Dear all, How to embed message bits in DWT coefficient values ?

I wanted to embed some message bits in DWT coefficient values of an image and transmit. After embedding the message bits when I have performed uint8() to transmit the image as a grayscale image, at the receiving end, I am not able to get back the message bit from the same coefficient values. On the other hand, if I don't perform uint8() function, I can retrive the message bit successfully.

Answer 1

[Walter Roberson]

Use an Integer Wavelet Transform (iwt)

https://www.mathworks.com/matlabcentral/answers/?term=tag%3A%22iwt%22

[Manashee Malita]

Thank you sir, I have read these(which are in the link) but, not able to get my answer. My problem is that after embedding process, the image is reconstructed, but, the values are in double and when I convert it into uint8, some pixel values are also get changed which create a problem in retrieving the message in the receiving side. Thank you

[Walter Roberson]

After you use the integer wavelet, use uint8() before you do the embedding.

[Manashee Malita]

Thank you sir. It is working with Integer Wavelet Transform.

[shimaa samy]

Hi, i am a beginner at image processing..i have the same problem after coverting to uint8 i cann't retrieve the hidden message.. i didn't get understand the solution of @Walter Roberson..when should i do the conversion and how?...plz i am a student and i need it so much..help me

[Walter Roberson]

Do not use dwt() at all. Use iwt() instead. The result will be integers that you can embed bits in.

[shimaa samy]

first..thanks for your reply :)

yes i use lwt ..and it is also the same error..here is my code..i need your help so much..plz tell me what is wrong in my code

% reading the image
img=imread('c:\head4.tif');

% the row (the host row) in which i want to embed the secret message as an example at row
% 305 and start column 3 to end column 570
row_img=img(305,3:570);

% secret message is a vector
secret=[100,200,20,40,50,80,60,230,140,1,2,0,210,205,190,9,0,32,80,100,200,201,202,203,199,189,187,180,170,0,1,0,1,0,100];
secret_bin=dec2bin(secret,8);
secret_bin=secret_bin';

length_secret = size(secret_bin,1)*size(secret_bin,2);

   wname = liftwave('haar','int2int');
   host_row=double(row_img);

   [CA, CD]=lwt(host_row,wname);

   length_CA = size(CA,2);
   c = 1;

   % embedding the secret_bin in the last signficant bit of each CA ( 1 LSB of CA )
   for b = 1:1:length_CA
             if b <= length_secret 
                      xb=CA(1,c);

                       if xb < 0 
                          xb= abs(xb);

                         if strcmp(secret_bin(b), '0')
                            xb=bitset(xb,1,0);
                         else
                            xb=bitset(xb,1,1);

                         end    
                         CA(1,c)=-xb;
                      else
                         if strcmp(secret_bin(b), '0')
                            CA(1,c) = bitset(CA(1,c),1,0);
                         else
                            CA(1,c) = bitset(CA(1,c),1,1);

                         end    
                      end% end if xb<0

                      c = c+ 1;
                       if (c > length_CA)
                         c = 1;
                       end
              end  % if b <= length_secret 
   end % end for loop b=8:-1:1

                    stego_host_uint8 = uint8(ilwt(CA,CD,wname));
                    stego_host_dble = (ilwt(CA,CD,wname));

   % Extracting the secret vector from the stego_host_uint8   
    watermarked_host=double(stego_host_uint8);

    [CA_ex, CD_ex] = lwt(watermarked_host,wname);  

    length_CA_ex = size(CA_ex,2);

    c = 1;

    secret_bits_ex = zeros(1,size_data);

      for b = 1:1:length_CA_ex

          if b <= length_secret
               xb=CA_ex(1,c);

               if xb < 0 
                 xb= abs(xb);
               end
             secret_bits_ex(b) = bitget(xb,1);
          %letter = bitset(letter,b,bitget(xb,1));
             c = c + 1;
          end
      end

      % function i created
      secret_ex=binRoundC2Dec(secret_bits_ex,8);

      % comparison between the input secret vector and the extracted
      message=secret';

      if secret_ex == message
          disp('yes equal');
      else
          disp('No Equal');
      end

      % the extracted output [100;200;20;40;114;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;162;0;1;0;1;0;100]
      % the input secret     [100;200;20;40;50;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;170;0;1;0;1;0;100]
      % they are diffrent at positions 5 , 29 ...why?

