Flash Frame-By-Frame Animation: Keyframe and In-Between Basics

01
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Animation Basics: Getting Started

Flash is a fun tool for quick and easy automated animation, allowing you to create shapes and then move them about without having to draw every frame of the animation. But you can also animate in the traditional style--drawing every frame of animation, describing motion frame by frame in exquisite detail. Flash lets you mimic cel-style animation, but with so much more freedom; no more light tables, no more plastic sheets, pencils, inks, flip books, paints, cameras. It's all in the code--brushes in binary, sketches in subroutines.

But in order to accomplish this, you still need to understand the principles of animation and how to use those basics in Flash. So for this lesson, we're going to learn how to choose keyframe points and a few techniques for in-betweening.

Although as we get deeper into these lessons we're going to discuss how to draw complex motion and detailed shapes, for this lesson we'll stay simple: a bouncing ball against a backdrop of a single horizon line. Create a new document with a frame rate of 12 and a 320w x240h size (4:3 aspect ratio) ; that's more than enough for web animation, though typical TV animation uses a 15 fps (4:3 ratio) with repeated frames, and film animation uses 30 (16:9 ratio).

02
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Starting Point: First Key

The best place to start animating is, naturally, the beginning. This animation is meant to be a ball bouncing into the scene and then out of it again, striking the ground line. So my first drawing--which will also be my first keyframe--will take place above the ground, and to the side of the stage, outside of the viewable area of my movie.

I use a graphics tablet to draw directly in Flash, using the Pencil Tool set to smooth my lines as I draw them. You may wonder why my ball isn't exactly circular; in fact, it's a rather stretched ovoid, and that's one of the principles of animation that you want to keep in mind. A normal ball, when it bounces, shifts shape if it has any pliancy to it at all, as forces act upon it: gravity pulling, its own velocity creating pressure from the air, the ground pushing on it to deform it with impact.

Animation takes these minute shifts and exaggerates them so that they're larger than life. We covered this somewhat with the bouncing snowman in Lesson 14; it's called squash and stretch. I'm drawing my ball at the apex of its arc of ascent and descent, so it should be stretched the most at this point--though if I really wanted to be accurate, it would stretch on ascent, snap back to a squashed shape at apex, then stretch again on descent.

03
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Creating More Keys

We need to set our primary keyframes. Keyframes are just that: key points in a sequence of motion that define pivotal points in that motion. The beginning and ending positions are always going to be your first keyframes, and most important, but equally important is defining other pivotal points inside that sequence. You may have one secondary keyframe, or ten; for example, if you're animating a character turning in a circle, you might define a secondary keyframe for facing left, facing right, and facing away, while your first and last keyframes would be the same (facing the viewer).

For this animation the primary points are the apex of the first arch, the point of impact, and the apex of the next arch, for a full cycle. (Tip: turn on Onion-Skinning so that you can see previous and future frames in outline while you work.) I started by copying my first frame to the very end of my cycle; I chose 13 frames, as an odd number makes it easier to divide at key points with the same number of frames to either side--and this lets me set it at one frame over a second. Once I copied that frame I moved it to the point that the ball would bounce to on its next cycle.

At my midpoint, Frame 7, I drew another circle--flattened from impact, resting to the ground at a point halfway between the two arc apexes. This is my midpoint, and the point where the ball strikes the ground.

04
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In-Betweening

With our key frames in place, we need to draw our in-betweens. In-betweens are exactly what they sound like: frames filling in the motion in between our primary points. Although keyframes are important, in-betweens are, to me, more difficult--because you can't just pick a point and draw. You have to accurately represent the transition between frames by drawing the state that the object/character is in at a point halfway between keyframes, and then halfway between again, and halfway between again--and that can take a great deal of time, concentration, and educated guesswork.

I'm going to show you a trick that I use when drawing frame-by-frame animation, whether by hand or in Flash. I tend to treat it a bit like geometry: I pick important points on my shape--four points on a circle, top, bottom, left and right, or say on an arm you may pick shoulder, outer elbow, inner elbow, wrist, fingertips--and then match those points on the next keyframe, before creating a new layer and drawing lines on that layer to connect those points. Then I just brush little dots or tic-marks to the halfway point of each line, eyeballing to estimate where those points would have traveled on a straight line on that in-between frame.

05
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In-Betweening II

With those points in place I can then place my cursor on that in-between frame (since it's halfway between, it would be on frame 4, between my keys at 1 and 7) and then use those points as guidelines to draw. Because I'm also keeping squash and stretch in mind and want to show the shape growing closer to flattening, I don't stick perfectly to the guides, but they do still help me keep everything positioned correctly. Once I'm done I can just set the guide layer to invisible so that it isn't showing over the animation.

06
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Viewing Motion Sequence

With onion-skinning on and these four frames in place, you can start to see the sequence of motion as well as the slight shifts in deformation in the quickly-sketched circles.

07
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Repeating and Adjusting the Timeline

Now the next step would be to repeat the steps again, this time between frames 7 and 13, on frame 10--though you may want to tighten your frames. After finishing the first five frames--your primary and secondary keys, and your primary in-betweens--you'll be able to play your timeline and see--albeit somewhat flickery--how the motion progresses. The great thing about Flash is that you don't have to do much work to adjust the timeline on your animation (while drawing it by hand might require redrawing many frames, which is why when drawing by hand it's usually best to do stick figures first to get the motion down before starting on detail) ; you can drag keyframes around as you wish to shorten or expand motion.

Mine was looking a bit slow, so I cut a few frames--bringing it down to nine with my keys at 1, 5, and 9, primary in-betweens at 3 and 7, leaving secondary in-betweens at 2, 4, 6, and 8. Each time you go down a level in in-betweens to fill in more of your timeline and add more detail, you'll have even more drawings--almost like a pyramid hierarchy, in expanding tiers of detail.

08
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Cleaning up the Line Art

Before moving any further, I took a little time to smooth our and adjust my drawings a bit. This isn't meant to be perfect; it's a sketched animation to demonstrate the techniques, and when I'm not taking screenshots in between I can finish something like this in about ten minutes. Making this smooth and fluid would require hours more of tweaking, though some would actually prefer to leave it in this rough style, as it has a quirky appeal all its own and some professional animations have been deliberately produced with the "sketchy" look.

Still, I do want to tighten this up a little bit. I've used the Smooth function to iron out my shapes a bit with just a few clicks, and then the Subselection tool to adjust individual vertices and their curves.

09
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Filling in Remaining Frames, Adjusting

You can fill in the remaining frames one at a time using the same technique to find the appropriate midpoints and then draw with those guidelines; with onion-skinning turned on you can actually see your entire path of motion, and use that to adjust accordingly. I've squashed mine a bit more in some areas, and adjusted the actual position of each stage of the circle's motion so that instead of zig-zagging along straight paths, it follows bouncing arcs.

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Finished Result

And here's my finished animation--crude, but it demonstrates the techniques appropriately, and to repeat the cycle all I had to do was copy the keyframes and then paste them, before moving their positions to reflect the advancing motion. Now that you've got the basic technique out of the way, get used to using it and spend some time just drawing in Flash to get accustomed to the feel of it so that you'll be more comfortable with the next lesson, where we'll start the basis for a more complex character drawing that we'll take through several stages: rough motion, detailed rough motion, smooth line work, solid color, and highlights and shadows.

Just a short animation will take several weeks of progressive steps, though the amount of actual working time that we'll put in will be negligible compared to the amount of time spend hand-drawing full-length feature films, and the workload will be much lighter. Working in Flash, we can single-handedly accomplish what normally requires a full team of animators.