ANIMATION

Generation of moving image is known as animation.

TOPIC 1:

DESIGN OF ANIMATION SEQUENCES

In general, an animation sequence is designed with the following steps:

Storyboard layout

Object definitions

Key-frame specifications

Generation of in-between frames

Storyboard layout:

The storyboard is an outline of the action. It defines the motion sequence as a set of basic events that are to

take place. Depending on the type of animation to be produced, the storyboard could consist of a set of rough

sketches or it could be a list of the basic ideas for the motion.

Object definition:

An object definition is given for each participant in the action. Objects can be defined in terms of basic shapes,

such as polygons or splines . In addition, the associated movements for each object are specified along with

the shape.

Key-frame specifications:

A key-frame is a detailed drawing of the scene at a certain time in the animation sequence. Within each key

frame, each object is positioned according to the time for that frame. Some key frames are chosen at extreme

positions in the action; others are spaced so that the time interval between key frames is uniform.

In-between frames:

In-betweens are the intermediate frames between the key frames. The number of in-betweens needed is

determined by the media to be used to display the animation. Film requires 24 frames per second, and

graphics terminals are refreshed at the rate of 30 to 60 frames per second. Typically, time intervals for the

motion are set up so that there are from three to five in-betweens for each pair of key frames. Depending on

the speed specified for the motion, some key frames can be duplicated. For a I-minute film sequence with no

duplication, we would need 1440 frames. With five in-betweens for each pair of key frames, we would need

288 key frames. If the motion is not too complicated, we could space the key frames a little farther apart.

TOPIC 2:

GENERAL COMPUTER-ANIMATION FUNCTIONS

Animation packages, such as Wave- front, for example, provide special functions for designing the animation

and processing individual objects. Those are listed below:

Functions to store and manage the object database. Object shapes and associated parameters are stored

and updated in the database.

functions for motion generation

functions for object rendering.

Motions can be generated according to specified constraints using two-dimensional or three-dimensional

transformations. Standard functions can then be applied to identify visible surfaces and apply the rendering

algorithms.

functions to simulates camera movements. Standard motions are zooming, panning, and tilting.

Finally, given the specification for the key frames, the in-between can be automatically generated.

TOPIC 3:

RASTER ANIMATIONS

On raster systems, we can generate real-time animation in limited applications using raster operations.

A simple method for translation in the xy plane is to transfer a rectangular block of pixel values from one

location to another.

Two dimensional rotations in multiples of 90 degrees are also simple to perform. To rotate a block of pixels,

we need to determine the percent of area coverage for those pixels that overlap the rotated block.

Sequences of raster operations can be executed to produce real-time animation of either two-dimensional or

three-dimensional objects, as long as we restrict the animation to motions in the projection plane.

We can also animate objects along two-dimensional motion paths using the color-table transformations. Here

we predefine the object at successive positions along the motion path, and set the successive blocks of pixel

values to color-table entries. We set the pixels at the first position of the object to "on" values, and we set the

pixels at the other object positions to the background color. The animation is then accomplished by changing

the color-table values so that the object is "on" at successively positions along the animation path as the

preceding position is set to the background intensity .

TOPIC 4:

COMPUTER-ANIMATION LANGUAGES

General purpose languages: Design and control of animation sequences are handled with a set of animation

routines. A general purpose language, such as C, Lisp, Pascal, or FORTRAN, is often used to program the

animation functions, but several specialized animation languages have been developed .

Animation functions include a graphics editor, a key-frame generator, an in-between generator, and standard

graphics routines.

The graphics editor allows us to design and modify object shapes, using spline surfaces, constructive solid-

geometry methods, or other representation schemes.

A typical task in an animation specification is scene description. This includes the positioning of objects and

light sources, defining the photometric parameters (light-source intensities and surface-illumination

properties), and setting the camera parameters (position, orientation, and lens characteristics).

