RePro3D: Full-parallax 3D Display using Retro-reflective Projection TechnologyTakumi Yoshida, Sho Kamuro, Kouta Minamizawa, Hideaki Nii, and Susumu Tachi
The University of Tokyo∗
Keio University†Figure 1: The 3D object that is projected onto the retro-reflective screen can be seen from a number of viewpoints with motion parallax, andthe user can operate this object using his/her hands.

1Introduction

Motion parallax is important to recognize the depth of a 3D image. In recent years, many 3D display methods that enable parallax
images to be seen with the naked eye have been developed. In addition, there has been an increase in research to design interfacesthat enable humans to intuitively interact with and operate 3D objects using their hands. However, realizing 3D object interaction
as if the user is actually touching the object in the real world isquite difficult. One of the reasons for this is that the screen shape inconventional methods is restricted to a flat panel. In addition, it isdifficult to achieve a balance between displaying the 3D image andsensing the user input. Therefore, we propose a novel full-parallax
3D display system that is suitable for interactive 3D applications.
We call this system RePro3D. Our approach is based on a retroreflective projection technology[Inami et al. 2000]. A number ofimages from a projector array are projected onto the retro-reflective
screen. When a user looks at the screen through a half mirror, heor she, without the use of glasses, can view a 3D image that has
motion parallax. We can choose the screen shape depending on
the application. Image correction according to the screen shape isnot required. Consequently, we can design a touch-sensitive softscreen, a complexly curved screen, or a screen with an automatically moving surface. RePro3D has a sensor function to recognize
the user input. Some interactive features, such as operation of 3Dobjects, can be achieved by using it.

Figure 2: Optical system configuration of RePro3D.

a screen. Lenses are located at an appropriate shift from the image
area on the LCD so that the projection areas due to each projectionlens may overlap. Shield plates are placed between the lenses toprevent light for other viewpoints from entering the lens. RePro3Dcan produce vertical and horizontal motion parallax; however, itcannot produce motion parallax in the front-back direction. We use
an infrared camera as a sensor to recognize the user input. Infrared
rays are emitted onto the screen through the half mirror near thecamera, and the camera captures the reflected rays. Because theretro-reflector causes an intense reflection of the rays, a clear distinction is possible between the screen and other objects such as theuser’s hands.

3 Prototype Implementation Results
2Method

When images from a number of projectors are projected onto a
retro-reflector, there is a strong reflection of light in the directionof each projection lens. Using a half mirror, a same number ofviewpoints are made at symmetrical points to the half mirror. By
arranging many projectors in a matrix, a 3D image can be seen frommultiple viewpoints. In order to show smooth motion parallax, thedensity of the projector array must be sufficiently high. Preliminary
experimental results show that the distance between two adjacentprojectors should be lesser than 1.5 cm. Commercially availableprojector arrays do not have adjacent projectors at such small distances because of the resulting increase in size and cost. Therefore,
we have developed a high-density projector array by arranging a
number of projection lenses in a matrix on a high-luminance LCD.
Figure 2 shows the optical system of RePro3D. The system consistsof a number of lenses, an LCD, a half mirror, and a retro-reflector as∗ e-mail: {takumi yoshida, sho kamuro}@ipc.i.u-tokyo.ac.jp† e-mail: {kouta, nii, tachi}@tachilab.org

We have developed a prototype of our proposed system. The luminance of the high-luminance LCD is 1000 cd/m2 . This area has 40
viewpoints, each with a size of 120 × 70 mm. The image resolution of each viewpoint was 60 × 60 pixels. We used an IEEE-1394
camera with a resolution of 640 × 480 pixels for sensing the user
input. Figure 1 shows the results of displaying 3D objects using theprototype system. Distortionless parallax images were displayed ona curved surface from 40 viewpoints. Users were able to intuitively
operate the 3D object by moving their hands. We plan to develop
devices that have higher resolution and to create interactive applications for demonstration of these devices.

References
I NAMI , M., K AWAKAMI , N., S EKIGUCHI , D., YANAGIDA , Y.,
M AEDA , T., AND TACHI , S. 2000. Visuo-haptic display using
head-mounted projector. In Proceedings of IEEE Virtual Reality
2000, 233–240.