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You've no doubt noticed that the Graph Editor in After Effects treats position graphs differently than it does graphs for other values. For example, when the display is set to Auto-Select Graph Type, for other values it shows the value graph, but for position, it shows the speed, or velocity graph. This is because it's bundling the X and Y coordinates--and if it was in 3D space the Z coordinates, as well--into one keyframe value, and then calculating what is the composite speed for changes in all of those dimensions at once.
I'll select Snowstorm Title so I can focus on just a position graph. Now I can indeed look at the Value Graph for position, and I can see a separate X and Y graphs. However, I'm kind of limited in what I can do with them. For example, if I hold the Command key down and hover the cursor over the graph to add a keyframe to the Y graph, it also adds a keyframe to the X graph. You'll notice that I can't select just one keyframe without its partner dimension being selected at the same time. Also, I don't get any influence handles in the Graph Editor for position values.
I have to do all of my editing with the motion path in the Comp panel. This bundling together of values into single keyframes actually makes animation a lot easier in many cases. However, there are a few cases where it makes animation more difficult. I'm going to open up the Comp: 04-Separate Dimensions, and here I have a volleyball I'd like to bounce across the screen. Well, this is exactly the type of animation that's a bit harder to do in a Graph Editor. I want to keep a constant speed in the X dimension, have the ball travel across the screen horizontally at an even speed, but I need to have it do something considerably fancier in the Y dimension.
I need it to come down here, instantly reverse direction without slowing down, slow down up here at the top of its bounce, then pick up speed again as it bounces again. Very complex movement in the Y dimension, while on the X dimension, it's doing something very simple. A very linear flow. You can indeed try to craft a motion path to do this, but it's going to be very hard to get the sort of speed that you want to out of it. Fortunately, in After Effects CS4 they've added a feature called Separate Dimensions that makes these sorts of moves more possible. With my volleyball selected, I'm going to press P to reveal position, enable keyframing.
This will be my first keyframe in time in the upper-left corner. Then I'll press End to go to the end of my Timeline. I decide that the ball is going to hit its last bounce here at the end of time. I'll select the Graph Editor, and I can actually see the separate X and Y dimensions. But as I mentioned before, I can't set the keyframe for one without also setting a keyframe for the other. When I set Auto-Select Graph Type, it's actually going to show me the constant velocity graph, not the more detailed positional graph, or the Value Graph.
To get around that, I want to go click on this brand-new Separate Dimensions button, and by doing so you'll see this one line separate into two, X and Y, and if this was a 3D layer, I'd have a Z graph as well. These are my two independent graphs, but now I can hold down Command or Ctrl, add a keyframe to one, and it's not going to add a keyframe to the other dimension; I have independent control. I also get Bezier handles, which I was lacking before. So let's see what we can do with this new flexibility. I'll undo back to where I was.
As I mentioned before, I want to have this ball travel in a constant speed in X across the screen. X is color coded red. So this is a red graph I'm looking at. I see it indeed has a little bit of a curve at the beginning and ending. This has to do with After Effects choosing Auto Bezier as its default spatial keyframe type. I'd prefer this would be perfectly constant, and this is one of the few cases where I do indeed want linear keyframe. So I'll go ahead and select the X dimension, double-click it so that both keyframes are selected. Only the X, not the Y keyframes are selected.
Then I'll go down to our very handy Convert selected keyframes to Linear button. Once you do that, you'll see that this line straightens out and I've got a perfectly even velocity. I will even go look at the Speed Graph, perfectly flat line for red whereas green has this little bit of bend in it still. I'll go back to Auto for now. I've got our X dimension sorted out. Let's work on Y. I've already set where I want the ball to be when it bounces off the floor, so let me go ahead and select that Y keyframe and copy it, because I want to reuse that value elsewhere in the Timeline.
Let's go back to where I might want my first bounce to be, say somewhere around 15 frames or so. When you're in Separate Dimensions mode, you must resist the temptation to go up to the Comp panel and drag the layer to reposition it. This creates keyframes for both X and Y, which is not what I wanted. I wanted to work on Y by itself. So I'll undo to deselect that. I can either scrub my Y position independently to go ahead and give it the value that I want, or with that keyframe selected, just paste the value that I copied down here.
