09-10-2012, 01:42 PM
Comparison of Digital Water Marking methods
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Abstract
In Digital watermarking, image or video is embedded
information data within an insensible form for human visual
system but in a way that protects from attacks such as common
image processing techniques. Spatial domain(Least significant
bit(LSB)) and transform domain (Discrete Cosine
Transform(DCT) and Discrete Wavelet Transform(DWT))
methods are used. DWT is best method because of using
embedded zero tree wavelet image compression scheme and high
frequency sub bands.
INTRODUCTION
The rapid expansion of the Internet in the past years has
rapidly increased the availability of digital data such as audio,
images and videos to the public. As we have witnessed in the
past few months, the problem of protecting multimedia
information becomes more and more important and a lot of
copyright owners are concerned about protecting any illegal
duplication of their data or work. Some serious work needs to
be done in order to maintain the availability of multimedia
information but, in the meantime, the industry must come up
with ways to protect intellectual property of creators,
distributors or simple owners of such data. Of the many
approaches possible to protect visual data, digital
watermarking is probably the one that has received most
interest.
The idea of robust watermarking of images is to embed
information data within the image with an insensible form for
human visual system but in a way that protects from attacks
such as common image processing operations. The goal is to
produce an image that looks exactly the same to a human eye
but still allows its positive identification in comparison with
the owner's key if necessary.
BASIC ON WATERMARKING
The increasing amount of applications using digital
multimedia technologies has accentuated the need to provide
copyright protection to multimedia data. A digital watermark
can be described as a visible or preferably invisible
identification code that is permanently embedded in the data .
It means that it remains present within the data after any
decryption process. A general definition can be given: "Hiding
of a secret message or information within an ordinary message
and the extraction of it at its destination. " Complementary to
encryption, it allows some protection of the data after
decryption. As we know, encryption procedure aims at
protecting the image (or other kind of data) during its
transmission. Once decrypted, the image is not protected
anymore. By adding watermark, we add a certain degree of
protection to the image (or to the information that it contains)
even after the decryption process has taken place. The goal is
to embed some information in the image without affecting its
visual content. In the copyright protection context,
watermarking is used to add a key in the multimedia data that
authenticates the legal copyright holder and that cannot be
manipulated or removed without impairing the data in a way
that removes any commercial value. In Figure 1 a general
watermarking scheme in order to give an idea of the different
operations involved in the process.
CONCLUSION
Digital Image Watermarking can protect image, video, audio
from unauthorized person, noise, copyright etc. DCT and
DWT domain watermarking is comparatively much better than
the spatial domain encoding since DCT domain watermarking
can survive against the attacks such as noising, compression,
sharpening, and filtering and also use JPEG compression
method and DWT is used embedded zero-tree wavelet (EZW)
image compression scheme and high frequency sub bands as
LH,HL,HH etc