The Study Of Digital Image Watermarking Technology Based On Wavelet Transform

With the rapid development of computers and internet, copyright protection of digital media as image, video and audio becomes more and more important. Digital watermarking is a new resolution for copyright protection and media security, and it is becoming a very active research area for information security. Digital watermarking is the technology which embeds copyright information including product ID, text content or image logo into multimedia for copyright protection, secret communication and discrimination of the data files. Perceptual invisibility, robustness and safeness are the digital watermarking system's central characteristics.This paper takes still digital image as research object, three kinds of embedding and extracting digital watermark algorithms are proposed.First of all, a watermarking algorithm for ROI (Regions of Interesting) authentication and tamper detection is proposed. The watermarking is embedded the DWT (Discrete Wavelet Transform) coefficients of the ROB (Regions of Background). The algorithm uses a hashing to detection whether tamper the ROI of image, and then use the watermarking to reconstruction the data of ROI. The experiment results show that the embedded watermark is perceptually invisible and robust to various image processing operations. Most importantly, the tampered place can be identified accurately.Next, this paper proposes a reversible visible watermarking algorithm based on luminance CSF (Contrast Sensitivity Function). For our removable visible watermarking algorithm, we compute composite coefficients using characteristics of the host and watermark image in the DWT domain. The visible watermark is securely embedded based on a use-key-controlled embedding mechanism. With correct user keys, authorized user can completely removed the watermark and lossless recover the original image. In contrast, unauthorized operations either overly or insufficiently remove the watermark due to wrong estimation of embedding parameters, and thus, the resulting image has apparent defect.Finally, an image watermarking scheme based on DT-CWT (Dual Tree Complex Wavelet Transform) resisting geometrical attacks is proposed. We make use of eigenmatrix to recover the attacked image by estimating the parameter when detecting the watermarks, original image being not needed. Experimental results show that the scheme can well withstand such geometrical attacks as rotation, scaling and geometric synchronization problem between the watermark embedding and detection is overcome.Along with the development of technology and the progress of society, digital watermarking technology will also get rid of the stale and bring forth the fresh. I hope that the algorithms proposed in this paper could make slender contribution to the development of digital watermarking technology.