The Research For Digital Image Watermarking Algorithm Based On Transform Domains

With the development of multimedia and network communications, digital products become more popular. But digital products can be illegally copied, duplicated and manipulated easily, so traditional encryption technology won’t be enough to solve the problem of digital media copyright to protect owner’s legitimate rights. Digital watermarking technology which has a specific mark hidden in digital products can play an important role in this application. In recent years, digital watermark also became the research focus in the field of signal processing and information security, whose core is that watermark is embedded in the original signal for protection with the premise of not affecting the usability of original data. At the same time, the watermarking information can be completely and correctly extracted or detected, to solve the problem of ownership disputes, piracy tracking and so on.Digital watermarking technique is an important branch of the information hiding technology; it is a technology that implements copyright protection and authentication and maintain data security. Digital watermarking and cryptology is closely linked, cryptography is the study of how to convert the original information to encrypt the secret information so as to achieve the purpose of protecting the original information, but the encryption technology can only provide protection in the data transmission and storage, and can not protect the data being processed. For the multimedia digital products, they must be decrypted while providing the users. But they once be decrypted cannot obtain the effective protection. As can be seen from the communication protocol, cryptography is usually used for secret communication between trusted two parties that not the existence of hidden information. Generally speaking, the attackers know the secret information and just not understand the specific content. If the key is obtained, the secret information will be decrypted and no longer protected. Along with the network parallel computing based on crack technology becomes more and more mature; the security of encryption algorithm is undertaking severe challenges. It is no longer feasible way that be increased the length of privacy key. Digital watermarking technology with its good performance characteristics is more concerned, it make mark information to directly embedded into the multimedia contents through a certain algorithm, and the value and use of original content is not effected, at the same time, is not found by the human visual system, and can be distinguished and extracted by special detector and reader. Digital watermarking technology does not limit the occurrence of piracy, but it can accurately distinguish objects be protected or not, monitor the transmit of the monitored data and protect the copyright.Generally speaking, digital watermarking should possess the following characteristics:(1) Imperceptibility:watermark information should not cause the obviously visual difference of digital products, and hidden information can’t be or easily be noticed.(2) Robustness:digital watermarking also can be extracted from the original image after transform and processing.(3) Maximum information:digital watermarking information should be embedded to the carrier as much as possible, in order to reach maximum quantity of secure information which the carrier can hide.(4) Determinacy:the owner of the digital works should be uniquely determined by digital watermarking copyright information. Even via the certain destruction, the watermarking can still identify it uniquely.According to the way of embedding, it can be divided into spatial domain and transform domain digital watermarking. The former means the amplitude of signal sampling point is changed in spatial domain while embedding the watermarking, whose representative is Least Significant Bit (LSB) algorithm; the latter means the coefficients of transform domain is changed while embedding the watermarking. Generally speaking, the basic idea of transform domain watermarking algorithm is that the original image is transformed and transform domain coefficient is changed to embed watermark, according to spreading spectrum communication principle. Transform domain digital watermarking technology has obvious advantages:(1) It can spread the watermarking information into all the pixels of spatial domain, guaranteeing imperceptivity of watermarking.(2) Concentrated energy distribution can guarantee more information of embedded watermarking with better imperceptivity, robustness and security.(3) It can be compatible with existing compression algorithm, embedding the watermarking in the compressed image.(4) It is consistent with human visual system, easy to implement watermarking masking. In view of the advantages of transform domain watermarking, this paper combine discrete Cosine transform, discrete Wavelet transform, fast Curvelet transform, and discrete Contourlet transform with Human Visual System to study watermarking technology, the main work and contributions are as follows.1. Digital image watermarking algorithm base on DCTDiscrete Cosine transform (DCT) is the orthogonal transformation method and the real part of the Fourier transform has many advantages, such as a high compression ratio, a small bit error rate, concentrate information and low computational complexity and has been applied to many fields such as image compression coding, speech signal processing, s information security and so on. According to the characteristics of DCT alternating current coefficients of digital image, using unmeaning watermark and menaningful watermark, two different watermarking algorithms are presented. One is an adaptive blind watermark detection algorithm based generalized Gaussian