This paper proposes a new way of forming an aerial three-dimensional (3D) image that gives viewers smooth motion parallax. The proposed aerial 3D display is composed of an arc 3D display and aerial imaging by retro-reflection (AIRR), which features a wide viewing angle, a large-size scalability, and a low cost with mass-productive process. The arc 3D display consists of arc-shaped scratches on a transparent plastic plate. The principle of the arc 3D display is based on directional scattering. When a light impinges an arc-shaped scratch, the light is scattered mainly to the radial direction. The position of the bright spot on an arc scratch depends on the pupil position. The distance between the bright spots for both eyes on an arc scratches is proportional to the radius of curvature and is equivalent to the binocular parallax. Thus, by changing the radius of curvature, we can show a 3D image by use of a single LED illumination. This paper proposes an optical system to form an aerial 3D image with AIRR. AIRR consists of a light source, a beam splitter, and a retro-reflector. Arc scratches are illuminated by a quasi-parallel light that is generated by a Fresnel lens and a lightemitting diode (LED). In order to extract the directional scattered lights, we place the retro-reflector parallel to the beam splitter. The transmitted light does not impinge the beam splitter. Only the scattered lights reflect on the beam splitter and form the aerial image of the arc 3D display.
Security is one of the big issues in automated teller machine (ATM). In ATM, two types of security have to be maintained. One is to secure displayed information. The other is to secure screen contamination. This paper gives a solution for these two security issues. In order to secure information against peeping at the screen, we utilize visual cryptography for displayed information and limit the viewing zone. Furthermore, an aerial information screen with aerial imaging by retro-reflection, named AIRR enables users to avoid direct touch on the information screen. The purpose of this paper is to propose an aerial secure display technique that ensures security of displayed information as well as security against contamination problem on screen touch. We have developed a polarization-processing display that is composed of a backlight, a polarizer, a background LCD panel, a gap, a half-wave retarder, and a foreground LCD panel. Polarization angle is rotated with the LCD panels. We have constructed a polarization encryption code set. Size of displayed images are designed to limit the viewing position. Furthermore, this polarization-processing display has been introduced into our aerial imaging optics, which employs a reflective polarizer and a retro-reflector covered with a quarter-wave retarder. Polarization-modulated light forms the real image over the reflective polarizer. We have successfully formed aerial information screen that shows the secret image with a limited viewing position. This is the first realization of aerial secure display by use of polarization-processing display with retarder-film and retro-reflector.
We will report our recent developments in DFD (Depth-fused 3D) display and arc 3D display, both of which have smooth movement parallax. Firstly, fatigueless DFD display, composed of only two layered displays with a gap, has continuous perceived depth by changing luminance ratio between two images. Two new methods, called “Edge-based DFD display” and “Deep DFD display”, have been proposed in order to solve two severe problems of viewing angle and perceived depth limitations. Edge-based DFD display, layered by original 2D image and its edge part with a gap, can expand the DFD viewing angle limitation both in 2D and 3D perception. Deep DFD display can enlarge the DFD image depth by modulating spatial frequencies of front and rear images. Secondly, Arc 3D display can provide floating 3D images behind or in front of the display by illuminating many arc-shaped directional scattering sources, for example, arcshaped scratches on a flat board. Curved Arc 3D display, composed of many directional scattering sources on a curved surface, can provide a peculiar 3D image, for example, a floating image in the cylindrical bottle. The new active device has been proposed for switching arc 3D images by using the tips of dual-frequency liquid-crystal prisms as directional scattering sources. Directional scattering can be switched on/off by changing liquid-crystal refractive index, resulting in switching of arc 3D image.
In this paper, we propose a new method that makes multi-layer images from a few viewpoint images to display a 3D image by the autostereoscopic display that has multiple display screens in the depth direction. We iterate simple “Shift and Subtraction” processes to make each layer image alternately. The image made in accordance with depth map like a volume slicing by gradations is used as the initial solution of iteration process. Through the experiments using the prototype stacked two LCDs, we confirmed that it was enough to make multi-layer images from three viewpoint images to display a 3D image. Limiting the number of viewpoint images, the viewing area that allows stereoscopic view becomes narrow. To broaden the viewing area, we track the head motion of the viewer and update screen images in real time so that the viewer can maintain correct stereoscopic view within +/- 20 degrees area. In addition, we render pseudo multiple viewpoint images using depth map, then we can generate motion parallax at the same time.
