HOLLYWOOD鈥橲 special effects will become even more realistic, thanks to a
lighting rig that can automatically recreate the illumination of any location,
researchers told the conference last week. It will reproduce the flash of light
from an explosion reflected on the face of the actors, for example.
Directors often film actors in a studio and then superimpose them on a
separately shot scene. Film crews have become so good at this long-established
technique that it is almost impossible, say, to tell that Keanu Reeves鈥檚
martial-arts feats in The Matrixwere filmed in a studio and not on top
of a towering skyscraper.
The technique works best when the ambient light is consistent, such as
backgrounds shot on cloudy days outdoors. The studio crew simply lights the
actor evenly from all sides. But when the scene features different colours of
light coming from various directions鈥攕uch as the light in a cathedral with
stained-glass windows鈥攅xisting lighting techniques fall short.
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To solve the problem, Paul Debevec from the University of Southern
California鈥檚 Institute for Creative Technologies in Marina Del Rey has developed
a lighting rig called Light Stage that automatically recreates the natural
lighting of any location. Before using Light Stage, a technician visits the
background location and measures the lighting during filming.
Back in the studio, the lighting crew feeds the digitised light data into
Light Stage鈥攁n egg-shaped cage with several small LEDs mounted at each
vertex to illuminate an actor standing in the middle. A computer then controls
the LEDs to illuminate the actor鈥檚 face with precisely the same lighting as the
background.
鈥淭he Light Stage 3.0 allows us to show an actor under a variety of lighting
conditions,鈥� says Debevec, who worked with Andreas Wenger from Brown University
to develop the apparatus. Previous versions used moving lights that swung around
the actor, but the egg-shaped LED array gives by far the most convincing
results, says Debevec.
In a demonstration at the conference, Debevec used Light Stage 3.0 to
recreate the lighting of a San Francisco cathedral on a person inside the cage.
Yellow light, as if reflected by the gold-coloured altar, cast a warm glow on
the face from the right, while greens and blues that could have been streaming
through a stained-glass window illuminated the face from the top left.
鈥淭his will change the way people create special effects in feature films,鈥�
says Jamie Waese, a former Hollywood producer who now works for the University
of Southern California. The next step is to build a larger version of the Light
Stage鈥攖he current version is only big enough to capture the head and
shoulders. Directors will want a cage large enough to contain several actors and
some serious action.
