21-12-2012, 04:57 PM
A Novel Robust Grayscale Watermarking Algorithm Based on Two-Levels DCT
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Abstract:
In this paper, a novel robust grayscale watermarking algorithm based on Two-Levels DCT and Two-Levels SVD is approached. The singular value decomposition (SVD) is a factorization of a real or complex matrix. A discrete cosine transform (DCT) expresses a sequence of finitely many data points in terms of a sum of cosine functions oscillating at different frequencies
The watermark signal is 32 cross 32 and 8 bit gray image. First, the original image is divided into blocks according to the size of the watermark; each block corresponds to each pixel value of watermark. Second, the DCT is applied in each block twice and form new blocks. Then, SVD on the each new block to get matrices U, S and V for each block and the first value of each matrix S is collected together to form a new matrix. Apply SVD on the new matrix again to get the S matrix .The pixel value of watermark is embedded into the new S matrix through some method. And the watermark can be detected with the original image. The experimental results show that the algorithm can satisfy the transparence and robustness of the watermarking system very well. Experimental evaluation demonstrates that the proposed scheme is able to withstand a variety of attacks very well.
Introduction:
Multimedia network systems have recently gained more and more popularity due to the increasing amount of information is stored and transmitted digitally; the expansion will continue at an even steeper rate when advanced multimedia services such as electronic commerce, interactive TV, teleworking , etc., will be widely available. A digital watermark is code carrying information about the copyright owner, the creator of the work, the authorized consumer and whatever is needed to handle the property rights associated to any given piece of information. The watermark is intended to be permanently embedded into the digital data so that authorized users can easily read it. At the same time, the watermark should not modify the content of the work but slightly (it should be unperceivable or almost unperceivable by human senses), and it should be virtually impossible for unauthorized users to remove it. By means of watermarking the work is still accessible, but permanently marked. To be really effective, a watermark should be [1, 2]: unobtrusive, readily extractable robust, unambiguous, innumerable Image watermarking techniques proposed so far can be divided into two main groups: those which embed the watermark directly in the spatial domain and those operating in a transformed domain, e.g. the frequency domain [3]. Techniques can also be distinguished according to the way the watermark is extracted from the possibly distorted version of the marked image. As one of the typical transforms, DCT is widely used in digital watermarking, but usually DCT is used only once when embedding watermarks, and DWT is used many times. How many times of DCT can be used in watermarking is still unknown to us. In [4], the Multiple-level idea is introduced from Discrete Wavelet Transform to Discrete Cosine Transform, and the multiple-level Discrete Cosine Transform is called about it.
Matlab:
MATLAB (matrix laboratory) is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages, including C, C++, and Fortran. Although MATLAB is intended primarily for numerical computing, an optional toolbox uses the MuPAD symbolic engine, allowing access to symbolic computing capabilities. An additional package, Simulink, adds graphical multi-domain simulation and Model-Based Design for dynamic and embedded systems. In 2004, MATLAB had around one million users across industry and academia.[2] MATLAB users come from various backgrounds of engineering, science, and economics. MATLAB is widely used in academic and research institutions as well as industrial enterprises.
System model:
We choose to work in the block DCT domain for the
following reasons: DCT has good energy compaction capability; it is feasible to incorporate the HVS characteristics; the sensitivity of HVS to the DCT basis images has been extensively studied resulting in a default JPEG quantization table .Generally speaking, the watermark has to be added to frequencies of high energy in order to be resistant to noise. So,
we embed the watermark to the largest value of the block which the two-levels DCT is applied in. The two-Level DCT is that the DCT is used two times when embedding watermark. The Two-level idea is introduced from Discrete Wavelet Transform to Discrete Cosine Transform, and it is called two-level Discrete Cosine Transform.The conventional DCT domain watermarking algorithms only use DCT on the original image once, and then choose the appropriate transform coefficients to modify the watermark information embedded. In this paper , to take full advantage of DCT’s “ energy concentration” characteristics, we use two level DCT on the original image which is divided into square blocks of size 8_8 pixels.