Classic Principles of Animation

This first section looks at the 2D and 3D applications of the original 12 Principles of Animation introduced by Disney in the 1930s. These include Squash and Stretch, Anticipation, Staging, Straight Ahead Action VS Pose to Pose Action, Follow-Through and Overlapping Action, Slow-In and Slow-Out, Arcs, Secondary Action, Timing, Exaggeration, Solid Drawing, and Appeal.

Principles in Action

The walking spider at right illustrates several principles we discuss below, including Secondary Motion on the body, Counterpose between legs and counter-rotating body, Squash and Stretch, and Exaggeration. This character is rigged with Bones in 3ds Max. Check out the spider in a game environment on the Games page, or see how to take a bones character into the Unity3d game engine via the Tutorials page.

Squash and Stretch

Squash and Stretch is best described by animating a bouncing ball, as shown at right, where the ball squashes when it hits the ground, deforming and becoming more flat, and then reforms as it continues back up again. A more exagerated version is shown at right, where the ball stretches upwards and then squashes against the walls at it bounces. This can be applied character movements (as during a sneeze, scream, or grimace) that exagerrated the movement and add a comical and dramatic sense to the animation.

Anticipation

Anticipation is a preparation for an action of some kind; in the animation above right, the ball is demonstrating anticipation as it trembles and then stretches upwards, getting ready for take-off. This can also take the form of a vase tipping and threatening to fall from a window, or a batter winding up to hit a ball.

Staging

Staging is presenting a scene so that the intent or mood of the scene will be clearly communicated to the audience. By paying attention to the character position, character movement, camera movements, and carefully considering all scene content, this can be achieved. Each of these factors can be used to guide the eye of the audience, and can contribute to or detract from the intent or mood of the scene. In the example at right, a scene is being worked out depicting a confrontation between three characters.

Straight Ahead vs Pose to Pose

Straight Ahead action is where you draw or animate the character from beginning to end, every single frame, without generating keyframes first. Pose to Pose action (also called Keyframing) is where there are a series of poses created, residing on "Key" Frames and the "tweens" or in-between frames are generated to complete the animation. In the example at right, the character goes from a root pose to a pose that prepares for a jump. The jump is made up of several poses, which are then tweened by the animation software automatically. Most animation today is done with Pose to Pose because it is faster and more efficient.

Follow-Through and Overlapping Action

Follow-through is easiest to visualize with a sports example - a golfer hits the ball, but the club doesn't stop there, it continues through its arc, long after the ball has been hit, as the golfer's body twists. Overlapping Action is what is happening with the golfer's limbs during this process; the start and stop points, as well as motion, overlap. The movement of a palm tree in the wind, shown at right with onionskinning enabled, illustrates this process.

Slow-In and Slow-Out

Also known as Ease-in, Ease-out; the bouncing ball example at right demonstrates this principle as the ball "eases in" to its fall (on the left), gathering speed while dropping, bounces on the floor, and "eases out" of its motion, gradually slowing while the forces of gravity take a hold on it. Ease-in and Slow-in are the same basic idea; you are slowly accelerating the motion of the object. Ease-out and Slow-out are also synonomous - you are slowly reducing the speed of your object's motion. Faster movements show fewer keyframes, slower movements show more keyframes.

Arcs

Everything living tends to move with arc-based motion. When a character runs or swings their arms or legs, those limbs are rotating. Feet rotate about ankles, lower legs rotate around knees, and entire legs rotate around hips. Whether the character is animated using keyframes or motion capture, key points in the anatomy of the character can be selected and moved or rotated to generate smoother arcs and therefore more realistic movement. Another aspect of the arc in motion is with the sinusoidal movement of the hips and head, up and down as the figure progresses across the screen.

Secondary Action

Secondary action can be seen in organic and mechanical movement, when a body that is only loosly attached to the body in primary motion moves. When a car goes around a corner too fast and a loose door swings open, or as shown at right, when a box in the back of a truck bounces around, we are seeing secondary action (also known as secondary motion).

