Multibit QIM watermarking using M-ary modulation and lifting

Abstract

Quantization index modulation (QIM) principle has shown superior performance in digital watermarking over spread-spectrum and low-bit(s) modulation based methods. In QIM based data hiding scheme, it is a challenging task to embed multiple bits of information into the same set of host signal samples. This work attempts to employ M-ary modulation for multibit QIM watermarking. The watermark embedding process may be divided into two phases. In the first phase, a binary watermark image is spatially dispersed using sequence of number generated by a secret key. In the second phase, host image is decomposed by integer wavelets and the encoded watermark bits are embedded into high-low (HL) and low-high (LH) subbands of DWT-coefficients using M-ary modulation. M-ary modulation is accomplished using near-orthogonal dither generated from the combination of random key, Hadamard matrix and step size. Simulation results show that robustness is increased, at the cost of increase in decoding complexity for high M-value.