CS 551/651Advanced Graphics

Introduction to Animation

Technical Background

Principles of Computer Animation

• John Lasseter, "Principles of Traditional Animation Applied to 3D Computer Animation", Computer Graphics, pp. 35-44, 21:4, July 1987 (SIGGRAPH 87).

• Ollie Johnston and John Lasseter, Course 1 at SIGGRAPH 94, "Animation Tricks".

Comments from LasseterKeyframing

• Computers are stupid– Worst case, keyframe require for every frame

• John discovered that some degrees of freedom (DOFs) require more keyframes than others to look natural

• You must start with a clear idea of the motion you desire

• Plan actions with thumbnail sketches and plot timing on exposure sheet

• Refer to sketches/timing frequently

Lasseter: 2-D vs. 3-D

• Native computer character is 3-D– Sometimes makes it harder

• A character’s hand may go through its body when seen from a certain angle

– Sometimes makes it easier• Animation reuse: An animation may look very

different when seen from different locations

Lasseter: Weight and Size

• Rendering can make realistic-looking objects (marble, feathers, steel)

• Good rendering benefits are lost if animation is poor

• Physics matters – heavy things take longer to start/stop moving…

• Proper timing/spacing of poses is more important than the poses themselves

Lasseter: Weight and Size

• See videos on desktop

Lasseter: Thinking Character

• Every motion must exist for a reason– Mood– Personality– Attitude

• You must convey the character’s thoughts to tell the story– Use anticipation

Lasseter: Anticipation

• Lead with the eyes– Move eyes first, with lock-in of focus a few

frames before the head– Head follows and leads the body by a few

frames– More delay implies more thought required

• Use this relationship as a tool

– External forces cause opposite timing relationship

Lasseter: Moving Holds

• Traditional 2-D animation permits “holds”– Reuse of one drawing for multiple frames– This is one way to control timing

• In computer animation action dies immediately– Perhaps due to realistic rendering and

smooth animations

• Eye picks it up every time

Lasseter: Moving Holds

• Have some part of the character continue to move in same direction during holds

• Remember to coordinate realism of character to realism of motions– More realistic characters (rendering style and

dimensions) require more realistic movements– This rule limits the straightforward reuse of human

facial mocap for non-human 3D characters

Lasseter: Emotion

• Character’s personality conveyed through emotion• Emotion dictates animation pace• Distinguish emotional state of two characters

through contrast in movement– No two characters perform same action in same manner

Lasseter: Readability of Actions

• To make sure an idea or action is unmistakably clear, the audience’s eye must be led to the right place at the right time– Timing

• Not too slow or audience eyes wander• Not too fast or action is misunderstood• The faster the motion, the more critical it is to

make the audience focus on it

Harold Whitaker and John Halas, Timing for Animation, 1981

Lasseter: Readability of Actions

• To make sure an idea or action is unmistakably clear, the audience’s eye must be led to the right place at the right time– Staging

• Audience can only see one idea at a time• Object of interest must be contrasted

against rest of scene–Pick strongest and simplest technique

–Ex: Still object vs. busy background

Lasseter: Readability of Actions

• To make sure an idea or action is unmistakably clear, the audience’s eye must be led to the right place at the right time– Anticipation

• First action should not be brought to complete stop before starting second

• Slight overlapping preserves flow• Ex: Luxo Jr.

Lasseter: Story Tricks

• Animation must be timed to stay slightly ahead or behind audience’s understanding– Ahead conveys suspense and surprise

• Initial scene of Luxo Jr. where Dad is surprised by ball

• Closing scene of Red’s Dream

– Behind reveals the story to the audience before a character to convey character’s discovery

Lasseter: Ask Why

• Why is this here?• Does it further the story?• Does it support the whole?

– Change of shape shows a character is thinking– “It is the thinking that gives the illusion of life.

It is the life that gives meaning to the expression”1

– “It’s not the eyes, but the glance – not the lips, but the smile”2

1. Frank Thomas and Ollie Johnston, Disney Animation – The Illusion of Life, 1981

2. Saint-Exupery, Wind, Sand, and Stars, 1932

Johnston Notes

• Use attitudes and actions to illustrate ideas and thoughts, not words and mechanical movements

• Squash and stretch the entire body for attitudes– Preserve volume– Useful for face too

Johnston Notes

• Change of expression and dialog are points of interest – don’t move head too much

• Concentrate on drawing clear, not clean• Everything has a function – know why• Let the body attitude echo the facial• Find best part of character’s pose to

squash and stretch

Johnston Notes

• The eye is pulled by the eyebrow muscles• Get a plastic quality in the face

– Cheeks, mouth, and eyes

• The audience has a difficult time reading the first 6 – 8 frames

• Actions can be eliminated and staging “cheated” if it simplifies the picture you are trying to show and it doesn’t disturb the audience

