Graphics Reference
In-Depth Information
Capton: Matchmoving has always been a visual effects problem, anytime you have
CG objects. In the early days they shot a lot more plates that were just static, so you
didn't have to worry about camera tracking as long as you got the perspective right.
When I first started in the industry, they didn't have these automatic camera track-
ing programs. You had to do it by hand, starting with the background plate, and just
manually put the camera in by eye, trying to match the motion of different features.
What now takes a simple program an hour to do would take weeks.
I remember an old commercial I worked on to advertise an SUV. The idea was
to show the SUV in place of a lifeboat on a cruise ship, to get across the idea that
it was so safe. They shot the
Queen Mary
with a fairly long lens, using a passing
shot to make it look like it was traveling through the ocean. That was a really long
shot, like 900 frames. It took three or four weeks to do a solid matchmove to put
that SUV into the plate and make it not move or shake. I was lucky enough to find
a book about the ship that had actual drawings of the rigging that held the lifeboats
in place, which helped a lot in figuring out the real shape, size, and dimensions of
things.
It was very tedious; you'd position the camera in space in the first frame, rough
in the shot and go twenty frames more, and then try to position the camera in space
again, and do that over the entire shot. Then you'd go back and fill in the moments in
between and the moments in between until the track was good enough. Depending
on how bad the camera move is, you might be doing it frame by frame through the
whole thing. Often you'd get to a point doing it by eye and then notice that it wasn't
working— you were slowly falling off to one side or the camera was doing something
it shouldn't have, and you had to throw that out and start again. It was terrible!
Nowadays, you'd be able to run that kind of shot through a piece of commercial
software and it would give you, if not an entirely solid track, something good enough
that you could tweak a little bit by hand to get the final result. On the other hand,
that early tedious experience is beneficial tome, since when the commercial software
doesn't work or I need to improve its result, I have that background of being trained
to do it by eye. Some other people have only ever known commercial software, and
if it doesn't track something they're like, “Well, I can't do anything.” No, you can try
and do it by eye!
RJR: Can you describe how an artist interacts with a matchmoving program to track a
difficult shot?
Capton: These days, it's great that there are a variety of commercial softwarepackages
for camera tracking. There's
boujou
,
PFTrack
,
SynthEyes
, and several more. I've found
that if oneprogramdoesn't work ona shot, sometimes I'll take it into another program
and forwhatever reason that one is able to track it. Another common trickonadifficult
shot is reversing it in time and feeding it back into the program — tracking the shot
backward. Over the years, you get a sense of the best way to approach a shot. For
example, if the shot starts out with a whip pan and ends on something more stable,
you know your programmay fail since it won't knowwhat feature points to pick until
it gets to the very end, so you reverse the shot to start off with solid points. You get
accustomed to what the program likes and dislikes and learn to work with it.
