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"Is CHILDHOOD always the best time ?”
13 years ago
The most important principle is called Squash and Stretch. When an object is moved, the movement emphasizes any rigidity 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, is alive with changing shapes in the cheeks, the lips, and the eyes. The squashed position depicts the form either flattened out by an external pressure or constricted by its own power. The stretched position always shows the same form in a very extended condition. The most important rule to 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 is sides squeezing in it would appear to grow. Consider the shape and volume of a half filled flour sack when dropped on the floor, it squashed out to its fullest shape. If picked up by the top corners, it stretched out to its longest 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 up 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 & stretch in bouncing ball 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 the 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 on itself, and stretches by extending out fully.
Squash & stretch in Luxo Jr.'s hop Squash and stretch is very important in facial animation, not only for showing the flexibility of the 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 cheeks. The cheeks squash and push up into the eyes, making the eyes squint, which brings down the eyebrows and stretches the forehead. When the face adopts a surprised expression, the mouth opens, stretching down 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 effect of strobing that happens with very fast motion because sequential positions of an object become spaced far apart. When the action is slow enough, the object's positions overlap, and the eye smoothes the motion out. However, as the speed of the action increases, so does the distance between positions. When the distance becomes far enough that the object does not overlap from frame to frame, the eye then begins to perceive separate images. Accurate motion blur is the most realistic solution to this problem of strobing, [8,9] but when motion blur is not available, squash and stretch is an 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 volume the same. Since the direction of the stretch should be along the path of action, a rotational transformation may be required to align the object along an appropriate axis.
Squash & stretch in bouncing ball 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 the 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 on itself, and stretches by extending out fully.
Squash & stretch in Luxo Jr.'s hop Squash and stretch is very important in facial animation, not only for showing the flexibility of the 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 cheeks. The cheeks squash and push up into the eyes, making the eyes squint, which brings down the eyebrows and stretches the forehead. When the face adopts a surprised expression, the mouth opens, stretching down 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 effect of strobing that happens with very fast motion because sequential positions of an object become spaced far apart. When the action is slow enough, the object's positions overlap, and the eye smoothes the motion out. However, as the speed of the action increases, so does the distance between positions. When the distance becomes far enough that the object does not overlap from frame to frame, the eye then begins to perceive separate images. Accurate motion blur is the most realistic solution to this problem of strobing, [8,9] but when motion blur is not available, squash and stretch is an 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 volume the same. Since the direction of the stretch should be along the path of action, a rotational transformation may be required to align the object along an appropriate axis.
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