spatialgabor.m

Fast Fourier Transform

% SPATIALGABOR - applies single oriented gabor filter to an image
%
% Usage:
%  [Eim, Oim, Aim] =  spatialgabor(im, wavelength, angle, kx, ky, showfilter)
%
% Arguments:
%         im         - Image to be processed.
%         wavelength - Wavelength in pixels of Gabor filter to construct
%         angle      - Angle of filter in degrees.  An angle of 0 gives a
%                      filter that responds to vertical features.
%         kx, ky     - Scale factors specifying the filter sigma relative
%                      to the wavelength of the filter.  This is done so
%                      that the shapes of the filters are invariant to the
%                      scale.  kx controls the sigma in the x direction
%                      which is along the filter, and hence controls the
%                      bandwidth of the filter.  ky controls the sigma
%                      across the filter and hence controls the
%                      orientational selectivity of the filter. A value of
%                      0.5 for both kx and ky is a good starting point.
%         showfilter - An optional flag 0/1.  When set an image of the
%                      even filter is displayed for inspection.
% 
% Returns:
%         Eim - Result from filtering with the even (cosine) Gabor filter
%         Oim - Result from filtering with the odd (sine) Gabor filter
%         Aim - Amplitude image = sqrt(Eim.^2 + Oim.^2)
%

% Peter Kovesi  
% School of Computer Science & Software Engineering
% The University of Western Australia
% pk at csse uwa edu au
% http://www.csse.uwa.edu.au/~pk
%
% October 2006

function [Eim, Oim, Aim, evenFilter] = spatialgabor(im, wavelength, angle, kx, ky, showfilter)

    if nargin == 5
        showfilter = 0;
    end
    
    im = double(im);
    [rows, cols] = size(im);
    newim = zeros(rows,cols);
    
    % Construct even and odd Gabor filters
    sigmax = wavelength*kx;
    sigmay = wavelength*ky;
    
    sze = round(3*max(sigmax,sigmay));
    [x,y] = meshgrid(-sze:sze);
    evenFilter = exp(-(x.^2/sigmax^2 + y.^2/sigmay^2)/2)...
	     .*cos(2*pi*(1/wavelength)*x);
    
    oddFilter = exp(-(x.^2/sigmax^2 + y.^2/sigmay^2)/2)...
	     .*sin(2*pi*(1/wavelength)*x);    

    evenFilter = imrotate(evenFilter, angle, 'bilinear');
    oddFilter = imrotate(oddFilter, angle, 'bilinear');    

    % Do the filtering
    Eim = filter2(evenFilter,im); % Even filter result
    Oim = filter2(oddFilter,im);  % Odd filter result
    Aim = sqrt(Eim.^2 + Oim.^2);  % Amplitude 
    
    if showfilter % Display filter for inspection
        figure(1), imshow(evenFilter,[]); title('filter'); figure, surf(evenFilter)
    end