Secured Overlapping Technique for Digital Watermarking

Information security is a mandatory issue in current information technology world. A secure overlapping method is proposed in this paper whose key functionality is to distribute the key words at different places inside an image. It requires the extraction of overlapping blocks of image of the size of 4x4 matrixes and taking its transpose. Afterwards arranging the block to linear form row-by-row and applying watermark on it, and finally converting the block back to its original form just like the first step. This technique results in the distribution of hidden data within the block. This scattering of data is beneficial because attacker is unable to find the precise localization of hidden data within the overlapped blocks

Image Watermarking Using Psychovisual Threshold Over the Edge

Currently the digital multimedia data can easily be copied. Digital image watermarking is an alternative approach to authentication and copyright protection of digital image content. An alternative embedding watermark based on human eye properties can be used to effectively hide the watermark image. This paper introduces the embedding watermark scheme along the edge based on the concept of psychovisual threshold. This paper will investigate the sensi-tivity of minor changes in DCT coefficients against JPEG quantization tables. Based on the concept of psychovisual threshold, there are still deep holes in JPEG quantization values to embed a watermark. This paper locates and utilizes them to embed a watermark. The proposed scheme has been tested against vari-ous non-malicious attacks. The experiment results show the watermark is robust against JPEG image compression, noise attacks and low pass filtering

Robust Image Watermarking Based on Psychovisual Threshold

Because of the facility of accessing and sharing digital images through the internet, digital images are often copied, edited and reused. Digital image watermarking is an approach to protect and manage digital images as intellectual property. The embedding of a natural watermark based on the properties of the human eye can be utilized to effectively hide a watermark image. This paper proposes a watermark embedding scheme based on the psychovisual threshold and edge entropy. The sensitivity of minor changes in DCT coefficients against JPEG quantization tables was investigated. A watermark embedding scheme was designed that offers good resistance against JPEG image compression. The proposed scheme was tested under different types of attacks. The experimental results indicated that the proposed scheme can achieve high imperceptibility and robustness against attacks. The watermark recovery process is also robust against attacks

A Simple Image-Adaptive Watermarking Algorithm with Blind Extraction

In this paper, we propose an adaptive, DCT based, blind image watermarking algorithm. The adaptability is developed, while exploring the properties of the human visual system (HVS), to embed robust watermarks in DCT matrices while making them the least visible in the space domain. In the algorithm, binary watermarks are embedded in image blocks having gray level variations sufficient to mask a certain level of signal alterations. The orientations of the variations in such a block are detected by examining the locations of the most significant DCT coefficients in the matrix and a particular DCT coefficient is then chosen for watermark embedding with a view to making the gray level changes resulting from the embedding have a similar orientation with the original image signal to mask the watermark better. Moreover, the embedding strength is made to depend on the DC component, as it indicates the brightness of the image block, to further reduce the visibility of the watermark. The algorithm is computationally simple because it extracts the needed features directly from the DCT coefficients. Simulation results show that the algorithm is highly robust against JPEG compression even at low quality factors while maintaining high visual quality. Furthermore, the computational simplicity of the algorithm makes it very useful in real-time applications

DCT-Based Image Feature Extraction and Its Application in Image Self-Recovery and Image Watermarking

Feature extraction is a critical element in the design of image self-recovery and watermarking algorithms and its quality can have a big influence on the performance of these processes. The objective of the work presented in this thesis is to develop an effective methodology for feature extraction in the discrete cosine transform (DCT) domain and apply it in the design of adaptive image self-recovery and image watermarking algorithms. The methodology is to use the most significant DCT coefficients that can be at any frequency range to detect and to classify gray level patterns. In this way, gray level variations with a wider range of spatial frequencies can be looked into without increasing computational complexity and the methodology is able to distinguish gray level patterns rather than the orientations of simple edges only as in many existing DCT-based methods. The proposed image self-recovery algorithm uses the developed feature extraction methodology to detect and classify blocks that contain significant gray level variations. According to the profile of each block, the critical frequency components representing the specific gray level pattern of the block are chosen for encoding. The code lengths are made variable depending on the importance of these components in defining the block’s features, which makes the encoding of critical frequency components more precise, while keeping the total length of the reference code short. The proposed image self-recovery algorithm has resulted in remarkably shorter reference codes that are only 1/5 to 3/5 of those produced by existing methods, and consequently a superior visual quality in the embedded images. As the shorter codes contain the critical image information, the proposed algorithm has also achieved above average reconstruction quality for various tampering rates. The proposed image watermarking algorithm is computationally simple and designed for the blind extraction of the watermark. The principle of the algorithm is to embed the watermark in the locations where image data alterations are the least visible. To this end, the properties of the HVS are used to identify the gray level image features of such locations. The characteristics of the frequency components representing these features are identifying by applying the DCT-based feature extraction methodology developed in this thesis. The strength with which the watermark is embedded is made adaptive to the local gray level characteristics. Simulation results have shown that the proposed watermarking algorithm results in significantly higher visual quality in the watermarked images than that of the reported methods with a difference in PSNR of about 2.7 dB, while the embedded watermark is highly robustness against JPEG compression even at low quality factors and to some other common image processes. The good performance of the proposed image self-recovery and watermarking algorithms is an indication of the effectiveness of the developed feature extraction methodology. This methodology can be applied in a wide range of applications and it is suitable for any process where the DCT data is available

Wavelet ヘンカン ニ モトズク ガシツ レッカ ヒョウカ シュホウ

博士(理学)佐賀大