Animation in Computers

An animation is defined as a visual change in a scene with respect to time. The visual change in the scene is not only associated with the change in the position of the object, but also with its shape, color, transparency, structure and texture. An important point about animation is that it usually signifies the hand drawn or artificially drawn sequence of images, which contrasts to the movies where actors' performances with real-world scenes are recorded. In early times, animations were made by hand by drawing every scene one by one on paper and then painted.This method was obviously very troublesome and time-consuming. Nowadays, the use of computer technology has made the animation process progressively simpler and more powerful. The process of drawing images and playing them back at a high speed with the help of computer software in order to create an illusion of movement is referred to as computer animation. The illusion of movement is created by displaying an image on the computer screen, then quickly replacing it by a new image, which is similar to the previous image, but shifted slightly.

The field of computer animation is a subset of both computer graphics and animation technologies. Computer animation is generally achieved through a series of geometric transformations-scaling, translation, rotation or any mathematical technique-to produce a sequence of scenes. In addition, the animation can be produced by varying any of the following:

• Camera parameters: It involves the camera position with respect to the object, distance from the object, orientation, and focus.
• Lighting conditions: It involves direction and color of light, number of lights, and so on.

These days computer animation is widely used in the entertainment industry for producing motion pictures, cartoon movies, and video games. In addition, it is being used in education and training, industrial applications, virtual reality systems, advertising, scientific visualization and many engineering applications.

In the early days, an animation sequence was created by drawing different images in different frames and then showing them at a high speed. However, these days, animations are created with the help of computers. In computer animation, the frames required for animation are generated using computers, and are then displayed on an output device at a high speed. A basic approach to design an animation sequence consists of the four stages, namely, storyboard layout, object definitions, key frame specifications, and generation of in-between frames.

i. Storyboard layout: The storyboard is an outline of the action. This stage basically defines the motion sequence of the object as a set of basic events that are to take place. For example, while creating an animation sequence of cricket play, the storyboard layout would consist of action and motion of batting, bowling, fielding, running, and so on. Depending on the type of animation to be created, the storyboard consists of a set of rough sketches, models, or even in some cases it could be verbal description or list of basic ideas of the motion.

ii. Object definitions: Once the storyboard layout has been prepared, the next step is to define all the objects or participants in the action. The objects are generally described in terms of their dimensions, shapes (such as polygons or spline surfaces), colors, movements, or any other additional information which can help in defining the objects. For example, while creating animation for cricket play, the object definitions could be player's dimensions, colors of their uniform, dimensions of the ball, bat, stumps, etc.

iii. Key frame specifications: The next step in the process of creating animation is to specify key frame specification. A key frame is a detailed drawing of the scene at a certain time in the animation sequence. In each key frame, the position, color, shapes, etc., of all the objects is positioned according to a particular point of time for that frame. More the number of frames, smoother will be the animation. For complex motions, one need to specify more key frames as compared to simple, slowly varying motions. Some key frames are specified at extreme positions, where others are spaced such that the time interval between them is not too large.

iv. Generation of in-between frames: Once the key frames are specified, the next step is to generate intermediate frames. The total number of in-between frames required for an animation depends on the display media that is to be used. For example, film requires 24 frames per second, and graphics terminals require more than 60 frames per second. Typically, time intervals for the motion are set up such that there are three to five intermediate frames between any two key frames. In addition, some key frames can also be duplicated depending on the speed specified for the motion. For example, for a one-minute film sequence with no duplication, 1440 frames would be required, and if we put five intermediate frames between any two key frames, then 288 key frames would only be required.

There are twelve basic principles of animation which were introduced by the Disney animators Ollie Johnston and Frank Thomas in 1981 in their book The Illusion of Life: Disney Animation. The main aim of the principles was to produce an illusion of characters adhering to the basic laws of physics. However, these laws also dealt with more abstract issues, such as emotional timing and character appeal. The twelve basic principles of animation are described as follows:

