[WM]: basic DCT Watermarking problem

[Gomper <gomper@wp.pl>]

Dear Watermarkers!

   Im using DCT transform for embendding watermark into the image.

   this are steps i make to embend it and restore:
   1. making DCT on whole image oryginal image  A_dct= dct2(A)
   2.   substract   minimum   of   dct   coefficients   A_dct=A_dct  -
   min(min(A_dct));
   3. rounds and binaryzing all coefficients  -> A_dct_bit ;
   each AC is writen on 16bits, A_dct(1:1)=DC -> length 16 bit
   4.  Adds  3  bits  of  binaryzed  oryginal  image  A (bit 8,7,6) to
   binaryzed coefficient A_dct_bit (bit 2,1,0)
   5. back to decimal
   6. inverse DCT

   problem I have is that i cant extract corect watermark in restoring
   process:
   1. the same as above
   2. the same as above
   3. the same as above
   4. extract watermark from bits 2,1,0
   5. the same as above
   6. the same as avove

   when  restoring  is  over,  extracted  watermark  is different then
   embendded, but there was no attack.

   i  realize  that  some  mistake  is  in  embendding  watermark  or
   restoring, but cant see it.

   im not hiddeing dct(watermark) but only watermark so is it possible
   that this is wrong? if yes, tell me please how to do this correct.

   Im trying implement most simple embandding algorithm as possible so
   I will apriciate for any suggestions or papers.
   
--
best regards,
 Gomper                          mailto:gomper@wp.pl


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