with water diluted with milk, is directly illuminated by the
laser pulse, entering through the bottom of the bottle along
its longitudinal axis. The pulse scatters inside the liquid;
we can see the propagation of the wavefronts. The geometry of the bottle neck creates some interesting lens effects,
making light look almost like a fluid. Most of the light is
reflected back from the cap, while some is transmitted or
trapped in subsurface scattering phenomena. Caustics are
generated on the table.
7. 2. Tomato-tape
This scene shows a tomato and a tape roll, with a wall
behind them. The propagation of the spherical wavefront,
after the laser pulse hits the diffuser, can be seen clearly as
it intersects the floor and the back wall (A, B). The inside of
the tape roll is out of the line of sight of the light source and
is not directly illuminated. It is illuminated later, as indirect
light scattered from the first wave reaches it (C). Shadows
become visible only after the object has been illuminated.
The more opaque tape darkens quickly after the light front
has passed, while the tomato continues glowing for a longer
time, indicative of stronger subsurface scattering (D).
7. 3. Alien
A toy alien is positioned in front of a mirror and wall. Light
interactions in this scene are extremely rich, due to the mirror,
the multiple interreflections, and the subsurface scattering
in the toy. The video shows how the reflection in the mirror
is actually formed: direct light first reaches the toy, but the
mirror is still completely dark (E); eventually light leaving
the toy reaches the mirror, and the reflection is dynamically
formed (F). Subsurface scattering is clearly present in the toy
(G), while multiple direct and indirect interactions between
wall and mirror can also be seen (H).
7. 4. Crystal
A group of sugar crystals is directly illuminated by the laser
from the left, acting as multiple lenses and creating caustics on
the table (I). Part of the light refracted on the table is reflected
back to the candy, creating secondary caustics on the table (J).
Additionally, scattering events are visible within the crystals (K).
7. 5. Tank
A reflective grating is placed at the right side of a tank filled
with milk diluted in water. The grating is taken from a commercial spectrometer, and consists of an array of small,
equally spaced rectangular mirrors. The grating is blazed:
mirrors are tilted to concentrate maximum optical power
in the first order diffraction for one wavelength. The pulse
enters the scene from the left, travels through the tank (L),
and strikes the grating. The grating reflects and diffracts the
beam pulse (M). The different orders of the diffraction are
visible traveling back through the tank (N). As the figure (and
the captured movie) shows, most of the light reflected from
the grating propagates at the blaze angle.
8. CONCLUSIONS AND OUTLOOK
Since the initial publication of this work numerous publi-
cations have advanced this field by improving numerical
models and introducing new, more accessible capture
technology. Heide et al.
5 and Kadambi et al.
methods of low resolution time of flight capture using in-
expensive photonic mixer devices. These new devices have
been used in different applications, for example to see
6, 13 although their temporal resolution is
still orders of magnitude lower than our system. Laurentzis
and Velten11 have recently demonstrated seeing around cor-
ners using intensified gated CCD cameras that are the state
of the art in gated viewing applications and are available for
example in military vehicles.
Optimization of the system hardware and software
requires further advances in optics, material science, and
compressive sensing. Beyond the potential in artistic and
educational visualization, we hope our work will spawn new
research in computer graphics and computation imaging
techniques towards useful forward and inverse analysis of
light interactions, which in turn will influence the rapidly
emerging field of ultra fast imaging.
Future research involves investigating other ultrafast
phenomena such as propagation of light in anisotropic
media and photonic crystals, or novel applications in scientific visualization (to understand ultrafast processes),
medicine (to image and reconstruct subsurface elements), material engineering (to analyze material properties), or quality control (to detect faults in structures).
This may in turn introduce new challenges in the realm
of computer graphics, to provide new insights via comprehensible simulations and new data structures to render transient light transport. For instance, our work has
recently inspired a novel method for the efficient simulation on time-resolved light transport,
7 while relativistic
rendering techniques have been developed using our captured data, departing the common assumption of constant
irradiance over the surfaces8 (Figure 9).
Belen Masia would like to acknowledge the support of the
Figure 9. Our work has inspired follow-up work in the field of
computer graphics with the development of simulation
frameworks departing the assumption of infinite speed of light
(top, time-resolved rendering using our peak time visualization
of a volumetric caustic),
7 including the simulation of relativistic
effects due to ultrafast camera motion (bottom, simulation of
frames recorded by an accelerating camera in a scene captured
using our system).