Illustrator tip: Live Trace
Adobe Illustrator’s Live Trace feature is a phenomenal way to transform a raster image into a vector image—or to put it more plainly—to turn a photograph into a drawing.
Placing a raster image into Illustrator CS2, CS3, or CS4 ( ) via File -> Place and access the Live Trace Options from Object -> Live Trace -> Tracing Options, or use the button on the Control panel.
The Preset menu A common misunderstanding of Live Trace stems from the Preset menu. Live Trace is not an effects tool, but rather a utility to convert pixel-based, fixed-resolution raster images to resolution-independent vector drawings. Thus the Preset menu doesn’t contain a list of effects to achieve, but rather prerecorded settings that provide a good starting point based on the type of raster image you’re working with.
So, begin your drawing by choosing the type of image you’re using from the Preset menu. Is it a hand-drawn sketch, a one-color logo, a high- or low- fidelity photo? Once you’ve chosen a preset starting point, activate the live preview (via the checkbox on the right), and then refine the tracing with the Adjustments and Trace Settings options. Adjustments are largely concerned with the source image, while the Trace Settings control the precision and complexity of the vector image or final drawing.
Mode This pulldown menu lets you choose whether your image and/or the tracing you want is color, grayscale, or strictly black and white.
Threshold If you chose the black and white mode, the Threshold field becomes active, allowing you to set the maximum grayscale value of white. You can enter a numerical value or use the slider bar that appears when you click the arrow on the right. For example, if you set Threshold to 200, all the image’s shades of gray that are 200 or higher (on a scale of 0-255), will be white in your black and white tracing; all values lower than 200 will become black.
Palette This pulldown menu says Automatic by default. However, if you’ve opened a pre-set swatch library such as a Pantone or Toyo, that library will be listed too, enabling you to target all your tracing colors to fit within those in the library. If you haven’t opened a library, your only choice will be Automatic, meaning Illustrator will build colors as needed depending on the Max Colors option.
Max Colors This pulldown menu lets you set the maximum number of colors in the final tracing. High values result in more realism, but also more complex tracings. Lower values can be used to create posterized areas and cartoon effects.
If you check the Output to Swatches checkbox, Illustrator will add colors from the tracing to the document’s swatch library.
Setting a Blur amount via the Blur pulldown manu is useful to smooth pixilation and artifacts from lower resolution or JPEG-compressed source images prior to tracing.
Checking the Resample checkbox will cause the resulting tracing to be produced based on a resampling of the image at the specified resolution.
Fills and Strokes, checkboxes under Trace Settings, determine whether to render vector objects as fills, strokes, or both.
When Strokes is selected, the Max Stroke Weight and Min Stroke Length controls are activated providing the options for, respectively, the maximum thickness at which a stroke may be rendered before it’s converted to a fill area and the shortest length of object acceptable as a stroke.
Path Fitting The control determines how closely the vector paths should match the edges of color areas in the source image. For example, a setting of 1 px on a low-resolution image will create vector paths that perfectly stair-step with the grid-based, square pixels. To avoid creating vector paths that look pixelated, increase the value of Path Fitting until the resulting paths are smooth, without losing crisp edges and color breaks.
Minimum Area is the smallest path size desired. Lower values create many more paths, making the document more complex and more likely to choke a printer’s processor, but low values also increase the fidelity of the vector to the original raster image data. Higher values, on the other hand, create a simpler composition, often ignoring smaller areas of color and combining them into adjacent colors for larger, single-color path areas.
By default, Live Trace creates anchor points as smooth (or curve) points. The Corner Angle value is the angle threshold beyond which a curve must be converted to a corner (or angle) anchor point.
Checking Ignore White will not produce paths for white areas of the image. This is very useful when tracing non-rectangular objects on white backgrounds, such as scanned drawings.
The two menus in the View section at the bottom of the Tracing Options dialog determine what you want to see in the final composition—do you want to see the raster image or the vector tracing, and how would you like them to appear? Typically the goal of tracing is to hide the raster image and show the vector, so No Image and Tracing Result, respectively, are the defaults.
Once you’ve tweaked all the settings necessary to give you the desired image, click the Trace button, and soon you’ll have a vector traced image.
Of course, it will still be a live Live Trace object, meaning that you can go back and adjust the tracing options even further at any point. To access the actual paths of the tracing you’ll need to break the Live Trace object into a standard group of paths, removing the ability to edit the tracing. You can do that by choosing Object -> Expand, or clicking the Expand button on the Control panel, and then ungrouping the traced paths.
Pariah S. Burke is the author of Mastering InDesign CS3 for Print Design and Production (Sybex, 2007), and other books; a freelance graphic designer; and the publisher of the Web sites GurusUnleashed.com, WorkflowFreelance.com, and CreativesAre.com. Pariah lives in Portland, Ore.