Free 3D training | Disney’s 12 principles of animation: slow in and slow out

Master Disney’s 12 classic principles of animation in 3D with Steve Lambert’s regular series of articles on the fundamentals of CG. This week: slow in and slow out, also known as ‘ease in and ease out’ or cushioning

This week Weta Digital’s animation director Steve Lambert explains how to apply the sixth classic principle to your animation: slow in and slow out (To find previous topics scroll to the bottom of this post.)

FOR: Any software | TIME TAKEN: 3 hours | TOPICS COVERED: Slow in and slow out |ALSO REQUIRED: Maya (to view scene files)

Download the project and animation files for this training: 
fundamentals_6.zip (20MB)

It’s rare for something to move at a constant rate: gravity, atmosphere, constraint and a range of other factors make sure of that.

When something starts to move, it will usually build up energy and speed – it won’t instantaneously achieve a terminal velocity. The same is true when it comes to a stop: the built-up energy needs time to disperse before coming to a halt.

Slow in and slow out (also known as ‘ease in and ease out’ or cushioning) are the ways you represent this phenomenon in animation.

They deal with the way you enter and exit key poses (as opposed to key frames). Spacing your in-betweens or modifying your curves can achieve this acceleration and deceleration. More in-betweens or a flatter curve creates a slower movement, while fewer frames or a steeper curve create a faster one.

Your approach to slowing in or out can be different depending on your medium: In 3D, you have the invaluable tool of a curve editor. However, people often rely too much on the computer to control these curves – as if the software knows what you’re trying to animate! You need to get stuck into the curve editor and take complete control over all of those tangents. Even then, it might be necessary to do frame-by-frame animation to get the exact result you’re after.

Download the training videos to see this principle in action

In the first example to show the principles in action (SlowInOut00.mov), I’ve created a clip that shows four versions of the same movement. Each has the same overall timing: all I’ve changed is the spacing leading into a key pose, either by modifying the curves in the Graph Editor or by shifting the in-betweens.

Scrub through the clip to observe the differences. You get a different attitude from the character in each example, even though they are identical in substance.

The next three clips are all based on a single five-second sequence. All three have the same timing: all I’ve changed is the entry or exit from each key pose.

In the first clip (SlowInOut01.mov), the action is completely linear. The movement is lifeless, and the characters have no real weight. The characters shouldn’t just launch off the ground.

The second clip (SlowInOut02.mov) is looking much better. Easing out of the crouch injects effort into their jumps as they overcome gravity. We slow into the peak of his jump and slow out of the peak as inertia fades and gravity takes over. However, the characters are slowing into their landing positions. This makes the landings a bit soft, so it’s better to change the landings to a ‘fast in’, as shown in the third clip (SlowInOut03.mov).

This has two effects: more ‘hang time’ for the characters and real punch to the landings. The absorption of the landing energy is reflected in the bending of the see-saw.

Slow in and slow out are essential to creating subtle and realistic movements. Choosing where to use them – or where not to use them – can greatly enhance your characters’ believability.

To see the examples of these animation principles in action download the fundamentals_6.zip

Next week we’ll show you how to achieve prefect timing in your animations using the seventh classic principle: arcs.