distribution. First, generalized Gaussian model is established form the alternating current coefficients, then combined with characteristics of symbol detector and linear detector, an adaptive blind watermark detection algorithm is proposed accomplish with wick signal theory, and deduced the detection efficiency of the adaptive detector have higher. The simulation experiment result show the detection performance of adaptive detector is better than that of linear correction detector. The other is a novel robust color image watermarking algorithm based on discrete Cosine transform. It analyzes the characteristics of the basic principles and coefficients feature of discrete cosine transfonn. The color image is divided into block first, and then digital watermark is embedded in original image by subtle perturbations of corresponding coefficients of discrete cosine transform. And various attacks are applied to the embedded watermark image. From the test results, it could be easily gotten that the algorithm has good imperceptibility and robustness, moreover, the algorithm is feasible and simple. Embedded watermark into the different alternating coefficients and the direct coefficient of discrete cosine transform will be further studied, and the effect will be compared.2. An adaptive color image watermarking algorithm based on DWTFourier analysis reveals the relationship between time function and spectrum reflects the signal frequency components in the time range. The time domain signal is accurately represented the sum of several frequency components. Although the Fourier transform has strong frequency local ability, but has not the time local ability. Wavelet analysis is evolved from Fourier ananysis,it is a mathematical theory and methods which is developed in the mid-1980s, it is pioneered by French scientists Grossma and Morlet when they analyzed of seismic signals. Wavelet analysis is considered to be the breakthrough progress of Fourier analysis, which has good local performance in time domain and frequency domain, it has multi-scale and detail analysis capacity for function or signal through scaling and shift calculations, can solve a lot of difficult problems that can not be solved by Fourier transform, so Wavelet transform is known as "Mathematical microscope". This paper analyzes the properties of coefficient of DWT image, combine with feature of human visual system. The carried image is partitioned into blocks firstly, execute DWT to each block, According to the different variance of high frequency coefficient of the sub-block, the watermarking information perturbation corresponding sub-block coefficients. The watermark is adaptive embedded and various attacks effect to the embedded watermark image is shown. The algorithm embodies good imperceptibility and robustness.3. Digital image watennarking algorithm based fast Curvelet transformCurvelet transform that constructed on the basis of monoscale Ridgelet analysis is a multiscale Ridgelet system. Curvelet transform in multiscale analysis range has more directional parameters than Wavelet transform, so it has better directional recognition ability, and can be optimal approximation of curve. Curvelet transform exhibit a great advantage in image processing and information security fields.According to multidirection multiscale and bandpass and characteristic of each layer parameters, two different watermarking algorithms are presented. One is embed the digital watermark to the high frequency part of the carrier image that be transformed by Curvelet,various attacks are applied to the embedded watermark image. From the test results, it is obvious that the algorithm has good imperceptibility and robustness. The other is According to human eye is more sensitive to low frequency information than to high frequency information, at the same time, taking into account robust and imperceptibility and maximum of digital watermark. First, digital watermark is scrambled by Arnold transform and decomposed though Wavelet transform, then the low frequency component of watermark information is embedded into sixteen direction coefficient matrix with the first maximum energy of the fourth layer of the original image that using Curvelet transform. Simulation experimental result shows the algorithm is effective and feasibility.4. A scrambling digital image watermarking algorithm based Contourlet transformContourlet transform which is also called Pyramidal Directional Filter Banks is a new expansion of wavelet transform. It is a kind of multi-resolution, local, directional image representation method. In Contourlet transform, first, Laplacian Pyramid is used to decompose the image in multi-scale to "capture" point singular. Then in order to capture high frequency component, singular points which are distributed in the same direction are gathered to synthesize into a coefficient by Directional Filter Banks. On the whole, Contourlet transform provides a flexible image decomposition method with multi-resolution and direction, because it allows for different Numbers of decomposition direction in each scale. The final result is similar to use the base structure of contour fragment to approximate the original image. This section introduced the basic theory of Contourlet Transform and the characteristics of its coefficient. Then a digital image watermarking algorithm in Contourlet domain is proposed. This algorithm achieves the purpose of embedding watermark information adjusting the watermark embedding strength according to the energy distribution difference on sub-band image which is decomposed by LP while taking digital watermark imperceptibility and robustness and the characteristics of human visual system into account. Then watermarking image is tested by various attacks. The results show that the algorithm keeps good imperceptibility and robustness.