Animation is something that a lot of people see as "magical" because they think it's hard. The truth is that animating is a skill like any other and pretty much anybody can learn to do it with enough practice and a willingness to learn. It's not that far off the flip books we all played with as kids.
This is the first of what may turn into a series of tutorials covering some of the basic exercises used to teach those new to animation the core principles. This and any tutorials that follow will all be the same exercises I did while going to college learning animation.
If you're serious about learning to animate, I strongly recommend a book called "The Animator's Survival Kit" by Richard Williams. It is a very good reference guide to have on hand whether you're just starting out or are a pro at animating.
Step 1: A Brief Look at Animation Methods
These days, animation can be done in a variety of ways. For this exercise - the ball bounce - I will be using Macromedia Flash and drawing frame-by-frame to illustrate the "squash and stretch" principle, but you can use other methods as well. The purpose of this tutorial is not to give an in-depth look at animation equipment, but here is a summary of other methods and what you need for them. You can still follow the tutorial and adapt it to your chosen method.
This is the method I'm using with this tutorial, but using Flash in place of pencil and paper. It is also known as frame-by-frame animation because there is no automatic means of doing the inbetweens. It results in smooth, lively animation.
To animate with paper and a pencil, you will need a light table (or in a pinch, a sheet of plexiglass and a small lamp) and a means to register your paper. In other words, a way to line it up perfectly.
Traditional animators achieve this with a peg bar which can be bought at art supply stores or online. If you go with the real deal, you will need to either buy pre-punched animation paper or an animation punch (neither is cheap). With a little patience and creativity you can construct a peg bar of your own that will be compatible with a standard 3-hole punch instead of the ACME standard registration used in studios.
To animate, just pile pieces of paper on your peg bar and number them as you work so you can tell what order they go in at a glance. The backlight helps you see where your previous drawings are in relation to the one you are working on currently. Once you are comfortable, you can flip your paper frames to get a feel for how a few frames at a time are working together - kind of like the flip books you had as a kid!
After you animate, you have to scan the frames and then line up the drawings properly. It's as simple as lining up the peg holes in the images. Then you can load them into your software of choice to create the video from the still frames.
The principles of this exercise can be applied to 3D. If you are familiar with Maya, 3D Studio Max, Lightwave or any other 3D animation software package, follow along! If you don't know the software, look up some basic tutorials before you tackle this one and they should explain the basics of manipulating primitives in 3D space. This method is more like sculpting than traditional animation is.
Step 2: Concepts Behind Squash and Stretch
Now, time for some theory.
If you have ever seen any sort of classical cartoon, you will notice how bouncy and squishy the characters can be in in their movement. Squash and stretch are one of the most important concepts in animation. Without it, the animation looks stiff and lifeless.
In this exercise, we'll be animating a bouncing ball. It's a very simple object, but the principles of squash and stretch are very strongly present, so it is very good practice.
For the squash aspect, think of gravity and how things react when they fall. If you drop a pie, it'll go "splat" because it's moving as it falls but then suddenly hits a hard surface and collapses because it has nowhere else to go. Any animated object follows the same idea, but generally has more substance to it. In the case of our ball, when it hits the ground, it will temporarily try to keep moving even though the ground is in the way. This means that for a brief moment in time, it'll change its shape (flatten out a bit) as the weight hits a hard surface and is forced to stop its decent. This also builds energy in the ball for its change of direction.
On the other hand, stretch is what happens when our ball takes off from that hard surface again to rebound into another arc as it moves. The ball goes from slightly flattened horizontally to shooting off in another direction because of the stored energy. This will cause it to stretch out as it "reaches" for its new destination. This is what gives cartoons that distinctive visual pop!
How is squash and stretch applied to more complicated animation? Many ways! As an example, think of how you move when you jump straight in the air. First you crouch down to build energy so you can jump really high (squash). Then you jump and your spine straightens out (stretch). When you land, your body weight hits the solid surface and collapses again before straightening out (again, squash!). These actions help visually anticipate movement in the animation so it flows.
The amount of squash and stretch varies depending on the nature of the object being animated. The more rigid the object, the less squash and stretch will be present.
Step 3: Timing
Timing is everything in animation! Time means frames and frames are what get your drawings from point A to point B.
