Lecture Nine
Figures from Gonzalez and Woods, Digital Image Processing, Copyright 2002.
DFT Filter Algorithms
operations N)) log M O(MN(log requires thisof All
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Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
World’s Simplest Filter
Filter out average
H(u,v) = 0 (u,v)=(M/2,N/2)
1 otherwise
Called a notch filter
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Low and High Pass Filters
• Low pass filters, deemphasize high frequencies. Have less sharp detail. Averaging filters are low pass.
• High pass filters. Does opposite. Pictures should appear sharper. Laplacian filters are high pass.
In next picture, see effects of low pass and high pass filters. Looks like Gaussian filter.
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Impulse and Gaussian Functions(1)
Both yield real and simple DFTs. Both lead to different ideals.
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Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Three types of Low Pass Filters
• Ideal Low Pass Filters (ILPF)
• Butterworth Low Pass Filters (BLPF)
• Gaussian Low Pass Filters (GLPF)
Top draws strongest line in the sand, but has ringing effect. Bottom has no ringing effect, but draws weaker line in the sand.
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain
Chapter 4Image Enhancement in the
Frequency Domain