Johnston Notes

• Spend half your time planning your scene and the other half animating

• How to animate a four-legged walk:– Work out acting patterns with squash and

stretch in body, neck, and head– Animate the legs– Adjust up and down motion of body

according to legs

Anticipation

• Can be anatomical– Swinging your foot back before kicking

• Device that attracts viewer’s attention– Staring off camera until character enters at

that position

• Can help convey mass. More wind-up or concentration implies increased scale

Staging

• Contrast is powerful staging technique– Motion is one example– Original Disney characters were black and

white (no grayscale)• Important motions had to be drawn in silhouette

because limbs passing in front of others were not easy to see

• Even when grayscale (and color) is possible, silhouette makes actions more visible

Follow through and Overlapping Action

• "It is not necessary for an animator to take a character to one point, complete that action completely, and then turn to the following action as if he had never given it a thought until after completing the first action. When a character knows what he is going to do he doesn't have to stop before each individual action and think to do it. He has it planned in advance in his mind."

Walt Disney

Ease-in and Ease-out

• A facsimile of physics– First, second, and third order continuity– Remember challenges getting splines to

interpolate endpoints

Production Line

• Film Sequences Shot/Scene Frames• Preliminary story Script Storyboard• Model Sheet

– Multiple drawings for each character

• Exposure Sheet– Sound track cues, camera moves, and compositing

info for each frame

• Route Sheet– Personnel responsible for each scene

Production Line

• Animatic or Story reel– First pass at motion

• Scratch track– First pass at audio (music, special fx, dialog)

Who Does What

• Story Department: build the storyboard• Art Department: build consistent look to

coloring, lighting, models• Modeling Department: build character

and prop models. Give character’s hooks that animators can use to move

• Layout Department: build 3-D world for staging and blocking

Who Does What

• Shading Department: builds texture maps, shaders, lighting models

• Animation Department: animate• Lighting Department: position lights

(hundreds) and camera to create final image

• Camera Department: I want to be a cowboy… render wrangling

Editing

• Nonlinear editing– Cut and paste frames anywhere in animation

• Film splicing• Video tape copying

– Source Destination (Assemble Editing)– Character generator and special effects– Cannot splice into middle of destination reel (linear

editing)– Industry standard: Sony BetaSP

• Frame accurate inserts• Low quality degredation

Analog Editing

• Nothing is consistent– Two decks play at different speeds (time-based

corrector / blackburst generator)– NTSC refresh signal helps to synchronize– Society of Motion Picture and Television

Engineers (SMPTE) time code is absolute 8-digit tag that is pre-striped onto the tape (the parts of the visual image TVs don’t show)

• Underscanning reveals

– Insert Editing allows flexible selection of insert points on destination tape

Digital Editing

• Frames are always represented digitally (no degeneration)

• Infinite compositing• 21Mb/sec required for playback• 1 hour of video = 76 Gb of storage• D1 and digital Betacam are industry

standard• Digital to analog or film?

Animation Heritage

• 1963 – Ivan Sutherland’s (MIT) Sketchpad• 1970 – Evans and Sutherland (Utah) start

computer graphics program (and Co.)• 1972 – Ed Catmull’s (Utah) animated hand

and face (later co-founded Pixar)• 1970’s – Norm Badler (Penn) Center for

Modeling and Simulation and Jack

Animation Heritage

• 1970’s – New York Institute of Technology (NYIT) produced Alvy Ray Smith (Cofounded Pixar and Lucasfilm) and Catmull

• 1980’s – Daniel and Nadia Magnenant-Thalmann (Swiss Universities) become European powerhouses

Animation Heritage

• 1980’s – z-buffer invented, SGI founded, and Alias/Wavefront founded

• 1977 – Starwars• 1982 – Tron (first extensive use of gfx)• 1982 – Early use of particle systems

(Star Trek II: The Wrath of Khan)• 1984 – The Last Starfighter (look for the

Cray X-MP in credits)

Animation Heritage

• 1986 – Young Sherlock Homes (first use of synthetic character in film)

• 1986 – First digital wire removal (Howard the Duck)

• 1988 – First digital blue screen extraction (Willow)

• The Abyss (1989) Terminator II (1991) Casper (1995), Men in Black (1997)

Animation Heritage• ILM: Jurassic Park (1993), Jumangi (1995), Mars

Attacks (1996), Flubber (1997), Titanic (1999)• Angel Studios: Lawnmower Man (1992)• PDI: Batman Returns (1995) • Tippett Studio: Dragonheart (1996), Starship

Troopers (1997)• Disney: Beauty and the Beast (1991), Lion King

(1994), Tarzan (1999)• Dreamworks: Antz, Prince of Egypt• Pixar: Toy Story, A Bug’s Life, Monster’s Inc.

Homework

• Download FLTK 1.1 (pronounced Fulltick)– www.fltk.org

• Compile visualc directory

• Get cube rendering program working

• We’re going to use fltk to build user interfaces for our OpenGL/glut programs