ASAM Image Processing 20082009

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ASAM - Image Processing2008/2009

• Lecture 2
• Intensity Transformation Functions

Ioannis Ivrissimtzis 23-Oct-2008
2
Overview
Intensity transformation functions Gamma
correction Contrast increasing functions
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Intensity transformation functions

• An intensity transformation function is a
  function f applied to the
• intensity of each pixel

f
Notice that here each pixel is processed by f
individually.
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Intensity transformation functions

• Example 2.1

f
5
Intensity transformation functions

• Example 2.2

f
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Intensity transformation functions

• Example 2.3

f
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Intensity transformation functions

• Example 2.4

f
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Intensity transformation functions

• Exercise 2.1 Draw the graphs of the intensity
  transformation functions
• in examples 2.1 - 2.4.

9
Overview
Intensity transformation functions Gamma
correction Contrast increasing functions
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Gamma correction

• The gamma correction is an intensity
  transformation function
• where ? is a constant.

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Gamma correction

• The graph of the gamma correction for ? lt 1

f(x)
1
x
1
0
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Gamma correction

• The graph of the gamma correction for ? 1

f(x)
1
x
1
0
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Gamma correction

• The graph of the gamma correction for ? gt 1

f(x)
1
x
1
0
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Gamma correction

• If ? lt 1 the image is weighted toward higher
  (brighter) output values.
• If ? gt 1 the image is weighted toward lower
  (darker) output values.
• If ? 1 the transformation has no effect on the
  image.

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Gamma correction

• Example 2.5

f
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Gamma correction

• Example 2.6

f
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Gamma correction

• The gamma correction is used to correct the
  tonality of an image.
• An underexposed photograph can be corrected using
  gamma correction with ? lt 1.
• An overexposed photograph can be corrected using
  gamma correction
• with ? gt 1.

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Gamma correction

• Example 2.7

? 1/2
? 1/3
? 1/4
? 1
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Gamma correction

• Example 2.7

? 2
? 3
? 4
? 1
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Overview
Intensity transformation functions Gamma
correction Contrast increasing functions
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Contrast-stretching transformations

• The contrast stretching function
• where E is a relatively large constant (e.g. E gt
  2), increases the
• contrast of the image.
• Pixel values below 0.5 are pushed nearer to 0.
• Pixel values above 0.5 are pushed nearer to 1.

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Contrast-stretching transformations

• The graph of the contrast stretching function for
  E 5

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Contrast-stretching transformations

• Example 2.8

f
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Contrast-stretching transformations

• The graph of the contrast stretching function for
  E 100

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Contrast-stretching transformations

• Example 2.9

f
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Contrast-stretching transformations

• Example 2.10 The higher the values of E the
  greater the increase of
• the contrast.

E 50
Original
E 2
E 10