Efficient tiled calculation of over-10-gigapixel holograms using ray-wavefront conversion

Hologram generation using light-field modulated zone plates

A hologram calculation technique is proposed in this study using a depth image and light-field information comprising multiple parallax images. The depth image is used to determine the phase distribution of the zone plates, and the amplitude distribution is modulated using the light-field information. An object wave of three-dimensional (3D) objects is obtained by adding the light-field modulated zone plates. The proposed technique can generate sharp and shaded 3D images in space. The occlusion effects of 3D images can also be supported by modifying the amplitude modulation scheme. The proposed technique was experimentally verified.

Correction of the wavelength error in transmission of a full-color holographic 3D image

When a digital holographic image represented by a sampled wavefield is transmitted and the wavelength used in the three-dimensional (3D) display devices does not agree exactly with the wavelength of the original image data, the reconstructed 3D image will differ slightly from the original. This slight change is particularly problematic for full-color 3D images reconstructed using three wavelengths. A method is proposed here to correct the holographic image data and reduce the problems caused by wavelength mismatch. The effectiveness of the method is confirmed via theoretical analysis and numerical experiments that evaluate the reconstructed images using several image indices.

Realistic rendering method for specular reflections with continuous motion parallax in a computer-generated hologram

A computer-generated hologram (CGH) enables the display of virtual images and videos as well as the communication and storage of holographic data. The point-based method, which is a CGH-calculation method for representing the surface of an object as a set of point-light sources, has not been sufficiently studied in terms of realistic representation. This paper proposes a CGH-calculation method for realistic rendering using ray tracing to be used with a point-based method. Experiments were conducted with an optical system to confirm the effectiveness of the proposed method in terms of hidden-surface removal in mirror images and its implementation on multiple mirror surfaces. The results indicate that the proposed method enabled hidden-surface removal with continuous parallax and reflection on mirror surfaces.

Image quality assessment procedure for holographic displays based on exact numerical reconstruction of computer-generated holograms

We proposed a technique for the computer-based reconstruction of computer-generated holograms and evaluation of the reconstructed 3D image quality. The proposed method mimics how the eye's lens works, thus allowing for viewing position and eye focus adjustments. The angular resolution of the eye was used to output reconstructed images with the requisite resolution, and a reference object was used to normalize the images. Such data processing enables the numerical analysis of image quality. By comparing the reconstructed images with the original image with incoherent illumination, the image quality was quantitatively evaluated.

Non-hogel-based computer generated hologram with occlusion processing between the foreground light field and background hologram

A novel technique is proposed to process the occlusion of a background hologram when synthesizing a front scene hologram from its light field. Unlike conventional techniques which process the occlusion in the light field domain after converting the background hologram to its light field, the proposed technique directly processes the occlusion between different domains, i.e., the background hologram and foreground light field. The key idea is to consider the background hologram as a carrier wave illuminating the front scene when synthesizing the front scene hologram from its light field. The proposed technique is not only computationally efficient as it does not require conversion between the light field and hologram domains but also accurate because all angular information of the background hologram and foreground light field is naturally considered in the occlusion processing. The proposed technique was verified by numerical synthesis and reconstruction.

Holographic 3D Display Using Depth Maps Generated by 2D-to-3D Rendering Approach

Holographic display has the potential to be utilized in many 3D application scenarios because it provides all the depth cues that human eyes can perceive. However, the shortage of 3D content has limited the application of holographic 3D displays. To enrich 3D content for holographic display, a 2D to 3D rendering approach is presented. In this method, 2D images are firstly classified into three categories, including distant view images, perspective view images and close-up images. For each category, the computer-generated depth map (CGDM) is calculated using a corresponding gradient model. The resulting CGDMs are applied in a layer-based holographic algorithm to obtain computer-generated holograms (CGHs). The correctly reconstructed region of the image changes with the reconstruction distance, providing a natural 3D display effect. The realistic 3D effect makes the proposed approach can be applied in many applications, such as education, navigation, and health sciences in the future.

