Tutorial on Computer Animation

Kerem Caliskan

Abstract

This tutorial heavily depends on “Computer Animation – Algorithms & Techniques” book by Rick Parent and the book slides. One can also find definitions from Oxford Dictionary, Wikipedia and many chapter related data from different tutorials / presentations.

This tutorial focuses on explaining computer animation and technical algorithm infrastructure it makes use of. The tutorial will cover main topics in Computer animation like :

– Keyframing, story-boarding,

– Kinematics, physically based dynamics modeling,

– Motion capture,

– Scene composition, lighting, and sound track generation

This tutorial will teach the readers about current techniques in computer animation. By the end of the tutorial, the reader should:

– have learned the computational methods for modeling of motions in the physical and virtual world,

– be able to understand how to storyboard, light, compose, and render an animated sequence,

– and be able to read and critically evaluate the current literature in computer animation.

Introduction

Computer animation refers to any computer-based computation used for generating images that creates the perception of motion. Besides position and orientation of an object, its shape, shading parameters, camera parameters, lighting, its texture coordinates can also be animated.

For many of the people around the world Computer Animation is just a part of the funny new generation cartoons and movies. It’s true that Hollywood is one of the biggest sector that makes use of computer animation but one should know that most of the computer animation done in the world has nothing to do with movies. Computer game industry has always been one of the most challenging industries that completely relied on computer animation. They’re now also taking the chance of being animated MUDs (Multi User Dungeons). Majority of the games are played online and they use the experience coming from both Computer Animation and MUD infrastructure. Computer games take advantage of state of the art technologies for exploiting both CPU and GPU in order to render more realistic figures.
Real-time performance driven computer animation has already appeared at every realistic application that needs to render more information. Virtual reality especially augmented reality makes use of computer animation for connecting real time images and computer generated images. Computer animation is getting a part of our life as both CPU and GPU manufacturers embed more power on their chips. So what is the main difference between flight simulators, electronic warfare simulators, nuclear reactor simulators, weapon simulators and standard computer games? Cost, inter process communication and distributed communication structure, generated image quality and real time issues are the most important differentiators between these two groups.

• Perception:

In philosophy, psychology, and the cognitive sciences, perception is the process of attaining awareness or understanding of sensory information. It is a task far more complex than was imagined in the 1950s and 1960s, when it was predicted that building perceiving machines would take about a decade, a goal which is still very far from fruition. The word comes from the Latin words perceptio, percipio, and means “receiving, collecting, action of taking possession, apprehension with the mind or senses.”. The notion that perception is a requisite property of animate action; without perception action would not be guided and without action perception would be pointless.
It’s well known that when a series of images are displayed in a rapid succession, they’re perceived as a moving image by an observer. This is possible because the eye-brain complex has the ability, under sufficient viewing conditions and within certain playback rates, to create a sensation of continuous imagery from such a sequence of still images. This experience is due to persistence of vision where eye retains a visual imprint of an image for a brief instant once the stimulus is removed. These imprint known as positive afterimages fill in the gaps between the images to produce the perception of a continuously changing image. Persistence of vision is not the same as perception of motion. Rotating a light source with high frequency may result in a stationary ring image. Although this effect can be attributed to persistence of vision, the result is static. Recently, the causality of the ( physiological ) persistence of vision mechanism has been called into question and the perception of motion has been attributed to a ( psychological ) mechanism known as phi phenomenon; the apparent motion is referred to as beta motion. A critical part of understanding these visual perception phenomena is that the eye is not a camera: there is no “frame rate” or “scan rate” in the eye; instead, the eye/brain system has a combination of motion detectors, detail detectors and pattern detectors, of which each output is combined to create the visual experience. In order to persuade the observer to the continuous imagery image sequences should be shown on decent frequencies. When the observer loses her perception of continuous imagery the display is said to flicker. This may change owing to observer distance, lighting etc. so the frequency depends on some external factors. This rate is referred as critical flicker frequency. There is also an upper frequency limit for the eye to respond accurately enough for the brain to distinguish sharply defined, individual detail. As a result motion blur occurs.
For a true perception of image motion we should also understand other technical constraints which depend on standards used for displaying the images. Update rate depends on the number of images that is shown per second whereas display rate is dependent on the ability of your display hardware to show images per second.
In hand-drawn animation, fast moving objects are typically stretched in the direction of travel so that the object’s images overlap.

