Why is raw motion-capture data or rotoscoped video footage such terrible animation? Exaggeration. Exaggeration is undoubtedly and without exception the most essential principle you will ever learn.
In broad terms, Exaggeration is less a tool in itself than the degree to which you apply all the other principles of animation: the amount of squash and stretch you use, the length of your holds, the curviness of your arcs, the distance of your follow-through and the shape of your poses.
Exaggeration is an effect especially useful for animation, as perfect imitation of reality can look static and dull in cartoons. The level of Exaggeration depends on whether one seeks realism or a particular style, like a caricature or the style of an artist.
The classical definition of exaggeration, employed by Disney, was to remain true to reality, just presenting it in a wilder, more extreme form.
Other forms of Exaggeration can involve the supernatural or surreal, alterations in the physical features of a character, or elements in the storyline itself. It is important to employ a certain level of restraint when using exaggeration; if a scene contains several elements, there should be a balance in how those elements are exaggerated in relation to each other, to avoid confusing or overawing the viewer.
Exaggeration isn’t a black-and-white concept: it can be the most subtle of enhancements or the most overstated distortion. It’s all about enhancing the essence of your idea or action. If your idea or action is wild and extreme, knock yourself out – push everything to its limits. This is where your judgment and the principle of appeal comes into play. The guiding principle is that you should at least be able to comprehend what’s going on.
You could also think of Exaggeration as a caricature of an action.
Even when the artist makes extreme distortions to the face, the elements that make the person unique are intact enough or enhanced enough to make an identification. With animation, this is much the same concept – enhancing the important aspects that help communicate the idea or action.
One reason for all this is that animation tends to need this emphasis to convey subtleties that don’t carry through very well otherwise.
Even if you religiously follow reference footage, you can be left with a performance that is lacking.
The Disney animators found out early on that even tracing action directly from film – creating a perfect capture of real motion – resulted in a stiff and unappealing animation. Motion Capture suffers from this as well.
Exaggeration is the amount of stylization and flair that you use to place your pen strokes – or, in the case of animation, your key frames.
From Frank Thomas and Ollie Johnson: