Unphotogenic Light: High-Speed Projection Method to Prevent
Secret Photography by Small Cameras
Ippei Suzuki

Yoichi Ochiai

University of Tsukuba
1heisuzuki@gmail.com

University of Tsukuba
wizard@slis.tsukuba.ac.jp
Frame period

Source image

Frame 2n-1

Projection period
Frame

Human vision

Frame 2nFrame division

TimeSuitable shutter speed/timing
Incomplete frameHigh frame rate projection

Incomplete frame

Camera vision

Figure 1: Left: overview of unphotogenic light. We project entire images by switching each divided image at high framerate. Humans can observe an entire image whereas cameras cannot capture complete photo. Right: theory and effect of theproposed method. The image is divided into multiple parts and projected in turns. We must synchronize camera shutter speedwith frame period to capture the entire image correctly.

CCS CONCEPTS•Human-centered computing →Displays and imagers;•Hardware →Displays and imagers;

KEYWORDS
Protection, secret photography, security, privacy, copyright.
ACM Reference format:
Ippei Suzuki and Yoichi Ochiai. 2017. Unphotogenic Light: High-SpeedProjection Method to Prevent Secret Photography by Small Cameras. In
Proceedings of SIGGRAPH ’17 Posters, Los Angeles, CA, USA, July 30 - August03, 2017, 2 pages.
DOI: 10.1145/3102163.3102164

1INTRODUCTION

We present a new method to protect projected content from secretphotography using high-speed projection. Protection techniques
for digital copies have been discussed over many years from theviewpoint of data protection. However, content displayed by general display techniques is not only visible to the human eye but
also can be captured by cameras. Therefore, projected content is, attimes, secretly taken by malicious small cameras even when protection techniques for digital copies are adopted. In this study, weaim to realize a protectable projection method that allows people toobserve content with their eyes but not record content with camera
devices.
To achieve this goal, we exploit the difference between the human vision system and the camera vision system. Notably, humans
cannot recognize the high-speed changes of light. We were inspired
SIGGRAPH ’17 Posters, Los Angeles, CA, USA© 2017 Copyright held by the owner/author(s). This is the author’s version of thework. It is posted here for your personal use. Not for redistribution. The definitive
Version of Record was published in Proceedings of SIGGRAPH ’17 Posters, July 30 August 03, 2017, http://dx.doi.org/10.1145/3102163.3102164.

by previous work that used these properties to show on-screen
invisible markers. There are several studies that aim to present
imperceptible on-screen markers using high-speed projection between the afterimage effect of human eyes and shutter speeds ofdigital cameras [Luiz et al. 2015; Yamamoto et al. 2014]. From another point of view, these techniques show specific content only tothe human eye while showing different content to a camera. Thus,
we can project images that can be seen by human eyes whereascameras only capture an incomplete frame as illustrated in Figure
1. Therefore, this means the projected light is unphotogenic.

2 IMPLEMENTATION
2.1 Overview
We use a high-speed programmable projector (DLPa Light Crafter
4500, Texas Instruments Inc.) that projects divided images withhigh speeds. If we attempt to capture the entire image with thecamera, we must match the projection period of the system andexposure period of the camera, as shown in Figure 1 (Right).

2.2

Evaluation from camera vision

We evaluate our system with the vision of a camera, as shown inFigure 3. First, we used a DSLR camera to evaluate the shutter
speed threshold in which the proposed method is most effective.
The results are shown in Figure 3 (c). When the shutter speed isfaster than 1/60, the effect of our method is noticeable in the picture.
Next, a smartphone (iPhone 6, Apple Inc.) was used to consider
the scene of practical secret photography. We used a camera application that can control the shutter and ISO speeds as shown inFigure 3 (d). Please note that the f-stop of the smartphone is notcontrollable. If the brightness of the screen is sufficiently high, thecamera speeds up the shutter speed to avoid blowing out highlights.

SIGGRAPH ’17 Posters, July 30 - August 03, 2017, Los Angeles, CA, USA(a) Vidible watermarks, protection marks

Ippei Suzuki and Yoichi Ochiai(c)(b) Inspection and security

Bad Experience CONFIDE

Baggage CheckNTIALTCNO PHOTOS(d)(e)ProjectorPaintingShowcase$10

Photo taken
in roller coaster

IGH
OPYR(f)

Projector
Sushi

Projector
Protected object

VisitorSecret Camera
ImageVisitors

Photo by Ted Murphy (CC BY 2.0)

EXIT

ConfiscatedCameraVisitor’s bag

PocketPen-shaped small
camera in visitor’s
pocketResultResultResultFigure 2: Practical stories of the proposed method. (a) Visible watermarks are simple and an effective method. However, itcreates bad experiences for visitors. (b) Inspection and security are other solutions; however, secret photography by small cameras is still feasible. The proposed method aims to prevent secret photography in this situation. (c)fi(f) Application examples;
top: schematic diagrams, bottom: applications taken by the smartphone.
(a)(c) DSLR (Canon EOS Kiss X4 with TAMRON B005 17-50 mm F/2.8, Shutter priority AE mode with ISO 100.)

