A Comparisonal Analysis of Computer Generated Holograms (CGHs) for the Application of Security in Communication System

In this work, various images were used in place of textual information as a source to develop a secure communication system with the assist of Fraunhofer, Gerchberg-Saxton & Fresnel holographic algorithm. The communicative hologram was developed by means of adding the far-field amplitude of the main object image and reference or noise image in the Fraunhofer algorithm. The output image overlapping constraints occurred at the receiver side. This problem can be resolved by using an algorithm called the GS algorithm. GS algorithm provides an iterative approach to improve the probability of success of phase retrieval. Because of its iterative nature, this process is relatively slow. Finally, the Fresnel algorithm was used where the wave amplitude was obtained by the Fresnel diffraction formula and the hologram is calculated by the Fast Fourier Transform (FFT). Among these fast algorithms, the contrast level of the 256×256 reconstructed image in the Fresnel algorithm was 0.875, where Fraunhofer and GS algorithm returned only 0.6643 and 0.7314 respectively, and the entropy was 7.9895, which was higher than the other two. Owing to having these promising results, the proposed Fresnel algorithm can be used for security in the field of communication.