Skeletal animation

Computer animation technique

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
Find sources: "Skeletal animation" – news · newspapers · books · scholar · JSTOR (December 2007) (Learn how and when to remove this message)

|

Joints or bones (in green) used to pose a hand. In practice, the joints themselves are often hidden and replaced by more user-friendly objects or simply toggled invisible. In this example from the open source project Blender, these "handles" (in blue) have been scaled down to bend the fingers. The joints are still controlling the deformation, but the animator only sees the handles.

Skeletal animation or rigging is a technique in computer animation in which a character (or other articulated object) is represented in two parts: a polygonal or parametric mesh representation of the surface of the object, and a hierarchical set of interconnected parts (called joints or bones, and collectively forming the skeleton), a virtual armature used to animate (pose and keyframe) the mesh.[1] While this technique is often used to animate humans and other organic figures, it only serves to make the animation process more intuitive, and the same technique can be used to control the deformation of any object—such as a door, a spoon, a building, or a galaxy. When the animated object is more general than, for example, a humanoid character, the set of "bones" may not be hierarchical or interconnected, but simply represent a higher-level description of the motion of the part of mesh it is influencing.

The technique was introduced in 1988 by Nadia Magnenat Thalmann, Richard Laperrière, and Daniel Thalmann.[2] This technique is used in virtually all animation systems where simplified user interfaces allows animators to control often complex algorithms and a huge amount of geometry; most notably through inverse kinematics and other "goal-oriented" techniques.

## Technique

[edit]

As described in an instructional article by Josh Petty:[3]

> Rigging is making our characters able to move. The process of rigging is we take that digital sculpture, and we start building the skeleton, the muscles, and we attach the skin to the character, and we also create a set of animation controls, which our animators use to push and pull the body around.

This technique constructs a series of bones (which need not correspond to any real-world anatomical feature), sometimes also referred to as rigging in the noun sense. Each bone has a three-dimensional transformation from the default bind pose (which includes its position, scale and orientation), and an optional parent bone. The bones therefore form a hierarchy. The full transform of a child node is the product of its parent transform and its own transform. So moving a thigh-bone will move the lower leg too. As the character is animated, the bones change their transformation over time, under the influence of some animation controller. A rig is generally composed of both forward kinematics and inverse kinematics parts that may interact with each other. Skeletal animation is referring to the forward kinematics part of the rig, where a complete set of bone configurations identifies a unique pose.

Each bone in the skeleton is associated with some portion of the character's visual representation (the mesh) in a process called skinning. In the most common case of a polygonal mesh character, the bone is associated with a group of vertices; for example, in a model of a human being, the bone for the thigh would be associated with the vertices making up the polygons in the model's thigh. Portions of the character's skin can normally be associated with multiple bones, each one having a scaling factors called vertex weights, or blend weights. The movement of skin near the joints of two bones, can therefore be influenced by both bones. In most state-of-the-art graphical engines, the skinning process is done on the GPU by a shader program.

For a polygonal mesh, each vertex can have a blend weight for each bone. To calculate the final position of the vertex, a transformation matrix is created for each bone which, when applied to the vertex, first puts the vertex in bone space then puts it back into mesh space. After applying a matrix to the vertex, it is scaled by its corresponding weight. This algorithm is called matrix-palette skinning or linear-blend skinning,[4] because the set of bone transformations (stored as transform matrices) form a palette for the skin vertex to choose from.

### Benefits and drawbacks

[edit]

#### Strengths

[edit]

* A bone represents a set of vertices (or some other object which represents something, such as a leg),
* The animator needs to control fewer characteristics of the model,
* The animator can focus on the large-scale motion,
* Bones are independently movable.
* An animation can be defined by simple movements of the bones, instead of vertex by vertex (in the case of a polygonal mesh).

