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Gabor filter

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Gabor filter

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11 Mar 2009 (Updated )

Generates Gabor filters using bandwidth, aspect ratio, phase, wavelength and angle as parameters.

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Description

#5237 implements a Gabor filter for image processing. From the comments and through my own use, the implementation seems to have limited freedom, and also the variances are defined in the original x,y instead of the rotated x', y' directions.

The code is a modified version based on http://en.wikipedia.org/wiki/Gabor_filter following the conventions and parameters used in http://matlabserver.cs.rug.nl/edgedetectionweb/web/edgedetection_params.html.

The function accepts scalar inputs only, and each call generates one filter. The filter generated is always real. Should you wish to build a complex Gabor filter, you may use (0 phase) + j(pi/2 phase). Filtering can be performed using conv2( ) or imfilter( ).

An example file is included, which mimics the behavior of http://matlabserver.cs.rug.nl/edgedetectionweb/web/index.html at default settings with Lena.jpg image as input. Note that the scaling of numbers is different from the web-app, but consistent with the formulae in http://matlabserver.cs.rug.nl/edgedetectionweb/web/edgedetection_params.html

Update 18-Nov-2010: Thanks to Rachel (see comment below), I have corrected a mistake in the example file. The results are unchanged though. Also, the cs.rug.nl website seems offline.

Acknowledgements

2 D Gabor Filter(Ver1,2,3) inspired this file.

This file inspired 2 D And 3 D Gabor Filter Creators.

Required Products Image Processing Toolbox
MATLAB release MATLAB 7.4 (R2007a)
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Comments and Ratings (20)
24 Apr 2014 Jack Jones

I would like to ask the following question. I have used this filter with an image of all ones (imgin = ones(100,100)).

I get an image that consists entirely of ones, although my original image has no edges. Could you please explain what am I doing wrong or is this the normal behaviour of this filter?

03 Feb 2014 Solana

I am ver new to matlab and image processing, can someone please explain to me the mathematical and theoretical reasoning behind the following lines:
gb = gabor_fn(bw,gamma,psi(1),lambda,theta)...
+ 1i * gabor_fn(bw,gamma,psi(2),lambda,theta);

and the line
img_out_disp = sum(abs(img_out).^2, 3).^0.5;
% default superposition method, L2-norm

what is this superposition method? is that the standard formula for it?

13 Nov 2013 vidya  
06 Nov 2013 vidya  
27 Jan 2013 Govt college of Engg Amravati

can this filter be used for speech processing

13 Dec 2012 sup'com

Gabor Filter

28 Jun 2012 Scott

Best Gabor Filter I've seen

13 May 2012 thong  
26 Feb 2012 wang  
26 Feb 2012 wang  
11 Jan 2012 Rakesh Chalasani  
22 Mar 2011 Jason

Great one, thanks a lot. By the way, may I know, what does the size denote? Also, I can't seem to understand how the meshgrid in your code works.

02 Mar 2011 shuai  
02 Dec 2010 Marc

Can someone explain me why when a bandwidth >1 is used the result differs from http://matlabserver.cs.rug.nl

using a bandwith of 10 I had to replace

img_out_disp = sum(abs(img_out).^2, 3).^0.5;
with
img_out_disp = sum(imag(img_out).^2, 3).^0.5;

in order to have the same results as http://matlabserver.cs.rug.nl

but don't know why. I believe this come from the ratio sigma to lamda < 0.5. Any mathematical explanation?

16 Nov 2010 Rachel

Very good implementation. And good job normalizing it! What I do notice is: you seem to do (a+b).^2 to get the modulus of the result. I thought for a complex number a+bj, you are supposed to do a.^2+b.^2 for the modulus. Lucky enough for this case, the cross term 2ab is simply zero because we are summing some trigonometric functions from 0 to 2pi.

04 Nov 2010 Jon Hornstein

Thanks I see now you are using just the real component

04 Nov 2010 Jon Hornstein

I superficially looked at the code and this looks like a gaussian filter with polar rotation of coordinates only 1/2 of the answer. Can you please advise.

My thoughts were:
2D gaussian = g(x,y) = 1/(2*PI*Theta(x)*Theta(y)) * exp(-0.5*[(x/theta(x)).^2 +(y/theta(y)).^2])

gabor = h(x, y) = g(x, y)* exp[j*2*pi*(U*x+V*y)]

29 Sep 2010 James Kelly

hey, do you have any idea how to convert this to c#? I want to convert it but have no idea on how this loops trough pixels on the source image and how it produces the output image...

If you can write c#/c++/java/c code or at least explain to me as in what happens to the pixels that would be great, thanks. :)

01 Aug 2010 Mario

Please, someone can add some usage example of this code to an image to reproduce "exactly" the same results of the matlab's website http://matlabserver.cs.rug.nl ?

01 Mar 2010 David Conger  
Updates
30 Sep 2010

Added an example file to mimic the behavior of a known web-app and to demonstrate the usage of the function.

17 Nov 2010

Corrected procedures in the example file. Results are the same but the principle is more generally applicable.

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