implementation of Thodi's paper Digital Watermarking using Prediction error

This is version 1,assume every pixsel is expandable or shiftable

 

 

%%%%This program implement thodi's paper about Prediction-Error%%%
f = imread('lena.bmp');
f = double(rgb2gray(f));
%q = imread('lena.bmp');
%q = rgb2gray(q);
%f = double(q(333:337,333:337));
 
h = f;
T = 3;
L = 256;
expandible = 0;
N = 0;
U = 0;
R = 0;
Data = round(rand(1,size(f,1)*size(f,2)));
k = 1;
 
%%%%%%%%%%%%Encode%%%%%%%%%%%%%%
for i = 1:size(f,1)-1
    for j = 1:size(f,2)-1
        a = f(i+1,j);
        b = f(i,j+1);
        c = f(i+1,j+1);
        if c<= min(a,b)
            x = max(a,b);
        elseif c>=max(a,b)
            x = min(a,b);
        else x = a + b -c;
        end
        pe = f(i,j) - x;
        %%%%%%%%%%%calculate the numbers of expandible,N,U and encode
        if abs(pe) < T && ((0<= f(i,j)+pe) && (f(i,j)+pe<=L-2))
            expandible = expandible + 1;
            pe1 = 2*pe + Data(k);
            f(i,j) = x + pe1;
            k = k + 1;
            
        elseif pe>=T && f(i,j)+T >=-1 && f(i,j)+T <=L-1
            N = N + 1;
            pe1 = pe + T  ;
            f(i,j) = x + pe1;
             
            elseif  pe <=-T && f(i,j)-T >=-1 && f(i,j)-T <=L-1
                N = N + 1;
                pe1 = pe -T+1;
                f(i,j) = x + pe1;
              
        else U = U + 1;
        end
       
       
      end
end
m = f;
 
%%%%%%%%%%%%%%%%%%decode%%%%%%%%%%%%%%%%%%%%%%%
Data_re = round(rand(1,size(f,1)*size(f,2)));
k = 1;
for i = 1:size(f,1)-1
    i = size(f,1)-i;
    for j = 1:size(f,2)-1
       
        j = size(f,2)-j;
        a = f(i+1,j);
        b = f(i,j+1);
        c = f(i+1,j+1);
        if c<= min(a,b)
            x = max(a,b);
        elseif c>=max(a,b)
            x = min(a,b);
        else x = a + b -c;
        end
        pe1 = f(i,j) - x;
           
        if pe1<2*T && pe1>-2*T+1;
            pe = floor(pe1/2);
            Data_re(k) = mod(pe1,2);
            k = k + 1;
            f(i,j) =  x + pe;
        elseif pe1 < 0
            pe = pe1 + T-1;
            f(i,j) = x + pe;
        elseif pe1>=0
            pe = pe1 - T ;
            f(i,j)  = x + pe;
        end
  
    end
end