#### Weaknesses

[edit]

* A bone can only represent a set of vertices (or some other precisely defined object), and is not more abstract or conceptual.
* Does not provide realistic muscle movement and skin motion. Possible solutions to this problem:
* Special muscle controllers attached to the bones.
* Consultation with physiology experts, to increase accuracy of musculoskeletal realism with more thorough virtual anatomy simulations.

## Applications

[edit]

Skeletal animation is the standard way to animate characters or mechanical objects for a prolonged period of time. It is commonly used by video game artists and in the film industry, and can also be applied to mechanical objects and any other objects made up of rigid elements and joints.

Performance capture (or motion capture) can speed up the process of skeletal animation, as well as increasing the level of realism.

Rigs may be driven by ragdoll physics which automatically calculate physics of motion and resistance with skeletal frames. Virtual anatomy properties such as weight of limbs, muscle reaction, bone strength, and joint constraints may be added for realistic bouncing, buckling, fracture, and tumbling effects.

Some popular software packages within which rigs may be created include Blender, Autodesk Maya, SideFX Houdini, Autodesk 3ds Max, Maxon Cinema 4D, Unreal Engine, and many others.

## See also

[edit]

* 3D computer graphics
* Morph target animation
* Interactive skeleton-driven simulation
* Cutout animation

## References

[edit]

1. ^ Soriano, Marc. "Skeletal Animation". Bourns College of Engineering. Retrieved 5 January 2011.
2. ^ Magnenat-Thalmann, Nadia; Laperrière, Richard; Thalmann, Daniel (6–10 June 1988). "Joint-Dependent Local Deformations for Hand Animation and Object Grasping". Proceedings of Graphics Interface '88. Edmonton: 26–33.
3. ^ Petty, Josh (26 July 2018). "What is 3D Rigging for Animation & Character Design?". Concept Art Empire. Retrieved 29 November 2018.
4. ^ Kavan, Ladislav. "Direct Skinning Methods and Deformation Primitives" (PDF). Skinning.org. University of Pennsylvania.

* v
* t
* e

Animation topics

By country|

* Azerbaijan
* Bangladesh
* Bhutan
* Brazil
* United Kingdom
* Canada
* China
* history
* Czechia
* Estonia
* France
* Hungary
* India
* history
* Iran
* Japan
* history
* Korea
* North
* South
* history
* Latvia
* Malaysia
* Mexico
* North Korea
* Philippines
* Portugal
* Romania
* Russia
* South Africa
* Spain
* Taiwan
* Thailand
* Ukraine
* United States
* Silent Era
* The Golden Age
* World War II
* Early TV broadcast era
* Modern TV cable and streaming era
* Vietnam

Industry|

* Animator
* List
* Animation department
* Animation director
* Story artist
* Animation studios
* List
* Animation database
* Art pipeline
* Biologist simulators
* Animation film festivals
* international
* regional
* Highest-grossing films (Opening weekends)
* Outsourcing
* International Animation Day

Works|

* Films
* Computer-animated
* Feature-length
* Lost or unfinished
* Package
* Short
* Short series
* Stop-motion
* Adult animated films
* Children's animated films
* Series
* Adult animated
* Children's animated
* Computer-animated
* Direct-to-video
* Flash
* Internet
* Television

Techniques|

| Traditional|

* Barrier-grid and stereography
* Flip book
* Limited animation
* Masking
* Rotoscoping
* Exposure sheet

|

Stop motion|

* Claymation
* clay painting, strata-cut
* Cutout (silhouette)
* Graphic
* Model
* go motion
* Object
* Brickfilm
* Pixilation
* Puppetoons

Computer|

| 2D|

* 2.5D
* Flash
* PowerPoint
* SVG
* CSS
* Multi-sketch
* Onion skinning

|

3D|

* T-pose
* Cel shading
* CGI
* Crowd
* Facial animation
* Morph target
* Motion capture
* facial
* hand tracking
* eye tracking
* Non-photorealistic rendering
* Physically based animation
* Procedural
* Skeletal
* Virtual cinematography

