In the following article, it is my intent to show you how to adapt conventional filmbased traveling matte and motion-control techniques for use in the 3D world using some wonderful freeware applications provided by some very generous folks in cyberspace. I know that I am in good company amongst the readers when I call myself a, “film geek,” having spent much time and energy watching special-effects intensive movies and intently thinking, “How did they do that?” Having said that, I’d like to talk about the conventional traveling matte technique that has been used in film for several decades, in one form or another. This will also help you to see who I, “stole,” the idea from! A number of different techniques have been used, but I will be discussing what is commonly known as the, “bluescreen technique,” followed by some explanation of the motion-control technology used to create complex traveling matte scenes with many levels of action. Afterwards, we’ll take these time-tested techniques into the digital world and make them work for us 3D “geeks.”
The special effects in the first Star Wars movie were quite an amazing technological feat at the time. The film industry had been using traveling mattes for a long time to produce scenes of foreground action in front of backgrounds that would have otherwise been difficult, unsafe or downright impossible to do on location. But at the behest of director George Lucas, John Dykstra, the genius behind the special effects powerhouse Industrial Light & Magic, took the traveling matte process to a whole new level of sophistication.
The conventional film-based process starts by filming an actor or a model (the foreground subjects) in front of an evenly lit pure blue or green screen, which will be removed later in post-production. Blue or green is used because they are least likely to be color components of the foreground subjects (usually an actor) and therefore won’t leave, “holes,” in them when that color is removed. Care also must be taken not to have any of the blue or green color reflect onto the subject, otherwise it will leave a visible line, or “halo,” around the subject in the final scene. In the processing laboratory, the foreground footage is passed through a series of colored filters and printed onto black and white film, ultimately creating a black background with a traveling, “hole,” and a “traveling matte,” or a moving black opaque mask in the shape of the subject with a clear background where the blue/green used to be.
The opaque traveling matte and the desired background footage (or “plate”) are then run through what the film industry refers to as an optical printer and onto a negative. So now we have a negative of the background with another traveling, “hole.” Now we take the original traveling hole with the opaque background and run it thought the optical printer with the bluescreen foreground footage onto a negative. Now we have two negatives: the foreground negative with a clear background and the background negative with a traveling hole in front of it. These two are run through the optical printer to get the final product of the moving foreground subject in front of the background footage.
As you can imagine, this is not a cheap process, especially with 35mm film! (Now you can see why a “low-budget film,” can run into the tens of millions of dollars, even in the 1970’s!)
Now imagine George Lucas coming along and saying to John Dykstra, “I have this scene that calls for an entire squadron of tie-fighters to fly in formation through space.” Well, being an inventive kind of guy, Mr. Dykstra came up with a computer-controlled camera, which would record and repeat its own movements (this was state-of-the-art technology at the time and was NOT an inexpensive project!) This computer-controlled camera (starting at different points) was used to make multiple passes on the same model in front of a bluescreen and then each pass was layered on top of one another using the previously explained traveling matte process, thereby giving the illusion of a squadron of space vessels flying in formation. Keep in mind that the model, generally speaking, is kept completely stationary and all of the motion is done with the camera: the truck, pan, tilt, crane, etc. This type of filmmaking requires a lot of choreography!
These days, a lot of TV shows and movies not only have their special effects done digitally in post-production, but more and more are actually being shot using digital formats (George Lucas strikes again!) Additionally, many of the subjects and some of the, “live-action,” characters you see on film and TV are merely animated 3D models. Sam Raimi’s Spiderman and Spiderman 2 (again, the special effects were done by John Dykstra!) had extensive CGI character footage, in addition to blue/green screen composite scenes.
Here comes the part we’ve all been waiting for, how WE can a make a traveling matte! You can use any 3D program that you want as long as it can render alpha channels for the animation. An alpha channel is simply the digital version of a matte (traveling for movies or stationary for stills); it is a black mask in the shape of the foreground subject, moving frame by frame exactly as the subject does. In my case, I am using Anim8or, a program by Steve Glanville, to model, animate and render my foreground subject and for my background, as well. I will be discussing the techniques from this perspective, because that is what I know. I hope that you’ll be able to adapt these techniques for use in your particular situation. I am using Wax, courtesy of Satish Kumar, as my, “optical printer,” for layering each camera pass on top of the background. I will list links to these applications under the resources section at the end of this article.
There’s no reason not to go wild with creativity. Heck, use rotten tomatoes instead of laserships! Have them spitting seeds instead of lasershots! Animate as many as you want, make them do a dance, like the Air Force’s Blue Angels!
If you have any questions or comments (even something like, “You don’t know what you’re doing!” would be fair game) please feel free to email me at the address given at the top of the page.
If there is an easier way to layer multiple traveling mattes, then please let me know. And if I have unintentionally made anything unclear, please tell me so I can tweak this article accordingly.
Thanks For Reading,