Abstract
Many digital watermarking methods have been proposed for copyright protection. Especially, methods to add a watermark in the frequency domain are often used. In those methods, only a few components of frequencies are changed according to watermark information, so that the pixel values sometimes exceed the dynamic range. This 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.
