ASIAGRAPH 2008 PROCEEDINGS

回転板式 3 次元テレビジョン
Spinning-disc 3D Television- Multiple parallax image camera and display using Nipkow disc 新居英明, 南澤孝太, 川上直樹, 舘暲/東京大学 大学院情報理工学系研究科
Hideaki NII, Kouta MINAMIZAWA, Naoki KAWAKAMI, Susumu TACHI/The University of Tokyo{hideaki_nii,kouta_minamizawa}@ipc.i.u-tokyo.ac.jp,{kawakami,tachi}@star.t.u-tokyo.ac.jp
Abstract:

In this study, we have incorporated a novel LED-projection technology into the simple structure of a spinning-disc television.
A spinning-disc television is a well-known vintage system used for transmitting television images. In order to display 3Dimages, we have replaced the conventionally used light bulbs in this system with an LED array. In order to capture theparallax images, we replaced the light-sensitive tube with a photo-diode array. With the aid of this technology, users cancapture multiangle images of the target and view different images from different viewing angles.

Keywords:

Nipkow-disc, 3D image, Parallax images, Autostereoscopic display.

1. Introduction
The aim of our study is to develop an image display
technology that eliminates the distance between two spaces
so that users can perceive an object in 3D. At present,
several stereoscopic systems such as head-mounted displays(HMDs) [Ivan65] and immersive multi-screen display units
such as CAVE [Carolina93]) are available. These systems
require the observer to wear special glasses for stereopsis.
However, it is more convenient to view a display withoutwearing special glasses. In order to overcome this problem,
parallax barriers and lenticular lenses have been used in a
number of systems. Keeping this in mind, we previously
developed two systems—TWISTER [Susumu96] andSeelinder [Tomohiro05]—that realize an autostereoscopic
display without requiring special equipment to be worn. TheTWISTER system works as a cylindrical display and has
multiple rotating LED (light emitting diode) boards. Each
LED board consists of a linearly-arranged LED array andhas a slit-shaped parallax barrier. The observer stands in thecylindrical drum and is able to view the entire
autostereoscopic image through a slit in the appropriate
LED array. The Seelinder system also works as a cylindricaldisplay. The differences between these systems lie in thedirection of the rays and the motion of the parallax barrier.
In the Seelinder system, the observer stands outside thecylindrical drum and views the image through the slit in theappropriate LED array. These systems provide level parallax
images only. Because the parallax barrier shaped thin andlong slit.
In this study, we extend the abovementioned prototypes
in order to be able to construct a more natural 3D “presence”
of objects. Next, we examine the possibility of realizing adisplay with a pinhole parallax barrier shaped small hole.
This type of parallax barrier can display both horizontal
parallax and vertical parallax at the same time. The conceptof this system is same as that of integral photography;
however, there is a trade-off between the resolution and thenumber of parallaxes. In order to resolve this problem, as
the pinholes rotate, the LEDs flash several times. As a result,

Figure 1: Photograph of the Televisor, which is currentlyowned by the Museum of Broadcasting, Tokyo, Japan

In this window,
pinholes scanline by line.

Figure 2: Illustration of the Nipkow disc. The pinholes areplaced in a spiral.

the system displays a compact image. We have utilized thisconcept in our study and have described the structure anduse of a spinning-disc television system that is capable ofproducing multiple parallax images.

2. Spinning-disc 3D television
The first spinning-disc television system, shown in
Figure 1, was publicly demonstrated by J. L. Baird in 1926
[Ronald33]. In the initial days, a number of these televisionunits were sold. This television system had a spinning disc,a light bulb located behind the disc, and a signal-receiving
circuit. The camera system also had a spinning disc and aphoto-detecting device located behind the disc. The disc in
the television spun in synchronization with the disc in thecamera system. Moreover, the bulb flashed insynchronization with the photo-detector in the camerasystem. The spinning disc in this system is also known as
the Nipkow disc and the structure is shown in Figure 2. It isimage scanning device to reconstruct the television image.
From this system, we found that the spinning disc can beused to display multiple parallax images. We therefore
extended its application to televisions used to display 3D
images. Next, we describe the concept, structure of thecamera unit, display unit, and the design of the parallax
image for the system developed in our study.

Figure 3: Schematic representation of spinning-disc 3D
television (this system has both a camera and a display unit).

