# Encryption of 3D or Higher-Dimensional Images: A Review
## 4 Literature Review
A weighted linear combination is employed to merge the encrypted features. Statistical and security analyses are carried outbased on the experimental results to evaluate the effectiveness of the method. The proposed encryption system required additional calculation of the EPI of the angular domain, which was generated from multiple views of the LF image. To analyze the complexity of the proposed scheme, the encryption speed was analyzed, which resulted in a value of 2.479 s for the encryption and decryption execution time. [PERSON] et al. [38] proposed a real-time 3D integral imaging (InIm) encryption method by employing a novel remapping algorithm and a random mode decomposition (RMD) encryption based on cellular automata (CA) in time and the Fourier domain. Furthermore, the method reduces computational complexity and achieves relevant real-time encryption performance. The results show the feasibility and robustness of the scheme. Through Internet transmissions and the losses that occurred in the EIA representation of the LF, which are easily corrupted, the authors performed a quantitative assessment of robustness against noise by evaluating the values of the peak signal-to-noise ratio (PSNR) and structural similarity index measure (SSIM) when Gaussian noise and salt and pepper noise were inserted into the cipher EIA with both portions of 1% and 0.1%. [PERSON] et al. [39] presented a light-field 3D image encryption based on computational integral imaging and dynamic cellular automata (CA). The scheme employed was based on the hexagonal lens array generation method, in which the generation of a high-quality hexagonal element image array (EIA) occurs by pixel mapping. The proposed method consisted of dividing the EIA into blocks, encrypting the light-field 3D image using dynamic CA rules according to the characteristics of each sub-image. The researchers did not determine specific values for the key size. They reported that it was large enough to make brute force attacks impractical. Due to the capture process used to analyze the quality of the deciphered image, noise was applied to carry out tests. [PERSON] et al. [40] proposed a light field image encryption based on pixel substitution and double random phase encoding (DRPE). The method employs an angular domain plane to represent the multi-view image and then the pixel substitution for a single view of the image, in which there is loss of information and, in sequence, uses the Fourier transform to achieve the encrypted image. [PERSON] et al. [41] proposed a parallel encryption scheme based on the maximum state transition diagram length cellular automata (MLCA) for three-dimensional imaging. This method reduced the time consumption of encryption when compared with the DNA sequence and chaotic system scheme by [PERSON] et al. [38], and in comparison with the random mode decomposition (RMD) scheme by [PERSON] et al. [42]: there was a five times reduction in the encryption time. Furthermore, taking advantage of MLCA's abundant rules, high parallelism, and straightforward hardware implementation, the scheme features flexible key selection, parallel processing capabilities, and easy hardware implementation. The results show that the method is robust against entropy and differential attacks, and has a key space equal to 2\({}^{100}\). This proposed method is applicable to large-scale images such as satellite remote sensing images and high-resolution film and television images. [PERSON] et al. [43] were pioneers in applying stereographic projections to 3D object encryption. They proposed 2D bijective representations of 3D point clouds, in which the topological equivalence between the Riemann sphere and the extended complex plane was used, whose representation is based on the stereographic projection (SGP) transformation, its geometric and topological properties. The points of the 3D point clouds were mapped on the Riemann sphere.