Puppetry|

* Traditional puppetry
* Digital puppetry
* Machinima
* Aniforms
* Virtual human
* Live2D
* Supermarionation

Mechanical|

* Animatronics
* Audio-Animatronics
* Linear Animation Generator
* Direct manipulation animation
* Humanoid animation
* Idle animation
* Ink-wash animation
* Magic Lantern
* Scanimate
* Shadowmation
* Squigglevision
* Whiteboard animation

Other methods|

* Blocking
* Character animation
* model sheet
* walk cycle
* lip sync
* off-model
* Chuckimation
* Drawn-on-film
* Erasure animation
* Hydrotechnics
* Inbetweening
* Morphing
* Paint-on-glass
* Pinscreen
* Pixel art
* Pose to pose
* Straight ahead
* Rubber hose
* Special effects
* Sand
* Syncro-Vox
* Zoetrope

Variants|

* Abstract animation (visual music)
* Adult animation
* Animated cartoon
* Animated sitcom
* Animated documentary
* Anime
* influenced
* Educational animation
* Erotic animation
* Independent animation
* Instructional animation
* Virtual newscaster

History|

* Early history
* History of computer animation
* timeline

Related topics|

* Animation music
* Bouncing ball
* Mickey Mousing
* Key frame
* Cel
* Character animation
* model sheet
* walk cycle
* lip sync
* off-model
* Creature animation
* Twelve basic principles
* Motion comic
* Films with live action and animation
* highest grossing
* Cartoon
* physics
* violence
* Most expensive animated films
* List of animated films by box office admissions
* List of animated television series by episode count

* Category
* Portal
* Outline

* v
* t
* e

Film crew (filmmaking)

Above the line

* Actor
* Leading actor
* Supporting actor
* Ensemble cast
* Character actor
* Child actor
* Cameo actor
* Bit actor
* Under-five
* Voice actor

Film director
* Screenwriter
* Film producer
* Executive producer
* Line producer
* Casting director

Below the line

| Pre-production/
Production|

* Unit production manager
* Production coordinator
* Production accountant
* Assistant director
* Production assistant
* Script supervisor
* Script coordinator
* Location manager
* Location scout
* Storyboard artist

|

Photography|

* Cinematographer / director of photography
* Camera operator
* Focus puller
* Clapper loader
* Steadicam
* Digital imaging technician
* Second unit
* Gaffer
* Best boy electric
* Lighting technician
* Key grip
* Best boy grip
* Dolly grip
* Grip

Production
design|

| Sets|

* Production designer
* Art director
* Set decorator
* Set dresser
* Swing gang
* Matte painter
* Scenic design
* Greensman

|

Props|

* Property master
* Weapons master

Wardrobe|

* Costume designer
* Wardrobe supervisor

Special
effects|

* Special effects supervisor
* Visual effects supervisor

Other|

* Hairdresser
* Make-up artist

Sound|

* Director of audiography / sound director
* Production sound mixer
* Boom operator
* Utility sound technician

Animation|

* Animator
* Visual effects
* Modeling
* Rigging
* Layout artist

Talent|

| Acting|

* Acting coach
* Body double
* Dialect coach
* Movement director
* Choreographer
* Extra
* Talent agent
* Stand-in
* Acting instructor
* Intimacy coordinator

|

Stunts|

* Stunt coordinator
* Stunt double
* Stunt performer
* Stage combat

Other|

* Animal wrangler

Post-production|

| Picture|

* Film editor
* Colorist

|

Sound|

* Sound editor
* Dialogue editor
* Re-recording mixer
* Foley artist
* Voice foley
* Dubbing
* ADR
* Subtitles

Score|

* Composer
* Music supervisor
* Music editor
* Orchestrator

Visual
effects|

* VFX creative director
* Visual effects editor
* Compositor
* Computer-generated imagery
* Rendering

Other|

* Technical director

Other|

* Unit still photographer
* Craft services

Authority control databases

National|

* United States
* Israel

Other|

* Yale LUX

*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template