M-ary reversible contrast mapping in reversible watermarking with optimal distortion control

A generalized form of reversible contrast mapping (RCM), analogous to M-ary modulation in communication, is developed here for reversible watermarking in digital images. Then an optimized distortion control framework in M-ary scheme is considered to improve data hiding capacity while meeting the embedding distortion constraint. Simulation results show that the combination of different M-ary approaches, using the different points representing the different RCM transformation functions, outperforms the embedding rate-visual quality-security of the hidden information compared to the existing RCM, difference expansion (DE) and prediction error expansion (PEE) methods during over embedding. Numerical results show that an average of 20% improvement in visual quality, 35% improvement in security of the hidden data at 1 bpp embedding rate is achieved for the proposed method compared to the existing PEE works. All these effectiveness are demonstrated with a number of simulation results.