Blind Watermarking Scheme Based On Wavelet Transform

In the recent few years, watermark technology has developed rapidly and been used extensively. And with the development of the society .The level requirement of the watermark technology is more and more higher. So that the technology developed more and more rapid .For its extensive use more and more learners are interesting in studying at it .In this paper in order to understand the watermark system, a communication model is established. Then some classic schemes are summarized .In present watermark system, there are two basic preconditions: one is robustness; the other is transparency. Transparency is that after the watermark is embedded in the original image and people can't find out the change of the picture only by their eyes . Robustness is the ability that although the image. Which has been embedded the watermark, is attacked, the watermark also can be extracted, and people can recognized it. When people extract the watermark, whether the original image is needed or not is a milestone .In present, extracting watermark without the original image is more and more popular with the businessman and the judicial department. And this is the focus and difficulty of the study. When the Wavelet transform appeared the schemes based on the transform are approved by a lot of learners . In this paper , a scheme based on Wavelet transform is put forward . The essence of Wavelet transform is that the low frequency coefficients describe the smooth part of the image and the high frequency coefficients describe the details .The algorithm takes advantage of this feature . According to the low frequency coefficients, searching the suitable place to embed the watermark, according to the feature of the corresponding coefficients, such as the data are odd or even, to change the coefficients .In this scheme, the process of extracting the watermark is easy .If people know the keys, then change the image by Wavelet transform and according to the similar process of the embedding and with the quantized data, the watermark can be extracted. This scheme carries out easily and it has very good robustness when it is attacked by cut, noise and compression. But it needs improvement when resisting geometric attack.