Koki Wakunami

Calculation for computer generated hologram using ray-sampling plane.

We introduce a new algorithm for calculating computer generated hologram (CGH) using ray-sampling (RS) plane. RS plane is set at near the object and the light-rays emitted by the object are sampled at the plane. Then the light-rays are transformed into the wavefront with using the Fourier transforms. The wavefront on the CGH plane is calculated by wavefront propagation simulation from RS plane to CGH plane. The proposed method enables to reproduce high resolution image for deep 3D scene with angular reflection properties such as gloss appearance.

Large size three-dimensional video by electronic holography using multiple spatial light modulators

In this paper, we propose a new method of using multiple spatial light modulators (SLMs) to increase the size of three-dimensional (3D) images that are displayed using electronic holography. The scalability of images produced by the previous method had an upper limit that was derived from the path length of the image-readout part. We were able to produce larger colour electronic holographic images with a newly devised space-saving image-readout optical system for multiple reflection-type SLMs. This optical system is designed so that the path length of the image-readout part is half that of the previous method. It consists of polarization beam splitters (PBSs), half-wave plates (HWPs), and polarizers. We used 16 (4 × 4) 4K×2K-pixel SLMs for displaying holograms. The experimental device we constructed was able to perform 20 fps video reproduction in colour of full-parallax holographic 3D images with a diagonal image size of 85 mm and a horizontal viewing-zone angle of 5.6 degrees.

Occlusion culling for computer generated hologram based on ray-wavefront conversion

We propose a new method for occlusion culling in the computation of a hologram based on the mutual conversion between light-rays and wavefront. Since the occlusion culling is performed with light-ray information, conventional rendering techniques such as ray-tracing or image-based rendering can be employed. On the other hand, the wavefront is derived for the calculation of light propagation, the hologram of 3-D objects can be obtained in high accuracy. In the numerical experiment, we demonstrate that our approach can reproduce a high-resolution image for deep 3-D scene with correct occlusion effect between plural objects.

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.

A real-time 3D system using electronic holography

Electronic holography—generating holograms using electrooptical apparatus—could enable the ultimate interactive 3D display system.1 The technique shows promise for 3D television, virtual workspaces for telework, and teleconferences, all of which require the construction of a moving 3D image without the need for 3D glasses. However, to realize a real-time electronic holography system requires processing a large amount of captured 3D data to generate the holograms. To resolve this issue we used integral photography (IP)—a 3D imaging technique— instead of the conventional depth camera (a system that captures a color image using a digital camera and a depth ‘map’ with IR light) and a graphics processing unit to capture 3D objects for parallel processing.2 In addition, we adapted the IP’s optical setup to use a fast Fourier transform algorithm for real-time hologram calculation. Figure 1 shows a schematic overview of our system for realtime image capturing and reconstruction. The setup consists of three component blocks: capture, calculation, and display, which are shown in Figures 2–4.2 The first block captures a 3D image with IP, using a system that comprises a lens array, a field lens, a spatial filter, and a 4K (386

View synthesis from sparse camera array for pop-out rendering on hologram displays

A hologram of a scene can be digitally created by using a large set of images of that scene. Since capturing such a large amount is infeasible to accomplish, one may use view synthesis approaches to reduce the number of cameras and generate the missing views. We propose a view interpolation algorithm that creates views inside the scene, based on a sparse set of camera images. This allows the objects to pop out of the holographic display. We show that our approach outperforms existing view synthesis approaches and show the applicability on holographic stereograms.

Occlusion processing for computer generated hologram by conversion between the wavefront and light-ray information

In the field of computational holography for three-dimensional (3D) display, the mutual occlusion of objects is one of the crucial issues. We propose a new mutual occlusion processing that is achieved by the conversion between the light-ray and wavefront on a virtual plane called ray-sampling (RS) plane located at near the interrupting object. The wavefront coming from background scene is converted into light-ray information at the RS plane by using Fourier transform based on the angular spectrum theory, then the converted light-rays are overwritten with those from interrupting object in the light-ray domain as an occlusion culling process. The ray information after the occlusion process is reconverted into wavefront by inverse Fourier transform at each RS point, then wave propagation from RS plane to hologram is computed by general light diffraction computation techniques. Since the light-ray information is used for the occlusion processing, our approach can realize a correct occlusion effect by a simple algorithm. In addition, high resolution 3D image can be reconstructed with wavefront-based technique. In the numerical simulation, we demonstrate that our approach for deep 3D scene with plural objects can realize a correct occlusion culling for varying observation angle and focusing distance.

Computer generated hologram of deep 3D scene from the data captured by integral imaging

Various techniques to visualize a 3-D object/scene have been proposed until now; stereoscopic display, parallax barrier, lenticular approach, integral imaging display, and holographic display. Application for a real existing 3-D scene is one of important issues. In this paper, at first the fundamental limitation of integral imaging display for deep 3-D scene is discussed. Then a two main types of holographic display; digital holography approach that digitally capturing an interference pattern and a computer generated hologram (CGH) approach from a set of perspective images are overviewed with describing the radical advantages and disadvantages.

Realistic 3D deep scene display by computational holography

Holography is a superior medium for high-quality 3D displays since it reproduces the depth cues of human vision. Its critical feature is a capability to reproduce 3D deep scenes, which is difficult by other methods. For electronic holographic display, it is necessary to develop methods for holographic fringe calculation that reproduce high-quality 3D images, as well as technologies for high-resolution display devices and highperformance computing. Computational holography simulates wave propagation, and it currently limits reproduced image quality, relative to common computer graphics. There are two common approaches for hologram computation. The wavefront-based method synthesizes spherical waves from point-sources on the object surface.1 It simulates physical phenomena of wavefront propagation and produces a high-resolution image, even of 3D deep scenes. However, it is challenging to overcome occlusion and surface reflection, which is vital for realistic 3D displays. Light-ray recording and reproduction is another approach.2 Advanced graphics techniques, such as ray-tracing and image-based rendering, are employed to generate a hologram fringe. However, spatial resolution decreases in the reconstructed image located far from the display plane due to light-ray sampling and the diffraction limit. We propose a hologram computation method that takes advantage of both approaches. Consider a rectangular window in 3D space, as shown in Figure 1. An ideal 3D display is generated by reproducing all light-rays that pass through the window, i.e. the light field. In our proposed method,3 the light field is sampled within the window, designated the ray-sampling (RS) plane, which is defined near the object to avoid a decrease in resolution. The sampled light field is converted to a wavefront by taking the Fourier transform of the light-ray intensity angular distribution. Wavefront propagation from the RS plane to the final hologram is Figure 1. Hologram calculation schematic using a ray-sampling (RS) plane. Light-ray angular distribution (top) is collected at each sampled point. A fast Fourier transform (FFT) is applied to ray information after random phase modulation, yielding the wavefront of a small area on the RS plane (bottom). A Fresnel transform is subsequently applied to derive the wavefront on the hologram plane.

Digital Color Management in Holoprinter

We applied digital color management by holoprinter, which produces full-color full-parallax hologram. The color reproducibility was tested by printing color chart hologram, and the CIELAB ΔE is fairly small.