Anticipation: Lifelike movement is a primary goal of animation. Early animators observed nature (including themselves) and experimented with techniques for making animated actions more closely resemble their natural counterparts. An important insight occurred. In many instances, a movement in one direction is preceded by a smaller preparatory movement in the opposite direction. My imitating and exaggerating these small anticipatory movements, animated drawings were given a more naturalistic appearance. By grossly exaggerating them, a comic effect is added.
Nature abounds with examples of this principle. The more carefully you observe living things, the more you will notice it. It is partly a matter of physics. In order to move a mass efficiently, a force must be directed against its center of gravity. Aligning the mover behind the center of gravity of the mass (for pushing) or in front of the mass (for pulling) produces part of the anticipation motion. Also, muscles work more effectively if used through their full range of motion. Thus, "winding up" your muscles and skeleton produces a more powerful stroke of the bat, the golf club, the ax or the boot.
Onionskin: The name is taken from the translucency of onionskin paper... This technique originates in traditional cel animation. By drawing on a translucent medium, with a light source beneath the drawing surface, an animator can see the position of an object on one page, while drawing it in a new position on the page above.
This useful property of paper has been brought forward into the digital age. Many software applications offer drawing layers with a translucent quality. This makes 'tweening a lot easier. In Macromedia Flash, the layers are shown progressively more opaque, to assist in identifying the stacking order of the layers.
In-between or Tween: An image drawn to show a character between the extreme moments of action or gesture. Tweens create smooth motion between keyframes where the action is most dramatic. Tweens are hand drawn in traditional animation, or computer generated for 3D and effects style animating.
Squash & Stretch: The judicial squashing or stretching of a character in motion. Stretching serves to emphasize the speed and direction of motion. Squashing highlights the effect of an abrupt change of direction or a sudden stop. I say judicial because like many other characteristics of animated drawing, the judgements made in the application of Squash and Stretch define the animators style.
3-D Coordinate Space - Cartesian Coordinate System
Imagine yourself (as is easy to do) at the very center of the universe. There are six directions ranged about you in three pairs:
* Left and right--the horizontal directions.
* Up and down--the vertical directions.
* Forward and backwards (or front and behind)--for which we have no general name.
Are all these pairs the same to us? Absolutely not. Because of gravity, up and down have a physical meaning quite distinct from left and right or forward and backward. Pasted as we are to the surface of what (for most practical purposes) is a flat plane, we do not have the same freedom to move up and down as we do to move in the other directions.
In an abstract 3-D space, such as that found in a 3-D computer graphics application, there is no gravity, and so there is no natural meaning to up and down, left or right, forward and backwards. We simply have a pure Cartesian space of 3-D dimensions (named for the great philosopher and mathematician Rene Descartes), and call the dimensions X, Y and Z. We choose a point in this space and call it the origin. As the origin, it is the location where X=0, Y=0, and Z=0, and the point is designated as (0,0,0). We run three axes right through this point, the X, Y, and Z axes, each perpendicular to the other two. Now we can designate the exact location of any point in our space relative to the origin. For example, a point at (3,2,1) can be reached by starting at the origin (0,0,0) moving 3 units of length (perhaps inches) in the X direction, then moving 2 units in the Y direction, and finally 1 unit in the Z direction. The numbers are called "coordinates" and therefore the defined space is called a 3-D coordinate space. The coordinates can be negative as well as positive. For example, to find the point at (-3,2,1), we would move down the X axis in the opposite direction as we did before. If the positive direction is left, the negative is right, and so forth.
Although the 3-D coordinate space in a computer application is a mathematical abstraction, our human experience guides it quite a bit. In the vast majority of objects and scenes you will develop, the direction of up and down will be evident and distinct from the other axes. In most applications the X dimension is horizontal to the gravitational sense of the scene. It is the horizon. Positive X values increase to the right, negative values to the left. The Y dimension will typically be vertical, positive coordinates increasing upwards, negative coordinates downward. Z will generally be depth, negative coordinates increasing as you move forward into the scene past the origin, positive coordinates increasing as you retreat backwards from the origin. But these are not hard and fast rules, and in fact, Fractal Design Ray Dream products make the Z axis the vertical one, up and down with respect to the gravitational sense of the scene. And Lightwave 3D orients the positive z axis toward the rear rather than the front.
Bump Map: A bump map is a method of creating the appearance of texture or relief on a surface without modifying the underlying geometry of the model.
A bitmap image or a procedural map generated by the 3-D application is applied (mapped) to the surface of the object. The greyscale value of the bitmap at every pixel is interpreted at every corresponding pixel on the rendered surface of the object. Lighter pixels on the bitmap are interpreted to increase the impression of relief, and darker pixels have less effect. The bump map can be interpreted positive or negatively. Thus a white pixel on the bump map may create either maximum relief or a maximum indentation in the surface, depending on the setting assigned by the user. Where a color bitmap is used for a bump map, only the greyscale data is used by the application.
A single image is often applied both as a bump map and as a TEXTURE MAP, to create a realistic effect of both color and texture.
