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|Part of||Illustrator CS5|
Introduction to Live Trace
The Live Trace tool in Illustrator turns a raster image file into objects, paths, and fills so that they can be edited. Quite often the linework is not very clean and will require a more detail tracing process, often by hand. Images and silhouettes, such as shadows from simple rendering programs, can be easily transformed into clean vector linework.
Live Tracing a Raster Image
To make a live trace, open a raster image of a shadow or silhouette. Select the image and click on Object --> Live Trace --> Make.
Comparing the raster image from before and the live trace vector artwork after reveals that the raster image contains fuzzy edges, while the vector artwork reads clear at the edges no matter what level of zoom. This is especially helpful when placing the work on presentation boards. It also makes the edges of the artwork easier to edit.
Live Trace Options
To change the options for the Live Trace, click on Object --> Live Trace --> Tracing Options. Select one of the Preset options. The presets affect how Live Trace will read the object in reference to lines versus filled object and overall precision. The Simple Trace preset works for most simple images. Uncheck the Ignore White option to ensure a cleaner result. A lower number for Path Fitting will increase the number of Anchors in the vector artwork because the trace will be more detailed and precise around edges. Adding more anchor points may help the lines become more sharp, but may become heavy linework later on. Click on Preview as you change the options to see what the resulting vector artwork will look like. Then, click Trace.
Expanding the Artwork
Illustrator now recognizes the traced object as a Tracing. In order to be able to edit the object's outline path and fill options, the object needs to be expanded. Select the object, then click Object --> Live Trace --> Expand. This could have been combined with the previous tracing step by selecting Object --> Live Trace --> Make and Expand. Now, the object is comprised of linework that is grouped together. To edit the object further, ungroup the objects by selecting them, and clicking Object --> Ungroup.
The vector linework can now be edited as a path. It can be brought into Rhino as a line. The anchor points can be selected and moved or deleted.
Limitations of Live Trace
There are limitations to the power of Live Trace. First, a large image will take much longer to trace; it may be faster to manually trace it. Second, an image that is much more complex than a simple silhouette or shadow will lose clarity and precision, despite tweaking the Tracing options as much as possible. The drawing's fine details, such as corners or lines that are close together, may be uneven or wavy. Once expanded and ungrouped, the linework may be muddled with overlapping and non-continuous lines, or lines may appear as objects with fills rather than simple strokes, making them difficult to edit. This is because it is difficult to control how Live Trace reads images as lines or objects with fill. It is best to avoid tracing high-detail, complex drawings.