Re: [WM]: buliding the digital watermarking software

[Peter Meerwald <pmeerw@bgnet.bgsu.edu>]

> >         Hm. and if the algorithm is based on the sptread spectrum .Do we
> > need the original image to extract the watermark ? 

> Depends. There are methods which require the orininal image in the extraction
> process and there are methods which don't. 

blind (original image NOT required): 

* Barni, 'Robust Watermarking of Still Images for Copyright Protection', 1997
Barni's scheme has to estimate the original coefficients, which makes
correlation problematic; therefore more signature energy has to be
embedded causing visual distortion, to overcome that perceptual masking is
required

* Koch, 'Towards Robust and Hidden Image Copyright Labeling', 1995
Koch's algorithm modifies the relationship between two or tree DCT
coefficients in NxN blocks
source code for a variant of that algorithm is available on Stefan's
homepage - I think that is the ONLY watermarking algorithm available 
in source code so far?!
-> http://stud3.tuwien.ac.at/~e9625414/robust-st.html

non-blind (requiring original image): 

Cox, 'Secure Spread Spectrum Watermarking for Multimedia', 1995

you might also want to check Craver's paper 'Can Invisible Watermarks
Resolve Rightful Ownerships?', 1996, on the invertability problem with
Cox' algorithm

Barni's and Cox' schemes take the DCT of the entire image -
you will need an efficient implementation for the DCT if the image is
reasonable large, the JPEG library doesn't help much here (since it only
optimized for 8x8 blocks), I like Ooura's FFT/DCT/DST code ->
http://momonga.t.u-tokyo.ac.jp/~ooura/fft.html

Koch's algorithm operates on small NxN blocks, no big deal

AFAIK fast code for the DCT on NxM images (N, M not a power of two) is not
available, am I wrong? anyone?

regards,
Peter

-- 

Peter Meerwald                   824 Sixth Street, Apt. #6
pmeerw@bgnet.bgsu.edu            43402 Bowling Green, Ohio
pmeerw@cosy.sbg.ac.at            USA
seawood@very.priv.at             ++1-419-353-3026

 "The day Microsoft makes something that doesn't suck, 
  is probably the day Microsoft starts making vacuum cleaners."


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