X=zeros(30,30);
for i=10:21
    for j=9:20
        X(i,j)=255;
    end;
end;
X=mat2gray(X);
subplot(1,2,1);imshow(X);
b=size(X);
M=1/b(1)*b(2);
Y=zeros(b);
for(u=4:b(1))
    for(v=4:b(2))
        for(x=4:b(1))
            for(y=4:b(2))
               Y(u,v)=(X(x,y)*exp(-j*2*pi*(u*x/b(1)+v*y/b(2))))+Y(u,v);
            end;
        end;
        Y(u,v)=M*Y(u,v);
    end;
end;
for(u=4:b(1))
    for(v=4:b(2))
           Y(u,v)=sqrt(real(Y(u,v))*real(Y(u,v))+imag(Y(u,v))*imag(Y(u,v)));
    end;
end;
Y=mat2gray(Y);
subplot(1,2,2);imshow(Y);