Character Animation Faces

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Character AnimationFaces

• Computer Animation SS2008

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Facial Modelling

• Body components are often modelled using spline
  meshes
• Splines (bi-cubic paramaterized equations)
  capture the curvature of surfaces

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The Basic Technique
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Create a Flat Mask

• Images can be used as templates for designing a
  character
• This is called rotoscoping
• Note how more curves are included for eye sockets
  and mouth
• This is only done for half of the face

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Add Depth

• Once a flat, 2-D mesh is created using a front
  view image, various points can be raised to add
  depth
• This is called lofting
• At this stage, additional control pints and edges
  can be added

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Extend Arcs to Back

• Once this mask has been created, various curves
  are extended to form the back of the head
• Additional curves are added, to complete the
  heads mesh
• But we still only have half of a head

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Copy, Flip Attach

• Once a half head has been created, a copy is made
• This copy is then flipped along the X-axis
  (mirrored) and attached to the original half

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Skin

• Real skin is translucent
• Light is scattered through the various layers,
  and reflected from a sub-layer
• Bidirectional reflectance distribution
  functions(BRDF) are often used

BRDF
No BRDF
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Hair

• Difficult to model
• Techniques
• Individual hairs
• Hairs groups (clumps)?
• Particles
• Surface with texture mapping

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HairHair Groups

• Hairs are divided into groups
• Each group is controlled by a singe vector
• In addition, hairs can be wavy/straight,
  thick/thin, etc.

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HairHair Groups

• A wet appearance can be achieved by clumping
  hairs in a patch

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Clothing

• Difficult to model
• May require physical model
• Techniques
• Surfaces with texture mapping
• Individual threads
• Others

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ClothTypical Model

• Section of cloth is modelled as a polygonal mesh
• Edges are modelled as springs
• Cloth is allowed to fall until a position of
  least energy is attained.

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Facial Expressions

• Facial Action Coding System
• Points on face are keyed to underlying muscles

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Facial Expressions

• Inner Brow RaiserFrontalis, Pars Medialis
• Outer Brow RaiserFrontalis, Pars Lateralis
• Brow Lowerer Depressor Glabellae Depressor
  Supercilli Corrugator
• Upper Lid Raiser Levator Palebrae Superioris
• Cheek Raiser Orbicularis Oculi, Pars Orbitalis
• Lid Tightener Orbicularis Oculi, Pars Palebralis
  
• Lips Toward Orbicularis Oris Each Other
• Nose Wrinkler Levator Labii Superioris, Alaeque
  Nasi
• Upper Lip Raiser Levator Labii Superioris, Caput
  Infraorbitalis

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Acting Emotions

• Emotions
• Lip-syncing
• Body movement

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Emotions

• Which is
• Happy
• Surprise
• Anger
• Disgust
• Curiosity
• Note direction of movement due to muscles

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Lip-Syncing

• Motion capture
• Dots are placed at key points on actors face
• As actor speaks, dots are tracked and positions
  recorded

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Phonemes

• Mouth orientation based on vocal sounds
• Note sound groupings

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Body movement

• Synthetic motions
• Motion capture

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Synthetic Motions

• Uses either physics or simulations
• Difficult to replicate nuances of human motion
• Often requires exaggeration to compensate

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Motion Capture

• Actors wear either markers or actuators to record
  either positional or rotational data,
  respectively
• Also called performance capture