Hologram Calculation Research Articles

Achieving fast computer-generated hologram calculations via parallelization

Achieving fast computer-generated hologram calculations via parallelization

ADVANCED CONCEPT FOR CREATION OF SECURITY HOLOGRAMS / PROGRESĪVĀ KONCEPCIJA AIZSARDZĪBAS HOLOGRAMMAS IZVEIDEI

Abstract A new concept is proposed for digital hologram production along with the relevant techniques developed in our laboratory. The main idea of the concept is to maximally separate the calculation of hologram from its optical recording on the light-sensitive media. A special file format containing information on each holographic pixel is created at the stage of calculation. The file is a device-independent by structure, and can be employed for recording a hologram using any of the existing techniques (dot-matrix, optical matrix lithography, e-beam lithography). An optical lithography device is applied to calculate the images for a spatial light modulator at the stage of hologram recording in accordance with the data from the file and in conformity with the hardware features of the device. The proposed method was tested and successfully used to record security holograms. For commercial use a software package and an optical recording system have been developed.

Fast distributed large-pixel-count hologram computation using a GPU cluster

Large-pixel-count holograms are one essential part for big size holographic three-dimensional (3D) display, but the generation of such holograms is computationally demanding. In order to address this issue, we have built a graphics processing unit (GPU) cluster with 32.5 Tflop/s computing power and implemented distributed hologram computation on it with speed improvement techniques, such as shared memory on GPU, GPU level adaptive load balancing, and node level load distribution. Using these speed improvement techniques on the GPU cluster, we have achieved 71.4 times computation speed increase for 186M-pixel holograms. Furthermore, we have used the approaches of diffraction limits and subdivision of holograms to overcome the GPU memory limit in computing large-pixel-count holograms. 745M-pixel and 1.80G-pixel holograms were computed in 343 and 3326 s, respectively, for more than 2 million object points with RGB colors. Color 3D objects with 1.02M points were successfully reconstructed from 186M-pixel hologram computed in 8.82 s with all the above three speed improvement techniques. It is shown that distributed hologram computation using a GPU cluster is a promising approach to increase the computation speed of large-pixel-count holograms for large size holographic display.

Reducing the memory usage for effectivecomputer-generated hologram calculation using compressed look-up table in full-color holographic display

A fast algorithm with low memory usage is proposed to generate the hologram for full-color 3D display based on a compressed look-up table (C-LUT). The C-LUT is described and built to reduce the memory usage and speed up the calculation of the computer-generated hologram (CGH). Numerical simulations and optical experiments are performed to confirm this method, and several other algorithms are compared. The results show that the memory usage of the C-LUT is kept low when number of depth layers of the 3D object is increased, and the time for building the C-LUT is independent of the number of depth layers of the 3D object. The algorithm based on C-LUT is an efficient method for saving memory usage and calculation time, and it is expected that it could be used for realizing real-time and full-color 3D holographic display in the future.

Calculation method of CGH for Binocular Eyepiece-Type Electro Holography

We had researched about eyepiece-type electro holography to display 3-D images of larger objects at wider angle. We had enlarged visual field considering depth of object with Fourier optical system using two lenses. In this paper, we extend our system for binocular. In the binocular system, we use two different holograms for each eye. The 3-D image for left eye should be observed like the real object observed using left eye and the same for right eye. So, we propose a method of calculation of computer-generated hologram (CGH) transforming the coordinate system of the model data to make two holograms for binocular eyepiece-type electro holography. The coordinate system of original model data is called the world coordinate system. The left and the right coordinate system are transformed from the world coordinate system. We also propose the method for correcting the installation error that occurs when placing the electronic and optical devices. The installation error is calculated and the model data is corrected using the distance between measured position and setup position of the reconstructed image Optical reconstruction experiments were carried out to verify the proposed method.

Computational hologram synthesis and representation on spatial light modulators for real-time 3D holographic imaging

In dynamic computer-generated holography that utilizes spatial light modulators, both hologram synthesis and hologram representation are essential in terms of fast computation and high reconstruction quality. For hologram synthesis, i.e. the computation step, Fresnel transform based or point-source based raytracing methods can be applied. In the encoding step, the complex wave-field has to be optimally represented by the SLM with its given modulation capability. For proper hologram reconstruction that implies a simultaneous and independent amplitude and phase modulation of the input wave-field by the SLM.In this paper, we discuss full complex hologram representation methods on SLMs by considering inherent SLM parameter such as modulation type and bit depth on their reconstruction performance such as diffraction efficiency and SNR. We review the three implementation schemes of Burckhardt amplitude-only representation, phase-only macro-pixel representation, and two-phase interference representation. Besides the optical performance we address their hardware complexity and required computational load. Finally, we experimentally demonstrate holographic reconstructions of different representation schemes as obtained by functional prototypes utilizing SeeReal's viewing-window holographic display technology. The proposed hardware implementations enable a fast encoding of complex-valued hologram data and thus will pave the way for commercial real-time holographic 3D imaging in the near future.

