Design Method for Gushed Light Field:
Aerosol-Based Aerial and Instant Display
Ippei Suzuki

Shuntarou Yoshimitsu

University of Tsukuba

Waseda University

1heisuzuki@gmail.com gogoyoshimy@gmail.com
Keisuke Kawahara
Nobutaka Ito
Atsushi Shinoda
University of Tsukuba

The University of Tokyo

University of Tsukuba

Akira Ishii

Takatoshi Yoshida

Yoichi Ochiai

University of Tsukuba

The University of Tokyo

University of Tsukuba

ABSTRACT
We present a new method to render aerial images using
aerosol-based fog screens. Conventional fog screens are easily aﬀected by air flow, and their fog generators occupy large
areas. In this study, we propose to add new tradeoﬀs between the display time and the payloads. We employ aerosol
distribution from oﬀ-the-shelf sprays as a fog screen that can
resist wind and has high portability. Results showed thatthe minimum weight of the entire system is approximately
600 g including all components, the screen raise time is approximately 0.5 s, the disappearance time is approximately
0.4 s, and the maximum wind speed at which we can project
images is approximately 10 m/s. We conducted user studies on wearable applications, aerial imaging with a drone orradio-controlled model car, multi-viewpoint display, and adisplay embedded in the environment. This study will contribute to the exploration of new application areas for fog
displays, and will augment expressions of entertainment andinteractivity.

CCS Concepts•Hardware → Displays and imagers;

Keywords
Display, aerial imaging, fog screen, design method, multicopter, projection, entertainment, communication

1.

INTRODUCTION

Fog screens [27] have been used as the primary diﬀusers inpassive aerial displays, and many studies have explored thistype of display technology. In this type of display systems,
diﬀusers are generated by the fog generator, and the projector projects images onto the fog. Previous studies aimed

Figure 1: Application example: wearable version of
our system (showing “OK” on man’s back).

to display fixed and large images. However, there are someissues to be considered. The first problem has to do with thedimension and weight of the system. In this case, the fog
Rgenerator is large and heavy. For example, FogScreen⃝eZ
has 103 cm width and 85 kg weight1 . The second problem isof low wind tolerance. Images cannot be projected in windy
locations or attached to moving objects, since conventional
fog screens are easily aﬀected by air flow. These problems interfere with mobile applications. In addition, a fog machine
cannot generate fog in a short period of time, and there isa delay before the fog can disappear. Therefore, we cannot
produce conventional system as a wearable device, nor canthese instantly project an image.
In this paper, we employ aerosol distribution from oﬀ-theshelf sprays as diﬀusers and we use a portable laser projector
as a projection source. Furthermore, we propose to add
new tradeoﬀs between the limited display time and payload.
Thus, we can solve the problems of conventional fog screensin some cases. Using aerosol distribution from sprays has
several advantages:• Because of its high projection speed, the system andits projected image can be moved and it has high windtolerance.

This is the author’s version of the work. It is posted here for your personaluse. Not for redistribution.
Copyright is held by the owner/author(s).

• Because the ingredients of the spray evaporate immediately, we can instantly project an image and remove
the screen.

AH ’17, March 16-18, 2017, Mountain View, CA, USA
ACM 978-1-4503-4835-5/17/03.
https://doi.org/10.1145/3041164.3041170• This enables the entire system to be lightweight andcompact.

Passive display

Volumetric display

Generator

Generator

Projector

Mirror

Bubbles

Projector

Diffuser

Fog screen [Rakkolainen et al.]Bubble generator
The Information Percolator [Heiner et al.]Interactive Volumetric Fog Display [Lam et al.][Jones et al.]Figure 2: Left: fields of related work. Passive display utilizes various properties of the object (e.g., diﬀusion
property, lens-like property). Volumetric display forms an object in three physical dimensions. Right:
example applications of proposed method. Our aerial imaging system can be attached to drone or dancer.

