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.
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.
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
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.
& 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.
Coordinate Space - Cartesian Coordinate System
yourself (as is easy to do) at the very center of the universe. There are six
directions ranged about you in three pairs:
and right--the horizontal directions.
and down--the vertical directions.
and backwards (or front and behind)--for which we have no general name.
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.
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.
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.
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.
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.
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
Keyframing: Keyframing is the process of assigning values to parameters
at specific moments in time--that is, to specific frames in an animated
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.
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."
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.
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.
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.
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
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.
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.
Operations are modeling methods that make use of two objects that overlap and
therefore share part of the same space.
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.
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.
intersection preserves the overlapping region only, eliminating all the rest of
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.
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
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.