Steve's Tips
Using the Bezier tool to control the speed and movement of keyframed effects and motion
A real tribute to the power and depth of Premiere Elements is the presence in the toolkit of Bezier curves to control effects and properties. With paths shaped using the Bezier tool, you can both vary the speed of movement along a motion path (or the speed of transition into and out of an effect) [Temporal Interpolation] and control the shape of the motion path itself [Spatial Interpolation]
Using the Bezier tool to vary the speed of movement on a motion path (Temporal Interpolation)
Once you create a series of keyframes (see the Steve’s Tips archives for January’s article on keyframing basics), right-click on one of the keyframe points in the Properties panel (called the Effects Control palette in version 1). Under the sub-menu of Temporal Interpolation you will find several settings which will vary the speed of the motion or effects along the path.
Some options, such as Ease In and Ease Out, are basically presets which either, respectively, start the motion slowly at the previous keyframe and then speed it up as it approaches the keyframe or start it quickly and start the motion slowly from this keyframe and speed it as it approaches the next. The Bezier control, on the other hand, allows you much greater control over this motion, giving you the ability to very precisely control either the speed of a motion along this path or the intensity of an effect along a keyframed path.
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To see the Bezier curve once you’ve selected one of these options, either select Large Tracks from the More menu on the Timeline panel or manually widen the video track by dragging on the seams between the video tracks at the left hand side of the Timeline, as illustrated in the figure to the right. (Click on the thumbnail image to see it full-sized.) Drop-down the properties menu on the clip and select whichever property or effect you want to see the keyframes and motion path for. (Motion: Position, for instance.)
You’ll notice that even presets such as Ease In and Ease Out create curves in this interpolation path. These curves can be further manipulated with the Bezier control handles.
If you've never used a Bezier tool before, it can be a bit tricky. Basically the shape of the curve is controlled by manipulating the "handles" on each of the curve’s endpoints. Lengthening the handle will widen the curve. Moving the handle up and down or from side to side will change the direction of the curve. And don’t be surprised if occasionally it seems to leap into some strange shape, completely out of control. Happens to the most experienced users. (Some effects give you more control over the shape of this curve. You are limited to a rather basic curve for motion paths, however.)
When the path of the lines is closer to the top of this track, motion will happen more quickly or effects settings will transition more rapidly; when closer to the bottom, less so. An angled line here means things go from more to less, or vice versa, at a Linear rate (the default); a curved shape means that the rate will be changing throughout the path. By manipulating the Bezier handles on adjacent keyframes, you can even create a sine wave!
Using the Bezier tool to vary the shape of a Motion Path (Spatial Interpolation)
A similar Bezier tool can also be use to control the shape of the motion path between keyframes. To see the Bezier control handles for your motion path, right-click on a keyframe point and select Bezier from the Spatial Interpolation sub-menu. You’ll notice that, when you do, the motion path will appear as a line or series of lines in your Monitor panel (by default, straight lines or Linear interpolation).
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Once you’ve activated the Bezier control , the keyframe points in the Monitor will display Bezier control handles. (The handles may not be obvious at first since, with a straight line of motion, they’ll be right on top of the motion path line.) With these handles (as illustrated the left), you can change the straight line of motion to a curved line, creating a swerving or swirling movement for your screen image rather than direct motion between the two positions.
As with Temporal Interpolation, the shape of the curve is controlled by manipulating the "handle" on each of the curve’s endpoints. Lengthening the handle will widen the curve. Moving the handle from side to side will change the direction of the curve.
March 2006
About Steve
Steve Grisetti earned a master's degree in writing for television and film from Ohio University. He has instructed college-level courses in television and video production, and has taught adult education classes on Photoshop and principles of design.
Steve spent nearly 10 years in the Los Angeles-based entertainment industry, working on the sets and in the production offices of several large television and film companies. Currently, he is employed as a graphic designer in the Marketing & Communications Department of a Milwaukee-based investment firm.
He also serves as host on Adobe's official Premiere Elements Support Forum and is author, with Chuck Engels, of "Adobe Premiere Elements 2.0 In a Snap," from Sams Publishing, Pearson Education.
