Technology Research On Color Image Watermarking For Copyright Protection

With the advances of multimedia and Internet technologies, digital data can be easily reproduced, manipulated and distributed without any quality degradation. This has resulted in strong demand for preventing illegal use of copyrighted data. Digital watermarking is an important technique for copyright protection and integrity authentication in an open network environment. Generally, digital watermarking is the technology of embedding information (watermark signal) into the multimedia data (such as video, image, audio, and text), called host signal or cover signal, in order to produce watermarked signal for use in certain applications. For different purposes, digital watermarking has been branched into two classifications:robust watermarking technique and fragile watermarking technique. Robust digital watermarking is used to protect ownership of the digital media. In contrast, the purpose of fragile watermarking technique is digital media authentication, that is, to ensure the integrity of the digital media.In recent years, there has been increasing research interest in robust gray image watermarking, and many robust gray image watermarking algorithms have been developed. With the introduction of color imaging, some of grayscale watermarking techniques have been extended to color images. But, they were mainly designed to mark grayscale images or use the color components, which ignore the significant correlation between different color channels, so they are always fragile to some attacks such as color variation. It is a challenging work to design a robust color image watermarking scheme.Based on the color image characteristic and the correlation between different color channels, we expanded the traditional robust gray image watermarking to color image, and proposed the new color image watermarking methods against desynchronization attacks. The main contributions of the paper are summarized as follows:(1) An effective color image watermarking based on new color image normalization is proposed. Firstly, the geometrically invariant space is constructed by using color image normalization. Then, a significant region is obtained from normalized color image by utilizing the invariant centroid theory. Finally, the digital watermark is embedded adaptively into the host color image by modifying the low frequency coefficients, in which the HVS masking is used to control the watermark embedding strength. In watermark detection, according to the high correlation among different color channels of the color image, the digital watermark can be recovered by using SVM technique.(2) Based on Legendre moment invariants, a robust color image watermark detection method is proposed. Firstly, by using the algebra of quaternions, the quaternion Legendre moments is derived and introduced to deal with the color images in a holistic manner. Secondly, a set of affine invariants is derived from quaternion Legendre moments, which are regarded as the effective feature vectors. Thirdly, the appropriate kernel function is selected for training, and a LS-SVM training model can be obtained. Finally, the watermarked color image is corrected with the well trained LS-SVM model, and the digital watermark is extracted from the corrected watermarked color image.(3) Based on local invariant histogram, a new color image watermarking model robust to desynchronization attacks is proposed. Firstly, the stable and uniform color image feature points are extracted by the new color image detector, in which the probability density gradient and color invariance model are used. Secondly, the affine invariant local feature regions are constructed adaptivcly according to the variation of local probability density. Finally, the digital watermark is embedded into the affine invariant local feature regions by modifying the significant bitplane histogram. Experimental results show that the proposed image watermarking model is not only invisible and robust against common image processing operation, but also robust against the global affine transforms and local geometric distortions.