• Principles of Computer Animation

• Simulating Physics

Squash & Stretch : defining the rigidity and mass of an object by distorting its shape during an action

Squash Stretch
Squash Stretch

Timing : Spacing actions to define the weight and size of objects and the personality of characters. Weight, size, and personality of an object should determine how the actions are spaced through time. Light objects move quickly, whereas heavier ones move slower.

Animation Timing
Animation Timing

Slow in & slow out: The spacing of the in-between frames to achieve subtlety of timing and movement. Inertia, friction, and viscosity should be taken into account. Rather than having a uniform velocity for an object, it is more appealing, and sometimes more realistic, to have the velocity vary at the extremes.

Slow In & Slow Out
Slow In – Slow Out

Arcs: Objects should follow an arc rather than a straight line. Independent curves should be used for position interpolation and speed control.

Arcs
Arcs

Secondary actions: The action of an object resulting from another action. They’re like a chain reaction and should follow the main action.

Secondary Action
Secondary Actions

• Designing Aesthetic Actions

  1. Exaggeration : Accentuating the essence of an idea via the design and the action. Draws attention to the action.
  2. Appeal : Creating a design or an action that the audience enjoys watching.
  1. Follow Through/Overlapping Action: Follow through is the termination part of an action. Overlapping establishes the next action’s relationship by starting it before the first action has completely finished. This keeps the interest of the viewer, since there is no dead time between actions.

Follow through:

Follow Through
Follow Through

Overlapping Action:

Overlapping Action
Overlapping Action


• Effective Presentation of Actions

  1. Anticipation: Preparation for an action
  2. Staging: Presenting an idea so that it is unmistakably clear. This idea can be an action, a personality, an expression, or a mood. An important objective of staging is to lead the viewers eye to where the action will occur so that they do not miss anything. Action environment has to be set up so that it is not missed by the audience.

Anticipation: An upcoming action should be set up so that audience knows it is coming. An action breaks down into:

Anticipation
Anticipation

Anticipation

Action

Reaction

Anatomical motivation: a muscle must extend before it can contract. Prepares audience for action so they know what to expect. Directs audience’s attention. Amount of anticipation can affect perception of speed and weight.

Anatomical motivation I
Anatomical motivation I
Anatomical motivation II
Anatomical motivation II
  • Timing : Appropriate duration for the action should be given so that the intended effect reaches the audience.
  • Production Technique
  1. Straight Ahead Action: In hand drawn animation when the animator starts at the first drawing in a scene and then draws all of the subsequent frames until he reaches the end of the scene. This creates very spontaneous and zany looking animation and is used for wild, scrambling action.
  2. Pose to Pose Action: When the animator carefully plans out the animation, draws a sequence of poses, i.e., the initial, some in-between, and the final poses and then draws all the in-between frames (or another artist or the computer draws the inbetween frames). This is used when the scene requires more thought and the poses and timing are important.

Animation Four-level hierarchy:

Four-level hierarchy
Four-level hierarchy

– Production: The entire animation

Sequence: A major episode with an associated staging area

Shot: A continuous camera recording

Individual frames: A single recorded image.

!!! A production usually consists of one to dozen sequences .

  • Animation Production Steps:

A preliminary story with a script is decided on

•A storyboard is developed

– It lays out the action scenes by sketching representative frames.

Storyboard
Storyboard

•A model sheet is developed that lists the characters in various poses.

• The exposure sheet records information for each frame such as camera moves, sound track cues.

• The route sheet records the statistics and responsibility of each scene.

Animatic: Also called a story reel. A prototype animation that helps to work on timing, revise storyboard, etc. To sum up, it is a storyboard with timing.

• Once the storyboard has been decided on a detailed story is developed.

• Key frames are produced by master animators

In-betweening: Associate and assistant animators produce the frames between the keys

Sound

• In lip-synched animation, sound-track is created first and then animation is produced to fit the sound-track.

• Music

• Special effects

• Voice

  • Conventional vs. computer animation

Computer animation borrows a lot of ideas from conventional animation in terms of production approaches.

• However, there are differences:

– The lighting, camera models, motion can be reused easily in computer animation

– Multiple detailed models can be used in computer animation

Test shot: short high quality rendering

Pencil test: low quality models and approximate motions

Editing for introducing special affects:

Linearnonlinear editing possible. Timeline for non-linear editing, we need digital video for non-linear editing

29 Responses to “A Tutorial on Computer Animation – I”

  1. soma sundar says:

    plese send me more examples of animation princepals

    i tried to search but i find something on this issue

    thanks a lot

  2. Hi Soma,
    I’ll release second part of the tutorial in several weeks, check for updates as I’m planning to put more examples.
    Kerem

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  4. what.. staging. the principles of animation

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