Playing with Maya: Researching Squash and Stretch, (also) Timing

Bounce Ball Animation Arc

Pixar – Luxo Jr, 1986

To Infinity and Beyond

Timing: or, the speed of an action important principle because it gives meaning to movement – the speed of an action defines how well the idea behind the action will read to an audience. It reflects the weight and size of an object, and can even carry emotional meaning.

Proper timing is critical to making ideas readable. It is important to spend enough time (but no more) preparing the audience for: the action. If too much time is spent on any of these, the audience’s reaction will wander. If too little time is spent, the movement may be finished before the audience notices it, thus wasting the idea.

The faster the movement, the more important it is to make sure the audience can follow what is happening. The action must not be so fast that the audience cannot read it  and understand the meaning of it.

More than any other principle, timing defines the weight of the object. Two objects, identical in size and shape, can appear to vastly different weights by manipulating timing alone. The heavier the object is, the greater its mass, and the  more force is required to change its motion. A heavy body is slower to accelerate and decelerate than a light one. It is a large force to get a cannonball moving, but once  moving, it tends to keep moving at the same speed and requires some force to stop it.  When dealing with heavy objects, one must allow plenty of time and force to start, stop or change their movements, in order to make their weight look convincing.

Light objects have much less resistance to change of movement and to need much less time to start moving. The flick of a finger is enough to make a balloon accelerate quickly away. When moving, it has little momentum and even the friction of the air quickly slows it up.

Timing can also contribute greatly to the feeling of size or scale of an object or character. A giant has much more weight, more mass , more inertia than a normal man; therefore he moves more slowly. Like the cannonball, he takes more time to get started and, once takes more time to stop. Any changes of movement take place more slowly. Conversely, a tiny character has less inertia than normal, so his movements tend to be quicker.

 

The way an object behaves on the screen, the effect of weight that it gives, depend entirely on the spacing of the pose and not on the poses themselves. No matter how well rendered a cannonball if it does not behave like one when animated. The same applies to any object or character.

The emotional state of a character can also be defined more by its movement than by its appearance, and  the very speed  of those movements indicates whether the character is lethargic, exited, nervous or relaxed. Thomas and Johnston describe how changing  the timing  of an action gives it new meaning:

Just two drawings of a head, the first showing it leans toward the right shoulder and the second with it over on the left and its chin slightly raised, can be made to communicate a multitude of  ideas, depending entirely on the timing used. Each in-between  drawing  added between these two “extremes” gives a new meaning to the action.

NO in-betweens…… The Character has been hit by a tremendous force. His head is nearly snapped off.

One inbetweens….. The Character has been hit by a brick, rolling pin, frying pan.

Two in-betweens….. The Character has a nervous tic, a muscle spasm, an uncontrollable twitch.

Three in-betweens….. The Character is dodging a brick, rolling pin, frying pan.

Four in-betweens….. The Character is giving a crisp order, “Get going!” “Move it!”

Five in-betweens…… The Character is more friendly, “Over here.” Come on-hurry!”

Six in-betweens……. The Character sees a good looking girl, or the sports car he has always wanted.

Seven in-betweens….. The Character tries to get a better look at something.

Eigth in-betweens ….. The Character searches for the peanut butter on the kitchen shelf.

Nine in-betweens…. The Character appraises, considering thoughtfully.

Ten in-betweens…… The Character stretches a sore muscle.

Squash and Stretch: The most important principle is called Squash and Stretch. When an object is moved, the movement empathizes rigidly in the object. In real life, only the most rigid shapes (such as chairs, dishes and pans) remain so during motion. Anything composed of living flesh, no matter how bony, will show considerable movement in its shape during an action. For example, when a bent arm with swelling biceps straightens out, only the long sinews are apparent. A face, whether chewing, smiling, talking, or just showing a change of expression, its alive with changing shapes in the checks, the lips, and the eyes.

The Squash position depicts the form either flattened out by an external pressure or constricted by its own power. The Stretch position always shows the same form in a very extended condition.

The most important rule of Squash and Stretch is that, no matter how squashed or stretched out a particular object gets, its volume remains constant. If an object squashed down without its sides stretching, it would appear to shrink; if it stretched up without its sides squeezing in it would appear to shrink; if it stretched up without its sides squeezing in it would appear to grow. Considering the shape and volume of a half filled flour sack: when dropped on the floor, it squashed out to its fullest shape. It never changes volume.

The standard animation test for all beginners is drawing a bouncing ball. The assignment is to represent the ball by a simple circle, and then have it drop, hit the ground, and bounce back into the air. A simple test, but it teaches the basic mechanics of animating a scene, introducing timing as well as squash and stretch. If the bottom drawing is flattened, it gives the appearance of bouncing. Elongating the drawings before and after the bounce increases the sense of speed, makes it easier to follow and gives more snap to the action.

Squash and Stretch also defines the rigidity of the material making up an object. When an object is squashed flat and stretches out drastically, it gives sense that the object is made out of a soft, pliable material and vice versa. When the parts of an object are of different materials, they should respond differently; flexible parts should squash more and rigid parts less.

An object need not deform in order to squash and stretch. For instance, a hinged object like Luxo Jr. (from the film, Luxo Jr.), squashes by folding over itself, and stretches out fully.

Squash and stretch is very important in facial animation, not only for showing the flexibility of flesh and muscle, but also for showing the relationship of between the parts of the face. When a face smiles broadly, the corners of the mouth push up into the checks. The checks squash and push up into the eyes, making the eyes squint, whichbrings down the eyebrows and stretches the forehead.  When the face adopts a surprised expression, the mouth opens, stretching down on the cheeks. The wide open eyes push the eyebrows up, squashing and wrinkling the forehead.

Another use of Squash and Stretch is to help relieve the disturbing effects of strobing that happens with very fast motion because sequenceial positions of an object become spaced far apart. When the action is slow enough, the object’s positions overlap, and the eye smooths the motion out. However, as the speed of the action increases, so does the distance of between positions. When the distance becomes far enough that the object does not overlap from frame to frame, the eye begins to perceive separate images. Accurate motion blur is the most realistic solution to this problem of strobing, but when the blur is not available, Squash and Stretch is alternative: the object should be stretched enough so that its positions do overlap from frame to frame (or nearly so),  and the eye will smooth the action out again.

In 3D keyframe computer animation, the scale transformation can be used for Squash and Stretch. When scaling up in Z, the object should be scaled down in X, and Y to keep the same. Since the direction of the stretch should be along the path of action, a rational transformation ,may be required to align the object along an appropriate axis.

 

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