RE: [WM]: Again need help in implementation of DWT

["Zou Dekun" <dekun.zou@Thomson.net>]

This is expected because the image does not have unlimited bit depth.
The rounding after IDWT will remove some energy of the watermark. You can not retrieve a exact copy of the watermark image but an
approximation of it.

- Dekun


-----Original Message-----
From: watermarking-owner@watermarkingworld.org
[mailto:watermarking-owner@watermarkingworld.org] On Behalf Of rupal agravat
Sent: Wednesday, May 30, 2007 4:24 AM
To: watermarking@watermarkingworld.org
Subject: [WM]: Again need help in implementation of DWT

Respected All,
   
  I have asked you all one doubt in matlab and i have received number of answers and due to that it was possible for me to do some
progress in my work.
   
  But now again i have stucked at one problem in implementation of DWT in digital watermarking. Steps of embedding watermark are as
follows:
   
  1) Apply DWT on cover image.
  2) Apply DWT on watermark.
  3) Do the process on both set of coefficients to get the watermarked image.
  4) Apply IDWT on those coefficients.
  4) Write the watermarked image to some file.
   
  Steps of extracting watermark are as follows:
  1) Apply DWT on cover as well as watermarked image.
  2) Do the inverse of the embedding process.
  3) Apply the IDWT on the recovered coefficients of watermark.
  4) Display the file.
   
  Now my problem is set of coefficients which i m getting after doing embedding process are different then the set of coefficients
which i m getting after apply DWT on the watermarked image. If these two sets are different extracted watermark coefficeints will
not be as it should be and hence i am not getting exact recovered watermark.
   
  I have tried number of ways but not getting proper output. 
   
  Will anybody help me in this? 
   
  Hoping for positive reply please.
   
  Thanks in advance.
   
  -Rupal Agravat
  Gujarat,
  India.




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