We present applications that utilize the benefits of ouraerosol-based display. These benefits include a high refreshrate, small size, low weight, high tolerance for wind, andselective narrow viewing angle. Figure 2 (right) shows example applications of the proposed method. Our study isbased on the demonstrations and discussions on applicationsin previous conferences [30, 31].
In addition, we considered the fabrication of this systemin this paper. We explored diﬀerent combinations of nozzles
and sprays as design factors. It is relatively diﬃcult to contaminate the surroundings while using oﬀ-the-shelf sprays
such as deodorant sprays or cooling sprays. On the other
hand, nozzles designed for graﬃti purposes have some properties that are beneficial for distribution. We have evaluatedseveral combinations of sprays and nozzles.
We also built a simple viewing angle simulator. The viewing angle of a fog screen is narrow because of Mie scattering.
When the fog screen was fixed, the narrowness of the viewing angle was no longer a serious problem. However, ourproposed method made the fog screen movable. Therefore,
it is important to be able to demonstrate the image to theintended target during a simulation.
The contributions of current work are as follows:• This study evaluates an aerosol spray as a screen.
• By simulating the scattering of aerosol distribution andevaluating diﬀerent combinations of nozzles and spray,
we present our design and fabrication method.
• By proposing a new method to render an aerial image,this study enables the exploration of new application
areas for fog displays, and expands the use of aerial
imaging for entertainment, communication, and interaction.
Conventional aerial imaging systems have been considered targets of appreciation. The proposed system can makethe aerial display wearable, and can augment human fromthe perspectives of entertainment and interaction [Figure 2(right)].

2.

RELATED WORKIn this section, we cite related work. Figure 2 (left) shows
the fields of related work.
1
http://www.fogscreen.com/products(last accessed January 25, 2017)

2.1 Passive displays
In this category, the projection area is filled with small
objects that can passively reflect projected light or environmental light.
Studies of fog screens [27] have a close relationship to ourstudy. There are several similarities between their studies
and ours. Each study projects an image onto the fog, whichhas properties of forward-scattering. This technique is quite
popular and has been studied for a long time. Despite theresults from the previous studies, the fog screen still has
two weak points: its system is sensitive to strong winds,
and there is a delay when the screen is prepared or cleaned.
Passive displays utilize various properties of objects. The
fog screen uses fog as a diﬀuser, while Bubble Cosmos [16]uses bubbles filled with fog. These displays utilize the diffusion property of the fog. Volumetric display with dust [4]and Pixie Dust [19] uses dust-like particles as diﬀusers. They
utilize the reflection property of dust or foamed beads. Colloidal Display [23, 22] uses a membrane screen controlled byultrasonic vibration. They can change their opacity and surface properties depending on the scales of ultrasonic waves.
Bubble Cloud [11] uses a bubble cluster that can change
shape, and there is no need to fill the bubble with fog. In[32], falling water droplets were utilized as a screen. The
lens-like property of water droplets delivered projected images directly to eyes of the viewer. Heiner et al. designed adisplay that aimed to realize an ambient display [5], which
is a passive midair display that uses water.
These studies were suitable for static and long-term projection. Our approach aims to render aerial images in different situations (e.g., mobile and fast moving), and can beextended to accommodate them.

2.2 Passive volumetric displays
In this category, the dimensions are extended to 3D. The
Interactive Volumetric Fog Display [12, 13] projects images
on a nonplanar and reconfigurable fog screen. The Movable
Immaterial Volumetric Display [28] is a prototype for thevolumetric slices of a fog display. HANASUI [7] is a movable volumetric fog screen that uses markers, an infrared
camera, and multiprojections. Splash Display [14] is a passive volumetric display that uses projectile beads as a projection medium. Holodust [25] illuminates small floating
particles with lasers. Nayar et al. uses Laser Induced Damage scatterers as a volumetric diﬀuser [17]. Pixie Dust [19]manipulates reflective object by 3D acoustic-manipulation
technology. However, their entire system was too large toattach to a drone or to use in wearable applications.
Three-dimensional displays based on the mechanical mo-⑥Mirror (c)⑦(b)⑥Mirror③Laser projector
Video signal⑤Arduino

Actuator

Nozzle Actuator

USB serial
Pin conector④Raspberry Pi⑦Servo④Raspberry Pi②Servo(d)

Pin conector①Spray②ServoMirrorSpray holder③Projector⑤Arduino

Mini size servo mounter

175mm①SpraySide panel
Base and partition

111mm

(a)