Key-frame systems: Key-frame systems are specialized animation languages designed simply to generate the

in-betweens from the user-specified key frames. Usually, each object in the scene is defined as a set of rigid

bodies connected at the joints and with a limited number of degrees of freedom. As an example, the robot in

the following Fig has six degrees of freedom, which are called arm sweep, shoulder swivel, elbow extension,

pitch, yaw, and roll.

Parameterized systems:

Parameterized systems : Characteristic parameters for motion are specified and interpolated .Less data is

required.

For example, for motion of an arm, the parameter could be rotation angle. The following figure illustrate the

rotation of arm by ϴ degrees:

It allow object-motion characteristics to be specified as part of the object definitions. The adjustable

parameters control such object characteristics as degrees of freedom, motion limitations, and allowable shape

changes.

Scripting systems : Scripting systems allow object specifications and animation sequences to be defined

with a user-input script. From the script, a library of various objects and motions can be constructed.

TOPIC 5:

KEY-FRAME SYSTEMS and Morphing:

We generate each set of in-betweens from the specification of two (or more) key frames. Motion paths can be

given with a kinematic(velocity, acceleration) description as a set of spline curves, or the motions can be

physically based by specifying the forces acting on the objects to be animated.

Transformation of object shapes from one form to another is called morphing. Morphing methods can he

applied to any motion or transition involving a change in shape.

The primary rule to achieve morphing is , Given two key frames for an object transformation, we first adjust

the object specification in one of the frames so that the number of polygon edges (or the number of vertices)

is the same for the two frames. This preprocessing step is illustrated in the following Fig.

A straight-line segment in key frame k transformed into two line segments in kev frame k +1. Since key frame

k + 1 has an extra vertex, we add a vertex between 1 and 2 in key frame k to balance the number of vertices

(and edges) In the two key frames. Using linear interpolation to generate the in-betweens. We transition the

added vertex in key frame k into vertex 3' along the straight-line path shown in Fig.

An example of a triangle linearly expanding into quadrilateral is given In the following figure.

We can state general preprocessing rules for equalizing key frames in terms of either the number of edges or

the number of vertices to be added to a key frame. Suppose we equalize the edge count, and parameters Lk

and Lk+1 denote the number of line segments in two consecutive frames. We then define

Where

Then the preprocessing is accomplished by

1. dividing N, edges of keyframe,, into N, + 1 sections

2. dividing the remaining lines of keyframe,, into N, sections

As an example, if Lk = 15 and Lk+1 = 11, we would divide 4 lines of keyframe k+1, into 2 sections each. The

remaining lines of keyframe k+1are left intact. If we equalize the vertex count, we can use parameters Vk and

Vk+1 to denote the number of vertices in the two consecutive frames. In this case, we define

and

Preprocessing using vertex count is performed by

1. adding N, points to N,, line sections of keyframe,,

2. adding N, - 1 points to the remaining edges of keyframe,,

For the triangle-to quadrilateral example, Vk = 3 and Vk+1 = 4. Both Nls and Np, are 1, so we would add one

point to one edge of keyframe k No points would be added to the remaining lines of keyframe k+1

TOPIC 6:

MOTION SPECIFICATIONS

Motion specifications control the animation. There are several ways in which the motions of objects can be

specified in an animation system. We can define motions in very explicit terms such as

Direct motion specifications

Goal directed specifications

Kinematics and Dynamics

Direct Motion Specifications : The most straightforward method for defining a motion sequence is direct

specifications. Here, we explicitly give the rotation angles and translation vectors. Then the geometric

transformation matrices are applied to transform coordinate positions

Alternatively, we could use an approximating equation to specify certain kinds of motions. For example, We

can approximate the path of a bouncing ball, for instance, with a damped, rectified, sine curve. The equation

used is as follows:

Y(x)=A | sin( wx + ϴ 0 | e -kx

where A is the initial amplitude, w is the angular frequence, ϴ 0 is the phase angle, and k is the damping

constant. These methods can be used for simple user-programmed animation sequences.

The following figure shows the bouncing ball along a sine curve path:

Goal-Directed Systems

Goal directed systems determine specific motion parameters given the goals of the animation.

