Makoto Okui

Projection-type see-through holographic three-dimensional display

Owing to the limited spatio-temporal resolution of display devices, dynamic holographic three-dimensional displays suffer from a critical trade-off between the display size and the visual angle. Here we show a projection-type holographic three-dimensional display, in which a digitally designed holographic optical element and a digital holographic projection technique are combined to increase both factors at the same time. In the experiment, the enlarged holographic image, which is twice as large as the original display device, projected on the screen of the digitally designed holographic optical element was concentrated at the target observation area so as to increase the visual angle, which is six times as large as that for a general holographic display. Because the display size and the visual angle can be designed independently, the proposed system will accelerate the adoption of holographic three-dimensional displays in industrial applications, such as digital signage, in-car head-up displays, smart-glasses and head-mounted displays.

Electronic generation of holograms by using depth maps of real scenes

Holography is one of the most promising candidates to realize a fully realistic 3D video communication system. We propose a hologram generation method by using depth maps of real scenes. In this study, we employed a static laser scanner and captured a depth map of real objects at 0.4mm resolution. Then, a Fresnel hologram was calculated off-line on a computer. We used two types of SLMs. One is 12micron transparent LCD, and the other is 10.4micron pixel reflective LCD panel. By irradiating He-Ne laser to the hologram, we observed 3D real object images are reconstructed in the space with approx. 5cm of depth range.

Cross talk elimination using an aperture for recording elemental images of integral photography

A major problem with integral photography using a lens array is overlapping recordings (cross talk) between elemental images. Another problem is the decrease in the number of pixels in the elemental images. We describe two methods (including analyses) of manipulating the aperture of a telecentric optical system to improve these problems. The first method locates the aperture on the focal plane of a field lens. The advantage of this method is that cross talk can be reduced without changing the size of the whole optical system. The second method establishes a telecentric optical system between objects and the lens array. The advantage of this method, even though the whole optical system becomes bigger, is that cross talk can be completely eliminated. In addition, the number of pixels in the elemental images can be increased by varying the aperture position sequentially with respect to time. We also describe how cross talk is reduced in both methods by taking diffraction into consideration. Experimental results are presented to verify this reduction.

Real-time IP-hologram conversion hardware based on floating point DSPs

Holography is a 3-D display method that fully satisfies the visual characteristics of the human eye. However, the hologram must be developed in a darkroom under laser illumination. We attempted hologram generation under white light by adopting an integral photography (IP) technique as the input. In this research, we developed a hardware converter to convert IP input (with 120×66 elemental images) to a hologram with high definition television (HDTV) resolution (approximately 2 million pixels). This conversion could be carried out in real time. In this conversion method, each elemental image can be independently extracted and processed. Our hardware contains twenty 300-MHz floating-point digital signal processors (DSPs) operating in parallel. We verified real-time conversion operations by the implemented hardware.

Computer Generated Electronic Holography of Natural Scene from 2D Multi-view Images and Depth Map

Electronic Holography, satisfying all 3D visual cues, is the most promising approach to ideal 3D image presentation. However, several problems have to be solved to realize high quality 3D images, such as handling huge amounts of data or insufficient display device capability. In order to solve these problems, this paper proposes an approach to high quality holographic image generation from 2D multi-view images and depth map. The approach includes phantom imaging elimination and occlusion-hole paving processes, as well as compensation of astigmatism and color aberration caused by the optical elements.

Half-zone-plate processing for objects on both sides of hologram display

Single-sideband holography with half-zone-plate processing is a well-known method of displaying computer generated holograms (CGHs) using electronic devices such as liquid crystal displays (LCDs) that do not have narrow pixel intervals. Half-zone plate only permits primary images to pass through a single-sideband spatial filter and cuts off conjugate and carrier images; however, there is a problematic restriction on this method in that objects being shot must be either in front of or behind the hologram. This paper describes a new approach to simultaneously placing them on both sides of the hologram, which means we can eliminate this restriction. The underlying idea is when half-zone plate permits the primary images in front of the hologram to pass through a single-sideband spatial filter, the conjugate images cannot pass through it. When we prepare a half-zone plate on the opposite side, the primary images on both sides of the hologram can pass through but the conjugate images cannot. This approach not only doubles the area of objects but also reduces computational time because objects can be placed close to the hologram. We implemented this approach, tested it, and confirmed its effectiveness.

