Left: Room with lights switched on.
Center: Lights switched to Grace Cathedral environment. Right: User
viewing the Grace Cathedral environment on an HDR display with
We introduce a
method for actively controlling the illumination in a room so that it
is consistent with a virtual world. In combination with a high dynamic
range display, the system produces both uniform and directional
illumination at intensity levels covering a wide range of real-world
environments. It thereby allows natural adaptation processes of the
human visual system to take place, for example when moving between
bright and dark environments. In addition, the directional illumination
provides additional information about the environment in the user’s
peripheral field of view. We describe both the hardware and the
software aspects of our system. We also conducted an informal survey to
determine whether users prefer the dynamic illumination over constant
room illumination in an entertainment setting.
Active Lighting Setup
In our prototype
implementation, we focus on methods that could conceivably be used in
entertainment applications, such as gaming environments or home
theaters. We use computer-controlled LED lights that are distributed
throughout the room. All lights are individually programmable to a 24
bit RGB color. This setup allows us not only to raise or lower the
ambient light in the room, but also to create some degree of
directional illumination, which results in a low-resolution dynamic
room illumination approximating an environment-map for the assumed
viewing position. Although the light sources are located outside of the
user’s direct field of view, the directional illuminationinteracts with
objects inside the field of view, such as the monitor or the wall
behind it. The goal of our system is to illuminate the room so that it
matches a low-frequency version of the virtual scene.
Room layout for lighting system
assembled our prototype system in a separate room, approximately 15.5’
long, 9’ wide, and 9.5’ high. The lighting system consists of 24 RGB
LED lights (ColorKinetics iColor Cove), each of which can be
individually programmed to a 24 bit RGB color value. We used seven
poles with stands to mount the 24 light sources. The lights were
positioned and oriented such that they predominantly illuminated the
ceiling, as well as the walls to the left, right and in front of the
Left: Color banding of iColor Cove. Right: Smooth pattern generated
To create a
smoothly varying illumination pattern we used strong diffusers at the
light sources, which also reduce color separation of the RGB elements.
The diffuser for each light consist of 2” diameter transparent acrylic
tubing that was cut in half along its axis, and spray-painted lightly
on the outside with white plastic paint (Krylon Fusion for plastic). To
avoid internal reflection losses we used reflective film to coat the
inside of the light source.
Opened iColor Cove light source with
reflective foil and plastic diffuser.
steps are necessary in order to control the system in a way consistent
with the virtual world and the image shown on the display. Geometric
calibration is necessary to determine the positions of the light
sources relative to the viewer, and their spread, which is modeled as a
Gaussian. Photometric calibration is subsequently performed to match
white points and illumination levels between the light sources and the
Light probe images acquired for each of the 24 light sources at the
intended viewing position.
geometric calibration information, we place a reflective ball at the
intended viewer position to act as a light probe. We take photographs
with a web camera (Creative NX Ultra) while switching on one light at a
time. We then model the impact of every light source by fitting a
Gaussian to the environment map. It is centered around the direction
corresponding to the brightest point in the environment map, and its
standard deviation is chosen such as to minimize the RMS error.
To test the
concept, we conducted an user survey with a set of three experiments.
As the evaluation criterion, we chose user preference rather than other
possible criteria such as perceived realism. This choice was made due
to our primary interest in entertainment applications for the current
Left: Uniform lighting corresponding to daylight. Right: Uniform
lighting corresponding to tunnel lighting.
We tested the
preference of participants for directionally uniform illumination level
over constant room illumination with an HDR driving video. All
participants preferred or strongly preferred dynamic illumination over
a constant brightness level, particulalry compared to a dark room. This
stronger preference can be explained by the ability of the HDR display
to produce light levels that are starting to be uncomfortable in very
Left: Directional lighting
corresponding to bright windows. Right: Directional lighting
corresponding to the alter.
We then tested the
preference of participants for directionally localized illumination
changes over uniform brightness changes with a rotation interface
to explore HDR panoramas. All participants preferred or strongly
preferred the directional illumination over the uniform one. With one
exception, all participants also felt an improved sense of orientation
in the presence of directional lighting.
Low Dynamic Range Footage
Our user survey
shows overwhelming support for this concept in combination with an HDR
display: all of our participants preferred the lighting system over
constant room illumination. We believe that this combination of HDR
display and lighting system comprises the best setup, since it makes it
possible to create similar brightnesses both on the display and in the
surrounding room. Even in combination with a conventional low-dynamic
range display, the participants were predominantly positive about the
NFS driving footage. Left: Lighting corresponding to passing
streetlamp. Right: Lighting corresponding to tunnel lighting.
To test the
usefulness of the lighting system in combination with low-dynamic range
displays, the participants were shown a footage from “Need for Speed
Underground 2” on a conventional display. In this experiment, the
preference for directional dynamic illumination was very strong. One
participant found the dynamic lighting distracting in the presence of a
conventional display, but not in the presence of an HDR display. We
believe that this ambivalence is in some sense caused by the lighting
system overpowering the conventional display, which cannot produce the
same intensities as the HDR display.
We believe that the work presented here also creates a variety of
promising directions for future research. One important area is
artistic tools for content creation, in particular for augmenting
existing film material with information about directional illumination.
At the moment, we focus on entertainment-style applications, where user
preference is arguably all that matters. An interesting topic for
future work is to analyze whether the system can also be helpful in
task-oriented applications, for example ones that require navigation in
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