Compact full-color holographic 3-D display based on undersampled computer-generated holograms and oblique projection imaging.

A compact full-color electro-holographic three-dimensional (3-D) display with undersampled computer-generated holograms (US-CGHs) and oblique projection imaging (OPI) is proposed. For its realization, undersampling conditions of the CGH enabling the complete recovery of image information are derived, and the OPI-based longitudinal-to-lateral depth conversion (LTL-DC) scheme allowing the simple reconstruction of full-color images is also proposed. Three-color off-axis US-CGHs are generated with their center-shifted principle fringe patterns (CS-PFPs) of the novel look-up table (NLUT) method, where center-shifts are calculated with the derived undersampling conditions of the CGH based on the generalized sampling theorem, and then multiplexed into the color-multiplexed hologram (CMH). The CMH is loaded on a SLM (spatial light modulator) and reconstructed by being illuminated with a multi-wavelength light source, where an original full-color image is reconstructed being spatially separated from the other color-dispersed images on the projected image plane with the OPI-based LTL-DC process, which enables us to view the original full-color image just with a simple filter mask. Performance analysis and successful experiments with the test 3-D objects in motion confirm the feasibility of the proposed system.

Faster generation of holographic videos of objects moving in space using a spherical hologram-based 3-D rotational motion compensation scheme.

A spherical hologram-based three-dimensional rotational-motion compensation (SH-3DRMC) method is proposed for the accelerated generation of holographic videos of a three-dimensional (3-D) object moving in space along the arbitrary trajectory with many locally-different curvatures. All those 3-D rotational motions of the object made on each arc can be compensated just by rotating their local spherical holograms along the spherical surfaces matched with the object's moving trajectory using the estimated rotation-axes and angles, which enables a massive reduction of computational complexity of the conventional hologram-generation algorithm and results in an accelerated calculation of holographic videos. Experiments with a test video show that the average calculation times of the conventional NLUT, WRP and 1-D NLUT methods employing the proposed SH-3DRMC scheme have been noticeably reduced by 34.75%, 41.37% and 31.64%, respectively, in comparison with those of their original methods. These good experimental results confirm the feasibility of the proposed system.

Single SLM full-color holographic three-dimensional video display based on image and frequency-shift multiplexing.

A single spatial-light-modulator (SLM) full-color holographic 3-D video display based on image and frequency-shift multiplexing (IFSM) is proposed. In the frequency-shift multiplexing (FSM), three-color holograms are multiplied with their respective phase factors for shifted-separations of their corresponding frequency-spectrums on the Fourier plane. This FSM process, however, causes three-color images to be reconstructed at the center-shifted locations depending on their multiplied phase factors. Center-shifts of those color images due to the FSM can be balanced out just by generation of three-color holograms whose centers are pre-shifted to the opposite directions to those of the image shifts with the novel-look-up-table (NLUT) based on its shift-invariance property, which is called image-shift multiplexing (ISM). These image and frequency-shifted holograms are then multiplexed into a single color-multiplexed hologram and loaded on the SLM, and from which a full-color 3-D image can be reconstructed on the optical 4-f lens system without any color dispersion just by employing a simple pinhole filter mask. Fourier-optical analysis and experiments with 3-D objects in motion confirm the feasibility of the proposed system.

Full-scale one-dimensional NLUT method for accelerated generation of holographic videos with the least memory capacity.

A full-scale one-dimensional novel-look-up-table (1-D NLUT) method enabling faster generation of holographic videos with the minimum memory capacity is proposed. Only a pair of half-sized 1-D baseline and depth-compensating principal-fringe-patterns (PFPs) is pre-calculated and stored based on the concentric-symmetry property of the PFP, and from which a set of half-sized 1-D PFPs for all depth planes are generated based on its thin-lens property, which enables minimization of the required memory size down to a few KB regardless of the number of depth planes. Moreover, all those hologram calculations are fully one-dimensionally performed with a set of half-sized 1-D PFPs based on its shift invariance property, which also allows minimization of its overall hologram calculation time. From experiments with test videos, the proposed method has been found to have the shortest hologram calculation time even with the least memory in comparison with several modified versions of the conventional NLUT and LUT methods, which confirms its feasibility.

Accelerated generation of holographic videos of 3-D objects in rotational motion using a curved hologram-based rotational-motion compensation method.

A new curved hologram-based rotational-motion compensation (CH-RMC) method is proposed for accelerated generation of holographic videos of 3-D objects moving on the random path with many locally different arcs. All of those rotational motions of the object made on each arc can be compensated, just by rotating their local curved holograms along the curving surfaces matched with the object's moving trajectory without any additional calculation process, which results in great enhancements of the computational speed of the conventional hologram-generation algorithms. Experiments with a test video scenario reveal that average numbers of calculated object points (ANCOPs) and average calculation times for one frame (ACTs) of the CH-RMC-based ray-tracing, wavefront-recording-plane and novel- look-up-table methods have been found to be reduced by 73.10%, 73.84%, 73.34%, and 68.75%, 50.82%, 66.59%, respectively, in comparison with those of their original methods. In addition, successful reconstructions of 3-D scenes from those holographic videos confirm the feasibility of the proposed system.