pixelrelationships in image processing enhancement

DIGITAL IMAGE
PROCESSING
Prepared by
K.Indragandhi,AP(Sr.Gr.)/ECE

DIGITAL IMAGE
PROCESSING
Basic Relationships between Pixels

Neighbors of a Pixel
f(0,0) f(0,1) f(0,2) f(0,3) f(0,4) - - - - -
f(1,0) f(1,1) f(1,2) f(1,3) f(1,4) - - - - -
f(x,y) = f(2,0) f(2,1) f(2,2) f(2,3) f(2,4) - - - - -
f(3,0) f(3,1) f(3,2) f(3,3) f(3,4) - - - - -
I I I I I - - - - -
I I I I I - - - - -

 A Pixel p at coordinates ( x, y) has 4 horizontal and vertical neighbors.
 Their coordinates are given by:
(x+1, y) (x-1, y) (x, y+1) &
(x, y-1)
f(2,1) f(0,1) f(1,2)
f(1,0)
 This set of pixels is called the 4-neighbors of p denoted by N4(p).
 Each pixel is unit distance from ( x ,y).
f(0,0) f(0,1) f(0,2) f(0,3) f(0,4) - - - - -
f(1,0) f(1,1) f(1,2) f(1,3) f(1,4) - - - - -
f(x,y) = f(2,0) f(2,1) f(2,2) f(2,3) f(2,4) - - - - -
f(3,0) f(3,1) f(3,2) f(3,3) f(3,4) - - - - -
I I I I I - - - - -
I I I I I - - - - -

 A Pixel p at coordinates ( x, y) has 4 diagonal neighbors.
 Their coordinates are given by:
(x+1, y+1) (x+1, y-1) (x-1, y+1) &
(x-1, y-1)
f(2,2) f(2,0) f(0,2)
f(0,0)
 This set of pixels is called the diagonal-neighbors of p denoted by
ND(p).

f(0,0) f(0,1) f(0,2) f(0,3) f(0,4) - - - - -
f(1,0) f(1,1) f(1,2) f(1,3) f(1,4) - - - - -
f(x,y) = f(2,0) f(2,1) f(2,2) f(2,3) f(2,4) - - - - -
f(3,0) f(3,1) f(3,2) f(3,3) f(3,4) - - - - -
I I I I I - - - - -
I I I I I - - - - -

Adjacency, Connectivity
Adjacency: Two pixels are adjacent if they are neighbors and
their intensity level ‘V’ satisfy some specific criteria of
similarity.
e.g. V = {1}
V = { 0, 2}
Binary image = { 0, 1}
Gray scale image = { 0, 1, 2, ------, 255}
In binary images, 2 pixels are adjacent if they are neighbors &
have some intensity values either 0 or 1.
In gray scale, image contains more gray level values in range 0
to 255.

4-adjacency: Two pixels p and q with the values from set ‘V’
are 4-adjacent if q is in the set of N4(p).
e.g. V = { 0, 1}
1 1 2
1 1 0
1 0 1
p in RED color
q can be any value in GREEN color.

8-adjacency: Two pixels p and q with the values from set ‘V’
are 8-adjacent if q is in the set of N8(p).
e.g. V = { 1, 2}
0 1 1
0 2 0
0 0 1
p in RED color
q can be any value in GREEN color

m-adjacency: Two pixels p and q with the values from set ‘V’
are m-adjacent if
(i) q is in N4(p) OR
(ii) q is in ND(p) & the set N4(p) n N4(q) have no pixels
whose values are from ‘V’.
e.g. V = { 1 }
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 i

are m-adjacent if
(i) q is in N4(p)
e.g. V = { 1 }
(i) b & c
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I

are m-adjacent if
(i) q is in N4(p)
e.g. V = { 1 }
(i) b & c
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I
Soln: b & c are m-adjacent.

are m-adjacent if
(i) q is in N4(p)
e.g. V = { 1 }
(ii) b & e
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I

are m-adjacent if
(i) q is in N4(p)
e.g. V = { 1 }
(ii) b & e
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I
Soln: b & e are m-adjacent.

