Volume 36, Issue 4 (July 2008)
Double Watermarking and Turbo Coding for Robust Image Watermarking
This paper is an attempt to describe the concept of double watermarking. The latter term refers to a new watermarking scheme based on embedding a mark (signature) in both spatial and multiresolution domains. This scheme is able of embedding 2000 bits of mark in medical images with dimensions 256 by 256 pixels. Experiments on a database of 30 medical images indicate the watermarks are robust to noises, filter attacks, JPEG compression, and cropping. For the purpose of increasing the image watermarking robustness against attacks of an image transmission and to perform a large number of bits to hide into images we encode with a turbo code an image-embedded mark. Fidelity of images is improved by incorporation of the relative peak signal-to-noise ratio as a perceptual metric to measure image degradation. We demonstrate by some experimental results that this unit of measurement is the best distortion metric which is correlated with the human visual system to evaluate the quality of images after the watermarking process. We show that each of these three components improves performance substantially.