All animation is based on an optical illusion, a trick played on your eyes. Anyone can try it: Just draw a walking stick figure on a notebook page and then draw the same stick figure on the next page, about to take another step. Repeat this enough times and when you later flip through the notebook rapidly, it seems as if the stick figure moves by itself. If done right, your eye and your brain simply cannot distinguish one image from the next separately, and thus create an illusion of motion from one drawing to the next. This is called "persistence of vision."
Drawings trying to capture motion have existed for millennia, from cave paintings to ancient Egyptian drawings to Victorian-era toys like the "bird in a cage" rotating disks which were popular in the 1800s. However, animation as we know it didn't come about until the advent of motion pictures at the end of the 19th century. By sketching several drawings, each slightly different from the next, and photographing each image or "frame," the resulting footage would then run through a projector at 24 to 30 frames per second, perfecting the illusion of motion. In this time-consuming manner, pioneers like Winsor McCay produced cartoons like "Gertie the Dinosaur" (1913).
The development of celluloid in 1913 made the animation process less time-consuming and labor intensive, and paved the way for hand-drawn animation for the rest of the 20th century. Celluloid allowed artists to render separate background and foreground sheets and animate hand-drawn characters over it on a third, transparent sheet. Techniques using celluloid further lowered costs when animators figured out they could use different sheets for different parts of a character. This way, they could animate a cartoon character's mouth when it was talking, while the rest of its body remained static. United Productions of America (UPA) first took up this method of "limited animation," and several other studios adopted it following the arrival of television and its "voracious appetite for rapidly produced product," according to Richard Williams, director of animation of the film "Who Framed Roger Rabbit?"
Together with celluloid and with tricks of perspective using detailed backgrounds, artists further reinforced the illusion of a three-dimensional, immersive world. Walt Disney in particular took advantage of this technique in the first animated feature film, "Snow White and the Seven Dwarfs," released in 1937 to resounding success. Disney also pioneered the usage of sound in hand-drawn cartoon shorts with the release "Steamboat Willie" in 1928 and "The Skeleton Dance" soon after.
Before long, countless productions became popular among young and old. Among these were the Max Fleischer cartoons, which were ground-breaking for their era; and the Merry Melodies and Looney Tunes series of shorts from Warner Bros., which employed such animation legends as Friz Freleng, Chuck Jones and Tex Avery. William Hanna and Joseph Barbera also became successful with their own series of cartoon shorts for kids. "At the same time there was a worldwide flourishing of personal, experimental and 'art house' animated films made in new ways with many different techniques," says Williams. Japanese animators also imparted their unique touch on animation--or anime, as people in Japan call it. Osamu Tesuka broke open the doors of Japanese animation and later on, Hayao Miyazaki would take the conceits of anime to new artistic heights. In recent years, Bill Plympton, Mike Judge, and Bruce Tim, among others, have made their mark on 2-D animation's continuing evolution.
However, the arrival of computer animation and specifically three-dimensional (3-D) animation has prompted another revolution in the last few decades, taking definite hold ever since Pixar Studios released the first fully computer animated feature, "Toy Story," to box-office gold. Since then, 3-D computer animation has been utilized in many successful animated movies and has become a fixture in live-action, effects-heavy productions. Despite the current ubiquity of 3-D animation, 2-D methods are far from dead, being used on several successful TV shows like "The Simpsons," "South Park" and "Family Guy." Even 3-D-animation mavericks like "Toy Story" director John Lasseter sing the praises of 2-D animation and have taken a hand in the production of new, hand-drawn animated features.