Nobody that has seen Star Wars can ever forget the exhilerating feeling of watching the spaceships fly through space in what was the pinacle of special effects in 1977. However, now George Lucas and Industrial Light and Magic are investing $10 million to recreate the Star Wars trilogy in special editions to be released in 1997. Almost all of the ships from the previous films will be replaced with computer generated vehicles. Which raises an interesting question: which works better? Hand-built models or computer graphics?
As in just about any effects shot, with models it's the details that count. Model builders, computer or otherwise, will spend hours working on the smallest items to bring the level of realism to the highest possible. After all, an audience will quickly get bored with an object if there isn't anything interesting to see after the first look. Details are a big part, and it's relatively easy to modify a hand-built model with a small piece from a battleship model, or other off-the-shelf set. However, computer graphics people can't do that. A little spray of paint for the model builder is several days of drawing textures and then applying them for the computer people. A quick dent in the plastic will translate into a couple hours of reworking the wireframe, and then rerendering the entire object. If it's one large, static model you're trying to build, a hand-built model will probably be the fastest, easiest and cheapest. But once you begin to grow beyond just the one model, the pros begin to move toward the computer's side.
When creating the large number of spaceships for his Star Wars films, Lucas had a couple of options to make the large space battles come to life. The first was much more time consuming: he could have the effects people build a different model for each craft. Or he could take a quicker and cheaper way, and take numerous shots of the same model, or a small number of models, and composite them together to make it appear as if there were a number of ships flying about. But there are problems with both of these approaches. To build a large number of models is expensive and takes time. But to shoot just a few models limits what the audience is seeing, and to pull off such an effect, the camera couldn't stay on one ship too long, or the viewers will realize it's the same ship over and over.
The 1977 release of Star Wars, using models
The problem is further complicated by lighting. To get a certain level of lighting on one ship is not a problem; just position a light and let the camera roll. But to get the lighting to fit the same on hundreds of ships is almost impossible. Small flaws quickly become amplified, and the shot becomes transparent. Computers can solve the lighting problem and the difficulty of creating numerous ships.
By taking the original model on the computer and replicating it several times, a graphics artist can make small changes on each of the wireframes to keep the ship from looking the same, and then combine the models into the same shot with a static light source. This ensures that all the models will have the same amount of shading, as if they were all being filmed at the same time.
A new image from the Star Wars Special Edition, using CG
Computer models also allow for a much greater degree of maneuverability. Rather than needing to reposition the wires and bars that keep a hand-built model in place, and then moving the camera to keep the shot right. With a computer model, moving the wireframe to fit the request is faster and easier. And rather than needing to set the camera on a robotic arm and move it past the model, often resulting in a blocky effect, a computer can simulate a path of motion for a ship and execute it numerous times without error or need for adjustment. Computer generated ships can also be manipulated to fit the constraints of gravity and centripital force. Mathematical models guarantee that a tight turn by a fighter plane will look as if the ship were turning in real life.
[Image courtesy of the VFXHQ]
For the most part, models and computer graphics each have their pros and cons. They work best when put together. A prime example is a certain shot from Twister. A oiltanker was scripted to fly down from the sky and then explode ahead of the character's truck. A CG rendered tanker was created to fly from the sky, and a large full scale model was built to drop in front of the truck and explode. A perfect combination of two technologies, the scene comes off flawlessly.
To conclude, each technique has it's own uses. Computers are quickly replacing what models used to do, but the models still have a position to fill. Until the next generation of computer artists works out the kinks in 3d rendering, we'll continue to see a small version of the White House exploding on screen, and we'll still be content.
Star Wars: Special Edition
Visual Effects HQ: Star Wars Special Edition
Computer Effects: Creatures, Twister
Visual Effects HQ: Independence Day