A=imread('C:\Dokumente und Einstellungen\joachim\Desktop\Bildgalerie\wasserflaeche.jpg');

variance=0.001;
f=imnoise(A,'gaussian',0,variance);
f=f(:,:,1);  % since f is an RGB image


Nxy=size(f);
hx=1/Nxy(2);
hy=1/Nxy(1);
tx=linspace(hx/2,1-hx/2,Nxy(2)); 
ty=linspace(hy/2,1-hy/2,Nxy(1)); 
[tx,ty]=meshgrid(tx,ty);

figure(1)
clf
imshow(f);

lambda=[1e4,1e5,1e6];
% dct of f 
fhat=dct2(f);

[facx,facy]=meshgrid(0:Nxy(1)-1,0:Nxy(2)-1);

% frequency filtering with various values for regularization parameter lambda
for ell=1:length(lambda)
    lam=lambda(ell);
    bhat=lam*fhat./(lam+(pi*facx).^2+(pi*facy).^2);
    B=idct2(bhat);
    figure(ell+1);
    clf
    imshow(uint8(B));    
end