Improved RobustWatermarking Based on Rational Dither Modulation - Advances in Image and Graphics Technologies - page 305

Improved Robust Watermarking Based on Rational
Dither Modulation

Zairan Wang 1 , 2 , Jing Dong 1 ,WeiWang 1 ,andTieniuTan 1 , 2

1 Center for Research on Intelligent Perception and Computing, National Laboratory of Pattern
Recognition, Institute of Automation, Chinese Academy of Sciences
2 College of Engineering and Information Technology,
University of Chinese Academy of Sciences
{zairan.wang,jdong,wwang,tnt}@nlpr.ia.ac.cn

Abstract. Rational dither modulation (RDM) watermarking was presented to re-
sist amplitude scaling attack. This property is achieved by quantizing the ratio of
consecutive samples instead of samples themselves. In this paper, we improve
the performance of basic RDM watermarking to resist more types of watermark-
ing attacks. We improve the robustness of our modified RDM watermarking by
the following three aspects: 1) The quantization step size is increased by modi-
fying two coefficients instead of only one coefficient in the basic RDM method,
2) Several modification rules are defined to reduce embedding distortion, and 3)
The coefficients with larger magnitudes in the lowest sub-band in DWT domain
are selected to embed watermark. A variety of attacks are implemented to eval-
uate the performance of our method. Experimental results demonstrate that our
method outperforms the basic RDM method and two state-of-the-art watermark-
ing methods over a wide range of attacks and it also has good imperceptibility.

Keywords: Watermarking, RDM, Amplitude scaling attack.

1 Introduction

Digital watermarking has always drawn extensive attention for digital copyright pro-
tection since it was born. So far, many watermarking schemes have been proposed in
the literature. One of the most popular algorithms is quantization based watermarking
scheme [1]. The main idea of quantization based watermarking is that the host data
is quantized into different quantization intervals according to different watermark in-
formation. Chen and Wornell [1] proposed a quantization based watermarking scheme
which they called quantization index modulation (QIM). Chen [2] quantized the mean
of a set of wavelet coefficients to embed watermark. Lin [3] embedded watermark by
quantizing the local maximum coefficients in mid-frequency wavelet sub-band. Chen
and Horng [4] embedded watermark by modulating the wavelet coefficients.
The main weakness of QIM based watermarking is that it is very sensitive to am-
plitude scaling attack. Therefore, many watermarking schemes have been proposed to
deal with this problem in recent years. Shterev [5] proposed a maximum likelihood
technique to estimate the amplitude scale in the watermark extraction process. Some
researchers made use of amplitude-scale invariant codes to combat amplitude scaling