First, a note - in order to decrease the number of drawings needed, most frame-by-frame animation is done on twos. This means that each drawing is held for two frames. In some cases you will need to animate on ones (mostly during very fast action, where animating on twos would make it look choppy), but that won't be the case in this exercise. Standard frame rate is 24 frames per second, so this means that you typically only do 12 drawings for every second of animation.
Now, one thing that will help you figure out your timing a lot more easily is if you have a good stopwatch and create a timing sheet (in animation lingo, this is called an "exposure sheet", "x-sheet" or "dope sheet"). The stopwatch will let you time your own actions to get a better idea of how long a motion actually takes. The dope sheet allows you to plan your animation before actually drawing.
Back to the dope sheet. You can set one up by creating a standard sheet for yourself to jot down in pencil on, or use a spreadsheet or table if you'd prefer to do things digitally. The dope sheet essentially consists of a table that notes different layers (in more complicated animations) across the top and the cells in the table represent frames for each of those animation layers. As you descend, it represents movement in time. You mark your drawing numbers in the cells. Key frames (discussed in the next step) are noted by being circled.
Since we're animating a ball, it'd be a good idea to get a bouncy ball and play with it. Observe how long it takes to get through each arc, how long it hangs in the air. Write down your observations and use them to construct your dope sheet. Mark down, with appropriate spacing to reflect the passage of time, a drawing for every high point and strike the ball will make in your animation.
Step 4: Key Frames
Now, time to start animating!
First thing you will want to do is draw your key frames. These are the key points in the movement of your ball. Or more simply put, they are the strike points on the floor, the highest points of the arcs the ball makes as it bounces and the stopping point. These are what you should have marked down on your dope sheet. Change your dope sheet if you need to.
Keep in mind that the ball loses energy each time it bounces, so the first arc will be the highest and each after that will decrease until the ball just rolls along the floor. The will affect the timing as well. Smaller arcs won't take as long and won't require as many drawings.
As noted earlier, with this exercise the ball will change its shape as it moves. At the top of each arc, it will regain its default round shape as it fights against gravity momentarily. When it hits the ground, it will flatten slightly. Be careful and make sure that your ball retains its overall volume even as it changes shape.
In Flash, be sure to follow your dope sheet and leave the proper number of frames between the keys so you can fill them in later.
Test your animation. Because it is just the keys, you need to hold each key for the entire time between the start of it and the start of the next key. This will look odd, but it will give you a better idea of whether the timing is right or not. If it doesn't feel right, play with the timing by adding or removing hold frames until it does.
Step 5: Inbetweens
Next, you will do inbetweens. Remember that each frame is held for two frames! Inbetweens are exactly as they sound - the frames that go between the key frames. This is where your dope sheet from earlier will be very important. Timing will dictate how many frames and drawings go between each pair of keys.
But that's not it! There's more theory to inbetweens than just randomly placing them.
Animation works because our eyes basically fill in the blanks between the animation frames. The frame rate is such that it doesn't appear choppy. But the placement of the drawings has a huge impact on how our eyes perceive the movements being shown.
If inbetweens are placed closely together, the movement is slower. If spaced further apart, the movement is faster. This is used in "easing in" and "easing out", which helps make the animation more life-like.
In the case of our ball, we want it to ease in and ease out of the top of each arc in the bounce. This will give it the visual hang-time you perceive in a real ball bouncing. With animation this is pushed a little further than really happens in real life - just don't have it hang in the air so long it looks like it's floating!
The other side of this is that the ball will drop quickly into each ground strike and take off just as quickly from it. Again, this helps the visual appeal.
Step 6: Test, Test, Test!
Once you fill in the inbetweens, test your animation again. One thing that is very important in animation is testing your work as you go. When in doubt, test your animation to see how it's turning out. In more complicated animations, this will same you a LOT of time in the end. Better to spend time testing than doing an entire animation and finding out it doesn't work at all.
If you like the way it looks, great! You're done!
If not, play with the inbetweens until you are happy with the result. If you are using Flash, it's really easy to try out different spacing on the inbetweens by using layers. If you do this it's really easy to compare the impact the spacing between inbetween drawings has on your finished animation.
Now that you've done this tutorial, you can try animating other things. Practice makes perfect!