .* a b a b A B a b a b        Array product Matrix product Array product operator Matrix product operator
  • 89. Weeks 1 & 2 89 Introduction to Mathematical Operations in DIP ► Linear vs. Nonlinear Operation H is said to be a linear operator; H is said to be a nonlinear operator if it does not meet the above qualification.   ( , ) ( , ) H f x y g x y  Additivity Homogeneity     ( , ) ( , ) ( , ) ( , ) ( , ) ( , ) ( , ) ( , ) i i j j i i j j i i j j i i j j H a f x y a f x y H a f x y H a f x y a H f x y a H f x y a g x y a g x y                   
  • 90. Weeks 1 & 2 90 Arithmetic Operations ► Arithmetic operations between images are array operations. The four arithmetic operations are denoted as s(x,y) = f(x,y) + g(x,y) d(x,y) = f(x,y) – g(x,y) p(x,y) = f(x,y) × g(x,y) v(x,y) = f(x,y) ÷ g(x,y)
  • 91. Weeks 1 & 2 91 Example: Addition of Noisy Images for Noise Reduction Noiseless image: f(x,y) Noise: n(x,y) (at every pair of coordinates (x,y), the noise is uncorrelated and has zero average value) Corrupted image: g(x,y) g(x,y) = f(x,y) + n(x,y) Reducing the noise by adding a set of noisy images, {gi(x,y)} 1 1 ( , ) ( , ) K i i g x y g x y K   
  • 92. Weeks 1 & 2 92 Example: Addition of Noisy Images for Noise Reduction     1 1 1 1 ( , ) ( , ) 1 ( , ) ( , ) 1 ( , ) ( , ) ( , ) K i i K i i K i i E g x y E g x y K E f x y n x y K f x y E n x y K f x y                               1 1 ( , ) ( , ) K i i g x y g x y K    2 ( , ) 1 ( , ) 1 1 ( , ) 1 2 2 2 ( , ) 1 g x y K g x y i K i K n x y i K i n x y K           
  • 93. Weeks 1 & 2 93 Example: Addition of Noisy Images for Noise Reduction ► In astronomy, imaging under very low light levels frequently causes sensor noise to render single images virtually useless for analysis. ► In astronomical observations, similar sensors for noise reduction by observing the same scene over long periods of time. Image averaging is then used to reduce the noise.
  • 94. Weeks 1 & 2 94
  • 95. Weeks 1 & 2 95 An Example of Image Subtraction: Mask Mode Radiography Mask h(x,y): an X-ray image of a region of a patient’s body Live images f(x,y): X-ray images captured at TV rates after injection of the contrast medium Enhanced detail g(x,y) g(x,y) = f(x,y) - h(x,y) The procedure gives a movie showing how the contrast medium propagates through the various arteries in the area being observed.
  • 96. Weeks 1 & 2 96
  • 97. Weeks 1 & 2 97 An Example of Image Multiplication
  • 98. Weeks 1 & 2 98 Set and Logical Operations
  • 99. Weeks 1 & 2 99 Set and Logical Operations ► Let A be the elements of a gray-scale image The elements of A are triplets of the form (x, y, z), where x and y are spatial coordinates and z denotes the intensity at the point (x, y). ► The complement of A is denoted Ac {( , , ) | ( , , ) } 2 1; is the number of intensity bits used to represent c k A x y K z x y z A K k z      {( , , ) | ( , )} A x y z z f x y  
  • 100. Weeks 1 & 2 100 Set and Logical Operations ► The union of two gray-scale images (sets) A and B is defined as the set {max( , ) | , } z A B a b a A b B    
  • 101. Weeks 1 & 2 101 Set and Logical Operations
  • 102. Weeks 1 & 2 102 Set and Logical Operations
  • 103. Weeks 1 & 2 103 Spatial Operations ► Single-pixel operations Alter the values of an image’s pixels based on the intensity. e.g., ( ) s T z 
  • 104. Weeks 1 & 2 104 Spatial Operations ► Neighborhood operations The value of this pixel is determined by a specified operation involving the pixels in the input image with coordinates in Sxy
  • 105. Weeks 1 & 2 105 Spatial Operations ► Neighborhood operations
  • 106. Weeks 1 & 2 106 Geometric Spatial Transformations ► Geometric transformation (rubber-sheet transformation) — A spatial transformation of coordinates — intensity interpolation that assigns intensity values to the spatially transformed pixels. ► Affine transform ( , ) {( , )} x y T v w      11 12 21 22 31 32 0 1 1 0 1 t t x y v w t t t t           
  • 107. Weeks 1 & 2 107
  • 108. Weeks 1 & 2 108 Image Registration ► Input and output images are available but the transformation function is unknown. Goal: estimate the transformation function and use it to register the two images. ► One of the principal approaches for image registration is to use tie points (also called control points)  The corresponding points are known precisely in the input and output (reference) images.