171mm
272mm

CameraScreenProjector(b)

Source1/30, F20

1/60, F141/100, F111/250, F7.1

(d) Smart phone (Apple iPhone 6, with App “ProShot” by Rise Up Games LLC. Shutter priority AE mode with F/2.2, fixed aperture.)

Source1/30, ISO32

1/60, ISO321/100, ISO32

1/250, ISO32

Figure 3: (a) Setup for evaluation from camera vision. (b)Images are divided into three parts. Projection period (seeFigure 1) is 4166 microseconds (approximately 240 Hz). (c),(d) Images from camera vision. Please note that f-stop ofsmartphones is fixed (specification).
Because small cameras tend to have this limitation, the proposedsystem is effective to prevent secret photography by small cameras.

3 APPLICATIONS
3.1 Protection of screen content
The main purpose of this method is to discover protection techniques to prevent secret photography. For example, it can be applied
to secret pages in a presentation. Speakers then do not need tocaution the audience members about taking photos. While oral
caution might be an effective method, it may be ignored. It also
hinders a smooth presentation and the attention of audiences frompresentations.
As another example, our system can be used in theme parks asshown in Figure 2 (c). There is a system that takes a picture ofpassengers in the middle of an attraction such as a roller coasterin theme parks. Pictures are previewed on a screen near the exit,
and a passenger has the option to purchase the picture. However, apassenger can also take photos of the screen with a smartphone. By
using the proposed method, these photos are prevented. In addition,
if the shape is divided into the silhouette of a character, people will
be able to enjoy theme parks even more.

3.2

camera with a large lens such as that of a DSLR camera. In thiscase, a small camera such as a smartphone will be used; however,the proposed method prevents this when installed as a spotlight.
As another example, the proposed system can be used in restaurants. If a restaurant chef dislikes the photography of food bysmartphones, the proposed system can be used as lighting. Because
the customers cannot take photos with their smartphones as shownin Figure 2 (f), they can instead concentrate on eating the food.

4 DISCUSSION
4.1 Camera parameter
If the shutter speed of a camera becomes higher than the thresholddefined by projection speeds, people cannot photograph a complete
image. Conversely, the image can be captured by long-term exposure. Therefore, high-specification cameras, such as DSLR cameras,
can evade our system. However, the situations shown in Figure 2(a) and Figure 2 (b) are assumed. Small cameras tend to be exploitedwhen taking secret photographs. They only have a non-adjustablef-stop. If the screen is sufficiently bright and has a fast shutter
speed, the proposed system protects the image content.
Further, it is very difficult to take a photo or video if the projected
content is a video. This is because the camera needs to synchronize
with the frame timing and cover shutter period to capture the entire
video. Furthermore, by changing the projection period randomly,
we can also prevent measures taken by a camera application suchas a detective function to remove the flicker from lighting.

4.2

FlickrWhen the screen viewpoint of a person changes, the person tends
to perceive a flicker on the screen using the proposed system. For
example, this may happen when people shake their heads or becauseof saccades. There are trade-offs between the flicker resistancestrength on the screen and the minimum acceptable shutter speedof the system. We need to explore suitable parameters and adjust
them for various viewers.

Protective illumination

The proposed system can be used not only as an image projector butalso as a lighting system. For example, the system can be installed
in an art gallery as a spotlight, as shown in Figure 2 (d).
It is worth noting that photos with DSLR cameras may still betaken. Therefore, the next example is a situation in which a visitor
cannot use a DSLR camera, as shown in Figure 2 (e). Because
the showcase surface has reflections, it is difficult to shoot with aREFERENCES
Sampaio Luiz, Yamada Yoshio, Yamamoto Goshiro, Taketomi Takafumi, Sandor Christian, and Kato Hirokazu. 2015. Detection of Imperceptible On-Screen Markers
with Unsynchronized Cameras. IPSJ SIG Notes. CVIM 2015, 64 (jan 2015), 1–4.
http://ci.nii.ac.jp/naid/110009882584/en/
Susumu Yamamoto, Hidenori Tanaka, Shingo Ando, Atsushi Katayama, and Ken
Tsutsuguchi. 2014. Visual SyncAR: Augmented Reality which Synchronizes Videoand Overlaid Information. The Journal of the Institute of Image Electronics Engineersof Japan 43, 3 (2014), 397–403. DOI:http://dx.doi.org/10.11371/iieej.43.397