Specifications

A flying saucer descends onto an open field and lands,
kicking up dust all around it. If this happened in a remake
of The Day the Earth Stood Still nobody would blink. But
imagine that instead of a big beautiful image executed with
the precision and care of a big-budget feature, what you’re
watching looks like it fell on the cutting-room floor of The
Blair Witch Project. You’re not seeing this in a comfortable
screening room at your local cinema, where the picture
is clean, sharp and bigger than life, but rather you’re
standing gathered around a booth at your local science-
fiction convention. The guy playing the video isn’t a producer.
He isn’t even an independent filmmaker. He’s a guy who’s
genuinely convinced that this video can’t be faked. If it
were, he says, the seams would show, and whoever gave
this to him really did record evidence of alien visitation that
the government is covering up, and that by showing this
publicly, he’s taking a terrible risk. But, he feels he must
expose the fraud that governments and aliens perpetrate
on unsuspecting citizens!
This scenario may sound like it clawed its way out of
the X-Files’ wastebasket, but as VisualFX technology gets
ever cheaper and more ubiquitous, faking a video like this
becomes no problem. Of course, it takes a lot of expertise
and dedication to get the colors, shadows and reflections
to match convincingly. One would think that getting the
movement to match as the camera person runs and zooms
with a handheld shot would be the most difficult part of
the equation. Once upon a time, this was true.
It used to be that the only way you could achieve the
movement precision necessary to sell an effect like this was
to put your camera on a motion control rig and have a
computer record the movements in the field and then
reproduce them exactly (though to a smaller scale) in the
post house where the artificial elements (in our case, the
flying saucer and the dust) were photographed. Aside from
being very cumbersome and expensive, this approach
sharply limited the kinds of shots that an FX artist could do
to those that could be reproduced by an electric gimbal
and a prime lens.
No longer. The late 1990s saw a great flowering of
research and development into the area of computerized
match moving—matching the movement of different visual
elements so that they appeared to exist organically in the same
scene. Putting the computer in the mix both at the match
moving and at the compositing stage gives a lot more control
and freedom than previously.
Why Use Match-Moving Software at All?
Human visual acuity isn’t the best on the planet, but it is
startlingly good. With a little practice, an ordinary fellow
sitting in the audience for The Matrix can spot the grain
mismatch in shots that were too hastily done. Our visual
cortex does the differential calculus to tell us “this doesn’t
belong here”. It follows that this same mental apparatus
could be employed to create the trickery in the first place.
With most VisualFX work, there are complicated tools, and
then there is doing it by hand. Like most other fields of
human endeavor, the better an artist is, the fewer training
wheels he or she generally will rely on. So, why not do
match moving by hand?
The short answer is that many artists do, under some
circumstances. Other times, there is an interaction between
the artist and the match-moving software, with the artist
choosing points for the software to track, either because the
tool doesn’t detect the right points, latches on to points that
aren’t appropriate or doesn’t do point detection at all.
However, the art of motion tracking is nontrivial.
Although our visual cortexes are excellent at detecting
error, they are somewhat less excellent at projecting per-
fection outward. We do not create grand, realistic paint-
ings naturally—indeed, we have to be taught to see light,
shadow, form and so on in a certain way in order ponder
even attempting to work like a Bouguereau or a Leonardo.
Similarly, our ability actually to distinguish motion that
doesn’t fit is quite keen, although our ability to create a
perfect motion path is coarse by comparison—something
we don’t notice until after we play it back and see the drift
creeping in even with the most careful hand-tracks.
Of course, a match-moving program won’t always get a
perfect track, but the interaction of a good artist with a good
program delivers top-notch results.
Why Get a Voodoo Doll?
Aside from the fact that it’s free, why use Voodoo for
this project?
The truth is that Voodoo isn’t going to solve every match-
moving problem, even leaving out the ultra-delicate moves
that the higher-end match movers handle better. The field of
match moving is basically divided in two: 2-D motion tracking
and 3-D camera tracking.
80 | august 2008 www.linuxjournal.com
INDEPTH
How to Fake a UFO Landing
The magic of Voodoo. DAN SAWYER
This scenario may sound like it
clawed its way out of the X-Files’
wastebasket, but as VisualFX
technology gets ever cheaper and
more ubiquitous, faking a video
like this becomes no problem.