A blind grayscale watermark algorithm based on chaos and mixed transform domain

This paper presents a blind grayscale watermark algorithm based on chaos and mixed transform domain. The adopted watermark signal is (32×32×8) bits gray image. Firstly, the watermark is pre-processed by hash disturbance, and then sixty-four bits sequence of every eight bytes in the disturbed watermark is scrambled by chaos map with control key. After Discrete Wavelet Transform (DWT) for the cover image, the block Discrete Cosine Transform (DCT) is applied on low frequency wavelet coefficients, and in DCT domain, the watermark information is embedded into the medium-high frequency coefficients which are determined by the quantized table. The algorithm is secure because only those who know the keys can extract the watermark. The experimental results show that the algorithm is robust against conventional signal processing and geometric distortion.