are m-adjacent if
e.g. V = { 1 }
(iii) e & i
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 i

are m-adjacent if
(i) q is in ND(p) & the set N4(p) n N4(q) have no pixels
e.g. V = { 1 }
(iii) e & i
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I

are m-adjacent if
(i) q is in ND(p) & the set N4(p) n N4(q) have no pixels
e.g. V = { 1 }
(iii) e & i
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I
Soln: e & i are m-adjacent.

are m-adjacent if
e.g. V = { 1 }
(iv) e & c
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I

are m-adjacent if
e.g. V = { 1 }
(iv) e & c
0 a 1 b 1 c
0 d 1 e 0 f
0 g 0 h 1 I
Soln: e & c are NOT m-adjacent.

Connectivity: 2 pixels are said to be connected if their exists a path
between them.
Let ‘S’ represent subset of pixels in an image.
Two pixels p & q are said to be connected in ‘S’ if their exists a path
between them consisting entirely of pixels in ‘S’.
For any pixel p in S, the set of pixels that are connected to it in S is
called a connected component of S.

Paths
Paths: A path from pixel p with coordinate ( x, y)
with pixel q with coordinate ( s, t) is a sequence of
distinct sequence with coordinates (x0, y0), (x1, y1),
….., (xn, yn) where
(x, y) = (x0, y0)
& (s, t) = (xn, yn)
Closed path: (x0, y0) = (xn, yn)

Paths
Example # 1: Consider the image segment shown in figure.
Compute length of the shortest-4, shortest-8 & shortest-m paths
between pixels p & q where,
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3

Paths
Example # 1:
Shortest-4 path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3

Paths
Example # 1:
Shortest-4 path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3
So, Path does not exist.

Paths
Example # 1:
Shortest-8 path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3

Paths
Example # 1:
Shortest-8 path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3
So, shortest-8 path = 4

Paths
Example # 1:
Shortest-m path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3

Paths
Example # 1:
Shortest-m path:
V = {1, 2}.
4 2 3 2 q
3 3 1 3
2 3 2 2
p 2 1 2 3
So, shortest-m path = 5

Regions & Boundaries
Region: Let R be a subset of pixels in an image. Two regions Ri
and Rj are said to be adjacent if their union form a connected set.
Regions that are not adjacent are said to be disjoint.
We consider 4- and 8- adjacency when referring to regions.
Below regions are adjacent only if 8-adjacency is used.
1 1 1
1 0 1 Ri
0 1 0
0 0 1
1 1 1 Rj
1 1 1

Regions & Boundaries
Boundaries (border or contour): The boundary of a region
R is the set of points that are adjacent to points in the
compliment of R.
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
RED colored 1 is NOT a member of border if 4-connectivity is
used between region and background. It is if 8-connectivity is
used.

Distance Measures
Distance Measures: Distance between pixels p, q & z with
co-ordinates ( x, y), ( s, t) & ( v, w) resp. is given by:
a) D( p, q) ≥ 0 [ D( p, q) = 0 if p = q] …………..called
reflexivity
b) D( p, q) = D( q, p) .………….called
symmetry
c) D( p, z) ≤ D( p, q) + D( q, z) ..………….called
transmitivity
Euclidean distance between p & q is defined as-
De( p, q) = [( x- s)2
+ (y - t)2
]1/2

Distance Measures
City Block Distance: The D4 distance between p & q is
defined as
D4( p, q) = |x - s| + |y - t|
In this case, pixels having D4 distance from ( x, y) less than or
equal to some value r form a diamond centered at ( x, y).
2
2 1 2
2 1 0 1 2
2 1 2
2
Pixels with D4 distance ≤ 2 forms the following contour of
constant distance.

Distance Measures
Chess-Board Distance: The D8 distance between p & q is
defined as
D8( p, q) = max( |x - s| , |y - t| )
In this case, pixels having D8 distance from ( x, y) less than or
equal to some value r form a square centered at ( x, y).
2 2 2 2 2
2 1 1 1 2
2 1 0 1 2
2 1 1 1 2
2 2 2 2 2
Pixels with D8 distance ≤ 2 forms the following contour of
constant distance.

 The AND operator is usually used to mask out
part of an image.

 Parts of another image can be added with a
logical OR operator.

pixelrelationships in image processing enhancement

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