Cooling
spray

Deodorant
spray

Figure 3: (a) System overview and data-flow diagram. (b) System appearance (acrylic-plate version). (c)Basic design of our system. These parts were formed with a laser cutter. (d) Oﬀ-the-shelf aerosol sprays
considered in this study. Specifications are listed in Table 1.
tion of a mirror or screen are discussed in [24]. A spinningmirror is used with a high-speed projector in [8], where different images are projected onto the mirror according to thecorresponding azimuthal angle expresses a 360◦ light fieldof an object. Similarly, a 100-million-voxel volumetric display [2] projects images onto a rotating screen, and VORTEX [9] projects images onto a rotating diﬀuser plate. In[1], multilayer water-droplet screens are created in air, andimages corresponding to the spatial position of the water
droplets are projected by synchronizing the projector withwater bulbs.

2.3

Emitting midair displays

In this category, we cite studies that render aerial images
that are not limited to passive midair displays. The basic
concept of laser-plasma 3D displays was demonstrated using
a nanosecond laser [10]. Fairy Lights in Femtoseconds [21]render touchable aerial and volumetric graphics by using
femtosecond lasers.

2.4

Free-floating displays

Some studies have examined attaching a display to a multicopter. Flying Display [18] is a movable display systemthat uses two drones. One drone has a projector, and theother one has a screen. BitDrones [3] is an interactive 3D
display that uses several nano-quadcopters. The Midair Display [29] involves a prototype in which a large tablet device
or E-ink device is installed under a multicopter. This systemshould be large because the entire size of the system depends
on the size of the monitor. Therefore, the researchers would
require to enlarge their system in order to expand the display area. In addition, the appearance of a display equippedwith a large tablet device or solid display is irregular andnot refined. By contrast, our study has the following advantages of midair imaging with no monitors, small size, andlow weight.
However, their system with a display panel has three advantages that our system does not possess. First, by using a
multifunction tablet device equipped with a high-resolution
display, the images shown are clear. Secondly, using an Eink display can attain high visual performance outside or inenvironments with bright light. Thirdly, their display canbe used near open flames in contrast to our system where
significant danger of ignition is present depending on thespray in use.

2.5

Table 1: Specifications for sprays.
(a) Cooling spray (b) Deodorant spray2(Fragrance-free)
Kiyou Jochugiku Kobayashi PharmacManuCo.,Ltd.
eutical Co., Ltd.
facturer
70 ml
280 mlVolumeFatty acid salt-based
Ingredient Isopentane
deodorant, Quaternaty ammonium compounds, Ethanol
NameInteraction with aerial display

Volumetric or/and aerial displays can usually interact withthe human hand. The fog screen enables users to interact

directly with the graphics [27, 13, 7]. Touchable Holography [6], HaptoMime [15], and RePro3D [35] show 2D and 3D
images in the air, and also provide haptic feedback. Fairy
Lights [21] renders touchable 3D graphics by using femtosecond lasers. Cross-Field Aerial Haptics [20] renders aerial
haptic images that uses femtosecond-laser light fields andultrasonic acoustic fields.

3. IMPLEMENTATIONIn this section, we introduce the implementation of oursystem. Figure 3 (a) shows the system configuration. The
system includes a portable laser projector, an aerosol spray,
servomotors for actuating the spray, embedded computers,
a servo-controlled mirror, a battery, and a frame on whichthese components are mounted. This system is intended togush the aerosol out automatically, and uses the laser projector to project the image onto the distribution from thespray. The minimum weight of the entire system is approximately 600 g when balsa wood was used for the frame. The
shape of the system, the spray to be used, and the nozzle ofthe can vary according to the purpose of use.

3.1 Aerosol spray
An oﬀ-the-shelf cooling spray for cooling human bodies
was used as a projection medium. Table 1 (a) lists its specifications. It consists of isopentane (47 ml) and liquefied
petroleum gas (LPG). Since these are highly volatile ingredients, they do not remain on surfaces of objects such as
floors or walls. The aerosol sprays cool water vapor in theair, which upon condensation acts as a fog screen. We consider its characteristics in section 5. In some applications,where we ignore the weight of the system to some extent(such as in embedded applications), we can employ larger
sprays such as those listed in Table 1 (b).

