Abstract
A digital hologram (DH) is so highly valued that it needs to be protected from exposure to an unpermitted person, which could be done by a content encryption. We propose an encryption scheme for digital holograms, whose goal is to hide their information with maximal visual distortion and minimal ration of the encrypted data. It uses the characteristics of the Fresnel transform and signal processing techniques. As the diffraction distance increases the region containing the object information relative to the whole diffraction plane becomes smaller. Therefore our scheme diffracts a given digital hologram twice: the first transform for reconstructing the image contained by the hologram and the second transform for concentrating the energy of the object into a small region. Then only the energy-concentrated region is encrypted to reduce the amount of data to be encrypted. Experimental results show that when the diffraction distance of the second transform is about 20 m, the encryption ratio is only 0.0058% of the hologram data, which is enough to hide the object information unrecognizably.
Highlights
A hologram is a collection of fringe patterns generated by interference between a reference light wave and an object light wave, in which the 3-dimensional object information is stored as differential phase or amplitude from that of the reference wave [1]
N is the resolution of the input hologram plane and the output planes of the Fresnel transform. δx1, λ1, and z1 are the parameters of the first Fresnel transform; and δx2, λ2, and z2 are the parameters of the second Fresnel transform
In this paper we proposed an encryption scheme for a digital hologram (DH) to hide the information contained in the DH by encrypting as small an amount of data as possible with the maximal encryption efficiency
Summary
A hologram is a collection of fringe patterns generated by interference between a reference light wave and an object light wave, in which the 3-dimensional object information is stored as differential phase or amplitude from that of the reference wave [1]. Seo et al [12] proposed a scheme to encrypt in the hologram domain and DCT (discrete cosine transform) and DWT (discrete wavelet transform) transform domain by calculating energy. Seo et al [13] used a DWT domain named the DWPT (discrete wavelet packet transform) domain It is a version of DWT for a subband that includes calculating the energy included. It showed that hiding only 30% of energy was enough to hide all of the information, which was 0.032% of the total hologram data. Our method encrypts a part of DH data to hide all of the information that the DH contains It can work with any kind of DH, no matter how it is acquired, optically or numerically. We conclude and discuss our scheme in the Section 5
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