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# Keyframe Interpolation in Adobe After Effects CS4

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## Specifying Spatial Interpolation in the Motion Path

In Chapter 7, “Properties and Keyframes,” you learned that you can change the spatial positioning of each keyframe by dragging it directly into a Composition or Layer panel. This section focuses on using spatial interpolation to change the course of the motion path from one keyframe to the next.

#### To move a position keyframe:

1. Select a layer with an animated property to reveal its motion path in a Composition or Layer panel.
2. Position and effect-point paths appear in the Composition panel (Figure 9.22); anchor-point paths appear in the Layer panel.

3. Using the selection tool, drag a keyframe to a new position (Figure 9.23).
4. In a motion path, a selected spatial keyframe appears as small solid box, or handle; a deselected keyframe appears as an outlined box.

#### To toggle between auto Bézier and linear interpolation:

1. Select a layer with an animated property to reveal its motion path in a Composition or Layer panel.
2. Position and effect-point paths appear in the Composition panel (Figure 9.24); anchor-point paths appear in the Layer panel.

3. In the Tools panel, select the Pen tool (Figure 9.25).
4. In the motion path, click a keyframe icon to convert it.
5. The Pen tool becomes the Convert Vertex tool when you position it over a keyframe. A keyframe using linear interpolation is converted to auto Bézier, with two equal control handles (motion path tangents) extending from the keyframe. Any Bézier-type keyframe is converted to linear, with no direction handles (Figure 9.26).

6. In the Tools panel, choose the Selection tool .
7. Once you convert a keyframe, adjust it with the Selection tool. Clicking it without changing tools converts it back.

#### To convert auto Bézier to continuous Bézier:

1. Select a layer with an animated property to reveal its motion path in a Composition or Layer panel.
2. Using the Selection tool, drag one tangent of an auto Bézier keyframe so that it’s shorter or longer than the other (Figure 9.27).
3. Both of the keyframe’s tangents form a continuous line, but they influence the path by different amounts.

#### To convert continuous Bézier to Bézier, and vice versa:

1. Select a layer with an animated property to reveal its motion path in a Composition or Layer panel.
2. Select one or more keyframes in the motion path (Figure 9.28).
3. The selected keyframe’s motion path tangents (control handles) become visible.

4. In the Tools panel, select the Pen tool (Figure 9.29).
5. In the motion path, drag a direction handle (Figure 9.30).
6. The Pen tool becomes the Convert Vertex tool when you position it over a motion path tangent, also called a direction handle. Dragging a direction handle of a Bézier keyframe converts it to continuous Bézier with two related tangents; dragging a tangent of a continuous Bézier keyframe splits the two tangents, converting it to Bézier.

7. In the Tools panel, choose the Selection tool .
8. Once you convert a keyframe, adjust its direction handles with the Selection tool. Otherwise, you’ll convert it back.

#### To toggle between the Selection tool and a Pen tool:

1. Position the mouse pointer over a motion path in a Comp or Layer panel, and do either of the following (Figure 9.31):
• To toggle the current Pen tool to the Selection tool, press and hold Command (Ctrl).
• To toggle the Selection tool to the Pen tool currently visible in the Tools panel, press and hold Command-Option (Ctrl-Alt).
2. Release the keyboard modifier to continue using the currently selected tool.