Eurographics Symposium on Rendering (2005)
Kavita Bala, Philip Dutré (Editors)
A Dual Light Stage
Tim Hawkins, Per Einarsson, and Paul Debevec
USC Institute for Creative Technologies
We present a technique for capturing high-resolution 4D reflectance fields using the reciprocity property of light
transport. In our technique we place the object inside a diffuse spherical shell and scan a laser across its surface.
For each incident ray, the object scatters a pattern of light onto the inner surface of the sphere, and we photograph
the resulting radiance from the sphere’s interior using a camera with a fisheye lens. Because of reciprocity, the
image of the inside of the sphere corresponds to the reflectance function of the surface point illuminated by the
laser, that is, the color that point would appear to a camera along the laser ray when the object is lit from each
direction on the surface of the sphere. The measured reflectance functions allow the object to be photorealistically
rendered from the laser’s viewpoint under arbitrary directional illumination conditions. Since each captured re-
flectance function is a high-resolution image, our data reproduces sharp specular reflections and self-shadowing
more accurately than previous approaches. We demonstrate our technique by scanning objects with a wide range
of reflectance properties and show accurate renderings of the objects under novel illumination conditions.
Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Capturing Real-World
Data for Rendering
Image-based relighting techniques simulate novel illumina-
tion on a subject based on images acquired in different basis
lighting conditions. Most commonly, the basis images of the
subject are taken under a discrete set of directional light-
ing conditions, and a linear combination of the basis images
formed to produce a rendering of the subject under novel
illumination. Distributing the lighting directions throughout
the sphere of incident illumination allows arbitrary distant
lighting environments to be simulated accurately.
In theory, this basic relighting process can reproduce the
full range of reflectance phenomena an object can exhibit
under distant illumination, including diffuse and specular re-
flection, self-shadowing, translucency, and caustics. In prac-
tice, however, the discretization of the incident lighting di-
rections limits the technique’s ability to accurately repro-
duce high-frequency reflectance characteristics: a shiny sur-
face reflecting a diffuse lighting environment can appear to
reflect many small light sources, and shadows cast by a mov-
ing virtual light source can appear to progress in a series of
steps rather than with continuous motion.
We present a novel technique for capturing reflectance
functions that exploits the reversibility of light transport, a
property known as reciprocity. Our device, which we call a
dual light stage, measures reflectance functions by revers-
ing the traditional roles of camera and light source. Where
a camera pixel would measure radiance along an incoming
ray of light R, we instead use a laser to send light out along
the reversed ray −R. Conversely, where a light source would
normally be placed to illuminate the object, we instead sense
the light radiating from the object toward the same direction.
We sense this reflected light by placing a diffuse spherical
surface around the object, photographing the image radiated
onto this sphere with a camera. While real cameras capture
many pixels in parallel, and real lighting conditions must be
acteristics: for a virtual camera pixel corresponding to the
current laser ray, our camera captures the response of that
pixel to all illumination directions simultaneously. From the
captured images, which represent reflectance functions, we
can produce novel renderings of the object under arbitrary
distant illumination conditions. As expected, these images
appear to be acquired from the position of the laser beam,
rather than from the position of the camera sensing the ob-
ject’s reflectance functions.
2. Background and Related Work
2.1. Image-Based Relighting
From the additive nature of light, a rendering of a scene
under novel illumination can be created as a linear com-
bination of renderings under basis lighting conditions
[Hae92, NSD94]. [DHT∗00] used a light stage device with
c ? The Eurographics Association 2005.
T. Hawkins, P. Einarsson, & P. Debevec / A Dual Light Stage
Figure 7: Renderings of three objects under the three different illumination environments shown at top. The environments are
rotated differently for each object to best demonstrate the results. The renderings demonstrate accurate reproduction of sharp
specular reflections, as well as other features of global light transport such as soft and hard shadows, caustics, and transparency
and translucency. Additional lighting conditions including sharp directional lighting are included in the video.
c ? The Eurographics Association 2005.