Digital Watermarking-A Combined Approach by DWT, Chirp-Z and Fast Walsh-Hadamard Transform

Digital Image Watermarking is one of the ways to protect intellectual property right and copyright of the information owner. Fidelity, Capacity and Robustness are the important requirements of digital watermarking techniques, but these requirements compete with each other; if one is improved the other two are affected. This paper presents a combined approach of DWT, Chirp-Z and Fast Walsh-Hadamard Transforms for digital image watermarking to minimize the gap between robustness and fidelity with limited capacity. The DWT is used for locating the suitable area in the cover image for watermark embedding. The chirp ztransform is the z-transform of input signal along a spiral contour defined by a scalar. The output of Chirp Z-transform is given to Fast discrete Walsh–Hadamard transform that returns the coefficients of the input. Then watermark is embedded depending on pseudo random sequence into predefined mid-band components of the block of cover image.