Abstract
Study of digital watermarking technique is making progress to protect intellectual property rights of digital contents. As a method of digital watermark, a method to add a watermark in the frequency domain is often used. In this method, only a few frequency components are changed according to watermark information, so that the pixel values sometimes exceed the dynamic range and watermark information is lost. This problem even occurs without attacks like image processing. In this paper, we propose two methods to prevent loss of watermark information, applicable to such cases, it is said that, one is the method called “inversion of increase and decrease” and another is “conservation of amounts of changes”. We can extract the watermark information correctly under the condition of no attacks by using these proposed methods.
