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# Keyframe Interpolation in Adobe After Effects CS4

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## Understanding Value and Speed Graphs

In the following sections, you’ll use the Graph Editor to (what else?) edit a graph of a property. But first, let’s take a moment to examine the two types of graphs you’ll encounter: the value graph and speed graph. As you proceed with the graph-editing tasks in the following sections, note how the shape of a value graph or speed graph corresponds to the animation (Figures 9.39 and 9.40, and Table 9.1).

Table 9.1 Recognizing Temporal Interpolation

 Temporal interpolation In the value graph In the speed/velocity graph No speed change Horizontal line Horizontal line Constant speed Straight line with any slope Horizontal line Sudden speed change Sharp corner Disconnected line/ease handles Acceleration Curve with steep slope Upward-sloping curve Deceleration Curve with shallow slope Downward-sloping curve Holding Horizontal line, unconnected Horizontal line, where current speed = 0

### Value graph

A value graph measures a property’s value vertically and its time horizontally. The units in which values are expressed depend on the type of property: Rotation is measured in rotations and degrees, Opacity in percentages, and so on. The slope of the line between keyframes represents the rate of change in units per second. Straight lines indicate a constant rate; curved lines indicate a changing rate, or acceleration.

A value graph is particularly easy to grasp when viewing properties such as Opacity and Audio Levels, because these properties correspond well with the “up and down” or “high and low” nature of the graph.

Note that some properties consist of more than one value, or dimension. For example, a Position property includes values for both an X and Y coordinate. Hence, a position value graph includes two color-coded lines: one representing the X coordinate value and the other representing the Y coordinate value.

### Speed graph

A speed graph measures rates of change in a property’s values. The units measured by a speed graph depend on the property type: degrees of rotation/sec, percentage opacity/sec, and so on. Regardless of the specific property, the rate of change (units/sec) is measured vertically, and time (sec) is measured horizontally in both graphs. Therefore, the slope of the line represents acceleration (units/sec/sec). Compared to interpreting a value graph, interpreting a speed graph isn’t as straightforward. For example, a property’s value may be increasing or decreasing—but if its rate of change is constant, it results in a horizontal line in the speed graph.