A robust multiple watermarking scheme for still image using DWT, DCT and spread spectrum

In this paper, the spread spectrum (SS) and discrete wavelet transform (DWT), discrete cosine transform (DCT) are used to construct a robust multiple image watermarking scheme. The wavelet decomposition algorithm subdivided the frequency of the host image into low-low, low-high, high-low, high-high frequency bands. However, the low-low frequency band is the most important band, because the energy of the image is concentrated within it. Further we let the low-low band transfer by DCT, then the watermarks bits stream modulated by SS are concealed into those coefficients of DCT block. Before embedding, the watermarks are chaotic by toral automorphism firstly then rearrange into bits stream. While the SS processing, the pseudo-random number (PN) sequence is employed to finish the job. From experiment results shown that our proposed scheme is robust, imperceptible, unambiguous, and non-removable under attacks such as JPEG lossy compression, cropping, rotation, painting, and resizing.