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Butterworth Bandpass Filter for Image Processing

version 1.2 (2.34 KB) by

This function performs butterworth bandpass filtering in the frequency domain

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Butterworth Bandpass Filter
This simple function was written for my Digital Image Processing course
at Eastern Mediterranean University taught by
Assoc. Prof. Dr. Hasan Demirel
for the 2010-2011 Spring Semester
for the complete report:
http://www.scribd.com/doc/51981950/HW4-Frequency-Domain-Bandpass-Filtering

Written By:
Leonardo O. Iheme (leonardo.iheme@cc.emu.edu.tr)
23rd of March 2011

  I = The input grey scale image
  d0 = Lower cut off frequency
  d1 = Higher cut off frequency
  n = order of the filter

The function makes use of the simple principle that a bandpass filter
can be obtained by multiplying a lowpass filter with a highpass filter
where the lowpass filter has a higher cut off frquency than the high pass filter.

Usage BUTTERWORTHBPF(I,DO,D1,N)
Example
ima = imread('grass.jpg');
ima = rgb2gray(ima);
filtered_image = butterworthbpf(ima,30,120,4);

Comments and Ratings (4)

Raul Ziranda

Leonardo

May I've just found a working solutions for my issue

adding a string input called type and then:

filter4(i,j)=1.0-filter3(i,j); % in the for loop

 if type == 'bandpass'
     % Update image with passed frequencies.
     filtered_image = fftI + filter3.*fftI;
 elseif type == 'bandreject'
     % Update image with passed frequencies.
     filtered_image = fftI + filter4.*fftI;
 end

Leonardo

Dear sir,
Your code is simple and effective.
Just one question; how should I modify the code to obtain a band reject filter instead of a band pass filter with the same parameters ??
It should be quite simple.
Any suggestions ?

Thank you in advance !!

Robin Martin

Very good code simple and effecient!

Updates

1.2

Updated the title

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MATLAB 7.10 (R2010a)

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