Parallax image information
Nipkow disc

Convex lens

2.1. Concept of proposed system
The basic concept of the system developed in this study
is based on that of the spinning-disc television, which isshown in Figure 3. We improved this system so that it
captures light rays from a specific direction and projects
them in a specific direction.
Our system can display multiple images based on theviewer’s line of sight. It is capable of displaying bothhorizontal and vertical parallaxes.
The concept of a 3D parallax display that utilizes aspinning disc was suggested by Yendo at el[Tomohiro06].
He developed an experimental display using the Nipkow
disk and emphasized the importance of time multiplexing insuch systems. We also focus on this concept and apply it tothe 3D television system developed in this study.
Figure 3 shows the principle of our system. The system
consists of a camera unit and display unit. Both units areconnected by a wire. Multi-parallax images are captured by
the camera unit and then transmitted to the display unit that
displays the multi-parallax images at the same time.

2.2. Structure of camera unit

Nipkow disc

Convex lens

PD array
Light ray

Motor

Camera unit

LED array
Motor

Light ray

Display unit
Synchronous rotation

Figure 4: The concept illustration of Spinning-disc 3Dtelevision

Nipkow disc
LED projection unit

LEDarrayRays of light

The camera unit used in our system comprises thefollowing three components:(1) The spinning disc, also known as the Nipkow disc,controls the rays of light that pass through the holes in thedisc. The holes are arranged in a spiral formation. The lightthat passes through the holes as the disk rotates produces araster scanning pattern with a rectangular area. As a result,the disc can either convert the temporal modulated light(2) A convex lens is located behind the Nipkow disc andit captures the rays incident on it. The focal length isequivalent to the distance between the lens and thephotodiode (PD) array. The convex lens focuses a ray

Convex lensarriving
specificdirection
specificlocation on
Figure 5: fromLight apath
from lightsourceonto
to theafront
sectionthe PD array.
(3) The PD array is located in the focal plane of the lens.
Each cell of the array captures light from a specific direction.
The output signal of the cell is a temporal signal that isθdNipkow discwith lensscanned by the Nipkow disc. The outputs of the PD arrayconvey information about the multi-parallax images.
Conventionally, the photodiode array employs only a single
light detector, which is placed behind the disc. However, in
our system a separate light detector array has been allocatedfor each viewing direction.
With the aid of these components, the system cancapture multiple parallax images.

θw

LDW

2.3. Structure of display unit

LED array

The display unit has a structure that is almost similar tothat of the camera unit except that the path of each ray oflight in the display unit is the reverse of that in the cameraunit. It comprises three components:Figure 8: Photograph of Spinning-disc 3D television.

(1) A Nipkow disc, which spins in synchronization withthe disc in the camera unit. As a result, the pinholes on boththe discs are aligned at the same angle and position.
(2) A convex lens, which converts the ray of light from apoint light source into a straight ray.
(3) An LED array that can display multiple images
simultaneously. The conventional Nipkow disc employs
only a single bulb and is capable of displaying only a single
image. However, in our new system, each LED element
displays different images and an observer can view different
LED elements through the hole in the disc. This principle isillustrated in Figure 5.

2.4. Design of the parallax images
In order to capture or display parallax images, we haveto design the system based on the number of images and thenumber of LED devices on the array. The importantparameters to be considered are as follows:(1) Size of the screen.
(2) Resolution of the screen.
(3) Viewing angle of the screen.
The main parameter that affects the size of the image isthe distance between the pinholes on the Nipkow disc.. The
resolution of the image is limited by the number of pinholeson the Nipkow disc. The size of the Nipkow disc can besolved by the product of the screen width and the number ofscanning line of image . However, the size of the Nipkow
disc is limited by the stress of the torque and the size of thedisplay unit.
The main parameter that affects the viewing angle is thedistance between the LED array and lens. This relationshipis shown in Figure 6. The width of the LED array is denotedby . The width of each LED is . The distance between theNipkow disc and the LED is denoted by . The observer
stands on the left hand side in this figure and can view theimage depending on the position of his/her head.
The viewing angle ( θ w ) can be calculated by thefollowing equation.

Figure 6: Explanatory drawing of the viewing area

θw

⎛W ⎞= arctan ⎜⎟2⎝ 2L ⎠The viewing angle of the individual image can beroughly calculated by the following equation.

