| You
might remember the classic TV show The Invisible
Man, about an English scientist, Dr. Peter Brady,
who discovered a way to make himself invisible.
Episodes featured floating coffee mugs and clothing
worn by a transparent figure. In 1959, making a
man invisible on-screen was a challenging task.
Today, it's really rather easy. In fact, with a
video mixer or a nonlinear editor, it's a snap.
The key is to use a video processing device that
has a chromakey function. |
Chroma
is the Key
Whether
you realize it or not, you are familiar with chromakey
technology. It's what TV news channels use to
place weather people in front of a variety of
computer-generated weather maps. In essence, chromakey
allows the user to select a color (any color)
in a video image and make it transparent, replacing
it with a layered image. Typically, the weather
person stands in front of a bright blue or green
wall. The bright color of the wall is electronically
selected as the "key" color.
A
neat thing about chromakey is that the electronics
involved do not distinguish between a colored
wall and a shirt of the same color. So if the
weatherman wears a shirt the same color as the
background, his chest becomes transparent, and
the viewer can see the middle-Atlantic states
right through his stomach. That's probably not
what most news stations are shooting for, but
it may be just what you need. By covering any
exposed skin (say a person's face, arms and hands)
with bright blue or green fabric or makeup, and
placing him in front of a background of the same
color, you can make your actor appear to disappear.
Hey,
Where'd He Go?
To
pull off the illusion, you'll need to choose an
appropriate environment for your invisible actor.
This location could be a computer generated "virtual"
set, a pre-recorded videotaped location or simply
a camcorder pointed at a postcard. We chose to
use two camcorders, one directed at our subject
(in the chromakey environment), the other pointed
at another wall in the same room. By placing a
small table with a few props on the chromakey
set with your actor, he'll be able to interact
with the environment, and the illusion will be
all the more believable. The important thing is
to cover not only the wall behind your actor,
but the floor he'll stand on as well. If you don't
want to paint a section of your home an ugly chroma
color, a large roll of colored paper will work
just fine. It's essential that the color of your
background and the color of the material used
to cover the actor's face and hands are the same.
Inconsistencies in color will result in poor keying
and a shoddy effect.
With
everything in position, simply activate the chromakey
feature on your mixer (or record the scenes to
tape and combine them later using a nonlinear
editor). Adjust the key-color to match the chromakey-colored
background and the actor's matching key-colored
flesh, and the effect will be complete. Your actor
is now invisible, and your viewers will go nuts
trying to figure out how you did it. See you next
time! Well, maybe.
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