remove_wm.m

Digital watermarking

function out = remove_WM(in_original,in_watermarked,len_WM,block,alpha)
% This function will remove the watermark from the input audio stream
% by comparing the original signal and with the help of 
% watermarking insertion formula
% in_original = original input file in time domain
% in_watermarked = watermarked file in time domian
% len_WM = length of the original watermark
% out = recovered watermark

%%%%%%%%%%%%%%% RECOVERY OF THE WATERMARK %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% FFT OF SEGMENTS OF THE ORIGINAL AND WATERMARKED SIGNAL 
FFT_of_original_string = (blkproc(in_original,[1 block],'fft'));
FFT_of_watermarked_string = (blkproc(in_watermarked,[1 block],'fft'));
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
abs_orginal = FFT_of_original_string;
abs_out_string = FFT_of_watermarked_string;

for i=1:len_WM
    [g,m] = max(FFT_of_original_string);
    out(i) = (FFT_of_watermarked_string(m)./FFT_of_original_string(m)-1)./alpha;
    FFT_of_original_string(m) = 0;   
end