Research On Digital Image Watermarking Based On Wavelet Transform

With the fast development of computer network, multimedia and information science, problems about copyright protection and integrity authentication of digital media have attracted more and more attention worldwide. Traditional security systems can only guarantee information transmitting process, but they can't meet the requirements of new conditions. As a key to solve those problems, digital watermarking has become a new research hot-point for researchers in signal processing.In this paper we first introduce the research background of digital watermarking, including types of digital watermarking, its design principles, as well as different application fields. Watermark attacks and relevant remedies against those attacks are also discussed.Secondly, this paper presents a digital watermarking technique based on discrete wavelet transform (DWT) with human visual properties considered. The JND values allow us to imperceptibly add a larger-amplitude watermark to the transform coefficients, thus the watermark will be more robust. And the watermark is a visually meaningful binary image, which will greatly facilitate the process of convincing the jury of an ownership claim. Experimental results show that the proposed technique is robust enough to some image processing operations and JPEG lossy compression.Thirdly, we discuss in detail how to factor wavelet transforms into lifting steps. The simulation results show that lifting scheme can speed up the watermark embedding and detection process apparently compared with the standard wavelet transform. In addition, lifting method has no requirements for image size.