Z-Transform Based Digital Image Watermarking Scheme with DWT and Chaos

Digital Image Watermarking has recently been used widely to address issues concerning authentication and copyright protection. Chaos is one of the promising techniques implemented in image watermarking schemes. In this paper, a new watermarking algorithm based on chaos along with discrete wavelet transform and z-transformation is proposed. The host image is decomposed into 3-level Discrete Wavelet Transform (DWT). The HH3 and HL3 sub-bands are then converted to z-domain using z-transformation (ZT). Arnold Cat Map (ACM), a chaotic map is applied to the watermark image and it is divided into two equal parts. The sub-bands HH3 and HL3 are chosen for embedding the watermark image. One part of the watermark is embedded in the z-transformed HH3 sub-band, and the other part is embedded in the z-transformed HL3 sub-band. The watermarked image is obtained by taking the inverse of the ZT and the inverse of DWT. The experimental results and the performance analysis show that the proposed method is efficient and can provide practical invisibility with additive robustness.