gistfile1.matlab

%2013/1/1
%Tzu-Wei Huang
%demo of 'derivative of Gaussian', Difference of Gaussians and
%'Laplacian of Gaussian' in matlab.

close all;

[x,y] = meshgrid(-5:0.1:5,-5:0.1:5);
%gaussian with sigma = 1
z = (1/sqrt(2*pi))./exp((x.^2+y.^2)/2);
%gaussian with sigma = 2
z_another = (1/(2*sqrt(2*pi)))./exp((x.^2+y.^2)/8);


surf(x,y,z);title('2D gaussian with sigma = 1');

dz_y = z*0;
for j=1:size(z,2)
    for i=2:size(z,1)-1
        dz_y(i,j) = z(i,j)-z(i-1,j);
    end
end
dz_x = dz_y';
figure;
surf(x,y,dz_x);title('derivative of Gaussian x');

figure;
surf(x,y,dz_y);title('derivative of Gaussian y');


ddz_yy = z*0;
for j=1:size(z,2)
    for i=2:size(z,1)-1
        ddz_yy(i,j) = dz_y(i,j)-dz_y(i-1,j);
    end
end
ddz_xx = ddz_yy';

figure;
surf(x,y,ddz_xx+ddz_yy);title('Laplacian of Gaussian');


figure;
surf(x,y,z_another-z);title('Difference of Gaussians');