Doc:Tutorials/Animation/BSoD/Principles of Animation/Principles/Slow In and Slow Out
From BlenderWiki
Contents |
[edit] Introduction
[edit] What
Slow-in means slowing down the speed of an action when reaching a main pose. Slow-out means accelerating again upon leaving a main pose. So with both the movement should be:
- slower in the frames closer to an extreme: right before reaching it and right after leaving it;
- faster in between two consecutive extremes.
Examples:
- When standing up we start slow, catch speed and then slow down again as we straighten up. So if the extremes are the two poses: sitting and standing, we have slow-out of the first and slow-in to the second.
- A ball thrown up: slow-out as the hand starts pushing against the ball and slow-in as the ball is reaching its maximum height before falling back.
[edit] Why
Real world Physics, again. For their own good, characters and objects don't come to a stop or drastically change velocity immediately. They are accelerated to a given speed or slowed down from it, even if this happens too fast to be noticed by naked eyes.
The effect is also present and very important in living creatures. Consider this: we use our muscles for the needed contracting and relaxing to bend and straighten joints and let us move. This system accelerates the moving parts from rest and slows them down for stoping (to stay or to change direction). Without slow-out and slow-in, we easily get hurt and wear out muscles, tendons and articulations.
And that's why we use it when animating -- no, not to protect the characters! It's to make them more believable, life-like.
MAIN BENEFIT
soften the actions and make them more natural.
|
[edit] How
[edit] Frame by frame
If we are animating all frames of an action, instead of leaving inbetweens for the software to interpolate, we add Slow-out and Slow-in much like traditional animators have done for many decades: create more inbetweens closer to the main poses and less farther away.
Example: if animating a character closing her hand, with extreme #1 being the open hand pose and extreme #2 the closed one, create more intermediary frames (inbetweens!) with the hand almost open, then few with it half-closed and again more with the hand almost closed. Since each frame is shown for a fixed amount of time when the animation is played, the hand will be seen open, then still almost open for some time (slow-out of extreme #1), then closing quickly in the middle part of the movement, but almost closed for some time (slow-in to extreme #2) before finally closing.
FPS
the more frames an action takes to complete, the slower it is, naturally: at 24 fps, a hand going from open to closed in 24 frames represents 1 second of animation, while using 48 frames it takes 2 seconds to close. Thus, we can vary the pace of movement by using less or more frames for a given part of an action. Using more right after a main pose we have slow-out; right before: slow-in.
|
[edit] With interpolation curves
If we use animation curves to interpolate between extremes, we can vary the speed of any part of an action by directly editing the curve's control points. Knowing how is a fundamental ability for CG animators.
Note: with animation curves, the way to set the speed of movements is to change the type of curve (constant, linear, Bezier spline) and directly edit its control points. The more vertical a piece of the curve is, the faster the action will happen there. So perfectly horizontal pieces represent objects at rest in relation to the attribute controlled by the curve (position, rotation, scaling, etc. etc.).
[edit] Fast-in, fast-out
To show that a character or object is accelerating, we can avoid slow-in and slow-out of a pose, and go for “fast-in and fast-out” transitions.
A bouncing ball is a perfect example of where to use both slow in/out and fast in/out:
- at the high part of the movement, the ball is going up and slows into the top pose, right before coming down (using slow-out);
- at the low part it comes fast into the bottom pose, where it collides with the ground, and also goes fast out up again.
[edit] Physics
[edit] Story Development
[edit] Notes
[edit] Cel Animation
This is how slow-in and slow-out work with traditional (drawn) sequences: as the action starts, there are:
- more drawings near the starting pose;
- few, maybe one or two, in the middle;
- and more drawings again near the next pose.
Fewer drawings make the action faster and more drawings make the action slower.
[edit] Pedal to the metal?!
In some circunstances it's a good idea to omit slow-out and slow-in, in analogy to what we discussed about anticipations: to surprise the audience, for a gag, to give the impression of great speed. Done properly, the omission can give the snap, the abrupt feel that the action needed.
Summer of documentation 2006 -- Willian 07:20, 5 July 2006 (CEST)
|
