Invited paper-“Three dimensional imaging and display”
A computer-generated holographic(CGH) algorithm based on layer structure using angular spectrum propagation theory was proposed in order to improve the calculation speed and the reconstruction quality. The 3D scene was stratified, and the sub holograms of each layer were obtained by angular spectrum diffraction method. The hologram of the whole 3D scene was generated by the superposition of these sub holograms. Because there was no paraxial approximation in angular spectrum diffraction method, the algorithm could be applied to different kinds of 3D models. Besides, the computational complexity of the algorithm depended on the number of layers rather than the complexity of 3D scenes, so the computation speed could be increased by 2-3 orders of magnitude. The algorithm provides an effective solution for dynamic 3D display.
2018, 47(6): 603002.
doi: 10.3788/IRLA201847.0603002
In the integrated imaging naked eye 3D display based on LED, the divergence angle of the pixel point of LED large screen was very large. Flat convex and double convex lens are often employed. The reconstructed light of the image diverges and the pixel crosstalk between adjacent lens units was large, resulting in unclear images during the reproduction of the three-dimensional scene with the reduced imaging quality. The imaging process of integrated imaging based on LED was analyzed according to the principle of ray tracing. The relationship of crosstalk between different shapes of the lens array and adjacent lens units of LED integrated imaging was investigated. A single meniscus lens was used to effectively control the divergence of the reconstructed light. The reconstructed light passing through the lens was more convergent and collimated. The emergent rays through the lens becomes more parallel and the crosstalk between adjacent lens units was reduced effectively. By comparing the simulation result of the letter model, the meniscus lens was more suitable for LED integrated imaging. The imaging effect of the meniscus lens is better than that of the other lens.
2018, 47(6): 603003.
doi: 10.3788/IRLA201847.0603003
In order to solve the problem of vulnerable to attacks caused by symmetry in traditional cryptographic systems, a new single-channel color image encryption using detour cylindrical diffraction and color space conversion algorithm was proposed in this paper. In the process of encryption, firstly, the color image was transformed into a single channel image in YCbCr4:2:0 format, then the image was encrypted by twice cylindrical diffraction and phase truncation operations. In the process of decryption, the keys were combined with the cipher text, and the color original image was reconstructed after twice inverse cylindrical diffraction. Because the cylindrical diffraction process was an asymmetric process, the proposed algorithm can overcome the symmetry characteristic of the encryption system based on plane diffraction. Applying it to the encryption system based on phase truncation can further improve the security of the encryption system. The simulation results show that the algorithm can effectively encrypt the color image with single channel, which not only can restore the original color image with high quality, but also has high security.
2018, 47(6): 603004.
doi: 10.3788/IRLA201847.0603004
A large-scale multi-projection light-field 3D display system based on multi-view sampling calibration was proposed. In this system 360 projectors were arranged in a circle under an anisotropic cylindrical diffuser with 3 m diagmeter and 1.8 m height and projecting images onto the diffuser. Light field of 3D scenes was accurately reconstructed inside the screen and can be observed by multiple viewers from different angles and positions simultaneously around 360, as well as providing smooth motion parallax. Rendering frame rate of dynamic scenes can achieve 30 frame/s and above, offering fluent visual experience. To realize this system, a wide-field projection lens with cylindrical lenses was designed to enlarge image of the projectors. Then an automatic light-field calibration method based on multi-view sampling was proposed to eliminate distortion, which was induced by non-linear distortion of the projection lens and system assembly error, from the projection images. After calibration, light field projected by 360 projectors can be fuszed together seamlessly.
2018, 47(6): 603005.
doi: 10.3788/IRLA201847.0603005
To resolve mutual restriction of viewing angle and optical efficiency, an integral imaging (Ⅱ) 3D displayer based on a variable-aperture pinhole array was proposed. The imaging model of the Ⅱ 3D displayer based on the variable-aperture pinhole array was established. The calculation formulas of the viewing angle and optical efficiency were obtained by using geometrical optics. How to adjust the viewing angle and optical efficiency by changing the aperture width of the pinhole was illustrated in detail. A prototype of the Ⅱ displayer based on the variable-aperture pinhole array was developed. The variable-aperture pinhole array was electrically controlled by using a liquid crystal display screen. The experimental results prove that the viewing angle and optical efficiency of the 3D image were respectively enhanced by increasing and decreasing the aperture width of pinhole.
2018, 47(6): 603006.
doi: 10.3788/IRLA201847.0603006
Holographic three-dimensional(3D) display can reconstruct the light field of a real scene, providing all depth cues and becoming one of the best solutions for true 3D display. Computer-generated holographic 3D display only needs to know the mathematical description of the object light wave, can flexibly control the wavefront, and display a virtual 3D object. However, the huge amount of data and the amount of calculations hinder the practical application of computer-generated holographic 3D display. This paper presented data compression coding techniques for multiple stages in computer-generated holographic 3D display, including sparse sampling of 3D objects, optimization and parameter optimization of holographic 3D video compression coding, holographic fractal compression algorithm, effectively reducing the amount of data. And the parallel computing capabilities of GPUs were utilized to enable fast calculation of holograms.