  • 109. Weeks 1 & 2 109 Image Registration ► A simple model based on bilinear approximation: 1 2 3 4 5 6 7 8 Where ( , ) and ( , ) are the coordinates of tie points in the input and reference images. x c v c w c vw c y c v c w c vw c v w x y           
  • 110. Weeks 1 & 2 110 Image Registration
  • 111. Weeks 1 & 2 111 Image Transform ► A particularly important class of 2-D linear transforms, denoted T(u, v) 1 1 0 0 ( , ) ( , ) ( , , , ) where ( , ) is the input image, ( , , , ) is the ker , variables and are the transform variables, = 0, 1, 2, ..., M-1 and = 0, 1, M N x y T u v f x y r x y u v f x y r x y u v forward transformation nel u v u v       ..., N-1.
  • 112. Weeks 1 & 2 112 Image Transform ► Given T(u, v), the original image f(x, y) can be recoverd using the inverse tranformation of T(u, v). 1 1 0 0 ( , ) ( , ) ( , , , ) where ( , , , ) is the ker , = 0, 1, 2, ..., M-1 and = 0, 1, ..., N-1. M N u v f x y T u v s x y u v s x y u v inverse transformation nel x y      
  • 113. Weeks 1 & 2 113 Image Transform
  • 114. Weeks 1 & 2 114 Example: Image Denoising by Using DCT Transform
  • 115. Weeks 1 & 2 115 Forward Transform Kernel 1 1 0 0 1 2 1 2 ( , ) ( , ) ( , , , ) The kernel ( , , , ) is said to be SEPERABLE if ( , , , ) ( , ) ( , ) In addition, the kernel is said to be SYMMETRIC if ( , ) is functionally equal to ( , M N x y T u v f x y r x y u v r x y u v r x y u v r x u r y v r x u r y v        1 1 ), so that ( , , , ) ( , ) ( , ) r x y u v r x u r y u 
  • 116. Weeks 1 & 2 116 The Kernels for 2-D Fourier Transform 2 ( / / ) 2 ( / / ) The kernel ( , , , ) Where = 1 The kernel 1 ( , , , ) j ux M vy N j ux M vy N forward r x y u v e j inverse s x y u v e MN        
  • 117. Weeks 1 & 2 117 2-D Fourier Transform 1 1 2 ( / / ) 0 0 1 1 2 ( / / ) 0 0 ( , ) ( , ) 1 ( , ) ( , ) M N j ux M vy N x y M N j ux M vy N u v T u v f x y e f x y T u v e MN                 
  • 118. Weeks 1 & 2 118 Probabilistic Methods Let , 0, 1, 2, ..., -1, denote the values of all possible intensities in an digital image. The probability, ( ), of intensity level occurring in a given image is estimated as i k k z i L M N p z z   ( ) , where is the number of times that intensity occurs in the image. k k k k n p z MN n z  1 0 ( ) 1 L k k p z     1 0 The mean (average) intensity is given by = ( ) L k k k m z p z   
  • 119. Weeks 1 & 2 119 Probabilistic Methods 1 2 2 0 The variance of the intensities is given by = ( ) ( ) L k k k z m p z      th 1 0 The moment of the intensity variable is ( ) = ( ) ( ) L n n k k k n z u z z m p z    
  • 120. Weeks 1 & 2 120 Example: Comparison of Standard Deviation Values 31.6   14.3   49.2  