Depth-Fused 3-D (DFD) Display with Multiple Viewing Zones

Munekazu Date*, Satoshi Sugimoto, Hideaki Takada, and Kenji Nakazawa

NTT Cyber Space Laboratories, Nippon Telegraph and Telephone Corporation,
3-9-11 Midori-cho, Musashino, Tokyo 180-8585, Japan

ABSTRACT

A new depth-fused 3-D (DFD) display for multiple users is presented. A DFD display, which consists of a stack of
layered screens, is expected to be a visually comfortable 3-D display because it can satisfy not only binocular disparity,
convergence, accommodation, but also motion parallax for a small observer displacement. However, the display cannot
be observed from an oblique angle due to image doubling caused by the layered screen structure, so the display is
applicable only for single-observer use. In this paper, we present a multi-viewing-zone DFD display using a stack of a
see-through screen and a multi-viewing-zone 2-D display. We used a film, which causes polarization-selective scattering,
as the front screen, and an anisotropic scattering film for the rear screen. The front screen was illuminated by one
projector, and the screen displayed an image at all viewing angles. The rear screen was illuminated by multiple
projectors from different directions. The displayed images on the rear screen were arranged to be well overlapped for
each viewing direction to create multiple viewing zones without image doubling. This design is promising for a large-
area 3-D display that does not require special glasses because the display uses projection and has a simple structure.

Keywords: 3-D display, stacked screens, multiple observers, large area display, no special glasses

1. INTRODUCTION
Hyper-realistic display technology that causes low visual stress for the user is important for natural communication.
High-contrast large area displays are good to enhance the realistic impression of an image. However, human vision
perceives depth information of actual objects. As a result, people are sometimes confused due to lack of depth
information when viewing 2-D images. Many types of 3-D displays1,2 have been proposed as more natural displays.
Though the best method for completely reproducing all the light waves from an object is holography3, the quantity of
information that must be transferred for moving images is too huge for the construction of electronic displays to be
feasible. Instead, two main approaches have been studied: a stereoscopic display 4,5 based on binocular disparity, and a
volumetric display that optically constructs a 3-D image made of multi-layer 2-D images of an object6.
The depth-fused 3-D (DFD) display is derived from the volumetric display. To efficiently produce a 3-D image, optics
for depth scanning and a high-speed 2-D display have been used7,8, but the amount of information that must be
transferred to the 2-D display is still quite large. As an alternative, a 3-D display technique using a stack of discrete 2-D
images has been studied9,10.
The DFD effect11-14 was originally found during a study on interpolating the layers of discrete 2-D images. Images at
intermediate depth can be produced by simply controlling the luminances of two stacked 2-D images. The DFD display
allows free inclination of the observer’s head, and the depth resolution is high even when the pixel density is low.
Moreover, DFD images can be easily perceived by people with unbalanced visual acuity15. The display satisfies the
requirements of binocular disparity, convergence, accommodation, and small-motion parallax, so on the basis of visual
sense, less visual fatigue would be produced than that of stereoscopic 3-D displays16. To obtain a stack of transparent
emitted images, we initially overlapped conventional 2-D display screens by using a half mirror11. Later, we developed a
flat-panel DFD display (compact DFD) by using a stack of two LCDs17-20. For large area applications, a projection type
DFD display that exhibit the see-through effect when using transparent screens was developed21.
However, the viewing position is limited to avoid doubled images induced by stacked screens. In this paper, we propose
a large-area DFD display with multiple viewing positions.

