Autotrace

The Autotrace menu cell in the Tools module processes a picture to extract its contours and creates Bezier curves from them. The main application is to extract curves from logos and text, providing an alternative to digitizing with a tablet.

First, the picture should be processed to create a high contrast picture. For this purpose, a threshold value is used to determine whether a pixel should be considered black or white. The threshold value represents the average value of the three RGB colour components and ranges from 0 to 1.

For example, consider a grey letter with an average RGB value of 0.2 on a black background. If you set the threshold to 0.3, no contour is extracted because both grey and black RGB averages are under the threshold value and are therefore considered similar in high-contrast representation. A threshold value of 0.001 to 0.2 would be appropriate.

Once the high contrast representation has been completed, it is analyzed to extract the contours.

Procedure

1. Choose the Autotrace menu cell. The database browser is displayed.
2. Select the image to be processed by double-clicking it. The Auto-Trace dialogue box is displayed.
3. Select the parameters you want and click Ok.

Parameters

Threshold

The value is used to evaluate each pixel value and categorize it as black or white. If you set the threshold to 0.3, no contour is extracted because both grey and black RGB averages are under the threshold value and are therefore considered similar in high-contrast representation. A threshold value of 0.001 to 0.2 is usually a good range of values (the default is 0.3).

Minimum Number of Points

Sets the curve's resolution.

Depth Search

Specifies the number of levels to search.

Last updated 03-apr-1998