High-resolution three-dimensional holographic display using dense ray sampling from integral imaging

We present a high-resolution three-dimensional (3D) holographic display using a set of elemental images obtained by passive sensing integral imaging (II). Hologram calculations using a high-density ray-sampling plane are achieved from the elemental images captured by II. In II display, ray sampling by lenslet array and light diffraction limits the achievable resolution. Our approach can improve the resolution since target objects are captured in focus and then light-ray information is interpolated and resampled with higher density on ray-sampling plane located near the object to be converted into the wavefront. Numerical experimental results show that the 3D scene, composed of plural objects at different depths from the display, can be reconstructed with order of magnitude higher resolution by the proposed technique.

Fast calculation of computer-generated hologram using the circular symmetry of zone plates

Computer-Generated Holograms (CGHs) can be generated from three-dimensional objects composed of point light sources by overlapping zone plates. A zone plate is a grating that can focus an incident wave and it has circular symmetry shape. In this study, we propose a fast CGH generating algorithm using the circular symmetry of zone plates and computer graphics techniques. We evaluated the proposed method by numerical simulation.

Fast high-resolution computer-generated hologram computation using multiple graphics processing unit cluster system

To overcome the computational complexity of a computer-generated hologram (CGH), we implement an optimized CGH computation in our multi-graphics processing unit cluster system. Our system can calculate a CGH of 6,400×3,072 pixels from a three-dimensional (3D) object composed of 2,048 points in 55 ms. Furthermore, in the case of a 3D object composed of 4096 points, our system is 553 times faster than a conventional central processing unit (using eight threads).

Fast calculation of computer-generated holograms based on 3-D Fourier spectrum for omnidirectional diffraction from a 3-D voxel-based object

We have derived the basic spectral relation between a 3-D object and its 2-D diffracted wavefront by interpreting the diffraction calculation in the 3-D Fourier domain. Information on the 3-D object, which is inherent in the diffracted wavefront, becomes clear by using this relation. After the derivation, a method for obtaining the Fourier spectrum that is required to synthesize a hologram with a realistic sampling number for visible light is described. Finally, to verify the validity and the practicality of the above-mentioned spectral relation, fast calculation of a series of wavefronts radially diffracted from a 3-D voxel-based object is demonstrated.

Simple wave-field rendering for photorealistic reconstruction in polygon-based high-definition computer holography

A simple and practical technique is presented for creating fine three-dimensional (3D) images with polygon-based computer-generated holograms. The polygon-based method is a technique for computing the optical wave-field of virtual 3D scenes given by a numerical model. The presented method takes less computation time than common point-source methods and produces fine spatial 3D images of deep 3D scenes that convey a strong sensation of depth, unlike conventional 3D systems providing only binocular disparity. However, smooth surfaces cannot be reconstructed using the presented method because the surfaces are approximated by planar polygons. This problem is resolved by introducing a simple rendering technique that is almost the same as that in common computer graphics, since the polygon-based method has similarity to rendering techniques in computer graphics. Two actual computer holograms are presented to verify and demonstrate the proposed technique. One is a hologram of a live face whose shape is measured using a 3D laser scanner that outputs polygon-mesh data. The other is for a scene including the moon. Both are created employing the proposed rendering techniques of the texture mapping of real photographs and smooth shading.

Holography and micro-holography of particle fields: A numerical standard

Holography is an ‘old’ technique for studying the behavior of clouds of droplets which finds a new interest with CCD cameras and real-time numerical reconstruction. Furthermore, the continued progress in camera characteristics (sensitivity, pixel number, digitalization level, and so on) opens the way to more accurate recording of the interference field. To gain a deep understanding of the technique, as well as an evaluation of the performance and limitations of digital holographic particle measurements under various conditions, standard holograms are required. In this paper, a general numerical standard of holograms of fields of particles based on rigorous near-field Lorenz–Mie scattering theory is presented. This theory makes possible the computation of holograms of fields of particles with an arbitrary number of particles of arbitrary size, arbitrary refractive index, arbitrary recording distance (near-field or far-field), and an arbitrary collecting angle (forward, off-axis, or backward scattering light). Several calculation examples are also given for the code validation and possible applications, including a new possible way to simultaneously measure the size, location, and refractive index of particles.