Timing and Spacing

Timing is the precision with which character movement occurs, and how long it lasts. How many frames per second is the animation, and how many frames does the character need to take a step, stretch their neck, yawn, blink, or throw a punch? It all comes down to timing. Spacing is the physical representation of timing. In the horse study shown at right, the different positions of the horse are spaced one keyframe apart; the distance between the legs indicate how fast the leg is moving through space; the more distance, the faster the movement.

Exaggeration

Exaggeration is used to make the character's expression or movement more dramatic. At right, a car hits a brick wall and the result is that it is smashed to half its length; even the wheels and tires are squashed. While this is blatant exaggeration, there are a whole range of possibilities. A more subtle exaggeration can be used to make the motions of a character read better, much the way that stage actors must sometimes overact so that their poses and expressions read at a distance.

Solid Drawing

Solid drawing refers to competent, drawings that are well-proportioned, demonstrating good form, with appropriate volume and weight to them. These factors help to make a character appear more real and lifelike. For example, Natasha and Boris (characters from "the Bullwinkle Show"); note the differences between these characters in height, form, posture, pose, expression, and weight. Note the similarities - pale skin, natural poses, downward-slanting eyebrows, mischevious smiles - and, if we had sound, thick Russian accents.

Appeal

Appeal is a somewhat deceptive term for what might better be described as charisma. The character should be well-developed and unique in form, color, texture, pose, expression, and movement (as in walk/run cycles and other physical movements). The design should be clear and clean. This individualized distinction helps to create character recognition and appeal, as well as making the character more believable for the audience. Appeal is necessary for all characters to be more authentic. Chicken Little (Disney, 2005) who is a great example of a clear, recognizable, and well-developed character.

Extended Principles of Animation

Since the first 12 principles of animation were codified by Disney in the 30s, there have been technological and artistic developments that are covered in this section. Some of these principles are implied in the original principles and some are not.

Shape, Form, and Anatomy

The shape or form being used for the animation is important for realism, believability, and consistency. A realistic horse animation needs the same angles expressed by the outer contours in this rendering, but even the cartoon horse needs some suggestion of these angles, or it will begin to look like a stuffed animal. Suggesting the anatomy of the horse even in a cartoon gives it recognizability and authenticity. And even if the creature being animated does not exist in reality, borrowing forms and anatomy from creatures that do exist can make the imaginary creature more authentic.

Weight

What is the object, and how much does it weigh? How can we tell this? How is the weight of the object apparent by the way other objects and characters interact with the object? Why is it moving? What is the purpose to the movement? The image at right illustrates how a character's entire posture changes when struggling with too much weight.

Action and Reaction

Action and reaction is illustrated by a rocketship, the most well-known example of this physical law; however, this principle applies to characters as well; not only physically, in that a pushed character will react to whatever pushed it by pushing back or falling down but actions and reactions can take place in dialogue and in emotional reactions of characters when things are going well or not so well. Sometimes the reaction is instant, as in the rocket - but the reaction can also be delayed, especially when dealing with emotional interactions.

Action Ahead of / Action Behind the Story

Action Ahead of the Story and Action Behind the Story can add great tension and suspense to an animation. Action ahead of the story is illustrated by the upper image at right; the surfer is seeing something we as the audience cannot see. This adds suspense. Action behind the story is illustrated by the lower image at right; the surfer is not aware that there is a shark following her rather closely. The tension in this case comes from not knowing how the character will react to what we already know about, and how it will turn out.

Perspective

In 3D animation a basic perspective is often handled automatically through the camera, unless there is a special angle you are working towards. With 2D animation, the perspective must be drawn with either One Point perspective (as shown at right), Two Point Perspective, or Three Point perspective. An unusual perspective, whether the animation is 2D or 3D, can make the animation much more interesting.

Direction

The overall direction a body is moving can greatly enhance or detract from an animation. Direction can also be exaggerated to magnify the effect of a character's movement. Whether exaggerated or not, the direction of the character should always match the intent of the animation and what the character is doing at that time.

