Research On Key Technologies In Generation And Reconstuction Of Digital Hologram

Preservation and reproduction of the real three-dimensional scene has always been a goal. Among the three-dimensional display technologies, taking into account the visual fatigue, three-dimensional effects and other issues, the holographic technology is recognized as the optimal and the most promising three-dimensional display technology. In recent years, digital holographic three-dimensional display technology has attracted much attention. The current development status and the exist problems of digital holographic three-dimensional display technology are investigated and analyzed firstly. The research work related to the generation and reconstruction on digital hologram are carried out, including the generation of the hologram based on depth map of a complex three-dimensional scene, the incoherent holographic methods, the acceleration of the computer generated holographic stereograms and reconstruction of the hologram based on compressed sensing. The relevant experimental system is designed for the experiment.The main contents and innovations are as follows:(1) The generation of the hologram based on a two-dimensional color images and a depth map is investigated. The Fresnel diffraction algorithm based on the Fourier transform is applied to tomography for the calculation of Fresnel hologram of a simple virtual three-dimensional scene. The optical experimental system for reconstructing the hologram based on a spatial light modulator is set up and the hologram is reconstructed successfully. Then, the computer generated Fresnel hologram of a complex 3D object based on a 2D color image and a stereo matched depth map is proposed. By using the depth map, the two-dimensional color image is divided into multiple slices and the depth value of each layer is converted into its Fresnel diffraction distance. According to the principle of tomography, the hologram of each slice is acquired and the whole hologram of the three-dimensional scene is achieved with the superposition of the all slices. By using the method, the hologram of the complex three-dimensional scenes is successfully recorded and reconstructed. The method of the intensity superposition significantly improves the quality of the reconstruction images.(2) A straightforward computer-generated incoherent Fresnel hologram based on multiple angular orthogonal projection images is demonstrated. As an important incoherent holography method, the multiple viewpoint projection holographic method is investigated. It can achieve white light illuminating hologram. Multiple viewpoint projection images are recorded by using an ordinary digital camera. The hologram of three-dimensional object is obtained by numerical calculation. The whole process does not require to record the interference of the coherent light. Thus, there is no conjugate image and laser speckle. A novel scheme for synthesizing the Fresnel holograms with computer generated multiple angular orthogonal projection images is presented. After the shifted angular orthogonal projection images are multiplied by the constant phase factors and integrated, a two-dimensional complex matrix including three-dimensional information is achieved. The proposed Fresnel hologram is synthesized directly from the projection images, which does not require to obtain the Fourier spectrum firstly. Since the diffraction and Fourier transform calculations are not necessary, the calculation complexity of the Fresnel hologram synthetic process can be greatly simplified.(3) Computer generated holographic stereogram based on the wavefront recording plane (WRP) is presented. Firstly, the characteristics of the traditional three-dimensional holographic stereogram and the computer generated holographic stereogram method are investigated. An accelerated calculation scheme for the generation of holographic stereograms from a sequence of parallax images is presented. A WRP closed to the parallax image plane is introduced to record the complex amplitude in a small region for each point in the parallax image. By using three times of fast Fourier transform (FFT) to execute the Fresnel diffraction calculation between the WRP and the holographic stereogram plane, the object wave contributed to the hologram pattern can be achieved. The computation complex of the proposed approach is dramatically reduced. The results show that the calculation time can be decreased by more than one order of magnitude.(4) Reconstruction the computer generated Fresnel hologram of complex three-dimensional (3D) object based on compressive sensing (CS) is presented. Theoretical model of compressed sensing (compressed sample), including the sparse representation of the signal, the measurement matrix and the reconstruction algorithm is analyzed. Digital holography satisfies the two preconditions of compressed sensing theoretical model of incoherent and sparsity. Thus, a novel method to reconstruct the CGH of complex 3D scene based on CS is presented. The hologram is synthesized from a color image and the depth map of the 3D object. With the depth map, the intensity of the color image can be divided into multiple slices, which satisfies the condition of the sparsity of CS. After the measurement matrix designed, by using the TwIST algorithm, the hologram can be reconstructed at different distances with the corresponding scene focused. The quality of the recovered images are greatly improved compared with that from the back-propagation method. What’s more, with the sub-sampled hologram, the images are ideally reconstructed by the CS method, which can reduce the data-rate for transmission or storage.