Fourier horizontal parallax only computer and digital holography of large size

Registration and reconstruction of high-quality digital holograms with a large view angle are intensive computer tasks since they require the space-bandwidth product (SBP) of the order of tens of gigapixels or more. This massive use of SBP severely affects the storing and manipulation of digital holograms. In order to reduce the computer burden, this work focuses on the generation and reconstruction of very large horizontal parallax only digital holograms (HPO-DHs). It is shown that these types of holograms can preserve high quality and large view angle in x direction while keeping a low use of SBP. This work first proposes a numerical technique that allows calculating very large HPO-DHs with large pixel size by merging the Fourier holography and phase added stereogram algorithm. The generated Fourier HPO-DHs enable accurate storing of holographic data from 3D objects. To decode the information contained in these Fourier HPO-DHs (FHPO-DHs), a novel angular spectrum (AS) technique that provides an efficient use of the SBP for reconstruction is proposed. Our reconstruction technique, which is called compact space bandwidth AS (CSW-AS), makes use of cylindrical parabolic waves that solve sampling issues of FHPO-DHs and AS. Moreover, the CSW-AS allows for implementing zero-padding for accurate wavefield reconstructions. Hence, suppression of aliased components and high spatial resolution is possible. Notably, the imaging chain of Fourier HPO-DH enables efficient calculation, reconstruction and storing of HPO holograms of large size. Finally, the accuracy and utility of the developed technique is proved by both numerical and optical reconstructions.

Simplified digital content generation based on an inverse-directed propagation algorithm for holographic stereogram printing

Holographic stereogram (HS) printing requires extensive memory capacity and long computation time during perspective acquisition and implementation of the pixel re-arrangement algorithm. Hogels contain very weak depth information of the object. We propose a HS printing system that uses simplified digital content generation based on the inverse-directed propagation (IDP) algorithm for hogel generation. Specifically, the IDP algorithm generates an array of hogels using a simple process that acquires the full three-dimensional (3D) information of the object, including parallax, depth, color, and shading, via a computer-generated integral imaging technique. This technique requires a short computation time and is capable of accounting for occlusion and accommodation effects of the object points via the IDP algorithm. Parallel computing is utilized to produce a high-resolution hologram based on the properties of independent hogels. To demonstrate the proposed approach, optical experiments are conducted in which the natural 3D visualizations of real and virtual objects are printed on holographic material. Experimental results demonstrate the simplified computation involved in content generation using the proposed IDP-based HS printing system and the improved image quality of the holograms.

Photorealistic computer generated holography with global illumination and path tracing

Computer generated holography (CGH) algorithms come in many forms, with different trade-offs in terms of visual quality and calculation speed. However, no CGH algorithm to date can accurately account for all 3D visual cues simultaneously, such as occlusion, shadows, continuous parallax, and precise focal cues, without view discretization. The aim is to create photorealistic CGH content, not only for display purposes but also to create reference data for comparing and testing CGH and compression algorithms. We propose a novel algorithm combining the precision of point-based CGH with the accurate shading and flexibility of ray-tracing algorithms. We demonstrate this by creating a scene with global illumination, soft shadows, and precise occlusion cues, implemented with OptiX and CUDA.

Roadmap on 3D integral imaging: sensing, processing, and display

This Roadmap article on three-dimensional integral imaging provides an overview of some of the research activities in the field of integral imaging. The article discusses various aspects of the field including sensing of 3D scenes, processing of captured information, and 3D display and visualization of information. The paper consists of a series of 15 sections from the experts presenting various aspects of the field on sensing, processing, displays, augmented reality, microscopy, object recognition, and other applications. Each section represents the vision of its author to describe the progress, potential, vision, and challenging issues in this field.

Image quality improvement of holographic 3-D images based on a wavefront recording plane method with a limiting diffraction region

This study aims to improve the image quality of holographic three-dimensional (3-D) images based on the wavefront recording plane (WRP) method. In this method, we place a WRP close to the 3-D objects to reduce the propagation distance of light from the objects to the WRP. The conventional WRP method has been implemented only under conditions that did not cause aliasing noise. This study proposes a WRP method with a limiting diffraction region from the WRP to the hologram such that we can perform the WRP method under any condition. As a result, we succeeded in improving the image quality of the 3-D images based on the WRP method.

