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Welcome

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Computer Animation&

Techniques

Seminar by Mahith Mohan

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Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of motion or life.

Name derived from “Anime” means life.

It’s just an optical illusion of motion due to persistence of vision

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Simple Example

A ball bouncing from just 6 frames

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For better smooth transition we must have higher frame rate.

Film 24 fpsNTSC TV 30 fps (interlaced)PAL TV 25 fps (interlaced)HDTV 60 fpsComputer ~60 fps

Frame Rate: No. of frames in unit second

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Animation

Traditional animation

Stop motion

Computer animation

Classification of animation techniques

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Traditional Animation

Also called Hand drawn animation Or Cel animation Pictures are drawn for each frames.The animators' drawings are traced or photocopied onto transparent acetate sheets called cels ( celluloid transparency) The completed character cels are photographed one-by-one onto motion picture film against a painted background by a rostrum camera.

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Example

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Walt Disney Walt Disney, an American cartoonist and film producer, started an entertainment empire with his creation of animated movies and world-renowned amusement parks. Disney appears here at his drawing board in 1950 with a drawing of Mickey Mouse, his most famous cartoon character. Disney won an honorary Oscar (Academy Award) in 1932 for his creation of Mickey.

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Stop Motion Animation

Stop-motion animation is used to describe animation created by physically manipulating real-world objects and photographing them one frame of film at a time to create the illusion of movement.

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Example

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Computer animation

Computer animation contains a variety of techniques, the unifying factor being that the animation is created digitally on a computer

Mainly 2 types-2D animation 3D animation

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ANIMATION SEQUENCES

Step 1: Storyboard layout

Outline of action

Consist set of rough sketches

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ANIMATION SEQUENCES

Step 2:

Object definition

Objects are defined in terms of basic shapes.

Associated movement of each object are specified with the shape.

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ANIMATION SEQUENCES

Step 3:

Key frame Specification

Key frame is a detailed drawing of the scenes at a certain time.

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ANIMATION SEQUENCES

Step 4:

Generation of in-between frames.

Frames between the key frames.

Determined by the media to be used to display.

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1

2

Key frame k

1’

2’

Key frame k+1In-between frame

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Raster Animation

Raster animation is the most basic type of computer animation.It involves creating an image, and then using a computer to put that image in motion Raster based animation frames are made up of individual pixels. These pixels each contain information about the colour and brightness of that particular spot on the image

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Example:

Step 1 (erase) Step 2 (move) Step 3 (draw)

Ship is redrawn in background color

Move ship

x’ = x + Dxy’ = y + Dy

(x,y)(x,y) (x+ Dx, , y+ Dy) (x’,y’)

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Color-table transformationSimple 2D animations can be easily implemented using colour lookup table.Here we set the successive blocks of pixel value to colour table. Object as “on”

rest as background color.Later successively positions along the path is changed to “on” and older position to background color.

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COMPUTER ANIMATION LANGUAGES

Key frame Systems:

Designed simply to generate the in-betweens from the user specified key frames

Each object is formed with set of rigid bodies connected by several joints with limited degree of freedom.

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COMPUTER ANIMATION LANGUAGES

Parameterized system :

Object-motion characteristics are specified as a part of the object definition like

Degree of freedomMotion limitationAllowable shape changes ….

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COMPUTER ANIMATION LANGUAGES

Scripting System:

Object specifications & animation sequences are defined with a user-input script

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Transformation of object shape from one form to another is called Morphing ( Metamorphosis)

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Three frames form a morph from George W. Bush to Arnold Schwarzenegger showing the mid-point between the two extremes

Key frame Key frameIn-between frame

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1

2

Key frame k

1’

2’

Key frame k+1

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added point

Halfway frame

Linear interpolation for transforming triangle into a quadrilateral

3 3’

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General preprocessing rules for Equalizing key frames

Using edge count:

Let Lk & L k+1 no of line segment in 2 consecutive key frame.Then

Lmax =max(Lk ,Lk+1 ) , Lmin =min(Lk , Lk+1 )And

Ne = Lmax mod Lmin

Ns = int(Lmax / Lmin )Then the preprocessing is accomplished by1. Dividing Ne edges of keyframemin into Ns +1 sections2. Dividing the remaining lines of keyframemin into Ns sections.

