[Figure 4] (left) The arc is indicated with a mark on the computer screen. [Figure 5] (right) The poses are set in accordance with the sketch. Tick marks provide additional information to the whereabouts of my keys.

This mark provides a template for the remaining keys that will be set. I can begin setting the in-between poses making the wrist conform to the sketch on the screen. In addition, tick marks at the various key frames give me an indication of the spacing of my poses. Each time a key is added, I’ll make an additional tick mark with the pen. Now there is a visual representation of how the arm is articulating and I can adjust the keys accordingly. (See Figure 5.)

As you can see, having the proper arcs and paths of action (especially in computer animation) is crucial. Setting those additional keys in-between major poses is essential. In-betweens put the control in the animator’s hands, where it belongs, and as I will show you next, impact the accuracy with which the characters move.

The In-Between
To accomplish the refined movements of the characters I’m animating, it’s important to understand the term “in-between.” This term refers to the parts of animation that occur between the defining poses of a scene. Animators can set these additional keys or the computer can interpolate and create the motion for you. Regardless of their origin, these in-between key frames directly affect how the motion appears.

Like many of the other fundamentals discussed, this technique dates back to the early days of hand-drawn animation where the animator would lay out the key or extreme poses. After those drawings are completed, a second artist would be responsible for adding the in-between drawings based on timing charts and notes from the animator. These additional drawings created the necessary transitions to create a fluid movement with natural arcs.

As you can see in Figure 6, the in-between poses influence the quality of arcs that characters and objects move along. The examples, however, have yet to take into consideration the sense of weight and timing. In-betweens have a direct effect on both.

[Figures 6a and 6b] (top) [6c and 6d] (bottom) The in-between drawings in a traditional scene are shown above. The first and last images are the keys and the two drawings in the middle are the in-betweens.