For example, we could specify that we want an object to "walk" or to "run" to a particular destination. Or we

could state that we want an object to "pick up" some other specified object. The input directives are then

interpreted in terms of component motions that will accomplish the selected task.

Kinematics

We can also construct animation sequences using kinematic or dynamic descriptions. With a kinematic

description, we specify the animation by giving motion parameters (position, velocity, and acceleration). For

constant velocity (zero acceleration), we designate the motions of rigid bodies in a scene by giving an initial

position and velocity vector for each object.

For example, if a velocity is specified as (3,0, -4) km/sec, then this vector gives the direction for the straight

line motion path and the speed (magnitude of velocity) is 5 km/sec. If we also specify accelerations (rate of

change of velocity), we can generate speed-ups, slowdowns, and curved motion paths. Kinematic specification

of a motion can also be given by simply describing the motion path. This is often done using spline curves.

Dynamics

Dynamics take physical laws into account. It is inverse to kinematics. A particle moves with an acceleration

proportional to the forces acting on it, and the proportionality constant is the mass of the particle.

Dynamic descriptions require the specification of the forces that produce the velocities and accelerations.

Descriptions of object behavior under the influence of forces are generally referred to as a physically based

modeling. Examples of forces affecting object motion include electromagnetic, gravitational, friction, and

other mechanical forces.

Object motions are obtained from the force equations describing physical laws, such as Newton's laws of

motion for gravitational and friction processes,

For example, the general form of Newton's second law for a particle of mass m is

F=d/dt (mv)

with F as the force vector, and v as the velocity vector If mass is constant, we solve the equation F = ma, where

a is the acceleration vector. Otherwise, mass is a function of time, as in relativistic motions or the motions of

space vehicles that consume measurable amounts of fuel per unit time

TOPIC 7:

Principles of animation: Squash and stretch

Illustration of the "squash and stretch"-principle:

Example A shows a ball bouncing with a rigid, non-dynamic movement. In example B the ball

is "squashed" at impact, and "stretched" during fall and rebound. The movement also

accelerates during the fall, and slows down towards the apex

The most important principle is "squash and stretch", the purpose of which is to give a sense of weight and

flexibility to drawn objects. It can be applied to simple objects, like a bouncing ball, or more complex

constructions, like the musculature of a human face. In realistic animation, however, the most important aspect

of this principle is the fact that an object's volume does not change when squashed or stretched. If the length of

a ball is stretched vertically, its width (in three dimensions, also its depth) needs to contract correspondingly

horizontally.

Anticipation

Anticipation is used to prepare the actor for an action, and to make the action appear more realistic. For

example A dancer jumping off the floor has to bend his knees first. The following figure shows the anticipation of

an actor for jumping.

Staging

This principle is similar to staging as it is known in theatre and film. Its purpose is to direct the audience's

attention, and make it clear what is of greatest importance in a scene; This can be done by various means,

such as the placement of a character in the frame, the use of light and shadow, and the angle and position of

the camera. The essence of this principle is keeping focus on what is relevant, and avoiding unnecessary detail.

Straight ahead action and pose to pose

These are two different approaches to the actual drawing process. "Straight ahead action" means drawing out a

scene frame by frame from beginning to end, while "pose to pose" involves starting with drawing a few key

frames, and then filling in the intervals later. "Straight ahead action" creates a more fluid, dynamic illusion of

movement, and is better for producing realistic action sequences. On the other hand, it is hard to maintain

proportions, and to create exact, convincing poses along the way. "Pose to pose" works better for dramatic or

emotional scenes, where composition and relation to the surroundings are of greater importance. A combination

of the two techniques is often used.

Follow through and overlapping action

Follow through and overlapping action is a general heading for two closely related techniques which help to

render movement more realistically, and help to give the impression that characters follow the laws of physics.

"Follow through" means that separate parts of a body will continue moving after the character has stopped.

"Overlapping action" is the tendency for parts of the body to move at different rates (an arm will move on

different timing of the head and so on). The following figure illustrate follow through and overlapping action.

