After an animator worked out the key poses or extremes the animation is “Blocked”, They have to start working on how to screen it in such a way that the audience gets what the animator is trying to convey. By putting the in-betweens close to the keyframes and only one set key halfway through the animation, the result would be very spirited. The animation would slow down wherever the in-between frames are set closer between the “extremes” and speed up where the in-betweens are spaced out. This concept is called the “Slow-in and Slow-out” or “Ease-in and Ease-out”. Though an animation would work without this principle, the subsistence of this technique ensures smooth timing and spacing for the scene. This principle mainly works for the in-betweens that the animator would have to fill in when following the Pose-to-Pose approach to animation.
However, if this principle is over-used, the action sequence would lose its normalcy and look more mechanical and the animation would lose the appeal.
If you want an animated sequence to look realistic, you would want the movement to start off slow and pick up speed as it goes and then slows down before coming to a complete stop. For example, a car does not automatically hit a 100 mile an hour mark as soon as the ignition is turned on, it slowly shifts gear to reach that mark. Similarly when the car comes to a stop. it gradually slows down before coming to a standstill.
The Principle was first recognised by Walt Disney when he felt their animation was lacking something. He strived to get their animations to look as lively and sincere as possible. “Our work must have a foundation of fact in order to have sincerity. The most hilarious comedy is always based on things actual.” as quoted by Frank and Ollie in their book – Illusion of life. The attention to detail at the Disney studios is what sets it apart from so many other studios.
Shraddha Mithinti 