⎛ D⎞⎟⎝ 2L ⎠θ d = arctan⎜

The number of images to be displayed is calculated bytaking into account the various positions that can beassumed by a human head.

2.5. Design of the control unit
This type of television system does not require the use ofa complex control unit. We use a simple technique tosynchronize the two discs and connect a wire from a cell in
the PD array to one in the LED array. The display unit iscapable of showing not only the captured image but also 3Dcomputer graphics (CG) images. In order to display CG
images, a video signal generator is required for the displayof the parallax images. The process involved in the displayof these images will be described later. The generator
consists of the following three components(1) A clock generator, which is synchronized with theLED outZ phasesignalFrequency
Multiplier
x*y times

Video RAMAddress
Generator
x*yVideo ROM
x*y*n

Figure 7: The function of the parallax image generator

Figure 8: Spinning-disc 3D Television

Nipkow disc and which acts as the time-base generator.
(2) An address generator, which is used to map theposition of the pixel on the screen to an address in thememory.
(3) A memory that is used to store the parallax images
that comprise the video signal.
Figure 7 shows the working of the parallax image
generator. The values x and y indicate the size of the screen
in pixels.

Figure 9: Photograph of internal components.

3. Implementation
We have developed a prototype television system (seeFigure 8).This prototype system has a 700-mm-diameter
Nipkow disc with 64 holes. This size is selected for thebaggage by the air. And it has one camera unit and two
display unit on the same Nipkow disc. Figure 9 show theNipkow disc with two display unit and there is one morecamera unit behind of the disc. Because of the sizelimitation, we decided to develop the camera and display onsame disc. It is clearly expandable to long distancetelevision.
As for the display unit, it has sixty-four full-color LEDs
placed behind the disc, and the observer can view eight byeight (sixty-four) different images from his/her viewing
position. The viewing angle is 60 degree and observer cansee autostereoscopic images from 300 mm distance at any
position. The camera unit is designed same method but thelimitation of the component size, the number of parallax
image is 32.
The screen resolution is 64 × 64 pixels and the screen
size is 32 mm × 32 mm (see Figure 10). This value isselected by the balance of the screen size and screen
resolution. The frame rate is about 12 frames per second(fps) because of the power limitation of the motor.
Therefore, 32 different images can be captured and 64
different images can be displayed. We describe several
components in detail.

3.1. Nipkow disc

Figure 10: Photograph of display image.

Figure 11: Photograph of Nipkow discFigure 11 show the Nipkow disc in practical use. This
disc has 64 pinholes. The pinhole has a cone-shaped hollow
and a diameter of 0.8 mm. The disc consists of apolycarbonate plate with a thickness of 2 mm. It isextremely important to shape and position the holes on thedisc accurately. The polycarbonate plate used is extremely
thin and hence must be supported by a translucent guideplate.
A motor (10 W DC motor from Maxon Motor Corp.) is
installed at the back of the Nipkow disc and has a speed of
12 rotations per second.

3.2. Display unit
The display unit consists of 64 full-color LEDs (over 2cd brightness, OSTA71A1D), which were mounted on a
printed circuit board with a pitch of 8.89 mm (see Figure 12).
Each LED is driven by a serial line from the control board.
Since the projecting rays from each LED are not of equal
intensity, we use a diffuser, which consists of Japanesepaper and black plastic, to decrease the stray light from thenext LED. The lens on the LED consists of a cemented
doublet with a diameter of 53.5 mm and a focal length of 75mm. The black covering for the display unit was preparedby using a 3D printer.

Figure 12: Photograph of display board.

3.3. Camera unit

Figure 13:Photograph of Camera board

8x8ColorLED
ArrayUnit

64bit*3 data

DC power unit
Nipkow disc

The camera unit consists of an array of 32 PDs (BPW34
from Vishay Corp.) (see Figure 13). This unit is designedfor enhancing up to the 64 PDs in the future. The unit also
has a current to voltage converter (OPA2335E from TI
Corp.) with an amplitude of 1 [V/mA]. In addition to theamplifier, a comparator with a sensitivity of approximately
0.05 [V/mA] is also present. The bandwidth of this system isapproximately 1 [MHz]. The low noise amplifier used inthis unit provides the most important challenge. The outputof the comparator is connected to the control board with aparallel line. The lens on the PD is the same as that on thedisplay unit.
If the sensitivity is too low to capture a clear image, ashadowgraph of the object is obtained.