Slow in and slow out

The movement of the human body, and most other objects, needs time to accelerate and slow down. For this

reason, animation looks more realistic if it has more drawings near the beginning and end of an action,

emphasizing the extreme poses, and fewer in the middle. This principle goes for characters moving between

two extreme poses, such as sitting down and standing up, but also for inanimate, moving objects, like the

bouncing ball in the below illustration.

Arcs

Most natural action tends to follow an arched trajectory, and animation should adhere to this principle by

following implied "arcs" for greater realism. This can apply to a limb moving by rotating a joint, or a thrown

object moving along a parabolic trajectory. The exception is mechanical movement, which typically moves in

straight lines.

Secondary action

Adding secondary actions to the main action gives a scene more life, and can help to support the main action. A

person walking can simultaneously swing his arms or keep them in his pockets, he can speak or whistle, or he

can express emotions through facial expressions. The important thing about secondary actions is that they

emphasize, rather than take attention away from, the main action. In the case of facial expressions, during a

dramatic movement these will often go unnoticed. The following example illustrate the importance of secondary

action.

Timing

Timing, or the speed of an action, is an important principle because it gives meaning to movement.

The speed of an action defines how well the idea will be read to the audience. Something like an eye blink can be fast or slow. If it's fast, a character will seem alert

and awake. If it's slow the character may seem tired and lethargic. Timing and Motion are tied together because in animation the two are basically the

same thing. Change the time that it takes a character to complete an action and it will change it's motion.

Timing can also defines the weight of an object. Two similar objects can appear to be vastly different weights by manipulating timing alone.

For example, if you were to hit a croquet ball and a balloon with a mallet, the result would be two different actions. The croquet ball would require more force to place it into motion, would go farther, and need more force to stop it. On the other hand, the balloon would require far less force to send it flying, and because of it's low mass and weight, it wouldn't travel as far, and would require less force to stop it.

Exaggeration

Exaggeration is an effect especially useful for animation, as perfect imitation of reality can look static and dull in

cartoons. The level of exaggeration depends on whether one seeks realism or a particular style, like a

caricature or the style of an artist. Other forms of exaggeration can involve the supernatural or surreal,

alterations in the physical features of a character, or elements in the storyline itself. The following figure

illustrate the exaggeration.

Solid drawing

The principle of solid drawing means taking into account forms in three-dimensional space, giving them volume

and weight. The animator needs to be a skilled draughtsman and has to understand the basics of three-

dimensional shapes, anatomy, weight, balance, light and shadow, etc. For the classical animator, this involved

taking art classes and doing sketches from life.

Appeal

Appeal in a cartoon character corresponds to what would be called charisma in an actor. A character who is

appealing is not necessarily sympathetic – villains or monsters can also be appealing – the important thing is

that the viewer feels the character is real and interesting.

TOPIC 8

Advanced animation techniques:

Already, the tools have gotten to the point where it seems anything that the mind can conceive, the animator can put to the screen. Some of the more recent developments in the field of animation are as follows:

Motion Capture Technology

This is the process of using actual motion to determine the motion of objects in a computer environment. Sensors are placed on a subject and motion data is collected, then translated into the computer and applied to a 3-Dimensional object. The result is extremely realistic motion obtained in a matter of seconds that would be extremely difficult and time-consuming to create by traditional means.

Compositing

This is the process of combining computer-generated imagery with live-action footage shot on film or video. Some examples of films that made this technique famous are Jurassic Park, Terminator 2, and Starship Troopers. As a result, a majority of movies released today have some sort of computer-aided imagery, even if you do not notice it. Prior to compositing technology, films had to be either live-action or animated. Today, the integration of these two techniques makes for exciting new possibilities for both the animator and the director.

Software

Today there are many different animation packages available on the computer, ranging from traditional animation programs to complex 3-D animation packages. State-of-the-art animation is no longer reserved for big budget companies. Anyone with a PC, a little software, and a lot of play time can learn to animate.

The constantly improving technology provides some exciting possibilities for animators. Remember that what makes an animation great is not the tools, but what you do with them