Research demonstrates that a Fresnel hologram can be generated and simultaneously encrypted numerically based on a secret symmetric key formed by the maximal length sequence (M-sequence). The method can be directly extended to encrypt a video holographic clip in a frame-by-frame manner. However, given the limited combination of signals in the family of M-sequence, hacking the secret key through trial and error can be time consuming but not difficult. In this letter, we propose a method that is difficult to crack with brute force for encrypting a holographic video sequence. An M-sequence is first randomly assigned to encrypt each frame of the holographic video signal. Subsequently, the index of the selected M-sequence, which is necessary to decrypt the hologram, is encrypted with the RSA algorithm before transmitting to the receiving end. At the receiving end, the decoder is provided with a private key to recover the index for each frame, and the corresponding M-sequence is used to decrypt the encoded hologram.

Past research has demonstrated that digital Fresnel holograms can be binarized in a non-iterative manner by downsampling the source image with a grid lattice prior to the hologram generation process. The reconstructed image of a hologram that is binarized with this approach is superior in quality compared with that obtained with direct thresholding, half-toning, and error diffusion. Despite the success, the downsampling mechanism results in a prominent texture of regularly spaced voids in the shaded regions. To alleviate this problem, an enhanced non-iterative method for the generation of binary Fresnel holograms is presented. Our method is based on a multi-direction line-sampling formed by a combined grid and cross lattice, which is capable of preserving a more solid texture in the shaded regions and enhancing the visual quality of the reconstructed image. Computer simulations and optical reconstructions are shown to demonstrate the effectiveness of our proposed technique.