The Technology Of Color Digital Image Watermark

With the rapid development of internet and communication techniques, the wide application of digital media, including digital image as well as digital video and audio data has led to an increasingly urgent demand for safe usage of digital media information and protection and authentication of intellectual property right. The traditional information encrypting methods can only guarantee a safe transmission of information. When the data has been accepted and decoded, the methods will be ineffective in protection. Furthermore, the encrypted files tend to stimulate the interests of those with strong desire to decode files of other people. As an effective complement for traditional methods of encryption, digital watermarking is a new technique, which can ensure safe protection of copyright, precise authentication of the source and completion of the data in an open internet environment. Due to its advantages, digital watermarking has gained much attention and has become a hot issue in the field of multimedia data processing.This article presents a series of systematic introductions of related concepts of watermarking, the history and background of watermarking development, the current domestic and overseas researches on watermarking, the typical algorithms of watermark scheme, the inter-transformation between YUV and RGB and the YUV color space as well. The article put a special emphasis on the watermark scheme based on discrete cosine transform (DCT) and the implementation of the algorithm embedding and extracting watermark based on discrete wavelet transform, realizing a complete watermark image experiment system. A summary of my work and achievement in the period of my postgraduate study is finally made along with a outlook for my future study. This article analyzes the significance of color space for the technique of colored image digital watermarking, makes a list of the inter-transformation between RGB and YUV. A further discussion is made on the four types of YUV partial sampling including YUV444(without compaction), YUV422, YUV411 and YUV 420.In this article, a scheme on the basis of embedding and extraction of watermarking for the 24-phase colored image is brought forward. The scheme first transforms the RGB digital colored image into YUV420, and then makes cosine transformation on the image. The transparence and robustness of watermarking can easily be seen through the results of test.We also bring forward a method on the basis of DWT embedding and extraction of watermarking for the 24-phase colored image and has made many study and tests on the watermarking embedding under the conditions of low frequency DWT, medium frequency DWT and high frequency respectively. A method of embedding under mixed frequencies is also deeply discussed. The method first transforms the RGB digital colored image into YUV420, and then makes cosine transformation on the image. The transparence and robustness of watermarking can easily be seen through the results of test. To give an objective and quantified evaluation to the method, and to illustrate the effect of the method with chart when necessary, we have designed and realized a test system of digital colored image watermarking.As a conclusion, I made a brief summary on my work when writing the graduation thesis, the tasks that haven't been finished, what I have learned and achieved through the work and my viewpoint of the future study as well.