Wow, okay. So, I realize this post is a bit on the looooong side, but what a great post. It's funny too, because the other night I was watching (by watching I mean studying the acting) the movie Up in the Air with George Clooney and I was really studying his facial expressions, as well as the other characters in the movie and starting thinking about all the subtleties and imperfections in their movement. Funky arcs, long/short anticipations, weird eye darts, stuff like that. I was comparing it to animation and thinking about the major difference between the two. With animation you have all the power and total control over your character and everything they think and do. I understand that with the actors they get multiple takes, but with you get the problems of something turning out really good (like a head nod) on one part of the shot, but then there's a random blink in another part that you might not like (as the Director). As Animators, we get multiple iterations to get the shot just right... as Animators we're responsible we're making our shots believable to where the audience should NEVER think about the fact that they're watching animation. So I think that's where the term "Animation Ninja" comes into play. Well this post goes into great detail about bringing your shot to that next level. Think of it as un-polishing your shot, or making your shot 'dirty' to enhance it's believability yet still keeping it 'cartoony' or animated. So without anymore babbling from me.... Thanks for sharing Cameron.
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Perfect Imperfection
I love animation that shows us something we recognize, and we all recognize imperfection.I wanted to do a post on how it can be really great to add imperfection to your animation, and in this case specifically how sometimes things like a perfect ease-in or overshoot can add an element of falseness to your work when creating animation in a certain style. I say this because I was watching the shots of a particular animator here at DreamWorks who does a wonderful job of this, and wanted to understand this a little more and include it more frequently in my own work.
When I used to animated in Maya, I was never a curve editor animator. I would just look at everything in the shotCamera, and track arcs in 3D using my motionTrail script. Here at work, the software we have for manipulating curves is so good, I quickly started doing a lot of stuff in the curve editor and making a habit of smoothing stuff out cleanly and watching to make sure that everything was easing in and out nicely.
I really love using the curve editor, and probably wouldn't go back to doing it all in the viewport, but I recently noticed that my movements were becoming too smooth, too calculated and my animation was losing some of that naturalistic punch that I used to see in my older stuff.
I usually go back to live action to figure out how things really move and how it relates to animation, and below I've shared a few videos that show examples of where we may be tempted to oversimplify and oversmooth the movement. In reality there is a lot of "imperfection" that we see in the arcs of movement without really realizing it, but its part of constructing our perception concerning whether or not something is real.
You can see immediately that the arc and the spacing on the foot is not what you might expect if you just started animating this from scratch...
The arc above shows how the curve might turn out based on our assumptions, and what were used to implementing. Its pretty "perfect" and quite different to how the real foot travels through the air. This would probably result in a semi-decent looking animation, but with something looking not quite right or as if not enough detail existed in the movement.
Instead of going nice and smoothly over the top of the arc, the foot drops slightly before it rises up again at the peak. This is the natural arc as the lower leg swings forward.
Theres an interesting section here where the foot slows down before it begins to fall. If you click back on the video, we see this as a slight pause in the leg, and it illustrates thought in the characters mind... a moment of calculation as his brain thinks about the best place to land the foot. 
Notice how the foot doesn't fall to the final contact pose with that perfectly accelerating downward motion, its spacing is almost linear after it starts to fall, then suddenly accelerated just before the contact. The foot is not an object freefalling through space - the leg above it can alter and "imperfect" the spacing as it falls.As the woman gestures, she holds out her hand, and for a part of the gesture she appears to hold it relatively still as she moves it screen right...
When we track this "smooth" part, its clear how irregular the arc is. Despite the fact its not obvious when we watch the video above, its all going on under the hood, and adding to our perceptions of whether or not the character is real.
The movements of the head are a particularly ideal place to use this idea. When we start animating, we quickly learn about what can make head moves appealing - such as dipping the nose on a turn, a slight nod or twist in the opposite direction before a change etc. These are by all means valid, and used wisely can really add to head animation. Take a look at some of these videos below where I tracked the nose to see how the head is moving, and you quickly see how "wobbly" and unsmooth the curves are. I find this stuff really interesting to study.
Here's another curve we might normally be tempted to smooth out - reducing its subtle realism. I love the little bump at the top, and the small "glitch" in the deceleration at the bottom of the curve.
The guy in the blue shirt above shows how erratic the arcs on a head can really be. Whether or not your shot would call for this kind of detail depends on many things, but its just really interesting to me to see how crazy it can get, on a move that isn't really that extreme at all.
Without getting into the subject of overlap and inherited motion, you can see clearly how a more complex action like sitting down and adjusting weight and balance can increase the scale of these direction changes.
Even movements that are supposed to appear smooth and elegant may contain these irregularities, they are just smaller and less noticeable.
The arcs are almost "smooth" but not quite. I might be tempted to round out the tops of the curves and even out the spacing, but these subtle effects can increase the believability.
As far as how to implement these irregularities, it is definitely something I would recommend doing right at the last stages of polish. You can do this by just playing with the curves and adding little bumps and notches, but it can be very hard to get it to look right, and not like you just screwed up smoothing your shot...The reason for calling this post "perfect imperfections" is because nature will always do this exactly right! If your software supports it, I would even recommend doing this on another animation layer, that way its easy to experiment and scale things bigger and smaller without changing your main acting underneath.
Its important to mention that in animation we don't strive for "realism", we strive for communication of the idea. If the idea is ultra realism, then yes we animate as realistically as we can, but normally we are extracting the essence of movement and simplifying it to make the statement clear. So then, are all these imperfections necessary? no, I don't think they are absolutely needed, but they do add a layer of information to the idea you are communicating - audiences all know instinctively that natural motion is varied and irregular, and by including this in your animation you help make your characters appear more lifelike - which may make the audience more likely to believe what they have to say.