(a)

(b)

(c)

(d)

Figure 4: Appearances of nozzles considered in this study. Specifications are listed in Table 2. Nozzles
designed for graﬃti purposes shown in (c) and (d) do not fit the aerosol spray body we used. However, apart was removed while disassembling the nozzle of aerosol spray (purple), which was used as a conversion
adapter.

Table 2: Specifications for graﬃti nozzles.
Brand
MOLOTOWName(c) Flat Jet Artist 1 (d) Flat Jet Artist 2
Black/Yellow
Red/Black
Stroke1.0-4.0 cm
1.0-6.0 cm
Properties
Adjustable, Wide jet nozzles
Pressure
Wide soft output
Suitable
Small calligraphic
Fill-ins and largeforeﬀects and tags
surfaces or large
calligraphic eﬀect

Table 3: Specifications for portable laser projector.
Nameseeser m1
Light source
RGB laser
Resolution
WXGA (800 × 480)
Image size
8-80 inch diagonal
Luminance
Up to 25 ANSI lumens
Size
60 × 118 × 20 mm
Weight148.5 gBattery
Li-Polymer, 3.7 V, 2200 mAh
Battery life
Approx. 120 min

3.2

and has considerably large strength per unit weight. In
other cases where weight is not as important, materials withgreater strength, such as acrylic plates, could be used.

Spray nozzle

We tested four spray nozzles, as shown in Figure 4. Twoof them are from sprays (a) and (b) (Table 1), while theothers are nozzles designed for graﬃti purposes3 (Table 2).
We expected that nozzles for calligraphy would enable us to
gush a thin and wide aerosol. We found that the shape ofthe nozzle can be quite sensitive to minor modifications in
our system. With high-precision molding, it may become
possible to design dedicated nozzles.

3.3

Spray actuator

Two servomotors are used as an actuator to gush theaerosol out automatically. The servomotors are fixed to theframe beside the spray. Power is supplied directly to theservomotors to prevent the loss of power to the Raspberry
Pi when it takes the load. The servomotors are controlled
by an Arduino microcontroller.
An actuator part made of an acrylic board was designed
to depress the nozzle down by fitting the form of the nozzle.
This part was also designed to be removable from the assembled state of the entire system. Therefore, we can change
out the sprays quickly and easily.
We also tried to use a solenoid instead of a servomotor.
However, we would need high voltage to depress the nozzle
using a solenoid. We need to depress the nozzle eﬀectively
using a limited and lightweight battery because we assume
that our system is used as a wearable or movable application. Therefore, we decided to use servomotors instead of asolenoid.

3.4

Body

We employed acrylic plates for our basic setup. This
acrylic model was used to evaluate our system. However,when we equip the system on a multicopter, we must consider the payload. In this case, balsa wood is suitable as
the material of the frame. Balsa wood is very lightweight2

http://www.kobayashi.co.jp/seihin/tsa 2/(in Japanese)
http://www.molotow.com/products/supplies/caps/(last accessed January 25, 2017)3

3.5 Controller
We used an Arduino microcontroller and a Raspberry Pi
as control devices. The Raspberry Pi sends the image tothe projector and sends serial signals to the Arduino via
USB. The Arduino controls the servomotors. When images
are projected, we can make the spray gush and rotate themirror. The programs on the Raspberry Pi are coded in
Python. OpenCV2 is used for image processing. The Arduino is coded with the Arduino Integrated Development
Environment (IDE).

3.6 Projection source
A portable laser projector was adopted to project images.
Its specifications are listed in Table 3. It has a built-in battery. We also added a servo-controlled mirror to our system
in order to obtain the optical path length and project a large
image.

