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JANUARY 13, 2004 After Effects 6 Auto-Trace, Part 1
Options section Tolerance. Depending on the pixel variation of your image and your mask shape requirements, you may have to experiment quite a bit with this value. The amount can be set to fractions, or sub-pixel values. The lower the number, the more precise the mask shape will be. Be warned, very low numbers will guide Auto-trace to account for very small variations, even anti-aliasing. Alternatively, high numbers will produce loose approximate boundaries of the determining channel.[an error occurred while processing this directive]Threshold. The percentage takes into account the channel map, and determines where the tracer will look for areas to set down points for the mask shape. In image F.1, circles 1-3 contain pure channels, where circles A-F are mixed r-g-b. A blue channel threshold of 30% produces the splines in F.2, whereas a blue channel threshhold of 99% produces the splines in F.3. Note: You cannot select a threshold of 100%, that would produce no splines at all.    Channel. This sets the channel you want to isolate. Red, Green, Blue, Alpha and luminance. Invert. This will invert the search area before it draws splines. Can be useful if your layer has unwanted or unruly alpha channels already applied to it. Blur. While blur's use is to simulate an antialiasing haze to your layer before setting to the task of Auto-tracing, it can unfavorably offset the values set in Tolerance and Threshold. A larger value will produce a fuzzier search area. Apply to New Layer. This is nice. With the advent of tons of plugins (including AE's own Stroke), you can design with these newly created splines on a New solid. The new solid created is a unique "white" solid. It shows up in your Solids folder. Instead of a color name, AE assigns "Auto-traced (source name)" as its name. You may want to rename this if you plan to make multiple new layers from your Auto-trace source (rename it in the Solids folder). Well, there's the overview. Next we'll take a look at what you can do with this using some cool plugins, including (yep) AE's stroke. While Auto-trace is a very cool and useful tool, I wouldn't rely on it for rotoscoping chores alone. It may help you start a rotoscoping project, but there is so much tweaking that goes into creating a good, clean roto that you'll find it's better to start from scratch. This is, however, a great tool for creating garbage masks, or defining splines for design purposes. Note: Adobe makes sure that your layer automatically switches to "Best" quality to ensure that you'll get the highest pixel resolution to analyze. If you tend to work in draft mode, switch it back after you've traced your layers (Command-Shift-U). Ko Maruyama is a freelance animator in Hollywood, California. You can unload questions and comments in the After Effects forum. Prev 1 2 Related sites: • AV Video • Creative Mac • Digital Post Production • Digital Producer • Film and Video Magazine • The WWUG Related forums: [an error occurred while processing this directive] 
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