How to extract watermark using Correlation for Spread Spectrum Watermarking

Question

Peter Eze 2017-3-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/329067-how-to-extract-watermark-using-correlation-for-spread-spectrum-watermarking

 % Genereate Spreading Sequence of 32-bit length
lengthofcode = 32;
goldcode=goldcodegenerator( lengthofcode);% GenerateSpreadingSequence(lengthofcode);
minuspluscode = zeros(1,lengthofcode);% utilised for - and + code generation
%Spreading the message with the Gold code
genkey='';
for i=1:lengthofcode
  if goldcode(1,i)==1
     genkey = strcat(genkey,'1');
     minuspluscode(1,i)=-1;
  else
      minuspluscode(1,i)=1;
      genkey = strcat(genkey,'0');
  end
end
% ============WATERMARK EMBEDDING USING DCT OR DWT ====================

subplot(3,2,3) imshow(im) title('\bf DICOM Cover Image')

% d=dct2(ca) % Check if there is enough space for embedding entire watermark [row col] = size(ch);% size of HL sub-band blocklengthrequired=lengthofcode*msglength watermark=zeros(1,blocklengthrequired);

if (row*col) < blocklengthrequired error('All watermark bits cannot be embedded in the HL subband'); else warning('Watermark embedding in the HL sub-band...') end HLvector = reshape(ch,1,row*col);

k=1; % Watermark generation for i=1:msglength if msg(1,i)==0 spread = c*minuspluscode;%c*minuspluscode; else spread = -c*minuspluscode; end for j=1:lengthofcode watermark(1,k)= spread(1,j); k=k+1; end end k=1; % Watermark embedding for i=1:blocklengthrequired HLvector(1,i)= HLvector(1,i)+watermark(1,k);%Watermark embedding done here end chorig=ch;% Original HL sub-band values ch=reshape(HLvector,row,col); stego = idwt2(ca,ch,cv,cd,'haar'); diff = sum(sum(chorig-ch)) imwrite(uint8(stego),'sspectrumstego.tiff') sim = ssim(uint8(stego),im) % simch = ssim(uint8(chorig),uint8(ch)) psn = psnr(uint8(stego),

The values of the DWT Coeffient changes when I try to extract the watermark using the stego image created from the above code. I get useless set of characters that is not what I embedded. Please can anyone identify what is wrong.