Tension and Relaxation

Tension can refer to the emotional or physical state of the character as well as to the state of the control curves that govern a rigged character's movement. The movements of a character who is under great emotional or physical strain are tighter and more tense than those of a character who is happy-go-lucky in their movements. One character is more controlled, even quick and precise; another is loose, flowing, with a slower reaction time.

Depth and Volume

Depth can be implied in even a 2D cartoon by putting different objects in front of other objects, and by fading the colors of the more distant objects. Depth is also implied by making more distant objects smaller. Many 2D and 3D animations use shadow to depict volume, whether it is drawn by hand, proceduralized by gradient features, or automated by light placement as in the case of 3D animation software. Depth and Volume add to the authenticity and immersion of a scene, whether you use 2D or 3D techniques.

Working from Extreme to Extreme

Extreme to Extreme refers to positions for 2D and 3D characters. In a walk cycle, it is more straightforward and efficient to draw the extremes of the walk cycle first, and go it to create the other key frames afterwards. This can be seen at right, where the biped (skeleton) for a game character is being animated for a backwards run cycle. The first frame, at right, is one extreme, the second position in the middle is the furthest the feet ever spread apart, and the third position is where the feet are closest again, nearly the same as in the first frame.

Rigging

Rigging is a 3D animation technique where bones or some other skeletal structure are assigned certain motion constraints (so that an elbow cannot move the wrong direction, for example), and then different parts of the character mesh are assigned to each bone. Later, in the animation process, when the skeletal members are animated, the character mesh moves also. Inverse or Forward Kinematics and Controllers can be applied to the rig as well, making the process easier to control and adjust. The character at right is in the process of having its mesh vertices assigned to different bones in the rig, through the use of "envelopes".

The Physics of Animation

What does physics have to do with animation? Everything. You've got to make it look right before you can make it look interesting or unique. Without a solid concept of real-world physics, you will not have a strong foundation to build upon as you develop as an animator. You will not find these guidelines in any book on Newtonian Physics, since they are in the language of animation - nevertheless these guidelines are based upon Newtonian Physics. For more a more in-depth look at animation physics, visit Alejandro Garcia's excellent site at www.animationphysics.com.

Respect Physical Boundaries

This first rule of physics simply refers to the fact that a character should not be able to walk through walls and their feet should not glide on a cushion of air or penetrate the ground. This is a common problem for beginning animators and can usually be resolved by simply paying attention as you animate, and sometimes means zooming in on the critical areas.

Make the Feet Stick

When the character walks or runs, the feet should not be sliding around on the ground, but should stick. Ice-Skating refers to the commonly seen error with beginning animators where the character's feet seem to be ice-skating across the floor. Usually this is a result of not properly using pivot points on the biped, a hard-to-control character rig, or simply not taking the time and effort to make the foot "stick" instead of slide.

Falling Objects Accelerate

This rule refers to the law of gravity which states that falling objects will accellerate until achieving terminal velocity. The opposite of this rule is also true; objects hurled up into the air will begin to slow down (unless they can break free of the local gravity system) due to the pull of gravity, until they once again fall to the ground.

Allow for Centrifugal Forces

As an object moves in a curve, centrifugal forces will cause it to fly or lean away from the center of the curve. This is evident in the image at right, where the car is leaning away from the center of the curve it is following (you can see the path as a spline curve in the image). With centrifugal lean, even a cartoonish car can achieve some measure of authenticity.

COG is the Key to Balance

The location of the COG (center of gravity) should inform all of our animations, whether of inanimate objects or characters. A bottle falling off of a table follows a path described by its COG, and a character putting most of his weight on one leg will naturally line up the rest of his posture to with his new COG. In the example at right, the centriod of the bottle is marked with a black dot. When the centroid is directly over the supporting edge, the object is perfectly balanced. However, in this case, because of the bottle's inertia from being hit by a ball, it will soon fall off the table.