4. SIMULATOR OF VIEWING ANGLE
In this section, we simulate the appearance of a screen.
We simulate the width of the viewing angle in our display.
Similar to a fog screen [26], we can project an image onto theaerosol distribution by using the forward scattering property of particles called Mie scattering [33]. Simulating theviewing angle is important in designing applications for oursystem since a display with a narrow viewing angle is able
to move freely. We can design positions and angles of nozzles, projectors, and mirrors according to the viewing angle.
For example, in an application to be installed on a drone,
the drone must be navigated in a way that observers always
enter the viewing angle.
Graphics are rendered using openFrameworks. First, wecreated a function that calculates the scattered light for eachscattering angle of one particle. The inputs are the wavelength of the incident light and the particle size, as shown

Figure 5: Viewing angle simulator, which simulates scattering of aerosol distribution.
(a)

(b)

(c)

90°

Cam

0°

0°

10°

20°

30°

40°

50°

60°

70°

80°

90°

Figure 6: (a) Setup for visibility experiment. (b) Source image (a yellow dolphin) for this experiment. (c)Results from every 10◦ .
(a)

5cm

10cm

15cm

20cm

25cm

30cm

(b)

10cm

5cm

10cm

15cm

20cm

25cm

30cm

10cm
(d)

(c)

10cm

10cm

Figure 7: Setup and results for the experiment of spray patterns: (a) nozzle of coooling spray, (b) nozzle ofdeodorant spray, and (c)(d) nozzles designed for graﬃti purposes.
on the left side of Figure 5. Second, we rendered our system and aerosol distribution. This simulator can render the
projected image on aerosol distribution seen from the frontof the projector. The thickness of the fog is not taken into
consideration. In other words, it is assumed that the particles are arranged in a plane. Therefore, it is possible tosee some lights from the side by Tyndall phenomena or theinternal mutual scattering of particles in the real world.

5.

EXPERIMENTS AND EVALUATIONSIn this section, we describe our experimental procedures
and results. All experiments were conducted in a dark room.

5.1

Viewing angle

The viewing angle of our system is limited since our display uses the forward scattering characteristics of the Miescattering theory [26]. We fixed the system at a point andrecorded it while moving the camera by 10◦ in the horizontal
direction. The experimental setup and results are shown in
Figure 6.
However, it is diﬃcult to determine the exact angle atwhich we can observe the system because of the turbulenceof the sprays and the unstable output of the aerosol. From
the results, we consider that the viewing angle of our display
is approximately less than ±10◦ around the central point
projected by the laser projector.

5.2

Spray pattern

Spray patterns play an important role in the experimentand therefore, the performance of various spray patterns
should be considered. If a spray pattern is planar, our dis-play creates a clear image because of simple scattering. In
order to evaluate the spray patterns, we used a red laser slit
light projector (5 W). The camera was placed in the direction of the injection, at the front of the nozzle. In a darkroom, the air that has been sprayed with the aerosol was
illuminated. The results are shown in Figure 7.
From the results of the experiment, the spray patternsof nozzles for deodorant spray and graﬃti are wide near
the nozzle. The distribution of aerosol from the nozzles for
graﬃti is high density; however, it is also narrow and short.
The ideal spray pattern for this system is flat and wide.
Although the nozzle for deodorant spray is optimal, when
it is attached to a small and low-pressure spray, the width
becomes narrow.

5.3 Length of distribution
The screen size of our system is determined by the spray
length. In order to evaluate the spray length, we used a redlaser slit light projector (5 W) set in front of the nozzle, similar to the one used in the experiment for the spray patterns.
Fifteen photos were captured from the vertical side of the
optical path. The photos of the results are lighten composed
15 frames to enhance the actual length of distribution. The
results are shown in Figure 8.
Distribution from the nozzle of spray (b) is the longest
and is moderately wide; however, it is not steady owing to
the low pressure of the spray. The distribution from thenozzles for graﬃti is of high density; however, they had anarrow width and short length. Nozzles should be chosen
depending on their objectives.

(a)

(b)

(c)

(d)

Laser source

50cm

50cm

50cm

50cm

Figure 8: Results for experiment on spray angle and length. Photos of results are lighten composed 15 frames
to enhance actual length. (a) Nozzle of cooling spray. (b) Nozzle of deodorant spray. (c)(d) Nozzles designed
for graﬃti purposes.
(c)Laser projector
Aerosol distribution

WindBlower

5cm

A

(b)

Cam

0 m/s

6 m/s

10 m/s

11 m/sGush from bottom

Projected imageA

Gush from above(a)

Figure 9: (a) Setup for wind resistance experiment. (b) Source image (The letter “A” written in Helvetica,
Regular) for this experiments. (c) Results of experiment.
0.10 sec

0.15 sec

0.20 sec

0.25 sec

Figure 10: Setup and results for experiment on response.
RX10M2, 960-fps mode).

