<title>Embedding watermarks into both DC and AC components of DCT</title>

Abstract

The invisibility, robustness, and capacity of watermarks are critical for data authentication. This paper proposes a watermarking scheme taking advantage of both AC and DC coefficients of DCT, to increase the robustness of watermarks in resisting different attacks caused by processing or degradation. In this scheme, watermark components are inserted into DC coefficient and some lower frequency AC coefficients. This enlarges the capacity of watermarks embedded and at the same time keeps the embedded watermarks invisible. The algorithms for embedding both meaningful and meaningless watermarks and detecting these watermarks are described in detail. The image is first divided into blocks and each block is classified into 3 different categories according to its light and texture characteristics. The embedded watermarks are then distributed into both AC and DC coefficients to get a suitable compromise between invisibility and robustness. Some experimental results with real images are presented and they demonstrate that the watermarks generated with the proposed algorithms are more robust against noise and commonly used image-processing techniques than the watermarks generated by using only DC or AC coefficients. The capacity enabled by the proposed algorithms is also bigger than that allowed by the algorithms using no DC coefficients.