Apply the Coefficient of Friction

Every material has its own coefficient of friction, which determines how quickly frictional forces will slow down a sliding or rolling member. A golf ball will roll better in short grass, worse in the "rough", and worse yet in the sand. It is not necessary for animators to calculate the exact frictional forces of any two objects, but it is necessary to think it through a little bit before animating.

Falling Object Break, Bounce, or Squash

It is common for beginning animators to hand in assignments where an object falls from a height, reaches the ground, and magically just stops (sometimes a few inches from the ground!). This never happens in the real world. If the object is a plastic bottle, it will bounce a few times first, based on its form and center of gravity. If it is a glass bottle, it might break. If it is soft, it might squash upon impact. And if it is especially heavy and hard, it might end up squashing the ground and leaving a crater, though this would also usually be accompanied by a bounce or two.

Camera Techniques for Animation

Camera techniques are one of the most overlooked aspects of animation, particularly among beginning animators. In this section we give a general overview of the most commonly used camera techniques, which can apply not only to animation, but to general cinematography.

Push the Camera In to Emphasize Drama

Pushing the camera in means simply to zoom the camera in closer to emphasize a dramatic moment. This can be done in 2D animation by enlarging the image, or in 3D animation by zooming the camera in.

Pull Focus to Emphasize Background

Pulling Focus so that the foreground becomes slightly blurry, and the background sharpens, is used to lead the viewers eye to something going on in the background. For example, a storm could be rolling in, an enemy ship could be appearing on the horizon, or another character could be watching from a distance. Pulling the Focus is a technique that should only be used when there is a good reason for it that is important to the story. In the example at right, focus has been pulled so that the final box (blue) is in sharp focus, and the closest objects are blurred-out.

Light the Subject with Classical Lighting

If you can't see the animation, it doesn't matter how good the camera work is. Utilize classical lighting principles unless you have a good reason not to. Classical lighting setup is: a key light, a back light, and a fill light. Too many dark shadows in the scene will not add to the alure of your shot. In 2D animation, the equivalent message would be to keep the animation bright and clear enough so that it "reads". At right is a sphere with a Key light in front for our main light, a Back light angled from the rear to help make the sphere stand out against the background, and a Fill light filling in the shadows on the left.

Block Moves Before Shooting

Look for the best angles and compositions. Think through how you will move from the first shot to the next shot, don't make these transitions haphazardly. This is a place where scrubbing the timeline can be a real help - make sure each scene looks pretty good, and the transitions from scene to scene look good, before taking the time to render.

Look for good Silhouettes

Good silhouettes have plenty of information and help to emphasize what the character is doing - they help the scene "read". Consider a camera following a car - the 3/4 view of the car is a lot more interesting than a view of the cars backside, because it is a more interesting silhouette. Some animators will adjust lighting and materials so that all they see are silhouettes to make achieving strong silhouettes easier. Once the silhouettes are satisfactory, the lights and materials go back on.

Use Dutch Angle to make scenes more interesting

Dutch Angle is where the camera is tilted so that the horizon line is no longer flat. This can be use to suggest drunkenness, dreamlike states, or similar wild / unorthodox moments in the animation. At right is a scene from the Batman TV series, which often incorporated Dutch Angle for the fight scenes.

Use Long Shots to Establish the Scene

Long shots are great for telling the audience where the action is taking place, and can help to establish the mood - but use them sparingly. I find novice animators staying wide for the majority of the animation, as the camera follows tiny jets or spaceships or other subjects as they move in the distance. Move the camera closer to these subjects once the shot has been established in order to bring the viewer into the action. When you do bring the camera in tight, it is also a good time to fade in or increase the sound of the immediate environment where the action is.

Vary the Camera Angles to Keep it Interesting

Vary the Camera's angle upon the subject – don't keep a static angle too long. The same viewing angle for too many frames looks flat and boring. Study car chase scenes from classic movies; you'll see the camera follow the action from behind the cars, from the front, sides, and different angles in-between.