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After Effects 6 Auto-Trace, Part 1Working with the Auto-trace parameters
After Effects' Auto-tracer is excellent for creating spline masks from alpha channels of 3D rendered graphic elements, but you can also use it to generate spline data from the Red, Green, Blue or Luminance values of your layer. If you haven't used splines in After Effects 6 yet, don't forget to turn on "view masks," the little polygonal icon next to current time in the comp window.
Because it is an operation applied to a specific layer, the command can be found in the Layer pull-down menu. This operation isn't available in the "right-click" options for the layer yet.
After selecting Auto-trace, you'll get an attribute window that allows you to set various parameters of the function. Note: Every time you see an ellipse after a word in the pull-down menus, an attribute window will popup, requiring further action.
Here is a quick breakdown of the options in the attribute window.
Time Span section
Current Frame. This generates masks from the pixel data in the current frame of the layer at the point your current-time indicator is.
Work Area. When selected, this generates mask shape keyframes for the duration of your selected work area. Be sure to limit your work area to what you need, as AE will look at each "Best" frame, then generate masks for each. It can be quite time consuming.
On the right side of the Time Span section is a visual reference of your start, end and duration.
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