Three-dimensional reflection screens fabricated by holographic wavefront printer

Abstract. Several wavefront printers have been recently proposed. Since the printers can record an arbitrary computer-generated wavefront, they are expected to be useful for fabricating complex mirror arrays used in front projection 3-D screens without using real existing optics. We prototyped two transparent reflective screens using our hologram printer in experiments. These screens could compensate for a spherically distorted reference wave caused by a short projection distance to obtain an ideal reference wave. Owing to the use of the wavefront-printed screen, the 3-D display was simply composed of a normal 2-D projector and a screen without using extra optics. In our binocular system, reflected light rays converged to the left and right eyes of the observer and the crosstalk was less than 8%. In the light field system, the reflected light rays formed a spatially sampled light field and focused a virtual object in a depth range of ±30  mm with a ±13.5-deg viewing angle. By developing wavefront printing technology, a complex optics array may easily be printed by nonprofessionals for optics manufacturing.

An analysis of printing conditions for wavefront overlapping printing

Wavefront printing for a digitally-designed hologram has got attentions recently. In this printing, a spatial light modulator (SLM) is used for displaying a hologram data and the wavefront is reproduced by irradiating the hologram with a reference light the same way as electronic holography. However, a pixel count of current SLM devices is not enough to display an entire hologram data. To generate a practical digitally-designed hologram, the entire hologram data is divided into a set of sub-hologram data and wavefront reproduced by each sub-hologram is sequentially recorded in tiling manner by using X-Y motorized stage. Due to a lack of positioning an accuracy of X-Y motorized stage and the temporal incoherent recording, phase continuity of recorded/reproduced wavefront is lost between neighboring subholograms. In this paper, we generate the holograms that have different size of sub-holograms with an overlap or nonoverlap, and verify the size of sub-holograms effect on the reconstructed images. In the result, the reconstructed images degrade with decreasing the size of sub-holograms and there is little or no degradation of quality by the wavefront printing with the overlap.

A real-time color holography system for live scene

We are studying electronic holography and have developed a real-time color holographic movie system which includes three functional blocks, capture block, processing block, and display block. We will introduce the system and its technology in this paper. The first block, capture block, uses integral photography (IP) technology to capture color 3-D objects in real time. This block mainly consists of a lens array with approximately 120(W)x67(H) convex lenses and a video camera with 1920(W)x1080(H) pixels to capture IP images. In addition to that, the optical system to reduce the crosstalk between elemental images is mounted. The second block, processing block, consists of two general personal computers to generate holograms from IP images in real time. Three half-zone-plated holograms for red, green and blue (RGB) channels are generated for each frame by using Fast Fourier Transform. The last block, display block, mainly consists of three liquid crystal displays for displaying the holograms and three laser sources for RGB to reconstruct the color 3-D objects. This block is a single-sideband holography display, which cuts off conjugate and carrier images from primary images. All blocks work in real time, i.e., in 30 frames per second.

Hologram printing for next-generation holographic display

In this paper, we introduce hologram printing technology. This technology includes the following technologies, computer-generated hologram, hologram printer, duplication, and application-depended technologies. When this technology is applied to static hologram, the media can present static 3D objects more clearly than traditional 3D technologies such as lenticular lens and integral photography(IP) because it is based on holography. When this technology is applied to holographic optical elements(HOE), the HOE will be useful for many purposes especially for large optical elements. For example, when it is used as screen, the visual system which consists of the screen and projector can present dynamic 2D or 3D objects. Since this technology digitally designs hologram/HOE and manufactures them by wavefront printer, it is good at generating small lot of production. As a result, it is effective for the research stage of both 2D and 3D display. In addition, it is also effective for commercial stage due to simple duplication method.