*date.munekazu@lab.ntt.co.jp; phone +81-422-59-2084; fax +81-422-59-5531;

Three-Dimensional TV, Video, and Display VI, edited by Bahram Javidi, Fumio Okano, Jung-Young Son,
Proc. of SPIE Vol. 6778, 677817, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.752564

Proc. of SPIE Vol. 6778 677817-1

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 2. DFD DISPLAY
2.1 Principle of DFD Effect
The basic operation of a DFD display is shown in Fig. 1. There are two transparent 2-D screens that emit light in front of
a black background. Those two 2-D images, which are almost overlapping from the observer’s perspective, are the same
shape. As shown in the figure, the observer perceives the depth of an object caused by a visual illusion that depends on
the ratio of the luminances in the two displays. Images at intermediate depth can be produced by controlling only the
luminances of the nearest two 2-D images.
Schematic retinal images of an observer at different luminance ratios are shown in Fig. 2. Though the two rectangles are
completely overlapping from the perspective of the center of the observer’s head, the retinal images were slightly shifted
because the eyes are not positioned in the center of the observer’s head. The widths of edge zones are almost the same as
the resolution of the observer’s eyes, so the observed image is blurred, as shown in Fig. 2(b). When the luminance ratio
of front and rear rectangles changes, the horizontal positions of the retinal images change with almost a constant change
in position such as those of an anti-aliased image. Therefore, the observer can perceive the depth by binocular disparity.
This effect has been explained as the spatial low-pass filter effect of human perception, which explains the depth
perception in DFD displays well14,22.

dark

intermediate

bright observer
transparent emitting displays

Fig. 1. Basic operation of DFD display. Overlapped 2-D images on two stacked screens fuse and produce 3-D image.

1 Far 1 Far
7/8 7/8

3/4 3/4
Luminance Ratio β

Luminance Ratio β

5/8 5/8

1/2 1/2

3/8 3/8

1/4 1/4

1/8 1/8

0 0
Near Near
Left eye Right eye Left eye Right eye
(a) (b)
Fig. 2. Left- and right-eye retinal images when DFD display is observed. Luminance ratio β is the ratio of the rear screen
luminance to the total luminance. (a) Schematically illustrated image (b) Image blurred by resolution of human eye.
(The edge width is exaggerated, so this figure is not suitable for fusing.)

Proc. of SPIE Vol. 6778 677817-2

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 When the head of an observer slightly moves, the width of the edge zone changes and produces a disparity. The direction
of motion parallax induced by this disparity is the same as that of an actual object. Therefore, the DFD display induces
lower visual fatigue than that of stereoscopic displays only based on binocular disparity, which produces motion parallax
in the opposite direction.
If the spacing between two layers is smaller than the depth of field of the observer's eyes, the inconsistency between
accommodation and convergence can be suppressed.
2.2 Various DFD Displays
Half-mirror type
The first DFD display was achieved by superimposing two 2-D display screens using a half mirror11. The luminance of
overlapping images was the accurate addition of the luminances of the two screens, so the perceived depth becomes
proportional to the luminance ratio of the two screens. The additional optical component is only a half mirror, so high-
quality 3-D images can be obtained easily. However, the depth of the image appeared farther than the distance of the half
mirror, and the size of the apparatus was large.
Compact type (Stack of 2 LCDs)
The compact type of DFD display was devised to reduce the size of the apparatus. The compact DFD display consists of
a stack of two LCD panels17-20. Though the compact DFD display is slightly thicker than conventional 2-D LCDs due to
the panel spacing, a flat-panel DFD display can be achieved. In this display, the distance between the image and observer
can be closer than that of the half-mirror type. Therefore, the observer can feel that the depth is realistic, even when the
screen separation is the same as that of the half-mirror type. Though luminance addition exhibits a slight nonlinearity,
optical loss caused by color filters is high. Rear image quality is affected by the front panel, so the half-mirror type is
suitable for replacing conventional 2-D flat panel displays. The touch panel application is also possible using this type of
display.
Projection type
The projection type DFD display was developed to overcome the limitation of size while maintaining its image quality.
The display consists of a stack of two transparent screens, whose display mechanism is based on diffraction23, with front
and rear projectors. That stack can be used to reduce the thickness of the display apparatus and distance of the image
from the observer to dimensions smaller than those of the half-mirror type. The luminance addition is linear. Optical loss
is low and moiré reduction is unnecessary, so a high-quality image is expected. To reduce the space between the rear
screen and rear projector, an ordinary flat-panel display can be used as a rear screen (hybrid type projection DFD
display).

transparent screen for

transparent screen for front projection
rear projection

circ
po ularl
lar
projector ize y
d projector

retardation film

PC

(a) (b)
Fig. 3. Projection type DFD display (see-through type) (a) optical setup (b) displayed image

