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+function gabor_example()
+% an example to demonstrate the use of gabor filter.
+% requires lena.jpg in the same path.
+% the results mimic:
+% http://matlabserver.cs.rug.nl/edgedetectionweb/web/edgedetection_examples
+% .html
+% using default settings (except for in radians instead of degrees)
+%
+% note that gabor_fn only take scalar inputs, and multiple filters need to
+% be generated using (nested) loops
+%
+% also, apparently the scaling of the numbers is different from the example
+% software at
+% http://matlabserver.cs.rug.nl
+% but are consistent with the formulae shown there
+lambda  = 8;
+theta   = 0;
+psi     = [0 pi/2];
+gamma   = 0.5;
+bw      = 1;
+N       = 8;
+img_in = im2double(imread('lena.jpg'));
+img_in(:,:,2:3) = [];   % discard redundant channels, it's gray anyway
+img_out = zeros(size(img_in,1), size(img_in,2), N);
+for n=1:N
+    gb = gabor_fn(bw,gamma,psi(1),lambda,theta)...
+        + 1i * gabor_fn(bw,gamma,psi(2),lambda,theta);
+    % gb is the n-th gabor filter
+    img_out(:,:,n) = imfilter(img_in, gb, 'symmetric');
+    % filter output to the n-th channel
+    theta = theta + 2*pi/N;
+    % next orientation
+end
+figure(1);
+imshow(img_in);
+title('input image');
+figure(2);
+img_out_disp = sum(abs(img_out).^2, 3).^0.5;
+% default superposition method, L2-norm
+img_out_disp = img_out_disp./max(img_out_disp(:));
+% normalize
+imshow(img_out_disp);
+title('gabor output, L-2 super-imposed, normalized');
+\ No newline at end of file