JANUARY 13, 2004
After Effects 6 Auto-Trace, Part 1
Working with the Auto-trace parameters
by Ko Maruyama

One of the cool new features in AfterEffects 6 is the Auto-trace feature. While it may appear to be as low-tech as its Photoshop cousin, the Magnet Lasso tool, it provides much more interesting data for the animator, the most basic of which is the automation of animated garbage masks. As part of a quick series of tutorials using AE's Auto-trace feature, this overview provides some basics.

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.[an error occurred while processing this directive]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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