1.arithmetic & logical operations

Amity School of Engineering & Technology

1


Digital Image Processing

Credit Units: 4

Mukesh Bhardwaj


Module I

Image Enhancement &

Restoration

2


3

Arithmetic and Logical Operations :

• Arithmetic operations between images are

array operations means that arithmetic

operations are carried out between

corresponding pixel pairs.

•


Addition

• Useful for combining information

between two images

0 <= a <= 1


Averaging (see Example 2.5, page 75)

• Image quality can be improved by averaging a

number of images together (very useful in astronomy

applications).5 10

20 50 100


Subtraction• Useful for “change” detection.


Subtraction (cont’d)• Medical application.

iodine medium injected

into the bloodstream

difference enhanced


Multiplication/Division• Use to adjust the brightness of the image.

multiplication by 2


Multiplication/Division (cont’d)• Suppose a sensor introduces some shading in the form:

g(x,y)=f(x,y) h(x,y)

• We can estimate h(x,y) and remove shading by division.

original shade pattern shade correction


Comments

• Arithmetic operation can produce pixel values outside

of the range [0 – 255].

• You should convert values back to the range [0 – 255]

to ensure that the image is displayed properly.

• How would you do the following mapping?

[fmin – fmax] [ 0 – 255]


Logical Operations


AND • The AND operator is usually used to mask

out part of an image.


OR• Parts of another image can be added with

a logical OR operator.


ExampleResult of AND Result of OR

OR