Terror at the movies.

This summer's blockbuster special effects may have you hiding under your seats.

"It's a nightmare come true. Walking along the streets of New York City, you happen to glance up. NO! IT CAN'T BE REAL! But the monster looks terrifyingly alive. Prehistoric, 20-stories high, slime gray, and a total gross-out! Stomping cars like match sticks, crashing through buildings, scattering pedestrians for their lives. IT'S COMING RIGHT AT YOU! NOT GODZILLA???

Yes, it is Godzilla. And the only way to avoid the terror this summer is to skip movie theaters. New innovations in special effects, like super-smart computer-graphics software and robotics, make it nearly impossible to detect the difference between movie magic and a real monster.

How did a special-effects crew create a frighteningly creepy Godzilla? How do clunky robots manage out-landish moves in Lost in Space? How can astronauts in Deep Impact hook up with a comet hurling toward Earth? Read on for the inside scoop.

COMPUTER HORROR

As you watch Godzilla--this summer's remake of the '50s Japanese monster hit--you'll think there's only one mammoth mutant reptile stalking across the screen. Guess what? Visual-effects supervisor Volker Engel created three different Godzillas to scare the wits out of you.

One Godzilla is a robotic model--just a head and upper torso--about six meters (20 ft) high. The model, operated by remote control, was perfect for close-up shots of the monster trashing New York City landmarks. For long-distance shots, a second Godzilla is really an actor inside a 2-m (7-ft) tall costume, thrashing amid an exact miniature replica of Manhattan. But in more than 90 percent of the movie, the monster that'll make your jaw drop is--sorry to shatter an illusion--a computer-generated fake.

"A man in a Godzilla suit doesn't always work," Engel explains. Monstrous reptiles simply don't sashay like humans. To create the computerized version, computer animators used a 3-D scanner to scan in the 2-meter-tall Godzilla model. Laser beams from the scanner measured the distance between different parts of the model and the light source. Using these measurements, the computer plotted points on the screen. When connected, the points formed Godzilla's shape. Animators then drew a "skeleton" inside the shape--a technique called inverse kinematics.

"It's like a real skeleton with bones," Engel says. All the bones are interconnected, so when the animator moves Godzilla's finger bone, part of the monster's hand automatically responds on the computer. In turn the hand--or claw--budges part of the monster's arm.

While the animators refined the skeleton, movie scenes filmed earlier were scanned into the computer to be used as backgrounds for the animation. In one pivotal moment, an army of soldiers lure Godzilla to Central Park and unleash a barrage of gunfire. The surly monster wasn't really there during filming. (You know how temperamental stars can be!) So actors trying to quell Godzilla fired fake bullets at the Plaza Hotel across from Central Park!

To help Godzilla make his "performance," animators superimposed the "skeleton" on the film and manipulated the reptile's movements through a process called key frame animation. In every second of film there are 24 frames, or still photos that slightly differ from one other. (When a movie camera runs the frames in real time, your brain fools your eyes into seeing one continuous motion.) That means creating 1,440 slightly different Godzillas for one minute worth of film!

But with advanced computer software, an animator needs to draw Godzilla, for example, only in frames one, 12, and 24--the key frames. Say Godzilla takes a step in one second of film. The computer animator would Godzilla with both feet on the ground in frame one. Then he draws the right foot in mid-air in frame 12, and back on the ground again a few meters forward in frame 24. The computer calculates all movement in between, and fills in the other frames.

Easy as paint-by-numbers? Not quite. Because the computer uses mathematical equations to fill the in-between frames, the monster's resulting motion looks too smooth--and not believable. "We have to tweak the final images--add jerky motions--to make Godzilla seem more real," Engel explains.

Once Godzillas movements seem perfectly--and frighteningly--real, it's time to make the monster look as creepy as a prehistoric lizard. Animators render or apply textured skin on Godzilla, and add shadows to give him depth for a 3-D look. Finally, they mix in the other essential elements, like lighting to heighten Godzilla's star power. In the Central Park scene, for example, large lamps called klieg lights scan across the monster and sky. The animators digitally superimposed spots of light across the computer-made Godzilla. In all, it took nearly 16 months to perfect the reptilian horror.

REAL ROBOTS 

Lost in Space is also jam packed with computer-created effects. But the two robots--a hefty, 1,360-kg (3,000-lb) robot called Big Blue, which gets blown up in the film, and a smaller one made from Big Blue's remains--are "reel" masterpieces too.

"The robots continually interact with everything on the set," says Verner Gresty, project supervisor for Jim Henson's Creature Shop. "People actually fight the robots and jump on their backs." Because the robots physically smash their way through the spaceship, computer-generated robots wouldn't work. Gresty wanted the real thing.

To coordinate the movements of Big Blue on screen, he used four performers. Here's the setup: Offstage sits a large frame from which four wired body suits hang. To control the robot on screen, the four actors strap themselves in the body suits. Each suit controls a specific part of the 'bot, like the head or arms.

Engineers designed each suit so that it replicates all the joints in the robot's body. For example, the robot arm contains 10 joints; so does the gear that controls it. Each joint has a potentiometer, a device that measures the amount of movement in a joint and sends an electrical signal to a central computer through wires.

The computer combines all data from the different suits and transmits instructions to the robot through another set of wires plugged to the robot's back. (The production crew made sure the wires stayed out of view during filming.) So when a performer raises his left arm offstage, the 'bot lifts its left arm too--think of a high-tech marionette. "It's a more natural way of controlling a robot," says Verster. "You do what you do naturally and the robot copies it."

The tricky part is getting four performers to move in sync! They had to choreograph their movements with total precision so that the robot wouldn't fall flat on its face.

KEEP IT SIMPLE

Sometimes the oldest tricks are enough to deceive you into mistaking the fake for real. Take the stray comet hurtling toward Earth in Deep Impact.

A comet is essentially a dirty snowball streaking through space. As it nears the sun, the snow turns into a gaseous cloud called a coma, which surrounds the ball and sweeps back to form a tail. For Deep Impact, designers constructed a comet using fiberglass-like material that's both strong and translucent. Shining lights from below the fiberglass lent the comet its icy sheen.

To fake the coma, the special-effects crew pumped high-pressure carbon dioxide and oxygen through the surface from pipes below. Finally, giant fans blowing vermiculite (the same white pellets you see in potting soil) simulate chunks of snow and ice blasting off the comet.

Creating special effects can be grueling. But if the payoff works, you should be gasping and screaming all summer long. Don't forget your popcorn!

RELATED ARTICLE: Mini Frame Animator

After an image flashes in front of your eyes, your eye retains the image for 1/10 of a second. See how moviemakers take advantage of this "persistence of vision" when they use key frame animation:

WHAT YOU NEED:

23-in. x 3-in. Post-it Notes (light-colored) * pencil * tape

WHAT TO DO:

1. Stick the 2-page Post-it "stack" on your desk. 2. In the center of the bottom note, draw a standing stick figure. 3.Trace the figure's head and body on the top note. Add new arms; and legs to make jumping figure. 4.Tape a pencil to the top note as shown. 5. Roll the top note around the pencil. 6. Using both hands, roll the pencil forward and back quickly on your desk. What happens when you roll very slowly? What if you roll really fast?

CONCLUSIONS

Why does the first figure appear to jump? How could you make the figure jump more smoothly? (Hint:Why do you think key frame animators use 24 images per second?)