Hisayuki Sasaki

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.

Image size scalable full-parallax coloured three-dimensional video by electronic holography.

In electronic holography, various methods have been considered for using multiple spatial light modulators (SLM) to increase the image size. In a previous work, we used a monochrome light source for a method that located an optical system containing lens arrays and other components in front of multiple SLMs. This paper proposes a colourization technique for that system based on time division multiplexing using laser light sources of three colours (red, green, and blue). The experimental device we constructed was able to perform video playback (20 fps) in colour of full parallax holographic three-dimensional (3D) images with an image size of 63 mm and a viewing-zone angle of 5.6 degrees without losing any part of the 3D image.

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.

Integral three-dimensional television with video system using pixel-offset method.

Integral three-dimensional (3D) television based on integral imaging requires huge amounts of information. Previously, we constructed an Integral 3D television using Super Hi-Vision (SHV) technology, with 7680 pixels horizontally and 4320 pixels vertically. We report on improved image quality through the development of video system with an equivalent of 8000 scan lines for use with Integral 3D television. We conducted experiments to evaluate the resolution of 3D images using an experimental setup and were able to show that by using the pixel-offset method we have eliminated aliasing produced by full-resolution SHV video equipment. We confirmed that the application of the pixel-offset method to integral 3D television is effective in increasing the resolution of reconstructed images.

Projection‐type integral 3‐D display with distortion compensation

— Our research is aimed at developing a spatial-imaging-type integral three-dimensional (3-D) display based on an integral photography method using an extremely high-resolution projector. One problem with the projection-type integral 3-D display is that geometrical distortion in projected elemental images causes spatial deformation of the displayed 3-D image. In this study, a general relationship between the geometric distortion of elemental images and the spatial deformation of reconstructed 3-D images were analyzed. A projection-type integral 3-D display with a distortion compensator which corrects the geometrical distortions of projected images in real-time have been developed. The deformation of the displayed 3-D images was significantly reduced by the distortion compensation, and the displayed 3-D images had a resolution of 182 (H) × 140 (V) pixels and a viewing angle of 24.5°.

Multiview image and depth map coding for holographic TV system

Abstract. A holographic TV system based on multiview image and depth map coding and the analysis of coding noise effects in reconstructed images is proposed. A major problem for holographic TV systems is the huge amount of data that must be transmitted. It has been shown that this problem can be solved by capturing a three-dimensional scene with multiview cameras, deriving depth maps from multiview images or directly capturing them, encoding and transmitting the multiview images and depth maps, and generating holograms at the receiver side. This method shows the same subjective image quality as hologram data transmission with about 1/97000 of the data rate. Speckle noise, which masks coding noise when the coded bit rate is not extremely low, is shown to be the main determinant of reconstructed holographic image quality.

Study of a holographic TV system based on multi-view images and depth maps

Electronic holography technology is expected to be used for realizing an ideal 3DTV system in the future, providing perfect 3D images. Since the amount of fringe data is huge, however, it is difficult to broadcast or transmit it directly. To resolve this problem, we investigated a method of generating holograms from depth images. Since computer generated holography (CGH) generates huge fringe patterns from a small amount of data for the coordinates and colors of 3D objects, it solves half of this problem, mainly for computer generated objects (artificial objects). For the other half of the problem (how to obtain 3D models for a natural scene), we propose a method of generating holograms from multi-view images and associated depth maps. Multi-view images are taken by multiple cameras. The depth maps are estimated from the multi-view images by introducing an adaptive matching error selection algorithm in the stereo-matching process. The multi-view images and depth maps are compressed by a 2D image coding method that converts them into Global View and Depth (GVD) format. The fringe patterns are generated from the decoded data and displayed on 8K4K liquid crystal on silicon (LCOS) display panels. The reconstructed holographic image quality is compared using uncompressed and compressed images.

Three-dimensional integral television using extremely high-resolution video system with 4,000 scanning lines

The integral method enables observers to see 3D images like real objects. It requires extremely high resolution for both capture and display stages. We present an experimental 3D television system based on the integral method using an extremely high-resolution video system. The video system has 4,000 scanning lines using the diagonal offset method for two green channels. The number of elemental lenses in the lens array is 140 (vertical) × 182 (horizontal). The viewing zone angle is wider than 20 degrees in practice. This television system can capture 3D objects and provides full color and full parallax 3D images in real time.

Integral imaging system with 33 mega-pixel imaging devices using the pixel-offset method

Integral 3D television based on integral imaging requires huge amounts of information. Earlier, we built an Integral 3D television using Super Hi-Vision (SHV) technology, with 7680 pixels horizontally and 4320 pixels vertically. Here we report on an improvement of image quality by developing a new video system with an equivalent of 8000 scan lines and using this for Integral 3D television. We conducted experiments to evaluate the resolution of 3D images using this prototype equipment and were able to show that by using the pixel-offset method we have eliminated aliasing that was produced by the full-resolution SHV video equipment. As a result, we confirmed that the new prototype is able to generate 3D images with a depth range approximately twice that of Integral 3D television using the full-resolution SHV.

Wavefront printing technique with overlapping approach toward high definition holographic image reconstruction

A hologram recording technique, generally called as “wavefront printer”, has been proposed by several research groups for static three-dimensional (3D) image printing. Because the pixel number of current spatial light modulators (SLMs) is not enough to reconstruct the entire wavefront in recording process, typically, hologram data is divided into a set of subhologram data and each wavefront is recorded sequentially as a small sub-hologram cell in tiling manner by using X-Y motorized stage. However since previous works of wavefront printer do not optimize the cell size, the reconstructed images were degraded by obtrusive split line due to visible cell size caused by too large cell size for human eyesight, or by diffraction effect due to discontinuity of phase distribution caused by too small cell size. In this paper, we introduce overlapping recording approach of sub-holograms to achieve both conditions: enough smallness of apparent cell size to make cells invisible and enough largeness of recording cell size to suppress diffraction effect by keeping the phase continuity of reconstructed wavefront. By considering observing condition and optimization of the amount of overlapping and cell size, in the experiment, the proposed approach showed higher quality 3D image reconstruction while the conventional approach suffered visible split lines and cells.