Re: [WM]: a question about cox's algorithm

[yanmiaobest <yanmiaobest@163.com>]

Hi,

   I am not a researhcer, I am a beginner and very interested in this field. the algorithm I used has been published, i just describe it in more detail, so people could help me. sorry for the misunderstandings.

 

hi

first any researcher doesn't tell all his idea with its details for others.

second it is better to put tyhe watermark into middle frequencies in DCT domain

Good luck

ENG Rania  

yanmiaobest <yanmiaobest@163.com> wrote:

Hi,
   thank you very much for you reply!

   my method is this:
              
            divid the original image into 8*8 subimages, and apply dct transform to the green channel of each block. And chose some coefficient to inject the signature.
            but I encounter a problem.  Injecting into the low frequency area is perceptable, injecting into the high frequency area is subjected to attack, is that right? but wharever area I inject the signature, it is more or less perceptible. My formula is:   x = x * ( 1 + a * p ), where  a = -1 when signature is 0, a = 1 when signature is 1. and p = 0.3. x is original image tranformed by dct. I could use smaller p value to avoid this, but that makes the extraction very difficult. Smaller p value means chaning the x very little. My extaction method is: sig = 1 when Xw > Xb, otherwise sig = 0. Xw is the watermarked image transformed by dct, and Xb is the original image transormed by dct( all applied on the green channel). when p is too small, this method sucks, because after injected the watermark, I have to transformed it into spatial domain using inverse dct, but many value is the same as the original image after inverse dct, so I can't extract the watermark.
           please help me
best
 regards

 

 

 

What do you mean by variance of cox's algorithm?=20    =20    The answer to your question is : It will depend upon the gray level of =  your image. For ex., if the image is represented by 8bpp  (256 color) then according to Cox, the 63 coefficients of every block =  will be sorted in descending order, barring DC coefficient  (0,0), select first few largest coefficients and insert the random =  number according to formula given in paper. The random numbers  will be real numbers with mean 0 and variance 1. After embedding them =  the pixels which were integers initially will be converted to  real. They will be rounded off to its nearest values. This does not =  result in much
 difference in perceptible quality and SIM or PSNR  values.    =20    Good Luck    =20    Anurag Mishra    =D1=D6=ED=B5 <yanmiao06@mails.gucas.ac.cn> wrote:    hi all  I am new in this field. And I am about to impelment a variance of cox's =  algorithm. The image is divided in 8 * 8 block, and dct  transform is applied to each block, then insert watermark into each =  block. My questions is this:  1. Dose each pixel in a 8 * 8 block can only be inserted one bit, which =  means a block can at most inject 64 bits infomation?  2. when trasformed using dct, the values are real numbers, but after =  inject the watermark, I have to round real numbers into  integer, because image gray-level or rgb value is represented by =  integer. Dose this affect my final result?    best regards