Thomas’s and Johnston’s landmark book on Disney animation, The Illusion of Life, features a chapter on the 12 “Principles of Animation.” This chapter has become the touchstone for understanding animation technique ever since, and no one studies character animation without these 12 principles coming up again and again. Many animators look at these principles as THE fundamentals. But I think there’s one principle missing — spacing.
What, you ask, is spacing? It’s the distance something moves from frame to frame, plotted on the two-dimensional screen space. In a moving body, every distinct body part has it’s own spacing, just as each follows its own arc. I’ve heard animators argue that the concept of timing includes spacing. This requires a convoluted conception of timing, to the point of unnecessary complexity. It’s really pretty simple. Timing is how long something takes to happen, arcs describe the paths of the moving elements, and spacing refers to the frame by frame displacement of the moving elements. If the element is accelerating, the spacing increases from frame to frame. If it’s decelerating, the spacing decreases. Everything that is moving is either accelerating or decelerating, period. Therefore the spacing should always be increasing or decreasing from frame to frame. Maybe not my much, but it’ll be there. Constant velocity, and therefore constant spacing, is a special case, like an arc that happens to be a perfectly straight line. Constant spacing and flat arcs make for mechanical animation.
I was fortunate to work with some animators who took spacing very seriously. From them I constantly heard “arcs and spacing” together. Like yin and yang, they fit. Frank and Ollie go into great detail about arcs (which is one of the Principles), but the closest they get to treating spacing as a fundamental principle is in making “slow in and slow out” a principle. Slow-ins and slow-out are important, but they’re a specific spacing solution to the problem of making something decelerate to a stop, or accelerate out of a stop, in a pleasing way. They’re a subtopic of the subject of spacing.
Because of the emphasis just on slow-ins and slow-outs, many people get the idea that spacing isn’t so crucial when something isn’t starting or stopping. Or rather, they don’t even think about it. It’s not an issue for them unless something really looks really wrong, then they’ll muck around till it looks better without really understanding what they’re doing. And in CG animation, it’s common to assume that the computer will take care of the spacing, especially if you make sure your curves are smooth in the Graph Editor. This is fatal to good animation.
If you’re doing CG animation, the spacing that matters is the spacing in the two-dimensional screen space. It’s not a theoretical concern, and it’s not what’s going on in the graph editor — it’s the spacing of your character that the audience will see. You can check your spacing using one of the plug-ins that are usually designed to track arcs, but I prefer good ol’ dry erase markers and stepping through a scene frame by frame (just be sure your monitor won’t get wrecked, so you might want to use a plastic overlay on if you’re unsure).
I have more to say on the topic, but this is already a long post. I apologize that I don’t have any animation examples with this post. I hate just putting up this wall of words, but if I wait till I have the clips I want this may never get done. Bear with me.