Visualization and Animation Technology (Computer Animation)

Computer Animation

Computer animation is the process of animating objects through the use of a computer.
Animating objects means to give life to objects through making it move according to an established behaviour.

Animation consists of establishing a number of drawing steps on a timeline, naed as key frames and in-between frames.
Animation exploits the illusion of movement
Animation is a synthetic (合成) process typically oriented (定向的) to entertainment: cinematographic sequences and 3D computer games.

Illusion of Movement

It is a process that provides viewers with an impression of movement for an object, which relies on phenomenon of Persistence of Vision.
Persistence of Vision refers to the optical illusion that occurs when the perception of an object does not cease for sometime after a shown images has disappeared.
human does not see gaps between subsequent images but a smooth transition.
The illusion of movement is an impression typically provided through animation sequences.

Division of Labour in Traditional Animation

Two different roles characterising animation production.

1. Master Animation establishing Key Frames
2. In-Betweener drawing frames in between key frames to fill in the gaps between the key frames.

Computer-based animation the In-between key frames are generated by computer, however, in traditional animation are generated by people.

Linear Interpolation & Non-linear Interpolation

Interpolation is calculating the positions between the end positions. In animation this corresponds to the position of the animated frames.

Linear Interpolation means the path between the key frames is divided into a number of equal-sized steps. The objects move in straight lines between key frames.
Advanages: requires lower computational load
Disadvantages: unrelistic

Non-Linear Interpolation means the path between key frames is divided into a number of not equal-sized steps. The objects move along curves between key frames.
Advanages: more realistic and less jerky movement; smooth changes in directions; realistic object slowdown; allows physics and world dynamic laws.
Disadvantages: large computation

Parametric Curve Editing

The curves developed by non-linear animation could be modified by points and the points can be provided as function parameters.

Parametric (rule-based) Animation

A parametric curve is a concise way to describe an animation path. This path can be defined through math function that includes parameters.
Parametric animation allows for physics or other rules to be applied to be applied to an animation path.
Parametric curves typically represent non-linear interpolated animations.

Camera Animation & Object Animation

Camera animation is diiferent from object animation as it represents a world observation viewpoint.
Camera animation can use key frames and interpolation (linear or non-linear). It has specific functions as it represent a world observation viewpoint, in particular: zooming and depth of field.

Camera and Object Animation can co-exist.

Camera animation can be simulated by object animation

Object Hierarchy

Object hierarchy establishes relations among objects that are part of a 3D model. It is relevant because it indicates how objects depend on each other, which is relevant when animating them. The object hierarchy ensures realistic movements and transforamtion.

It is a Top-down approch, typically expressed as tree-structure, which follows the rule that transformations at one level affect all the lower levels, but not higher levels.

Kinematics (运动学)

Motion kinematic applies to graphic objects that needs to be animated. It is relevant in order to understand of how objects move.

1. Forward kinematics : applies to transformations in a top-down approach. The motion of all joints is explicitly specified. It provides faster computation, but may result in robotic and jerky movements.
2. Inverse kinematics : applies to transformations in a bottom-up approach by specifying the final position of the lowest level in a tree structure. It provides more realistic animation, but it has a higher computational cost.

Image Warping & Image Dissolving & Image Morphing

Image Warping is like drawing an image on a rubber sheet, and stretching or compressing. It is defined through setting old and new positions of a number of control lines. This can establish an uneven (不平整的) amount of stretch and compression throughout the image.

Image Dissolving gradually change each old pixel value to the corresponding new value. It relies on a weighted average. It is possible to dissolve between still images and animated sequences, real and virtual images.

Image Morphing stands for ‘Metamorphosing’. It combines image warping and image dissolving. The image warping control lines are relevant to secure that the shown features match.

Motion Capture

Motion Capture is a technique to acquire object motion by recording real motion. It is used in computer graphics to animate objects and characters.

Real Motion is captured through images or inertial sensors with or without markers. The captured motion is replicated on a synthetic (合成的) module.

The captured images are used as key frames or animation frames.

Advantage: realistic animation
Disadvantage: expensive to set up and require motion capture