Shading of a computer-generated hologram by zone plate modulation

We propose a hologram calculation technique that enables reconstructing a shaded three-dimensional (3D) image. The amplitude distributions of zone plates, which generate the object points that constitute a 3D object, were two-dimensionally modulated. Two-dimensional (2D) amplitude modulation was determined on the basis of the Phong reflection model developed for computer graphics, which considers the specular, diffuse, and ambient reflection light components. The 2D amplitude modulation added variable and constant modulations: the former controlled the specular light component and the latter controlled the diffuse and ambient components. The proposed calculation technique was experimentally verified. The reconstructed image showed specular reflection that varied depending on the viewing position.

Hidden-Surface Removal Based on Babinet's Principle and Partial Wave Field Propagation in High-Resolution Computer-Generated Holograms

A novel method for hidden-surface removal is proposed for accelerating computation of full-parallax computer-generated holograms (CGHs). When creating high-definition CGHs, the silhouette method is probably the only realistic technique to produce occluded 3D scenes. However, the conventional silhouette method is inefficient and more time-consuming for calculating sparse 3D scenes that include many small objects. Although derived from the silhouette method, the proposed method considerably reduces the computation time for sparse scenes by using Babinet's principle and partial wave field propagation. A definite algorithm as well as formulation is presented in this paper. Furthermore, high-definition CGHs created by the proposed method are demonstrated for verifying the validity of the method.

Creation of Extremely High-Definition Computer Holograms Over Several Giga-Pixels Using Polygon-Based Method

Creation of Extremely High-Definition Computer Holograms Over Several Giga-Pixels Using Polygon-Based Method

Consideration of time to create real-time video of a kinoform using a web camera

Using a two-dimensional fast Fourier transform is an efficient way to calculate a kinoform. High-speed processing of large amounts of data points (e.g., a 512×512 matrix) can be accomplished using a kinoform. Real-time computer-generated hologram calculation has been widely pursued. To this end, use of the graphics processing unit (GPU) or multiprocessing methods are becoming popular for high-speed processing. We used the GPU method coupled with multiprocessing to construct a kinoform and measured the efficiency of this method.

Zone plate method for electronic holographic display using resolution redistribution technique

The resolution redistribution (RR) technique can increase the horizontal viewing-zone angle and screen size of electronic holographic display. The present study developed a zone plate method that would reduce hologram calculation time for the RR technique. This method enables calculation of an image displayed on a spatial light modulator by performing additions of the zone plates, while the previous calculation method required performing the Fourier transform twice. The derivation and modeling of the zone plate are shown. In addition, the look-up table approach was introduced for further reduction in computation time. Experimental verification using a holographic display module based on the RR technique is presented.

New method for the design of a phase-only computer hologram for multiplane reconstruction

A new iterative method for creating a pure phase hologram to diffract light into two arbitrary two-dimensional intensity profiles in two output planes is presented. This new method combines the Gerchberg-Saxton (GS) iterative algorithm and the compensation iterative algorithm. Numerical simulation indicates that the new method outperforms the most frequently used method in accuracy when it is used to generate large size images. A preliminary experiment of optical reconstruction has been taken and used to verify the feasibility of our method.

Cell-based hardware architecture for full-parallel generation algorithm of digital holograms

This paper proposes a new hardware architecture to speed-up the digital hologram calculation by parallel computation. To realize it, we modify the computer-generated hologram (CGH) equation and propose a cell-based very large scale integrated circuit architecture. We induce a new equation to calculate the horizontal or vertical hologram pixel values in parallel, after finding the calculation regularity in the horizontal or vertical direction from the basic CGH equation. We also propose the architecture of the computer-generated hologram cell consisting of an initial parameter calculator and update-phase calculators based on the equation, and then implement them in hardware. Modifying the equation could simplify the hardware, and approximating the cosine function could optimize the hardware. In addition, we show the hardware architecture to parallelize the calculation in the horizontal direction by extending computer-generated holograms. In the experiments, we analyze hardware resource usage and the performance-capability characteristics of the look-up table used in the computer-generated hologram cell. These analyses make it possible to select the amount of hardware to the precision of the results. Here, we used the platform from our previous work for the computer-generated hologram kernel and the structure of the processor.

Improved phase hologram design for generating symmetric light spots and its application for laser writing of waveguides

The improved method for calculation of a phase hologram and its application to laser writing of waveguides with a spatial light modulator are presented. It was found that the amplitude and phase distributions of light spots generated by a phase hologram can be distorted compared to those of a focused single beam. The distortion of light spots could be reduced by adding a simple constraint, in which light intensities around a light spot should be as small as possible, to the conventional calculation method of a phase hologram. It was also demonstrated that the improved calculation method can be considered essential for laser writing of waveguides.