• Squash and stretch:It is the most important principle of animation. Its main purpose is to give a sense of weight and flexibility to the drawn objects. Stretch and squash technique is basically used for simulating accelerating effects especially for non-rigid objects. This technique can be applied to simple objects like a bouncing rubber ball, as well as to complex constructions like musculature of a human face. For example, when a rubber ball bounces and hits the ground, it tends to get flatten on hitting the ground. This is squash principle. As soon as the ball starts bouncing up, it stretches in the direction of its movement. This is stretch principle. Another example is the stretching and squashing of a human face. When the muscles of human face are stretched or squashed to an exaggerated degree, it can give a comical effect. The most important aspect of this principle is the fact that the stretching and squashing of an object does not affect its volume. That is, no matter how an object is deformed, it should still appear to retain its volume.
• Timing: Timing is the most vital element of an animation. It refers to the spacing between motion frames.The more is the spacing between the frames, the faster the object will appear to move. The speed at which an object is moving gives a sense of what the object is, what can be the weight of an object and why it is moving. Timing in an animation is significant for establishing the mood, emotion, and reaction of a character. For example, the blinking of an eye can be fast or slow. If it is slow, a character seems to be tired and lethargic. However, if it is fast, a character seems to be alert and awake. Timing can also be used to communicate important aspects of the personality of a character.
• Anticipation: It is used to prepare the audience for the upcoming motion or action and to make such action more live and realistic. For example, a person throwing a ball has to first swing his or her arm backwards, or a dancer jumping off the floor must bend his or knees first. These are preliminary actions that are used to emphasize the object movements. Anticipation can also be used for less physical actions, such as a character looking off-screen to anticipate someone's arrival, or attention focusing on an object that a character is about to pick-up.
• Follow through and overlapping actions: Follow through refers to the actions that are performed at the end of the actual motion. Follow through actions emphasize the fact that characters follow the laws of physics, which state that separate parts of a body will continue to move even after the character has performed the specified action. In other words, follow through captures how parts of an object continue to move even after other parts of that object have stopped moving. For example, the arm of a person continues to move even after throwing a ball. This is a follow through action. Overlapping action is another important principle of animation. It is the tendency for parts of the body to move at different speeds and different times. For example, when a dog is running, all its body parts are moving at different rates. The timing of his legs is different from the timing of the movement of his tail, or ears. By overlapping the actions of an object's body, hair, tail, clothing, etc., you can make your animation more fluid, natural and realistic. It is to be noted that while creating an animation sequence, an action should never be brought to a complete stop before starting another action. Overlapping maintains a continual flow between whole phrases of actions.
• Staging: It refers to the presentation of an idea in such a way that it is completely and clearly understood. An idea could be an action, a personality, an expression or a mood. Its main aim is to draw the attention of the audience to the most relevant action, personality, expression or a mood in a scene so that it is easily recognizable. Staging helps in keeping focus on what is relevant, and avoiding unnecessary details. It can be performed in several ways such as placing a character in a frame, using a light and shadow, and setting an appropriate angle and position of the camera.
• Straight ahead action and pose-to-pose action: These two are the basic approaches of creating animation. In straight ahead animation, the animator draws a scene frame by frame from beginning to end. That is, he or she first draws the first frame of the animation, then the second, and so on until the sequence is complete. Pose-to-pose animation, on the other hand, is created by drawing a few key frames, and then creating in-between images. The straight ahead action allows you to create a more fluid, dynamic illusion of movement and is better for producing realistic action sequences. On the other hand, pose-to-pose allows you to create better dramatic or emotional scenes, where composition and relation to the surrounding are more important. With computers, people generally use a combination of the two techniques. That is, they first plan out the overall process using pose-to-pose approach, and then create the in-between images using the straight ahead approach.
• Slow in and slow out (or ease in and ease out): The basic idea behind this principle is that when the human body or other objects move, they need time to accelerate and slow down. For this reason, we add more drawings near the beginning and end of our animation sequence to emphasize the extreme poses, and fewer drawings in the middle. This makes the animation looks more natural and realistic. For example, a bouncing ball tends to have a lot of ease in and out when at the top of its bounce. As it goes up, gravity affects it and slows down (ease in), then it moves in downward direction more and more rapidly (ease out), until it hits the ground.
• Arcs: In real world, generally the actions tend to follow an arched trajectory. That is, all actions move in an arc. For example, when a ball is thrown or kicked, it moves along a parabolic trajectory. Thus, while creating an animation sequence, the animator should try to have motion following curved paths rather than straight line paths. This will make the animation look more natural and realistic.
• Exaggeration: Generally, a perfect imitation of reality makes the cartoons or animation static and dull. To make the animation lively and entertaining, the exaggeration is used. This effect is used to emphasize an action. One can exaggerate motion, for example, moving an arm just a bit too far briefly in an extreme swing. Exaggeration may also involve the supernatural alterations to the physical features of a character, or elements in the storyline itself. However, exaggeration should be employed in a careful and balanced manner, not arbitrarily. The main idea is to make something more extreme in order to give it more life, but not so much that it becomes unbelievable.
• Secondary actions: They are generally used to make animation look more interesting and realistic. Adding secondary actions to the main actions add more life to the scene, and can help to support the main action. For example, if a person is walking, he/she can simultaneously swing his or her arms, or keep them in the pocket, or express his/her feelings through facial expressions, and so on. The main idea behind secondary actions is to emphasize the main action, rather than taking attention away from the main action. Secondary actions are generally included at the beginning and end of the movement, and not during the action.
• Solid drawing: The main idea behind solid drawings is to create three-dimensional drawings, and giving them weight and volume. It is very important for an animator to understand the basics of 3D shapes, weight, balance, anatomy, light and shadow and other relevant characteristics. Though these days, the computer animators need to draw less images because of the facilities provided by computers, still they need to have a basic understanding of animation principles and artwork.
• Appeal: While creating an animation sequence, it is necessary to include something that appeals the audience. Appeal in a cartoon character is similar to charisma in an actor. An appeal can be quality of charm, design, simplicity, communication or magnetism. It is important to note that an appealing character is not necessarily sympathetic or good-evils or monsters can also be appealing. It is basically the charm and charisma added to the character to make it real and interesting.

To handle the design and control of animation sequences, several animation functions such as a graphics editor, a key frame generator, an in-between generator, and standard graphics routines are required. Though these animation functions can be programmed using a general-purpose programming language, such as C, Lisp, Pascal, or FORTRAN, still several specialized animation languages have also been developed. These animation languages are categorized into three types, which are as follows:

• Key frame systems: These are specialized animation languages which are designed to generate the intermediate frames from the user-specified key frames. Originally, these systems were designed as a separate set of animation routines, but now these routines are often form a component in a more general animation package. In the simplest case, 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. For example, for a single-arm robot, one can specify six degrees of freedom including arm sweep, shoulder spin, elbow lengthening, pitch, yaw, and roll. If we specify 3-D translational and rotational for the base, then we can extend the number of degrees of freedom for this robot arm to twelve. However, for a human body, one can specify more than 200 degrees of freedom.
• Parameterized systems: These systems allow specifying the object motion characteristics as a part of the object definitions. The adjustable parameters control such object characteristics as degrees of freedom, motion limitations, and allowable shape changes.

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