function  rsmp_core(file) 
% ********************************************************
% The basic part of the resampling detection method proposed in:
% B. Mahdian and S. Saic. Blind authentication using periodic properties of interpolation. 
% IEEE Transactions on Information Forensics and Security, 3(3):529–538, September 2008.
% Example: rsmp_core('images/lena.tiff');
% © Babak Mahdian, January 2007
% This source code is provided only for non-commercial and research
% pruposes.
% ********************************************************

order=2;           
radon_step=1;
radon_max=179;

if nargin==0
   error('Error! Missing image.');     
end;

im=double(imread(file));

if size(im,3)==3 
    warning('Color image. In this experimental version only green channel is investigated.'); 
    im=im(:,:,2);
end;

%%%%%%%%%%%%%%%%
%im=imresize(im,.9,'bicubic',0);
%im=imrotate(im,-15,'bilinear');im=crop_my_image(im,p1,p2);
%%%%%%%%%%%%%%%%

figure(1); 
clf;

subplot(3,1,1); 
imagesc(im);
colormap('gray')
axis image

theta =0:radon_step:radon_max;
d=diff(im,order,1);
[r,xp] = radon(abs(d),theta);
r=diff(r,1); 
subplot(3,1,2); 
ft=abs(fft(xcov(r(:,1)))); 
for i=1:size(r,2)
    ft=max(ft,abs(fft(xcov(r(:,i)))));
end;
ft=ft/norm(ft);
plot(ft(1:end,:));


theta =0:radon_step:radon_max;
d=diff(im,order,2);
[r,xp] = radon(abs(d),theta);
r=diff(r,1); 
subplot(3,1,3); 
ft=abs(fft(xcov(r(:,1)))); 
for i=1:size(r,2)
    ft=max(ft,abs(fft(xcov(r(:,i)))));
end;
ft=ft/norm(ft);
plot(ft(1:end,:));

return;