This document discusses image enhancement and restoration techniques in digital image processing. It describes various arithmetic and logical operations that can be performed on images, including addition, averaging, subtraction, multiplication/division, AND, and OR. These operations allow images to be combined, adjusted for brightness, and manipulated to enhance features or remove artifacts. Pixel value ranges must be normalized back to 0-255 after arithmetic operations.

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Amity School of Engineering & Technology
Digital Image Processing
Credit Units: 4
Mukesh Bhardwaj

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Module I
Image Enhancement &
Restoration
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Arithmetic and Logical Operations :
• Arithmetic operations between images are
array operations means that arithmetic
operations are carried out between
corresponding pixel pairs.
•

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Addition
• Useful for combining information
between two images
0 <= a <= 1

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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

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Subtraction
• Useful for “change” detection.

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Subtraction (cont’d)
• Medical application.
iodine medium injected
into the bloodstream
difference enhanced

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Multiplication/Division
• Use to adjust the brightness of the image.
multiplication by 2

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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

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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]

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Logical Operations

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

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

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Example
Result of AND Result of OR
OR