Proc. of SPIE Vol. 6778 677817-3

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 Problem in DFD displays
DFD displays with various sizes, luminances, and image qualities compatible with human depth sense factors were
achieved. However, these all produce doubled images when someone observes the displays from inclined directions.
Therefore, the displays are suitable for one-observer applications such as navigation, games, and amusement, for
example. However, for large-area applications, some users prefer to share a display.
2.3 Oblique Angle View of DFD Display
The observed image of a DFD display when the observer views from an oblique direction explained in Fig. 4. When the
observer views from just in front of the screens, the images of the two screens are overlapping from the center of the
observer head. Though the thin doubled edge is observed on the retinal image as shown in Fig. 2, the width is so narrow
to resolve that the edges were detected as a single line and a natural 3-D image was observed.
When the observer changes his position to an oblique view, the positions of the images on the screens were shifted in
opposite horizontal directions such as with motion parallax, and thick doubled edges were observed. The width of the
doubled edge is sufficiently wide compared to the resolution of the observer's eyes, so two edges were perceived. Front
and rear layers were perceived separately. The perceived depth well matches with calculations using the low-pass filter
model22. The width of the viewing zone, where observers can see non splitting images, depends on the screen spacing,
viewing distance, observer's pupil distance and required depth accuracy. In typical DFD displays, the width of viewing
zone is almost the same as distance of observer's eyes.

rear screen

front screen

doubled image

doubled image
well overlapped image

Fig. 4. Image doubling observed in conventional DFD displays, when the observer is not immediately in front of the screens.

3. EXPERIMENT AND RESULTS

3.1 Architecture of Our Display
The concept of our proposed display, which has two viewing zones, is shown in Fig. 5. When one observer is in the
viewing zone, he will observe a well-overlapped image. However, another observer is outside of the viewing zone and
observes a doubled image. By displaying a shifted rear image that is overlapped depending on the viewing angle, the
second observer can see a good 3-D image. In this experiment, we used a dual-viewing-zone 2-D display as a rear screen
and produced two viewing zones for DFD images. Outside the viewing zones, the rear image is dark, and only a front
image can be observed to reduce the stress of a doubled image.

Proc. of SPIE Vol. 6778 677817-4

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 rear screen

front screen

well overlapped image front image only well overlapped image

Fig. 5. Concept of multi-viewpoint DFD display. Left and right observers can see good 3-D image based on DFD effect. The
center observer, who is outside the viewing zone, will see only the front image.

light polarized parallel

to figure

incident light transparent

light polarized perpendicular

to figure

incident light

scattering
Fig. 6. Characteristics of polarization selective scattering film. The film is transparent for a polarized light, which is
perpendicular to the scattering axis of the film and diffusive for the other polarization, which is parallel to the scattering
axis of the film.

3.2 Polarization-Selective Scattering

Polarization-selective scattering can be observed in a dispersion of aligned optically anisotropic material in isotropic
media or in a dispersion with isotropic material in anisotropic media. For one angle of polarization, the refractive indexes
of medium and dispersoid match, and the film becomes transparent. For the other polarization, the mismatch of the
refractive indexes induces optical scattering. As shown in Fig. 6, the screen using polarization-selective scattering is a
kind of a polarizer. Though a typical polarizer allows polarized light to pass and absorbs light that has the other

