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We propose a flicker-reduced time-division light ray quadruplexing technology to improve both the spatial and angular resolutions of three-dimensional (3D) images. The proposed method uses an image-shift optical device with polarization gratings. By optimizing the design of the image-shift optical device and incorporating it into the display system, we confirmed that the resolution characteristics of 3D images displayed at a depth of 30 mm or more can be improved by up to 1.58 times. Furthermore, by developing the display system using a 120 Hz 8K projector with wobbling device and a wavelength-selective λ/2 plate for reducing flicker, we achieved high-resolution 3D image display with deeper depth.

In this study, we investigate three-dimensional (3D) video technology based on spatial imaging to implement a next-generation broadcasting service. This technology allows viewers to watch 3D videos without the need for specialized glasses. However, the main challenge associated with the application of this technology is the large amount of ray information that needs to be acquired and reproduced to improve the quality of the 3D videos. Therefore, we are in the process of actively developing methods to acquire high-density ray information from multiviewpoint images, captured using a multicamera system; in addition, we are devising 3D display methods using multiple display devices. In this paper, we present the most recent results of our research regarding 3D television technologies, including a prototype system based on our novel display method called “Aktina Vision.” This system can reproduce 3D videos of real objects at a resolution of approximately 330,000 pixels, three times that of conventional full-parallax spatial imaging methods using a lens array.

Conversion between three-dimensional (3D) and high-definition two-dimensional (2D) images is required to reproduce various video content. Conventional 3D/2D conversion methods based on integral 3D displays mainly aim to convert between 3D and 2D images on the entire display screen. Here, we propose a display method for partial conversion between 3D and 2D images using a geometric phase lens (GPL) array for the backlight control of a liquid crystal (LC) panel. In our method, the backlight is switched between a point light source (PLS) array and diffused light using a GPL array, diffusion plate, and polarization switching element. Integral 3D and high-definition 2D images are simultaneously reproduced on the same screen by displaying elemental images and 2D images on the LC panel according to the state of the backlight. Through numerical simulation experiments, we analyzed the resolution characteristics of 3D images and obtained the design policy of the PLS size and pixel size of the LC panel. Based on the analysis results, we prototyped a display system using a monochromatic LC panel with 8K resolution and evaluated the quality of backlight switching and resolution characteristics of 3D images. Further, we confirmed that 3D images with approximately 16,000 pixels and 2D images with 8K resolution are partially convertible.

The integral three-dimensional (3D) display is an ideal visual 3D user interface. It is a display method that fulfills many of the physiological factors of human vision. However, in integral 3D displays for mobile applications that use direct-view flat panels to display elemental images, color moire is a problem that occurs because of the sampling of subpixels by elemental lenses and the insufficient resolution and depth reproduction of the reconstructed 3D image. In the conventional moire reduction method, the degree of defocus of elemental lenses has to be set to a large value, which is one of the factors that reduces the performance in terms of depth reproduction. In contrast, only one-step optics can be installed and the installation positions are limited in the conventional wobbling method. This is because, in the method, which uses a birefringent optical element, two-step optics are thicker than the focal length of the lens array. For this reason, it was difficult to achieve ideal moire reduction and depth reproduction performance improvements. To solve these problems, we propose a method that utilizes multiple optical wobbling spatiotemporal multiplexing using polarization diffractive elements and liquid-crystal polarization controllers. Using the proposed method, the wobbling optics can be designed to be thin, allowing two-step optics to be installed between the display panel and lens array. When the moire modulation degree without wobbling is normalized as 100%, it decreases to 25% with wobbling. The proposed method not only achieves effective color moire reduction without deteriorating the 3D image quality, but also can double the resolution of the elemental images to improve the depth reproduction.

Light field displays technologies are popular glasses-free three-dimensional (3D) display methods, whereby natural 3D images can be viewed by precisely reproducing light rays from the objects. However, sufficient display performances cannot be obtained with conventional display techniques because reproduction of a great number of high-density light rays is required for high quality 3D images. Therefore, we develop a novel light field display method named Aktina Vision, which consists of a special 3D screen with isotropic narrow diffusion characteristics and a display optical system for projecting high-density light rays. In this method, multi-view images with horizontal and vertical parallaxes are projected onto the 3D screen at various angles in a superposed manner. The 3D screen has narrow diffusion angle and top-hat diffusion characteristics for optimal widening of the light rays according to the discrete intervals between the rays. 3D images with high resolution and depth-reproducibility can be displayed by suppressing crosstalk between light rays and reproducing them with continuous luminance distribution. We prototype a display system using 14 exclusively designed 4K projectors and develop a light field calibration technique. The reproduction of 3D images with a resolution of approximately 330,000 pixels, which is three times higher than that of conventional display methods using a lens array, and viewing angles of 35.1° in the horizontal direction and 4.7° in the vertical direction is realized by projecting 350 multiview images in a superposed manner.

The integral three-dimensional (3D) display is an ideal visual 3D user interface. It is a display method that fulfills many of the physiological factors of human vision. However, in integral 3D displays for mobile applications that use a direct viewing flat panel to display elemental images, the occurrence of color moire is a problem owing to the sampling of subpixels by the elemental lenses and the insufficient resolution and depth reproduction performance of the reconstructed 3D image. We propose a method to solve these problems that utilizes optical wobbling spatiotemporal multiplexing using a birefringent element and a polarization controller. With the conventional moire reduction method, the degree of defocus of el-ementallenses has to be set to a large value, which has also been a factor that reduces the depth reproduction performance. We show that effective color moire reduction can be achieved with a slight defocus of elemental lenses and without deteriorating depth reproducibility by using the proposed optical wobbling method.

We propose an integral 3D display system that enhances the viewing zone and depth range of reconstructed 3D images using eye-tracking technology and a lens array with a long focal length. To reduce crosstalk due to flipped images caused by the movement of the viewer, a lens arrangement that forms a horizontally widened optical viewing zone by rotating the lens array is designed. Unlike the conventional design, the viewing angle expanded 2.9 times to 81.4° horizontally and 1.7 times to 47.6° vertically, and the depth range doubled. Results of the evaluation experiment confirmed that crosstalk was sufficiently suppressed.

This paper presents an integral three-dimensional (3D) display that efficiently enhances both the pixel densities and viewing angles of 3D images with parallel projection of elemental images. In the proposed method, ultra-high-definition (UHD) elemental images are projected and superimposed as parallel light rays from densely arranged compact UHD projectors onto a lens array. Three-dimensional images with enhanced pixel densities and viewing angles can be displayed by optimizing the projector positions and system design. The prototype yielded a horizontal pixel density of 63.5 ppi, approximately 97,000 pixels, and a viewing angle of approximately 30°, making it superior to previous integral 3D display systems.