Digital hologram authentication using a hadamard-based reversible fragile watermarking algorithm

This paper presents a novel reversible fragile watermarking algorithm for hologram authentication. In the algorithm, the watermark is embedded in the transform domain. The marked hologram is then stored in the spatial domain with finite resolution level. The resolution level is allowed to be pre-specified for attaining different degrees of transparency. The algorithm is based on Hadamard transform for both watermark embedding and extraction. The Hadamard transform and its inverse can be operated by simple addition, subtraction and shift operations. Due to the simplicity of the transform, a sufficient condition on the resolution level of marked holograms is derived for guaranteeing the reversibility of watermarking. In addition, from the condition, it is also observed that the hiding capacity for reversible watermarking increases with the resolution level. The proposed algorithm therefore provides high flexibility for reversible watermarking allowing transparency and hiding capacity to be varied by selecting different resolution levels. Moreover, a novel scheme is presented for supporting self-containedness for 3D object reconstruction without requiring the delivery of additional files consisting of parameters for diffraction computation. Because of its low degradation in transparency, the algorithm is also able to operate in conjunction with the existing spatial domain based reversible algorithms to further enhance the hiding capacity while maintaining high visual transparency.