And now I've got that exact same bouncing-off-the-floor position I had before. I'm going to point a later in time like around 1:15, and I'll paste again, and now I've got my bounces on the floor in the Y dimension. The only problem is that this curve doesn't do exactly what I was intending. If I go ahead and RAM Preview, you see that the ball kind of slithers along the floor. It doesn't exactly bounce. Now normally I'd say it's time to go edit the motion path in the Comp panel, but when you're in Separate Dimensions mode you do not edit the motion path in the Comp panel, oddly enough.
You do all of your editing down in the Graph Editor, by tugging out the handles for the layer. I basically want the Y value to have a graph, a curve, that follows the bouncing shape, or path, that I desire the ball to take. I am going to start in this first keyframe, start tugging out handles. There we go. The problem is that the handles, by default, are connected as continuous Bezier, but that's okay. I'll hold down the Option key on Mac, Alt key on Windows, get to Convert Vertex tool, and break the handles.
Now when I do that, I've got separate control. As I started to bend the Y graph into a bouncing shape, you'll see the corresponding motion curve in the Comp panel takes on the same shape. I'll select the second keyframe, hold down Option or Alt, drag out its handle, and do the same to its other handle here. As I drag in the Graph Editor, I'm going to watch what's going on in the Comp panel to get the shape that I want. Do I want it to bend in that direction, bend it the left instead, or have a more even arch there in the middle? I start dragging these other keyframes out to go ahead and shape the sort of bounce that I want.
I want my last bounce to be not as tall as the initial bounce. I do want my initial throw of the ball to maybe come out straight a little bit before bouncing, and that's roughly the curve that I like. Maybe a little bit more influence down this direction there. There, let's try that. RAM Preview. Bounce, bounce, bounce. That's exactly the animation I was going for. I could have tried to get something close by doing a normal motion path edit, but there is no way I would have had the velocity this smooth, because the ball is going continuously in X, but jerking back and forth in Y.
Another nice thing about having the dimensions separated like this is I can edit one of them without affecting the other. Now let's say the client comes along and says, well, it's a cool animation, but I don't want the ball to travel as far across screen. Well, previously that would have required me to edit all of the position keyframes to make that happen. But in this case the client is talking about X. So I can take just the X parameter at the second keyframe and say don't travel as far, don't go too high of a value. Here I'll collapse the bouncing motion. Much less travel.
On the other hand, the client might say, I want it to go off the screen. So I'll go ahead and drag the X graph, add the Shift key to constraint it in time to where the ball goes off the screen. I've got a constant speed going across screen. If I want the ball to slow down, I might go ahead and take this, hold down Option for the Convert Vertex tool and pull out a handle and say go ahead and ease into it. Now if I hold down the Shift key the constraint its movement, it's going to come like an Easy Ease to no motion at all in X. But since I want it to be moving a little bit next to slower, I'm going to put these handles at an angle and just give a bit of a bowing motion.
So it goes faster in X and slows down gradually as it gets to the second keyframe. I will RAM-preview that. Boom, boom! Going too far now. Let's just drag it down, so it doesn't travel as far in X. Preview again. Now the ball is slowing down gradually as it goes across the screen, but it keeps the same up and down movement in the Y dimension. Trust me, this was much easier and went much faster than if I was trying do to tug of war with motion path handles in the old mode, in the Normal mode without Separated Dimensions.
Now once you've created a path like this, if you want to go back to the old mode where every one is bundled together, you can indeed select your parameter and turn off separate X, Y, Z, Separate Dimensions. And it will revert to the old keyframe type where you get a motion path in the Comp panel. However, you see that the approximation is not that great. It kind of goes out at an odd angle here it, and it doesn't really work there. The velocity's really linear in- between the keyframes where I have something more subtle going on.
Really, for moves like this, Separate Dimensions just makes it much easier to execute, and you really realize it when you're start doing camera moves in 3D as well. Anyway, that was a tour of Graph Editor. I know it takes a bit of thinking to get your head wrapped around it, but it's a very powerful tool. But don't worry. For the rest of this lesson, we're going to play with some fun stuff.
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