5.4

Wind tolerance

We measured durability of the system when it was mechanically shaken or when it experienced strong winds. First,
we set the outlet of the blower to hit to the emitted aerosol
distribution. This blower can change the extent of the air
flow. Next, we measured the wind speed with an anemometer. Then, we projected the image onto the aerosol distribution, and recorded its appearance while maintaining thewind speed.
The experimental setup and results are shown in Figure
9. The image is the same as in the situation with no wind
until the wind speed reaches 10 m/s. When the wind speed
increased, we were unable to project the image because the
distribution and motion of the particles were aﬀected by thewind. However, in practice, we could continue to project
images if we can change the angle of the mirror dependingon the jet flow.

5.5

0.30 sec

Response speed

We measured the time from pressing the button for thespray to completing preparations for projecting the image,and the time when the aerosol distribution disappears. We

0.35 sec

0.40 sec

0.45 sec

0.50 sec

50cm

LED

0.05 sec

50cm

0 sec

We used a high-speed camera (SONY DSC-

modified the system to turn an LED on and oﬀ when the
servomotor is activated. Strong light was irradiated continuously into the distribution and was recorded using a highspeed camera. The duration of actuating spray was 10 swith the cold spray attached the nozzle for the deodorant
spray being adopted. The experimental setup and photos
are shown in Figure 10. We report that the approximate
rise time was 0.5 s and the approximate disappearance time
was 0.4 s.

5.6 Display time
In order to evaluate the endurance of our system, we held
the spray nozzle down and maintained the projection of theimage. The results are shown on the left side of Figure 11.
The time from the beginning of the image projection to its
disappearance was ∼120 s. However, when the aerosol sprayis nearly depleted, the density of the aerosol distribution
drops. Aerosol sprays are not designed for long-duration
gushing; therefore, we conducted another experiment that
repeats 1 s of gushing at 1 s intervals. The results show thatthe latter approach has a slightly higher density than theformer.

(a)(b) Continuous gush(c) 1 sec gush & 1 sec rest interval (Timecode shows the total time.)

Source image

Figure 11: Results of the experiment on display time. Timecodes are SMPTE for non-drop 30 fps. Timecodefor trial below (c) has interval and shows total of gushed time.
(a)

(b)

(c)

(d)

Projector

Aerosol
1

1

2

3

4

5

Cams

2

3

4

5

Figure 12: Application examples: (a) “Gas Ghost” lobby decoration at a live music club. (b) A radiocontrolled model car with our system. (c) A drone with our system. (d) Multi-viewpoint aerosol-based fog
display. Photos were taken from diﬀerent angles.

6.

APPLICATIONSIn this section, we introduce some aerial display applications that use the advantages of our system.

6.1

Wearable use

As a proof of concept with regard to the mobility and low
weight of our system, we present a wearable application. For
our first example, we present an entertainment applicationin which we install the system on the back of a performer
such as a dancer. If we use a conventional fog screen, theperformer cannot move swiftly, since movement results inthe displacement of air that can distort the fog screen. A
large 2D display can be used as a wearable display; however,
it is too heavy to wear and lacks an attractive appearance.
For another wearable example, we can communicate visually with other people using our system. People can project
aerial images over their heads or on their backs, as shownin Figure 1. For example, in a television program such asa quiz show, people can express surprise by projecting an
overhead image of an exclamation point that is produced byour system.

6.2

Floating or fast moving midair display

We fabricated a prototype of the display that we installed

Table 4: Specifications for Drone.
DJI Phantom 2
Name
1000g
Weight(Battery and propellers included)
350mm
Diagonal length
15 m/sMax flight speed
3S Li-Polymer,
Battery
11.1 V, 5200 mAh
25 minFlight time

on a drone, as in [29]. This is shown in Figure 12 (c). The
system can be easily installed on a small drone since our system weighs approximately 600 g in its smallest configuration,
including all components. The drone can compensate for the
narrow viewpoint of our system by adjusting the angles ofdisplay. If the drone is controlled according to the position of
the observers, the image is always visible to them. Furthermore, we can install our system on a radio-controlled model
car, as shown in Figure 12 (b). We can also demonstrate
a sudden aerial image by using the instantaneous feature of
the system, which will constitute an attractive componentof the interaction of the audience.

