RE: [WM]: Want to get some infor about watermark

["Nizar Sakr" <nsakr@site.uottawa.ca>]

Hi everyone,
I'm currently working on an image watermarking technique, and it's based = on Cox et al.'s scheme. In brief the algorithm divides
the image into 8*8 blocks and I use an HVS to embed into the perceptually significant components of the image (in the DCT domain).
My algorithm is very robust against JPEG and cropping, however it is very weak against scaling = attacks, I can't detect the
watermark when scaled by 50% (256*256 --> 128bt128), = does it have to do with the fact that I'm dividing my image into 8*8 blocks?
= Any suggestions? (I'm using the baboon image for now)

Another brief question, I'm choosing a specific region to embed my = watermark (within an 8*8 blocks), for some images, I'm able to
generate a = watermarked image with excellent PSNR, for other images though, I get a very low = psnr and the watermark is no longer
detectable (even without the presence of = any attacks). What could be the cause of that? I don't think it has to do = with the HVS,
it's something related to the DCT domain that I don’t quiet understand. How would I be able to choose the appropriate area in any
= image that would insure that a watermark will remain detectable (again under = no attacks)?  Any papers discuss these issues?

Thank you in advance,
Nizar

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Nizar Sakr
M.a.sc. Candidate (http://www.site.uottawa.ca/~nsakr)
School of Information Technology and Engineering  University of Ottawa  800 King Edward Ave. SITE 3010
Tel: 1 (613) 562-5800 ext.2197






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