Download Full ArticleDigital Watermarking Using Wavelet Transforms
With the rapid growth of Internet and networks technique, multimedia data transforming and sharing is common to many people. Multimedia data is easily copied and modified, so necessity for copyright protection is increasing. It is the imperceptible marking of multimedia data to “brand” ownership. Digital watermarking has been proposed as technique for copyright protection of multimedia data. Digital watermarking invisibly embeds copyright information into multimedia data. Thus, digital watermarking has been used for copyright protection, finger printing, copy protection and broadcast monitoring. Indeed, a watermarking algorithm requires both invisibility and robustness, which exist in a trade-off relation. Thus good watermarking algorithm must be satisfied the requirements.
The process of digital watermarking involves the modification of the original multimedia data to embed a watermark containing key information such as authentication or copyright codes. The embedding method must leave the original data perceptually un-changed, yet should impose modifications which can be detected by using an appropriate extraction algorithm. Common types of signals to watermark are images, music clips and digital video. The application of digital watermarking to still images is concentrated here. The major technical challenge is to design a highly robust digital watermarking technique, which discourages copyright infringement by making the process of watermarking removal tedious and costly.
1.1 Advantage of frequency domain watermarking
In general, the digital watermarking is classified into two classes by depending on the domain of watermarking embedding: the spatial domain watermarking and the frequency domain watermarking. The spatial domain watermarking algorithms usually embed the watermark to the least significant bits (lsbs) of the image pixels. The watermark is embedded on randomly selected pixels using neighbours dependant function. In the detection process, the idea is to verify the surrounding pixels to decide if one has truly been modified. The detection of changes in small details of the image is based on mathematical morphology. Furthermore, it is able to reject small distortion introduced by high quality image compression. However, the technique suffers from the major drawback of spatial domain watermarking: frequency localization of modifications is difficult. Because the marks are on certain particular pixels, it is often impossible to detect frequency alterations applied to the entire image. .
Download Full ArticleDigital Watermarking Using Wavelet Transforms