6.3

Display embedded in the environment

We developed another application in which an aerial image suddenly appears and disappears. A conventional fog
generator takes some time to generate fog to a state inwhich images can be projected. By contrast, our display can
prepare the projection area within 0.5 s. We suggest “Gas
Ghost” as a specific example. We incorporated “Gas Ghost”
in the decorations of a live music club [Figure 12(a)]. Whena person came close to the projection point, the system emitted aerosol and projected an aerial skull image. Some of theaudience members who observed the image of a skull suddenly appear expressed strong reaction and departed fromthe area.

6.4

Multi-viewpoint aerosol based fog display

We implemented a multi-viewpoint aerosol display thatcreates motion parallax to the observer, as in [34]. In our
prototype, we used two laser projectors, as shown in Figure
12 (d). The aerosol distribution shows forward scattering,in the form of a cylinder. This technique enables users tocreate multiview aerial images instantly.

7.

DISCUSSION AND FUTURE WORK

7.1

Risk

When the system is set on a human body or in the environment, there is a risk that large quantities of the aerosol
distribution may come in contact with the face. In addition,
the environmental impact of the system should be considered. Even if there are few negative eﬀects of the cooling
spray on humans, these sprays typically contain ingredientsthat are toxic and harmful to the environment.
Problems regarding safety also exists as the gas containedin the spray is flammable. If our system is used in a situationthat includes fire, the spray could ignite or cause an explosion. Moreover, considerable attention should be paid whenusing the system with real fire, such as that of a flame machine. When we use the system indoors, we must ventilate
the area.

7.2

Spray performance

The spray has several functional issues: the angle of aerosol
distribution is narrow; therefore, aerosol distribution is blurred
when the moving speed exceeds 10 m/s. This problem canbe resolved by increasing the gas pressure and increasing the
kinetic energy of the particles instead of the volume.
There are also tradeoﬀs between the display time and payloads. Since oﬀ-the-shelf sprays are not designed to jet fora long duration, the quality of the created screen is better
when we release the jet in small intervals than when we jet
continuously, as described in the previous section.
In future works, we would like to try the design for not
only the nozzle but also the overall structure of the spray.
We will consider points of design as the following: (1) forming the spray made with safe ingredients and (2) increasing
the gas pressure in order to increase the output and widen
the angle of output. We consider sprays of the proposedsystem as cartridge and they are used accordingly.

7.3

Image qualities

This system employs turbulent aerosol, which aﬀects the
projected appearance. Since the jet distribution is not stable, it is very diﬃcult to measure the actual viewing angle.

However, we can clearly see the image through the naked
eye using conventional fog screens because the turbulenceoccurs at high speed.

7.4 Narrow viewing angle
Our system has a limited viewing angle, which is as narrowas conventional fog screens. There are many approaches tosolving this problem for conventional fog screens, including
the 360-degree fog projection interactive display [34] proposed by Yagi et al., or HANASUI [7] proposed by Ishikawa
et al. We can apply these techniques to our system since ourmethod of projection of images is based on the same theory.

8. CONCLUSION
In this paper, we introduced a new method to render aerial
images using aerosol-based fog screens. We employed aerosol
distribution from oﬀ-the-shelf sprays as a fog screen thatcan resist wind and has a high portability. We evaluatedthe feasibility of the aerosol type of fog screen. The sizeof the screen depends on the pressure of the aerosol sprayand the nozzle used. We presented a design of the systemsetup and evaluated our experiments, system scalability, andapplications. Our system enables a new type of applicationby combining it with a multicopter, wearable item, multiviewpoint aerosol-based fog display, or embedding it in theenvironment. Our system allows for the exploration of new
application areas for fog displays, and augment expressionsof entertainments and interactivity.

9. ACKNOWLEDGMENTS
We would like to express our sincere appreciation to Takanari Kawasumi, who provided technical support for our drone.
We also thank contributors who supported Digital NatureGroup via crowdfunding project.

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