Bump mapping is used to add detail to an image without increasing the number of polygons. Bump mapping relies on light-reflection calculations to create small bumps on the surface of the object in order to give it texture; the surface of the object is not changed. Bumps are applied by matching up a series of grayscale pixels with colored pixels on the rendered, colored object. Lighter grayscale pixels create a sense of maximum relief or maximum indentation; darker pixels have less effect. A computer must contain a supporting 3D graphics card when it runs an application that has been coded to include bump maps. If the graphics card does not support bump mapping, then the bumps won't be seen. In the case of computer games, the programmer usually will code an alternate version that doesn't use bump maps. This version will look flatter and less real.
Keyframing: Keyframing is the process of assigning values to parameters at specific moments in time--that is, to specific frames in an animated sequence.
The most important parameters to be keyframed are the transformations of models (objects), the camera, and lights. Thus all objects in the scene can be scaled (resized), rotated and transformed (moved) the the course of the animated sequence. The lights can be translated and rotated (if they are directional lights). The rendering camera can also be tranformed and rotated, providing the freedom of camera movement characteristic of motion pictures.
But all parameters may be keyframed and therefore animated. The surface material characteristics of an object, the color or intensity of a light, the zoom ratio of the camera, and even the geometry of objects can be keyframed. Some applications refer to the creation of keyframes for parameters other than transformations as the creation of "envelopes."
The application interpolates between the keyframes, creating the frames in between the keyframes when rendering. The control of this process of interpolation is very important in creating effective animation. Interpolation can occur in both space and time. For example, most applications will create curved path between translation keyrames where possible. But the speed of the interpolation may be curved as well, so that the change begins slowly, speeds up, and slows down into the next keyframe.
Parenting: Parenting is the process of creating a hierarchical organization of objects in a SCENE.
In parenting, an object (called the parent object) is "parented" to another object (called the child object). Parenting relationships can be nested to any degree, so that one or more objects are the children of another object, which is in turn the child of another.
Transformations of the parent object affect all child objects (sometimes called "descendants") as well. The effect is to allow separately modeled objects to be used in a scene as a single functional unit. For example, the chest of a human character may be made the parent of the two arms. In this manner, the arms will stay connected to the chest as the chest is rotated or translated. Likewise, the arms will be scaled up and down as the chest is resized. The arms, however, as child objects, can be transformed without affecting the chest.
Specular Reflection: Specular reflection is what we most commonly think of as highlights, the reflection of the light source off an object and back into the viewer's eye. Specular reflection is very important in 3-D graphics because it suggests curvature in 3-D space. The color of a specular reflection is typically that of the light source itself.
Specularity is controlled in both its degree (or intensity) and its spread (sometimes called "decay"). Very few natural objects have no specularity at all, and controlling the precise degree of specularity, in both parameters, is essential to creating the illusion of a wide range of realistic materials. Glossiness and shininess are attributes controlled by specularity.
Specularity is especially important in animation because a specular reflection necessarily changes as the object (or the camera viewpoint) moves, thus reinforcing the illusion of action in 3-D space.
Boolean Operations: Boolean Operations are modeling methods that make use of two objects that overlap and therefore share part of the same space.
In Boolean union, the geometry of the overlapping area is eliminated and a single object is created from the two using all of the exposed surface area. Union is generally used to merge objects that are most easily built from component parts that have been modeled separately.
Boolean subtraction is used to sculpt out the overlapping volume from one object or the other. After the operation, one object is left, minus its overlapping region with the other object.
Boolean intersection preserves the overlapping region only, eliminating all the rest of both objects.
Boolean operations are very computationally intensive, and often do not work reliably even with the most powerful applications and processors. Booleans are especially unwieldy with complex surfaces, and good modeling often requires careful planning for Boolean operations. If at all possible, Boolean operations should be performed at the earlier, and simpler, stages of modeling.
Primitives: Primitives are the basic 3D geometric shapes that are automatically generated by 3D modeling applications, and which therefore need not be constructed from scratch. A very considerable amount of modeling (perhaps most) begins with primitives, which are then edited and used with other primitives to create more complex objects.
All applications provide spheres, cubes, cylinders (sometimes called disks) and cones. Some provide a wider array. All primitives have parameters that define their size and shape. A sphere necessarily has a center point and a radius, though the application may also provide for defining the sphere by its x,y and z extents--in effect defining the sphere by a cube into which the sphere will fit. Some applications will always generate a primitive using default parameters, which the user must then edit after the object is created. High-end modeling applications typically allow the user to enter parameters numerically before the object is created. In all applications, the dimensions and locations of primitives can be edited either interactively (by dragging lines and points on the screen) or by entering values into a dialog box.
Spline: In computer graphics, a smooth curve that passes through two or more points. Splines are generated with mathematical formulas. Two of the most common types of splines are Bezier curves and b-spline curves.
Sprite: A graphic image that can move within a larger graphic. Animation software that supports sprites enables the designer to develop independent animated images that can then be combined in a larger animation. Typically, each sprite has a set of rules that define how it moves and how it behaves if it bumps into another sprite or a static object.