This paper proposes a stereoscopic model for DFD display that explains the continuous depth modulation and protruding
depth perception. The model is composed of four steps: preparation of DFD images, geometrical calculation of viewed
images, human visual function for detecting intensity changes, and stereoscopic depth perception. In this paper, two
types of displayed images for DFD display are prepared: the former pairs are for conventional DFD, where a fused image
is located between the layered images; the latter pairs are for protruding DFD, where a fused image is located closer than
the foreground image or further than the background image. Viewed images at both eye positions are simulated
geometrically in computer vision optics model. In order to detect intensity changes, we have utilized Laplacian operation
on a Gaussian blurred image. Stereoscopic depths are calculated by matching the zero crossing position on the Laplacian
operated images. It is revealed that our stereoscopic model explains both conventional and protruding DFDs.
We propose a new optical configuration to form aerial 3D LEDs by use of retroreflective sheeting. The proposed configuration is composed of LEDs, a half mirror, and retroreflective sheeting. A half of the LED lights are reflected by the half mirror and impinge on the retroreflective sheeting. The retroreflective sheeting reflects the lights back to their sources. On the way to the sources, a half of the lights transmit through the half mirror and form the real images of LEDs. Although less than 25 % of the output lights are contributed to the aerial image, recent LED panels have enough luminance to enjoy the aerial image with a quarter of the luminance. We have made a prototype of the proposed aerial LED display. An aerial image of the LED panel has been successfully formed in free space. Its viewing angle was significantly improved compared to the aerial display by use of crossed mirrors, which limit the viewing angle by aperture size and height of mirror walls. The viewing angle in the proposed configuration is mainly limited by the size of the retroreflective sheeting. Furthermore, by using LEDs in different depths, we realized an aerial 3D display in free space.
We can successfully solve the problem in DFD display that the maximum depth difference of front and rear planes is limited because depth fusing from front and rear images to one 3-D image becomes impossible. The range of continuously perceived depth was estimated as depth difference of front and rear planes increases. When the distance was large enough, perceived depth was near front plane at 0~40 % of rear luminance and near rear plane at 60~100 % of rear luminance. This maximum depth range can be successfully enlarged by spatial-frequency modulation of front and rear images. The change of perceived depth dependence was evaluated when high frequency component of front and rear images is cut off using Fourier Transformation at the distance between front and rear plane of 5 and 10 cm (4.9 and 9.4 minute of arc). When high frequency component does not cut off enough at the distance of 5 cm, perceived depth was separated to near front plane and near rear plane. However, when the images are blurred enough by cutting high frequency component, the perceived depth has a linear dependency on luminance ratio. When the images are not blurred at the distance of 10 cm, perceived depth is separated to near front plane at 0~30% of rear luminance, near rear plane at 80~100 % and near midpoint at 40~70 %. However, when the images are blurred enough, perceived depth successfully has a linear dependency on luminance ratio.
3D representation of digital signage improves its significance and rapid notification of important points. Real 3D display techniques such as volumetric 3D displays are effective for use of 3D for public signs because it provides not only binocular disparity but also motion parallax and other cues, which will give 3D impression even people with abnormal binocular vision. Our goal is to realize aerial 3D LED signs. We have specially designed and fabricated a reflective optical device to form an aerial image of LEDs with a wide field angle. The developed reflective optical device composed of crossed-mirror array (CMA). CMA contains dihedral corner reflectors at each aperture. After double reflection, light rays emitted from an LED will converge into the corresponding image point. The depth between LED lamps is represented in the same depth in the floating 3D image. Floating image of LEDs was formed in wide range of incident angle with a peak reflectance at 35 deg. The image size of focused beam (point spread function) agreed to the apparent aperture size.
3D representation of digital signage improves its significance and rapid notification of important points. Our goal is to
realize floating 3D LED signs. The problem is there is no sufficient device to form floating 3D images from LEDs. LED
lamp size is around 1 cm including wiring and substrates. Such large pitch increases display size and sometimes spoils
image quality. The purpose of this paper is to develop optical device to meet the three requirements and to demonstrate
floating 3D arrays of LEDs. We analytically investigate image formation by a crossed mirror structure with aerial
aperture, called CMA (crossed-mirror array). CMA contains dihedral corner reflectors at each aperture. After double
reflection, light rays emitted from an LED will converge into the corresponding image point. We have fabricated CMA
for 3D array of LEDs. One CMA unit contains 20 x 20 apertures that are located diagonally. Floating image of LEDs
was formed in wide range of incident angle. The image size of focused beam agreed to the apparent aperture size. When
LEDs were located three-dimensionally (LEDs in three depths), the focused distances were the same as the distance
between the real LED and the CMA.
