Multichannel Watermarking for Color Images by Using Quantization Visibility Thresholds

In this paper, a wavelet-based watermarking scheme for color images is proposed. The watermarking scheme is based on the design of a color visual model that is the modification of a perceptual model used in the image coding of gray scale images. The model is designed to estimate and utilize the noise detection threshold of each wavelet coefficient in luminance and chrominance components in order to satisfy the transparency and robustness required by color image watermarking techniques. Besides the visual masking given by taking into account the luminance content and the texture, the crossed masking effect and the effect given by the variance within the local region of the target coefficient are investigated such that the estimated noise detection threshold is more close to the real noise detection threshold. In a locally adaptive fashion based on the wavelet decomposition, the thresholds of subband coefficients in each color component are derived to construct a perceptually lossless quantization matrix for embedding watermarks. Performance in terms of robustness and transparency is obtained by embedding the maximum strength watermark while maintaining the perceptually lossless quality of the watermarked color image. Simulation results show that the proposed scheme is more robust than the existing schemes while retaining the watermark transparency.