14-11-2012, 05:10 PM
A Biorthogonal Wavelet Transform Based Robust Watermarking Scheme
A Biorthogonal Wavelet.pdf (Size: 663.33 KB / Downloads: 52)
Abstract
This paper presents a robust watermarking technique
using biorthogonal wavelet transform. In proposed method the
blue channel of the color host image is selected for embedding
watermark because it is more resistant to changes compared to
red and green channels. The blue channel is decomposed into n
levels using biorthogonal wavelet transform because biorthogonal
wavelet transform is an invertible transform and has the
property of exact reconstruction and smoothness. This method is
shown to be robust against many signal processing operations as
well as geometrical attacks.
INTRODUCTION
In the present scenario the rapid growth of the internet and
digital media manifests itself in widespread in the form of the
digital image, audio, video and so on, because digital media
are easy to copy and transmit. Issues related to digital media
are copyright protected, content authentication, proof of
ownership, etc. The watermarking technique provides the best
solutions of these problems. This technique embeds
information so that it is not easily perceptible; Human visual
system not able to see any information embedded in the
contents. The other important issues in the watermarking
system are the watermark must be robust enough to resist
common image processing attacks, geometric attacks.
The main objective of this paper is to present a novel
watermarking technique that uses the biorthogonal wavelet
transform. The technique makes use of DWT; it aims to
improve the robustness of existing watermarking techniques.
With proposed technique watermark is extracted even if the
watermarked image is attacked. Another important goal is to
keep the watermarked image imperceptible
2D DISCRETE WAVELET TRANSFORM
The 2D DWT is computed by performing low-pass and highpass
filtering of the image pixels as shown in Figure 1. In this
figure, the low-pass and high-pass filters are denoted by h (n)
and g (n), respectively. This figure depicts the one level of the
2D DWT decomposition. At each level, the high-pass filter
generates detailed image pixel information, while the low-pass
filter produces the coarse approximations of the input image
[7].
At the end of each low-pass and high-pass filtering, the
outputs are down-sampled by two (↓ 2). In order to compute
2D DWT, 1D DWT is applied twice in both horizontal and
vertical dimension. In other words, a 2D DWT can be
performed by first performing a 1D DWT on each row, which
is referred to as horizontal filtering, of the image followed by
a 1D DWT on each column, which is called vertical filtering
as shown in figure 1. Figure 2 shows the structure of II level 2
D wavelet decomposition.
PROPOSED WATERMARKING METHOD
In embedding process, first separate the R, G & B channels of
the color image and the blue channel is selected for the
embedding because this channel is more resistant to changes
compared to red and green channels and the human eye is less
sensitive to the blue channel, a perceptually invisible
watermark embedded in the blue channel can contain more
energy than a perceptually invisible watermark embedded in
the luminance channel of a color image. The blue channel is
decomposed into n-level using biorthogonal wavelet transform
[5].
CONCLUSIONS
In this paper watermark is embedded into second level
subband of DWT decomposition. Results show that when the
embedding factor (Alpha) value increases then distortion in
the watermarked image increases and quality of the extracted
watermark also improves. This method is implemented using
both bi-orthogonal wavelet and orthogonal wavelet transforms
for analysis. If we use Bi-orthogonal wavelets for
decomposition then distortion in the watermarked image is
less compared with the Haar wavelet transform. The technique
makes use of DWT; it aims to improve the robustness of other
watermarking techniques. With this technique the watermark
is extracted even if the watermarked image is attacked. First,
the embedded watermark should not degrade the quality of the
image and should be perceptually invisible to maintain its
protective secrecy. Second, the watermark must be robust
enough to resist common image processing attacks and not be
easily removable; only the owner of the image is able to
extract the watermark.