We have developed a new volumetric 3-D display using the multi-varifocal lens and high-speed 2-D display. Floating
clear 3-D image in space can be successfully obtained. Our volumetric 3-D image is composed of many 2-D layered
images by using multi-varifocal lens. Many 2-D images can be layered by changing their depth position using the
discrete focal length change of multi-varifocal lens. The high-speed multi-varifocal lens is composed of several sets of a
birefringent lens and a polarization switching device. The total lens power is the sum of the lens powers of these sets.
The number of lens sets, N, can yield 2<sup>N</sup> variations of total focal lengths. In order to re-position many 2-D images within
afterimage time, high-speed 2-D display is newly constructed by compact projector array using LED light sources. These
projector images are projected to the same position of one screen. By switching these projectors quickly, 2-D images on
the screen can be displayed at high-speed. This high-speed 2-D display can successfully provide bright and clear 2-D
layered images by using point light sources of LED.
In this paper, we report development of a high-frame-rate LED display. Full-color images are refreshed at 480 frames per
second. In order to transmit such a high frame-rate signal via conventional 120-Hz DVI, we have introduced a
spatiotemporal mapping of image signal. A processor of LED image signal and FPGAs in LED modules have been
reprogrammed so that four adjacent pixels in the input image are converted into successive four fields. The pitch of LED
panel is 20 mm. The developed 480-fps LED display is utilized for stereoscopic 3D display by use of parallax barrier.
The horizontal resolution of a viewed image decreases to one-half by the parallax barrier. This degradation is critical for
LED because the pitch of LED displays is as large as tens of times of other flat panel displays. We have conducted
experiments to improve quality of the viewed image through the parallax barrier. The improvement is based on
interpolation by afterimages. It is shown that the HFR LED provides detailed afterimages. Furthermore, the HFR LED
has been utilized for unconscious imaging, which provide a sensation of discovery of conscious visual information from
Live three-dimensional movies are acquired with stereoscopic cameras. Since there is a limitation of disparity for
binocular fusion, it is necessary to restrict objects of shooting within an allowable range. This problem is more severe for
stereoscopic LED display because of its large pitch. One of the answers to this problem is to control the depth of field.
Objects outside the allowable range are blurred and objects inside the allowable range are in focus. In this study, we
propose a method to control the depth of field of stereoscopic images continuously by lens-tilt imaging. There are two
types of configurations in the lens-tilt stereoscopic imaging. One is a convergent configuration and the other is a
divergent configuration. We analyze the relationships between the lens-tilt angle, the ratio of the lens-to-imaging device
distance to focal length, and the plane-of-sharp-focus angle. Then the near and far limits of the depth of field of
stereoscopic cameras in lens-tilt configurations are formulated geometrically. It is revealed that the depth of field in the
divergent configuration is larger than that in the convergent configuration even if the distance between the two lenses is
the same. The analyses and continuous control of the depth of field are also confirmed experimentally.
Visual cryptography is a powerful method to share secret information, such as identification numbers, between plural
members. There have been many papers on visual cryptography by use of intensity modulation. Although the use of
intensity modulation is suitable for printing, degradation of image quality is a problem. Another problem for
conventional visual cryptography is a risk of theft of physical keys. To cope with these problems, we propose a new field
of visual cryptography by use of polarization. In this study, we have implemented polarization decoding by stacking
films. Use of polarization processing improves image quality of visual cryptography. The purpose of this paper is to
construct visual cryptography based on polarization processing. Furthermore, we construct a new type of visual
cryptography that uses stacking order as a key for decryption. The use of stacking order multiplies the complexity of
encryption. Then, it is effective to prevent secret against theft because the theft cannot determine the secret only by
collecting encrypted films.
A multi-functional display is realized by utilizing optical processing based on spatial coding. The proposed
display performs 2-D, 3-D, and peeping-prevention display. The display consists of two spatial light modulators
of polarization-processing type. By use of optical encryption, the viewing zone is limited in three-dimensional
space. By use of information sharing, stereoscopic images are provided. By use of modulation based on depth,
depth-fused 3-D display is also realized. Without spatial modulation, conventional 2-D images are provided.
Thus, the proposed display performs multi-functions without changing hardware configuration.
A depth-fused three dimensional (DFD) display composed of two two-dimensional (2-D) images displayed at different depths enables an observer to perceive a three dimensional image without the assistance of extra equipment. The original data for the display are a 2-D image and a depth map of objects. The two 2-D images are formed by dividing the luminance of a 2-D image of objects between the two 2-D images according to the depth data of the objects. This paper presents the effect of compressing the depth map on a DFD image. The results of subjective evaluations of still pictures using JPEG revealed that compression noises appearing on the decoded image appeared as position errors in depth on the DFD image; however, less data are possible for the depth map data than for a conventional 2-D image. This means that compressing the depth map is advantageous when transmitting a DFD image.