Proc. of SPIE Vol. 6778 677817-5

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 polarization, this film also allows polarized light to pass, but scatters light that has the other polarization. That is, the film
acts as a scattering screen for a linearly polarized light and transparent film for the perpendicularly polarized light.
Therefore, the film is suitable for stacking displayed images24.
3.3 Display System
The optical setup of our display, which consists of a pair of screens and three projectors, is shown in Fig. 7. The spacing
between the two screens was 50 mm. The front screen was designed to be a wide-viewing-angle 2-D display. The rear
screen was designed to be a 2-D display, which can display two different images at two different angles.
The front screen is a polarization-selective screen made of stretched PET (polyethylene terephthalate) (PSS, Teijin
DuPont Films Japan), which is illuminated by a LCD projector (LT-380J, NEC). The rear screen is an anisotropic screen
(Light Shaping Diffuser, POC), whose scattering angle is 10 degrees in the horizontal direction and 50 degrees in the
vertical direction. The screen is illuminated by two LCD projectors, through a Fresnel lens. The positions of projectors
were arranged to be in the focal plane of the Fresnel lens to collimate illumination and homogenize the luminance
distribution of the rear screen image. The one front and two rear images were anamorphic, so we minimized the
difference in the images by keystone correction of the projectors. The positions of the rear images were shifted
horizontally to appear to overlap, as viewed from the positions of two observers. The polarization of the front projector
was arranged to be parallel to the scattering axis of the front screen using a color-selective polarization rotator (Color
Select GM, Color Link) and linear polarizer to obtain a bright image and stop the passage of light to the rear screen. The
polarizations of the two rear projectors were perpendicular to the scattering axis to allow light to pass through the front
screen avoiding blur.

projectors
observers
f

Fresnel lens anisotropic directional polarization-selective

screen scattering screen

Fig. 7. Optical setup of DFD display with two viewing zones.

3.4 Display Characteristics

The displayed images for three viewing directions are shown in Fig. 8. The left and right views (Fig. 8(a), (c)), which are
in the viewing zone, were well overlapped and a good 3-D image can be observed. The center view, which is outside the
viewing zone, was as shown in Fig. 8(b). The rear screen image was very dark, blurred, and 3-D. The image displayed by
the front screen is dominant.

Proc. of SPIE Vol. 6778 677817-6

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 The luminance distribution of images illuminated by three projectors at different viewing angles is shown in Fig. 9. The
front screen luminance was uniform for all viewing angles. The direction of rear projection was well controlled.

4. CONCLUSION
We demonstrated the feasibility of a DFD display with multiple viewing zones. Since it does not require special grasses,
which are made with color filters or polarizers, and it satisfies many factors of human depth sense, it is visually
comfortable to observers, which would contribute natural communication.
Though projection was used in this paper, a flat-panel multi-view 2-D display is effective to reduce the display size. The
combination of two multi-view displays is effective to create continuous viewing zones because the overlapping
condition can be maintained for all viewing angles.

(a) (b) (c)

Fig. 8. Photography of displayed images at different observation positions. (a) and (c) are the best viewing positions at left
and right, -17 and 17 degrees, respectively. (b) is the center view, which is outside of the optimal viewing position.

104
rear rear
Luminance （cd/m2）

103

front

102

101
- 60 - 30 0 30 60
Observation Angle （
deg.）
Fig. 9. Luminance distribution of DFD display with two viewing zones.

