The area of the image to be traced must be set. The active area is displayed as a flickering gray and blue rectangle around the image.

Choose Set Region from the Trace menu. Drag the control points on the corners of the rectangle to the desired area. When this command is repeated, the new rectangle replaces the old one.

After the tracing region has been defined, select Outline from the Trace menu. The Tracing Parameters dialog box appears. These parameters determine the smoothness and accuracy of the vector image. The parameters can be set by adjusting the scroll bars, or by entering values into the edit boxes to the right of each parameter.

Figure 2.28. Tracing Parameters Dialogue

After the parameters have been set, press OK or CR to activate the trace mode. Press Cancel or Esc to exit trace mode without modifying the image. The following parameters may be set:

Noise reduction factor	This parameter determines how the vectoring algorithm treats small noise pixels that appear in an image. The values range from 1 to 20. Values from 8 to 14 are used in most cases. A small value results in a sharper, more detailed vector image. A larger value leads to a smoother image that is less faithful to the original raster image.
Sharp corner detection	This parameter sets the detection of sharp corners in the original raster image. The values range from 1° to 90°. A low value detects corners everywhere on the image, while a high value will treat blunt angle corners as curves.
Accuracy/Tension	This parameter determines how faithful the resulting image will be to the original image. The values range from 1 to 2000. Higher values lead to a smoother vector image. Lower values fit the vector image more accurately to the actual pixels in the raster image, but the resulting image is not as smooth.
	Save tracing parameters to a file. All trace parameters files are given the default extension *.TRC. When the Save Trace Parameters dialog box appears, enter a file name, select the directory where you want the file to be saved, and press Save.
	Open a trace parameter file. When the Open Trace Parameters dialog box appears, select the desired parameter file. Press Open or double-click the file name to load the stored parameter into the Tracing Parameters dialog box.
	Trace an area of a particular color. Use the Near Color dialog box to select the color tolerance. Figure 2.29. Near Color Dialogue Use the Near Color dialog box to select the Match Mode and set the color tolerance. The color tolerance setting determines how close the color of a pixel must be to the color of the chosen pixel in order to be selected. If you move the track bar to the left (Selected) only pixels with a perfect match will be selected, and as you move the track bar to the right (Near) more colors that are close in Hue, RGB Value or Brightness will be selected. After you select the color tolerance, press on the area to trace with the left mouse button. You can add a selection or remove from a selection by clicking Shift. To trace selection click the Trace Selection button in order to trace. When finished click the Close button.
Filter Colors	Filter will only trace selected colors from your image. Using the left mouse button you define an area in the picture. All the colors inside that area will be traced. Figure 2.30. Filter Colors Dialogue Zoom All Ctrl-A Show the entire picture. Zoom Double Ctrl-D Expand the picture by a factor of two. (A roller-mouse can be used for this operation). Zoom Half Ctrl-H Reduce the picture by a factor of two. (A roller-mouse can be used for this operation). Reset Reset the picture. All the selected colors will become unselected.

After the tracing region has been defined, select Centerline from the Trace menu. The Tracing Parameters dialog box appears. The Tracing Parameters dialog box appears (these parameters are explained in Trace → Outline). This function creates the centerline of the selected picture.