Robust color image watermarking using the Spatio-Chromatic Fourier Transform and semi-random LDPC codes

The paper proposes a color image watermarking scheme based on the Spatio-Chromatic Fourier Transform (SCFT) with direct-sequence spreading enhanced by low density parity check (LDPC) error correcting codes. The SCFT transform enables efficient use of the embedding properties of the complex Fourier representation without incurring additional computational complexity. The watermark detection is based on a statistical maximum likelihood approach using a Weibull distribution found to be well-suited for modeling the SCFT coefficients. The embedding scheme is image-adaptive, and provides control over the watermark embedding strength according to the local properties of the SCFT host image representation. The efficiency and data hiding capacity of the proposed watermark scheme are shown to be greatly enhanced by the use of semi-random LDPC codes. Simulation results and comparisons with color-component Discrete Fourier Transform (DFT)-based schemes demonstrate the increased robustness of the proposed LDPC-coded, SCFT-based image watermarking algorithm against standard attacks (including additive white Gaussian noise and JPEG compression), and show a reduction in bit error rate (BER) by an order of magnitude.