Illustrator’s Object > Image Trace commands are used to automatically trace a raster image, creating vector geometry. These commands are especially useful as a step in constructing digital contour models from scanned topographical maps, and other similar tasks.
AN IMAGE TRACE WORKFLOW:
1. Open a raster image (e. g., a scan or a photograph) in Photoshop.
2. Using Photoshop, convert the image to a bitmap figure-ground. You will probably need to experiment with the right combination of options to achieve good results. Try using Photoshop’s Filter > Gaussian Blur command to blur the image before converting it to a bitmap (Image > Mode > Bitmap). When converting the image, the 50% Threshold option will usually give the best results. After converting it, change the image mode to Grayscale, and try blurring it again. (The right combination of commands will depend on the resolution and composition of the image.) Save the bitmap image as a TIF file.
3. Open or Place the image in Illustrator.
4. Use the Selection tool (the arrow tool) to select the image.
5. Choose Window > Image Trace. This brings up the Image Trace options panel.
6. In the Image Trace options panel, set the Preset to Line Art.
7. Experiment with other settings (including the Advanced settings) to achieve optimal results, depending again on the resolution and composition of your original image.
8. After completing the trace, click on the resulting object and choose Object > Image Trace > Expand.
9. Copy the resulting object into a new Illustrator file. You can also save it as a .DWG or .DXF file, which you can open, import, or link to Rhino, AutoCAD, SketchUp, or Revit.