+-Motor3.4. Control unit
control board detects a Z phase signal (this is a pulse
signal that indicates the instant at which the disc startsrotating) and it generates a clock depend on the resolution ofthe image. In our system, a board generate a clock which ismultiplied 4096 times for the 64 × 64 pixels image. In thisconfiguration, the frequency of the dot clock isapproximately 50 [kHz]. In a single pixel period, the pixel
data of 64 different parallax images is transmitted.
The second mode is used to render a captured image. In
this mode, the camera unit is connected to the control board
using a parallel line, while the display unit is connectedusing a series line. Each board used in this unit generates
some error. Hence, the control board adjusts the signal

FPGABoardZ phase sensor

8x4
CameraUnit

32bit dataFigure 14: The block wiring diagram of proposal systemtiming and converts the parallel data into serial format. The

final system is shown in Figure 14. Figure 15 shows thetypical images on the display at the same time.

4. Discussion
The television system developed in this study wasexhibited at SIGGRAPH 2007, San Diego and at Asiagraph2007, Tokyo. Our system was viewed by a large number ofpeople. The feedback given by the observers was also taken
into consideration. Many observers were able to clearlyview the 3D CG image clearly (Figure 16 shows the one ofthe sample image )by adjusting the positions of their heads.
Given below are some of the limitations of our system as
pointed out by the observers and the possible explanations
for these limitations.
(1)The size of the screen is quite small: This is true.
(2)The clarity of perception decreases with distance:
This may be due to the fact that the positions of the heads ofthe observers varied from the ideal setting, resulting in
reduced clarity of the image.
(3) Flickering of the screen: This is due to the fact thatthe number of frames per second (12 frames per second) is
too slow to show the natural image. The slow frame rate is
because the power of the motor is too low and a strong
driver is required.
(5)The image from the camera unit is unrecognizable:
This problem occurs due to insufficient image sensitivity.
Thus, our television system has been implemented
successfully and allows users to observe 3D images without
the use of special equipment.. However, the camera unit still
has some drawbacks..

Figure 15: Photograph of display images from 64 view points.

5. Conclusions
In this study, we examined the possibility of realizing apinhole-type parallax barrier display, and we described aspinning-disc television system that is capable of displaying
multiple parallax images.
We developed a prototype television system which has a
64 × 64 pixel screen and is capable of displaying 64 parallax
images at the same time.
Our system was exhibited at a conference and feedbackwas collected from the observers. It was confirmed that oursystem is capable of successfully displaying 3D images. In
order to improve the camera unit, we plan to replace thecurrent PD component with a higher sensitivity PD. This
will enable our system to produce more realistic 3D images.

References
Carolina Cruz-Neira, Daniel J. Sandin, Thomas A. DeFanti, 1993.
Surround-screen projection-based virtual reality: The design
and implementation of the CAVE. In Proceedings of
SIGGRAPH 1993, Computer Graphics Proceedings, Annual
Conference Series, pp. 135–142, ACM, ACM Press/ACMSIGGRAPH.
Ivan. E. Sutherland, 1965. The ultimate display. In Proceedings ofIFIP Congress, pp. 506–508.

Figure 16: Photograph of display images of a solid cube.
Ronald F. Tiltman, 1933. Baird of television: the life story of John
Logie Baird. London: Seeley Service.
Susumu Tachi, Taro Maeda, Yasuyuki Yanagida, Masaaki
Koyanagi and Hiroki Yokoyama, 1996. A method of mutual
tele-Existence in a virtual Environment, Proceedings of The
6th International Conference on Artificial Reality and TeleExistence, (ICAT'96), pp.9–18
Tomohiro Endo, Naoki Kawakami and Susumu, Tachi, 2005.
Seelinder: The cylindrical lightfield display. In Conference
Abstracts and Applications of ACM SIGGRAPH 2005.
Tomohiro Yendo, Yongxin Eum, Toshiaki Fujii and Masayuki
Tanimoto, 2006. Study of full parallax 3D display using time
multiplexing, In Proceedings of 3D Image Conference 2006, pp.
61–64.(In Japanese)