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Image watermarking using SVD

Asked by Taha rassem on 18 Feb 2011

I tired to write code to insert 256*256 image as watermark in a host image 256*256. I am using SVD in my algorithm. I just convert the original image to SVD and adding the watermark image(W) to the singular value as SM=S+aW. a is scaling factor. Then I do SVD for SM and select to singular value of SM to construct the watermarked image.

Please, kindly tell me if my the following code is correct.

The PSNR between original watermark and extracted watermark is very high (> 265 db). Is this value is acceptable?

The code:

%-------------------------
%Embedding 
%-------------------------
clear;
clc
img= imread('lena2.tif');
img=imresize(img,[256 256]);
[M,N]=size(img);
img=double(img);
[Uimg,Simg,Vimg]=svd(img);
Simg_temp=Simg;
% read watermark
 img_wat= imread('cameraman.tif');
 img_wat=imresize(img_wat,[256 256]);
   alfa= input('The alfa Value = ');
   [x y]=size(img_wat);
   img_wat=double(img_wat);
   for i=1:x
       for j=1:y
          Simg(i,j) =Simg(i,j) + alfa * img_wat(i,j);
       end 
   end 
   % SVD for Simg (SM)
  [U_SHL_w,S_SHL_w,V_SHL_w]=svd(Simg);
Wimg =Uimg* S_SHL_w * Vimg';
figure(1)
imshow(uint8(img));
title('The Original Image')
figure(2)
imshow(uint8(img_wat));
title('The Watermark ')
figure(3)
imshow(uint8(Wimg));
title('The Watermarked Image')
%%%%%%%%%%%%%%%%%%%%%%%%%%%
%calculate image quality degradation after inserting watermark
%%%%%%%%%%%%%%%%%%%%%%%%%%%
mse=mean(squeeze(sum(sum((double(img)-double(Wimg)).^2))/(M*N)));
PSNR=10*log10(255^2./mse);
msg=sprintf('\n\n-------------------------\nWatermark by SVD  PSNR=%fdB\n-----------------------------\n\n', PSNR);
    disp(msg);
%--------------------------------------------------------------------------
% %% Extraction Part
% -------------------------------------------------------------------------
[UWimg,SWimg,VWimg]=svd(Wimg);
D_1=U_SHL_w * SWimg * V_SHL_w';
for i=1:x 
  for j=1:y
     Watermark(i,j)= (D_1(i,j) - Simg_temp(i,j) )/alfa ;
  end 
end
figure(8)
imshow(uint8(Watermark));
mse=mean(squeeze(sum(sum((double(img_wat)-(Watermark)).^2))/(M*N)));
PSNR=10*log10(255^2./mse);
msg=sprintf('\n\n-------------------------\nWatermark by SVD  PSNR=%fdB\n-----------------------------\n\n', PSNR);
disp(msg);

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Taha rassem

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1 Answer

Answer by meenakshi on 30 Aug 2011

no, normally the psnr must be between 20 to 45.in calculation of mse instead of squeeze use, mean.

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meenakshi

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