Arithmetic and Logical Operations Chapter 2

1
Arithmetic and Logical Operations (Chapter 2)

• CS474/674 Prof. Bebis

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Addition

• Useful for combining information between two
  images

0 lt a lt 1
3
Averaging (see Example 2.5, page 75)

• Image quality can be improved by averaging a
  number of images together (very useful in
  astronomy applications).

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5
images must be registered!
20
100
50
4
Subtraction

• Useful for change detection.

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Subtraction (contd)
iodine medium injected into the bloodstream

• Medical application.

enhanced
difference
6
Multiplication/Division

• Use to adjust the brightness of the image.

multiplication by 2
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Multiplication/Division (contd)

• 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.

shade pattern
shade correction
original
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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
10
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