Fundamentals of Computer Animation

Wrap-up Overview

Animation

• Timeline in Movies

• Conventional Animation (Techniques/Process)

• Role of the Computer

• 3D Animation

Reading:Jessica K. Hodgins and James F. O'Brien “Computer Animation”(check web site)

Timeline The Illusion of Motion

• 1824, Peter Mark Roget,"Persistence of Vision with Regard to Moving Objects“

• a series of images shown in rapid sequence can appear to move fluidly (i.e. a flip book or film projector)

Timeline Movies

• (1895) age of movie camera and projector begins– experimentors discover they can stop the crank and restart it again to

obtain special effects

• (1914) Gertie, Windsor McCay (newspaper cartoonist)– first popular animation

• (1928) Steamboat Willie, Disney– an early cartoon w/ sound– cartoons seem plausible as entertainment

• (1933) King Kong, Willis O’Brien

• (1930’s & 40’s) Golden age of cartoons– Betty Boop, Popeye, Porky Pig, Daffy Duck, Bugs Bunny, Woody

Woodpecker, Mighty Mouse, Tom & Jerry

• (1937) Snow White, Disney– animated feature film– cost is $1.5M

Timeline Movies (cont)

• (1982) Tron, MAGI– movie with a computer graphics premise

• (1984) Last Starfighter– computer graphics was used interchangably with actual models of the

spaceship

• (1993) Jurassic Park– computer graphics is used to create living creatures that are meant to

appear realistic

• (1995) Toy Story, Pixar– full-length feature film done entirely with 3D computer animation

• (2000) CyberWorld 3D, IMAX– 3D IMAX full-length feature film including characters from popular 3D

movies such as ANTZ and The Simpsons’ Homer

Conventional Animation Techniques

• Drawing on film• Multiple drawings• Rotoscoping (project film of real actors

onto drawing paper)• Stop motion animation• Acetate cels, multiple plane cells

Conventional Animation Process

• Storyboard• Key frames drawn

– Straight ahead vs. pose-to-pose

• Intermediate frames filled in (inbetweening)

• Trial film is made (called a pencil test)

• Pencil test frames transferred to cels

Conventional Animation Process

Role of the Computer

• In-betweening– artistic example: Hunger, Peter Foldes 1974

• Disney’s CAPS system– scanned artist drawings are read in– "cels" are colored online (broad color palette, exact color matching)– compositing is done online (background, 2D drawings, 3D animation)– 3D effects can be created with 2D drawings (e.g. Beauty and the

Beast)– used in every film since Beauty & Beast

• 3D graphical worlds– can experiment more easily with actor position, camera position– can perform more complex camera moves– exchange labor to create drawings with labor to build and animate 3D

world

3D Animation

• 3D animation is similar to stop motion animation

King Kong (1932)

Flash Gordon (1972)http://www.stopmotionanimation.com/

3D Animation

• Stop motion animation (Nightmare Before Christmas)

• 3D keyframing(Luxo Jr.)

• Performance animation and motion capture (Donkey Kong Country)

• Which must be done straight-ahead and which can be animated pose-topose?

Keyframing• Key frames mark important visual transitions

(extremes of action)• Inbetweening is creation of intermediate frames

between the key frames• Can easily be calculated by computer

Temporal Sampling

• Film recording takes samples of an image at fixed time intervals– 24 frames per second for film– 30 frames per second for video

• human eye "sees" continuous motion

Sometimes, fewer keyframes are required to describe the motion, especially for “pencil tests” or rough choreography (e.g., Lost World)

• No internal energy source and move only when an external force acts on them.

• Read for use when: – physical laws encoded – initial conditions specified

• Pools of water, clothing, hair, leaves

Smooth Motion (1) Passive Physics

• Clothing (Geri’s Game)

• Water (Antz)

• “Rigid” body physics (crashing space pods in Phantom Menace)

Geri’s Game, Pixar Animation Studios

Smooth Motion (3) Passive Physics

• User specifies keyframes (start, end, middle)• User specifies constraints (e.g. laws of physics)• System searches for minimum energy motion to

accomplish goals

A. Witkin and M. Kass,“Spacetime Constraints”,SIGGRAPH ‘88.

Smooth Motion (2) Active Physics

Smooth Motion (3) Active Physics and Simulation

• Control an animated character as we would control a robot

• behavior is simulated

• a "control system" sends proper signals to the character’s "muscles" over time

Mark Raibert’s leg lab at MIT

http://www.ai.mit.edu/projects/leglab/

Noise Motion• We generally don’t want motion to be too smooth• The eye picks up symmetries and smooth curves and

interprets them as artificial or fake• By adding noise, we can add texture to smooth motion

K. Perlin, “An Image Synthesizer”,Computer Graphics, 19(3), July 1985.

Perlin, Improv system(K. Perlin and A. Goldberg, SIGGRAPH ‘96).

Applets: http://www.mrl.nyu.edu/~perlin/

Noise Motion

• Motion capture (natural noise!)