myffttrunc2(s,n,m)

function S = myffttrunc2(s,n,m)
%MYFFTTRUNC(s,n) returns the low-pass filtered content of the signal s
%
%   s    = s(x,y) where
%   x(j) = x(1)+(j-1)*(x(N)-x(1)+x(2)-x(1))/N,   i = 1...N, N = 2^k1
%   y(i) = y(1)+(i-1)*(y(N)-y(1)+y(2)-y(1))/M,   i = 1...M, M = 2^k2
%
%   S is the low-passtruncated signal S = W*s, where W is the Fourier 
%   transfer function
%
%   See also myffttrunc

%   Author(s): A. Almqvist
%   Copyright 2009- Andreas Almqvist
%   $Revision: 1$  $Date: 2009/11$
%   Homemade function

[M,N]   = size(s);

% Creating the transfer function W
wx  = (1:N/2-1);
wy  = (1:M/2-1);

[Wx,Wy] = meshgrid(wx,wy);
                                    % wy          N/2+1
W1  = 1.*(Wx<=n & Wy<=m);           % |           |
W2  = fliplr(W1);                   % |   W3      |    W4
W3  = flipud(W1);                   % |_ _ _ _ _ _|_ _ _ _ _ _ M/2+1
W4  = flipud(W2);                   % |           |
                                    % |   W1      |    W2
W   = zeros(M,N);                   % |___________|______________wx 
W(M/2+2:M   ,2:N/2  )   = W3;       %
W(M/2+2:M   ,N/2+2:N)   = W4;       %
W(2:M/2     ,2:N/2  )   = W1;       % W = [W1,W2;W3,W4]
W(2:M/2     ,N/2+2:N)   = W2;       %

W(1                             ,[1:min(n,N),max(end-n-1,1):N]  )   = 1;
W([1:min(m,M),max(end-m-1,1):M] ,1                              )   = 1;
W(M/2+1                         ,[1:min(n,N),max(end-n-1,1):N]  )   = 1;
W([1:min(m,M),max(end-m-1,1):M] ,N/2+1                          )   = 1;

% Truncating the signal in the frequency space and return it to the time
% domain
S   = real(ifft2(W.*fft2(s)));