26-06-2012, 01:44 PM
A Digital Watermarking Algorithm Based On DCT and DWT
A Digital Watermarking Algorithm.pdf (Size: 410.17 KB / Downloads: 238)
INTRODUCTION
With the redundancy of the medium as image and voice,
digital watermarking technology is to use the digital
embedding method to hide the watermarking information
into the digital products of image, visible and video. Seen
form the field of signal process, the watermarking signal
being embeded into carrier is as a feeble signal to add into
a strong background. As long as the intensity of
watermarking is lower than the contrast restriction of
human visible system(HVS) or the apperceive restriction
of human audio system(HAS), the wartermaking signal
won’t be felt by HVS or HAS. With the characters and
important application, digital wartermaking technology
has been got more and more attention [1][2]. In the future
the main development of digital wartermaking is like this:
copyright protection, pirate tracking, copying protection,
image authentication, cover-up communication,
classification control of digital wartermaking video and so
on. And the common charaters of digital watermarking is:
insensitivity, secrecy, robustness and insurance.
DISCRETE COSINE TRANSFORM
With the character of discrete Fourier transform(DFT),
discrete cosine transform(DCT) turn over the image edge
to make the image transformed into the form of even
function. It’s one of the most common linear
transformations in digital signal process technology. Twodimensional
discrete cosine transform(2D-DCT) is
defined as
DISCRETE WAVELET TRANSFORM
Wavelet tramsform is a time domain localized analysis
method with the window’s size fixed and form convertible.
There is quite good time differentiated rate in high
frequency part of signals DWT transformed. Also there is
quite good frequency differentiated rate in its low
frequency part. It can distill the information from signal
effectively.
WATERMARK EMBEDDING AND DISTILLING
The decomposing process of delamination DWT for
image frequency is alike the signal disposeing process of
HVS. By using the characters of delamination DWT, the
concealing and the robustness of watermark can be
balanced. Then it become the main choice of watermark
embedding in transformed domain.
DISCRETE WAVELET TRANSFORM
Wavelet tramsform is a time domain localized analysis
method with the window’s size fixed and form convertible.
There is quite good time differentiated rate in high
frequency part of signals DWT transformed. Also there is
quite good frequency differentiated rate in its low
frequency part. It can distill the information from signal
effectively.
The basic idea of discrete wavelet transform(DWT) in
image process is to multi-differentiated decompose the
image into sub-image of different spatial domain and
independent frequency district [5][6]. Then transform the
coefficient of sub-image. After the original image has
been DWT transformed, it is decomposed into 4
frequency districts which is one low-frequency district(LL)
and three high-frequency districts(LH,HL,HH).