[shimaa samy]

% reading the image

img=imread('c:\head4.tif');

% the row (the host row) in which i want to embed the secret message as an example at row  305 and start column 3 to end column 570

row_img=img(305,3:570);

% secret message is a vector

secret=[100,200,20,40,50,80,60,230,140,1,2,0,210,205,190,9,0,32,80,100,200,201,202,203,199,189,187,180,170,0,1,0,1,0,100];

secret_bin=dec2bin(secret,8);

secret_bin=secret_bin';

length_secret = size(secret_bin,1)*size(secret_bin,2);

   wname = liftwave('haar','int2int');
   host_row=double(row_img);

   [CA, CD]=lwt(host_row,wname);

   length_CA = size(CA,2);
   c = 1;

   % embedding the secret_bin in the last signficant bit of each CA ( 1 LSB of CA )

   for b = 1:1:length_CA
             if b <= length_secret 
                      xb=CA(1,c);

                       if xb < 0 
                          xb= abs(xb);

                         if strcmp(secret_bin(b), '0')
                            xb=bitset(xb,1,0);
                         else
                            xb=bitset(xb,1,1);

                         end    
                         CA(1,c)=-xb;
                      else
                         if strcmp(secret_bin(b), '0')
                            CA(1,c) = bitset(CA(1,c),1,0);
                         else
                            CA(1,c) = bitset(CA(1,c),1,1);

                         end    
                      end% end if xb<0

                      c = c+ 1;
                       if (c > length_CA)
                         c = 1;
                       end
              end  % if b <= length_secret 
   end % end for loop b=8:-1:1

                    stego_host_uint8 = uint8(ilwt(CA,CD,wname));
                    stego_host_dble = (ilwt(CA,CD,wname));

   % Extracting the secret vector from the stego_host_uint8   
    watermarked_host=double(stego_host_uint8);

    [CA_ex, CD_ex] = lwt(watermarked_host,wname);  

    length_CA_ex = size(CA_ex,2);

    c = 1;

    secret_bits_ex = zeros(1,length_secret);

      for b = 1:1:length_CA_ex

          if b <= length_secret
               xb=CA_ex(1,c);

               if xb < 0 
                 xb= abs(xb);
               end
             secret_bits_ex(b) = bitget(xb,1);
          %letter = bitset(letter,b,bitget(xb,1));
             c = c + 1;
          end
      end

      % function i created
      secret_ex=binRoundC2Dec(secret_bits_ex,8);

      % comparison between the input secret vector and the extracted
      message=secret';

      if secret_ex == message
          disp('yes equal');
      else
          disp('No Equal');
      end

      % the extracted output [100;200;20;40;114;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;162;0;1;0;1;0;100]
      % the input secret     [100;200;20;40;50;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;170;0;1;0;1;0;100]
      % they are diffrent at positions 5 , 29 ...why?

      % Extracting the secret vector from the stego_host_dble   
    watermarked_host_dbl=double(stego_host_dble);

    [CA_ex_dbl, CD_ex_dbl] = lwt(watermarked_host_dbl,wname);  

    length_CA_ex = size(CA_ex_dbl,2);

    c = 1;

    secret_bits_ex_dbl = zeros(1,length_secret);

      for b = 1:1:length_CA_ex

          if b <= length_secret
               xb=CA_ex_dbl(1,c);

               if xb < 0 
                 xb= abs(xb);
               end
             secret_bits_ex_dbl(b) = bitget(xb,1);
          %letter = bitset(letter,b,bitget(xb,1));
             c = c + 1;
          end
      end

      % function i created
      secret_ex_dbl=binRoundC2Dec(secret_bits_ex_dbl,8);

      % comparison between the input secret vector and the extracted 
      message=secret';

      if secret_ex_dbl == message
          disp('yes equal from stego dble');
      else
          disp('No Equal from stego dble');
      end

      % the extracted output [100;200;20;40;50;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;170;0;1;0;1;0;100]
      % the input secret     [100;200;20;40;50;80;60;230;140;1;2;0;210;205;190;9;0;32;80;100;200;201;202;203;199;189;187;180;170;0;1;0;1;0;100]
      % they are equal when extracting directly from double lwt without  conversion to uint8

[Walter Roberson]

You appear to have posted this question as https://www.mathworks.com/matlabcentral/answers/338974-help-embedding-secret-message-using-lwt-cannot-extract-the-secret-message-correctly