Proc. of SPIE Vol. 6778 677817-7

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms

 REFERENCES

1. T. Ohkoshi, "Three-dimensional displays," Proc. of IEEE, 68, 548-564 (1980).

2. A. R. L. Travis, "The display of three dimensional video images," Proc. of IEEE, 85, 1817-1832 (1997).
3. D. Gabor, "A new microscopic principle," Nature, 161, 777-778 (1948).
4. F. E. Ives, Parallax stereogram and process of making same, U.S. patent 725,567, 1903.
5. M. G. Lippmann, "Epreuves reversibles donnant la sensation du relief," J. de Phys., 7, 821-825 (1908).
6. J. D. Lewis, C. M. Verber and R. B. Mcghee, “A true three-dimensional display,” IEEE Trans. on Electron Devices,
18, 724-732 (1971).
7. A. C. Traub, “Stereoscopic display using rapid varifocal mirror oscillations,” Appl. Opt., 6, 1085-1087 (1967).
8. S. Suyama, M. Date and H. Takada, “Apparent 3-D image perceived from luminance-modulated two 2-D images
displayed at different depths,” Jpn. J. Appl. Phys., 39, 480-484 (2000).
9. S. Tamura and K. Tanaka, “Multilayer 3-D display by multidirectional beam splitter,” Appl. Opt., 21, 3659-3663
(1982).
10. T. S. Buzak, “A field-sequential discrete-depth-plane three-dimensional display,” SID International Symposium
Digest of Technical Papers, 345-348, Anaheim, 1998.
11. S. Suyama, H. Takada, S. Ohtsuka, K. Uehira, and S. Sakai, “A novel direct-vision 3-D display using luminance-
modulated two 2-D images displayed at different depths,” SID International Symposium Digest of Technical Papers,
1208-1211, Long Beach, 2000.
12. S. Suyama, H. Takada, K. Uehira, S. Sakai, and S. Ohtsuka, “A new method for protruding apparent 3-D images in
the DFD (depth-fused 3-D) display,” SID International Symposium Digest of Technical Papers, 1300-1303, San Jose,
2001.
13. S. Suyama, H. Takada, and S. Ohtsuka, “Apparent 3-D image perceived from luminance-modulated two 2-D images
displayed at different depths,” IEICE Trans. Electron., E85-C1, 911-1915 (2002).
14. S. Suyama, S. Ohtsuka, H. Takada, K. Uehira, and S. Sakai, “Apparent 3-D image perceived from luminance-
modulated two 2-D images displayed at different depths,” Vision Res., 44, 785-793 (2004).
15. N. Sekimoto, M. Mizuno, K. Okai, A. Akaike, Y. Takami, S. Asonuma, J. Hosohata, S. Suyama, H. Takada, S.
Sakai, and T. Fujikado, “A development of stereotest using luminance modulation,” Proceedings of Progress in
Strabismus 9th Meeting of International Strabismological Association, 117-119 (2003).
16. Y. Ishigure, S. Suyama, H. Takada, K. Nakazawa, J. Hosohata, Y. Takao, and T. Fujikado, “Evaluation of Visual
Fatigue Relative in the Viewing of a Depth-fused 3-D Display and 2-D Display,” Proceedings of 11th International
Display Workshops, 1627-1630, Niigata, 2004.
17. H. Takada, S. Suyama, K. Hiruma, and K. Nakazawa, “A compact depth-fused 3-D LCD,” SID International
Symposium Digest of Technical Papers, 1526-1529, Baltimore, 2003.
18. M. Date, H. Takada, S. Suyama, and K. Nakazawa, “Luminance additivity in compact depth-fused-3D display using
a stack of two TN-LCDs,” in Proceedings of 10th International Display Workshops, 1409-1412, Fukuoka, 2003.
19. M. Date, T. Hisaki, H. Takada, S. Suyama, and K. Nakazawa, “Luminance addition of a stack of multidomain
liquid-crystal displays and capability for depth-fused three-dimensional display application,” Applied Optics, 44, 898-
905 (2005).
20. M. Date, T. Hisaki, H. Takada, S. Suyama, and K. Nakazawa, “Reduction of Power Consumption in Compact DFD
Display by Using FS Color Technology,” IEEE Trans. on Electron Devices, 52, 190-193 (2005).
21. M. Date, H. Takada, S. Suyama, K. Tanaka, and K. Nakazawa, "Projection-Type Depth Fused 3D (DFD) Display,"
Proceedings of 13th International Display Workshops, 1393-1396, Otsu, 2006.
22. M. Date, H. Takada, Y. Goth, and S. Suyama, "Depth Reproducibility for Inclined View in DFD (Depth Fused 3-D)
Display," Proceedings of 12th International Display Workshops in conjunction with Asia Display, 1793-1794,
Takamatsu, 2005.
23. M. Umeya, M. Hatano, and N. Egashira, “New Front-Projection Screen Comprised of Cholesterol-LC Films,” SID
International Symposium Digest of Technical Papers, 842-845, Seattle, 2004.
24. M. Date, H. Takada, T. Hisaki, S. Suyama, and K. Nakazawa, "Projection-type Depth Fused 3-D (DFD) Display
Using Scattering Screens with Polarization Selectivity," 3D Image Conference, 176-179, Tokyo, 2007 [in Japanese].

Proc. of SPIE Vol. 6778 677817-8

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/19/2015 Terms of Use: http://spiedl.org/terms