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1

2

Key frame k 1’

2’

Key frame k+1

4’

General preprocessing rules for Equalizing key frames

Example for by using edge count:

L k =3 L k+1 =4L max =4 , L min =3, N e = 1 , Ns =1

1. Divide 1 (N e ) edges of keyframe k (keyframe min ) to 2 (N s+1 ) section

2. Since Ns =1 leave the remaining sections.

3 3’

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General preprocessing rules for Equalizing key frames

Using vertex count:

Let Vk & Vk+1 no of vertex in 2 consecutive key frame.Then

Vmax =max(Vk ,Vk+1 ) , Vmin =min(Vk , Vk+1 )And

Nis = (Vmax -1) mod( Vmin -1)

Np = int((Vmax -1) / (Vmin -1)

Then the preprocessing is accomplished by1. adding Np points to Nis line section of key framemin.2. Adding Np -1 points to the remaining edges of key framemin

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1

2

Key frame k 1’

2’

Key frame k+1

4’

General preprocessing rules for Equalizing key frames

Example for by using vertex count:

V k =3 V k+1 =4

V max =4 , V min =3, N is = 1 , Np =1

1. Add 1 (N p ) point to 1 (N is ) line of keyframe k (keyframe min )

2. Since Np -1 =0 leave the remaining edges

3 3’

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Simulating Accelerations

It perform non linear spline interpolation

Here the speed is not constantNon linear path is taken at the in-between frames.To stimulate acceleration we adjust the time spacing for the in-betweens

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For constant speed we use equal interval of time spacing.Let consider key frames at times t1 and t2 and having n in-between frames between these. then

dt= (t2 – t1)/ n+1And time for any in-between as:

tBj = t1 +j* dt

For accelerating we can use functions like

1-cos , 0<q < /2q pThen time for any in-between is:

tBj = t1 +dt ( 1-cos(jp/2(n+1) )

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Motion Specifications

Direct Motion Specification:

Explicitly give the rotation angles and translation vector.

Then transformation matrices are applied to transform coordinate positions .

Or we can use approximate equation to specify some motion.

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Path of a bouncing ball

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This show the path of a bouncing ball acquired from damped sine function

y(x) = A sin(wx+ q0 ) e-kx

where A =initial amplitude =w angular

frequency q0 = phase anglek= damping constant

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Goal-Directed Systems

Referred as goal directed because they determine the specific motion parameters given as the goals of the animation.

At the opposite extremes we specify the motions in general terms which describes the action.

Later input directives will interpret in terms of component motion.

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Kinematics Specification

Determines parameters needed for a jointed, flexible object to achieve a pose.

Also factors in maintaining balance, joint angle limitations, and collisions between the body and limbs.

And all this will be mentioned in kinematic description of the respective points. It’s alternate approach is inverse kinematics.

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Inverse Kinematics

Here we will mention the parameters at the initial & final positions of object only.

Rest motion parameters are computed by the system.

Disadvantage: There is no general analytical solution.Must be solved through non-linear programming techniques.

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Dynamic Specification

Here force acting on the body will also mention with the motion parameters.

Referred as Physically based system.

Motion is obtained from the force equations like Newton’s Law etc.

It give realistic effects in motion.

So it is used in case of complex rigid body system and some non rigid bodies like cloth etc

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Motion Capture

A person wears sensors near each joint

Computer software records positions, angles, velocities, accelerations, and impulses for all sensors

Typically captures sub-millimeter positions

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Advantages: Faster than manually creating animations

Can have much more natural looking motions and catch all movements of the object.

Disadvantages: Can’t do anatomically impossible motions

Motion is restricted to the laws of physics.

Sensors attached to the skin can shift out of position during human movement causing real performance to differ from data recorded.

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Special Effects (Movies, TV)Video GamesVirtual RealitySimulation, Training, MilitaryMedicalRoboticsVisualizationCommunication

APPLICATIONS OF COMPUTER ANIMATION

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