Efficient calculation scheme for high pixel resolution non-hogel-based computer generated hologram from light field

We propose a method that reduces the computation time and memory requirement in non-hogel-based hologram synthesis from light field data. The non-hogel-based technique synthesizes coherent complex field for a three-dimensional scene from its light field. Unlike conventional holographic stereogram, the non-hogel-based technique reconstructs continuous parabolic wavefront for individual three-dimensional object point by globally processing the light field. However, the global processing increases the computational load significantly, making it hard to synthesize holograms with high pixel resolution. The proposed technique reduces the computational burden by processing each two-dimensional angular frequency slice of the four-dimensional light field independently. Hologram tiling technique is also proposed to make the hologram synthesis process scalable. Using the hologram tiling and the angular-frequency-slice-based processing, 25K×25 K pixel resolution hologram was synthesized successfully.

Reconstruction of a three-dimensional color-video of a point-cloud object using the projection-type holographic display with a holographic optical element

Here, we managed to reconstruct a three-dimensional color video of a point-cloud object using a projection-type holographic display with a holographic optical element as an optical screen. The holographic optical element has the function of an off-axis concave mirror and has been created by the wavefront printer digitally. We defined and implemented an algorithm to reconstruct a three-dimensional image at a chosen position considering the specification of the holographic optical element designed digitally. We successfully demonstrated a reconstruction of the color video in question, composed of three-dimensional images through the holographic optical element.

Efficient algorithms for the accurate propagation of extreme-resolution holograms

Display-sized full-parallax holograms with large viewing angles require resolutions surpassing tens of Gigapixels. Unfortunately, computer-generated holography is computationally intensive, particularly for these huge display resolutions. Existing algorithms designed for diffraction of typical Megapixel-sized holograms do not scale well for these large resolutions. Furthermore, since the holograms will not fit in the RAM of most of today's computers, the algorithms should be modified to minimize disk access. We propose two novel algorithms respectively for short-distance and long-distance propagation, and accurately compute the diffraction of a 17.2 Gigapixel hologram on a standard desktop machine. We report a 500-fold speedup over the reference rectangular tiling algorithm for the short-distance version, and a 50-fold speedup for the long-distance version.

Real-time three-dimensional video reconstruction of real scenes with deep depth using electro-holographic display system

Herein, we demonstrate a real-time, three-dimensional (3D) video-reconstruction system using electro-holography in real-world scenes with deep depth. We calculated computer-generated holograms using 3D information obtained through an RGB-D camera. We successfully reconstructed a 3D video (in real time) of a person moving in real-world space and confirmed that the proposed system operates at ~14 frames per second. In addition, we successfully reconstructed a full-color 3D video of the person. Furthermore, we varied the number of persons moving in the real-world space and evaluated the proposed system's performance by varying the distance between the RGB-D camera and the person(s).

Coherent subhologram-based computer generated display hologram

A modification of the subhologram-based approach to the calculation of a computer generated display hologram of a 3-D scene is presented. The hologram area is split into subholograms. For each of them, a perspective image with depth coordinate is rendered and converted to a point cloud. These points are processed in a novel way and the optical field in the subhologram is calculated. The processing guarantees that the points used for the optical field calculation are the same for all subholograms (i.e., coherent). The coherence provides sharp hologram reconstruction. The parameters of the processing are designed to match the human vision requirements.

Fast generation of full analytical polygon-based computer-generated holograms

A fast calculation method to obtain the full-analytical frequency spectrum of a spatial triangle based on the three-dimensional (3D) affine transformation is presented. Computer-generated holograms (CGHs) of an object can then be generated rapidly using the angular spectrum for propagation. The derivation process in the theory, which has more preciseness, indicates a difference from previous methods based on affine transformations ([Appl. Opt.47, 1567 (2008)Appl. Opt.52, A290 (2013)]). The proposed method to achieve 3D transformation from an arbitrary triangle to a primitive triangle includes two steps: 3D rotation and 2D affine transformation. The overall transform matrix is given by the product of a rotation matrix and a 2D affine matrix. A modified back-face culling is also introduced based on exterior normal for correct occlusion relation. Several complex 3D objects are implemented successfully using the proposed method in numerical simulations and optical experiments. The resulting computation time demonstrates that the efficiency of the proposed method is enhanced as compared to that of previous works.